Function Of Substrate Temperature Research Articles

Effect of substrate temperature on the suitability of thermally deposited cadmium sulfide thin films as window layer in photovoltaic cells

Cadmium sulfide has been studied as an important material in solar energy research because of its energy band gap and attractive electrical characteristics. While thin films of cadmium sulfide have been found to be useful as window layer in a solar cell, the role of various deposition parameters is yet to be understood. In the current study, the role of substrate temperature on the characteristics of the CdS thin films is analyzed. Thin films of cadmium sulfide (∼450 nm thick) were deposited at various substrate temperatures viz., 300 K, 323 K, 373 K, and 423 K onto clean glass substrates by vacuum thermal evaporation method. The structural, morphological, and opto-electrical properties of the deposited films were studied as a function of substrate temperature. X-ray diffraction (XRD) study revealed that the thin films are polycrystalline in nature and having a hexagonal wurtzite crystal structure along (002) plane. Scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS) revealed that the grown films are homogeneous, uniform and pin-hole free. All the films deposited at various substrate temperature displayed high optical transmittance (>60%) in the visible range. The optical energy band gap of the films was estimated using Tauc's plot and was found to increase by a slight margin with an increase in the substrate temperature and decrease at higher substrate temperature. The photosensitivity was found to be highest for the CdS thin film grown at a substrate temperature of 373 K.

Thermal expansion studies of electron beam evaporated yttria films on Inconel-718 substrates

In this paper, phase pure cubic yttrium oxide (Y2O3) films deposited by electron beam physical vapor deposition technique on Inconel-718 substrate at different substrate temperatures (773–973 K) are investigated. The structure and phase evolution in the films of Y2O3 as a function of substrate temperature have been evaluated by X-ray diffraction. Atomic force microscopy and scanning electron microscopy were used to examine the surface roughness and morphology of the as-deposited Y2O3 films. The adhesion behavior of the Y2O3 film with Inconel-718 substrate was investigated using scratch indentation testing. The thermal expansion coefficient (TEC) of Inconel-718 substrate and Y2O3 film coated on Inconel-718 substrate were determined by high temperature X-ray diffraction (HTXRD) measurement in the temperature range of 298–1273 K with temperature interval of 100 K. The linear TECs of Inconel-718 and Y2O3 film at 1273 K were found to be 1.22 × 10−5 K−1 and 7.02 × 10−6 K−1, respectively. Thermal stability of the Y2O3 coated Inconel-718 substrate tested at 1273 K in air over a period of 100 h is also discussed.

Structural defects and electronic phase diagram of topological insulator bismuth telluride epitaxial films

In this work, bismuth telluride films are grown by molecular beam epitaxy (MBE) on (111) BaF2 substrates, using stoichiometric Bi2Te3 and additional Te solid sources. The growth dynamics and structural defects are investigated in detail as function of substrate temperature, Bi2Te3 flux and extra Te supply, by means of atomic force microscopy, Raman spectroscopy and reciprocal space mapping. The growth rate increases linearly with the Bi2Te3 flux and the most appropriate conditions to grow high-quality Bi2Te3 single layers is found to be in a narrow window of MBE parameters. At low growth temperatures Te clusters are formed, while the Te deficit increases with raising substrate temperature and decreasing deposition rate. It results in films with Bi-richer phases due to the formation of Bi double layers in between Bi2Te3 quintuple layers. The electronic transport properties are also studied by temperature dependent resistivity and Hall measurements. By properly changing the substrate temperature and/or the extra Te supply, the behavior of the films can vary from insulating to metallic as well as the major carriers from p- to n-type. The electronic phase diagram presented here provides a fast route to control the bulk conductance properties of bismuth telluride, which enables the production of intrinsic bulk insulating films. In addition, the results suggest the possibility of growing intrinsic sharp p-n junctions of Bi2Te3 by properly monitoring the occurrence of structural defects, which is the first step for practical applications of this topological insulator material.

Effect of substrate temperature on the structural, morphological and optical properties of copper bismuth sulfide thin films deposited by electron beam evaporation method

Copper bismuth sulfide thin films were deposited at 200 °C, 300 °C, 400 °C and 500 °C on the glass substrates by electron beam evaporation method. X-ray diffraction study revealed that the copper bismuth sulfide films of single and mixed phases were formed as a function of substrate temperatures. Substrate temperature of 300 °C and 400 °C formed single phase Cu4Bi4S9 and Cu4Bi5S10 films respectively whereas substrate temperature of 500 °C formed mixed phases of Cu4Bi4S9 and Cu4Bi5S10 film. Crystallite size, dislocation density and microstrain of the films were modified by the various substrate temperatures. Surface morphology of the film Cu4Bi5S10 deposited at 400 °C examined by scanning electron microscopy showed the distribution of spherical shaped particles on the film surface. The presence of copper, bismuth and sulfur elements in the deposited films was confirmed using energy dispersive spectral studies. The calculated direct optical band gap energy of the films deposited at different substrate temperature varied from 1.47 to 1.64 eV and the absorption coefficient is in the order of 106 cm−1.

Microstructural and Nanomechanical Properties of Aluminium Nitride (AlN) Thin Films Deposited by RF Magnetron Sputtering

Aluminium nitride (AlN) thin films were deposited on AISI-1018 low carbon steel substrates at different substrate temperature (Room temperature −600 °C) using RF magnetron sputtering technique. The microstructural, mechanical and corrosion properties were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), nanoindentation and salt spray test respectively. The microstructural and properties were investigated as a function of substrate temperature. The XRD analysis of the AlN thin films prepared at RT and 200 °C indicated the poor crystallinity of the films, while the films prepared in the temperature 400–600 °C range indicated the increased crystallinity with hexagonal (0002) and cubic (002) structure. The AFM analysis showed the average roughness of 7 nm, 5.5 nm and 16 nm for room temperature, 200 °C and 500 °C temperature respectively. The hardness of the AlN thin films were found to be 11.99 GPa, 13.05 GPa, 12.29 GPa, 23.0 GPa and 11.12 GPa at room temperature, 200 °C, 400 °C, 500 °C and 600 °C, respectively. The salt spray analysis indicated no corrosion on low carbon steel substrates for 12 hours.

Effect of substrate temperature on microstructure and nanomechanical properties of Gd2Zr2O7 coatings prepared by EB-PVD technique

In the present work, gadolinium zirconate (Gd2Zr2O7) coatings have been developed on Inconel-718 substrates by electron beam physical vapor deposition (EB-PVD) technique. The structural, morphological and mechanical properties as a function of substrate temperature have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation and scratch tests. XRD analysis revealed that the coatings showed cubic defect fluorite phase, and no secondary phase formation was observed in the coatings during deposition. The decrease in the lattice constant of the fluorite phase with increasing deposition temperature was explained on the basis of strain relaxation and vacancy concentration. Increased surface roughness of the coatings has been found with increasing substrate temperature as a result of increased crystallite size. An improved coating adhesion achieved for the coating deposited at higher substrate temperature of 973 K was confirmed by scratch test. Nanoindentation measurements indicated higher hardness (7.7 GPa) and resistance to plastic deformation and better capability to accommodate deformation energy for the coatings prepared at higher deposition temperature.

Effects of substrate temperature on microstructure, morphology and optical properties of ZnSe:Co films obtained by pulsed laser deposition

ZnSe:Co thin films were grown on sapphire (Al2O3) substrates by pulsed laser deposition at different substrate temperature. Evolutions of the microstructure, morphology and optical properties of the ZnSe:Co thin films as a function of substrate temperature were analyzed. The results indicated that the crystalline quality was promoted and the films demonstrated increasing (111) preferred orientation with increasing substrate temperature. Excellent crystalline quality and (111) preferred oriented thin film was grown at substrate temperature of 800 °C. The refractive index and dielectric constant analyzed by the transmission spectra increased with elevating substrate temperature, which may be due to the promotion of the film packing density. The thin films with wider optical band gap in range of 2.73 eV to 3.27 eV were obtained in the experiment. The band gap decreased when the substrate temperature was increased from 25 °C to 600 °C, and then increased with a further increase of substrate temperature to 800 °C. The evolution of band gap associates with the quantum confinement effect.

Nanoink bridge-induced capillary pen printing for chemical sensors

Single-walled carbon nanotubes (SWCNTs) are used as a key component for chemical sensors. For miniature scale design, a continuous printing method is preferred for electrical conductance without damaging the substrate. In this paper, a non-contact capillary pen printing method is presented by the formation of a nanoink bridge between the nib of a capillary pen and a polyethylene terephthalate film. A critical parameter for stable printing is the advancing contact angle at the bridge meniscus, which is a function of substrate temperature and printing speed. The printed pattern including dots, lines, and films of SWCNTs are characterized by morphology, optical transparency, and electrical properties. Gas and pH sensors fabricated using the non-contact printing method are demonstrated as applications.

(Invited) In Situ scanning Tunneling Microscopy Studies of hBN Layer Growth Kinetics and the Influence of Substrate on Electronic Structure of the Layers

Two-dimensional (2D) layered materials, owing to a wide range of properties (e.g., graphene is metallic, hBN is insulating, and MoS2 is semiconducting), have attracted considerable attention over the past decade. hBN is isostructural to graphene and is considered an ideal dielectric for the fabrication of vertical 2D layered heterostructures with potential applications in optoelectronics and nanoelectronics. hBN layers are commonly grown on metal substrates. In contrast to free-standing hBN layers, substrate-supported hBN can be metallic, semiconducting, or insulating, depending on the chemistry and electronic structure of the hBN/substrate interface. Moreover, due to relatively weak van der Waals interactions between the 2D layer and the substrate, orientational registry of the layers with the substrate is not expected and is often difficult to control. While the growth and electronic structure of graphene layers have been fairly well studied, relatively little is known concerning the mechanisms underlying the growth of the hBN layers and the influence of hBN domain orientation (with respect to the substrate) on its electronic properties. Using in situ ultra-high vacuum scanning tunneling microscopy (UHV STM), we investigated the chemical vapor deposition (CVD) kinetics of hBN on Pd(111). STM images are acquired during CVD of borazine as a function of substrate temperature, borazine flux, and deposition time. We observe the nucleation and growth of chemisorbed borazine islands on the Pd surfaces. Furthermore, we investigated the surface structure of hBN domains on Pd(111) using STM, scanning tunneling spectroscopy (STS), and density functional theory (DFT) calculations. STM images acquired from the hBN/Pd(111) sample reveal moiré patterns with at least four different periodicities λ corresponding to four rotational domains of hBN. From the STM images, we measured the surface corrugations in each of the moiré patterns and found that the corrugation amplitude Δz depends on the tunneling bias and increases with increasing λ. We suggest that Δz is a measure of hBN-Pd(111) interaction strength and attribute the higher corrugation amplitudes to stronger interactions between the hBN domains and the Pd(111). We expect that similar approach could be used to investigate growth kinetics and orientation-dependent interactions in other substrate-supported 2D layers with large lattice mismatch with respect to the substrate.

Correlation of structural ordering with magnetic properties of pulsed laser deposited Co2FeGa Heusler alloy thin films

In the present contribution, structural and magnetic properties of Pulsed laser deposited (PLD) Co2FeGa (CFG) thin films have been studied as a function of substrate temperature. Structural investigation carried out by X-Ray Diffraction (XRD) measurement reveals mixed phase cubic structure of the films which changes from a nearly ordered to highly disordered phase with an increase in substrate temperature. Grazing Incidence X-Ray Diffraction (GIXRD) study shows the presence of disordered A2 phase similar to the bulk target. Grazing Incidence X-Ray Reflectivity (GIXR) measurement reveals the formation of bi-layer structure in the films with different density and thickness though the overall thickness remains same. Field Emission Scanning Electron Microscopy (FESEM) study shows the formation of a droplet-like morphology of the films. Extended X-ray Absorption Fine Structure (EXAFS) study serves a major role in complementing the XRD results and also shows a strong hybridization of Co with Ga maintaining the half metallicity. A novel approach in analyzing the EXAFS data additionally gives quantitative estimation of the different kinds of disorders present in the samples at the atomic level. In addition to this, magnetization result suggests that the films grown at lower substrate temperatures acts as proper ferromagnet following the well known spin wave theory with higher value of spontaneous magnetization in comparison to other samples. A lesser value of saturation magnetization in the films compared to bulk also supports the presence of antisite disorders.

Fabrication of Thin Functional Films by Solution Aerosol Thermolysis (SAT)

The technique of air-pressurized solution spray pyrolysis was used to fabricate thin films of La0.75Sr0.25MnO3 (LSM) and CuO-CeO2 on dense YSZ substrates. These films are widely used in several applications such as high temperature ceramic electrochemical cells, membranes and sensors. The technique was tailored to produce films with differing morphologies and thicknesses in terms of applied substrate deposition temperatures. The droplet drying and decomposition kinetics is discussed as a function of substrate temperature, given the other processing parameters (i.e. nozzle to substrate distance, solution flow rate, air pressure/air flow rate and deposition time) constant. A graph-map is drawn containing morphology and quality of fabricated films in terms of substrate temperatures and concentration levels for this particular set of precursor salts in aqueous solutions. Within the deposition temperature range examined, film thicknesses were found to decrease with increasing substrate temperature along with a concomitant change in quality from irregular texture to smoother and of more uniform thickness. A maximum deposition temperature of about 280°C was identified for 0.025M concentration for both types of films which correlates quite well with the Leidenfrost point measured in the literature for solvents with boiling point less than 150°C.

Investigation of boron incorporation in delta doped diamond layers by secondary ion mass spectrometry

Boron incorporation into ultra-thin boron doped epitaxial grown diamond layers of thickness of 1 to 2nm was investigated. Time of flight secondary ion mass spectroscopy was used to examine the boron concentration as a function of depth of the samples. The boron depth profiles were deconvoluted by modeling and measuring the depth resolution function with specially grown multiple delta doped layers on the same substrate. Boron incorporation in the delta layers as a function of substrate temperature and B/C ratio in the reactant gas was determined. A diamond deposition regime in which the doped delta layers with thickness of 1–2nm and with boron concentrations of about 4–5·1020 cm−3 was obtained. Such layers are suitable for implementation of two-dimensional hole “gas” in diamond with high mobility and high carrier concentrations.

Structural and optical properties of pulsed laser deposited cadmium telluride thin films

Cadmium telluride thin (< 1 μ) films were grown by pulsed laser deposition method on glass substrates from room temperature up to 300°C. The structural and optical properties were analyzed as a function of substrate temperature and laser radiation intensity.

Dependence of Nanostructure and the Optical Properties of Ni Thin Films with Different Thicknesses on the Substrate Temperature

Nickel films with the thicknesses of 30 and 120 nm were deposited on glass substrates, at different substrate temperatures (313 to 600 K) under uhv condition. The nano-structure of the films and mean diameter of grains was obtained for each films using atomic force microscopy (AFM). Their optical properties were measured by spectrophotometry in the spectral range of 190-2500 nm. Kramers-Kronig method was used for the analysis of the reflectivity curves. The Effective Medium Approximation (EMA) analysis was used to determine the values of volume fraction of voids (fv)and establish the relationship between the nanostructure of the film and EMA predictions. Qualitatively good agreements between structure Zone Model (SZM) as a function of substrate temperature and the values of (fv), is achieved. There is good agreement between these values and the results of mean diameter of grains for Ni films too. The absorption peaks of Ni thin films at ~ 1.4 eV and 5 eV are observed, with an additional bump at about 2 eV. The 1.4 eV peak is in particular much stronger than that obtained in earlier works on Ni thin films (Johnson and Christy (1974)) and on bulk Ni sample (Lynch et al (1971) and Ehrenrich et al (1963)). This is resulted from producing thin films under uhv condition. The conductivities σ1 and σ2 calculated from ɛ1 and ɛ2 for Ni films and were plotted vs energy.

The structural characterizations of Ti-17 alloy films prepared by magnetron sputtering

Abstract One of the most attractive structural features of titanium (Ti) alloys is its α + β dual-phase growth. Previous work focused on α- or β-Ti phase films, but dual-phase growth in films has not yet been studied. This paper investigates the magnetron-sputtered structures of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy as a function of substrate temperature from 125 °C to 530 °C. The film shows a phase transformation from single β to α + β growth as substrate temperature rises. We discuss the morphology and texture evolutions that arise in sputtering deposition in reference to the structure zone model. We use nanoindentation to assess the mechanical properties of the films. The phase evolution, zone 1–zone T transition, and texture growth with the increasing substrate temperature all contribute to mechanical property improvements of the films.

Formation of metastable cubic phase in SnS thin films fabricated by thermal evaporation

Metastable cubic SnS phase (π-SnS) is an emerging material having attractive properties for solar cell applications. In this study, we have investigated the thermal evaporation process of SnS with substrate temperatures of 250–350°C, and have observed the formation of π-SnS together with the stable orthorhombic phase (α-SnS) for the first time by using only SnS as a starting material. X-ray diffraction analysis shows that a single-phase α-SnS film is obtained at 350°C, and the fraction of π-SnS increases with decreasing the substrate temperature to 250°C. The grain shape of the SnS film grown at 250°C observed by scanning electron microscopy was more isotropic than 350°C, consistent with the cubic lattice of π-SnS. Electrical characterization by Hall measurement reveals the existence of the maximum point of carrier density as a function of substrate temperature, which is understood by the competition between the increases of crystal defects and the fraction of wider-gap π-SnS than α-SnS with decreasing substrate temperature. The formation of π-SnS brings about lowering of absorption coefficients below the absorption edge of π-SnS, which are analyzed from transmittance and reflectance spectra. The reason of π-SnS formation is discussed by comparing the conditions of film deposition with previous reports.

Reduction of residual stress in AlN thin films synthesized by magnetron sputtering technique

We report the reduction in residual stress, the crystal structure, surface morphology and nano-mechanical properties of magnetron sputtered AlN thin films as a function of substrate temperature (Ts, 35–600 °C). The residual stress of these films are varying from tensile to compression with temperature (Ts), calculated by sin2ψ technique. Evolution of crystalline growth of AlN films have been studied by GIXRD and transmission electron microscopy (TEM) and at 400 °C a preferred a-axis orientation is observed. The cross-sectional TEM micrograph and the selected area electron diffraction (SAED) of these film exhibit a high degree of orientation as well as a columnar structure. Hardness (H) has been measured by nanoindentation technique on these films ranged between 12.8 and 19 GPa.

Substrate temperature-dependent physical properties of nanocrystalline zirconium titanate thin films

Nanocrystalline zirconium titanate thin films were deposited by direct current magnetron reactive sputtering on to glass substrates at room temperature and at different substrate temperatures of 423, 473, 523, and 573 K under high vacuum conditions. The deposited films have been characterized to study the physical properties of the films as a function of substrate temperature. Though the film exhibited amorphous characteristics at room temperature the higher temperatures resulted in the evolution of crystallites in the films. The crystallinity increased with temperature from 423 K onwards and the film deposited at 523 K exhibited a high crystallite size of 22 nm. The SEM images of the films revealed the improvement in the crystallinity from 423 to 523 K with dense columnar structure normal to the substrate. Further higher treatment deteriorated the film properties. The films showed a good transmittance of above 80%. A high optical transmittance of 91% and a high packing density of 96% have been observed for the film deposited at 523 K. The thickness of the films remained consistent at ~230 nm (±6 nm). It is noticed that an increase in the substrate temperature enhanced the structural, optical, and electrical properties of the films up to 523 K.

Structural and magnetic characterization of the Ni55Fe19Ga26 shape memory alloy thin film

The structural evolution of the Pulsed Laser Deposited Ni55Fe19Ga26 ferromagnetic Heusler alloy thin films has been studied as a function of substrate temperature. Room temperature Grazing Incidence X-Ray Diffraction (GIXRD) measurement reveals the polycrystalline nature of the films consisting of cubic austenite and non-cubic martensite phases. The cubic phase consists of the mixture of an ordered (L21) and disordered (γ) phases, the disordered phase gets suppressed with an increase in the substrate temperature while low temperature X-Ray Diffraction study shows structural modification of the samples. Field Emission Scanning Electron Microscopy (FESEM) study shows the droplet-like morphology of the films. Extended X-ray Absorption Fine Structure (EXAFS) study agrees with the X-ray diffraction results about the phase evaluation and further reveals the local structure information of the constituent atoms which leads to the hybridization effect and finally govern the macroscopic properties of the material. In addition, magnetization studies show the ferromagnetic nature of the film with a mixture of anti-ferromagnetic ordering arising due to antisite disorder of the atoms revealed by the EXAFS measurements.

In Situ variable-Temperature Scanning Tunneling Microscopy Studies of 2D Graphene and Hexagonal Boron Nitride (hBN) Layer Growth Kinetic

The rich physical phenomena and properties associated with two-dimensional (2D) graphene layers have led to a surge in research efforts focused on synthesis, characterization, and, even large-scale production of a variety of 2D crystals. In the newly emergent class of 2D layered materials (and devices), some of the highly exciting developments are a result of leveraging the properties of individual layers via stacking of dissimilar 2D materials held together by van der Waals (vdW) forces. Such vdW-layers exhibit new properties (e.g., valleytronics) and are ideal for ultrathin flexible devices. Graphene is semi-metallic, while its insulating 2D layered analog is hexagonal boron nitride (hBN). Graphene and hBN are isostructural and nearly lattice matched. Composite, lateral, and vertical heterostructures of graphene and hBN layers are expected to exhibit new physical phenomena and properties: tunable bandgap, magnetism, unique electronic and thermal transport properties, robust half-metallic behavior without applied electric fields, and more. Access to such new properties and hence novel applications, hinge on the ability to assemble the 2D materials in desired architecture. This requires fundamental understanding of the mechanisms governing the formation of epitaxial stacks of desired stacking sequences and layer thicknesses, atomically-abrupt graphene-hBN interfaces and domain widths within a single atomic layer, and desired composition within a 2D sheet. As a first step toward this goal, we investigated the chemical vapor deposition (CVD) kinetics of monolayer graphene and hBN on Pd(111) using ultra-high vacuum (UHV) variable-temperature scanning tunneling microscopy (VT-STM). In this talk, we present in situ VT-STM observations of graphene growth using ethylene and hBN growth using borazine on Pd(111) as a function of substrate temperature, borazine flux, and deposition time. We observe the formation of monolayer graphene islands bounded by Pd surface steps. Using scanning tunneling spectroscopy (STS) measurements along with density functional theory (DFT) calculations, we show that graphene/Pd(111) exhibits a bandgap due to the strong interaction between graphene and the Pd substrate. During the CVD of borazine, we observe the nucleation and growth of chemisorbed borazine islands on Pd(111). Using STS, we determined the effect of hBN domain orientation with respect to Pd(111) on its bandgap. From the STM experiments, we identified the growth parameters critical to the formation of single-domain hBN layers on Pd(111). Our studies, which provide new insights into the growth of graphene and hBN monolayers, are useful in developing recipes for the growth of heterostructures of desired architecture.