Control Of Substrate Temperature Research Articles

Control of effective cooling rate upon magnetron sputter deposition of glassy Ge15Te85

Reducing the enthalpy of as-deposited amorphous films is desirable as it improves their kinetic stability and enhances the reliability of resulting devices. Here we demonstrate that Ge15Te85 glass films of lower enthalpy are produced by increasing the voltage during magnetron sputter deposition. An increase of ~100 V leads to a drop in effective cooling rate of almost three orders of magnitude, thereby yielding markedly lower enthalpy glasses. The sputtering voltage therefore constitutes a novel parameter for tuning the fictive temperature of glass films, which could help to obtain ultra-stable glasses in combination with substrate temperature control.

Highly oriented (111) CoO and Co3O4 thin films grown by ion beam sputtering

We demonstrate that ion beam sputtering is a suitable deposition technique to obtain single-phase and highly (111)-oriented CoO and Co3O4 thin films. The control of substrate temperature and composition of the reactive atmosphere during deposition allows tailoring the phase structure and preferential growth of the films. Optimum substrate temperatures of 773 K and 603 K for CoO and Co3O4, respectively, have been determined and the presence of the single CoO and Co3O4 phases on the films has been confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. Transmittance differences in the visible region higher than 50% have been observed between low transmittance in Co3O4 films and high transmittance in CoO films. The semiconducting behavior of Co3O4 thin films was confirmed by temperature dependent resistance measurements. The Co3O4 thin films also show a dual optical band gap at energies of 1.47 and 2.14 eV associated to d-d and p-d transition, respectively. Additionally, at intermediate temperatures between the optimum ones to growth (111)-oriented single phase CoO and Co3O4 films, only one single phase, either CoO or Co3O4, is present in the films, in which the electrical and structural properties can be controlled by the oxygen partial pressure used during deposition.

Tailoring low energy electron absorption via surface nano-engineering of cesiated chromium films

In this letter, we demonstrate that improved low energy electron absorption is achieved by suppressing the crystallinity of chromium thin-films grown on W[110], which points to a promising route for achieving highly efficient thermionic energy converters. Using low energy electron microscopy (LEEM) and in situ film growth, we show that substrate temperature control permits well-controlled fabrication of either epitaxial Cr[110] films or nanocrystalline Cr layers. We show that the work function of cesium saturated nanocrystalline Cr thin-films is ∼0.20 eV lower than that of epitaxial Cr[110] films. Our LEEM measurements of absorbed and reflected currents as a function of electron energy demonstrate that nanocrystallinity of cesiated chromium films results in 96% electron absorption in the range up to 1 eV above the work function, compared to just 79% absorption in cesiated crystalline Cr[110] films. These results point to metal films with suppressed crystallinity as an economical and scalable means to synthesize nanoengineered surfaces with optimized properties for next generation anode materials in high performance thermionic energy converters.

Hot-substrate deposition of all-inorganic perovskite films for low-temperature processed high-efficiency solar cells

An excellent PCE of 13.8% was achieved for low-temperature processed CsPbI2Br PSCs using a hot-casting method with precisely controlled substrate temperature.

Multimicrometer Noncovalent Monolayer Domains on Layered Materials through Thermally Controlled Langmuir-Schaefer Conversion for Noncovalent 2D Functionalization.

As functionalized 2D materials are incorporated into hybrid materials, ensuring large-area structural control in noncovalently adsorbed films becomes increasingly important. Noncovalent functionalization avoids disrupting electronic structure in 2D materials; however, relatively weak molecular interactions in such monolayers typically reduce stability toward solution processing and other common material handling conditions. Here, we find that controlling substrate temperature during Langmuir-Schaefer conversion of a standing phase monolayer of diynoic amphiphiles on water to a horizontally oriented monolayer on a 2D substrate routinely produces multimicrometer domains, at least an order of magnitude larger than those typically achieved through drop-casting. Following polymerization, these highly ordered monolayers retain their structures during vigorous washing with solvents including water, ethanol, tetrahydrofuran, and toluene. These findings point to a convenient and broadly applicable strategy for noncovalent functionalization of 2D materials in applications that require large-area structural control, for instance, to minimize desorption at defects during subsequent solution processing.

Temperature dependence of protection layer formation on organic trench sidewall in H2/N2 plasma etching with control of substrate temperature

For the etching of organic films in H2/N2 plasma, etched profiles are significantly determined by substrate temperature. Here, we control the substrate temperature variation within 3 °C during processing by modulating the plasma-discharge time. The evolution of the cross-sectional profile of line-and-space patterns was observed every 10 s. At 60 and 100 °C, sidewall etching was observed during overetching, but not at 20 °C. During the main etching, the sidewalls were protected by the adsorption of by-products at various temperatures. Moreover, we investigated the temperature dependence of protection layer formation by analyzing the surface components of the organic film. The CN layer formed by N radicals has a protective effect that depends on the components of the CN layer. It was found that the ratio of C–N sp3 to C–N sp2 in the sidewall was highest at 100 °C. By evaluating the radical contribution to CN layer formation, C–N sp3 bonds were observed to be formed by ions and radiation-assisted reaction.

Direct growth of VO2 nanoplatelets on glass and silicon by pulsed laser deposition through substrate temperature control

In this contribution, we explore the influence of substrate temperature on the phase evolution, morphology and transition properties of vanadium dioxide nanostructured thin films grown by pulsed laser deposition technique on glass and silicon substrates. The main objective is to grow directly on the top of substrates surface vanadium dioxide nanostructures with high density and high aspect ratio. Structural analysis using X-ray diffraction method showed highly oriented (011) VO2 films in the temperature range of 500–700°C. Successfully, catalyst free and dense VO2 nanoplatelets were obtained at 600 and 700°C. While the aspect ratio was limited for the nanoplatelets grown on silicon substrate, those grown on glass showed an aspect ratio of around 5. The study of the metal-insulator phase transition using a four probe technique evidenced the effect of the growth temperature on the transition properties through its influence on the stoichiometry, grain size and shape. Mechanisms behind the growth of elongated VO2 nanoplatelets on glass substrate are evidenced throughout substrate nature influence. The amorphous nature of glass which acts as a free standing environment at high temperature is suggested to be the key factor to grow elongated nanoplatelets in an open structure of particular morphology. As summary, using pulsed laser deposition, we have established a one-step growth protocol of dense VO2 nanoplatelets with a high surface-to-volume ratio which can find a potential application in gas sensing devices.

Growth of BaSi2 film on Ge(100) by vacuum evaporation and its photoresponse properties

We have successfully grown a polycrystalline orthorhombic BaSi2 film on a Ge(100) substrate by an evaporation method. Deposition of an amorphous Si (a-Si) film on the Ge substrate prior to BaSi2 evaporation plays a critical role in obtaining a high-quality BaSi2 film. By controlling substrate temperature and the thickness of the a-Si film, a crack-free and single-phase polycrystalline orthorhombic BaSi2 film with a long carrier lifetime of 1.5 µs was obtained on Ge substrates. The photoresponse property of the ITO/BaSi2/Ge/Al structure was clearly observed, and photoresponsivity was found to increase with increasing substrate temperature during deposition of a-Si. Furthermore, the BaSi2 film grown on Ge showed a higher photoresponsivity than that grown on Si, indicating the potential application of evaporated BaSi2 on Ge to thin-film solar cells.

Molecular Beam Epitaxy of lithium niobium oxide multifunctional materials

The role of stoichiometry and growth temperature in the preferential nucleation of material phases in the Li-Nb-O family are explored yielding an empirical growth phase diagram. It is shown that while single parameter variation often produces multi-phase films, combining substrate temperature control with the previously published lithium flux limited growth allows the repeatable growth of high quality single crystalline films of many different oxide phases. Higher temperatures (800–1050°C) than normally used in MBE were necessary to achieve high quality materials. At these temperatures the desorption of surface species is shown to play an important role in film composition. Using this method single phase films of NbO, NbO2, LiNbO2, Li3NbO4, LiNbO3, and LiNb3O8 have been achieved in the same growth system, all on c-plane sapphire. Finally, the future of these films in functional oxide heterostructures is briefly discussed.

Droplet-Assisted Laser Direct Nanoscale Writing on Silicon

Nano-structuring using laser direct writing technology has shown great potential for industrial applications. A novel application of water droplets to this technology is proposed in this paper. With a hydrophobic layer and a controlled substrate temperature, a layer of randomly distributed water droplets with a high contact angle is formed on the substrate. These liquid droplets can be used as lenses to enhance the laser intensity at the bottom of the droplets. As a result, nanoscale holes can be fabricated on the substrate by controlling the laser energy density. We successfully fabricated holes with a diameter of 600 nm at a substrate temperature of 12 ∘C and a power density of 1.2 × 108 W/cm2 in our experiments. We also found that the hole diameter was around a ninth of the water droplet diameter. Meanwhile, the machined holes are not affected much by the focal length of the lens, but a hole with less than 100 nm in diameter at the center was observed.

Effects of intentionally introduced nitrogen and substrate temperature on growth of diamond bulk single crystals

Aiming at stable growth of bulk single-crystal diamond, multiple effects of intentional nitrogen introduction and substrate temperature on the growth were studied. The intensity of fluorescence of the nitrogen-vacancy (NV0) center was qualitatively correlated with the concentrations of nitrogen in the grown layers. Growth rates and morphologies varied with nitrogen concentration in the gas phase and substrate temperature. It was shown that appropriate control of substrate temperature allows continuous growth, which makes the substrate thicker. The mechanism underlying the effect of nitrogen on growth rate is discussed on the basis of the obtained results, which suggest also the importance of substrate temperature in controlling migration and the surface reactions of radicals.

Novel gas hydrate reactor design: 3-in-1 assessment of phase equilibria, morphology and kinetics

A novel reactor equipped with a bilateral, temperature-control stage was developed to study gas hydrates. The design allowed for tight control of the crystallization substrate temperature, independent of ambient conditions. Methane hydrate formation was investigated on a surface with a uniform temperature and on a surface with a constant temperature gradient. The uniform temperature experiments showed a previously unreported transition point in methane hydrate morphology and displayed closely reproducible film morphologies. A single temperature-gradient experiment showed transitions in morphology with respect to driving force. These transitions were found to be consistently reproducible, and occurred due to a change from continuous crystal growth to polycrystalline, adhesive type growth. The temperature gradient was also used to control the solid–liquid interface position during gas hydrate dissociation, providing a simple and fast method for hydrate-liquid-vapor (H–L–V) equilibrium measurements. The temperature gradient was used to correlate film velocity and supercooling in order to assess apparent kinetics of hydrate growth. Overall, the ability to observe gas hydrate growth on tightly controlled temperature gradients was found to reduce multi-trial methods to a single experiment that: (1) quantifies morphology/growth mechanism transitions with respect to temperature, (2) measures the H–L–V equilibrium temperature at the experimental pressure, and (3) correlates the apparent kinetics with respect to temperature. Thus, the new design was shown to operate as a 3-in-1 reactor, effectively allowing assessment of phase equilibria, morphology and apparent kinetics of gas hydrates.

Substrate temperature control for the formation of metal nanohelices by glancing angle deposition

The targets of this study are to develop a device to precisely control the temperature during glancing angle deposition, to make films consisting of low melting temperature metal nanoelements with a controlled shape (helix), and to explore the substrate temperature for controlling the nanoshapes. A vacuum evaporation system capable of both cooling a substrate and measurement of its temperature was used to form thin films consisting of arrays of Cu and Al nanohelices on silicon substrates by maintaining the substrate temperature at Ts/Tm < 0.22 (Ts is the substrate temperature and Tm is the melting temperature of target material). The critical Ts/Tm to produce Cu and Al nanohelices corresponds to the transitional homologous temperature between zones I and II in the structure zone model for the solid film, where surface diffusion becomes dominant. X-ray diffraction analysis indicated that the Cu and Al nanohelix thin films were composed of coarse oriented grains with diameters of several tens of nanometers.

Ultraviolet Pretreatment of Titanium Dioxide and Tin-Doped Indium Oxide Surfaces as a Promoter of the Adsorption of Organic Molecules in Dry Deposition Processes: Light Patterning of Organic Nanowires.

In this article we present the preactivation of TiO2 and ITO by UV irradiation under ambient conditions as a tool to enhance the incorporation of organic molecules on these oxides by evaporation at low pressures. The deposition of π-stacked molecules on TiO2 and ITO at controlled substrate temperature and in the presence of Ar is thoroughly followed by SEM, UV-vis, XRD, RBS, and photoluminescence spectroscopy, and the effect is exploited for the patterning formation of small-molecule organic nanowires (ONWs). X-ray photoelectron spectroscopy (XPS) in situ experiments and molecular dynamics simulations add critical information to fully elucidate the mechanism behind the increase in the number of adsorption centers for the organic molecules. Finally, the formation of hybrid organic/inorganic semiconductors is also explored as a result of the controlled vacuum sublimation of organic molecules on the open thin film microstructure of mesoporous TiO2.

Fabrication of ZnS Zigzag Sculptured Nanostructured thin Films

In This work, the design, manufacture and implementation of new attached equipment to the physical vapor deposition system was reported. Using this system ZnS films were prepared under glancing angle deposition (GLAD) technique with the help of varying polar and azimuthal angles of substrate simultaneously without vacuum drop during deposition process. In addition, the designed system will help to control substrate temperature which makes the growth of sculpture thin films possible. The whole system is controlled by a programmable microcontroller. The formation of ZnS zigzag sculptured nanostructured thin films was confirmed by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) analyses.

Self-regulated growth and tunable properties of CuSbS2 solar absorbers

Polycrystalline thin film copper chalcogenide solar cells show remarkable efficiencies, and analogous but less-explored semiconducting materials may hold similar promise. With consideration of elemental abundance and process scalability, we explore the potential of the Cu–Sb–S material system for photovoltaic applications. Using a high-throughput combinatorial approach, Cu–Sb–S libraries were synthesized by magnetron co-sputtering of Cu2S and Sb2S3 targets and evaluated by a suite of spatially resolved characterization techniques. The resulting compounds include Cu1.8S (digenite), Cu12Sb4S13 (tetrahedrite), CuSbS2 (chalcostibite), and Sb2S3 (stibnite). Of the two ternary phases synthesized, CuSbS2 was found to have the most potential, however, when deposited at low temperatures its electrical conductivity varied by several orders of magnitude due to the presence of impurities. To address this issue, we developed a self-regulated approach to synthesize stoichiometric CuSbS2 films using excess Sb2S3 vapor at elevated substrate temperatures. Theoretical calculations explain that phase-pure CuSbS2 is expected to be formed over a relatively wide range of temperatures and pressures, bound by the sublimation of Sb2S3 and decomposition of CuSbS2. The carrier concentration of CuSbS2 films produced within this regime was tunable from 1016–1018cm−3 through appropriate control of Sb2S3 flux rate and substrate temperature. CuSbS2 displayed a sharp optical absorption onset indicative of a direct transition at 1.5eV and an absorption coefficient of 105cm−1 within 0.3eV of the onset. The results of this study suggest that CuSbS2 holds promise for solar energy conversion due to its tolerant processing window, tunable carrier concentration, solar-matched band gap, and high absorption coefficient.

Substrate temperature control in a system fordeposition of carbon nanostructures at atmospheric pressure

The paper presents a plasma-enhanced chemical vapor deposition system for synthesis of carbon nanostructures on a metal substrate at atmospheric pressure with a system for substrate temperature control. It is realized by using a miniature microwave plasma source with a surface-wave discharge. An important part of the system is the movable target holder which allows adjustment of the distance between the plasma flame and the substrate. The substrate temperature increases during the deposition process due to the heating by the plasma flame. A constant value of the substrate temperature (400 – 700 °C) is essential for the synthesis of various carbon structures. An electronic system with sensors positioned in the holder is designed for measurement and control of the substrate temperature. The substrate temperature is measured in continuous and pulsed modes of the discharge, with the temperature value being controlled by the amplitude, repetition rate and duration of the microwave pulses.

Pulsed laser deposition of BiFeO3 thin films with large polarization on Pt(111)/Ti/SiO2/Si by controlling substrate temperature

Bismuth ferrite (BiFeO3) thin films with large polarization were grown on Pt(111)/Ti/SiO2/Si by optimizing the substrate temperatures (T sub). The BiFeO3 thin films were prepared by pulsed laser deposition and the effects of T sub (T sub = 853–913 K) on crystallization orientation, surface morphology and properties of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T sub. The film prepared at T sub = 893 K had a relatively high degree of (111) preferential orientation and densely packed morphology. A large polarization with the maximum remanent polarization of 108 μC/cm2 was obtained, which was due to the high degree of preferential orientation and the dense surface morphology at the optimum substrate temperature.

Insertion of fullerene layer for bulk heterojunction organic photovoltaic cell fabricated by electrospray deposition method

AbstractAn improved power conversion efficiency (PCE) of bulk heterojunction organic photovoltaic cell (OPV) was achieved by inserting an n‐type [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) layer between the active layer and a metal electrode. The controlled substrate temperature was found to be a useful parameter for the multilayer structure (active layer/ PCBM) by the electrospray deposition method. Under optimized substrate temperature during the PCBM deposition, a multilayer structure could be formed, and the PCE was improved up to 1.94%.magnified image(© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Realization of Na-doped p-type non-polar a-plane Zn1−Cd O films by pulsed laser deposition

Na-doped non-polar Zn1−xCdxO thin films with different Cd content were grown on r-plane sapphire substrates by pulsed laser deposition. The Cd content in the Zn1−xCdxO thin films was adjusted via controlling substrate temperature. Based on the X-ray diffraction analysis, Na-doped Zn1−xCdxO films with Cd content below 5.3 at.% exhibit unique non-polar 〈112¯0〉 orientation, while the films with Cd content above 5.3 at.% present 〈0 0 0 1〉 and 〈112¯0〉 mixed orientations. With an effective incorporation of Na, Na-doped non-polar Zn1−xCdxO films exhibit p-type conductivity, as confirmed by rectification behavior of n-ZnO/p-Zn0.947Cd0.053O:Na homojunction. An optimized result with a resistivity of 67.43 Ω cm, Hall mobility of 0.28 cm2/V s, and hole concentration of 3.31 × 1017 cm−3 is achieved, and electrically stable over several months. The chemical states of Na were analyzed by X-ray photoelectron spectro scopy. Room-temperature photoluminescence measurements exhibit redshift of the near-band-edge emission by alloying Cd.