The Dynamics of Plasmon-Induced Hot Carrier Creation in Colloidal Gold

The Dynamics of Plasmon-Induced Hot Carrier Creation in Colloidal Gold | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article The Dynamics of Plasmon-Induced Hot Carrier Creation in Colloidal Gold Jacinto Sa, Anna Wach, Jakub Szlachetko, Alexey Maximenko, Tomasz Sobol, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3799527/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Mar, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract There is an increasing interest in nonequilibrium “hot” carrier generation, created by the decay of collective electronic oscillations on metals known as surface plasmons. Despite extensive efforts, direct observation of the mechanism responsible for generating hot carriers due to plasmon decay has proven challenging. Here, the dynamics of hot carrier generation on gold nanoparticles (Au NPs) are followed with unparalleled detail through ultrafast X-ray absorption spectroscopy (XAS) at the X-ray free-electron laser (XFEL). In Au NPs, the plasmon dephases after 25 fs and the hot carrier population peaks within 105 fs, reaching thermal equilibrium within 1.5 ps. The nonequilibrium carriers display an energy dispersion governed by the density of states of the metal, with some carriers possessing energies surpassing that of a single photon, consistent with the involvement of an Auger heating mechanism distinct from the expected impact excitation that dominates the carrier multiplication step. The most energetic carriers exhibit relatively shorter lifespans, a property that may be critical for exploiting them in applications. This study substantiates hot carrier formation through nonradiative decay as the main decay channel of plasmon resonance. The proposed methodology provides a straightforward approach for real-time tracking of plasmon-induced hot carrier dynamics. Physical sciences/Nanoscience and technology/Nanoscale materials/Nanoparticles Physical sciences/Chemistry/Physical chemistry/Excited states Figures Figure 1 Figure 2 Figure 3 Introduction Surface plasmons, the collective oscillations of conduction electrons in metallic nanostructures, have emerged as an essential elementary excitation in condensed matter, giving rise to multiple practical applications. They can capture distant radiation and focus it within subwavelength regions, defying diffraction limits, 1,2 resulting in potent near-fields and profound field amplifications. 3 These attributes have propelled innovative applications of plasmonics, such as highly sensitive biosensing, 4 photothermal therapy for cancer, 5 photovoltaics, 6,7 and photocatalysis. 8 Surface plasmons exhibit finite lifetimes, decaying either by photon emission (radiatively) or the creation of electron-hole pairs (nonradiatively). Over the past decade, the radiative decay pathway has been researched extensively, yielding the development of efficient nanoantennas that amplify and steer emissions from individual emitters. 9,10 Recent research has focused on leveraging nonradiative decay for applications. 11 Hot carriers can initiate chemical reactions in adjacent molecules, even those that demand high energy under conventional thermal conditions. 12,13 Moreover, plasmon-induced hot carriers offer a potent means to transform light into electrical currents, 14 fostering novel solar energy converters 15 and circumventing the bandgap limitations of traditional photodetectors. 16 While the direct excitation of hot carriers on metal surfaces using high-intensity laser pulses has been a longstanding practice in surface femtochemistry, exploiting surface plasmon decay to amplify hot carrier generation is a recent development. This significant advance stems from the remarkably boosted light harvesting ability of collective plasmon excitations, combined with the substantial enhancement of the plasmon-induced field when metals are nano-confined. Comprehending the underlying physical mechanisms driving plasmon-induced hot carrier generation is essential to leverage these benefits fully. Although theoretical frameworks elucidating this phenomenon exist, 17-18[i]19[ii]20[iii]21[iv]22 a suitable experimental methodology to validate these models still needs to be developed. X-ray absorption spectroscopy (XAS) provides a way to investigate the interplay between X-ray photons and matter, simultaneously unveiling unparalleled insights into a material’s electronic and chemical characteristics. When X-ray photons are directed toward a material, they can be absorbed by core electrons, resulting in these electrons shifting to higher energy states. The precise energy at which this absorption occurs depends on the specific element's electronic structure and its local environment. Hot carriers emerge from the interaction between external electric fields and valence electrons, creating electrons and holes with energies above and below the Fermi level (E F ). Transient XAS (aka time-resolved XAS (TR-XAS)) probes empty states around theFermi energy and, in the case of d 10 metals with the L 3 -edge transition, provides direct information about the amount of carrier participation and their nonequilibrium energy distributions. 23 At synchrotrons, such dynamical measurements are typically hampered by limited temporal resolution (~ 5 ps) and photon density, 24 impeding real-time observations of the hot carrier generation process. 8 However, this limitation has been surpassed by the advent of hard X-ray free electron lasers (XFELs), 25 capable of delivering intense and ultrashort hard X-ray pulses (up to 30 keV at the European XFEL 26 and 12 keV at SwissFEL (used in this study) 27 ) of less than 50 fs in duration. 27 ,28 With this unique combination of high photon energies and ultrashort pulses, time-resolved XAS has become an exceptionally valuable experimental probe of dynamical processes. Typical time-resolved measurements are implemented in a pump-probe scheme, where an optical-frequency pump laser triggers electron dynamics, and the X-ray probe captures the evolving nonequilibrium electron distribution. Over the past few years, femtosecond TR-XAS studies have been used to probe photoinduced electronic and structural changes in photoexcited transition metal oxides 29 and complexes. 30 In this study, TR-XAS was used to observe the generation and relaxation of plasmon-induced hot carriers in gold nanoparticles directly. 31,32 The widely accepted understanding of how localised surface plasmon resonance (LSPR) excitation leads to hot carrier formation and subsequent thermalisation, including the hypothesised timescales for each process, is summarised in Figure 1A. 8 , 22 Briefly, the light electric field induces a coherent excitation of Au valence electrons. The excited electrons' coherence dephases due to Landau damping after the light excitation elapses. The process is expected to take 10-100 fs, resulting in a non-Fermi-Dirac distribution of hot carriers. The carriers undergo multiplication, eventually reaching a Fermi-Dirac distribution and thermal relaxation after ~1 ps. This description of hot carrier formation has been deduced from physical models that underpin our understanding. Still, it has never been validated experimentally due to the lack of element-specific techniques with sufficient temporal resolution. However, the attempts from Bigot et al. 33 and Lehmann et al. 34 with femtosecond optical pump-probe investigations with ionising probe pulses, which provided earlier evidence for hot electrons and their dynamics, should be mentioned. Nevertheless, no information could be extracted about the hot holes. Figure 1B illustrates the TR-XAS approach for tracking the density of states (DOS) changes induced by LSPR excitation. More specifically, the study focuses on the X-ray absorption near edge structure (XANES) part of the XAS spectrum, which contains the electronic changes in the element, i.e., information on LSPR-induced hot carrier formation. The transient data was collected using the classic pump-probe methodology for optical spectroscopy. The technique involves "pumping" a sample with an initial laser pulse and then "probing" it with a delayed pulse to observe the changes induced by the pump pulse. In the present case, the probe is an fs X-ray pulse from the XFEL. To prevent the excitation of damaged Au NPs induced by intense XFEL pulses, a liquid jet was employed to circulate the Au NPs and the solution was refreshed every four hours. Since nanoparticle measurements at XFELs are uncommon, it was essential to validate that the XANES spectra collected with this radiation represent the sample. Figure S1 shows the steady-state XANES spectra of Au foil and nanoparticles measured at the Au L 3 -edge transition (2 p 3/2 à 5 d ) at the synchrotron (Solaris synchrotron, Poland). Au has a [Xe] 4 f 14 5 d 10 6 s 1 electronic structure, i.e., with a filled d -shell, which results in a slight absorption edge only visible due to some level of s-d shell hybridisation. For comparison purposes, the signal was plotted against Pt ([Xe] 4 f 14 5 d 9 6 s 1 ) (Fig. S2), revealing the method sensitivity to empty states within the metal 5 d shell and, to some extent, the s -shell due to this hybridisation. In this study, Au NPs with an average particle size of 8 ± 2 nm were used, as confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS) (Figs. S3 and S4). The Au NPs have a LSPR centered at nominally 520 nm (2.38 eV) according to UV-vis spectroscopy (Fig. S5). The steady-state XANES analysis established that the Au NPs exhibit an electronic structure resembling bulk gold, as reported elsewhere. 22 ,35 This agreement is further corroborated by our theoretical calculations, showing the evolution of the DOS as function of particle size (Fig. S6). The unexcited XANES spectrum of the Au NPs, measured at XFEL (SwissFEL, Switzerland) and the synchrotron, displayed a consistent shape. This consistency supports the applied methodology's ability to capture the transient alterations in the electronic structure of gold before the sample gets damaged, i.e., probe-before destruction concept. 36, 37 XFELs have only recently provided access to hard X-ray energies, allowing one for the first time to probe the Au L 3 -edge. Ultrafast time-resolved XANES data were acquired with the XFEL source as a probe, following the excitation of 5 mM Au NPs at 532 nm (~ 2.33 eV), utilising a 15 nm full width at half maximum (FHWM) bandwidth, a pulse duration of approximately 75 fs, and a power density of 98 mJ/cm 2 (equivalent to 4 µJ within a 60 x 60 µm 2 spot). The choice of this precise plasmon excitation energy was to induce LSPR through intra-band s - to s -shell excitation while minimising interband excitation ( d - to s -shell excitation). The centre of the Au d -shell is located at 2.5-2.58 eV (~ 496-480 nm) from the metal Fermi level (E F ), 38 ,39 meaning that the laser pulse with 2.33±0.13 eV (15 nm FHWM) photon energy can only excite the low energy tail of the d -shell at best. Figure 1C compares the XANES spectra of unexcited (unpumped spectrum) and excited (pumped spectrum) recorded at Dt =100 fs time delay after excitation at 532 nm. Optical excitation induced a spectral downshift in energy and decreased XANES whiteline intensity, corroborating that it induced changes in the gold electronic structure around its Fermi-level energy, and the TR-XAS can track the changes. To better illustrate the results, the XANES difference spectrum (pumped-unpumped XANES spectra) is also shown in Figure 1C. The difference spectrum is dominated by the positive signal below and a negative signal above the Au E F . Transient L 3 -edge XANES readily capture changes in the density of unoccupied states, particularly those induced in the d -shell, either directly or through processes like hybridisation with the s -shell. Accordingly, a positive signal correlates with an increase in density of states (DOS); conversely, a negative signal (i.e., a bleached signal) indicates a decrease in empty states. Therefore, the positive signal below the Au E F is ascribed to the formation of a hot hole population induced by the plasmon optical excitation. In contrast, hot electrons give rise to the negative signal above the Au E F , consistent with empty states filling. The transient signal directly demonstrates the generation of hot carriers through LSPR decoherence via Landau damping (the non-radiative pathway dominant in small nanoparticles). 21 , 24 ,40 Most notably, the hot hole and electron signals are neither symmetric nor have the same integrated magnitude. This is related to the XANES higher sensitivity to empty states formation and the L 3 -edge transition changes in the d -shell that is part of the valence, where the hot holes are formed. To establish the time scales for plasmon damping (g) and the average lifetime of carriers (t), kinetic traces were extracted at the maximum of the hot hole intensity (11916 eV, 2.5 eV below Au E F (Figure 2B)) and the excited electron intensity (11922 eV, 3.0 eV above Au E F (Figure 2C)) populations, as depicted in (Figure 2A). The kinetic data from the time scans were fitted by a model published elsewhere, 41 described in SI equations S1 and S2. In brief, the data collected at 11916 and 11922 eV were fitted with a convolution of temporal instrument response function (Gaussian) with a monoexponential decay (with a time constant ). The resulting fit is the solid green in Figure 2B. Due to the low signal-to-noise ratio for the hot electron data, the error bars are relatively large. However, qualitatively, it is possible to see that the signal has dynamics similar to the hot holes. The γ time can be extracted from the transient signal onset time because it is the point at which the Au DOS starts to change, i.e., the fingerprint for hot carrier formation. In this particular case, it was estimated to be 24.6 ± 6 fs, corroborating that plasmon decoherence occurs between 10-100 fs. 24 Following plasmon damping, the hot carriers undergo a carrier multiplication reaching a maximum at 105 ± 8 fs, estimated from rising edge analysis. The lifetimes of the hot carriers were determined from a single exponential decay to be 498 ± 35 fs with complete carrier thermalisation occurring within 1.5 ps. These time constants align with previous postulations 24 but are here substantiated through direct measurement. The confirmed ultrafast hot carrier dynamics in plasmonic nanoparticles are the primary bottleneck in plasmonic applications. To estimate the number of electrons engaged when exciting 5 mM Au NPs at 532 nm, utilising a 15 nm full width at half maximum (FHWM) bandwidth, a pulse duration of approximately 75 fs, and a power density of 98 mJ/cm 2 , the positive signal variance at 0 and 100 fs were integrated. This integrated signal was then juxtaposed with the signal difference between the Au and Pt L 3 -edges (Fig. S2). Note that the signal difference between Au and Pt relates to 1 e - less in Pt valence states, i.e., the integrated positive signal of the difference between Pt and Au corresponds to the equivalent of having 1 e - from each Au atom participating in the resonance. Employing this simple methodology, we estimated that each gold atom contributed with 0.19 e - at the start of the resonance, which underwent multiplication until 105 fs, reaching a maximum of 0.46 e - from each Au atom contributing to hot carrier formation at this excitation power. Assuming an excitation volume of 60 x 60 x 100µm 3 and considering the Au solution concentration (5 mM), one can expect 1.5 x 10 8 nanoparticles in the excited volume. An 8 nm Au NP has »12000 atoms, equating to about 1.8 x 10 12 Au atoms in the excited volume. The photon density in the optical pulses is about 10 13 , from which 20% is absorbed according to UV-Vis, implying that the excited volume absorbs around 2x10 12 photons. This suggests an excitation of about 1 e - per atom of Au, from which 19% are converted into hot carriers at the onset, multiplying to about 46% within 100 fs. The observation suggests that hot carrier generation is a prime decay channel of Au LSPR and undoubtedly the most significant mechanism in nonradiative decay. After verifying the generation of hot carriers, the next step is the investigation of the dynamics of their energy distribution - a significant yet elusive aspect in the realm of plasmonic hot carriers, particularly when it comes to holes. Our understanding is derived mainly from theoretical studies 20 ,4243 and indirect techniques. 22 , 33 , 34 ,44 For example, internal quantum efficiency measurements have inherent limitations as they solely quantify carriers injected into an acceptor layer, like a semiconductor, failing to provide insights into the dynamic behaviour of the carriers in the metal. While the hot electrons can only populate the empty states within the sp -shells, the holes can be in sp - and d -shells, confirmed by valence band – X-ray photoelectron spectroscopy (VB-XPS) shown in Figure 3A. It is evident when the VB-XPS is overlapped with the transient XANES spectrum (recorded at time zero) that the generated holes are indeed located throughout the entire valence, including the d -shell, despite the optical pulse energy allowing primarily sp -shell excitation. Figure 3B shows the energy distribution and population of the carriers at different time delays after excitation. As expected, the plasmonic excitation depopulates and populates states below and above the Fermi energy. The ultrafast carrier-carrier interactions during dephasing and multiplication determine their energy and respective population. The hot carrier energy distribution goes beyond single photon energy for hot electrons and holes. Moreover, it is noticeable that both carrier populations and the width of their energy distributions increase until about 100 fs, decreasing asymptotically after that. A slight asymmetry exists between hot electron and hot hole populations, which cannot be fully explored here due to the probe's lower sensitivity to hot electrons. The rapid depopulation of electrons in the d -shell is expected due to the broad energy overlap between the d and sp -band, which provides a high density of d -electrons that couples with the plasmonic resonance and dissipates its energy. 43 However, this does not explain the observation of carriers having energies above the photon energy, even considering that the Au core-hole lifetime broadening is 5.41 eV at the L 3 -edge, 45 which inevitably broadens the energy scale. Achieving precise energy distributions of carriers requires high-resolution measurements, 46 which implies extended acquisition times rarely offered at XFEL facilities. Nonetheless, hot holes are distributed across the entire valence electronic structure, and their energy distribution increases up to 250 fs (Figure 3C) before relaxing. These two observations indicate the involvement of carrier multiplication mechanisms that can increase the carrier population and their energy distribution, an effect that has yet to be reported. 43 Note that the low optical laser fluency and short pulse duration used in this experiment make it highly unlikely that multiphoton excitation of single electrons occurs. Regarding carrier multiplication, there are two scattering mechanisms: impact excitation and Auger heating, 47,48 The predominant mechanism in carrier multiplication is impact excitation, where an excited electron (hole) undergoes Coulomb scattering, losing energy and momentum and giving rise to an additional electron-hole pair. The distinctive feature of impact excitation is a rise in the number of carriers and a simultaneous reduction in their energy. Conversely, Auger heating characterises the non-radiative recombination of an electron with a hole, where the energy and momentum are transferred to an electron (hole) within the same shell. The hallmark of Auger heating is a decline in the number of carriers and an increase in their energy. To enhance the visualisation and comprehension of the hot hole multiplication process, the shape of different spectra regarding charge width and charge energy was analysed (see Figure 3C). The details of the data analysis procedure are outlined in the SI. Commencing with the average hot carrier distribution energy, it remained constant until 100 fs before exhibiting a subsequent decrease. This implies the LSPR dephasing process extends to 100 fs, increasing the nonequilibrium hot carrier population through the impact excitation scattering mechanism. However, examining the hot carrier distribution width, reflecting the energy distribution of the hot holes unveils a relative surge in the energy distribution beyond the time when the hole population is at its maximum (approximately 100 fs), i.e., the energy distribution of hot holes increases up to 250 fs. This observation is noteworthy, especially considering this process competes with hole thermalisation, occurring within tens of femtoseconds in metals. The broadening induced by the core hole relaxation cannot account for the increase in distribution width, as it should have smeared the energy resolution from the outset, preventing the difference signal from accurately reflecting the valence state of gold. This suggests the involvement of a mechanism that generates carriers with higher energy than the dephasing process produces - specifically, the participation of Auger heating. This mechanism has yet to be considered in plasmon relaxation dynamics, altering the current understanding of hot carrier formation, multiplication, and relaxation in plasmonic materials. In this work, we presented the results from an ultrafast X-ray absorption experiment conducted at the XFEL involving citrate-capped gold nanoparticles excited at their LSPR with minimum intraband excitation. This experiment enabled the real-time observation of the generation and subsequent relaxation of hot carriers. The plasmon damping was determined to be 25 fs, with a maximum hot carrier population of 0.46 e - from each Au atom detected at 105 fs after excitation. The lifetimes of the hot carriers were estimated to be 498 fs, with complete carrier thermalisation occurring within 1.5 ps. Energy scans conducted at varying delay times revealed that the energies of these carriers conform to the density of states of the metal, with some carriers possessing energies that exceed the photon energy, consistent with an Auger heating scattering mechanism. The observation impacts hot carrier applications, particularly those that are based on the energy of the hot carriers, such as photocatalysis and photovoltaics. For instance, without the Auger process, chemical reactions with redox windows larger than photon energy could not be catalysed. Similarly, the open circuit voltage of photovoltaic devices could not exceed the voltage offered by a single photon. The novel insight into plasmon induced hot carrier generation and dynamics provided here is likely to significantly impact applications for years to come. [i]. Kornbluth, M., Nitzan, A., Seideman, T. Light-Induced Electronic Non-Equilibrium in Plasmonic Particles. J. Chem. Phys. 138 , 174707 (2013). [ii]. Govorov, A. O., Zhang, H., Demir, H. V., Gun'ko, Y. K. Photogeneration of Hot Plasmonic Electrons with Metal Nanocrystals: Quantum Description and Potential Applications. Nano Today 9 , 85–101 (2014). [iii]. Manjavacas, A., Liu, J. G., Kulkarni, V., Nordlander, P. Plasmon-Induced Hot Carriers in Metallic Nanoparticles. ACS Nano 8 , 7630–7638 (2014). [iv]. Rossi, T. P., Erhart, P., Kuisma, M. Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure. ACS Nano 14 , 9963-9971 (2020). Declarations Acknowledgements We acknowledge the Paul Scherrer Institut, Villigen, Switzerland, for providing beamtime at the Alvra beamline of the SwissFEL facility. We also acknowledge SOLARIS National Synchrotron Radiation Centre, Krakow, Poland, for the access to the ASTRA and PHELIX beamline. The simulations were performed using computational resources provided by the Swedish National Infrastructure for Computing (SNIC) at UPPMAX and NSC, for which we want to thank. Funding : J.Sa acknowledges funding from Olle Engkvists Stiftelse (grant no. 210-0007), Knut & Alice Wallenberg Foundation (Grant No. 2019-0071) and Swedish Research Council (grant no. 2019-03597). A.W. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement no. 884104 (PSI-FELLOW-III-3i). N.J.H. and P.N. acknowledge support from the Robert A. Welch Foundation under grants C-1220 and C-1222 and the Air Force Office of Scientific Research via the Department of Defense Multidisciplinary University Research Initiative under AFOSR Award No. FA9550-15-1-0022. The work is partially supported under the Polish Ministry and Higher Education project: “Support for research and development with the use of research infrastructure of the National Synchrotron Radiation Centre SOLARIS” under contract nr 1/SOL/2021/2. The work is partially funded by the National Science Centre in Poland under grant number 2020/37/B/ST3/00555. Author contributions : Conceptualization and methodology: A.W., J. Sz. and J.Sa; formal data analysis: A.W., J. Sz. and J.Sa; experimental investigations: A.W, C.B., C.C., P.J.M.J., R.G.C., V.R.S., P-B., J.K., A.M., T.S., E.P.-J. and J.Sa; data visualisation concepts: A.W., J. Sa, J.Sz and N.J.H., draft preparation: A.W., N.J.H., J. Sz. and J.Sa; writing-review and editing: all the authors. All authors have read and agreed to the published version of the manuscript. Competing interests : The authors declare that they have no competing interests. Data and materials availability : All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors. References Novotny, L., Hecht, BPrinciples of Nano-OpticsCambridge University Press: New York, (2006). 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Gierz, I, Calegari, F., Aeschlimann, S., Chávez Cervantes, M., Cacho, C., Chapman, RT., Springate, E., Link, S., Starke, U., Ast, CR., Cavalleri, ATracking primary thermalization events in graphene with photoemission at extreme time scalesPhysRevLett115, 086803 (2015). Sidiropoulos, TPH., Di Palo, N., Rivas, DE., Severino, S., Reduzzi, M., Bauerhenne, B., Krylow, S., Vasileiades, T., Danz, T., Elliot, P., Sharma, S., et alProbing the energy conversion pathways between light, carriers, and lattice in real time with attosecond core-level spectroscopyPhysRevX 11, 041060 (2021). Additional Declarations There is NO Competing Interest. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3799527","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":266344068,"identity":"9baa353f-58ad-4c14-a312-0059d2b5c62d","order_by":0,"name":"Jacinto Sa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIie3RsQqCQBjA8U8OnK5mJdBXOHFp8GEMwcmGXiCcailc7TkE5+AbWnwAVxGcGgwXg4K0k8YPx4b7D+cH3o/zEECl+sO0GOAqR4bDYswl/jjqwTwi+xLuztvMjljhrvfAPhadeERrEKXP2pb6sFMoMPVDEMU221xyYyS6mVIkjgC5jyBgm+FiIoxTJLlLYif3Gt+SsO5FkXQ6BcqIBZoksKKur6WNQB6GXJSN65xzg5tFdTBPBHGSoO6451n2MBjPfG8tbwG2PUVi+fzdl8vfS2STb1UqlUo19gFn6UuB9HO+qgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-2124-9510","institution":"Uppsala University","correspondingAuthor":true,"prefix":"","firstName":"Jacinto","middleName":"","lastName":"Sa","suffix":""},{"id":266344069,"identity":"200a9d64-ed20-491b-875b-c6e7499d11f4","order_by":1,"name":"Anna Wach","email":"","orcid":"","institution":"SOLARIS National Synchrotron Radiation Centre, Jagiellonian University","correspondingAuthor":false,"prefix":"","firstName":"Anna","middleName":"","lastName":"Wach","suffix":""},{"id":266344070,"identity":"6aa89336-955a-4ae6-a2cf-fc44397a6e09","order_by":2,"name":"Jakub Szlachetko","email":"","orcid":"","institution":"SOLARIS National Synchrotron Radiation Centre, Jagiellonian University","correspondingAuthor":false,"prefix":"","firstName":"Jakub","middleName":"","lastName":"Szlachetko","suffix":""},{"id":266344071,"identity":"9ca6b549-4d2b-471f-bdec-8c946b92add9","order_by":3,"name":"Alexey Maximenko","email":"","orcid":"","institution":"SOLARIS National Synchrotron Radiation Centre, Jagiellonian University","correspondingAuthor":false,"prefix":"","firstName":"Alexey","middleName":"","lastName":"Maximenko","suffix":""},{"id":266344072,"identity":"c79d0e3e-b54e-4e12-816f-b97a8a2965e6","order_by":4,"name":"Tomasz Sobol","email":"","orcid":"https://orcid.org/0000-0002-9661-0932","institution":"SOLARIS National Synchrotron Radiation Centre, Jagiellonian University","correspondingAuthor":false,"prefix":"","firstName":"Tomasz","middleName":"","lastName":"Sobol","suffix":""},{"id":266344073,"identity":"15b06e63-da53-4a2e-a0c0-561fadb65a88","order_by":5,"name":"Ewa Partyka-Jankowska","email":"","orcid":"","institution":"SOLARIS National Synchrotron Radiation Centre, Jagiellonian University","correspondingAuthor":false,"prefix":"","firstName":"Ewa","middleName":"","lastName":"Partyka-Jankowska","suffix":""},{"id":266344074,"identity":"deb242ea-04a0-4c39-9083-901277aac800","order_by":6,"name":"Camila Bacellar","email":"","orcid":"https://orcid.org/0000-0003-2166-241X","institution":"Paul Scherrer Institute","correspondingAuthor":false,"prefix":"","firstName":"Camila","middleName":"","lastName":"Bacellar","suffix":""},{"id":266344075,"identity":"be23916f-c7b1-4987-8b53-0dd8d1e6427e","order_by":7,"name":"Claudio Cirelli","email":"","orcid":"https://orcid.org/0000-0003-4576-3805","institution":"Paul Scherrer Institute","correspondingAuthor":false,"prefix":"","firstName":"Claudio","middleName":"","lastName":"Cirelli","suffix":""},{"id":266344076,"identity":"2c2ff4ef-9d12-4584-a36a-a4fb85e3cd87","order_by":8,"name":"Philip Johnson","email":"","orcid":"https://orcid.org/0000-0002-7251-4815","institution":"Paul Scherrer Institut","correspondingAuthor":false,"prefix":"","firstName":"Philip","middleName":"","lastName":"Johnson","suffix":""},{"id":266344077,"identity":"953745b6-d887-4371-a7dd-c9b7caeb024f","order_by":9,"name":"Rebeca Gomez Castillo","email":"","orcid":"","institution":"École Polytechnique Fédérale de Lausanne","correspondingAuthor":false,"prefix":"","firstName":"Rebeca","middleName":"Gomez","lastName":"Castillo","suffix":""},{"id":266344078,"identity":"7201d8cb-d0e9-4c57-b386-faa3ab024988","order_by":10,"name":"Vitor R. Silveira","email":"","orcid":"","institution":"Uppsala University","correspondingAuthor":false,"prefix":"","firstName":"Vitor","middleName":"R.","lastName":"Silveira","suffix":""},{"id":266344079,"identity":"3a5976b4-201a-4095-8197-86acef9dd312","order_by":11,"name":"Peter Broqvist","email":"","orcid":"","institution":"Uppsala University","correspondingAuthor":false,"prefix":"","firstName":"Peter","middleName":"","lastName":"Broqvist","suffix":""},{"id":266344080,"identity":"5c379ff3-4b7d-4252-b232-b966a1213b6b","order_by":12,"name":"Jolla Kullgren","email":"","orcid":"","institution":"Uppsala University","correspondingAuthor":false,"prefix":"","firstName":"Jolla","middleName":"","lastName":"Kullgren","suffix":""},{"id":266344081,"identity":"4967dbb3-35cf-49fa-9a08-796647c23e52","order_by":13,"name":"Naomi Halas","email":"","orcid":"https://orcid.org/0000-0002-8461-8494","institution":"Rice University","correspondingAuthor":false,"prefix":"","firstName":"Naomi","middleName":"","lastName":"Halas","suffix":""},{"id":266344082,"identity":"51769674-5627-42ee-a439-fb3edf4332c8","order_by":14,"name":"Peter Nordlander","email":"","orcid":"https://orcid.org/0000-0002-1633-2937","institution":"Rice University","correspondingAuthor":false,"prefix":"","firstName":"Peter","middleName":"","lastName":"Nordlander","suffix":""}],"badges":[],"createdAt":"2023-12-24 08:20:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3799527/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3799527/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-57657-1","type":"published","date":"2025-03-07T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54319748,"identity":"43503bb3-b717-493c-9cc1-a4e1f0248a32","added_by":"auto","created_at":"2024-04-08 18:58:04","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":590405,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eX-ray absorption signatures of gold nanoparticles.\u003c/strong\u003e (A) Illustration depicting the temporal progression of the plasmonic resonance decay mechanism, including hypothesized time constants for associated processes. (B) The generation of hot carriers was investigated using the concept of ultrafast transient XANES, presented schematically. (C) Superimposed L\u003csub\u003e3\u003c/sub\u003e-edge spectra of steady-state (\u003cem\u003eblack trace\u003c/em\u003e) and excited-state (\u003cem\u003ered trace\u003c/em\u003e) Au nanoparticles with excited spectrum recorded at △t =100 fs time delay after excitation at 532\u0026nbsp;nm. The transient XAS spectrum (\u003cem\u003eblue trace\u003c/em\u003e) is the difference between excited (pumped) and stead-state (unpumped) spectra. A positive signal in the difference spectrum equates to an increase in empty states (holes) and vice-versa.\u003c/p\u003e","description":"","filename":"Figure1Final122023Nature.png","url":"https://assets-eu.researchsquare.com/files/rs-3799527/v1/335931065146afc12fc8303d.png"},{"id":54319751,"identity":"d07aff81-12e2-4597-bf16-201bb8b144ad","added_by":"auto","created_at":"2024-04-08 18:58:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":482772,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTemporal evolution of the generated hot carriers.\u003c/strong\u003e\u0026nbsp; (A) The difference spectrum (pumped-unpumped signal) shows kinetic traces of energy extraction points. (B) \u0026amp; (C) Time traces (intensities vs time delay) extracted at 11916 eV (i.e. hot holes, green trace) and 11922 eV (i.e. hot electrons, orange trace) X-ray photon energies, respectively. The solid line in the figures (B) and (C) refers to the fitting using the methodology presented elsewhere\u003csup\u003e41\u003c/sup\u003e and described in SI.\u003c/p\u003e","description":"","filename":"Figure2Final122023Nature.png","url":"https://assets-eu.researchsquare.com/files/rs-3799527/v1/6c5506bf27d18fdb0e275ccf.png"},{"id":54319750,"identity":"b5c81da8-1930-4ea1-ab66-1b0e333783f3","added_by":"auto","created_at":"2024-04-08 18:58:04","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":511404,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eUltrafast energies distribution dynamics of excited state evolution of gold nanoparticles. \u003c/strong\u003e(A) Comparison of the valence band photoelectron spectrum (VB-XPS) with the Au L\u003csub\u003e3\u003c/sub\u003e-edge transient XANES spectrum collected at time zero. The relevant energy scale is given to the Fermi level. (B) The transient XANES measured at the Au L\u003csub\u003e3\u003c/sub\u003e-edge absorption spectra collected at different pump-probe time delays (0 fs corresponds to the best possible overlap between pump and probe). (C) Relative changes in hot holes mean energy (red trace) and width (blue trace) distributions.\u003c/p\u003e","description":"","filename":"Figure3Final122023Nature.png","url":"https://assets-eu.researchsquare.com/files/rs-3799527/v1/82885d5a1665bb86650b4e0a.png"},{"id":77955098,"identity":"43cb4158-6540-4a93-ac80-d60a38f2032a","added_by":"auto","created_at":"2025-03-07 08:05:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2461514,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3799527/v1/f7f0e042-9961-4d8d-ac99-0f8c0774c908.pdf"},{"id":54320238,"identity":"d74f25c2-db06-4646-99ae-e7485d5da2ce","added_by":"auto","created_at":"2024-04-08 19:06:04","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1573633,"visible":true,"origin":"","legend":"Supporting information","description":"","filename":"Supportinginformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3799527/v1/68baddb59f62515acd8f3609.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"The Dynamics of Plasmon-Induced Hot Carrier Creation in Colloidal Gold","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSurface plasmons, the collective oscillations of conduction electrons in metallic nanostructures, have emerged as an essential elementary excitation in condensed matter, giving rise to multiple practical applications. They can capture distant radiation and focus it within subwavelength regions, defying diffraction limits,\u003csup\u003e1,2\u003c/sup\u003e resulting in potent near-fields and profound field amplifications.\u003csup\u003e3\u003c/sup\u003e These attributes have propelled innovative applications of plasmonics, such as highly sensitive biosensing,\u003csup\u003e4\u003c/sup\u003e photothermal therapy for cancer,\u003csup\u003e5\u003c/sup\u003e photovoltaics,\u003csup\u003e6,7\u003c/sup\u003e and photocatalysis. \u003csup\u003e8\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSurface plasmons exhibit finite lifetimes, decaying either by photon emission (radiatively) or the creation of electron-hole pairs (nonradiatively). Over the past decade, the radiative decay pathway has been researched extensively, yielding the development of efficient nanoantennas that amplify and steer emissions from individual emitters.\u003csup\u003e9,10\u003c/sup\u003e Recent research has focused on leveraging nonradiative decay for applications.\u003csup\u003e11\u003c/sup\u003e Hot carriers can initiate chemical reactions in adjacent molecules, even those that demand high energy under conventional thermal conditions.\u003csup\u003e12,13\u003c/sup\u003e Moreover, plasmon-induced hot carriers offer a potent means to transform light into electrical currents,\u003csup\u003e14\u003c/sup\u003e fostering novel solar energy converters\u003csup\u003e15\u003c/sup\u003e and circumventing the bandgap limitations of traditional photodetectors.\u003csup\u003e16\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWhile the direct excitation of hot carriers on metal surfaces using high-intensity laser pulses has been a longstanding practice in surface femtochemistry, exploiting surface plasmon decay to amplify hot carrier generation is a recent development. This significant advance stems from the remarkably boosted light harvesting ability of collective plasmon excitations, combined with the substantial enhancement of the plasmon-induced field when metals are nano-confined. Comprehending the underlying physical mechanisms driving plasmon-induced hot carrier generation is essential to leverage these benefits fully. Although theoretical frameworks elucidating this phenomenon exist,\u003csup\u003e17-18[i]19[ii]20[iii]21[iv]22\u003c/sup\u003e a suitable experimental methodology to validate these models still needs to be developed.\u003c/p\u003e\n\u003cp\u003eX-ray absorption spectroscopy (XAS) provides a way to investigate the interplay between X-ray photons and matter, simultaneously unveiling unparalleled insights into a material\u0026rsquo;s electronic and chemical characteristics. When X-ray photons are directed toward a material, they can be absorbed by core electrons, resulting in these electrons shifting to higher energy states. The precise energy at which this absorption occurs depends on the specific element\u0026apos;s electronic structure and its local environment. Hot carriers emerge from the interaction between external electric fields and valence electrons, creating electrons and holes with energies above and below the Fermi level (E\u003csub\u003eF\u003c/sub\u003e).\u003c/p\u003e\n\u003cp\u003eTransient XAS (aka time-resolved XAS (TR-XAS)) probes empty states around theFermi energy and, in the case of \u003cem\u003ed\u003c/em\u003e\u003csup\u003e10\u003c/sup\u003e metals with the L\u003csub\u003e3\u003c/sub\u003e-edge transition, provides direct information about the amount of carrier participation and their nonequilibrium energy distributions.\u003csup\u003e23\u003c/sup\u003e At synchrotrons, such dynamical measurements are typically hampered by limited temporal resolution (~ 5 ps) and photon density,\u003csup\u003e24\u003c/sup\u003e impeding real-time observations of the hot carrier generation process.\u003csup\u003e8\u003c/sup\u003e However, this limitation has been surpassed by the advent of hard X-ray free electron lasers (XFELs),\u003csup\u003e25\u003c/sup\u003e capable of delivering intense and ultrashort hard X-ray pulses (up to 30 keV at the European XFEL\u003csup\u003e26\u003c/sup\u003e and 12 keV at SwissFEL (used in this study) \u003csup\u003e27\u003c/sup\u003e) of less than 50 fs in duration.\u003csup\u003e27\u003c/sup\u003e\u003csup\u003e,28\u003c/sup\u003e With this unique combination of high photon energies and ultrashort pulses, time-resolved XAS has become an exceptionally valuable experimental probe of dynamical processes. Typical time-resolved measurements are implemented in a pump-probe scheme, where an optical-frequency pump laser triggers electron dynamics, and the X-ray probe captures the evolving nonequilibrium electron distribution. Over the past few years, femtosecond TR-XAS studies have been used to probe photoinduced electronic and structural changes in photoexcited transition metal oxides\u003csup\u003e29\u003c/sup\u003e and complexes.\u003csup\u003e30\u003c/sup\u003e In this study, TR-XAS was used to observe the generation and relaxation of plasmon-induced hot carriers in gold nanoparticles directly.\u003csup\u003e31,32\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe widely accepted understanding of how localised surface plasmon resonance (LSPR) excitation leads to hot carrier formation and subsequent thermalisation, including the hypothesised timescales for each process, is summarised in Figure 1A.\u003csup\u003e8\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e22\u003c/sup\u003e Briefly, the light electric field induces a coherent excitation of Au valence electrons. The excited electrons\u0026apos; coherence dephases due to Landau damping after the light excitation elapses. The process is expected to take 10-100 fs, resulting in a non-Fermi-Dirac distribution of hot carriers. The carriers undergo multiplication, eventually reaching a Fermi-Dirac distribution and thermal relaxation after ~1 ps. This description of hot carrier formation has been deduced from physical models that underpin our understanding. Still, it has never been validated experimentally due to the lack of element-specific techniques with sufficient temporal resolution. However, the attempts from Bigot et al.\u003csup\u003e33\u003c/sup\u003e and Lehmann et al.\u003csup\u003e34\u003c/sup\u003e with femtosecond optical pump-probe investigations with ionising probe pulses, which provided earlier evidence for hot electrons and their dynamics, should be mentioned. Nevertheless, no information could be extracted about the hot holes.\u003c/p\u003e\n\u003cp\u003eFigure 1B illustrates the TR-XAS approach for tracking the density of states (DOS) changes induced by LSPR excitation. More specifically, the study focuses on the X-ray absorption near edge structure (XANES) part of the XAS spectrum, which contains the electronic changes in the element, i.e., information on LSPR-induced hot carrier formation. The transient data was collected using the classic pump-probe methodology for optical spectroscopy. The technique involves \u0026quot;pumping\u0026quot; a sample with an initial laser pulse and then \u0026quot;probing\u0026quot; it with a delayed pulse to observe the changes induced by the pump pulse. In the present case, the probe is an fs X-ray pulse from the XFEL.\u0026nbsp;To prevent the excitation of damaged Au NPs induced by intense XFEL pulses, a liquid jet was employed to circulate the Au NPs and the solution was refreshed every four hours.\u003c/p\u003e\n\u003cp\u003eSince nanoparticle measurements at XFELs are uncommon, it was essential to validate that the XANES spectra collected with this radiation represent the sample. Figure S1 shows the steady-state XANES spectra of Au foil and nanoparticles measured at the Au L\u003csub\u003e3\u003c/sub\u003e-edge transition (2\u003cem\u003ep\u003csub\u003e3/2\u003c/sub\u003e\u003c/em\u003e\u0026agrave;\u0026nbsp;5\u003cem\u003ed\u003c/em\u003e) at the synchrotron (Solaris synchrotron, Poland). Au has a [Xe] 4\u003cem\u003ef\u003c/em\u003e\u003csup\u003e14\u003c/sup\u003e 5\u003cem\u003ed\u003c/em\u003e\u003csup\u003e10\u003c/sup\u003e 6\u003cem\u003es\u003c/em\u003e\u003csup\u003e1\u003c/sup\u003e electronic structure, i.e., with a filled \u003cem\u003ed\u003c/em\u003e-shell, which results in a slight absorption edge only visible due to some level of \u003cem\u003es-d\u003c/em\u003e shell hybridisation. For comparison purposes, the signal was plotted against Pt ([Xe] 4\u003cem\u003ef\u003c/em\u003e\u003csup\u003e14\u003c/sup\u003e 5\u003cem\u003ed\u003c/em\u003e\u003csup\u003e9\u003c/sup\u003e 6\u003cem\u003es\u003c/em\u003e\u003csup\u003e1\u003c/sup\u003e) (Fig. S2), revealing the method sensitivity to empty states within the metal 5\u003cem\u003ed\u003c/em\u003e shell and, to some extent, the \u003cem\u003es\u003c/em\u003e-shell due to this hybridisation. In this study, Au NPs with an average particle size of 8 \u0026plusmn; 2 nm were used, as confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS) (Figs. S3 and S4). The Au NPs have a LSPR centered at nominally 520 nm (2.38 eV) according to UV-vis spectroscopy (Fig. S5).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe steady-state XANES analysis established that the Au NPs exhibit an electronic structure resembling bulk gold, as reported elsewhere.\u003csup\u003e22\u003c/sup\u003e\u003csup\u003e,35\u003c/sup\u003e This agreement is further corroborated by our theoretical calculations, showing the evolution of the DOS as function of particle size (Fig. S6). The unexcited XANES spectrum of the Au NPs, measured at XFEL (SwissFEL, Switzerland) and the synchrotron, displayed a consistent shape. This consistency supports the applied methodology\u0026apos;s ability to capture the transient alterations in the electronic structure of gold before the sample gets damaged, i.e., probe-before destruction concept.\u003csup\u003e36,\u003c/sup\u003e \u003csup\u003e37\u003c/sup\u003e XFELs have only recently provided access to hard X-ray energies, allowing one for the first time to probe the Au L\u003csub\u003e3\u003c/sub\u003e-edge.\u003c/p\u003e\n\u003cp\u003eUltrafast time-resolved XANES data were acquired with the XFEL source as a probe, following the excitation of 5 mM Au NPs at 532 nm (~ 2.33 eV), utilising a 15 nm full width at half maximum (FHWM) bandwidth, a pulse duration of approximately 75 fs, and a power density of 98 mJ/cm\u003csup\u003e2\u003c/sup\u003e (equivalent to 4 \u0026micro;J within a 60 x 60 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e spot). The choice of this precise plasmon excitation energy was to induce LSPR through intra-band \u003cem\u003es\u003c/em\u003e- to \u003cem\u003es\u003c/em\u003e-shell excitation while minimising interband excitation (\u003cem\u003ed\u003c/em\u003e- to \u003cem\u003es\u003c/em\u003e-shell excitation). The centre of the Au \u003cem\u003ed\u003c/em\u003e-shell is located at 2.5-2.58 eV (~\u0026nbsp;496-480 nm) from the metal Fermi level (E\u003csub\u003eF\u003c/sub\u003e),\u003csup\u003e38\u003c/sup\u003e\u003csup\u003e,39\u003c/sup\u003e meaning that the laser pulse with 2.33\u0026plusmn;0.13 eV (15 nm FHWM) photon energy can only excite the low energy tail of the \u003cem\u003ed\u003c/em\u003e-shell at best. Figure 1C compares the XANES spectra of unexcited (unpumped spectrum) and excited (pumped spectrum) recorded at Dt =100 fs time delay after excitation at 532 nm. Optical excitation induced a spectral downshift in energy and decreased XANES whiteline intensity, corroborating that it induced changes in the gold electronic structure around its Fermi-level energy, and the TR-XAS can track the changes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo better illustrate the results, the XANES difference spectrum (pumped-unpumped XANES spectra) is also shown in Figure 1C. The difference spectrum is dominated by the positive signal below and a negative signal above the Au E\u003csub\u003eF\u003c/sub\u003e.\u0026nbsp;Transient L\u003csub\u003e3\u003c/sub\u003e-edge XANES readily capture changes in the density of unoccupied states, particularly those induced in the \u003cem\u003ed\u003c/em\u003e-shell, either directly or through processes like hybridisation with the \u003cem\u003es\u003c/em\u003e-shell. Accordingly, a positive signal correlates with an increase in density of states (DOS); conversely, a negative signal (i.e., a bleached signal) indicates a decrease in empty states. Therefore, the positive signal below the Au E\u003csub\u003eF\u003c/sub\u003e is ascribed to the formation of a hot hole population induced by the plasmon optical excitation. In contrast, hot electrons give rise to the negative signal above the Au E\u003csub\u003eF\u003c/sub\u003e, consistent with empty states filling. The transient signal directly demonstrates the generation of hot carriers through LSPR decoherence via Landau damping (the non-radiative pathway dominant in small nanoparticles).\u003csup\u003e21\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e24\u003c/sup\u003e\u003csup\u003e,40\u003c/sup\u003e Most notably, the hot hole and electron signals are neither symmetric nor have the same integrated magnitude. This is related to the XANES higher sensitivity to empty states formation and the L\u003csub\u003e3\u003c/sub\u003e-edge transition changes in the \u003cem\u003ed\u003c/em\u003e-shell that is part of the valence, where the hot holes are formed.\u003c/p\u003e\n\u003cp\u003eTo establish the time scales for plasmon damping (g) and the average lifetime of carriers (t), kinetic traces were extracted at the maximum of the hot hole intensity (11916 eV, 2.5 eV below Au E\u003csub\u003eF\u003c/sub\u003e (Figure 2B)) and the excited electron intensity (11922 eV, 3.0 eV above Au E\u003csub\u003eF\u003c/sub\u003e (Figure 2C)) populations, as depicted in (Figure 2A). The kinetic data from the time scans were fitted by a model published elsewhere,\u003csup\u003e41\u003c/sup\u003e described in SI equations S1 and S2. In brief, the data collected at 11916 and 11922 eV were fitted with a convolution of temporal instrument response function (Gaussian) with a monoexponential decay (with a time constant ). The resulting fit is the solid green in Figure 2B. Due to the low signal-to-noise ratio for the hot electron data, the error bars are relatively large. However, qualitatively, it is possible to see that the signal has dynamics similar to the hot holes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe \u0026gamma; time can be extracted from the transient signal onset time because it is the point at which the Au DOS starts to change, i.e., the fingerprint for hot carrier formation. In this particular case, it was estimated to be 24.6 \u0026plusmn; 6 fs, corroborating that plasmon decoherence occurs between 10-100 fs.\u003csup\u003e24\u003c/sup\u003e Following plasmon damping, the hot carriers undergo a carrier multiplication reaching a maximum at 105 \u0026plusmn; 8 fs, estimated from rising edge analysis. The lifetimes of the hot carriers were determined from a single exponential decay to be 498 \u0026plusmn; 35 fs with complete carrier thermalisation occurring within 1.5 ps. These time constants align with previous postulations\u003csup\u003e24\u003c/sup\u003e but are here substantiated through direct measurement. The confirmed ultrafast hot carrier dynamics in plasmonic nanoparticles are the primary bottleneck in plasmonic applications.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo estimate the number of electrons engaged when exciting 5 mM Au NPs at 532 nm, utilising a 15 nm full width at half maximum (FHWM) bandwidth, a pulse duration of approximately 75 fs, and a power density of 98 mJ/cm\u003csup\u003e2\u003c/sup\u003e, the positive signal variance at 0 and 100 fs were integrated. This integrated signal was then juxtaposed with the signal difference between the Au and Pt L\u003csub\u003e3\u003c/sub\u003e-edges (Fig. S2). Note that the signal difference between Au and Pt relates to 1\u003cem\u003ee\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e less in Pt valence states, i.e., the integrated positive signal of the difference between Pt and Au corresponds to the equivalent of having 1\u003cem\u003ee\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e from each Au atom participating in the resonance. Employing this simple methodology, we estimated that each gold atom contributed with 0.19\u003cem\u003ee\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e at the start of the resonance, which underwent multiplication until 105 fs, reaching a maximum of 0.46\u003cem\u003ee\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e from each Au atom contributing to hot carrier formation at this excitation power.\u003c/p\u003e\n\u003cp\u003eAssuming an excitation volume of 60 x 60 x 100\u0026micro;m\u003csup\u003e3\u003c/sup\u003e and considering the Au solution concentration (5 mM), one can expect 1.5 x 10\u003csup\u003e8\u003c/sup\u003e nanoparticles in the excited volume. An 8 nm Au NP has \u0026raquo;12000 atoms, equating to about 1.8 x 10\u003csup\u003e12\u003c/sup\u003e Au atoms in the excited volume. The photon density in the optical pulses is about 10\u003csup\u003e13\u003c/sup\u003e, from which 20% is absorbed according to UV-Vis, implying that the excited volume absorbs around 2x10\u003csup\u003e12\u003c/sup\u003e photons. This suggests an excitation of about 1\u003cem\u003ee\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e per atom of Au, from which 19% are converted into hot carriers at the onset, multiplying to about 46% within 100 fs. The observation suggests that hot carrier generation is a prime decay channel of Au LSPR and undoubtedly the most significant mechanism in nonradiative decay.\u003c/p\u003e\n\u003cp\u003eAfter verifying the generation of hot carriers, the next step is the investigation of the dynamics of their energy distribution - a significant yet elusive aspect in the realm of plasmonic hot carriers, particularly when it comes to holes. Our understanding is derived mainly from theoretical studies\u003csup\u003e20\u003c/sup\u003e\u003csup\u003e,4243\u003c/sup\u003e and indirect techniques.\u003csup\u003e22\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e33\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e34\u003c/sup\u003e\u003csup\u003e,44\u003c/sup\u003e For example, internal quantum efficiency measurements have inherent limitations as they solely quantify carriers injected into an acceptor layer, like a semiconductor, failing to provide insights into the dynamic behaviour of the carriers in the metal. While the hot electrons can only populate the empty states within the \u003cem\u003esp\u003c/em\u003e-shells, the holes can be in \u003cem\u003esp\u003c/em\u003e- and \u003cem\u003ed\u003c/em\u003e-shells, confirmed by valence band \u0026ndash; X-ray photoelectron spectroscopy (VB-XPS) shown in Figure 3A. It is evident when the VB-XPS is overlapped with the transient XANES spectrum (recorded at time zero) that the generated holes are indeed located throughout the entire valence, including the \u003cem\u003ed\u003c/em\u003e-shell, despite the optical pulse energy allowing primarily \u003cem\u003esp\u003c/em\u003e-shell excitation.\u003c/p\u003e\n\u003cp\u003eFigure 3B shows the energy distribution and population of the carriers at different time delays after excitation. As expected, the plasmonic excitation depopulates and populates states below and above the Fermi energy. The ultrafast carrier-carrier interactions during dephasing and multiplication determine their energy and respective population. The hot carrier energy distribution goes beyond single photon energy for hot electrons and holes. Moreover, it is noticeable that both carrier populations and the width of their energy distributions increase until about 100 fs, decreasing asymptotically after that. \u0026nbsp;A slight asymmetry exists between hot electron and hot hole populations, which cannot be fully explored here due to the probe\u0026apos;s lower sensitivity to hot electrons.\u003c/p\u003e\n\u003cp\u003eThe rapid depopulation of electrons in the \u003cem\u003ed\u003c/em\u003e-shell is expected due to the broad energy overlap between the \u003cem\u003ed\u003c/em\u003e and \u003cem\u003esp\u003c/em\u003e-band, which provides a high density of \u003cem\u003ed\u003c/em\u003e-electrons that couples with the plasmonic resonance and dissipates its energy.\u003csup\u003e43\u003c/sup\u003e However, this does not explain the observation of carriers having energies above the photon energy, even considering that the Au core-hole lifetime broadening is 5.41 eV at the L\u003csub\u003e3\u003c/sub\u003e-edge,\u003csup\u003e45\u003c/sup\u003e which inevitably broadens the energy scale. Achieving precise energy distributions of carriers requires high-resolution measurements,\u003csup\u003e46\u003c/sup\u003e which implies extended acquisition times rarely offered at XFEL facilities. Nonetheless, hot holes are distributed across the entire valence electronic structure, and their energy distribution increases up to 250 fs (Figure 3C) before relaxing. These two observations indicate the involvement of carrier multiplication mechanisms that can increase the carrier population and their energy distribution, an effect that has yet to be reported.\u003csup\u003e43\u003c/sup\u003e Note that the low optical laser fluency and short pulse duration used in this experiment make it highly unlikely that multiphoton excitation of single electrons occurs.\u003c/p\u003e\n\u003cp\u003eRegarding carrier multiplication, there are two scattering mechanisms: impact excitation and Auger heating,\u003csup\u003e47,48\u003c/sup\u003e The predominant mechanism in carrier multiplication is impact excitation, where an excited electron (hole) undergoes Coulomb scattering, losing energy and momentum and giving rise to an additional electron-hole pair. The distinctive feature of impact excitation is a rise in the number of carriers and a simultaneous reduction in their energy. Conversely, Auger heating characterises the non-radiative recombination of an electron with a hole, where the energy and momentum are transferred to an electron (hole) within the same shell. The hallmark of Auger heating is a decline in the number of carriers and an increase in their energy. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo enhance the visualisation and comprehension of the hot hole multiplication process, the shape of different spectra regarding charge width and charge energy was analysed (see Figure 3C). The details of the data analysis procedure are outlined in the SI. Commencing with the average hot carrier distribution energy, it remained constant until 100 fs before exhibiting a subsequent decrease. This implies the LSPR dephasing process extends to 100 fs, increasing the nonequilibrium hot carrier population through the impact excitation scattering mechanism. However, examining the hot carrier distribution width, reflecting the energy distribution of the hot holes unveils a relative surge in the energy distribution beyond the time when the hole population is at its maximum (approximately 100 fs), i.e., the energy distribution of hot holes increases up to 250 fs. This observation is noteworthy, especially considering this process competes with hole thermalisation, occurring within tens of femtoseconds in metals. The broadening induced by the core hole relaxation cannot account for the increase in distribution width, as it should have smeared the energy resolution from the outset, preventing the difference signal from accurately reflecting the valence state of gold. This suggests the involvement of a mechanism that generates carriers with higher energy than the dephasing process produces - specifically, the participation of Auger heating. This mechanism has yet to be considered in plasmon relaxation dynamics, altering the current understanding of hot carrier formation, multiplication, and relaxation in plasmonic materials.\u003c/p\u003e\n\u003cp\u003eIn this work, we presented the results from an ultrafast X-ray absorption experiment conducted at the XFEL involving citrate-capped gold nanoparticles excited at their LSPR with minimum intraband excitation. This experiment enabled the real-time observation of the generation and subsequent relaxation of hot carriers. The plasmon damping was determined to be 25 fs, with a maximum hot carrier population of 0.46\u003cem\u003ee\u003csup\u003e-\u003c/sup\u003e\u003c/em\u003e from each Au atom detected at 105 fs after excitation. The lifetimes of the hot carriers were estimated to be 498 fs, with complete carrier thermalisation occurring within 1.5 ps. Energy scans conducted at varying delay times revealed that the energies of these carriers conform to the density of states of the metal, with some carriers possessing energies that exceed the photon energy, consistent with an Auger heating scattering mechanism. The observation impacts hot carrier applications, particularly those that are based on the energy of the hot carriers, such as photocatalysis and photovoltaics. For instance, without the Auger process, chemical reactions with redox windows larger than photon energy could not be catalysed. Similarly, the open circuit voltage of photovoltaic devices could not exceed the voltage offered by a single photon. The novel insight into plasmon induced hot carrier generation and dynamics provided here is likely to significantly impact applications for years to come.\u0026nbsp;\u003c/p\u003e\n\u003cdiv id=\"edn1\"\u003e\n \u003cp\u003e[i]. Kornbluth, M., Nitzan, A., Seideman, T. Light-Induced Electronic Non-Equilibrium in Plasmonic Particles. \u003cem\u003eJ. Chem. Phys.\u003c/em\u003e \u003cstrong\u003e138\u003c/strong\u003e, 174707 (2013).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"edn2\"\u003e\n \u003cp\u003e[ii]. Govorov, A. O., Zhang, H., Demir, H. V., Gun\u0026apos;ko, Y. K. Photogeneration of Hot Plasmonic Electrons with Metal Nanocrystals: Quantum Description and Potential Applications. \u003cem\u003eNano Today\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e, 85\u0026ndash;101 (2014).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"edn3\"\u003e\n \u003cp\u003e[iii]. Manjavacas, A., Liu, J. G., Kulkarni, V., Nordlander, P. Plasmon-Induced Hot Carriers in Metallic Nanoparticles. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 7630\u0026ndash;7638 (2014).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"edn4\"\u003e\n \u003cp\u003e[iv]. Rossi, T. P., Erhart, P., Kuisma, M. Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure. \u003cem\u003eACS Nano\u003c/em\u003e \u003cstrong\u003e14\u003c/strong\u003e, 9963-9971 (2020).\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe acknowledge the Paul Scherrer Institut, Villigen, Switzerland, for providing beamtime at the Alvra beamline of the SwissFEL facility. We also acknowledge SOLARIS National Synchrotron Radiation Centre, Krakow, Poland, for the access to the ASTRA and PHELIX beamline. The simulations were performed using computational resources provided by the Swedish National Infrastructure for Computing (SNIC) at UPPMAX and NSC, for which we want to thank.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e: J.Sa acknowledges funding from Olle Engkvists Stiftelse (grant no. 210-0007), Knut \u0026amp; Alice Wallenberg Foundation (Grant No. 2019-0071) and Swedish Research Council (grant no. 2019-03597). A.W. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement no. 884104 (PSI-FELLOW-III-3i). N.J.H. and P.N. acknowledge support from the Robert A. Welch Foundation under grants C-1220 and C-1222 and\u0026nbsp;the Air Force Office of Scientific Research via the Department of Defense Multidisciplinary University Research Initiative under AFOSR Award No. FA9550-15-1-0022. The work is partially supported under the Polish Ministry and Higher Education project: “Support for research and development with the use of research infrastructure of the National Synchrotron Radiation Centre SOLARIS” under contract nr 1/SOL/2021/2. The work is partially funded by the National Science Centre in Poland under grant number 2020/37/B/ST3/00555.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e: Conceptualization and methodology: A.W., J. Sz. and J.Sa; formal data analysis: A.W., J. Sz. and J.Sa; experimental investigations: A.W, C.B., C.C., P.J.M.J., R.G.C., V.R.S., P-B., J.K., A.M., T.S., E.P.-J. and J.Sa; data visualisation concepts: A.W., J. Sa, J.Sz and N.J.H., draft preparation: A.W., N.J.H., J. Sz. and J.Sa; writing-review and editing: all the authors. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e: The authors declare that they have no competing interests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData and materials availability\u003c/strong\u003e: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eNovotny, L., Hecht, BPrinciples of Nano-OpticsCambridge University Press: New York, (2006).\u003c/li\u003e\n\u003cli\u003eMaier, SAPlasmonics: Fundamentals and ApplicationsSpringer: New York (2007).\u003c/li\u003e\n\u003cli\u003eHalas, NJ., Lal, S., Chang, W., Link, S., Nordlander, PPlasmons in Strongly Coupled Metallic NanostructuresChemRev111, 3913\u0026ndash;3961 (2011).\u003c/li\u003e\n\u003cli\u003eXu, H., Bjerneld, EJ., K\u0026auml;ll, M., B\u0026ouml;rjesson, LSpectroscopy of Single Hemoglobin Molecules by Surface Enhanced Raman ScatteringPhysRevLett83, 4357\u0026ndash;4360 (1999).\u003c/li\u003e\n\u003cli\u003eO\u0026apos;Neal, DP., Hirsch, LR., Halas, NJ., Payne, JD., West, JLPhoto-Thermal Tumor Ablation in Mice Using Near Infrared-Absorbing NanoparticlesCancer Lett209, 171\u0026ndash;176 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Kuisma, MHot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic StructureACS Nano 14, 9963-9971 (2020)\u003c/li\u003e\n\u003cli\u003eKhurgin, JBFundamental limits of hot carrier injection from metal in nanoplasmonicsNanophotonics 9, 453\u0026ndash;471 (2020).\u003c/li\u003e\n\u003cli\u003eS\u0026aacute;, J., Tagliabue, G., Friedli, P., Szlachetko, J., Rittmann-Frank, MH., Santomauro, FG., Milne, CJ., Sigg, HDirect observation of charge separation on Au localized surface plasmonEnergy EnvironSci6, 3584\u0026ndash;3588 (2013).\u003c/li\u003e\n\u003cli\u003eHe, J., Liu, M., Yin, C., Liu, Z., Dong, X., Zhang, Z., Wang, JExperimental studies on the X-ray single-pulse jitter at the SSRFNuclear InstMethPhysRes1025, 166038 (2022).\u003c/li\u003e\n\u003cli\u003ePellegrini, CThe history of X-ray free-electron lasersEurPhysJH 37, 659\u0026ndash;708 (2012).\u003c/li\u003e\n\u003cli\u003ehttps://www.xfel.eu/news_and_events/news/index_eng.html?openDirectAnchor=1772 (Accessed on 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pathways between light, carriers, and lattice in real time with attosecond core-level spectroscopyPhysRevX 11, 041060 (2021).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3799527/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3799527/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThere is an increasing interest in nonequilibrium “hot” carrier generation, created by the decay of collective electronic oscillations on metals known as surface plasmons. Despite extensive efforts, direct observation of the mechanism responsible for generating hot carriers due to plasmon decay has proven challenging. Here, the dynamics of hot carrier generation on gold nanoparticles (Au NPs) are followed with unparalleled detail through ultrafast X-ray absorption spectroscopy (XAS) at the X-ray free-electron laser (XFEL). In Au NPs, the plasmon dephases after 25 fs and the hot carrier population peaks within 105 fs, reaching thermal equilibrium within 1.5 ps. The nonequilibrium carriers display an energy dispersion governed by the density of states of the metal, with some carriers possessing energies surpassing that of a single photon, consistent with the involvement of an Auger heating mechanism distinct from the expected impact excitation that dominates the carrier multiplication step. The most energetic carriers exhibit relatively shorter lifespans, a property that may be critical for exploiting them in applications. This study substantiates hot carrier formation through nonradiative decay as the main decay channel of plasmon resonance. The proposed methodology provides a straightforward approach for real-time tracking of plasmon-induced hot carrier dynamics.\u003c/p\u003e","manuscriptTitle":"The Dynamics of Plasmon-Induced Hot Carrier Creation in Colloidal Gold","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-08 18:57:59","doi":"10.21203/rs.3.rs-3799527/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"558ae84a-d00b-4ec2-a434-bfc3cbd17d93","owner":[],"postedDate":"April 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":28070545,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Nanoparticles"},{"id":28070546,"name":"Physical sciences/Chemistry/Physical chemistry/Excited states"}],"tags":[],"updatedAt":"2025-03-07T08:05:34+00:00","versionOfRecord":{"articleIdentity":"rs-3799527","link":"https://doi.org/10.1038/s41467-025-57657-1","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-03-07 05:00:00","publishedOnDateReadable":"March 7th, 2025"},"versionCreatedAt":"2024-04-08 18:57:59","video":"","vorDoi":"10.1038/s41467-025-57657-1","vorDoiUrl":"https://doi.org/10.1038/s41467-025-57657-1","workflowStages":[]},"version":"v1","identity":"rs-3799527","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3799527","identity":"rs-3799527","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}