Formation of erbium-doped tellurite-modified silica film via femtosecond laser ablation

Formation of erbium-doped tellurite-modified silica film via femtosecond laser ablation | 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 Research Article Formation of erbium-doped tellurite-modified silica film via femtosecond laser ablation Suraya Ahmad Kamil, Gin Jose This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3381512/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Femtosecond (fs) laser technology has evolved as an alternative technique to fabricate thin film by blending the plasma produced from the target material with a substrate. This ultrafast laser was used to fabricate the erbium-doped tellurite-modified silica (EDTS) thin film that is beneficial for optical waveguide and laser applications. There are several very important parameters in this process, among which are the conditions of the substrate used and also the time required to obtain a certain thickness. Film thickness increases with time; however, there is a limitation whereby the substrate becomes fragile at a certain period due to exposure to particle bombardment that has very high energy for a long period. For the sample where the EDTS reaches the surface of the sample substrate, there are small crystallites appear at the interface between the silicon and the EDTS. On the other hand, the fs laser ablation process is quite challenging for a short period because the film obtained is not completely uniform. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Introduction Transitioning from long optical fibres to slab waveguides is essential for miniaturising integrated optical circuits (IOC) parallel with continued development in information technology [ 1 ]. A typical IOC comprises a few components, such as modulators, splitters, photodetectors, waveguide arrays, filters and lasers. This dense integration could experience inherent losses, and it can be mitigated by the on-chip optical amplifier. Among the various optical amplifiers, an erbium-doped waveguide amplifier (EDWA) is a potential candidate to solve this issue due to its advantages, which are low noise in the third (or C) band of the optical communication window, flexible design that is compatible with CMOS fabrication technology and cost-effective features [ 2 ]. The selection of host material for erbium is crucial as it can affect its performance, especially the gain per unit length because it is related to the optical and structural properties [ 3 ]. Numerous studies have been done pertaining to a host material for erbium for EDWA application with the aim of producing optimal device performance. At a fundamental level, the performance of an EDWA largely depends on the host material for erbium. Generally, a waveguide amplifier should produce a high output gain with the shortest possible waveguide length for practical applications. This can be achieved by doping a host material with a high erbium concentration. Nevertheless, as the number of Er 3+ ions per unit volume increases in the host material, the distance between erbium ions shortens, and they start to cluster beyond certain limits. Not all host materials doped with erbium are suitable for fabricating an EDWA, as each host material has its limit for erbium doping concentration [ 4 ]. Plus, although many materials have been identified as potential host materials for erbium, only a few material systems have demonstrated their ability to be an on-chip device for gain that is compatible with existing PIC technology. Silica-based waveguides can be the ideal material for building EDWAs for their excellent compatibility with well-developed silica-based fibre optics and microelectronics [ 5 ]. However, as has been discussed before, silica has a serious issue with the solubility of Er 3+ ions. The issue of solubility of Er 3+ ions in silica can be mitigated by adding other oxide materials into the glass composition. Aluminosilicate displayed the characteristics of a good host material for erbium. Based on a buried waveguide that had been fabricated by Pan et al. [ 6 ], the erbium doping concentration was 2.9 x 10 20 cm − 3 . The refractive index and lifetime were reported as 1.508 and 5 ms, respectively. However, this 20 cm long waveguide hinders a small integrated optical device. Nakazawa and Kimura fabricated a 6.45 cm long ridge waveguide based on Er-doped SiO 2 -GeO 2 . It produced a very low gain (0.16 dB/cm) with a loss of 0.06 dB/cm and has a low refractive index, which is 1.46 [ 7 ]. The reported low gain leads to the conclusion that waveguides based on Er-doped SiO 2 -GeO 2 are also unsuitable for the compact integrated amplifier. On the other hand, a few non-silicate-based host materials were also used to study the suitability of the said material to be used for an EDWA. Erbium-doped tellurite glass is interesting due to its attractive features such as its high refractive index, the good solubility of erbium ions, wide band emission spectrum, high emission cross section at 1550 nm and low phonon energy (750 cm − 1 ) [ 8 , 9 ]. All these properties make tellurite glass a great candidate for an EDWA. Nevertheless, tellurite-based glass has a severe drawback because it naturally has low thermal stability [ 10 ]. Additionally, without the presence of stabilising oxides, this material is chemically unstable. These attributes only make tellurite-based glass to be less than practical for applications [ 11 ]. Integrating TeO 2 and SiO 2 is attractive because this mixture could offer a potential solution to the solubility Er 3+ limit in SiO 2 . However, the blending of these two oxides is difficult to achieve without having phase separation [ 12 , 13 ]. The combination can be prepared without or with minimal phase separation via femtosecond laser ablation. The obtained layer consisting of SiO 2 , TeO 2 and Er 3+ is called erbium-doped tellurite-modified silica (EDTS). This technique is highly dependent on process parameters such as repetition rate, fs-laser energy, background gas pressure and type of background gas. Generally, the thickness of the fabricated layer will increase with time; however, the optimum period is yet to be discovered. Besides that, the ultra-thickness EDTS layer is also not fully investigated. Methodology Sample preparations A femtosecond laser was used to ablate the 79.5%TeO 2 -10%Na 2 O-10%ZnO-0.5%Er 2 O 3 (Er-TZN) target glass material. The melt-quenching technique was employed to prepare the target glass material. The properties of the fs-laser used are a repetition rate of 1 kHz, 100-fs pulsed, 50 µJ of energy and 800 nm wavelength. SiO 2 -on-silicon (SOS) and silica on silicon-on-insulator (SOI) substrate was placed 7 cm above the Er-TZN. The substrate was heated with a programmable heating element at a rate of up to 50°C per minute until it reached 570°C. O 2 gas, which acts as a background gas, was released into the vacuum chamber at a pressure of 70 mTorr. For the SOS substrate, the ablation process was done for 4, 6, 8 and 10 hours, while for silica on silicon-on-insulator (SOI) substrate, the ablation period is only 2–11 minutes. The plasma plume generated from Er-TZN blends with the substrate surface, forming EDTS. Sample characterizations Hitachi SU8230 scanning electron microscope (SEM) and FEI Tecnai TF20 transmission electron microscope (TEM) were employed to determine the morphology cross section and thickness of EDTS. The thickness of EDTS was verified by Metricon 2010 prism coupler with a wavelength of 633 nm and a prism with a refractive index of 1.9648. Energy dispersive X-ray (EDX) was used to determine the elemental concentration. The crystallinity of the obtained layer was analysed by Philips X’Pert X-ray diffraction. Photoluminescence spectroscopy (Edinburgh Instruments FLS920 series) was utilized to record the PL emission spectra and lifetime. The excitation source used is a 980 nm laser. For lifetime measurement, time-resolved PL spectra with a pulsed laser source of 100 ms period and width of 10 µs were employed. Results and discussion Four samples were prepared with SOS substrate having a 1 µm silica layer. The ablation period varied between four to ten hours. Sample ID of F4, F6, F8, and F10 with respect to the ablation period of 4 hours, 6 hours, 8 hours and 10 hours are included in Table 1 . Table 1 The parameters used to dope Er-TZN into SOS substrate using different ablation periods. Process parameter Operating conditions Substrate Silica (t = 1 µm)-on-silicon (SOS) Target material 79.5TeO2-10ZnO-10Na2O-0.5Er2O3 (Er-TZN) Fs-laser energy 50 µJ Fs-laser repetition rate 1.0 kHz Substrate temperature 570°C Ablation period (sample name) 4 hours (F4), 6 hours (F6), 8 hours (F8) and 10 hours (F10) Background gas pressure 70 mTorr O 2 Figure 1 (a)-(c) showing a backscattered cross-section SEM for three samples fabricated with different ablation periods (4, 6 and 8 hours). The EDTS layer thickness measured using SEM and the prism coupler is listed in Table 2 . As anticipated, the thickness of the EDTS increased when a longer ablation period was used as more elements from Er-TZN entered into the silica. Unfortunately, sample F10 broke into pieces in the UHV chamber during the process. This could have been due to a substrate which exceeded its limit and could no longer withstand the bombardment of a high-energy plume. At a certain limit, the substrate became fragile and finally shattered. No characterisation could be done for this sample. Interestingly, in sample F8, the silica layer was completely modified, and small crystallites appeared at the interface between the silicon and the EDTS. This phenomenon could have happened due to the failure of elements from Er -TZN to penetrate the silicon and accumulate at the silicon border. Elements from Er-TZN, which is rich with oxygen, would have difficulty modifying the silicon and subsequently crystallised at the interface due to oxygen deficiency at the interface. Furthermore, the resultant EDTS layer for this sample had an adhesion problem. This can be seen in Fig. 2 where the film disengaged slightly from silicon when conventional TEM sample preparation was done for that sample. The problem did not persist for other samples with no small crystallite on the interface, as shown in Fig. 1 previously. Wax that was used to stick the sample back to back, which is one of the conventional procedures to prepare a TEM sample, is believed to have pulled the doped layer away from the substrate. This case is often associated with intrinsic tensile stress that might have been due to lattice mismatch between the film and substrate, incorporation of foreign atoms, crystallite coalescence at the grain boundaries, a variation of interatomic spacing with crystal size and phase transformation [ 14 , 15 ]. Figure 3 shows the line scan EDX-STEM that is performed at the area. It clearly showed that the black area in the image to be the empty space with very high noise surrounding the area. Table 2 Thickness of the EDTS layer and remaining silica layer underneath the EDTS and the refractive index of the EDTS prepared with different ablation periods. Sample EDTS thickness measured with SEM (µm) EDTS thickness measured with prism coupler (µm) SiO2 thickness below EDTS layer measured with SEM (µm) Refractive Index F4 0.81 ± 0.06 0.834 ± 0.05 0.56 ± 0.06 1.5587 ± 0.0004 F6 1.36 ± 0.03 1.307 ± 0.05 0.11 ± 0.03 1.5915 ± 0.0005 F8 1.94 ± 0.02 1.928 ± 0.05 - 1.6172 ± 0.0003 Despite this, the primary element for a crystallite particle is Te as the line scan shown in Fig. 3 . To investigate more about the element that might be present for the small crystallite, an area scan measurement using EDX-STEM was made. Figure 4 (a)–(g) shows the cross-section and the area scan for an element that is present in the sample. This small crystallite was again identified as Te as shown in the area scan in Fig. 5 . Te concentration is at the highest around the area where the small crystallite accumulated. The point scan measured from EDX-SEM also showed that Te concentration is as high as 8.81 at. % in the area as illustrated in Fig. 6 and Table 3 . Commonly, Te concentration in a typical EDTS is within the range 1–3 at. % depending on the parameter used. Apart from the adhesion issue, the presence of crystallite particles needed to be avoided as it would only contribute to the escalation of optical propagation loss for waveguide application [ 16 ]. Table 3 Elemental concentration at the measured area shown in Fig. 4.22 obtained by EDX-SEM. Element Atomic percent (at. %) O 51.05 Si 27.64 Na 6.78 Zn 4.69 Te 8.81 Er 1.03 The prism coupler measurement also showed that the EDTS refractive index increased in parallel with the ablation period increment (Table 2 ). This was due to the increased amount of elements from Er-TZN entering the silica over time, as exemplified in Table 4 . Table 4 Elemental density of the EDTS layer measured by EDX-SEM for different ablation period samples. Element Elemental concentration (at.%) F4 F6 F8 O 61.01 60.96 57.81 Si 21.47 19.24 18.5 Na 8.57 10.5 11.45 Zn 6.77 6.86 7.98 Te 1.74 1.82 3.15 Er 0.44 0.62 1.11 From the XRD patterns, as shown in Fig. 6 , the halo around 30ºC is more visible for the longer ablation period because EDTS network better resembles a silicate network due to the entrance of a generous amount of materials from Er-TZN into silica. However, for sample F8, a few peaks pointed to the presence of crystallite particles in the EDTS which are believed originated from small crystallite located at the border of the EDTS and silicon. For these patterns, twelve peaks which corresponded to 2θ of 23.05º, 27.62º, 38.40º, 40.44º, 43.31º, 46.22º, 49.62º, 51.28º, 56.88º, 62.95º,63.74º and 82.19º were observed. All peaks corresponded to Te (ICCD reference code: 00-036-1452), and this matched with the inference of Te crystal formation on analysing EDX-SEM and EDX-STEM. The PL spectra, as exhibited in Fig. 7 , showed that the PL intensity increased with the ablation period. The intensity of the sample with an ablation period of 8 hours was the most, followed by those with 6 and 4 hours. This is a direct consequence of increased Er 3+ ions with a longer ablation period. All samples had similar FWHM, which was ~ 20 nm, while the PL lifetime decreased with the ablation period, as shown in Table 5 . This decrease clearly indicates that the ablation period affects not only the thickness of the layer but also the doping concentration. The decrease in lifetime is a direct consequence of increased Er 3+ ion concentration and is associated with concentration quenching [ 17 ]. Table 5 FWHM and PL lifetime for sample fabricated using different ablation periods. Sample FWHM (nm) PL lifetime (ms) F4 20 12.29 F6 20 10.69 F8 20 9.71 Table 6: The parameters used to dope Er-TZN into silica on SOI substrate using different ablation periods and silica thicknesses. Process parameter Operating conditions Substrate Silica (t=10 nm, 15 nm and 25 nm) on silicon-on-insulator (SOI) Target material 79.5TeO 2 -10ZnO-10Na 2 O-0.5Er 2 O 3 (Er-TZN) Fs-laser energy 50 μJ Fs-laser repetition rate 1.0 kHz Substrate temperature 570 °C Ablation period (sample name) 2 minutes for 10 nm (G10), 6 minutes for 15 nm (G15) and 11 minutes for 25 nm (G25) Background gas pressure 70 mTorr O 2 Cross-section images for these three samples were recorded under bright-field TEM as the EDTS layer created for each sample was extremely thin. The images obtained are shown in Figure 8. On observing these images, it is evident that there are some darker regions/spots in the EDTS layer. It can be concluded that the mixing of Er-TZN and silica is not homogeneous in these samples. The very short process duration has caused the elements of Er-TZN to be crystallised or phase-separated within the silica. Further tuning of the laser pulse energy and duration of the process would be required to optimise such very thin EDTS layers. Because of the very low concentration of elements from Er-TZN and their uneven distribution in the EDTS due to the very short ablation period, quantitative estimations from EDX-STEM are prone to errors. Furthermore, the very low concentration of elements from Er-TZN in sample G10 resulted in the area scan for this sample having too much noise contributing to unreliable and inaccurate results. Therefore, an area scans to detect the presence of species from Er-TZN in the EDTS was only done for samples G15 and G25 (Figure 9 and 10). Comparing the image contrast in Figure 9 and Figure 10, it can be inferred that more Er-TZN elements are present in the EDTS layer when the ablation period is longer. A line scans, as shown in Figure 11 and 12, also confirmed the presence of Er-TZN elements in the doped layer. Iridium presence is due to the use of it as a surface protective layer when FIB sample preparation was performed. Furthermore, the thickness of the upper layer as shown in Table 7 increased from the initial thickness. It could be ascertained that there is an expansion of the silica layer because of the doping process. For this sample set, PL characterisation could not be done accurately because of the very thin EDTS and very low PL intensity. Table 7: EDTS layer thickness for different ablation periods used for different silica thicknesses on SOI substrate determined by TEM. Sample EDTS thickness measured with TEM (nm) G10 24.0 ± 0.4 G15 40.2 ± 0.1 G25 65.3 ± 0.4 Conclusion In summary, the correlation between the ablation period with structural, optical, chemical and physical properties of EDTS was studied. Film thickness increases with time; however, there is a limitation whereby the substrate becomes fragile at a certain period due to exposure to particle bombardment that has very high energy for a long period. The presence of crystallite particles at the interface between EDTS and substrate affects the adhesion of the thin film. The primary element for a crystallite particle is Te. Apart from the adhesion issue, the presence of crystallite particles needed to be avoided as it would only contribute to the escalation of optical propagation loss for waveguide application. For ultra-thickness EDTS, the fs laser ablation process is quite challenging because the film obtained is not completely uniform. The very short process duration has caused the elements of Er-TZN to be crystallised or phase-separated within the silica. Declarations Author Contributions SAK wrote the main manuscript and prepared all figures and data. SAK also obtained experimental data. SAK and GJ contributed to the conception and reviewed the manuscript. Funding This study was funded by an Engineering and Physical Sciences Research Council (EPSRC) (EP/M015165/1). Data availability The data generated and analysed during the current study are available from the corresponding author on reasonable request. Conflict of interest: The authors have no relevant fnancial or non-financial interests to disclose. The authors declare no competing interests. References Y. Chen, M. Zhang, Z. Shan, C. Wang, B. Zhang, J. Xu, R. Wang, High content Er 3+ -doped 25La 2 O 3 -75Ga 2 O 3 glass: A potential material for high-power lasers or EDWA, J. Alloys Compd. 837 ,155477 (2020). doi:10.1016/j.jallcom.2020.155477. S.A. Kamil, J. Chandrappan, M. Murray, P. Steenson, T.F. Krauss, G. Jose, Ultrafast laser plasma doping of Er 3+ ions in silica-on-silicon for optical waveguiding applications, Opt. Lett. 41 , 4684–4687 (2016). doi:10.1364/OL.41.004684. A. Madhu, N. Srinatha, B. 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Johnson, Crystallite coalescence during film growth based on improved contact mechanics adhesion models, J. Appl. Phys. 96 , 1348–1359 (2004). doi:10.1063/1.1766099. R. Eason, Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials, John Wiley & Sons, New Jersey, 2007. A. Vonderhaar, M.P. Stone, J. Campbell, T.W. Hawkins, J. Ballato, P.D. Dragic, Concentration quenching and clustering effects in Er:YAG-derived all-glass optical fiber, Opt. Mater. Express. 11 , 3587 (2021). doi:10.1364/ome.437825. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted 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. 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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-3381512","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":236142714,"identity":"8de50531-0cc0-4661-bd5d-9c5a5b289160","order_by":0,"name":"Suraya Ahmad Kamil","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYDADCfYGhgNg1gGitfAcYDhwgDQtEglQ1YS0yM/IffiZp4ZBXnLmG8PDH3MY5PhuJLBu5sGjxeBGurE0zzEGw9nSOQYHDm5jMJa8kcB2G68WiTQGaR42BsZ5UC2JGwhpkZ+Rxvyb5x+D/TzJM2At9QS1MNxIY5PmbWNInC3BA9aSYEDQYWeesVnO7WNIntmTVnDg7DYJw5lnHrbdnIPPYe1pzDfefGOwnXH88OYPldts5PmOJx+78Qafw4CAiYfhP4wtAcSMDUx4/QJS8oOwyCgYBaNgFIxkAACc31FmMR7qEwAAAABJRU5ErkJggg==","orcid":"","institution":"Universiti Teknologi MARA","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Suraya","middleName":"Ahmad","lastName":"Kamil","suffix":""},{"id":236142715,"identity":"41557654-b03b-457d-a593-c3003d58a084","order_by":1,"name":"Gin Jose","email":"","orcid":"","institution":"University of Leeds","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Gin","middleName":"","lastName":"Jose","suffix":""}],"badges":[],"createdAt":"2023-09-24 12:59:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3381512/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3381512/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":44048609,"identity":"9cbf2bf1-e0e3-494e-8f54-e79a1358b0cc","added_by":"auto","created_at":"2023-10-03 23:13:05","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":46420,"visible":true,"origin":"","legend":"\u003cp\u003eBackscattered cross-section SEM image of samples doped with Er-\u003c/p\u003e\n\u003cp\u003eTZN when the target had been ablated for (b) 4 hours (F4), (b) 6 hours (F6) and\u003c/p\u003e\n\u003cp\u003e(c) 8 hours (F8).\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/ac3c8b8bb2f2cacda0988cf3.jpg"},{"id":44047646,"identity":"810c2f58-de05-4082-8c42-863e6b9099c8","added_by":"auto","created_at":"2023-10-03 23:05:05","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":20783,"visible":true,"origin":"","legend":"\u003cp\u003eDoped layer is observed been peeled off after conventional TEM\u003c/p\u003e\n\u003cp\u003epreparation. The black area between the film and silicon substrate is an empty\u003c/p\u003e\n\u003cp\u003espace.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/05a44f6a0a06d28c60130509.jpg"},{"id":44046810,"identity":"3cf5453b-721e-48b9-83e4-3a36d3f1e9a8","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":75885,"visible":true,"origin":"","legend":"\u003cp\u003eLine scan obtained from EDX-STEM showing that no element was\u003c/p\u003e\n\u003cp\u003edetected at the empty space between the film and the silicon substrate.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/aa3b675c6b251adb35781ecc.jpg"},{"id":44046811,"identity":"da18c214-1c1a-49eb-9a37-e869b6d72249","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":96562,"visible":true,"origin":"","legend":"\u003cp\u003eArea scan measured by EDX-STEM for sample F8 with (a) the area\u003c/p\u003e\n\u003cp\u003ebeing measured. The distribution of species present in it are (b) oxygen, (c) silicon,\u003c/p\u003e\n\u003cp\u003e(d) tellurium, (e) sodium, (f) zinc and (g) erbium.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/0827bcb9700fc88feb85e022.jpg"},{"id":44046807,"identity":"380470e3-d0b7-4fbe-87de-345730978e4d","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":13366,"visible":true,"origin":"","legend":"\u003cp\u003ePoint EDX-SEM measurement done at crystallite particle accumulation\u003c/p\u003e\n\u003cp\u003earea.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/0eeb3287d70ea7ec3a7885fe.jpg"},{"id":44046806,"identity":"59f6c807-3b68-47ca-986b-3d145d53fd13","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":30532,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns for the EDTS layer prepared by ablating the Er-TZN for\u003c/p\u003e\n\u003cp\u003e(a) 4 hours (F4), (b) 6 hours (F6) and (c) 8 hours (F8).\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/b4f7c9ba103d3f83e863ce58.jpg"},{"id":44048608,"identity":"c7f10555-8e95-4678-af24-5d654f7cba95","added_by":"auto","created_at":"2023-10-03 23:13:05","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":24210,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the photoluminescence intensity of the EDTS layer with\u003c/p\u003e\n\u003cp\u003eablation period.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/99f2e164b3b75c8c610c2353.jpg"},{"id":44046813,"identity":"7064ea5d-0a9c-44d1-abf6-cf97e3b33909","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":64402,"visible":true,"origin":"","legend":"\u003cp\u003eBright-field image of the sample prepared using different silica\u003c/p\u003e\n\u003cp\u003ethicknesses on SOI substrate. For (a), it is the sample which has an initial silica\u003c/p\u003e\n\u003cp\u003ethickness of 10 nm while (b) and (c) have initial silica thicknesses of 15 nm and 25 nm.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/069606e25def3474ed79b982.jpg"},{"id":44046815,"identity":"42f60fb6-51b9-4d5f-b588-d00c6678d1bb","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":86502,"visible":true,"origin":"","legend":"\u003cp\u003eArea scan for sample using silica (15 nm) on SOI substrate that underwent an ablation period of 6 minutes (G15).\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/8a9b2c59bad9bffc1e3a9be9.jpg"},{"id":44048610,"identity":"196bd82b-1bb3-4102-b238-24c6d7b38d37","added_by":"auto","created_at":"2023-10-03 23:13:05","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":206552,"visible":true,"origin":"","legend":"\u003cp\u003eArea scan for sample using silica (25 nm) on SOI substrate that underwent an ablation period of 11 minutes (G25).\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/aeef29893c0f11dfaa3750f8.jpg"},{"id":44047664,"identity":"f2249b5b-e95e-4454-8c30-6e8e343b076f","added_by":"auto","created_at":"2023-10-03 23:05:05","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":93167,"visible":true,"origin":"","legend":"\u003cp\u003eLine scan of the sample using silica (15 nm) on SOI substrate that underwent an ablation period of 6 minutes (G15).\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/c02db1874b0ccfc7a6ba6bee.jpg"},{"id":44046817,"identity":"d69ff748-af57-48fb-9786-5c838e834a91","added_by":"auto","created_at":"2023-10-03 22:57:05","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":97862,"visible":true,"origin":"","legend":"\u003cp\u003eLine scan of the sample using silica (25 nm) on SOI substrate that underwent an ablation period of 11 minutes (G25).\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/688a53e51c140960813bc72e.jpg"},{"id":46550640,"identity":"39762e2e-360c-4a80-b23a-77ccff754487","added_by":"auto","created_at":"2023-11-16 10:59:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":889529,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3381512/v1/6ec1ad1c-2bff-4f77-9afe-a6dc06a042ec.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Formation of erbium-doped tellurite-modified silica film via femtosecond laser ablation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eTransitioning from long optical fibres to slab waveguides is essential for miniaturising integrated optical circuits (IOC) parallel with continued development in information technology [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. A typical IOC comprises a few components, such as modulators, splitters, photodetectors, waveguide arrays, filters and lasers. This dense integration could experience inherent losses, and it can be mitigated by the on-chip optical amplifier. Among the various optical amplifiers, an erbium-doped waveguide amplifier (EDWA) is a potential candidate to solve this issue due to its advantages, which are low noise in the third (or C) band of the optical communication window, flexible design that is compatible with CMOS fabrication technology and cost-effective features [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe selection of host material for erbium is crucial as it can affect its performance, especially the gain per unit length because it is related to the optical and structural properties [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Numerous studies have been done pertaining to a host material for erbium for EDWA application with the aim of producing optimal device performance. At a fundamental level, the performance of an EDWA largely depends on the host material for erbium. Generally, a waveguide amplifier should produce a high output gain with the shortest possible waveguide length for practical applications. This can be achieved by doping a host material with a high erbium concentration. Nevertheless, as the number of Er\u003csup\u003e3+\u003c/sup\u003e ions per unit volume increases in the host material, the distance between erbium ions shortens, and they start to cluster beyond certain limits. Not all host materials doped with erbium are suitable for fabricating an EDWA, as each host material has its limit for erbium doping concentration [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Plus, although many materials have been identified as potential host materials for erbium, only a few material systems have demonstrated their ability to be an on-chip device for gain that is compatible with existing PIC technology.\u003c/p\u003e \u003cp\u003eSilica-based waveguides can be the ideal material for building EDWAs for their excellent compatibility with well-developed silica-based fibre optics and microelectronics [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, as has been discussed before, silica has a serious issue with the solubility of Er\u003csup\u003e3+\u003c/sup\u003e ions. The issue of solubility of Er\u003csup\u003e3+\u003c/sup\u003e ions in silica can be mitigated by adding other oxide materials into the glass composition. Aluminosilicate displayed the characteristics of a good host material for erbium. Based on a buried waveguide that had been fabricated by Pan et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], the erbium doping concentration was 2.9 x 10\u003csup\u003e20\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. The refractive index and lifetime were reported as 1.508 and 5 ms, respectively. However, this 20 cm long waveguide hinders a small integrated optical device. Nakazawa and Kimura fabricated a 6.45 cm long ridge waveguide based on Er-doped SiO\u003csub\u003e2\u003c/sub\u003e-GeO\u003csub\u003e2\u003c/sub\u003e. It produced a very low gain (0.16 dB/cm) with a loss of 0.06 dB/cm and has a low refractive index, which is 1.46 [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The reported low gain leads to the conclusion that waveguides based on Er-doped SiO\u003csub\u003e2\u003c/sub\u003e-GeO\u003csub\u003e2\u003c/sub\u003e are also unsuitable for the compact integrated amplifier. On the other hand, a few non-silicate-based host materials were also used to study the suitability of the said material to be used for an EDWA. Erbium-doped tellurite glass is interesting due to its attractive features such as its high refractive index, the good solubility of erbium ions, wide band emission spectrum, high emission cross section at 1550 nm and low phonon energy (750 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. All these properties make tellurite glass a great candidate for an EDWA. Nevertheless, tellurite-based glass has a severe drawback because it naturally has low thermal stability [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Additionally, without the presence of stabilising oxides, this material is chemically unstable. These attributes only make tellurite-based glass to be less than practical for applications [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIntegrating TeO\u003csub\u003e2\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e is attractive because this mixture could offer a potential solution to the solubility Er\u003csup\u003e3+\u003c/sup\u003e limit in SiO\u003csub\u003e2\u003c/sub\u003e. However, the blending of these two oxides is difficult to achieve without having phase separation [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The combination can be prepared without or with minimal phase separation via femtosecond laser ablation. The obtained layer consisting of SiO\u003csub\u003e2\u003c/sub\u003e, TeO\u003csub\u003e2\u003c/sub\u003e and Er\u003csup\u003e3+\u003c/sup\u003e is called erbium-doped tellurite-modified silica (EDTS). This technique is highly dependent on process parameters such as repetition rate, fs-laser energy, background gas pressure and type of background gas. Generally, the thickness of the fabricated layer will increase with time; however, the optimum period is yet to be discovered. Besides that, the ultra-thickness EDTS layer is also not fully investigated.\u003c/p\u003e"},{"header":"Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSample preparations\u003c/h2\u003e \u003cp\u003eA femtosecond laser was used to ablate the 79.5%TeO\u003csub\u003e2\u003c/sub\u003e-10%Na\u003csub\u003e2\u003c/sub\u003eO-10%ZnO-0.5%Er\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Er-TZN) target glass material. The melt-quenching technique was employed to prepare the target glass material. The properties of the fs-laser used are a repetition rate of 1 kHz, 100-fs pulsed, 50 \u0026micro;J of energy and 800 nm wavelength. SiO\u003csub\u003e2\u003c/sub\u003e-on-silicon (SOS) and silica on silicon-on-insulator (SOI) substrate was placed 7 cm above the Er-TZN. The substrate was heated with a programmable heating element at a rate of up to 50\u0026deg;C per minute until it reached 570\u0026deg;C. O\u003csub\u003e2\u003c/sub\u003e gas, which acts as a background gas, was released into the vacuum chamber at a pressure of 70 mTorr. For the SOS substrate, the ablation process was done for 4, 6, 8 and 10 hours, while for silica on silicon-on-insulator (SOI) substrate, the ablation period is only 2\u0026ndash;11 minutes. The plasma plume generated from Er-TZN blends with the substrate surface, forming EDTS.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eSample characterizations\u003c/h2\u003e \u003cp\u003eHitachi SU8230 scanning electron microscope (SEM) and FEI Tecnai TF20 transmission electron microscope (TEM) were employed to determine the morphology cross section and thickness of EDTS. The thickness of EDTS was verified by Metricon 2010 prism coupler with a wavelength of 633 nm and a prism with a refractive index of 1.9648. Energy dispersive X-ray (EDX) was used to determine the elemental concentration. The crystallinity of the obtained layer was analysed by Philips X\u0026rsquo;Pert X-ray diffraction. Photoluminescence spectroscopy (Edinburgh Instruments FLS920 series) was utilized to record the PL emission spectra and lifetime. The excitation source used is a 980 nm laser. For lifetime measurement, time-resolved PL spectra with a pulsed laser source of 100 ms period and width of 10 \u0026micro;s were employed.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eFour samples were prepared with SOS substrate having a 1 \u0026micro;m silica layer. The ablation period varied between four to ten hours. Sample ID of F4, F6, F8, and F10 with respect to the ablation period of 4 hours, 6 hours, 8 hours and 10 hours are included in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe parameters used to dope Er-TZN into SOS substrate using different ablation periods.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eProcess parameter\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOperating conditions\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\u003eSubstrate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSilica (t\u0026thinsp;=\u0026thinsp;1 \u0026micro;m)-on-silicon (SOS)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTarget material\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.5TeO2-10ZnO-10Na2O-0.5Er2O3 (Er-TZN)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFs-laser energy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50 \u0026micro;J\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFs-laser repetition rate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0 kHz\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSubstrate temperature\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e570\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAblation period\u003c/p\u003e\n \u003cp\u003e(sample name)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4 hours (F4), 6 hours (F6), 8 hours (F8) and 10 hours (F10)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBackground gas pressure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70 mTorr O\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (a)-(c) showing a backscattered cross-section SEM for three samples fabricated with different ablation periods (4, 6 and 8 hours). The EDTS layer thickness measured using SEM and the prism coupler is listed in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. As anticipated, the thickness of the EDTS increased when a longer ablation period was used as more elements from Er-TZN entered into the silica. Unfortunately, sample F10 broke into pieces in the UHV chamber during the process. This could have been due to a substrate which exceeded its limit and could no longer withstand the bombardment of a high-energy plume. At a certain limit, the substrate became fragile and finally shattered. No characterisation could be done for this sample.\u003c/p\u003e\n\u003cp\u003eInterestingly, in sample F8, the silica layer was completely modified, and small crystallites appeared at the interface between the silicon and the EDTS. This phenomenon could have happened due to the failure of elements from Er -TZN to penetrate the silicon and accumulate at the silicon border. Elements from Er-TZN, which is rich with oxygen, would have difficulty modifying the silicon and subsequently crystallised at the interface due to oxygen deficiency at the interface. Furthermore, the resultant EDTS layer for this sample had an adhesion problem. This can be seen in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e where the film disengaged slightly from silicon when conventional TEM sample preparation was done for that sample. The problem did not persist for other samples with no small crystallite on the interface, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e previously.\u003c/p\u003e\n\u003cp\u003eWax that was used to stick the sample back to back, which is one of the conventional procedures to prepare a TEM sample, is believed to have pulled the doped layer away from the substrate. This case is often associated with intrinsic tensile stress that might have been due to lattice mismatch between the film and substrate, incorporation of foreign atoms, crystallite coalescence at the grain boundaries, a variation of interatomic spacing with crystal size and phase transformation [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows the line scan EDX-STEM that is performed at the area. It clearly showed that the black area in the image to be the empty space with very high noise surrounding the area.\u003c/p\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThickness of the EDTS layer and remaining silica layer underneath the EDTS and the refractive index of the EDTS prepared with different ablation periods.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEDTS\u003c/p\u003e\n \u003cp\u003ethickness\u003c/p\u003e\n \u003cp\u003emeasured\u003c/p\u003e\n \u003cp\u003ewith SEM\u003c/p\u003e\n \u003cp\u003e(\u0026micro;m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEDTS\u003c/p\u003e\n \u003cp\u003ethickness\u003c/p\u003e\n \u003cp\u003emeasured\u003c/p\u003e\n \u003cp\u003ewith prism\u003c/p\u003e\n \u003cp\u003ecoupler (\u0026micro;m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSiO2\u003c/p\u003e\n \u003cp\u003ethickness\u003c/p\u003e\n \u003cp\u003ebelow\u003c/p\u003e\n \u003cp\u003eEDTS layer\u003c/p\u003e\n \u003cp\u003emeasured\u003c/p\u003e\n \u003cp\u003ewith SEM\u003c/p\u003e\n \u003cp\u003e(\u0026micro;m)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRefractive Index\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\u003eF4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.834\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5587\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0004\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.307\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5915\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0005\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.928\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.6172\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eDespite this, the primary element for a crystallite particle is Te as the line scan shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. To investigate more about the element that might be present for the small crystallite, an area scan measurement using EDX-STEM was made. Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e (a)\u0026ndash;(g) shows the cross-section and the area scan for an element that is present in the sample. This small crystallite was again identified as Te as shown in the area scan in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. Te concentration is at the highest around the area where the small crystallite accumulated. The point scan measured from EDX-SEM also showed that Te concentration is as high as 8.81 at. % in the area as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e and Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Commonly, Te concentration in a typical EDTS is within the range 1\u0026ndash;3 at. % depending on the parameter used. Apart from the adhesion issue, the presence of crystallite particles needed to be avoided as it would only contribute to the escalation of optical propagation loss for waveguide application [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eElemental concentration at the measured area shown in Fig.\u0026nbsp;4.22 obtained by EDX-SEM.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAtomic percent (at. %)\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\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27.64\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.69\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe prism coupler measurement also showed that the EDTS refractive index increased in parallel with the ablation period increment (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). This was due to the increased amount of elements from Er-TZN entering the silica over time, as exemplified in Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eElemental density of the EDTS layer measured by EDX-SEM for different ablation period samples.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eElemental concentration (at.%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF4\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF6\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF8\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\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e57.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e19.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eZn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.98\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFrom the XRD patterns, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the halo around 30\u0026ordm;C is more visible for the longer ablation period because EDTS network better resembles a silicate network due to the entrance of a generous amount of materials from Er-TZN into silica. However, for sample F8, a few peaks pointed to the presence of crystallite particles in the EDTS which are believed originated from small crystallite located at the border of the EDTS and silicon. For these patterns, twelve peaks which corresponded to 2\u0026theta; of 23.05\u0026ordm;, 27.62\u0026ordm;, 38.40\u0026ordm;, 40.44\u0026ordm;, 43.31\u0026ordm;, 46.22\u0026ordm;, 49.62\u0026ordm;, 51.28\u0026ordm;, 56.88\u0026ordm;, 62.95\u0026ordm;,63.74\u0026ordm; and 82.19\u0026ordm; were observed. All peaks corresponded to Te (ICCD reference code: 00-036-1452), and this matched with the inference of Te crystal formation on analysing EDX-SEM and EDX-STEM.\u003c/p\u003e\n\u003cp\u003eThe PL spectra, as exhibited in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, showed that the PL intensity increased with the ablation period. The intensity of the sample with an ablation period of 8 hours was the most, followed by those with 6 and 4 hours. This is a direct consequence of increased Er\u003csup\u003e3+\u003c/sup\u003e ions with a longer ablation period. All samples had similar FWHM, which was ~\u0026thinsp;20 nm, while the PL lifetime decreased with the ablation period, as shown in Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. This decrease clearly indicates that the ablation period affects not only the thickness of the layer but also the doping concentration. The decrease in lifetime is a direct consequence of increased Er\u003csup\u003e3+\u003c/sup\u003e ion concentration and is associated with concentration quenching [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\n\u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eFWHM and PL lifetime for sample fabricated using different ablation periods.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFWHM (nm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePL lifetime (ms)\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\u003eF4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.69\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.71\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable 6: The parameters used to dope Er-TZN into silica on SOI substrate using different ablation periods and silica thicknesses.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eProcess parameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eOperating conditions\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eSubstrate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003eSilica (t=10 nm, 15 nm and 25 nm) on silicon-on-insulator\u003c/p\u003e\n \u003cp\u003e(SOI)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eTarget material\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e79.5TeO\u003csub\u003e2\u003c/sub\u003e-10ZnO-10Na\u003csub\u003e2\u003c/sub\u003eO-0.5Er\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Er-TZN)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eFs-laser energy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e50 \u0026mu;J\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eFs-laser repetition rate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e1.0 kHz\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eSubstrate temperature\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e570 \u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eAblation period\u003c/p\u003e\n \u003cp\u003e(sample name)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e2 minutes for 10 nm (G10), 6 minutes for 15 nm (G15) and 11 minutes for 25 nm (G25)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.44758735440932%\" valign=\"top\"\u003e\n \u003cp\u003eBackground gas pressure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"68.55241264559068%\" valign=\"top\"\u003e\n \u003cp\u003e70 mTorr O\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eCross-section images for these three samples were recorded under bright-field TEM as the EDTS layer created for each sample was extremely thin. The images obtained are shown in Figure 8. On observing these images, it is evident that there are some darker regions/spots in the EDTS layer. It can be concluded that the mixing of Er-TZN and silica is not homogeneous in these samples. The very short process duration has caused the elements of Er-TZN to be crystallised or phase-separated within the silica. Further tuning of the laser pulse energy and duration of the process would be required to optimise such very thin EDTS layers.\u003c/p\u003e\n\u003cp\u003eBecause of the very low concentration of elements from Er-TZN and their uneven distribution in the EDTS due to the very short ablation period, quantitative estimations from EDX-STEM are prone to errors. Furthermore, the very low concentration of elements from Er-TZN in sample G10 resulted in the area scan for this sample having too much noise contributing to unreliable and inaccurate results. Therefore, an area scans to detect the presence of species from Er-TZN in the EDTS was only done for samples G15 and G25 (Figure 9 and 10). Comparing the image contrast in Figure 9 and Figure 10, it can be inferred that more Er-TZN elements are present in the EDTS layer when the ablation period is longer. A line scans, as shown in Figure 11 and 12, also confirmed the presence of Er-TZN elements in the doped layer. Iridium presence is due to the use of it as a surface protective layer when FIB sample preparation was performed. Furthermore, the thickness of the upper layer as shown in Table 7 increased from the initial thickness. It could be ascertained that there is an expansion of the silica layer because of the doping process. For this sample set, PL characterisation could not be done accurately because of the very thin EDTS and very low PL intensity.\u003c/p\u003e\n\u003cp\u003eTable 7: EDTS layer thickness for different ablation periods used for different silica thicknesses on SOI substrate determined by TEM.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.410579345088163%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"78.58942065491183%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eEDTS thickness measured with TEM (nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.410579345088163%\" valign=\"top\"\u003e\n \u003cp\u003eG10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"78.58942065491183%\" valign=\"top\"\u003e\n \u003cp\u003e24.0 \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.410579345088163%\" valign=\"top\"\u003e\n \u003cp\u003eG15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"78.58942065491183%\" valign=\"top\"\u003e\n \u003cp\u003e40.2 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"21.410579345088163%\" valign=\"top\"\u003e\n \u003cp\u003eG25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"78.58942065491183%\" valign=\"top\"\u003e\n \u003cp\u003e65.3 \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, the correlation between the ablation period with structural, optical, chemical and physical properties of EDTS was studied. Film thickness increases with time; however, there is a limitation whereby the substrate becomes fragile at a certain period due to exposure to particle bombardment that has very high energy for a long period. The presence of crystallite particles at the interface between EDTS and substrate affects the adhesion of the thin film. The primary element for a crystallite particle is Te. Apart from the adhesion issue, the presence of crystallite particles needed to be avoided as it would only contribute to the escalation of optical propagation loss for waveguide application. For ultra-thickness EDTS, the fs laser ablation process is quite challenging because the film obtained is not completely uniform. The very short process duration has caused the elements of Er-TZN to be crystallised or phase-separated within the silica.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSAK wrote the main manuscript and prepared all figures and data. SAK also obtained experimental data. SAK and GJ contributed to the conception and reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by an Engineering and Physical Sciences Research Council (EPSRC) (EP/M015165/1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data generated and analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest:\u003c/strong\u003e The authors have no relevant fnancial or non-financial interests to disclose. The authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eY. Chen, M. Zhang, Z. Shan, C. Wang, B. Zhang, J. Xu, R. Wang, High content Er\u003csup\u003e3+\u003c/sup\u003e-doped 25La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-75Ga\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e glass: A potential material for high-power lasers or EDWA, J. Alloys Compd.\u003cstrong\u003e 837\u003c/strong\u003e,155477 (2020). doi:10.1016/j.jallcom.2020.155477.\u003c/li\u003e\n\u003cli\u003eS.A. Kamil, J. Chandrappan, M. Murray, P. Steenson, T.F. Krauss, G. Jose, Ultrafast laser plasma doping of Er\u003csup\u003e3+\u003c/sup\u003e ions in silica-on-silicon for optical waveguiding applications, Opt. Lett. \u003cstrong\u003e41\u003c/strong\u003e, 4684\u0026ndash;4687 (2016). doi:10.1364/OL.41.004684.\u003c/li\u003e\n\u003cli\u003eA. Madhu, N. Srinatha, B. Munisudhakar, Concentration dependent enhanced luminescence and its quenching effect in erbium incorporated heavy metal oxide - borate glasses, Mater. Res. Express. \u003cstrong\u003e6,\u003c/strong\u003e 125212 (2019). doi:10.1088/2053-1591/ab71c6.\u003c/li\u003e\n\u003cli\u003eM. Zhang, J. Lu, Y. Chen, Y. Wei, Y. Shao, Z. Li, F. Ma, S. Huang, Z. Li, Z. Chen, R. Wang, Z. Li, Study on Er\u003csup\u003e3+\u003c/sup\u003e-Yb\u003csup\u003e3+\u003c/sup\u003e co-doped La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026ndash;Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e glasses for C-band optical waveguide amplifier with high luminous efficiency and low pump threshold, Ceram. Int. \u003cstrong\u003e48\u003c/strong\u003e, 32236\u0026ndash;32240 (2022). doi:10.1016/j.ceramint.2022.07.165.\u003c/li\u003e\n\u003cli\u003eJ. Hui Chen, Y. Feng Xiong, F. Xu, Y. Qing Lu, Silica optical fiber integrated with two-dimensional materials: towards opto-electro-mechanical technology, Light Sci. Appl. \u003cstrong\u003e10\u003c/strong\u003e, 78 (2021). doi:10.1038/s41377-021-00520-x.\u003c/li\u003e\n\u003cli\u003eT. 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Hooda, S.K. Sharma, Synthesis and characterization of LPCVD polysilicon and silicon nitride thin films for MEMS applications, J. Mater. \u003cstrong\u003e2014\u003c/strong\u003e, 1\u0026ndash;8 (2014). doi:10.1155/2014/954618.\u003c/li\u003e\n\u003cli\u003eA.Y. Suh, N. Yu, K.M. Lee, A.A. Polycarpou, H.T. Johnson, Crystallite coalescence during film growth based on improved contact mechanics adhesion models, J. Appl. Phys. \u003cstrong\u003e96\u003c/strong\u003e, 1348\u0026ndash;1359 (2004). doi:10.1063/1.1766099.\u003c/li\u003e\n\u003cli\u003eR. Eason, Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials, John Wiley \u0026amp; Sons, New Jersey, 2007.\u003c/li\u003e\n\u003cli\u003eA. Vonderhaar, M.P. Stone, J. Campbell, T.W. Hawkins, J. Ballato, P.D. Dragic, Concentration quenching and clustering effects in Er:YAG-derived all-glass optical fiber, Opt. Mater. Express.\u003cstrong\u003e 11\u003c/strong\u003e, 3587 (2021). doi:10.1364/ome.437825.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"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":"","lastPublishedDoi":"10.21203/rs.3.rs-3381512/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3381512/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFemtosecond (fs) laser technology has evolved as an alternative technique to fabricate thin film by blending the plasma produced from the target material with a substrate. This ultrafast laser was used to fabricate the erbium-doped tellurite-modified silica (EDTS) thin film that is beneficial for optical waveguide and laser applications. There are several very important parameters in this process, among which are the conditions of the substrate used and also the time required to obtain a certain thickness. Film thickness increases with time; however, there is a limitation whereby the substrate becomes fragile at a certain period due to exposure to particle bombardment that has very high energy for a long period. For the sample where the EDTS reaches the surface of the sample substrate, there are small crystallites appear at the interface between the silicon and the EDTS. On the other hand, the fs laser ablation process is quite challenging for a short period because the film obtained is not completely uniform.\u003c/p\u003e","manuscriptTitle":"Formation of erbium-doped tellurite-modified silica film via femtosecond laser ablation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-10-03 22:57:00","doi":"10.21203/rs.3.rs-3381512/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":"9266c85c-6d78-4dd0-b199-3f3dff0d2fba","owner":[],"postedDate":"October 3rd, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-11-16T10:59:18+00:00","versionOfRecord":[],"versionCreatedAt":"2023-10-03 22:57:00","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3381512","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3381512","identity":"rs-3381512","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}