Varying Substrate Temperature Research Articles

Fe-Al alloy single-crystal thin film preparation for basic magnetic measurements

Fe100–xAlx (x = 0, 4, 10, 20, 30 at. %) alloy films of 40 nm thickness are prepared on MgO(001) single-crystal substrates by varying substrate temperature from room temperature to 600 °C. Single-crystal films of (001) orientation with bcc-based disordered A2 structure are obtained for the Al content range of x = 0 - 20 at. %. An ordered phase of DO3 structure is observed in Fe70Al30 films prepared at temperatures higher than 200 °C, whereas (001) oriented single-crystal films of A2 structure are obtained when prepared at room temperature. The film surface profile does not depend much on the film composition, while the surface roughness increases with increasing substrate temperature. Island-like crystals are observed for films prepared at 600°C for all compositions. Difference in lattice spacing measured parallel and perpendicular to the substrate is noted for the single-crystal thin films and it increases with increasing Al content. The lattice strain in single-crystal film is caused possibly to accommodate the lattice mismatch with the MgO substrate. The (001)-oriented single-crystal films with A2 structure show four-fold symmetries in in-plane magnetic anisotropy with the easy magnetization axis A2[100] and the hard magnetization axis A2[110], whereas the films with DO3 ordered structure show almost isotropic magnetic properties.

Effect of substrate temperature on quality of copper film catalyst substrate: A Molecular Dynamics Study

Copper film growth using thermal evaporation methods was studied using molecular dynamics simulations. The AlSiMgCuFe modified embedded atom method potential was used to describe interaction of Cu-Cu, Si-Si and Cu-Si atoms. Our results showed that the variations of substrate temperature affected crystal structure composition and surface roughness of the produced copper film catalyst substrate. In this study, we observed intermixing phenomenon after deposition process. The increasing of substrate temperature affected the increasing of the total silicon atoms had diffusion into copper film.

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.

Parametric investigations to enhance the thermomechanical properties of CuAlNi shape memory alloy Bi-morph

The influence of growth substrate temperature on the development of CuAlNi shape memory alloy (SMA) over Kapton Polyimide sheet and its effect on tuning the thermomechanical behavior has been investigated. The SMA bi-morph was synthesized at varying substrate temperatures ranging from 100 °C–200 °C. Two-way shape memory effect could be demonstrated by the bi-morps without any post-processing and training, due to pre-straining of the flexible substrates. The deposited SMA film was responsible for the forward displacement and the return was achieved because of flexible kapton polyimide substrate. To investigate the life cycle behavior of the as developed SMA bi-morph, an in-house life cycle setup was developed with Joule heating as the actuation source. The cyclic behavior was investigated for 500 cycles, at three varying voltages of 2 V, 2.5 V and 3 V with an actuation frequency of 0.5 Hz. The film deposited with growth substrate temperature of 100 °C and 200 °C showed a maximum displacement of 0.6 mm and 0.9 mm, whereas samples prepared with substrate heating at 150 °C showed a maximum displacement of 2.6 mm with actuation voltage of 3 V. To probe the influence of substrate temperature in tuning the thermomechanical behavior, an analysis on the structural, morphological, and thermal properties of the bi-morphs has been investigated in detail.

Oxygen vacancies dependent phase transition of Y2O3 films

Y2O3 films have great application potential in high-temperature metal matrix composite and nuclear engineering, used as interface diffusion and reaction barrier coating owing to their excellent thermal and chemical stability, high melting point and extremely negative Gibbs formation energy, and thus their structural and mechanical properties at elevated temperature are especially important. Oxygen vacancies exist commonly in yttrium oxide (Y2O3) thin films and act strongly on the phase structure and properties, but oxygen vacancies dependent phase transition at elevated temperature has not been well explored yet. Y2O3 thin films with different oxygen vacancy concentrations have been achieved by reactive sputtering through varying substrate temperature (Ts), in which oxygen vacancies increase monotonously with increasing Ts. For as-deposited Y2O3 films, oxygen vacancies present at high Ts can promote the nucleation of monoclinic phase, meanwhile, high Ts can induce the instability of monoclinic phase. Thus their competition results in forming mixed phases of cubic and monoclinic at high Ts. During vacuum annealing at 1000°C, a critical oxygen vacancy concentration is observed, below which phase transition from monoclinic to cubic takes place, and above which phase transfer from monoclinic to the oxygen defective phase (ICDD file no. 39-1063), accompanying by stress reversal from compressive to tensile and maintenance of high hardness.

Impact of structure and morphology of nanostructured ceria coating on AISI 304 oxidation kinetics

Nanostructured ceria-based coatings are shown to be protective against high-temperature oxidation of AISI 304 due to the dynamics of oxidation state and associated defects. However, the processing parameters of deposition have a strong influence in determining the structural and morphological aspects of ceria. The present work focuses on the effect of variation in substrate temperature (50–300°C) and deposition rate (0.1–50Å/s) of ceria in electron beam physical vapour evaporation method and correlates the changes in structure and morphology to high-temperature oxidation protection. Unlike deposition rate, substrate temperature exhibited a profound influence on crystallite size (7–18nm) and oxygen vacancy concentration. Upon isothermal oxidation at 1243K for 24h, bare AISI 304 exhibited a linear mass gain with a rate constant of 3.0±0.03×10−3kg2m−4s−1 while ceria coating lowered the kinetics by 3–4 orders. Though the thickness of the coating was kept constant at 2μm, higher deposition rate offered one order lower protection due to the porous nature of the coating. Variation in the substrate temperature modulated the porosity as well as oxygen vacancy concentration and displayed the best protection for coatings deposited at moderate substrate temperature. The present work demonstrates the significance of selecting appropriate processing parameters to obtain the required morphology for efficient high-temperature oxidation protection.

Combining a distributed flow manifold and 3D woven metallic lattices to enhance fluidic and thermal properties for heat transfer applications

The fluidic and heat transfer capabilities of 3D woven lattice materials were reported recently under axial and bifurcated flow patterns, but three critical performance indices – pressure drop, average surface temperature and temperature uniformity – could not be optimized simultaneously using these flow patterns. Here we combine the 3D weaves with manifolds to create a novel 3D flow pattern that enhances temperature uniformity, while also maintaining low pressure drops and surface temperatures. These three properties were characterized at room temperature for a range of flow rates using water as the working fluid. Three different weaves thicknesses were investigated: 12.7mm, 6.4mm, and 3.2mm, with manifold thicknesses of 12.7mm, 19.0mm, and 22.2mm, respectively, to provide a constant, combined weave-manifold thickness of 25.4mm. The properties of this new weave/manifold system are compared to those obtained using just the manifold (with no weave) and just the weave (with no manifold). Comparisons show that the addition of the weave lowers the average substrate temperature and temperature variations significantly, although pressure drop is increased. They also show that the addition of the manifold improves temperature uniformity significantly, and also lowers the average substrate temperature and the pressure drop. No specific ratio of weave to manifold thickness was found to be superior in all of the performance indices. The thermal performances are then evaluated at different pumping powers: the weave/manifold system and its distributed array flow pattern prevail. Finite element simulations were performed on a reduced and simplified model to explain the observed experimental trends, and manifold opening patterns were manipulated to demonstrate further potential property enhancements. The multiple benefits of this manifold system can be extended to common heat exchanger media beyond weaves.

Structural and Optical Properties of Nanostructured Cu2O Thin Films for Optoelectronic Devices

In the present work nanostructured cuprous oxide thin films were deposited on glass substrates by DC reactive magnetron sputtering by varying substrate temperature from 100 to 400 °C. X-ray diffraction patterns of Cu2O films deposited at different substrate temperatures show (1 1 1) orientation. The surface topography of the films was studied by atomic force microscopy (AFM). Energy dispersive spectroscopy (EDS) is carried out to determine the compositional analysis of thin films. The optical transmittance of Cu2O films increased with the increase of substrate temperature from 100 to 400 °C. Optical study is performed to calculate refractive index (n), absorption coefficient (α), extinction coefficient (k), optical band gap (Eg) and urbach energy (EU) using the transmission spectra in the wavelength range of 300 - 800 nm.

Effects of Substrate Heating and Wettability on Evaporation Dynamics and Deposition Patterns for a Sessile Water Droplet Containing Colloidal Particles.

Effects of substrate temperature, substrate wettability, and particle concentration are experimentally investigated for evaporation of a sessile water droplet containing colloidal particles. Time-varying droplet shapes and temperature of the liquid-gas interface are measured using high-speed visualization and infrared thermography, respectively. The motion of the particles inside the evaporating droplet is qualitatively visualized by an optical microscope and the profile of the final particle deposit is measured by an optical profilometer. On a nonheated hydrophilic substrate, a ring-like deposit forms after the evaporation, as reported extensively in the literature, while on a heated hydrophilic substrate, a thinner ring with an inner deposit is reported in the present work. The latter is attributed to Marangoni convection, and recorded motion of the particles as well as measured temperature gradient across the liquid-gas interface confirms this hypothesis. The thinning of the ring scales with the substrate temperature and is reasoned to stronger Marangoni convection at larger substrate temperature. In the case of a nonheated hydrophobic substrate, an inner deposit forms due to very early depinning of the contact line. On the other hand, in the case of a heated hydrophobic substrate, the substrate heating as well as larger particle concentration helps in the pinning of the contact line, which results in a thin ring with an inner deposit. We propose a regime map for predicting three types of deposits-namely, ring, thin ring with inner deposit, and inner deposit-for varying substrate temperature, substrate wettability, and particle concentration. A first-order model corroborates the liquid-gas interface temperature measurements and variation in the measured ring profile with the substrate temperature.

III-V/Si Hybrid Laser Stabilization Using Micro-Ring Feedback Control

We present a real-time approach for stabilizing a III-V/Si hybrid external-cavity laser implemented using microring monitoring and a feedback control loop. Laser mode stabilization over bias current and stage temperature variations are experimentally demonstrated. We achieved single-mode and mode-hop-free laser operation as the bias current was swept across 320 mA. The same feedback control also enabled wavelength-locked laser operation using an intracavity phase control. The feedback control was also applied to an integrated on-chip hybrid laser, and mode-hop-free laser operation was demonstrated over 23 °C substrate temperature variation.

Photo-assisted splitting of dielectric microdroplets in a LN-based sandwich structure.

We demonstrate an active and controllable photo-assisted splitting of dielectric microdroplets inside a LiNbO3-based sandwich structure by utilizing the pyroelectric and photovoltaic effects of LiNbO3 crystals. Basing on electrostatic simulation results, the mechanism of the photo-assisted splitting is explained; meanwhile, the microdoplet pre-polarizing and the inclined electrostatic force induced by the photovoltaic charges inside the sandwich structure are emphasized. We also study the dependence of the splitting part size on the substrate temperature variation, the irradiation intensity, and the duration. Featured dependence is found to follow the theoretical curve predicted by the compensation between the photo-excited and bound surface charges.

Proper In deposition amount for on-demand epitaxy of InAs/GaAs single quantum dots**Project supported by the National Key Basic Research Program of China (Grant No. 2013CB933304), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB01010200), and the National Natural Science Foundation of China (Grant No. 65015196).

The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots (SQDs) to raise the growth repeatability. Here, through many growth tests on rotating substrates, we develop a proper In deposition amount (θ) for SQD growth, according to the measured critical θ for test QD nucleation (θc). The proper ratio θ/θc, with a large tolerance of the variation of the real substrate temperature (Tsub), is 0.964−0.971 at the edge and > 0.989 but < 0.996 in the center of a 1/4-piece semi-insulating wafer, and around 0.9709 but < 0.9714 in the center of a 1/4-piece N+ wafer as shown in the evolution of QD size and density as θ/θc varies. Bright SQDs with spectral lines at 905 nm–935 nm nucleate at the edge and correlate with individual 7 nm–8 nm-height QDs in atomic force microscopy, among dense 1 nm–5 nm-height small QDs with a strong spectral profile around 860 nm–880 nm. The higher Tsub in the center forms diluter, taller and uniform QDs, and very dilute SQDs for a proper θ/θc: only one 7-nm-height SQD in 25 μm2. On a 2-inch (1 inch = 2.54 cm) semi-insulating wafer, by using θ/θc = 0.961, SQDs nucleate in a circle in 22% of the whole area. More SQDs will form in the broad high-Tsub region in the center by using a proper θ/θc.

Engineering the polar magneto-optical Kerr effect in strongly strained L10–MnAl films

We report the engineering of the polar magnetooptical (MO) Kerr effect in perpendicularly magnetized L10–MnAl epitaxial films with remarkably tuned magnetization, strain, and structural disorder by varying substrate temperature (Ts) during molecular-beam epitaxy growth. The Kerr rotation was enhanced by a factor of up to 5 with Ts increasing from 150 to 350 °C as a direct consequence of the improvement of the magnetization. A similar remarkable tuning effect was also observed on the Kerr ellipticity and the magnitude of the complex Kerr angle, while the phase of the complex Kerr angle appears to be independent of the magnetization. The combination of the good semiconductor compatibility, the moderate coercivity of 0.3–8.2 kOe, the tunable polar MO Kerr effect of up to ~0.034°, and giant spin precession frequencies of up to ~180 GHz makes L10–MnAl films a very interesting MO material. Our results give insights into both the microscopic mechanisms of the MO Kerr effect in L10–MnAl alloys and their scientific and technological application potential in the emerging spintronics and ultrafast MO modulators.

Properties of nano-thick BaSnO3/Cu/BaSnO3 multilayer thin films: the role of substrate temperature

The nano-thick BaSnO3/Cu/BaSnO3 multilayer thin films have been designed and fabricated on glass by magnetron sputtering. The thickness of BaSnO3, Cu, and BaSnO3 layer in the multilayer thin films was set at 50, 10, and 50 nm, respectively. The structural, electrical, and optical properties of multilayer thin films were investigated with respect to the variation of substrate temperature. The average optical transmittance in the visible range of wavelengths (400–800 nm) shows an increase for the multilayer thin films grown at a temperature below 250 °C. A low resistivity (<10−4 Ω cm) for the multilayer thin films is found to be retained until 200 °C, followed by a quickly increase as the substrate temperature further increases to 300 °C. In addition, a mechanism for the variation of electrical and optical properties with the substrate temperature was proposed.

Use of Acoustic Emission During Scratch Testing for Understanding Adhesion Behavior of Aluminum Nitride Coatings

In this work, acoustic emission during scratch testing of the aluminum nitride coatings formed on stainless steel substrate by reactive magnetron sputtering was analyzed to assess the coating failure. The AlN coatings were formed under the variation of substrate temperature, substrate bias potential, and discharge power. The coatings deposited in the temperature range of 100 to 400 °C showed peak acoustic emission less than 1.5%, indicating ductile nature of the coating. However, for coatings formed with substrate negative bias potential of 20 to 50 V, numerous sharp acoustic bursts with maximum emission approaching 80% were observed, indicating brittle nature of the coatings with large number of defects present. The shift in the intensity of the first major acoustic peak toward higher load, with the increasing bias potential, confirmed improved adhesion of the coating. Also, the higher discharge power resulted in increased acoustic emission.

Highly transparent conducting CdO thin films by radiofrequency magnetron sputtering for optoelectronic applications

Cadmium oxide (CdO) thin films with low electrical resistivity and higher transparency have been deposited by radiofrequency (RF) magnetron sputtering on glass substrates. Sputtering process was carried out at RF power of 40 W and with varying substrate temperatures. The structural, morphological, electrical, and optical properties of the deposited films are investigated. The structural properties reveals that the as-deposited CdO films shows preferential orientation along (111) plane exhibiting face centered cubic structure. The surface morphology shows that all the films possess well defined grain boundaries with high uniformity. CdO samples deposited at substrate temperature of 150°C with RF power of 40 W exhibits above 95% transparency within the visible wavelength with lower electrical resistivity value in the order of 10−5 Ω·cm. The Raman spectroscopy analysis reveals the possible modes present in CdO films and its dependence on substrate temperature. The comparatively high value of the figure of merit for the optimum sample of CdO deposited at 150°C indicates that these films are suitable for optoelectronic device applications.

Optimized substrate temperature range for improved physical properties in spray pyrolysis deposited Tin Selenide thin films

Tin diselenide (SnSe2) thin films have been deposited on glass substrate using the spray pyrolysis technique by varying substrate temperatures (Tsub) from 250 °C to 400 °C. These films were characterized for structural, morphological, electrical and thermoelectric properties by using X-ray Diffraction, Field Emission Scanning Electron Microscopy (FESEM), four probe resistivity/conductivity and thermoelectric measurement respectively. X-Ray Diffraction patterns revealed that substrate temperature plays a critical role in phase formation and a single phase SnSe2 film were formed at a critical temperature range 275–375 °C. FESEM study of single phase film at 300 °C shows uneven and irregular shape grains throughout the film and the EDX shows the stoichiometric ratio of deposit. The variations of the micro-structural parameters, such as crystallite size (D), dislocation density (δ), and micro-strain (ε), were investigated for all films. The results showed that the crystallite sizes increase with an increase in substrate temperature, whereas the dislocation density and micro-strain decreases with increasing substrate temperature. The resistivity (ρ) of SnSe2 film was found to be decreasing with increasing temperature and also with substrate temperature. The predefined substrate temperature range (275–375 °C) was further narrowed down using 4-probe resistivity measurement. It shows that, although 275–375 °C is enough formation of single phase SnSe2, but there is a small temperature range 325–375 °C where one will get low resistive sample, which influence the flow of charge carrier. Low electrical resistance or inversely high electrical conductivity is one of the prime requirements of thermoelectric samples. The 4-probe resistivity measurement of single phase thin films shows that the lowest electrical resistance obtained for substrate temperature of 350 °C. Thermoelectric measurement confirms that the coated films were n-type semiconductor materials and the thermo-emf increases with an increase in substrate temperature. Among all the films the film with substrate temperature of 350 °C shows enhanced behaviour to be used in industrial applications.

Spatial environmental heterogeneity affects plant growth and thermal performance on a green roof

Green roofs provide ecosystem services, including stormwater retention and reductions in heat transfer through the roof. Microclimates, as well as designed features of green roofs, such as substrate and vegetation, affect the magnitude of these services. Many green roofs are partially shaded by surrounding buildings, but the effects of this within-roof spatial environmental heterogeneity on thermal performance and other ecosystem services have not been examined. We quantified the effects of spatial heterogeneity in solar radiation, substrate depth and other variables affected by these drivers on vegetation and ecosystem services in an extensive green roof. Spatial heterogeneity in substrate depth and insolation were correlated with differential growth, survival and flowering in two focal plant species. These effects were likely driven by the resulting spatial heterogeneity in substrate temperature and moisture content. Thermal performance (indicated by heat flux and substrate temperature) was influenced by spatial heterogeneity in vegetation cover and substrate depth. Areas with less insolation were cooler in summer and had greater substrate moisture, leading to more favorable conditions for plant growth and survival. Spatial variation in substrate moisture (7%–26% volumetric moisture content) and temperature (21°C–36°C) during hot sunny conditions in summer could cause large differences in stormwater retention and heat flux within a single green roof. Shaded areas promote smaller heat fluxes through the roof, leading to energy savings, but lower evapotranspiration in these areas should reduce stormwater retention capacity. Spatial heterogeneity can thus result in trade-offs between different ecosystem services. The effects of these spatial heterogeneities are likely widespread in green roofs. Structures that provide shelter from sun and wind may be productively utilized to design higher functioning green roofs and increase biodiversity by providing habitat heterogeneity.

VHF-PECVD grown silicon nanoneedles: Role of substrate temperature

Achieving highly aligned and dense silicon (Si) nanoneedles (NNs) is ever demanding for optoelectronics. We report the substrate temperature assisted Au-catalyzed SiNNs synthesis via very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique. The effects of varying substrate temperatures (350–550 °C) on the growth process are examined. The maximum density of SiNNs (∼10 NN/μm2) is obtained at the optimum temperature of 550 °C. These NNs have diameters ranging from 38 to 87 nm and the lengths are extended up to 2.96 ± 0.09 μm. Furthermore, the sample prepared at 350 °C is totally devoid of any SiNNs. The axial NNs growth rate increased from 35.3 ± 2.3 nm/min (at 400 °C) to 138.8 ± 8.9 nm/min (at 550 °C). XRD analysis demonstrated the SiNNs cubic structure with preferred orientation along <111>. The NNs prepared at 550 °C displayed better crystallinity than those obtained at other temperatures. This enhanced crystallinity is further supported by Raman measurements. High resolution transmission electron microscopy (HRTEM) confirmed that these NNs are composed of crystalline Si core with an oxide shell. Sample grown at 400 °C revealed a reflectance of 28.642% in the visible region. However, the highly dense SiNNs grown at 550 °C showed a noticeable suppression in the reflectance (15.787%), indicating excellent anti-reflection attributes. The excellent features of the presented results suggest that our systematic method may constitute a basis for the temperature mediated tunable growth of SiNNs suitable for optoelectronics devices.

Morphological evolution of zinc oxide thin films with variation in sputtering power and substrate temperature

Zinc oxide (ZnO) thin films were deposited on silicon substrates by reactive RF magnetron sputtering technique in order to investigate the evolution of the morphological and the optical properties as a function of different RF power and substrate temperature. Analysis of RF power and the substrate temperature have played a significant role in the morphological and the optical properties of the sputtered ZnO thin films. X-ray diffraction pattern of ZnO thin film has shown the appearance of c-axis-oriented (002) peak for all samples with variation in the degrees of crystallinity. The surface roughness as well as the average grain size of the ZnO films found to be decreased with RF power, where as the films grown at higher temperature has shown the evolution of larger grains. ZnO films, deposited at 150 W RF power and substrate of 200°C, have shown better optical properties.