Ar Ambient Research Articles

Influence of different annealing ambient on terbium oxide passivation layers sputtered using the RF sputtering on silicon substrate

This study investigates the influence of different annealing ambient on terbium oxide (Tb4O7) passivation layers sputtered using radio frequency (RF) sputtering on silicon (Si) substrates. The passivation layers were subjected to annealing in various ambient, including oxygen (O2), nitrogen (N2), argon (Ar), and nitrogen-oxygen-nitrogen (NON). The structural, morphological, compositional, topological, and optical properties of the passivation layers were characterized using various techniques. The obtained results indicate that the annealing ambient has a significant impact on the properties of Tb4O7 passivation layers. Annealing in Ar ambient leads to the formation of Tb4O7 with improved crystallinity close to 49.75 nm and higher surface roughness at (2.32 nm). In contrast, annealing in the O2 ambient results in broad GIXRD peaks with the lowest surface roughness around (1.34 nm). Notably, annealing in N2 ambient exhibits an intermediate behavior, with partial crystallized size values (31.80 nm) compared to the Tb4O7 passivation layer annealed in Ar ambient and moderate surface roughness. The optical bandgap (Eg) was estimated by applying the Kubelka–Munk (KM) approach and the obtained values were 3.28, 3.17, 2.37, and 2.27 eV for annealed in O2, N2, Ar, and NON ambients, respectively. The investigation of Tb4O7 as a passivation material expands the range of materials available for semiconductor device fabrication, offering potential advancements in optoelectronics applications. Therefore, the significance of this study lies in its contribution to the optimization of Tb4O7 passivation layers in the field of semiconductor device technology. Hence, the sample annealed in an Ar ambient demonstrated the best results in terms of structural, morphological, compositional, topological, and optical properties of Tb4O7 passivation layers as compared to other samples.

The impact of post-deposition annealing durations on the formation of Tb4O7 passivation layer on silicon substrate

In this study, we have effectively utilized radio frequency (RF) sputtering to sputter the Tb4O7 passivation layer on an n-type silicon (Si) substrate in an argon (Ar) ambient. Various characterization approaches were used to investigate the impact of varying annealing durations on structural, morphological, compositional, and optical properties. The grazing incidence X-ray diffraction (GIXRD) pattern confirmed that all investigated Tb4O7 passivation layers (as grown) and annealed at (15, 30, and 45 min) showed a crystalline structure, respectively. As observed, the sample annealed for 30 min attained the highest crystallinity, around 39.51 nm. Surface morphology analysis revealed different surface structures in response to different annealing durations when observed using the field emission scanning electron microscopy (FESEM) technique. Atomic force microscopy (AFM) was utilized to investigate the top surface of the examined samples, and a higher surface roughness of around 2.37 nm was obtained for the sample annealed for 30 min. The band gap energies (Eg) were estimated by applying the Kubelka-Munk (KM) approach for all the investigated samples, and the obtained values were within a range between (1.94–3.07 eV) earlier reported in the literature. Previous studies have shown that the Tb4O7 passivation layer deposited onto Si substrates using RF sputtering and then annealed for 5 min at 900 °C in an Ar atmosphere, resulted in the formation of a highly crystalline passivation layer. However, there is a lack of a clear explanation for the observation, and the authors mainly concentrated on the electrical properties of the Tb4O7 material. This inspired us to carry out this study to investigate the impact of various annealing durations on the formation of Tb4O7 passivation layers, focusing on their structure, composition, morphology, and optical properties.

The influence of laser fluences on surface properties, plasma formation, and microhardness of Mg-alloy

The impact of variation in laser fluence on the surface modifications and plasma parameters of biocompatible, Magnesium (Mg) alloy has been studied. A 1064 nm Nd: YAG laser with, 10 ns pulse duration and a repetition rate of 1 to 10 Hz has been used for this purpose. Mg-alloy targets were subjected to fluences ranging from 1.3 J·cm−2 to 10.47 J·cm−2 in Argon (Ar) ambient. The surface morphology of irradiated targets was analyzed using a Scanning Electron Microscope (SEM). Formation of ripples, ridges, conical structures, pores, and cavities are observed on the surface of the irradiated Mg targets and are shown in the SEM topographical images. A higher initial fluence causes a rise in the size and density of these structures, which subsequently falls off as the fluence increases more to its highest value. Plasma parameters, such as electron temperature (Te) and number density (ne), are measured using Laser-Induced-Breakdown-Spectroscopy (LIBS). It was also found that both Te and ne increase with increasing fluence. XRD analysis is performed to study properties such as phase purity and structural studies were carried out through X-ray diffraction (XRD) technique, aiding in the investigation of material behavior and guiding the development of new materials with specific properties. Using a Vickers Micro hardness tester, we haveinvestigated the hardness of irradiated Mg targets. From the present investigation it is observed that the hardness value of irradiated targets is higher than the pristine Mg target. It is also found that Te and ne play a significant role for the enhancement of hardness as well as for the growth of surface structures on Mg-alloy.

Optical emission features of laterally colliding laser-produced plasmas at different ambient pressures

Optical emission characteristics of seed plasma and stagnation region of laterally colliding laser produced aluminium plasmas are investigated under various background gas pressures of air and argon ambient. The intensity of ionic and neutral emissions from seed plasma region increases with the increase of ambient pressure. Neutral emission from the stagnation region increases whereas the intensity of ionic emission decreases with the increase of ambient pressure. Decrease of collision rate between the seed plasmas results in the decrease of ionic emission from the interaction region. For higher inter seed plume separation, maximum spectral emission from stagnation region is observed at an intermediate pressure range of 10−2 mbar. Emission intensity and the life time of both ionic and neutral emission are greater in heavier Ar ambient. In the case of seed plasmas, the electron density decreases whereas the electron temperature increases with the increase of ambient gas pressure and is greater in Ar ambient. The variations of plasma parameters are quite less in stagnation region.

Thermal defect healing of single-walled carbon nanotubes assisted by supplying carbon-containing reactants

We experimentally investigated the effect of carbon-containing reactants (C2H2) on healing the defects in single-walled carbon nanotubes (SWCNTs) by thermal processes at high temperatures (∼1100 °C). Introducing C2H2 notably improved the crystallinity of healed SWCNTs compared with the thermal process in Ar ambient without C2H2. The defect healing rate increased with increasing C2H2 partial pressure, and the healing effect of C2H2 was more remarkable for relatively thinner SWCNTs (<1.1 nm). Combined with the relevant theoretical work reported previously, we propose a healing model in which C2H2 helps to heal the vacancy defects and increases the healing rate at high temperatures.

Dynamics of angularly colliding laser-produced plasmas in air and argon ambient

The effects of ambient gas pressure on the dynamics of angularly colliding laser-produced plasmas are investigated in air and Ar ambient. Fast formation of intense stagnation region is observed even in the low-pressure regime, and the tendency of interpenetration is also greater because of the involvement of the fast forward expansion velocity of seed plasmas. An intense and spherical stagnation region is observed at an intermediate pressure regime of Ar ambient. At higher pressure regime, shock front interaction in air ambient and at 10−1 mbar of Ar ambient is due to the regular reflection of shock waves. At 1 mbar of Ar ambient, a channel is formed at the collision front, and its width increases with time which is due to the Mach reflection of shock waves. Increasing inter-plume separation or the increase of angle between the targets significantly influences the shock wave reflections. Mach reflection of shock waves is observed even at 10−1 mbar of Ar ambient in higher angular separation. A peculiar plume splitting is also observed at 750 ns in 10−1 mbar of Ar ambient. Optical emission spectroscopic analysis was also done to understand the spectral emission from interaction region and its variation with ambient gas pressure.

(Digital Presentation) SiGe Epitaxial Growth on Si Substrate Using Al-Ge Paste

Silicon-germanium (SiGe) has been considered as an important alternative material to silicon due to its high carrier mobility, low power consumption and excellent performance [1]. However, due to both material unique phase diagram with melting points separated by 376 °C, it is too difficult to realize a good bulk quality of polycrystalline-free SiGe single crystals with controlled Ge contents.In this work, crystalline thick epitaxial layers of SiGe with Ge contents exceeding 30% are fabricated by screen-printing technology on Si wafers. As illustrated in Figure 1, Aluminum-germanium (AlGe) paste with a mole ratio of 7:3 was prepared and screen-printed on p-type Cz-Si <111> substrate, dried at 100 °C for 10 minutes and then annealed in Ar ambient using IR image furnace at 900 °C for 5 minutes. The Al begins to melt at 660 °C, dissolving the silicon wafer surface and the Ge in the paste. The melted Al, Si and Ge form the liquid phase of the Al-Si-Ge, which when cooling process start, regrown epitaxially at the melt/Si interface to form the Al-doped SiGe crystalline layer.The formed SiGe was observed by scanning electron microscope (SEM), and energy dispersive X-ray spectrometry (EDX). As can be seen in the cross-sectional SEM image in Figure 2, SiGe layer of about 20mm was formed on the Si substrate surface. It is worth mentioning that the SiGe/Si interface is formed straight as the reaction stopped perfectly on façade <111> forming SiGe layer. EDX mapping of elements suggests that the Al in the Al-Si-Ge liquid phase formed at high temperature is segregated from the liquid to the Al-Ge paste layer during the cooling process and remains only as dopant in the SiGe layer due to its low solid solubility in Si and Ge. The Al-Ge paste residue layer will be etched chemically and further step of chemical mechanical polishing will be performed to improve the surface flatness of SiGe layer to be an epi-ready SiGe/Si substrate for different semiconductor devices applications.Reference[1] M. L. Lee and E. A. Fitzgerald, Strained Si/strained Ge dual-channel heterostructures on relaxed Si0.5Ge0.5 for symmetric mobility p-type and n-type metal-oxide-semiconductor field-effect transistors, Appl. Phys. Lett. 83, 4202 (2003). Figure 1

Anomalous time of flight behavior of fast ions in laser produced aluminum plasma

In this work, dynamics of multi-charged ions emitted from an aluminum plasma produced by Q switched Nd: Yag laser is studied using time of flight (TOF) measurements from Langmuir probe and spectroscopy under Ar ambient of 0.02 mbar. The temporal evolution of multi-charged ions, background neutrals, and ions is systematically studied for varying laser intensities. The temporal evolution shows all species have double-peak structure for all laser intensities considered in the study. The fast peak is sharp whereas the slow peak is broadly similar to that observed in previous studies. Moreover, higher charged ions have higher velocity, indicating acceleration from the transient electric field produced at the very initial temporal stages of expansion. Interestingly, the fast peak gets delayed, whereas the slow peak advances in time with increased laser intensity, which has not been reported in earlier studies. The observations point toward the possible role of ambipolar electric fields in the unexpected observed behavior of the TOF profiles.

Fabrication and Characterization of Epitaxial Graphene Field Effect Transistor Devices Based on a Monolithic Bottom Gate

Current electronics technology increasingly demands higher integration, flexibility, higher efficiency, and performance aspects such as compatibility with higher temperature operation of the semiconductor devices, which may find limitations when silicon is used. The superior intrinsic properties of SiC, eventually combined with the ability of growing monolithically epitaxial, high quality graphene on a SiC wafer (1), makes it a reliable alternative for some electronic applications, such as field effect transistors (FET), radio frequency (RF) power amplifiers, integrated circuits (IC), or sensors. In this work, we describe the fabrication and preliminary electrical characterizations of epitaxial graphene (EG) on a SiC substrate FET devices based on an alternative back gate architecture. We propose a new approach in which the FET device is built on a 4◦ off-axis cut, N+ doped 4H-SiC substrate (the back gate) with, on top of, it a 1μm semi-insulating homoepitaxial layer of SiC compensated with vanadium (the dielectric layer). EG will be used as FET conduction channel. Using this V-compensated dielectric layer is aimed to minimize effects on the FET characteristics such as from defects in the SiC crystal, especially below the FET active areas, which would have occurred when using ion implantation to create a buried gate. The EG film was grown by the high temperature Si sublimation method under an Ar ambient. Raman spectroscopy, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were applied in the structural characterization of epigraphene. The lack of D-peak in Raman spectra, together with SEM and AFM images, indicate that high quality monolayer to few layer epitaxial graphene fully covering the SiC surface is deposited. The electrical characteristics of the EG channel-devices and the functionality of the bottom gate were examined with 2-probe and 4-probe method. The electrical properties of the FET devices were also investigated with 3 terminal configuration.

Synthesis of Nanoparticles of Aluminium–Boron complex for Radiation Sensor

Radiation sensors based on thermo luminescence from nanoparticles of aluminium-boron complex for gamma radiation have been reported. Crystal chemistry of aluminium boride is quite complicated and is derived from complex tetragonal modification of boron. The crystal structure varies with the method of preparation and energy band gap contains defect states governed by the temperature during synthesis. There are various methods of preparing nanoparticles like boll milling, sol-gel and RF-thermal plasma. In the present studies Aluminum boron complex nanoparticles were synthesized by DC- transferred arc thermal plasma method. The DC-transferred arc thermal plasma has been received great attention as a useful method to synthesize nanoparticles. Since a substance is easily evaporated in large volume of thermal plasma. A pure aluminium and boron powders were mixed together and made to evaporate from water cooled graphite after impinging thermal plasma plume. Argon with flow rate of 3L/min was used as a plasma forming gas for the evaporation of raw powder mixture in Ar ambient in the plasma reactor. The obtained nanoparticles of aluminum –boron complex were characterized using X-ray diffraction technique for structural analysis, Transmission electron microscopy (TEM) for morphological analysis and energy dispersive analysis by X-ray (EDAX) for elemental analysis. The aluminum boron complex so obtained was investigated for thermoluminscence properties.

Effect of plume dynamics on surface contamination during interaction of millisecond infrared fiber laser with titanium

Dynamics of the plume produced due to the interaction of millisecond infrared fiber lasers having different spectral profiles with titanium is investigated by high-speed imaging (HSI) and optical emission spectroscopy (OES) at different ambient atmospheres and pressures. The surface quality is associated with different plume dynamics that depends on the processing conditions. Reabsorption of the laser pulse by the neutral titanium atoms due to overlap of laser spectral profile with corresponding transition energies causes deposition of nanoparticles on the surface around the spot produced by the laser, which results in surface contamination and darkness around the spot. Increasing confinement of plume in Ar ambient than Ar/He leads to more darkness around the spot due to more availability of Ti species in a smaller volume for reabsorption. In vacuum/at low pressures, larger size of the expanding plume causes a smaller number of Ti species to interact with the laser pulse that produces clean surface around the spot. The surface contamination is prevented irrespective of the processing conditions by using the laser with customized spectral profile, which does not overlap with any neutral titanium atomic transitions (Ti I).

Shock front interaction and dynamics of laterally colliding laser-produced plasmas

The effects of ambient gas pressure on the propagation dynamics of laterally colliding laser-produced aluminum plasma is investigated under various ambient conditions. In lower pressure range the interaction zone formed in between the seed plasmas exist for a short span of time. A strong stagnation region is observed at 10−2 mbar pressure in Ar ambient. Interaction zones are formed due to the shock waves generated at the seed plasmas at pressures above 0.1 mbar. A peculiar type of plume splitting is also observed at 0.15 mbar in air ambient at 150 ns. In Ar ambient, a channel like structure is observed in between the plasma plumes whose width increased with time. Shock interaction in air ambient is explained by regular reflection of shock waves where an illuminated interaction zone was formed where as in heavier Ar ambient, Mach reflection of shock waves occurs.

Hybrid structures of Si Nanocrystals-Carbon Nanotubes with bead architecture

In present work, hybrid structures of Si Nanocrystals (Si-ncs) and Carbon Nanotubes (CNTs) with bead-like architecture have been synthesized by exposing pristine CNTs to silane (SiH4) at 200 ºC. The exposed CNTs were annealed in Ar ambient at 500ºC in a catalytic chemical vapor deposition chamber. High-resolution transmission electron microscopy (HRTEM) elucidated that the bead-like architecture has well-defined crystalline nature. X-ray photoelectron spectroscopy (XPS) was used to study the nature of chemical bonding and structural functionalization/defects caused by silane exposure and annealing on the nanotube surface. XPS results indicated in-diffusion of Si in the CNT cavity as well reduction in oxygen content on the top surface of the CNTs. X-ray diffractometry was used to further confirm the formation of the crystalline hybrid structures. From the present work it is inferred that a controlled synthesis of hybrid structures (CNT-Si ncs) with bead-like architecture can be achieved by a simple CVD method for various applications

Growth of ZnO Nanoflower Arrays on a Patterned Sapphire Substrate

In this study, we investigated a novel technology to grow the ZnO nanoflower arrays on a patterned sapphire substrate using hydrothermal method. The process to prepare the substrate and grow ZnO nanoflower arrays were that the patterned concave sapphire substrates were cleaned using acetone, isopropyl alcohol, and D.I. water in an ultrasonic cleaner. Al sacrificial layer with the thickness of 600 nm was deposited using a thermal evaporation technology. The sol-gel process was used to deposit the ZnO seed layer on the patterned concave sapphire substrates, and then the ZnO seed layer was annealed at 500°C in Ar ambient for 1 h. The optical grade silicone A-B glue was coated on the ZnO seed layer and then the mixed solution of K3Fe(CN)6 : KOH : H2O = 10 g : 1 g : 100 ml was used to etch the sacrificial Al layer. (f) A lift-off technology was used to move the ZnO seed layer/silicone A-B glue to silicon substrate. Finally, a hydrothermal method was used to grow the ZnO nanorods on the ZnO seed layer/silicone A-B glue/silicon substrate at 90oC with the different durations of 10 to 60 min. Focused ion beam system (FIB) was used to observe the cross sectional morphology of patterned ZnO seed layer. The crystal structural of the flower-like ZnO nanostructures was analyzed using X-ray diffraction (XRD) pattern, the morphological of the flower-like ZnO nanostructures was observed using FIB and field emission scanning electron microscope (FESEM). Also, the optical properties of the flower-like ZnO nanostructures were investigated.

In situ monitoring of electrical resistivity and plasma during pulsed laser deposition growth of ultra-thin silver films

Ultra-thin silver films of thicknesses of the order of 10 nm and less were prepared in different ambient conditions (vacuum, Ar, and N2) by pulsed laser deposition on glass and fused silica substrates. The in situ monitoring of electrical resistance of deposited films and optical emission spectroscopy of plasma were implemented as real-time analysis techniques. Change in the growth mechanism of the Ag layer in N2 ambient is expressed by an acceleration of the coalescence process, which shifts the percolation point toward lower mass thicknesses. The films prepared in vacuum and Ar ambient were found to be unstable for a final resistance in the range from 1 to 100 MΩ while the films deposited in N2 revealed stable electrical resistance. The percolation point was further lowered by introducing a sublayer of AgxOy for the film deposited in N2 gas. Based on data provided by AFM, SEM, and spectroscopic ellipsometry, different film formation mechanisms are discussed in relation to surface morphology and optical properties. Optical emission spectroscopy was used to monitor the deposition process and identify the species presented during the deposition process. The energy of the ejected particle is affected by the addition of ambient gas and depends on the properties of the working gas.

Microstructural evolution of oxygen incorporated CdTe thin films deposited by close-spaced sublimation

In this work, cadmium telluride (CdTe) thin film was deposited in vacuum (pure argon ambient) as well as different argon (Ar) and oxygen (O2) ambient conditions using close-spaced sublimation (CSS) method at the deposition pressure of 1 Torr. The deposited films were characterized via X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), UV–Vis spectrophotometer and Hall Effect measurement for the analysis of structural properties, morphology, optical properties and electrical properties, respectively. XRD patterns exhibited almost similar preferential orientation plane at (111) irrespective of the O2 concentration. SEM surface morphology microstructure revealed that O2 presence had a substantial effect on grain size reaching up to 7.19 µm. Optical properties also demonstrated insignificant changes in the direct band gap values of around 1.48 eV. Carrier concentration showed an upward trend in the order of 1013 cm−3, whereby resistivity and mobility did not change substantially either in vacuum (pure Ar ambient) or in Ar/O2 ambient.

Tunable Narrowband Silicon-Based Thermal Emitter with Excellent High-Temperature Stability Fabricated by Lithography-Free Methods.

Thermal emitters with properties of wavelength-selective and narrowband have been highly sought after for a variety of potential applications due to their high energy efficiency in the mid-infrared spectral range. In this study, we theoretically and experimentally demonstrate the tunable narrowband thermal emitter based on fully planar Si-W-SiN/SiNO multilayer, which is realized by the excitation of Tamm plasmon polaritons between a W layer and a SiN/SiNO-distributed Bragg reflector. In conjunction with electromagnetic simulations by the FDTD method, the optimum structure design of the emitter is implemented by 2.5 periods of DBR structure, and the corresponding emitter exhibits the nearly perfect narrowband absorption performance at the resonance wavelength and suppressed absorption performance in long wave range. Additionally, the narrowband absorption peak is insensitive to polarization mode and has a considerable angular tolerance of incident light. Furthermore, the actual high-quality Si-W-SiN/SiNO emitters are fabricated through lithography-free methods including magnetron sputtering and PECVD technology. The experimental absorption spectra of optimized emitters are found to be in good agreement with the simulated absorption spectra, showing the tunable narrowband absorption with all peak values of over 95%. Remarkably, the fabricated Si-W-SiN/SiNO emitter presents excellent high-temperature stability for several heating/cooling cycles confirmed up to 1200 K in Ar ambient. This easy-to-fabricate and tunable narrowband refractory emitter paves the way for practical designs in various photonic and thermal applications, such as thermophotovoltaic and IR radiative heaters.

Oxidation protective coating of Y2O3-Na2SixO2x+1 composite on graphite crucible for high temperature applications

Oxidation and corrosion protective coatings on graphite are essential for its high temperature applications. In the present work, oxidation protective coating on graphite was achieved with a combination of Y2O3 and SiO2 suspension with NaOH in methanol. Study showed that the optimized composition of the desired coating was Y2O3–15 wt% SiO2 (i.e., 2 g mixture of Y2O3 and SiO2 powder containing 0.3 g of SiO2 which is 15% of the total powder content if expressed in weight) with 5 M NaOH in 10 mL methanol. This protective coating on graphite was stable up to 1473 K for 30 min in Ar ambient before visible cracks appeared. The compositions of SiO2: NaOH were varied (5 mmol:5 M, 10 mmol:5 M and 5 mmol:10 M) to examine the roles of these two components in the overall adhesiveness of the coating. SiO2 and NaOH acted as inorganic binders and formed in-situ intermediate layers during sintering which held Y2O3 layer with the graphite surface. The coated graphite blocks and crucibles were characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDS), differential thermal analysis and thermogravimetric analysis (DTA/TGA) and Fourier transform infrared spectroscopy (FTIR). The oxidation protective nature of the coating was tested by heating the coated crucible at 1273 K for 1-15 h in air atmosphere. The effective adhesion of oxidative coating on graphite was explained.

Carrier lifetime control by intentional boron doping in aluminum doped p-type 4H-SiC epilayers

The carrier lifetime control in p-type 4H-SiC epilayers with intentional aluminum (Al) and boron (B) doping is demonstrated as part of work to develop a p-type “recombination-enhancing layer” for n-channel insulated gate bipolar devices fabricated on p-type substrates. The (Al + B)-doped epilayers (Al: 5 × 1017, B: 4 × 1016 cm−3) showed a very short minority carrier lifetime of less than 20 ns at 293 K, resembling that of highly Al-doped epilayers (Al: 1 × 1019 cm−3). Besides, the minority carrier lifetimes in (Al + B)-doped epilayers are stable against post-annealing in Ar and H2 ambient, while that of Al-doped epilayers varied considerably. PiN diodes with a 10 μm-thick (Al + B)-doped buffer layer inserted on p-type substrates showed no evident degradation after a stress test under a pulse current density of 2000 A/cm2.

Structural and physical characteristics of sputter deposited zirconium nitride thin films by sputtering at various time in Ar-N2 atmosphere

Zirconium nitride films were deposited by RF reactive magnetron sputtering at room temperature in an N2 and Ar ambient. The X-ray diffraction analysis indicated that the growth of ZrN with preferred orientations (111) and (200) on the soda-lame glass substrates was reached. The particle size formed on the surface of the synthesized layers increases from 15.9 to 42.1 nm as deposition time increases. The N/Zr ratio decreases from 2.0 to 1.43 with increasing deposition time from 10 to 30, and the average surface roughness increased from 0.88 to 5.58 nm. Increasing the deposition time reduced the bandgap from 2.91 to 2.06 eV and also increased the resistance from 19.84 × 10–6 to 40.69 × 10−6Ω cm. The thermal coefficient of resistance was 9.27 × 10–8 $$\frac{{\Omega \cdot {\text{cm}}}}{{^{ \circ } K}}$$ for the thickest sample and 5.26 × 10–8 $$\frac{{\Omega \cdot {\text{cm}}}}{{^{ \circ } K}}$$ for the thinnest sample. At a wavelength of 600 nm, the refractive index was 2.028 and 0.889 for the samples deposited for 10 and 30 min, respectively.