Function Of Substrate Temperature Research Articles

Mechanosynthesis, deposition and characterization of CZTS and CZTSe materials for solar cell applications

Mechanosynthesis of nanocrystalline powders of CZTS and CZTSe by ball milling technique and the physical properties of thermally evaporated CZTS and CZTSe thin films as a function of substrate temperature are investigated. Nanocrystalline Cu–Zn–Tin–Sulphide (CZTS) and Cu–Zn–Tin–Selenide (CZTSe) powders synthesized by ball milling at different milling time using the source materials of Cu, Zn, Sn, S (or) Se in the ratio 2:1:1:4 are investigated. The above synthesized powder was thermally evaporated on glass substrate kept at room temperature and 673K under a vacuum of 10−6mbar to prepare quaternary compound semiconducting thin films in a single step process. The synthesized powder and deposited CZTS and CZTSe thin films belong to tetragonal crystal system. Raman spectra reveal that the synthesized nanocrystals are pure without any secondary phases. A gradual reduction in optical bandgap of films was observed with increasing substrate temperature due to increased crystallinity of the films. The changes in surface morphology of the films with respect to substrate temperature were studied by scanning electron microscopy and atomic force microscopy. Electrical studies indicate that the deposited films have p-type conductivity.

Effects of substrate temperature on the structural, morphological, electrical and optical properties of Al and Ga co-doped ZnO thin films grown by DC magnetron sputtering

In this work, Al and Ga co-doped zinc oxide (AGZO) thin films were deposited on glass substrates by DC magnetron sputtering under different substrate temperatures. Evolutions of the structural, morphological, electrical and optical properties of the AGZO thin films as a function of substrate temperature were analyzed. Results showed that the average transmittance in the visible range (400–800nm) for all the thin films was over 82%, which did not change obviously with the substrate temperature. The average grain size increased from 20.6nm to 51.4nm and the RMS surface roughness decreased from 21.1nm to 4.0nm with substrate temperatures ranging from 150°C up to 450°C. The carrier concentration, Hall mobility of the thin films increased when the substrate temperature was increased from 150°C to 350°C, and then decreased with a further increase of substrate temperature. The film deposited at 350°C exhibited a lowest resistivity of 3.0×10−4Ωcm with the highest carrier concentration of 5.0×1020cm−3 and Hall mobility of 42cm2V−1s−1.

Crystallographic structure and magnetic properties of polycrystalline FePd thin films on glass substrate

Polycrystalline FePd films with thicknesses of 30 ± 2 nm were prepared by magnetron sputtering on glass substrate. The crystallographic structure and magnetic properties as a function of substrate temperatures (Ts = 400–800 °C) and chemical composition (Pd = 36–62 at.%) were further characterized. The X-ray diffractometry with synchrotron radiation source shows that L10 ordering occurred for the Fe49Pd51 films deposited at 600 °C. The ordering parameter and coercivity of the Fe49Pd51 films were revealed to increase as increasing substrate temperature. High-temperature preparation (800 °C) causes the appearance of disordered A1 phase. For the FePd films (Ts = 800 °C) with different Pd concentrations, the evolution of crystallographic structure and magnetic properties is correlated. For the Fe-rich FePd films, the A1 disordered phase and soft magnetic properties were found. The highest coercivity of 4.1 kOe is obtained for the FePd films with Pd concentration of 51 at.%. With further increasing Pd content up to 62 at.%, the crystal structure changes from L10 to L12 phase which exhibits a room temperature ferromagnetism with coercivity of 0.1 kOe and saturated magnetization 782 emu/cm3.

Bioactive, nanostructured Si-substituted hydroxyapatite coatings on titanium prepared by pulsed laser deposition.

The aim of this work was to deposit silicon-substituted hydroxyapatite (Si-HAp) coatings on titanium for biomedical applications, since it is known that Si-HAp is able to promote osteoblastic cells activity, resulting in the enhanced bone ingrowth. Pulsed laser deposition (PLD) method was used for coatings preparation. For depositions, Si-HAp targets (1.4 wt % of Si), made up from nanopowders synthesized by wet method, were used. Microstructural and mechanical properties of the produced coatings, as a function of substrate temperature, were investigated by scanning electron and atomic force microscopies, X-ray diffraction, Fourier transform infrared spectroscopy, and Vickers microhardness. In the temperature range of 400-600°C, 1.4-1.5 µm thick Si-HAp films, presenting composition similar to that of the used target, were deposited. The prepared coatings were dense, crystalline, and nanostructured, characterized by nanotopography of surface and enhanced hardness. Whereas the substrate temperature of 750°C was too high and led to the HAp decomposition. Moreover, the bioactivity of coatings was evaluated by in vitro tests in an osteoblastic/osteoclastic culture medium (α-Modified Eagle's Medium). The prepared bioactive Si-HAp coatings could be considered for applications in orthopedics and dentistry to improve the osteointegration of bone implants.

Compositions of Mg and Se, surface morphology, roughness and Raman property of Zn1−xMgxSeyTe1−y layers grown at various substrate temperatures or dopant transport rates by MOVPE

The growth of undoped and phosphorus (P)-doped Zn1−xMgxSeyTe1−y layers on (100) ZnTe substrates by metalorganic vapor phase epitaxy was carried out. The compositions of Mg and Se, surface morphology, roughness and Raman property were characterized as a function of substrate temperature. Not only the compositions of Mg and Se but also the crystal quality of undoped Zn1−xMgxSeyTe1−y layer strongly depended upon the substrate temperature. Furthermore, the growth of Zn1−xMgxSeyTe1−y layer nearly-lattice-matched to ZnTe substrate was achieved independent of the transport rate of trisdimethylaminophosphorus. Undoped Zn1−xMgxSeyTe1−y layer nearly-lattice-matched to ZnTe led to improvement of surface roughness. On the other hand, P doping brought about deterioration of crystalline quality.

Synthesis and fabrication of Y2O3:Tb3+ and Y2O3:Eu3+ thin films for electroluminescent applications: Optical and structural characteristics

Terbium, europium and yttrium β diketonates have been synthesized from acetylacetone and inorganic metal salts and used as precursors for the deposition of Tb3+ or Eu3+ doped Y2O3 polycrystalline films by the ultrasonic spray pyrolysis technique. The films were deposited on c-Si substrates at temperatures in the 400–550 °C range. The optical and structural characterization of these films as a function of substrate temperature and Tb3+ and Eu3+ concentration was carried out by means of photoluminescence (PL), cathodoluminescence (CL), infrared (IR), ellipsometry, and UV–visible spectroscopy and atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and X ray diffraction (XRD) measurements respectively. The PL intensity from these films was found to depend on deposition temperature. Films deposited above 450 °C exhibited the characteristic PL peaks associated with either Tb3+ or Eu3+ intra electronic energy levels transitions. The most intense PL emission was found for dopant concentration of 10 at% for Tb3+ and at 8 at% for Eu3+ ions into precursor solution. In both cases concentration quenching of the PL emission was observed for concentrations above these values. The films had a refractive index (1.81), low average surface roughness (∼62 Å) and a UV–Vis. transmission of the order of 90 %T.

Consequence of source material on the surface properties of nebulizer spray coated cerium oxide thin films

Cerium oxide thin films are coated on glass substrates by nebulizing spray pyrolysis technique using cerium nitrate and cerium chloride as a source material. Their crystallographic structures, surface morphology, optical properties and I–V characteristics are analyzed as a function of substrate temperature (300–500 °C). XRD is used to estimate the crystallographic texture, crystalline size, strain and lattice constant. All films exhibit a cubic fluorite structure with different preferred orientation depending on the preparation conditions. All the films exhibit dense, smooth and crack-free spherical nanostructures with some uneven surfaces in the range 400 nm. PL analysis indicates the presence of indigo and blue emission in the visible region centered at ∼425 and ∼467 nm respectively. UV-ViS spectra revealed that the films are transparent (70%) in the visible region. Optical parameters like refractive index, optical conductivity and band gap are calculated for different Ts. XPS analysis revealed the existence of Ce, O and C in the films. It demonstrates the prevalent occurrence of Ce4+ rather than Ce3+. I–V characteristics confirm the semiconducting behavior of cerium oxide thin films due to its linear response to applied voltage.

Improved electrochemical hydrogen storage properties of Mg-Y thin films as a function of substrate temperature

Pd-capped Mg78Y22 thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated. It is found that rising substrate temperature to 60 °C can coarsen the surface of thin film, thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to ~1725 mAh·g−1. Simultaneously, the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature. In addition, the specimen exhibits a very long and flat discharge plateau at about −0.67 V, at which nearly 60% of capacity is maintained. The property is favorable for the application in metal hydride/nickel secondary batteries. The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.

Highly oriented, free-standing, superconducting NbN films growth on chemical vapor deposited graphene

NbN films are grown on chemical vapor deposited graphene using dc magnetron sputtering. The orientation and transition temperature of the deposited films is studied as a function of substrate temperature. A superconducting transition temperature of 14 K is obtained for highly oriented (111) films grown at substrate temperature of 150 °C, which is comparable to epitaxial films grown on MgO and sapphire substrates. These films show a considerably high upper critical field of ∼33 T. In addition, we demonstrate a process for obtaining flexible, free-standing NbN films by delaminating graphene from the substrate using a simple wet etching technique. These free-standing NbN layers can be transferred to any substrate, potentially enabling a range of novel superconducting thin-film applications.

Critical surface phase of α2(2 × 4) reconstructed zig-zag chains on InAs(001)

The critical condition for InAs(001) surface phase transition has been studied, the surface phase transition of InAs(001) showed discontinuity with hysteresis cycle as a function of substrate temperature. A mixed reconstruction surface and zig-zag chain α2(2×4) reconstruction surface have been observed by scanning tunneling microscopy. Considering the interaction and dynamics of surface arsenic atoms, the zig-zag chains of α2(2×4) reconstruction were found to be actually caused by the selective adsorption and desorption of surface arsenic dimers, they played a critical role in the surface phase transition between (2×4) and (4×2).

Influence of temperature on the controlled growth kinetics and superstructural phase formation of indium on a reconstructed Si (113) 3 × 2 surface

The kinetics of growth, thermal stability and superstructural phase formation of the indium atom on a reconstructed Si (113) 3 × 2 surface at room temperature (RT), as well as at high substrate temperature (HT), is discussed. It was observed that at a very low flux rate of 0.08 ML min−1, In-adsorption at RT follows the Frank-van der Merwe (FM) growth mode, while for HT (>200 °C), In-islands (the Volmer–Weber-growth mode) were formed. The residual thermal desorption (RTD) analysis revealed the anomalous behaviour of temperature-driven layering to the clustering rearrangement of In atoms on the Si (113) surface for RT- and 200 °C-grown systems. The RTD study also demonstrates the effect of temperature on growth kinetics as well as on the multilayer/monolayer desorption pathway. The calculated bilayer desorption energy was found to be different for RT- (TB, 0.48 eV) and HT- (TB, 1.57 eV) grown In/Si(113) systems, while the monolayer desorption energy (TM, 2.56 eV) was the same in both the cases. Various coverage-dependent superstructural phases, such as Si(113) 3 × 2 + 3 × 1, 3 × 1, 3 × 2 + 1 × 3 and 1 × 1, have been observed during the RT- and HT-growth of In on the Si (113) surface. A complete phase diagram of In/Si(113) is deduced which depicts the evolution of novel phases as a function of substrate temperature and coverage.

Structural analysis of hydrogenated nanocrystalline silicon thin films as a function of substrate temperature during deposition

In this contribution, the micro- and macro-structure of plasma grown hydrogenated nanocrystalline silicon (nc-Si:H) thin films were followed with respect to substrate temperature ( T s ) ranging from 80 °C to 200 °C. nc-Si:H films were deposited by plasma enhanced chemical vapor deposition technique using silane gas highly diluted by hydrogen and high RF power density. Micro-structure analysis was performed with grazing angle X-ray diffraction (GAXRD) and dispersive Raman spectroscopies. Parallelly, morphological properties of the films were investigated via field emission scanning electron microscopy (FE-SEM) by taking both surface and cross-sectional micrographs. GAXRD results suggest the presence of 4–5 nm nanocrystallites with the size almost independent of T s . The detailed analysis of the Raman spectra reveals one- and two-phonon modes due to amorphous and crystalline silicon (c-Si), where all c-Si related peaks shifted to lower frequencies. Raman nanocrystalline volume fraction is found to be greater than 50% for all T s ; it increases together with the short-range order at elevated T s . This micro-structural improvement with T s is considered to be slight when compared to the FE-SEM-observed drastic changes of morphology, particularly the size of large conglomerates (35–250 nm). The behavior of micro- and macro-structure with T s is correlated well with the previously determined bonding and lateral conductivity measurements. It seems to be the macro-structure that accounts for bonding and electrical properties of nc-Si:H thin films.

Luminescent and Structural Characteristics of Y2O3:Tb3+ Thin Films as a Function of Substrate Temperature

An inexpesive synthesis of terbium and yttrium β diketonates from acetylacetone and metal chlorides was carried out. Later, the β diketonates were used as precursors for the synthesis of Y2O3:Tb3+thin films by the ultrasonic spray pyrolysis technique. The β diketonates are sometimes preferred as precursors for thin films because they lead to high quality films; such as a very low surface roughness and a high homogeneity. With the later idea films of Y2O3:Tb3+ were deposited on c-Si substrates at temperatures in the 400–550°C range. Yttrium β diketonate was used as precursor of Y2O3 host lattice and terbium β diketonate was used as source of Tb3+ activator. The optical and structural characterization of the thin films were carried out by means of photoluminescence (PL) and cathodoluminescence (CL) spectroscopies, infrared spectroscopy (IR), ellipsometry, atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and X ray diffraction (XRD). From PL and CL spectra, the luminescence intensity depended strongly on substrate temperature, the thickness of the film, and the Tb3+-activator concentration. Y2O3:Tb3+thin films exhibited one main band centered at 547 nm which was due to the well-known 5D4 → 7F5 electronic transition. In addition, a concentration quenching of the luminescence intensity was observed. At high temperatures the cubic crystalline phase of Y2O3 was obtained as well as a reduction of organic residues. Additionally, at elevated temperatures,a low average surface roughnesswas obtained in the films with a high density and a high transparency.

Effects of temperature on the polymorphism of α,ω-dioctylterthiophene in thin films

Polymorphism of α,ω-dioctylterthiophene (DOTT) thin films (less than 100nm-thick) deposited onto standard silicon substrates is investigated by combining specular and in-plane grazing incidence X-ray diffraction measurements. Two crystal phases are revealed: the bulk phase (b) and the surface-induced phase (s). Previous results showed that s-phase was the most favored close to the substrate surface while b-phase is predominant at the DOTT-air interface. We show here that the relative proportion of these polymorphs is related to sample preparation. Indeed, the preferential crystallization of one phase or the other can be tuned as a function of substrate temperature during film deposition, s-phase being mainly present at high substrate temperature while b-phase is most observed at low substrate temperature. Particularly noteworthy is that thin films exhibiting only b-phase or only s-phase can be obtained according to sample preparation. Furthermore, when samples are annealed above the melting temperature (smectic G phase), the polymorph observed after cooling back to room temperature depends upon the cooling rate, s-phase being predominant at high cooling rate while it is rather b-phase for slow cooling. This behavior is independent of the crystalline phase that was present at room temperature before annealing.

The effect of substrate temperature on structural and morphological properties of Au/Si(1 1 1) thin films

We report here the effects of substrate temperature on the orientation and surface morphology of 100nm thick gold films, using scanning tunneling microscopy and X-ray diffraction. The gold films were deposited using molecular beam epitaxy technique onto Si(111) 7×7 substrates. Ex situ characterizations are performed using scanning tunneling microscope at room temperature. X-ray diffraction measurements reveal the (111) orientation of the film deposited at 580°C. We present data showing the evolution of the RMS roughness amplitude of the gold films as a function of substrate temperature during deposition. For our purposes, the best compromise between roughness and grain size is found to occur for a substrate temperature maintained at 580°C.

CdTe thin films grown by pulsed laser deposition using powder as target: Effect of substrate temperature

CdTe thin films were deposited by pulsed laser deposition on Corning glass slides using CdTe powder as target. Films were grown at substrate temperatures ranging from room temperature (~25°C) to 300°C. The structural, compositional and optical properties were analyzed as a function of substrate temperature. X-ray diffraction shows that CdTe films grown at room temperature have hexagonal phase, while for higher temperatures the films have cubic phase. Raman and EDS indicate that films grew with Te excess, which suggests that CdTe films have p-type conductivity.

Preparation and characterization of nanostructures of in-doped ZnO films deposited by chemically spray pyrolysis: Effect of substrate temperatures

We deposited undoped (ZnO) and indium-doped ZnO (IZO) films onto glass substrate via ultrasonic spray pyrolysis technique. The variation in structural, surface morphology, electrical, optical and photoluminescent properties as a function of substrate temperature is investigated. X-rays pattern confirms that as-synthesized IZO phase is grown along a (002) preferential plane. Nanosized grains (<50nm) are determined by X-ray analysis. Morphology of as-grown films shows broadened nanostructures which have grown along c-axis and nanostructures are found to be smooth (RMS∼60nm). Study by spectrophotometer reveals that the as-grown films are highly transparent in the visible and IR spectra (T∼88%), and that the bandgap is slightly narrowed (3.17eV). Electrical measurements confirm the enhancement of conductivity, ρ<1Ωcm, due to indium incorporation into the starting solution. An electron concentration of 1017cm−3 and a mobility of 3cm2/Vs are found for IZO films grown at 400°C. The photoluminescence analysis demonstrates strong yellow (2.1eV) and blue (2.8eV) light and weak green (2.3eV) emissions.

High-Throughput Ellipsometric Characterization of Vapor-Deposited Indomethacin Glasses

A method for the high-throughput preparation and characterization of vapor-deposited organic glasses is presented. Depositing directly onto a substrate with a large temperature gradient allows many different glasses to be prepared simultaneously. Ellipsometry is used to characterize these glasses, allowing the determination of density, birefringence, and kinetic stability as a function of substrate temperature. For indomethacin, a model glass former, materials up to 1.4% more dense than the liquid-cooled glass can be formed with a continuously tunable range of molecular orientations as determined by the birefringence. By comparing measurements of many properties, we observe three phenomenological temperature regimes. For substrate temperatures from Tg + 11 K to Tg - 8 K, equilibrium states are produced. Between Tg - 8 K and Tg - 31 K, the vapor-deposited materials have the macroscopic properties expected for the equilibrium supercooled liquid while showing local structural anisotropy. At lower substrate temperatures, the properties of the vapor-deposited glasses are strongly influenced by kinetic factors. Different macroscopic properties are no longer correlated with each other in this regime, allowing unusual combinations of properties.

Improvement in plasma illumination properties of ultrananocrystalline diamond films by grain boundary engineering

Microstructural evolution of ultrananocrystalline diamond (UNCD) films as a function of substrate temperature (TS) and/or by introducing H2 in Ar/CH4 plasma is investigated. Variation of the sp2 and sp3 carbon content is analyzed using UV-Raman and near-edge X-ray absorption fine structure spectra. Morphological and microstructural studies confirm that films deposited using Ar/CH4 plasma at low TS consist of a random distribution of spherically shaped ultra-nano diamond grains with distinct sp2-bonded grain boundaries, which are attributed to the adherence of CH radicals to the nano-sized diamond clusters. By increasing TS, adhering efficiency of CH radicals to the diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nano-sized diamond grains break, whereas the addition of 1.5% H2 in Ar/CH4 plasma at low TS induces atomic hydrogen that preferentially etches out the t-PA attached to ultra-nano diamond grains. Both cases make the sp3-diamond phase less passivated. This leads to C2 radicals attaching to the diamond lattice promoting elongated clustered grains along with a complicated defect structure. Such a grain growth model is highly correlated to explain the technologically important functional property, namely, plasma illumination (PI) of UNCD films. Superior PI properties, viz. low threshold field of 0.21 V/μm with a high PI current density of 4.10 mA/cm2 (at an applied field of 0.25 V/μm) and high γ-coefficient (0.2604) are observed for the UNCD films possessing ultra-nano grains with a large fraction of grain boundary phases. The grain boundary component consists of a large amount of sp2-carbon phases that possibly form interconnected paths for facilitating the transport of electrons and the electron field emission process that markedly enhance PI properties.

Influence of substrate temperature on the properties of CeO2 thin films by simple nebulizer spray pyrolysis technique

Cerium oxide thin films are coated on glass substrates by nebulizer spray pyrolysis technique using cerium nitrate as a source material. Their crystallographic structures, surface morphology, optical properties and I–V characteristics are studied as a function of substrate temperature (300–500 °C). XRD is used to estimate the crystallographic texture, grain size, strain and lattice constants. All the films exhibit a cubic fluorite structure with different preferred orientations depending on the preparation conditions. Optical analysis reveals that the films are transparent (70%) in the visible region. The optical bandgap (Eg) is calculated in the range 3.28–3.52 eV. The optical parameters like absorption coefficient, extinction coefficient, packing density and refractive index are calculated for different substrate temperatures. SEM images exhibit golf-ball like morphology with small cracks and pores. The maximum conductivity obtained is 2.90×10−6 S/cm at 400 °C.