Thin Films Of Different Thicknesses Research Articles

Multifunctional CZTS thin films: Structural, optoelectrical, electrical and photovoltaic properties

High-quality Cu2ZnSnS4 (CZTS) thin films of different thicknesses (240 nm–418 nm) have been prepared onto pre-cleaned glass substrates using a low-cost chemical bath deposition technique. Influence of deposition conditions on the variation of the structural, optical, optoelectrical and electrical properties of the CZTS films has been inspected. The XRD patterns revealed that CZTS thin films exhibited a polycrystalline nature and follow the kieserite crystal structure. The studied films have exhibited direct energy gap transition that decreased from 1.54 to 1.48 eV. Profound analysis has been made to investigate the variation of the optical and optoelectrical properties of CZTS as a function of deposition time. A prominent increase in the nonlinear parameters has been noticed with the increase in the deposition time. This finding could shed lights on the possibility of using CZTS in nonlinear devices. The variation of the DC conductivity with temperature for the CZTS thin films has been discussed. The values of the activation energies have been decreased with increasing the film thickness which confirms the increase in film uniformity. Good correlations have been established between the structural aspects of the films to their optical and optoelectrical parameters. Cu2ZnSnS4 film (418 nm) has been selected to be utilized in fabricating the Al/n-Si/P-CZTS/Au heterojunction. Photovoltaic behavior was observed for the fabricated device which had a solar conversion efficiency of 3.37%.

Morphological, elemental, and optical characterization of plasma polymerized n-butyl methacrylate thin films

Plasma polymerized n-butyl methacrylate (PPnBMA) thin films of varying thicknesses were prepared at room temperature by AC plasma polymerization system using a capacitively coupled parallel plate reactor. Field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energy-dispersive X-ray (EDX) analysis, and ultraviolet–visible (UV–Vis) spectroscopic investigation have been performed to study the morphological, elemental, and optical properties of the PPnBMA thin films, respectively. The flat and defect-free nature of thin films were confirmed by FESEM and AFM images. With declining plasma power, average roughness and root mean square roughness increase. Allowed direct transition (Egd) and indirect transition (Egi) energy gaps were found to be 3.64–3.80 and 3.38–3.45 eV, respectively, for PPnBMA thin films of different thicknesses. Values of Egd as well as Egi increase with the increase of thickness. The extinction coefficient, Urbach energy, and steepness parameter were also determined for these thin films.

Unveiling the nature of adsorbed species onto the surface of MgO thin films during prolonged annealing

Present work investigates the nature of adsorbed species onto the surface of MgO thin films during prolonged annealing. The prolonged annealing (300 °C, 24 h) was performed on MgO thin films of different thicknesses ranging from 6.5 to 56.2 nm in order to exactly identify the related effect. Deposited films of different thicknesses exhibited local electronic structure very much analogues to the bulk MgO as investigated through near edge X-ray absorption fine structure measurements. These measurements further revealed that local electronic structure was significantly modified by prolonged annealing. It was contemplated that oxygen molecules were adsorbed on the surface of MgO thin films during prolonged annealing. Apart from this, onset of H2O adsorption was also identified using Fourier transform infrared spectroscopy.

Room-temperature optical detection of hydrogen gas using palladium nano-islands

Palladium thin films of different thicknesses have been processed by oxidation and subsequent reduction in hydrogen atmosphere. Hydrogen optical sensing properties of as-deposited (Pd) and processed (r-Pd) samples have been experimentally tested with a H2 concentration of 5% and 1%, discovering that the reduced films show improved performances in term of response/recovery time. As reveled by SEM images, the oxidation/reduction process modifies the surface appearance, which assumes a nano-islands structured morphology. The porosity of the processed films may explain the reduction of the response/recovery time, while the larger effective sensing surface in thinner samples justifies the responsivity performances.

Near-zero IR transmission of VO2 thin films deposited on Si substrate

Vanadium dioxide (VO2) thin films of different thickness have been deposited on Si substrates by using DC magnetron sputtering. The effects of substrate pre-treatment by means of seeding (spin coating and ultrasonic bathing) and biasing on the structure and optical properties were investigated. Seeding results in a smaller grain size in the oxide film, whereas biasing results in square-textured crystals. VO2 thin films of 150 nm thick show a near-zero IR transmission in switched state. Especially, the 150 nm thick VO2 thin film with seeding treatment shows an enhanced switching efficiency.

Effect of seed layer thickness on optoelectronic properties of ZnO-NRs/p-Si photodiodes

In this work, the effect of seed layer thickness on the optical and electrical properties of a photodiode based on zinc oxide nanorods (ZnO-NRs)/p-Si was studied. ZnO thin films of different thicknesses were deposited on a p-type single crystalline silicon substrate by the spin-coating method, and then well-aligned ZnO-NRs were grown on a seed layer by the hydrothermal method. The seed layer thickness increment enhanced the NR lengths and improved their crystallinity. Longer NRs showed lower reflectance and band gap measurements were carried out using the reflectance spectrum. The current-voltage (I–V) measurements were performed under dark and UV illumination to study the photo-detection properties of the ZnO-NRs/p-Si photodiode with different seed layer thicknesses. The diode ideality factor, barrier height, saturation current and series, and shunt resistance were determined by the dark current-voltage measurements. The dark current-voltage characteristics demonstrated an excellent rectifying behavior, and the seed layer thickness increment decreased the diode ideality factor. It was shown that the current-voltage characteristics of the fabricated devices with different seed thicknesses under UV light illumination had good sensitivities.

Saturable Absorption in 2D Ti3 C2 MXene Thin Films for Passive Photonic Diodes.

MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti3 CNTx (Tx represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti3 C2 Tx thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z-scan method, it is found that the SA behavior in Ti3 C2 Tx MXene arises from plasmon-induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti3 C2 Tx MXene is observed to be dependent on the film thickness. Unlike other 2D materials, Ti3 C2 Tx is found to show higher threshold for light-induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti3 C2 Tx MXenes, a Ti3 C2 Tx MXene-based photonic diode that breaks time-reversal symmetry to achieve nonreciprocal transmission of nanosecond laser pulses is demonstrated.

Kinetic Study of the Initial Lithiation of Amorphous Silicon Thin Film Anodes

The mechanisms and kinetics of lithiation and delithiation of amorphous silicon were investigated using potentiostatic techniques and thin films of different thickness, with a focus on the initial lithiation process that occurs in the first cycle. In potentiostatic tests, distinct kinks were observed in the current vs. time curves, and the time at which the kink occurred increased for thicker films. This behavior can be explained using a model in which a sharp interface between an amorphous LixSi phase and Li-saturated amorphous Si propagates through the film. Using this model, the rate-limiting process was determined to be diffusion of Li in the LixSi phase rather than reaction at the lithiation front. The Li diffusivity in the lithiated phase was determined to be in the 10−13 cm2/s range, independent of film thickness above 135 nm. The thin-film potentiostatic technique used in this study should prove useful in investigation of the mechanisms and rate parameters for other phase transitions that occur during lithiation of silicon and for kinetic studies of other electrode materials.

Superiority of localized surface plasmon resonance technique in characterization of ultra-thin metallic films

The comparison and correlation of morphological, optical and crystallographic properties of ultra-thin Au films obtained using field-emission scanning electron microscopy (FESEM), x-ray reflectivity (XRR), UV-visible transmission, and grazing incidence x-ray diffraction (GIXRD) are presented. The Au thin films of different thickness are grown on the glass substrate using the sputtering technique. The particle size, number density and the covered area fraction of Au thin film are obtained from FESEM images. The XRR technique is used to determine the film thickness and surface roughness. The localized surface plasmon resonance (LSPR) response of Au thin films is obtained using UV-Vis transmission spectroscopy. The LSPR peak position and its strength are correlated with film morphology and thickness. Finally, it is shown that LSPR based spectroscopy techniques can provide much better information about morphology and thickness of the Au films up to a resolution of ~1 nm.

Efficiency enhancement of natural dye sensitized solar cell by optimizing electrode fabrication parameters

AbstractEfficiency of dye-sensitized solar cell (DSSC) depends on several interrelated factors such as type and concentration of dye, type and thickness of photoelectrode and counter electrode. Optimized combination of these factors leads to a more efficient cell. This paper presents the effect of these parameters on cell efficiency. TiO2nanoporous thin films of different thicknesses (5 μm to 25 μm) were fabricated on indium doped tin oxide (ITO) coated glass by doctor blading method and characterized by inverted microscope, stylus surface profiler and scanning electron microscope (SEM). Natural organic dye of different concentrations, extracted from turmeric, was prepared with ethanol solvent. Different combinations of dye concentrations and film thicknesses along with different types of carbon catalyst have been investigated by I-V characterization. The result shows that the cell made of a counter electrode catalyst material prepared by candle flame carbon combined with about 15 μm thick photoelectrode and 100 mg/mL dye in ethanol solvent, achieves the highest efficiency of 0.45 %, with open circuit voltage of 566 mV and short circuit current density of 1.02 mA/cm2.

Co-based amorphous thin films on silicon with soft magnetic properties

The present work investigates the emergence of multiple modes in the high-frequency permeability spectrum of Co-Zr-Ta-B amorphous thin films. Amorphous thin films of different thicknesses (t=100-530 nm) were deposited by DC magnetron sputtering. Their static and dynamic soft magnetic properties were investigated to explore the presence of multi-magnetic phases in the films. A two-phase magnetic behavior of the thicker films (≥333 nm) was revealed by the in-plane hysteresis loops. Multiple resonance peaks were observed in the high-frequency permeability spectrum of the thicker films. The thickness dependent multiple resonance peaks below the main ferromagnetic resonance (FMR) can be attributed to the two-phase magnetic behaviors of the films.

Investigation of composition of boron carbide thin films by resonant soft x-ray reflectivity

Boron carbide thin films of different thicknesses deposited by ion beam sputtering were studied. The deposited films were characterized by grazing incidence hard x-ray reflectivity (GIXR), resonant soft x-ray reflectivity (RSXR), x-ray photo electron spectroscopy (XPS), resonant Rutherford backscattering spectrometry (RRBS), and time of flight secondary ion mass spectrometry (TOF-SIMS). Depth profile of the chemical elements constitute the films is reconstructed based on analysis of reflectivity curves measured in the vicinity of B K-edge. The composition of films is closely dependent on film thickness. Boron to Carbon (B/C) ratio reaches to ~4 as the thickness of deposited films increases. The B/C ratio estimated from RSXR measurements are in agreement with the RRBS measurements. TOF-SIMS data also suggested that decrease in boron content with decrease in film thickness. XPS measurements confirm the presence of little amount of B atoms on the surface of low thickness film.

Thin films of an axially chiral bibenzo[c]phenanthrene diol and its enantiomers: Film structure, optical property, and photoelectrochemical response

A helically distorted and polycondensed bisphenol [1,1′-bibenzo[c]phenanthrene]-2,2′-diol (HEBPOL) and its separated optically pure enantiomers were used to prepare thin films and to explore their optoelectronic properties. Due to both hydrophobic aromatic rings and hydrophilic −OH groups the compound possessed amphiphilic characters, which helps to form a stable layer at the air-water interface. The stable film from the air-water interface was then transferred to different types of solid substrates by Langmuir-Blodgett (LB) technique. In the atomic force microscopic (AFM) images, circular-shaped islands were observed for the films of racemic mixture and their enantiomers deposited at different surface pressures. Thin films of different thickness were also prepared by spin coating (SP) method. The information about thickness, roughness, and electron density of layers or films was determined through X-ray reflectivity (XR) experiments. The multilayer formation was observed in the LB film, which was suggested by the height of islands in AFM images and the thickness determined by the XR experiments. The generation of photocurrent was measured by a conventional three-electrode system with a light source of the Xenon lamp. The photocurrent generation was speculated higher for the films having a higher thickness and experimentally found above 0.4μA/cm2 for 100Å. The compound is axially chiral and both the enantiomers respond to circularly polarized light irradiation in solution as well as in LB and SP films.

Preparation and spectroscopic analysis of zinc oxide nanorod thin films of different thicknesses

AbstractZinc oxide thin films with different thicknesses were prepared on microscopic glass slides by sol-gel spin coating method, then hydrothermal process was applied to produce zinc oxide nanorod arrays. The nanorod thin films were characterized by various spectroscopic methods of analysis. From the images of field emission scanning electron microscope (FESEM), it was observed that for the film thickness up to 200 nm the formed nanorods with wurtzite hexagonal structure were uniformly distributed over the entire surface substrate. From X-ray diffraction analysis it was revealed that the thin films had good polycrystalline nature with highly preferred c-axis orientation along (0 0 2) plane. The optical characterization done by UV-Vis spectrometer showed that all the films had high transparency of 83 % to 96 % in the visible region and sharp cut off at ultraviolet region of electromagnetic spectrum. The band gap of the films decreased as their thickness increased. Energy dispersive X-ray spectroscopy (EDS) showed the presence of zinc and oxygen elements in the films and Fourier transform infrared spectroscopy (FT-IR) revealed the chemical composition of ZnO in the film.

Thickness dependence of ac electrical conductivity and dielectric behavior of plasma polymerized 1, 1, 3, 3–tetramethoxypropane thin films

AC electrical conductivity (σac), dielectric constant (ɛ′), and dielectric loss tangent (tan δ) of plasma polymerized 1, 1, 3, 3‐tetramethoxy‐propane (PPTMP) thin films of thicknesses 100, 150, and 200 nm prepared by plasma polymerization technique using a capacitively coupled glow discharge reactor have been investigated in the frequency range of 30–106 Hz. It is observed that σac increases as frequency increases with a higher slope in the medium frequency (<105Hz) region in the PPTMP thin films of three thicknesses. These observations suggest that the conduction may be dominated by hopping of carriers between the localized states. The general trend of ɛ′ is to increase with increasing thickness, ɛ′ remains independent of frequency upto about 104Hz and then falls rapidly. The dependence of tanδ with frequency for PPTMP thin films of different thicknesses showed small relaxation peak at the very low frequencies (<102Hz) and then it decreases slightly with a broad minimum at 103 Hz and again increases. Cole–Cole plot reveals that Debye type of mechanism is operative in the experimental frequency range. POLYM. ENG. SCI., 58:1342–1345, 2018. © 2017 Society of Plastics Engineers

Optical fiber sensors based on gold nanorods embedded in polymeric thin films

In this work, we present a study about the generation and analysis of optical resonances caused by gold nanorods (GNRs) embedded in films. GNRs were embedded in polymeric thin films using the Layer-by-Layer nanoassembly (LbL) deposition technique. Polymer/GNRs thin films of different thicknesses were deposited on the surface of cladding removed optical fibers for sensing. The spectral responses of the optical fiber sensors were monitored during the build-up of the thin films. The generation of two Localized Surface Plasmon Resonances (LSPRs) associated to the GNRs was observed in thinner coatings. These devices with around 12 polymer/GNRs bilayers were characterized as refractometers, providing an intensity-based sensitivity up to 75.69dB/RIU. For thicker polymer/GNRs overlays, both LSPRs bands were also generated and, additionally, it was observed a new Lossy Mode Resonance (LMR) band due to modes coupled to the sensitive coating. The dependence of these three resonance bands with the surrounding refractive index was studied. Finally, these sensors were tested in a climatic chamber in the 20–90% relative humidity (RH) range and the LMR showed a good sensitivity to RH changes while the LSPR bands remained very stable in comparison. Results showed an excellent sensitivity of 11.2nm/%RH for the LMR, confirming the potential of this type of optical fiber sensor based on the combination of LSPRs and LMRs bands.

Effect of variation of thickness of TiO2 on the photovoltaic performance of n-TiO2/p-Si heterostructure

Fabrication of heterojunctions of Si along with oxide based semiconductors like TiO2 is an alternative method to produce cost effective solar cells. To study the photovoltaic performance of the n-TiO2/p-Si heterostructure, TiO2 thin films of different thicknesses were deposited on p type Si substrates using pulsed laser deposition technique. All the films were characterized using XRD, AFM, Spectroscopic ellipsometry and I–V characteristics with solar simulator and other monochromatic light sources of different wavelengths. Optical properties of the thin films were correlated with the I–V characteristics under dark and illumination conditions. It has been shown that thickness plays a crucial role on the photovoltaic performance of the n-TiO2/p-Si heterostructure. Further, it has been observed that the optical reflectivity of TiO2 thin film of particular optimized thickness deposited on p type Si could be lowest. Consequently, photocurrent of the n-TiO2/p-Si heterostructure is found to decrease with an increment of the thickness of the TiO2 thin film. This is attributed to the increment of series and sheet resistance with increase of TiO2 film thickness. Moreover, increase of TiO2 film thickness can also create surface states and defects in the n-TiO2/p-Si heterojunction which are also responsible for poor efficiency of the photovoltaic cells.

Characterization of optical and morphological properties of chalcone thin films for optoelectronics applications

Thin films of a chalcone 1-(4-chlorophenyl)-3-(4- N, N dimethyl amino phenyl)-2-propen-1-one (CDP) were prepared. The chalcone was dissolved in acetone with different concentrations to achieve thin films of different thicknesses. The solution was deposited by spin coating technique on glass substrates. The optical spectra of the chalcone thin films (CDP-TFs) were recorded. FTIR, DRS, NMR, TGA and DSC were used to characterize and investigate the chalcone properties as power and thin films. XRD and SEM have demonstrated the structure and surface morphology of the (CDP-TFs) depends strongly on film thickness. The findings revealed that the variations of the thickness from 150 to 400nm have led increasing the crystal size from 2.92 to 78.51nm. In contrast, the macrostrain was shifted to lower values. Furthermore, the energy band gaps of CDP-TFs increased by increasing the film thickness. To the best of our knowledge, this is a first report on the structural and optical properties chalcone as thin films.

Effect of Thickness on Micro-Structural and Optical Properties of Al-Doped ZnO Films Prepared by Sol-Gel Spin Coating

Aluminium (Al) doped Zinc oxide (ZnO) thin films of different thicknesses were prepared on glass substrates by sol-gel spin coating method. The effect of thicknesses on micro-structural and optical properties was investigated for transparent conducting oxide (TCO) application in solar cells and other optoelectronic applications. Grazing incidence x-ray diffraction (GIXRD) showed maximum orientation along (002) plane of c-axis. The variation of different structural parameters like crystallite size, micro-strain, c-axis strain, dislocation density as a function of film thickness was investigated. The FTIR spectra confirmed the formation of Al-doped ZnO film. FESEM images showed spherical shaped nanosized grains and formation of micro pores. The optical absorption increased and absorption peak shifted towards longer wavelength (red shift) with increase in the thickness of the film respectively. The optical transmittance of all the films has a transparency of more than 75% in the visible region. The optical band gap (Eg) decreased with increase in the film thickness. The diffused reflectance (DRS) showed very low reflectance in the region of 400-800 nm, but increased in the 800-900 nm region. Photoluminescence (PL) spectra of the prepared films showed intense band edge UV and low intense visible emissions respectively. The effect of thickness of Al-doped ZnO film on micro-structure, surface morphology, optical absorption and transmittance, diffused reflectance and PL have been investigated and the results are reported.

Unique Crystal Orientation of Poly(ethylene oxide) Thin Films by Crystallization Using a Thermal Gradient

Poly(ethylene oxide) (PEO) thin films of different thicknesses (220, 450, and 1500 nm) and molecular masses (4000, 8000, and 20 000 g/mol) have been fabricated by spin-coating of methanol solutions onto glass substrates. All these samples have been recrystallized from the melt using a directional thermal gradient technique. Millimeter-size domains with crystallites uniformly oriented in the direction of the thermal gradient are observed. Futhermore, the crystallites size and orientation distribution are enhanced (e.g., increases and decreases, respectively) when film thickness is decreased, ultimately leading to a single-crystal-like behavior for 220 nm thick PEO films of mass 8000 g/mol. Interestingly, this fine microstructure is partially retained after melting and subsequent cooling back to ambient temperature for the highest molecular weight polymer allowing, in this particular case, to significantly decrease the distribution of crystal orientation obtained after crystallization using the thermal grad...