Surface Roughness Of Thin Films Research Articles

Vapor‐Transport‐Deposited Orthorhombic‐SnSe Thin Films: A Potential Cost‐Effective Absorber Material for Solar‐Cell Applications

The power‐conversion efficiencies of orthorhombic tin selenide (α‐SnSe)‐based thin‐film solar cells (TFSCs) are very low—less than 1% in most cases—due to the poor crystallinity, small grains, and large number of defects. Herein, the highest cell efficiency of 2.51% together with a high short‐circuit current density of 28.07 mA cm−2 for α‐SnSe TFSCs grown via vapor‐transport‐deposition (VTD) is reported. The grain size and surface roughness of the SnSe thin films greatly influence the shunt properties of the device. Significantly large shunt losses are detected in the case of both small and extremely large grains. The shunt losses for SnSe thin film with small grains are associated with high grain‐boundary scattering. The presence of extremely large grains results in high surface roughness of the SnSe thin film, which causes nonuniform deposition of the CdS buffer layer and, consequently, higher shunt losses. The SnSe thin film with moderate‐sized grains and inferior surface roughness exhibits improved shunt properties owing to uniform deposition of the CdS buffer layer and subsequent layers and thereby significant improvement in the device performance. The potential of orthorhombic VTD‐SnSe thin films as an emerging cost‐effective absorber layer for TFSCs is experimentally demonstrated.

Work Function Modulation of Few-Layer Graphene by Swift Heavy Ion Irradiation.

Here, we report the structural and electronic modification induced in chemical vapor deposited graphene by using swift heavy ions (70 MeV Ni6+).Raman spectroscopy was used to quantify the irradiation-induced modification in vibrational properties. The increase in defect density with fluence causes an increase in the intensity ratio of its characteristic Raman D and G band. The increase in defect density also results in a decrease in crystallite size. The changes in the crystal structure are observed from X-rays diffraction measurement. Swift heavy ion irradiation induced defect, modified the surface roughness and surface potential of graphene thin film as measured from atomic force microscopy and scanning Kelvin probe microscopy respectively. The increase in the work function, surface roughness as well as defect concentration with fluence, indicate the possibility of linear correlation between them. Presence of defects in graphene sheets strongly affects surface electronic and optical properties of the material that can be used to tailor the optoelectronics device performance.

Favourable tuning of optical absorbance, bandgap and surface roughness of ZnO thin films by C ion implantation at the critical angle

Low energy ion implantation with exquisite control of angle allows manipulating the applications of thin films. Here we present a favourable and efficient strategy of 50 keV Carbon ion implantations on ZnO thin films at three different tilt angles 0°, 30° and 60°. This plays a significant role in tuning of optical absorbance, bandgap, grain size and surface roughness simultaneously. The TRIM simulations are performed to elucidate the theoretical understanding and to compare the modifications in the physical properties using different characterization tools. These experimental results demonstrate that the ion implantations at 30° result in a significant reduction of 89% in the grain size and 35% reduction in the optical transmittance along with an improvement of 25% in the surface roughness of these thin films. The optical bandgap is also tuned from 3.27 to 3.20 eV. These results establish a new approach in designing the exotic materials with lower grain size, lower bandgap and smoother surface along with higher absorbance of ultraviolet (UV) light that will help increasing the data storage capacity and getting higher energy efficiency with reduced UV light emissions.

Effect of a seed layer on microstructure and electrical properties of Ga2O3 films on variously oriented Si substrates

The realization of the free interface strain between a Ga2O3 material and a substrate is significantly critical to fulfill the requirements for the fabrication of high-quality Ga2O3 material. In this work, a seed layer (SL) was utilized to circumvent the interface strain issue for enhancing quality and reducing surface roughness. The smooth surface and high-quality Ga2O3 thin film on (100)-Si substrate can be achieved under the growth parameters of 700 °C and 6 mTorr. The as-annealed Ga2O3 thin films grown on variously oriented Si substrates host various microstructure and surface roughness due to the different lattice mismatches at interfaces. The differences in surface roughness of Ga2O3 thin films are greatly eliminated by the deposition of a SL of Ga2O3 thin film on Si substrate. The PL spectra of as-annealed Ga2O3 thin films consist of three peaks at UV and green emission regions. The green luminescence intensity is reduced through the deposition of a SL, indicating lower surface defects and oxygen vacancy concentration. The Ga2O3 thin film with a SL presents a small RMS, high quality and limited dark-current. The work offers a promising strategy to make Ga2O3 film with high-quality and smooth surface on Si for fabricating the functional devices.

Preparation, Raman spectroscopy, surface morphology and optical properties of TiPcCl2 nanostructured films: thickness effect

Phthalocyanines are of a broad interest in photovoltaic applications. In this study, films of titanium-phthalocyanine-chloride (TiPcCl2) were prepared by the thermal evaporation method. The molecular structure was studied by a Raman spectrometer, showing a match between the spectra of the powder and the prepared films. The films' surface was examined by the atomic force microscope, revealing grain size and surface roughness of TiPcCl2 thin films to be 223 and 41 nm, respectively, for a 100 nm thickness. The energy gap was determined to be 1.5 eV, with no observable effect by the thickness change. Additionally, the linear and nonlinear optical constants were calculated from reflectance and transmittance measurements. The values of third nonlinear susceptibility are in order of 10–12 esu, which is compatible with other phthalocyanines. The nonlinear optical constants indicate that TiPcCl2 films could also be used for optical laser limiters.

Electronic Speckle Pattern Interference technique for measuring thickness of metallic nano thin films

Electronic Speckle Pattern Interference (ESPI) is a non-contact optical technique generally used for the measurement of surface deformations of various kinds. With the help of phase retrieval algorithms, phase of the deformed object is calculated in this method which can be then converted into displacement information. This paper demonstrates the use of ESPI method to measure the thickness of some nano-sized metallic thin films. Calculated thickness values are in good agreement with the values measured via Profilometer. The least thickness (z-axis) measured by this method is ~ 52 ± 3.1 nm. The z-axis resolution of the used method is at par with other expensive microscopy techniques like atomic force microscopy. Therefore, a low-cost alternative to expensive microscopy techniques is presented in this paper as far as z-axis is concern. Surface roughness of thin films can also be calculated using retrieved surface profiles and they are also found to be in the nanometer range.

Ellipsometry Study of CdSe Thin Films Deposited by PLD on ITO Coated Glass Substrates.

Cadmium selenide (CdSe) thin films were deposited on indium tin oxide (ITO) coated glass substrates using pulsed laser deposition (PLD) technique under different growth temperatures. Samples were investigated for their structural, morphological, and optical properties through X-ray diffraction (XRD), atomic force microscopy (AFM), and UV-Vis-NIR spectroscopy. AFM analysis revealed that the surface roughness of the as-grown CdSe thin films increased with the increase in deposition temperature. The optical constants and film thickness were obtained from spectroscopic ellipsometry analysis and are discussed in detail. The optical band gap of the as-grown CdSe thin films, calculated from the Tauc plot analysis, matched with the ellipsometry measurements, with a band gap of ~1.71 eV for a growth temperature range of 150 °C to 400 °C. The CdSe thin films were found to have a refractive index of ~3.0 and extinction coefficient of ~1.0, making it a suitable candidate for photovoltaics.

Morphology changes of In-doped ZnO nanosheets via ZnCl2 and InCl3 vapor formation during thermal dissipation annealing process and improved UV photoresponse properties

Ultraviolet (UV) photodetectors that are fabricated using ZnO thin films exhibit higher photocurrent stability, without a complex filter, than that exhibited by Si-based UV photodetectors. However, the ZnO-based UV photodetectors possess several drawbacks such as slow response speed, low on/off current ratio, and low sensitivity. These drawbacks can be overcome by regulating the number of free carriers and point defects that affect the photocurrent increment and the response speed of the UV photodetectors. In this study, indium (In)-doped ZnO (IZO) thin films were deposited via sol-gel spin coating. Subsequently, the amorphous IZO thin films were crystallized via thermal dissipation annealing (TDA). This facilitated the regulation of the number of point defects and free carriers, and the surface roughness of the IZO thin films decreased with the increase in the doping concentration. The UV photosensitivity of the IZO thin films was higher than that of the undoped ZnO thin films. The IZO thin films also exhibited the highest photoresponsivity and UV photoresponse speed. The technique that was devised in the study was concluded to be a feasible route for the fabrication of ZnO-based UV photodetectors with high photosensitivity, photoresponsivity, and UV photoresponse speed.

Tuning the optical and morphological features of CuxO thin films via La doping

In the present investigation, the undoped and La doped CuxO thin films are deposited on glass substrates by sol-gel spin coating method. The effect of various La doping concentrations on the chemical composition, morphological and optical properties of CuxO thin films have been extensively studied using X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), Scanning electron microscopy (SEM), and UV–Vis diffuse spectrophotometer. The valence states of Cu, La and O have been identified by X-ray photoelectron spectroscopy (XPS) method. The AFM have demonstrated that the surface roughness of CuxO thin films decreases with increasing La concentration. Optical analyses have revealed that the optical band gap energy of CuxO thin films widens from 2.063 eV to 2.090 eV as the La concentration increases from 0% to 10%. Moreover, the Urbach energies, Eu, of the undoped and La substituted CuxO thin films have been determined.

Effect of The Cu Doping on The Structural and Optical Properties of AlSb Thin Films Deposited by Thermal Evaporation Method

AlSb thin film was prepared on a glass substrate with a thickness of (200 nm) at room temperature using the thermal evaporation technique under high vacuum conditions (10−6 mbar). The effect of Cu doping at ratios (1%, 3% and 5%) on the structural and optical properties were investigated. The structural properties of the films were evaluated by X-Ray Diffraction technique (XRD) and atomic force microscopy (AFM). The optical properties of the films were measured using the (UV-Vis ) spectra in the ranges from 400 to 1000 nm. XRD results showed that all the samples have a polycrystalline cubic structure, and the average grain size of AlSb increases with increasing the Cu ratios. According to the AFM analysis, it is noticed that the average surface roughness (RMS) of AlSb nanocubic thin film decreases with increasing Cu doped concentration. From UV–Vis absorption spectra, it is noticed that all the samples have high absorption in the visible region, and the direct energy gap values for the samples were 1.83 eV, 1.81 eV, 1.80 eV, and 1.78 eV for pure, 1% Cu, 3% Cu and 5% Cu respectively.

The improvement of CoZrTaB thin films on different substrates for flexible device applications

In this paper, the CoZrTaB thin films are fabricated using sputtering on different substrates and characterized comprehensively. The CoZrTaB thin films have been fabricated in the single-layer and multi-layer structures with SiO2 as the insulator layer, of which the vibrating sample magnetometer results suggest that the saturation field and the coercivity change of the multi-layer structure can be minimized while the lamination structure can suppress the eddy current at high working frequency. Compared with the continuously sputtered 400 nm CoZrTaB thin film, the multi-layer thin film shows a hysteresis loop with a single domain and small coercivity. The surface roughness of each CoZrTaB thin film and two kinds of polyimide substrates is extracted by the atomic force microscope instrument. Besides, material characterization such as X-ray powder diffraction and Rutherford backscattering spectrometry have been conducted to acquire the information of phase and element ratio of the CoZrTaB thin film. Also, the different process conditions that could affect the magnetic properties are investigated and verified. A comparison is made with the previously reported results, sustaining the improvement of the CoZrTaB thin film on different substrates.

Structural properties of ferroelectric characteristics of mixed NiTiO3-BiFeO3 thin film by the sol-gel method

In this study, we studied the structural properties and ferroelectric characteristics of the pure BeFiO3 (BFO) and mixed NiTiO3-BiFeO3 (NTO-BFO) thin films by the sol-gel method and spin-coating process. We employed atomic force microscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy to analyze the surface roughness, chemical bonding, surface morphology, crystal structure, and film microstructure of both thin films. The mixed NTO-BFO film showed better electrical characteristics, such as a smaller leakage current density (9.66 × 10−5 A/cm2) and a higher remanent polarization (59.02 μC/cm2), than the pure BFO one. Moreover, the mixed film demonstrated diamagnetism behavior in the magnetic-hysteresis loop. This finding may be attributable to the NTO film deposited on the BFO film avoiding the volatilization of Bi ions and increasing the domain walls, hence giving rise to a decreased leakage current and an increased ferroelectric characteristic.

Impact of Charge Trapping On Epitaxial p-Ge-on-p-Si and HfO2 Based Al/HfO2/p-Ge-on-p-Si/Al Structures Using Kelvin Probe Force Microscopy and Constant Voltage Stress

The quest for the high speed, low power digital logic circuits urge an imperative demand of compatible high-κ dielectric integration on novel Germanium (Ge) based channel material. Here, first ever a methodical nanoscopic and microscopic probes were attempted to Atomic Layer Deposited, Hafnium Dioxide (HfO2) dielectrics on Molecular Beam Epitaxy (MBE) of p-Ge-on-p-Si stack. Kelvin Probe Force Microscopy based contact potential difference (CPD) analysis reveals that the disintegration of trapped charges lasting for ∼18 hours. The impact of constant voltage stress (CVS) on trapped charges results in variation of threshold voltage (Vth) and hysteresis window (W) were studied. The cyclic Capacitance-Voltage (C-V) characteristics at 0.5 MHz exhibit the shift in the flat band (ΔVfb), ΔVth, and ΔW at 10V stress were ∼0.84V, ∼0.62V, and ∼0.47V, respectively. While the computed interface trap density (Dit) and total effective charge density (Qeff) were ∼8.49 × 1012 eV−1cm−2 and ∼1.81 × 1012 cm−2, respectively. The gate leakage current density, (J) at 5V is 26.53 × 10−6 A/cm2 and reduced by a factor of ∼6.8 after 10V, CVS. Whereas the current density (J) increases from ∼26.53 × 10−6 A/cm2 at 25 °C by a factor of ∼2 at 125 °C. To study the retention and effect of charge trapping, the stress-time analysis was performed for 8000s at 3V (CVS). The r.m.s. surface roughness of HfO2 thin films was found to be ∼0.23 nm. X-ray photoelectron spectroscopy (XPS) depth profiling categorized the elemental composition of thin films. These investigations would help to HfO2/p-Ge-on-p-Si system interfacial engineering well before the Ge based nano device realization.

Improvement of the Surface Roughness of LTPS Thin Films with Additional Laser Irradiation

Improvement of the Surface Roughness of LTPS Thin Films with Additional Laser Irradiation

Spray deposited nanostructured ZnO:Mn thin films for ammonia vapour sensing application

The performance of ammonium vapour sensors (pure and doping with Mn ions into the ZnO films) were fabricated via simple Spray deposited technique is reported along with its phase identification, topographical and bandgap properties. Phase identification and crystallinity of the samples have been examined using XRD technique. From the results, it is found that ZnO:Mn(0.002) thin film have better crystallinity and fewer defect. AFM images depict the closely packed spherical structures with increasing surface roughness of ZnO thin films with Mn content. Uv–Vis spectral results show a clear downshift in bandgap from 3.39 eV to 3.10 eV upon infusing Mn ions. The sensitivity characteristics too proves to be better for this selected composition than compared to pristine and other Mn doped ZnO films.

Thermal-assisted brush printing of water-based In-Ga-Zn oxide transistors

As an environment-friendly technique, the water-based solution process has attracted numerous attention. Due to the ability to fabricate oxide semiconductor films for transistors with acceptable electric properties at relatively low temperatures (~200 °C lower compared with organic solvent), it has great potential in future display technology, and various correlation technologies are keeping emerging. Here, an efficient and facile water route thermal-assisted brush printing is demonstrated, which can be applied to fabricate the semiconductor layer of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) by the solution process. The synergistic effects of thermal-annealing and brush printing on the film formation process were comprehensively investigated, implying the synergistic effects induce the acceleration of the evaporation of the precursor solvent and promotes the lower surface roughness of as-prepared thin-film, resulting in improved transistor properties. Mechanically, the proposed film-forming model of thermal-assisted brush printing is also elaborated, which is expected to be a general guideline for the solution processing of metal-oxide semiconductor thin-films.

Effects of Mn doping on the characterization of nanostructured TiO2 thin films deposited via chemical spray pyrolysis method

Nanostructured TiO2:Mn thin films at diverse concentrations of Mn were deposited via chemical spray pyrolysis method (CPM). The XRD patterns hexagonal wurtzite structure with a dominant peak towards (101) plane. The Grain size of the deposited films is about (10.71-12.71) nm with Mn, whereas the strain (%) parameter decrease from 32.34 to 27.26 with Mn. AFM images show the TiO2:Mn effects surface morphology of the film, The grain size was in the area of (91.13), (67.79) and (64.94) nm for the (TiO2, TiO2:2% Mn, TiO2:4% Mn) respectively. Surface roughness of TiO2 Thin films are RSM 16.6 to 3.68 nm, The average transmittance of the samples was 75 to 85% in the visible wavelength range from 300 to 900 nm. The bandgap values were 3.35 eV (undoped) to 3.15 eV (4 % Mn).

A compact, modular, multi-wavelength (200–850nm) rotating-analyzer ellipsometer for optical constant characterization of nanostructured materials

We have developed a compact modular rotating-analyzer ellipsometer (RAE) with a spectrum range of 200–850 nm. Spectroscopic ellipsometry is a non-destructive characterization based on an optical method. It is used widely to obtain the dielectric constant, thickness, and surface roughness of thin films. Our homemade RAE comprises standard modular components that are available on the market, such as (i) a deuterium–halogen DH-2000-BAL light source made by Ocean Optics, (ii) a Rochon prism with an α-BBO substrate from Edmund optics for the polarizer and analyzer, and (iii) a Red Tide USB650UV mini detector from Ocean Optics and a compact ellipsometer arm design to ensure its ease-of-use and future development. Data acquisition is automated and can be controlled using a computer program, and all the moving parts are motorized. The dielectric constant of Au film with a thickness of 300 nm has been measured for calibration of the apparatus. The result was compared with reference measurements that used a commercial ellipsometer, and showed considerable accuracy with a similarity of ∼95%.

Performance enhancement of heterojunction ZnO/PbS quantum dot solar cells by interface engineering

Effective charge transport through heterojunction interface in Quantum dots (QDs) based solar cells is difficult due to the spherical structure of QDs. Therefore tuning of QDs size for uniform and defect free heterojunction interface becomes very important to get optimum device performance. Here we have optimized the performance of ZnO Nanocrystals (NCs)/lead sulfide (PbS) QDs heterojunction solar cell by controlling the surface roughness of ZnO NCs thin films. The synthesized ZnO NCs aggregation was tuned by varying the binary solvent volume ratio of chloroform and methanol (CF:MeOH), which leads to the different surface roughness. The thin film of ZnO NCs having surface roughness comparable to the size of PbS QDs performs better as compared to those devices having different surface roughness. The optimum device fabricated in an ambient atmosphere with ZnO NCs thin film having surface roughness 4.36 nm, and nanocrystal size 3.32 nm as synthesized with (CF:MeOH) volume ratio of (2:1), shows the highest efficiency of 2.94% among other devices in the same structure due to decreased leakage current and improved junction interface contact between active materials. This work reveals that the controllability of ZnO NCs surface roughness and its correlation with the size of QDs can contribute to further improvement of low cost QDs based solar cells.

Combined experimental and DFT-TDDFT computational studies of doped [PoDA+PpT/ZrO2]C nanofiber composites and its applications

[Poly(o-phenylenediamine)+poly(p-toluidine)/Zirconium oxide nanoparticles] nanofiber composites thin film [PoDA + PpT/ZrO2]C is fabricated by using oxidative polymerization method at pH~0.65/anhydrous FeCl3. In PEG200 as a soft template, the copolymerization process is performed at 25 °C. The nanofiber composite [PoDA + PpT/ZrO2]C thin film is studied using various methods, including FT-IR, 1HNMR, XRD, SEM, TEM, and AFM techniques. [PoDA + PpT/ZrO2]C thin films with a thickness of 200 ± 5 nm are manufactured by PVD technique at a low deposition rate with basic pressure of the chamber was 5 × 10−5 mbar. The thin film's surface roughness is measured by calculating the roughness parameters, calculated by studying the topography scans using AFM. The optical constants and optical conductivity for [PoDA + PpT/ZrO2]C nanofiber composites are computed and compared by using experiment and CATSTEP. The structural and optical characteristics of the simulated [PoDA + PpT/ZrO2]C nanofiber composites as single isolated molecules are in a good agreement with the experimental study. DC-electrical characteristics of these fabricated thin films were applied to indicates the [ZrO2]NPs nanofibers could be attached to promote electrical conduction, where the form of the nanofibers permitted the desired routes to be constant. The fiber nanocomposite thin films present a promising result to be a good candidate for polymer solar cell applications.