Perylene-Based Columnar Liquid Crystal: Reveling Unipolar Resistive Switching for Nonvolatile Memory Devices

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Avila, P. Chulkin, P.A. Serrano, J.P. Dreyer, M. Berteau-Rainville, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3931670/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 May, 2024 Read the published version in Journal of Molecular Liquids → Version 1 posted You are reading this latest preprint version Abstract Perylene-based columnar liquid crystal (LC) devices exhibit unipolar resistive switching (RS), clearly identified on cyclic J-V curve hysteresis, stable for several cycles. Trap-controlled SCLC conduction is responsible for the charge transport in the active layer, where the “set” and “reset” processes occur. The incorporation of ZnO@SiO2 quantum dots significantly enhances the RS response. The distinguishing result presented here is the ability to write-read-erase-read, controlling the "on" and "off" states by applying an external electric field, allowing to store and read information multiple times. An endurance of nearly one order of magnitude between the low and high RS states was determined over 50 consecutive cycles. The device proved to be resilient, preserving the resistive switching effect and memory capacity even after one year maintained at room temperature in ambient atmosphere. DFT calculations indicate a conduction mechanism based on reversible reductions of the perylene LC molecules. This article highlights the ability of LCs to store and process information via their resistivity, with potential for the production of low-cost and large-area nonvolatile printed organic memories. Electronic Materials and Devices liquid crystal resistive switching Printed organic memories Memory capacity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction A memristor (memory resistor - MR) is a passive two-terminal electronic component able to store non-volatile information by resistance variations based on the resistive switching (RS) effect, an effect which has already been observed in the 60s for several oxides [ 1 ]–[ 3 ]. In 1971 Leon Chua theoretically proposed the circuit element that could describe the experiments, and identified it as one of the fundamental elements to compose two-terminal circuits [ 4 ]. MR devices remained an object of theoretical study until 2008, when they were realized by Hewlett-Packard (HP) [ 5 ]. The RS effect allows different electronic applications, such as logical and analog operations, unconventional computing, pattern recognition, and neural networks [ 6 ]. The resistive random-access memory (RRAM) is a non-volatile device with local resistance control through voltage pulses of low power consumption and sub-nanosecond switching times (read and write). The RS effect is mostly observed in inorganic materials[ 7 ]–[ 10 ]. However, RRAMs based on organic semiconductors were recently shown to be promising [ 11 ]–[ 15 ]. Columnar LCs present strong π-π interactions of the aromatic cores, surrounded by flexible aliphatic side chains, which generates high charge mobility and a “quasi-one-dimensional” electrical conductivity [ 18 ]. The potential of perylene-based columnar LCs has been recognized as promising for organic electronic devices, where the electro-optical properties can be substantially improved by controlling the molecular alignment [ 19 ] [ 12 ]. So far, only few reports of the RS effect with columnar LCs are available [ 20 ], [ 21 ] [ 22 ]. The effect was also demonstrated in a bio-based ionic LC [ 23 ]. Recently, the potential of a nematic LC for storing and processing information was theoretically proposed [ 24 ]. However, as far as we know, there are no reports investigating the RS effect for perylene-based columnar LCs. Here, we report on a nonvolatile resistive switching memory whose active layer is a perylene tetraester (PerLC) presenting a columnar hexagonal LC mesophase between – 25 o C and 148 o C. Scheme 1 shows its molecular structure. The electrical properties of solution processed thin films were previously investigated for this material (compound 1 in [ 25 ]),. Surprisingly, with the PerLC confined between ITO electrodes, we observed a prominent unipolar RS effect, which was enhanced upon doping with ZnO@SiO 2 quantum dots. The “on” and “off” states occur in the space charge limited current (SCLC) regime with a high degree of reproducibility. Devices are stable for at least one year, with the device preserved in ambient atmosphere at room temperature. We demonstrate that the devices have the ability to write-read-erase-read .[ 8 ], [ 26 ]. 2. Results and discussion PerLC-based memory devices were electrically characterized in diode-like structures, consisting of a cell with the organic material sandwiched between two ITO-coated glass plates using 8 µm-thick spacers. Cyclic voltage measurements were performed from − 30V to + 30V and back. The effect of PerLC doping with ZnO@SiO 2 quantum dots (QDs) was also investigated. Information about the synthesis of the PerLC and ZnO@SiO 2 QDs, as well as the cell preparation, are in the supporting information. Electric impedance spectroscopy (EIS) was performed to determine the resistive and capacitive properties of the pure PerLC and PerLC:QD (10%, 20% and 40% wt.) layers to investigate the RS mechanism. The results are usually interpreted in terms of equivalent circuits consisting of electrical components such as resistors and capacitors. The best electrical response was obtained with 20%wt. QD doping, resulting in a significant reduction of the bulk resistance. The detailed discussion and the EIS results concerning the PerLC:QD doping are presented in the supporting information. The effect of different QD concentrations on the PerLC hexagonal columnar structure was evaluated by X-Ray diffraction (XRD) measurements, see Fig. 1 . The main peak at low angle ( d 001 =15.5 Å) is associated to the distance between the molecular columns. Pure PerLC shows the highest intensity compared to the doped films, suggesting a greater correlation length, related to the size of the macroscopic columnar hexagonal domains (MCHDs). With the addition of QDs the intensity of the (100) peak decreased sharply. However, the position does not change significantly, which indicates that the distance between the columns in the hexagonal structure is not affected by the presence of the QDs. The peak between 2θ = 25 and 26° (d 001 =3.5 Å) represents the molecular stacking within the columns. There is also no change in position and only little variation in intensity upon doping. Inset of Fig. 1 shows the ratio between peak intensities ( \({I}_{100}\) / \({I}_{001}\) ), confirming that the reduction of the main (100) peak intensity by QD doping is not related to the amount of material, but rather to the reduction in size of the MCHDs. It indicates that the QDs fragment the macroscopic domains, but it seems that for 20% wt. doping an equilibrium with larger MCHDs is achieved. It is well known that doping columnar LCs with metallic nanoparticles or QDs improves charge carrier conductivity [ 27 ]–[ 30 ], where the optimized doping percentage may depend on the distinct interactions occurring in the film [ 31 ]. In the PerLC:QD system, we have to consider interactions between LC-LC molecules (i), LC-QD (ii) and QD-QD (iii). The XRD data suggest that (ii) are dominant for the lower concentration of 10%, with the QDs homogeneously distributed around the smaller MCHDs. For 40% the (i) and (iii) interactions are dominant within QD agglomerations, but due to high concentration the size of the MCHDs is lower compared to 20% doping, where the three kinds of interactions seem to find an equilibrium, which optimizes the electrical properties. Scheme S5 in supporting information illustrates these situations. Thus, the optimized 20% wt. QD content was used for the memory effect studies. Figure 2 a shows the superimposed electrical measurements for pure PerLC (red curve) and PerLC:QD (blue curve), with the peak current at the same position at ± 16 V. A typical RS J-V curve is observed in both cases, where the “set” and “reset” processes occur at the same polarity, being characterized as unipolar RS [ 32 ][ 33 ] [ 34 ] [ 35 ]. The inset graph shows in detail the shape of the J-V curve for pure PerLC, clearly demonstrating that the RS effect already occurs for the pure PerLC and suggesting that the QDs act as current enhancers. Figure 2 b illustrates the cycle starting at -30 V with the switching steps occurring at positive bias (forward cycle) and at negative bias (backward cycle) for the PerLC:QD cell. The “set” process takes place at 8V, where the device switches to the low-resistivity state (LRS) and remains there until the current reaches a peak at 16V, where the "reset" process occurs, with the system returning to the high-resistivity state (HRS). The same effect is symmetrically observed in the backward cycle at negative bias. Figure 2 c shows the J-V curves in positive polarity for the pure PerLC and PerLC:QD 20% plotted on a log-log scale. For low voltage an ohmic conduction takes place until 8.0 V, \(J \propto {V}^{n}\) with n ≈ 1.0, when a space charge limited current (SCLC) occurs due to hopping transport of injected charges according to the Child–Langmuir law [ 34 ]. For PerLC and PerLC:QD 20% the slope is n = 2.4 and n = 3.2, respectively, indicating that the density of states is altered by doping. The SCLC regime dominates until 16.0 V, thus a trap-limited conduction is responsible for the charge transport in the device until the “reset” process above 16.0 V. This mechanism is closely related to the charge carrier trapping or de-trapping by defects[ 36 ], in agreement with literature[ 37 ]. In order to determine the charge carrier mobility of the undoped and 20% QD doped PerLC, our previously published model was used [ 38 ] where an electric field dependent mobility of the form \(\mu \left(E\right)={\mu }_{0}{e}^{\gamma \sqrt{E}}\) was considered. The parameters µ 0 and γ implicitly include the trap distribution and can be obtained from fitting the SCLC regimes of the J-V curves. The fits for each device are shown as red solid lines in Figure S3 of the Supporting Information, where the obtained values of µ 0 and γ are also displayed. The Poole-Frenkel coefficient γ implies that the hopping transport is made easier by QD doping. Figure 2 d shows the calculated mobility as a function of the voltage, using the \(\mu \left(E\right)\) equation with µ 0 and γ values, which shows that the mobility in the 20% QD doped PerLC is one order of magnitude higher than in undoped PerLC. Thus, the QDs enhance the charge transport through the active layer and consequently the RS effect. Figure 3 a shows the J-V curve of the PerLC:QD 20% device, which exhibits the butterfly fingerprint shape characteristic of the RS effect [ 39 ][ 35 ] [ 40 ]. The HRS (read segment) and the LRS (blue segment) are highlighted. Figure 3 b compares the RS characteristics of the 1st and 50th cycle. Despite a certain narrowing of the hysteresis which occurs after consecutive cycles, the HRS and LRS values at 16.0 V demonstrate a good stability of the device performance. The HRS/LRS ratio of one order of magnitude (Fig. 3 c) is a very reasonable value for an organic LC device [ 35 ][ 41 ]. This retention property was measured at room temperature and under ambient atmosphere. Although the device presents the RS effect, it is essential that it also shows the ability to retain and process information. The tests of write-read-erase-read were done using the EIS technique. The Nyquist plot presented in Fig. 4 a shows the memory effect where the red and orange arrows indicate the “set” process, decreasing the resistance, and the blue and green arrows indicate the “reset” process, increasing the resistance. In binary language, the arrows indicate the change between the states “1” and “0”. Initially, EIS measurement was performed by applying 1.0 V (DC) to confirm the HRS as a pristine state (black curve). Then, 10.0 V (DC) was applied for 30 seconds to “set” the LRS. With this process, the resistance should decrease; nevertheless, it is necessary to check if the information was stored. To confirm this state, EIS was repeated with 1.0 V (DC) (reading process), as shown in Fig. 3 a (red curve). Since this is a switch device, the “reset” was carried out aiming to go back to the previous state, with higher resistance. For this, -10.0 V (DC) were applied for 30 seconds. To confirm if the information was deleted, the EIS measurement was repeated under 1.0 V (DC), as presented in the blue curve (resistance increased). The “set” and “reset” was repeated once more to demonstrate that the write-read-erase-read effect is stable (orange and green curves). The write-read-erase-read effect was identically observed after one year with the device stored under ambient atmosphere at room temperature, thus confirming stability of the memory effect of PerLC over long periods of time. The layer long polarization leads to a decrease of the impedance (Fig. 4 b), which is more evident at lower frequency. With phase shift (Fig. 4 c), a slight change is observed, which indicates an increase of conductivity and loss of capacitance of the organic layer. The semicircle in Fig. 4 a indicates that only one time constant describes the charge transport process, at least in the considered frequency range. Therefore, a three-element equivalent electric circuit (inset) was used to fit the experimental results. R S represents the resistance of electrodes and connectors, in series with the parallel combination of the bulk capacitance (C) and resistance (R P ). The parallel connection of R P and C describes the charge transport along the PerLC:QD layer. R P stands for the resistance of the charge transfer, whereas C describes the charging capacity. These parameters describe the total resistance and capacitance of the layer. The fact that no additional elements are necessary to fit the spectrum within the considered frequency range means that all the layer components have similar charge transfer properties and remain in a similar electronic state. Figure 5 shows the results obtained from the fitting process. The error bars correspond to a 0.05 confidence interval with respect to accordance between experimental and simulated spectra. In other words, deviation of each parameter up to the indicated error would cause an overshoot of 5% of the experimental versus the simulated spectra from the equivalent circuit model. The change of parameters caused by the “set” and “reset” are reproducible. The set increases the capacitance, while the layer resistance R P decreases. The series resistance R S shows an opposite behaviour, representing the resistance of the electrodes and connectors and is not related to the storage effect. It is negligible since R S is in the range of three orders of magnitude smaller than R P , and therefore has no impact on the memory characterization. The parallel resistance R P is the only relevant numerical parameter to be used as a memory storage response due to relatively low error and significant change during “set” and “reset” cycles. We have performed density functional theory (DFT) calculations on PerLC molecules without side chains, as these do not take part in defining the electronic properties (more details can be found in the Supporting Information, notably for the methodology and the distribution of charge density on the neutral molecule). We have first examined how the excess charge and spin density is localized on the radical anion, which is shown in Fig. 6 . The additional electron leads to a net decrease in local side-chain dipoles via the transfer of charge density from the terminating carbon to the carbonyl carbon; besides, charge density delocalizes relatively uniformly over the conjugated core, in a similar manner to the spin density. Relevant molecular orbitals for charge transport, in general, i.e. the HOMO and LUMO of PerLC in its neutral state, are shown in Fig. 7 . The HOMO of the dianion is calculated to be unbound (see Table 1 , third column, providing HOMO energies for four different charge states) which indicates the inability of PerLC to accommodate two supplementary electrons and the resulting instability of PerLC in its dianionic state. The energy cost of the charge transitions to the radical anion and dianion have been calculated and are shown in Table 1 , second column, too. Values represent the total energy change across the transition; negative values indicate reactions liberating energy and positive values indicate reactions requiring energy inputs. Therefore, these results also support the fact that PerLC can only accept one supplementary electron. The positive HOMO of the dianion indicates that the last electron is unbound, which is also reflected in the 1.19 eV energy cost to form the dianion. Forming positive species also requires significant energy input, but they are stable, nonetheless. We have additionally investigated the formation of PerLC radical cation and dication and found that, albeit stable, both species require significant energy to form. In summary, these results support a conduction mechanism based on the electrochemical single reduction of PerLC, where charge transfer occurs within PerLC columns, between polycyclic aromatic cores of adjacent molecules. Table 1 Charge transitions (a) from the neutral molecule to the radical anion, (b) from the radical anion to the dianion, (c) from the neutral molecule to the radical cation, and (d) from the radical cation to the dication. The first number in brackets indicates the charge; the second number indicates the spin multiplicity (equal to 2S + 1). Transition ΔE (eV) HOMO of target (eV) (a) (0,1) → (-1,2) -1.78 -2.27 (b) (-1,2) → (-2,1) + 1.19 + 0.61 (c) (0,1) → (+ 1,2) + 7.04 -10.99 (d) (1,2) → (+ 2,1) + 10.62 -15.46 3. Conclusions The PerLC layer doped with QDs (ZnO@SiO2) is shown to be a functioning material for memory-storage devices, with ability to change resistivity after applying an external voltage, as well as its reversibility. The EIS studies revealed the electrical parameters that can be used as markers of the memory-storage effect. The reversible reduction of the organic molecules at the origin of the conduction mechanism was investigated by DFT calculations. The device shows good endurance with LRS/HRS ratios of about one order of magnitude over 50 cycles. The RS effect and memory capability are preserved over one year. We experimentally confirmed that the device can be used to perform the basic logical operations of write-read-erase-read , which are fundamental for building a storage and processing device. To the best of our knowledge, our study represents the first observation of RS effect for a perylene-based columnar liquid crystal, which opens new possibilities for this class of molecules already well investigated in organic electronic devices. Declarations Declaration of competing interests The authors declare that there are no competing interests. Acknowledgments This work was funded by CNPq, CAPES (#001), FAPESC, INCT-INEO, CAPES/COFECUB (#937-20 and PhC 962/20) and H2020-MSCA-RISE-2017 (OCTA, #778158). 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Chiu, “A Review on Conduction Mechanisms in Dielectric Films,” Adv. Mater. Sci. Eng. , vol. 2014, p. 18, 2014. J. Eccher, G. C. Faria, H. Bock, H. von Seggern, and I. H. Bechtold, “Order Induced Charge Carrier Mobility Enhancement in Columnar Liquid Crystal Diodes,” ACS Appl. Mater. Interfaces , vol. 5, no. 22, pp. 11935–11943, Nov. 2013, doi: 10.1021/am403681q. X. Zhao, H. Xu, Z. Wang, Y. Lin, and Y. Liu, “Memristors with organic‐inorganic halide perovskites,” InfoMat , no. April, p. inf2.12012, May 2019, doi: 10.1002/inf2.12012. D. B. Strukov, G. S. Snider, D. R. Stewart, and R. S. Williams, “The missing memristor found,” Nature , vol. 453, no. 7191, pp. 80–83, 2008, doi: 10.1038/nature06932. H. Patil et al. , “Stable and Multilevel Data Storage Resistive Switching of Organic Bulk Heterojunction,” Nanomaterials , vol. 11, no. 2, p. 359, Feb. 2021, doi: 10.3390/nano11020359. Scheme Scheme 1 is available in the Supplementary Files section. Additional Declarations The authors declare no competing interests. Supplementary Files SupportingInformationLindiomar28Sep23withoutauthors.docx Scheme1.png Scheme 1. Molecular structure of the PerLC. Cite Share Download PDF Status: Published Journal Publication published 01 May, 2024 Read the published version in Journal of Molecular Liquids → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-3931670","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":271201332,"identity":"e844314d-51e1-40f8-8d1c-e0df14ca742b","order_by":0,"name":"L.B. Avila","email":"","orcid":"","institution":"Universidade Federal de Santa Catarina","correspondingAuthor":false,"prefix":"","firstName":"L.B.","middleName":"","lastName":"Avila","suffix":""},{"id":271201333,"identity":"bbbc1538-2726-404b-9910-f82367453d04","order_by":1,"name":"P. Chulkin","email":"","orcid":"","institution":"Chemistry Faculty, Silesian University of Technology","correspondingAuthor":false,"prefix":"","firstName":"P.","middleName":"","lastName":"Chulkin","suffix":""},{"id":271201334,"identity":"4aaa0a53-4e27-4d5f-8f9e-938dffe3fc7d","order_by":2,"name":"P.A. Serrano","email":"data:image/png;base64,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","orcid":"","institution":"Universidade Federal de Santa Catarina","correspondingAuthor":true,"prefix":"","firstName":"P.A.","middleName":"","lastName":"Serrano","suffix":""},{"id":271201335,"identity":"f259d7e1-c824-45df-8325-ac3eaef57812","order_by":3,"name":"J.P. Dreyer","email":"","orcid":"","institution":"Universidade Regional de Blumenau","correspondingAuthor":false,"prefix":"","firstName":"J.P.","middleName":"","lastName":"Dreyer","suffix":""},{"id":271201336,"identity":"d6e1d39e-ee9a-4c07-b4c1-20d10f8c888e","order_by":4,"name":"M. Berteau-Rainville","email":"","orcid":"","institution":"Institut national de la recherche scientifique, Centre Énergie Matériaux Télécommunications","correspondingAuthor":false,"prefix":"","firstName":"M.","middleName":"","lastName":"Berteau-Rainville","suffix":""},{"id":271201337,"identity":"f6b06ee3-13a0-4065-a56b-42024eee3169","order_by":5,"name":"E. Orgiu","email":"","orcid":"","institution":"Institut national de la recherche scientifique, Centre Énergie Matériaux Télécommunications","correspondingAuthor":false,"prefix":"","firstName":"E.","middleName":"","lastName":"Orgiu","suffix":""},{"id":271201338,"identity":"417fa599-a0b0-419c-8977-1192de543754","order_by":6,"name":"L.M. Zimmermann","email":"","orcid":"","institution":"Universidade Federal de Santa Catarina","correspondingAuthor":false,"prefix":"","firstName":"L.M.","middleName":"","lastName":"Zimmermann","suffix":""},{"id":271201339,"identity":"19936581-b6a1-4d87-a272-a5d823f8d1d7","order_by":7,"name":"H. Bock","email":"","orcid":"","institution":"Centre de Recherche Paul Pascal, Université de Bordeaux \u0026 CNRS","correspondingAuthor":false,"prefix":"","firstName":"H.","middleName":"","lastName":"Bock","suffix":""},{"id":271201340,"identity":"f84f7f94-6952-45df-b4b3-b3704cf3832c","order_by":8,"name":"G.C. Faria","email":"","orcid":"","institution":"Instituto de Física de São Carlos, Universidade de São Paulo","correspondingAuthor":false,"prefix":"","firstName":"G.C.","middleName":"","lastName":"Faria","suffix":""},{"id":271201341,"identity":"dd88b0d6-59aa-4279-9b16-fb975b6c3170","order_by":9,"name":"J. Eccher","email":"","orcid":"","institution":"Universidade Federal de Santa Catarina","correspondingAuthor":false,"prefix":"","firstName":"J.","middleName":"","lastName":"Eccher","suffix":""},{"id":271201342,"identity":"a42eff92-8fba-4e4d-9c7c-fb2213e2eebb","order_by":10,"name":"I.H. Bechtold","email":"","orcid":"","institution":"Universidade Federal de Santa Catarina","correspondingAuthor":false,"prefix":"","firstName":"I.H.","middleName":"","lastName":"Bechtold","suffix":""}],"badges":[],"createdAt":"2024-02-05 17:59:13","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-3931670/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3931670/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1016/j.molliq.2024.124757","type":"published","date":"2024-05-01T22:09:53+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":50731196,"identity":"4efcb26f-da24-442f-810b-d26f19d7739f","added_by":"auto","created_at":"2024-02-06 12:55:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":34528,"visible":true,"origin":"","legend":"\u003cp\u003eXRD for pure PerLC and PerLC:QD at different doping wt. concentrations (10, 20 and 40%) at room temperature after cooling down from the isotropic phase.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/a0dd84b913ed4945ffe86c4d.png"},{"id":50730742,"identity":"e96164a8-4f65-4914-985d-cd83936129bb","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":62947,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic J–V curves showing the RS effect. a) Comparison of pure PerLC (blue) and PerLC:QD 20% wt. (red). The inset graph shows pure PerCL in detail. b) PerLC:QD 20% wt. with arrows indicating the cycle starting at -30 V. The \"set\" and \"reset\" processes are also indicated. c) J-V log-log plot of the positive bias voltage for the PerLC and PerLC:QD 20%. d) Mobilities of PerLC and PerLC:QD 20% determined from the SCLC regime as a function of applied voltage.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/d39d1e0110f8ea1008dd95f1.png"},{"id":50730744,"identity":"a342c079-905f-4fbc-928b-63eda2726eb2","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":46840,"visible":true,"origin":"","legend":"\u003cp\u003eMeasurements with PerLC:QD 20% wt. a) \u003cstrong\u003e|\u003c/strong\u003eJ-V\u003cstrong\u003e|\u003c/strong\u003e semi-log plot indicating the region of HRS and LRS. b) Plot comparing the 1\u003csup\u003est\u003c/sup\u003e and 50\u003csup\u003eth\u003c/sup\u003e cycles. c) Switching resistance of the device between the LRS and HRS at 16V as a function of the number of cycles.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/90cb43d7993683d48a9369b1.png"},{"id":50731197,"identity":"017f30e3-e551-45d0-ab47-3743ef0d0f70","added_by":"auto","created_at":"2024-02-06 12:55:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":340327,"visible":true,"origin":"","legend":"\u003cp\u003eEIS of the PerLC:QD 20% wt. resistive switching memory device in set and reset state. a) Nyquist plot with the arrows indicating the set and reset processes. Inset: equivalent electric circuit used to fit the data. b) Impedance modulus vs. frequency, c) Phase shift vs. frequency.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/65e67a3ca24089279c3afbc0.png"},{"id":50730741,"identity":"7c946d11-e5b2-4d3b-a11c-c85567ff0c3f","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":135741,"visible":true,"origin":"","legend":"\u003cp\u003eEquivalent electric circuit parameters obtained from fitting the IES curves of Figure 4. Repeatable write-read-erase-read processes of the resistive switching memory device.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/52430289cac75584635d8011.jpg"},{"id":50730740,"identity":"50fe7f8b-de8a-4c38-94bd-c9b6b4e7af7d","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":189688,"visible":true,"origin":"","legend":"\u003cp\u003eLeft: Reorganization of charge density upon the formation of the radical anion. The arrows schematize the local dipole induced in the side chains by the additional electron. Right: Reorganization of spin density upon the formation of the radical anion.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/d2248cb7f40eab2104c254d8.png"},{"id":50730745,"identity":"2e11a8b6-7f2d-48e0-bbf5-382fd05491cd","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":557288,"visible":true,"origin":"","legend":"\u003cp\u003eHOMO (left) and LUMO (right) isosurfaces of PerLC, drawn at an isovalue of 0.005.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/29ce388be4d2f6bff7b49b5e.png"},{"id":55689622,"identity":"c4408121-16bf-4074-ad95-8f0cbaf2eee5","added_by":"auto","created_at":"2024-05-01 22:09:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1458996,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/53d3bcf1-b71c-411f-9b35-cefac2920fe3.pdf"},{"id":50730739,"identity":"21a23a43-e22d-407e-a15b-8546a1612f4b","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2132279,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformationLindiomar28Sep23withoutauthors.docx","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/2095d94efda1c2832109ba53.docx"},{"id":50730738,"identity":"b73b845a-205e-47d2-b4b6-fba1f8c612b1","added_by":"auto","created_at":"2024-02-06 12:47:21","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":15283,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e. Molecular structure of the PerLC.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-3931670/v1/42457c606bfcfcc8a265a17e.png"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003ePerylene-Based Columnar Liquid Crystal: Reveling Unipolar Resistive Switching for Nonvolatile Memory Devices\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eA memristor (memory resistor - MR) is a passive two-terminal electronic component able to store non-volatile information by resistance variations based on the resistive switching (RS) effect, an effect which has already been observed in the 60s for several oxides [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In 1971 Leon Chua theoretically proposed the circuit element that could describe the experiments, and identified it as one of the fundamental elements to compose two-terminal circuits [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. MR devices remained an object of theoretical study until 2008, when they were realized by Hewlett-Packard (HP) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe RS effect allows different electronic applications, such as logical and analog operations, unconventional computing, pattern recognition, and neural networks [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The resistive random-access memory (RRAM) is a non-volatile device with local resistance control through voltage pulses of low power consumption and sub-nanosecond switching times (read and write). The RS effect is mostly observed in inorganic materials[\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, RRAMs based on organic semiconductors were recently shown to be promising [\u003cspan additionalcitationids=\"CR12 CR13 CR14\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eColumnar LCs present strong π-π interactions of the aromatic cores, surrounded by flexible aliphatic side chains, which generates high charge mobility and a \u0026ldquo;quasi-one-dimensional\u0026rdquo; electrical conductivity [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The potential of perylene-based columnar LCs has been recognized as promising for organic electronic devices, where the electro-optical properties can be substantially improved by controlling the molecular alignment [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. So far, only few reports of the RS effect with columnar LCs are available [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The effect was also demonstrated in a bio-based ionic LC [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Recently, the potential of a nematic LC for storing and processing information was theoretically proposed [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. However, as far as we know, there are no reports investigating the RS effect for perylene-based columnar LCs.\u003c/p\u003e \u003cp\u003eHere, we report on a nonvolatile resistive switching memory whose active layer is a perylene tetraester (PerLC) presenting a columnar hexagonal LC mesophase between \u0026ndash; 25 \u003csup\u003eo\u003c/sup\u003eC and 148 \u003csup\u003eo\u003c/sup\u003eC. Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows its molecular structure. The electrical properties of solution processed thin films were previously investigated for this material (compound \u003cb\u003e1\u003c/b\u003e in [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]),. Surprisingly, with the PerLC confined between ITO electrodes, we observed a prominent unipolar RS effect, which was enhanced upon doping with ZnO@SiO\u003csub\u003e2\u003c/sub\u003e quantum dots. The \u0026ldquo;on\u0026rdquo; and \u0026ldquo;off\u0026rdquo; states occur in the space charge limited current (SCLC) regime with a high degree of reproducibility. Devices are stable for at least one year, with the device preserved in ambient atmosphere at room temperature. We demonstrate that the devices have the ability to \u003cem\u003ewrite-read-erase-read\u003c/em\u003e.[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Results and discussion","content":"\u003cp\u003ePerLC-based memory devices were electrically characterized in diode-like structures, consisting of a cell with the organic material sandwiched between two ITO-coated glass plates using 8 \u0026micro;m-thick spacers. Cyclic voltage measurements were performed from \u0026minus;\u0026thinsp;30V to +\u0026thinsp;30V and back. The effect of PerLC doping with ZnO@SiO\u003csub\u003e2\u003c/sub\u003e quantum dots (QDs) was also investigated. Information about the synthesis of the PerLC and ZnO@SiO\u003csub\u003e2\u003c/sub\u003e QDs, as well as the cell preparation, are in the supporting information.\u003c/p\u003e\n\u003cp\u003eElectric impedance spectroscopy (EIS) was performed to determine the resistive and capacitive properties of the pure PerLC and PerLC:QD (10%, 20% and 40% wt.) layers to investigate the RS mechanism. The results are usually interpreted in terms of equivalent circuits consisting of electrical components such as resistors and capacitors. The best electrical response was obtained with 20%wt. QD doping, resulting in a significant reduction of the bulk resistance. The detailed discussion and the EIS results concerning the PerLC:QD doping are presented in the supporting information.\u003c/p\u003e\n\u003cp\u003eThe effect of different QD concentrations on the PerLC hexagonal columnar structure was evaluated by X-Ray diffraction (XRD) measurements, see Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The main peak at low angle (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003ed\u003csub\u003e001\u003c/sub\u003e=15.5 \u0026Aring;)\u003c/span\u003e\u003c/span\u003e is associated to the distance between the molecular columns. Pure PerLC shows the highest intensity compared to the doped films, suggesting a greater correlation length, related to the size of the macroscopic columnar hexagonal domains (MCHDs). With the addition of QDs the intensity of the (100) peak decreased sharply. However, the position does not change significantly, which indicates that the distance between the columns in the hexagonal structure is not affected by the presence of the QDs.\u003c/p\u003e\n\u003cp\u003eThe peak between 2\u0026theta;\u0026thinsp;=\u0026thinsp;25 and 26\u0026deg; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e(d\u003csub\u003e001\u003c/sub\u003e=3.5 \u0026Aring;)\u003c/span\u003e\u003c/span\u003e represents the molecular stacking within the columns. There is also no change in position and only little variation in intensity upon doping. Inset of Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the ratio between peak intensities (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({I}_{100}\\)\u003c/span\u003e\u003c/span\u003e/\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({I}_{001}\\)\u003c/span\u003e\u003c/span\u003e), confirming that the reduction of the main (100) peak intensity by QD doping is not related to the amount of material, but rather to the reduction in size of the MCHDs. It indicates that the QDs fragment the macroscopic domains, but it seems that for 20% wt. doping an equilibrium with larger MCHDs is achieved.\u003c/p\u003e\n\u003cp\u003eIt is well known that doping columnar LCs with metallic nanoparticles or QDs improves charge carrier conductivity [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]\u0026ndash;[\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e], where the optimized doping percentage may depend on the distinct interactions occurring in the film [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. In the PerLC:QD system, we have to consider interactions between LC-LC molecules (i), LC-QD (ii) and QD-QD (iii). The XRD data suggest that (ii) are dominant for the lower concentration of 10%, with the QDs homogeneously distributed around the smaller MCHDs. For 40% the (i) and (iii) interactions are dominant within QD agglomerations, but due to high concentration the size of the MCHDs is lower compared to 20% doping, where the three kinds of interactions seem to find an equilibrium, which optimizes the electrical properties. Scheme S5 in supporting information illustrates these situations.\u003c/p\u003e\n\u003cp\u003eThus, the optimized 20% wt. QD content was used for the memory effect studies. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the superimposed electrical measurements for pure PerLC (red curve) and PerLC:QD (blue curve), with the peak current at the same position at \u0026plusmn;\u0026thinsp;16 V. A typical RS J-V curve is observed in both cases, where the \u0026ldquo;set\u0026rdquo; and \u0026ldquo;reset\u0026rdquo; processes occur at the same polarity, being characterized as unipolar RS [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e] [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e] [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. The inset graph shows in detail the shape of the J-V curve for pure PerLC, clearly demonstrating that the RS effect already occurs for the pure PerLC and suggesting that the QDs act as current enhancers. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb illustrates the cycle starting at -30 V with the switching steps occurring at positive bias (forward cycle) and at negative bias (backward cycle) for the PerLC:QD cell. The \u0026ldquo;set\u0026rdquo; process takes place at 8V, where the device switches to the low-resistivity state (LRS) and remains there until the current reaches a peak at 16V, where the \u0026quot;reset\u0026quot; process occurs, with the system returning to the high-resistivity state (HRS). The same effect is symmetrically observed in the backward cycle at negative bias.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec shows the J-V curves in positive polarity for the pure PerLC and PerLC:QD 20% plotted on a log-log scale. For low voltage an ohmic conduction takes place until 8.0 V, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(J \\propto {V}^{n}\\)\u003c/span\u003e\u003c/span\u003e with \u003cem\u003en\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;1.0, when a space charge limited current (SCLC) occurs due to hopping transport of injected charges according to the Child\u0026ndash;Langmuir law [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. For PerLC and PerLC:QD 20% the slope is \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.4 and \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3.2, respectively, indicating that the density of states is altered by doping. The SCLC regime dominates until 16.0 V, thus a trap-limited conduction is responsible for the charge transport in the device until the \u0026ldquo;reset\u0026rdquo; process above 16.0 V. This mechanism is closely related to the charge carrier trapping or de-trapping by defects[\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e], in agreement with literature[\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eIn order to determine the charge carrier mobility of the undoped and 20% QD doped PerLC, our previously published model was used [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e] where an electric field dependent mobility of the form \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mu \\left(E\\right)={\\mu }_{0}{e}^{\\gamma \\sqrt{E}}\\)\u003c/span\u003e\u003c/span\u003e was considered. The parameters \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026gamma;\u003c/em\u003e implicitly include the trap distribution and can be obtained from fitting the SCLC regimes of the \u003cem\u003eJ-V\u003c/em\u003e curves. The fits for each device are shown as red solid lines in Figure S3 of the Supporting Information, where the obtained values of \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026gamma;\u003c/em\u003e are also displayed. The Poole-Frenkel coefficient \u0026gamma; implies that the hopping transport is made easier by QD doping. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed shows the calculated mobility as a function of the voltage, using the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mu \\left(E\\right)\\)\u003c/span\u003e\u003c/span\u003e equation with \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026gamma;\u003c/em\u003e values, which shows that the mobility in the 20% QD doped PerLC is one order of magnitude higher than in undoped PerLC. Thus, the QDs enhance the charge transport through the active layer and consequently the RS effect.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the J-V curve of the PerLC:QD 20% device, which exhibits the butterfly fingerprint shape characteristic of the RS effect [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e] [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. The HRS (read segment) and the LRS (blue segment) are highlighted. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb compares the RS characteristics of the 1st and 50th cycle. Despite a certain narrowing of the hysteresis which occurs after consecutive cycles, the HRS and LRS values at 16.0 V demonstrate a good stability of the device performance. The HRS/LRS ratio of one order of magnitude (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec) is a very reasonable value for an organic LC device [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]. This retention property was measured at room temperature and under ambient atmosphere.\u003c/p\u003e\n\u003cp\u003eAlthough the device presents the RS effect, it is essential that it also shows the ability to retain and process information. The tests of \u003cem\u003ewrite-read-erase-read\u003c/em\u003e were done using the EIS technique. The Nyquist plot presented in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea shows the memory effect where the red and orange arrows indicate the \u0026ldquo;set\u0026rdquo; process, decreasing the resistance, and the blue and green arrows indicate the \u0026ldquo;reset\u0026rdquo; process, increasing the resistance. In binary language, the arrows indicate the change between the states \u0026ldquo;1\u0026rdquo; and \u0026ldquo;0\u0026rdquo;. Initially, EIS measurement was performed by applying 1.0 V (DC) to confirm the HRS as a pristine state (black curve). Then, 10.0 V (DC) was applied for 30 seconds to \u0026ldquo;set\u0026rdquo; the LRS. With this process, the resistance should decrease; nevertheless, it is necessary to check if the information was stored. To confirm this state, EIS was repeated with 1.0 V (DC) (reading process), as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea (red curve). Since this is a switch device, the \u0026ldquo;reset\u0026rdquo; was carried out aiming to go back to the previous state, with higher resistance. For this, -10.0 V (DC) were applied for 30 seconds. To confirm if the information was deleted, the EIS measurement was repeated under 1.0 V (DC), as presented in the blue curve (resistance increased). The \u0026ldquo;set\u0026rdquo; and \u0026ldquo;reset\u0026rdquo; was repeated once more to demonstrate that the \u003cem\u003ewrite-read-erase-read\u003c/em\u003e effect is stable (orange and green curves). The \u003cem\u003ewrite-read-erase-read\u003c/em\u003e effect was identically observed after one year with the device stored under ambient atmosphere at room temperature, thus confirming stability of the memory effect of PerLC over long periods of time.\u003c/p\u003e\n\u003cp\u003eThe layer long polarization leads to a decrease of the impedance (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb), which is more evident at lower frequency. With phase shift (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec), a slight change is observed, which indicates an increase of conductivity and loss of capacitance of the organic layer.\u003c/p\u003e\n\u003cp\u003eThe semicircle in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea indicates that only one time constant describes the charge transport process, at least in the considered frequency range. Therefore, a three-element equivalent electric circuit (inset) was used to fit the experimental results. R\u003csub\u003eS\u003c/sub\u003e represents the resistance of electrodes and connectors, in series with the parallel combination of the bulk capacitance (C) and resistance (R\u003csub\u003eP\u003c/sub\u003e). The parallel connection of R\u003csub\u003eP\u003c/sub\u003e and C describes the charge transport along the PerLC:QD layer. R\u003csub\u003eP\u003c/sub\u003e stands for the resistance of the charge transfer, whereas C describes the charging capacity. These parameters describe the total resistance and capacitance of the layer. The fact that no additional elements are necessary to fit the spectrum within the considered frequency range means that all the layer components have similar charge transfer properties and remain in a similar electronic state.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows the results obtained from the fitting process. The error bars correspond to a 0.05 confidence interval with respect to accordance between experimental and simulated spectra. In other words, deviation of each parameter up to the indicated error would cause an overshoot of 5% of the experimental versus the simulated spectra from the equivalent circuit model.\u003c/p\u003e\n\u003cp\u003eThe change of parameters caused by the \u0026ldquo;set\u0026rdquo; and \u0026ldquo;reset\u0026rdquo; are reproducible. The set increases the capacitance, while the layer resistance R\u003csub\u003eP\u003c/sub\u003e decreases. The series resistance R\u003csub\u003eS\u003c/sub\u003e shows an opposite behaviour, representing the resistance of the electrodes and connectors and is not related to the storage effect. It is negligible since R\u003csub\u003eS\u003c/sub\u003e is in the range of three orders of magnitude smaller than R\u003csub\u003eP\u003c/sub\u003e, and therefore has no impact on the memory characterization. The parallel resistance R\u003csub\u003eP\u003c/sub\u003e is the only relevant numerical parameter to be used as a memory storage response due to relatively low error and significant change during \u0026ldquo;set\u0026rdquo; and \u0026ldquo;reset\u0026rdquo; cycles.\u003c/p\u003e\n\u003cp\u003eWe have performed density functional theory (DFT) calculations on PerLC molecules without side chains, as these do not take part in defining the electronic properties (more details can be found in the Supporting Information, notably for the methodology and the distribution of charge density on the neutral molecule). We have first examined how the excess charge and spin density is localized on the radical anion, which is shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. The additional electron leads to a net decrease in local side-chain dipoles via the transfer of charge density from the terminating carbon to the carbonyl carbon; besides, charge density delocalizes relatively uniformly over the conjugated core, in a similar manner to the spin density.\u003c/p\u003e\n\u003cp\u003eRelevant molecular orbitals for charge transport, in general, \u003cem\u003ei.e.\u003c/em\u003e the HOMO and LUMO of PerLC in its neutral state, are shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. The HOMO of the dianion is calculated to be unbound (see Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, third column, providing HOMO energies for four different charge states) which indicates the inability of PerLC to accommodate two supplementary electrons and the resulting instability of PerLC in its dianionic state. The energy cost of the charge transitions to the radical anion and dianion have been calculated and are shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, second column, too. Values represent the total energy change across the transition; negative values indicate reactions liberating energy and positive values indicate reactions requiring energy inputs. Therefore, these results also support the fact that PerLC can only accept one supplementary electron. The positive HOMO of the dianion indicates that the last electron is unbound, which is also reflected in the 1.19 eV energy cost to form the dianion. Forming positive species also requires significant energy input, but they are stable, nonetheless. We have additionally investigated the formation of PerLC radical cation and dication and found that, albeit stable, both species require significant energy to form. In summary, these results support a conduction mechanism based on the electrochemical single reduction of PerLC, where charge transfer occurs within PerLC columns, between polycyclic aromatic cores of adjacent molecules.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eCharge transitions \u003cstrong\u003e(a)\u003c/strong\u003e from the neutral molecule to the radical anion, \u003cstrong\u003e(b)\u003c/strong\u003e from the radical anion to the dianion, \u003cstrong\u003e(c)\u003c/strong\u003e from the neutral molecule to the radical cation, and \u003cstrong\u003e(d)\u003c/strong\u003e from the radical cation to the dication. The first number in brackets indicates the charge; the second number indicates the spin multiplicity (equal to 2S\u0026thinsp;+\u0026thinsp;1).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTransition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026Delta;E (eV)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHOMO of target (eV)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e (0,1) \u0026rarr; (-1,2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-2.27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e(b)\u003c/strong\u003e (-1,2) \u0026rarr; (-2,1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;1.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e(c)\u003c/strong\u003e (0,1) \u0026rarr; (+\u0026thinsp;1,2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;7.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-10.99\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e(d)\u003c/strong\u003e (1,2) \u0026rarr; (+\u0026thinsp;2,1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;10.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-15.46\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"3. Conclusions","content":"\u003cp\u003eThe PerLC layer doped with QDs (ZnO@SiO2) is shown to be a functioning material for memory-storage devices, with ability to change resistivity after applying an external voltage, as well as its reversibility. The EIS studies revealed the electrical parameters that can be used as markers of the memory-storage effect. The reversible reduction of the organic molecules at the origin of the conduction mechanism was investigated by DFT calculations. The device shows good endurance with LRS/HRS ratios of about one order of magnitude over 50 cycles. The RS effect and memory capability are preserved over one year. We experimentally confirmed that the device can be used to perform the basic logical operations of \u003cem\u003ewrite-read-erase-read\u003c/em\u003e, which are fundamental for building a storage and processing device. To the best of our knowledge, our study represents the first observation of RS effect for a perylene-based columnar liquid crystal, which opens new possibilities for this class of molecules already well investigated in organic electronic devices.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of competing interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that there are no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was funded by CNPq, CAPES (#001), FAPESC, INCT-INEO, CAPES/COFECUB (#937-20 and PhC 962/20) and H2020-MSCA-RISE-2017 (OCTA, #778158). Pavel Chulkin acknowledges the European Union Horizon 2020 program for funding the OCTA project under grant agreement No 778158 and the Polish Ministry of Education and Science for the funding 2018\u0026ndash;2023 allocated to the implementation of an international co-financed project. The XRD experiments were carried out in the Laborat\u0026oacute;rio de Difra\u0026ccedil;\u0026atilde;o de Raios X (LDRX/UFSC) and TEM in the LCME-UFSC.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eT. W. Hickmott, \u0026ldquo;Low-frequency negative resistance in thin anodic oxide films,\u0026rdquo; \u003cem\u003eJ. Appl. Phys.\u003c/em\u003e, vol. 33, no. 9, pp. 2669\u0026ndash;2682, 1962, doi: 10.1063/1.1702530.\u003c/li\u003e\n\u003cli\u003eF. 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Patil \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Stable and Multilevel Data Storage Resistive Switching of Organic Bulk Heterojunction,\u0026rdquo; \u003cem\u003eNanomaterials\u003c/em\u003e, vol. 11, no. 2, p. 359, Feb. 2021, doi: 10.3390/nano11020359.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"Universidade Federal de Santa Catarina","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"liquid crystal, resistive switching, Printed organic memories, Memory capacity","lastPublishedDoi":"10.21203/rs.3.rs-3931670/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3931670/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePerylene-based columnar liquid crystal (LC) devices exhibit unipolar resistive switching (RS), clearly identified on cyclic J-V curve hysteresis, stable for several cycles. Trap-controlled SCLC conduction is responsible for the charge transport in the active layer, where the “set” and “reset” processes occur. The incorporation of ZnO@SiO2 quantum dots significantly enhances the RS response. The distinguishing result presented here is the ability to write-read-erase-read, controlling the \"on\" and \"off\" states by applying an external electric field, allowing to store and read information multiple times. An endurance of nearly one order of magnitude between the low and high RS states was determined over 50 consecutive cycles. The device proved to be resilient, preserving the resistive switching effect and memory capacity even after one year maintained at room temperature in ambient atmosphere. DFT calculations indicate a conduction mechanism based on reversible reductions of the perylene LC molecules. This article highlights the ability of LCs to store and process information via their resistivity, with potential for the production of low-cost and large-area nonvolatile printed organic memories.\u003c/p\u003e","manuscriptTitle":"Perylene-Based Columnar Liquid Crystal: Reveling Unipolar Resistive Switching for Nonvolatile Memory Devices","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-06 12:47:17","doi":"10.21203/rs.3.rs-3931670/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"383c31b2-6137-4cac-a2ca-0bbd9336861d","owner":[],"postedDate":"February 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":28585403,"name":"Electronic Materials and Devices"}],"tags":[],"updatedAt":"2024-05-01T22:09:53+00:00","versionOfRecord":{"articleIdentity":"rs-3931670","link":"https://doi.org/10.1016/j.molliq.2024.124757","journal":{"identity":"journal-of-molecular-liquids","isVorOnly":true,"title":"Journal of Molecular Liquids"},"publishedOn":"2024-05-01 22:09:53","publishedOnDateReadable":"May 1st, 2024"},"versionCreatedAt":"2024-02-06 12:47:17","video":"","vorDoi":"10.1016/j.molliq.2024.124757","vorDoiUrl":"https://doi.org/10.1016/j.molliq.2024.124757","workflowStages":[]},"version":"v1","identity":"rs-3931670","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3931670","identity":"rs-3931670","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}