Flat Surface Morphology Research Articles

Effects of heat treatment on the properties of Co–P–TiO2 nanocomposite coatings

ABSTRACTThe effects of heat treatment on the properties of electrodeposited Co–P–TiO2 nanocomposite coatings were systematically investigated. The TiO2 nanoparticles-reinforced Co–P–TiO2 nanocomposites were heat-treated at different temperatures. Thermal analysis was conducted to characterize the structural transitions. The phase constituents and surface morphology of nanocomposites were identified. The mechanical properties including microhardness and wear tests were examined, and the electrochemical behaviour of Co–P–TiO2 was determined. At the increasing heating temperature, the structure of Co–P–TiO2 was gradually changed from amorphous into crystalline, with its surface morphology being smoother. Proper heat treatment can significantly improve the mechanical properties and corrosion resistance of coatings. When Co–P–TiO2 coating was heat-treated at 350°C, a smooth and flat surface morphology was obtained and optimal physicochemical performance among the examined coatings was achieved.

Analysis of growth rate and crystal quality of AlN epilayers by flow-modulated metal organic chemical vapor deposition

Abstract AlN templates have been grown on sapphire by flow-modulated metal organic chemical vapor deposition (MOCVD). By analyzing the TMAl duty ratio R, TMAl utilization ratio β and parasitic reaction ratio α, we obtained the quantitative relationship between flow-modulated modes and growth rate, and then proposed two kinds of flow-modulated modes to increase the growth rate of AlN. Besides, we found the continuous growth in flow-modulated mode can transform the AlN growth mode from the step-bunching growth into the two-dimension growth and accordingly improve the crystal quality of AlN. Finally, the AlN template with a relatively fast growth rate (0.98 μm/h) and flat surface morphology (RMS = 0.5 nm) was obtained by NH3 pulse-flow mode with a small duty ratio of NH3.

P-type spinel ZnCo2O4 thin films prepared using sol-gel process

In the present study, the sol-gel process was used to deposited thin films of the p-type spinel ZnCo2O4 onto glass substrate. Spinel ZnCo2O4 thin films were obtained by annealing the sol-gel derived specimens at 300–400 °C in oxygen for 2 h, and were confirmed by four Raman active modes at approximately 470 cm−1, 514 cm−1, 600 cm−1, and 670 cm−1. The nanostructured and flat surface morphologies of the obtained ZnCo2O4 thin films were observed by field-emission scanning electron microscopy and atomic force microscopy. Uniform film thickness and good adhesion with the substrate were also observed. The binding energy of Zn-2p at 1020.7 ± 0.2 eV (2p3/2) and 1043.8 ± 0.2 eV (2p1/2) revealed the presence of Zn2+. Additionally, the presence of both divalent and trivalent Co cation was indicated by deconvolution of the binding energies at 779.5 ± 0.2 eV (2p3/2) and 795.1 ± 0.2 eV (2p1/2) for Co3+, and at 781.5 ± 0.2 eV (2p3/2) and 796.6 ± 0.2 eV (2p1/2) for Co2+. Two optical bandgaps of the obtained spinel ZnCo2O4 thin films were deduced at 2.38–2.39 eV and 3.95–3.99 eV. The p-type characteristic was confirmed using the hot-probe test. Furthermore, the resistivities of the spinel ZnCo2O4 thin films were 1.58 × 10 2 –2.45 × 103 Ω-cm with corresponding carrier concentrations of 5.57 × 1012-4.29 × 1014 cm−3. Hence, the sol-gel process provides a feasible method for the preparation of p-type spinel ZnCo2O4 thin films.

Effects of laser pulse energy on the structural, optical and electrical properties of pulsed laser deposited Ga-doped ZnO thin films

Transparent conducting Ga-doped ZnO (GZO) thin films were deposited on glass substrate by pulsed laser deposition (PLD). The effects of laser pulse energy ranging from 80 to 200 mJ on microstructural, surface morphology, electrical and optical properties of GZO films were investigated in detail. XRD patterns have shown that all samples were hexagonal wurtzite structure presenting predominant orientation along the (002) c-axis direction, and the film obtained at 160 mJ showed the optimal crystallinity. The Raman spectra demonstrate that GZO films have oxygen vacancies, Zinc interstitials, and residual stress. The compact, homogenous and flat surface morphology of GZO films were observed by AFM. Hall effect measurements revealed that the electrical properties of samples were dominated largely by the crystallinity and the minimum resistivity of 6.10 × 10−4 Ω cm was obtained when GZO film grown at 160 mJ. Optical transmission spectra displayed an average transmittance higher than 90.6% for all GZO samples in the visible range. The film deposited at 160 mJ exhibited the maximum figure of merit of 22.70 × 10−3 Ω−1, owing to the low resistivity and high transmittance.

Phase Control of Ga<sub>2</sub>O<sub>3</sub> Thin Films Grown by Metal-Organic Chemical Vapor Deposition

In this paper, Ga2O3 thin films were grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). There was phase transition for samples grown with different flow rates of triethyl-gallium (TEGa) and deionized water (H2O). It is found that ε-Ga2O3 is difficult to coalesce and the phase mixture by β­Ga2O3 takes place if the flow rates of TEGa and H2O are too high. However, by using multiple-step growth method, the film became fully coalesced. High-quality ε-Ga2O3 thin film with atomically flat surface and multilayer morphology was obtained.

Transferable GaN Films on Graphene/SiC by van der Waals Epitaxy for Flexible Devices

Van der Waals epitaxy (vdWE) of GaN films on two‐dimensional (2D) materials can overcome a lattice mismatch during crystalline growth. Moreover, this type of epitaxy allows the GaN films to be released from 2D materials because of the weak van der Waals force. However, it is difficult to directly grow a single‐crystalline film on graphene. Here, using metal‐organic chemical vapor deposition (MOCVD), transferable single‐crystalline GaN films are synthesized on multilayer graphene (MLG)/SiC. The films exhibit a flat and continuous surface morphology and c‐axis orientation. Moreover, the GaN films are released from the graphene and transferred to flexible substrates by direct mechanical exfoliation. Furthermore, flexible ultraviolet (UV) photosensitive devices are fabricated and show excellent photoelectric performance in the UV‐range. This research lays a foundation for the application of GaN films in foldable‐display and flexible‐devices.

Transparent Sn-doped In2O3 electrodes with a nanoporous surface for enhancing the performance of perovskite solar cells

We report on a simple and efficient process to enhance the performance of perovskite solar cells by using ITO electrodes with a nanoporous surface formed by wet-etching of self-agglomerated Ag nanoparticles. Effective removal of the Ag nanoparticles embedded in the surface of the ITO electrodes result in a nanoporous structure without changing the ITO's sheet resistance (10.17 Ω/square) and optical transmittance (89.08%) at a 550 nm wavelength. Examinations with a scanning electron microscope, a transmission electron microscope, and two-dimensional porous mapping show that the nanoporous ITO surface has an increased contact area with the electron transport layer, which enhanced the carrier extraction efficiency of the perovskite solar cells. Compare to perovskite solar cells fabricated on typical ITO with a flat surface morphology, the perovskite solar cells fabricated on the nanoporous-surface ITO show a higher fill factor of 81.1% and a power conversion efficiency of 20.1%. These results indicate that modified ITO surfaces with nano-scale porosity provide a simple and efficient method to improve the power conversion efficiency of perovskite solar cells without a complicated process.

Enhanced Wear Performance of Cu-Carbon Nanotubes Composite Coatings Prepared by Jet Electrodeposition.

Cu-carbon nanotubes (CNTs) composite coatings with high CNT content and uniformly distributed CNTs were successfully prepared via jet electrodeposition. Pristine CNTs, without any treatment like acid functionalization, were used. Anionic surfactant sodium dodecyl sulfate (SDS) was used to increase the wettability of the CNTs and improve the content of incorporated CNTs. With an appropriate SDS concentration (300 mg/L) in the electrolyte, the incorporated CNT content is as high as 2.84 wt %, much higher than the values reported using conventional electrodeposition (0.42–1.05 wt %). The high-content CNTs were uniformly distributed in the composite coating. The surface morphology of this composite coating (2.84 wt % CNTs) was flat due to the uniform electric field in jet electrodeposition. In the wear test a with load of 1 N and sliding speed of 0.02 m/s, the wear rate of this composite coating was 1.3 × 10−2 mg/Nm, 85.4% lower than that of pure Cu. The enhanced wear performance of Cu-CNTs composite coatings can be attributed to high CNT content and flat surface morphology.

Physicochemical properties, bioaccessibility and antioxidant activity of the polyphenols from pine cones of Pinus koraiensis

This study investigated the physicochemical properties, bioaccessibility and in vitro antioxidant ability of the polyphenols isolated from the pine cones of Pinus koraiensis (PKP) under the simulated gastrointestinal digestion. The results found that PKP was mainly composed by derivatives of apigenin, phloretin, quercetin, myricetin, ellagitannin, and chlorogenic acid, and possessed the flat and smooth lump surface morphology. Through respective establishment of saliva, gastric fluid and small intestinal fluid digestive model in vitro, the compositions of phenolic compounds were totally different due to biotransformation. Compared with the phenolic composition of undigested PKP, the derivatives of apigenin, quercetin and ellagitannin were still detected after simulated digestion. A decrease of antioxidant capacity on free radical in vitro was observed throughout the simulated digestion processes, corresponding to the variation in phenolic content and composition. Our results highlighted that gastrointestinal digestion process might essentially influence the absorption of polyphenols, leading to the reduction of bioavailability.

Micro Optical-Interference-Plate Featuring Highly Efficient Diamagnetic Rotation of Biogenic Crystals

Optical interference, which enhances or reduces intensity of light propagating, is very important for many kinds of shape analysis methods. It will be available to detect a morphology change in micro- to nano-scale by using optical interference when we can obtain a new optical material from the animal kingdom. This paper focused on the light interference in biogenic guanine crystals which is derived from fish skin/scale. So far, it has been reported that two cross-stacked guanine crystals show stripe patterns which are produced by the optical interference between guanine crystals [1]. In this study, we have found that a very clear moire effect pattern is generated on a single guanine crystal plate combining with the mirror surface substrate. The observation system is consisted with telecentric lens and coaxial vertical illumination using blue LED. Guanine crystals in water are set on a mirror polishing Si substrate. Figure 1(a) shows the optical image of guanine crystal plates in water using our observation system. It can be clearly seen that homogeneous light and shade stripe patterns are observed on the plates when the surface of the guanine plates are parallel to the Si substrate reflecting that their very flat surface morphology. By contrast, when the guanine crystals in water are set on the substrates having the diffused reflection surface such as the black vinyl tape and Teflon plate, the light and shade stripe pattern is not observed on the single guanine crystal but observed on two crossstacked crystals as reported before (Fig.1(b)). These results suggest that moire pattern on the guanine crystal plate is perturbed or disappears when the substance or the defect which changes the reflective state of the light exists under the crystal plate. Next, we have investigated the response of guanine crystal to the magnetic field by using the moire pattern to determine that the guanine plate is parallel to the substrate. Furthermore, it makes possible to estimate the quite small angle between the guanine crystals and substrate surface from the pattern period of moire stripes measured by optical observation system. The time dependences of the ratio of guanine crystals oriented in the horizontal magnetic field direction are measured by changing the magnetic field amplitude as shown in Fig.2. The experimental procedure is as follows: First, the horizontal magnetic field of 500 mT is applied and guanine crystals are aligned as the long axis of the guanine plate is parallel to the field (step A). Next, the vertical magnetic field of 200 mT is applied in order to align guanine crystals as the long axis of guanine plate is orthogonal to the field and the moire pattern disappear (step B) [2]. From this state, the horizontal magnetic field which is orthogonal to the first horizontal filed is applied and moire patterns appear again (step C). As shown in the figure, the guanine crystal plates quickly oriented to the horizontal direction with the magnetic field of 350 mT or more. This suggests that the magnetic field operates moire pattern switching which is effective to obtain a reference signal. The dependence of orientation time of guanine crystal upon the angle between the long axis of guanine plate and horizontal magnetic field and the tilt angle dependence of reflection brightness from the guanine plate will also be presented.

Electro-Caloric Properties of BT/PZT Multilayer Thin Films Prepared by Sol-Gel Method.

In this study, Barium Titanate (BT)/Lead Zirconate Titanate (PZT) multilayer thin films were fabricated by the spin-coating method on Pt (200 nm)/Ti (10 nm) SiO2 (100 nm)/P-Si (100) substrates using BaTiO3 and Pb(Zr0.90Ti0.10)O3 metal alkoxide solutions. The coating and heating procedure was repeated several times to form the multilayer thin films. All of BT/PZT multilayer thin films show X-ray diffraction patterns typical to a polycrystalline perovskite structure and a uniform and void free grain microstructure. The thickness of the BT and PZT film by one-cycle of drying/sintering was approximately 50 nm and all of the films consisted of fine grains with a flat surface morphology. The electrocaloric properties of BT/PZT thin films were investigated by indirect estimation. The results showed that the temperature change ΔT can be calculated as a function of temperature using Maxwell's relation; the temperature change reaches a maximum value of ~1.85 °C at 135 °C under an applied electric field of 260 kV/cm.

(Invited) Fabrication of Copper/Carbon Nanotube Composite Films Using Plating Techniques

Carbon nanotubes (CNTs) [1,2] have excellent thermal conductivity [3], extremely high current-carrying capacity (ampacity), i.e., stable electrical resistance in the presence of high currents [4], and superior mechanical properties [5,6]. Metal/CNT composites are therefore expected to be potential functional materials, and there have been many investigations concerning the fabrication of metal/CNT composites [7,8]. Composite plating is one promising process for the fabrication of metal/CNT composite films, and its application to such has been investigated [9]. In particular, Cu/CNT composite films are expected to be used for electronics applications. CNTs are generally categorized into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs). CNTs have anisotropic electrical and thermal conductivity, i.e., they have higher electrical and thermal conductivity in the axis direction than in the direction perpendicular to the axis direction. In this study, Cu/MWCNT and Cu/SWCNT composite films were fabricated using composite plating techniques, including electroplating and electroless plating. The dispersibility of CNTs in the plating baths is extremely important for composite plating with CNTs that are hydrophobic. Polyacrylic acid (mean molecular weight 5000) is an effective dispersant for MWCNTs in an acidic copper sulfuric bath [10], and Cu/MWCNT composite films with a homogeneous MWCNT distribution have been formed by electroplating using such a Cu/MWCNT composite bath [11,12]. Metal/MWCNT composite films, including the Cu/MWCNT composite film, intrinsically have a tendency toward a bumpy surface morphology due to the (anisotropic) electrical conductivity of MWCNTs [13]. However, a relatively flat surface morphology could be obtained using appropriate current densities (cathode overpotentials) [14] or surfactants [15]. In addition, reverse current electrodeposition could be used to increase the MWCNT content in Cu/MWCNT composite films [16]. Cu/MWCNT composite films have also been obtained by electroless plating using an alkaline bath. Ethylenediaminetetraacetic acid (EDTA), glyoxylic acid and sodium dodecyl sulfate (SDS) + hydroxypropyl cellulose (HPC) were used as a complexing agent, a reducing agent and surfactants for MWCNTs, respectively [17]. The Cu/MWCNT composite films were also successfully fabricated on an acrylonitrile butadiene styrene resin substrate [18]. SWCNTs have the smallest diameter among CNTs and have a tendency to form a characteristic aggregate known as a bundle. This bundle cannot be disintegrated to a primary particle, i.e., single SWCNTs, with the addition of dispersants alone. The use of both a powerful mechanical disintegration method and a dispersant is effective for the disintegration of SWCNT bundles. The selection of dispersants for SWCNTs is also important. In this study, trimethyl stearyl ammonium chloride (TMSAC), which is a cationic surfactant, was selected to prepare a Cu/SWCNT composite electroplating bath [19]. Cu/SWCNT composite films with relatively homogeneous SWCNT distribution were formed by electroplating. Cu/SWCNT composite films with homogeneously dispersed SWCNTs were also fabricated by electroless plating using a bath containing EDTA, glyoxylic acid, SDS+HPC (Fig. 1) [20]. References A. Oberlin, M. Endo and T. Koyama, J. Cryst. Growth, 32, 335 (1976).S. Iijima, Nature, 354, 56 (1991).S. Berber, Y.K. Kwon and D. Tomanek, Phys. Rev. B, 84, 4613 (2000).Z. Yao, C.L. Kane and C. Dekker, Phys. Rev. Lett., 84, 2941 (2000).M.F. Yu, O. Lourie, M.J. Dyer, K. Moloni, T.F. Kelly and R.S. Ruoff, Science, 287, 637 (2000).J.P. Lu, Phys. Rev. Lett., 79, 1297 (1997).S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi, A. Kawasaki and T. Tsukada, Scr. Mater., 63, 375 (2010).A.K. Shukla, N. Nayan, S.V.S.N. Murty and S.C. Sharma, Mater. Sci. Eng. A, 560, 365 (2013).X.H. Chen, J.C. Peng, X.Q. Li, E.M. Deng, J.X. Wang and W.Z. Li, J. Mater. Sci. Lett., 20, 2057 (2001).S. Arai and M. Endo, Electrochem. Commun., 5, 797 (2003).S. Arai and M. Endo, Electrochem. Solid-State Lett., 7(3), C25 (2004).S. Arai and M. Endo, Electrochem. Commun., 7, 19 (2005).S. Arai, M. Endo and N. Kaneko, Carbon, 42, 641 (2004).S. Arai, T. Saito and M. Endo, J. Electrochem. Soc., 157(3), D147 (2010).S. Arai, T. Saito and M. Endo, J. Electrochem. Soc., 157(3), D127 (2010).S. Arai, Y. Suwa and M. Endo, J. Electrochem. Soc., 158(2), D49 (2011).S. Arai and T. Kanazawa, ECS J. Solid State Sci. Technol., 3, P201 (2014).S. Arai and T. Kanazawa, J. Electrochem. Soc., 162 (1), D68 (2015).T. Ogasawara, M. Shimizu and S. Arai, Proc. ADMETA Plus 2017, pp. 54-55 (2017).S. Arai, T. Osaki, M. Hirota and M. Uejima, Mater. Today Commun., 7, 101 (2016). Figure 1

Revisitation of the structure zone model based on the investigation of the structure and properties of Ti, Zr, and Hf thin films deposited at 70–600 °C using DC magnetron sputtering

The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantitative data on the lattice strain, crystallite size, surface roughness, and electrical resistivity reduced to that of the bulk material were plotted both against the unnormalized and normalized substrate temperatures. The latter data plots show a smaller dispersion than the former ones. The lattice strain and reduced resistivity of all Ti, Zr, and Hf thin films display a sharp bend at a normalized temperature of ∼0.30–0.35. The film surface, cross-sectional morphologies, and film property changes display a clear transition from zones 1 to 2 through zone T. The data obtained in this paper are utilized to systematically explain the effectiveness and appropriateness of the use of the normalized substrate temperature to categorize the film structure, morphologies, and properties of thin films.The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantit...

Effects of deposition time and current density on PbO2 electrosynthesis from methanesulfonate electrolyte

This work investigated the effects of current density and deposition time on the properties of electrodeposited PbO2. The PbO2 preparation was conducted on Ti/SnO2–Sb substrates by galvanostatic anodic deposition in a newly proposed methanesulfonate electrolytic solution. Phase constituents and microstructures of the deposited PbO2 coatings were characterized. Increasing current density in the range ≤ 100 mA cm− 2 leads to the formation of highly textured coatings with an increased content of α-PbO2 phase. Concurrently, a high current density favors a compact and flat surface morphology. The study of deposition time indicates a change of crystallite growth manner from an initially random growth to a later-stage preferred growth along distinct orientations. The change of crystallite growth is corroborated by the cross-sectional microstructures of the PbO2 deposits. The microstructural transition occurs only in the initial deposition stage. After a brief period, prolonged electrodeposition barely changes the surface morphology of PbO2 coatings.

Kinetically Controlled Growth of Phase‐Pure SnS Absorbers for Thin Film Solar Cells: Achieving Efficiency Near 3% with Long‐Term Stability Using an SnS/CdS Heterojunction

AbstractFacile control over the morphology of phase pure tin monosulfide (SnS) thin films, a promising future absorber for thin film solar cells, is enabled by controlling the growth kinetics in vapor transport deposition of congruently evaporated SnS. The pressure during growth is found to be a key factor in modifying the final shape of the SnS grains. The optimized cube‐like SnS shows p‐type with the apparent carrier concentration of ≈1017 cm−3 with an optical bandgap of 1.32 eV. The dense and flat surface morphology of 1 µm thick SnS combined with the minimization of pinholes directly leads to improved diode quality and increased shunt resistance of the SnS/CdS heterojunction (cell area of 0.30 cm2). An open‐circuit voltage of up to 0.3068 V is achieved, which is independently characterized at the Korea Institute of Energy Research (KIER). Detailed high‐resolution transmission electron microscopy analysis confirms the absence of detrimental secondary phases such as Sn2S3 or SnS2 in the SnS grains or at intergrain boundaries. The initial efficiency level of 98.5% is maintained even after six months of storage in air, and the final efficiency of the champion SnS/CdS cell, certified at the KIER, is 2.938% with an open‐circuit voltage of 0.2912 V.

Mapping of n‐GaN Schottky Contacts With Wavy Surface Morphology Using Scanning Internal Photoemission Microscopy

We characterized the effects of surface morphology on the electrical properties of n‐GaN drift‐layers by using scanning internal photoemission microscopy (SIPM). We grew 12‐μm‐thick low carrier concentration (approximately 1 × 1016 cm−3) n‐GaN layers with both flat and wavy surface morphologies on freestanding GaN substrates by metal organic chemical vapor deposition. In the SIPM results, the samples with flat surfaces exhibited a uniform photocurrent distribution independently of the carrier concentration. In contrast, wavy patterns in the photocurrent maps were the same as the surface morphology for samples with low carrier concentration. These results indicate that the amount of C incorporated during the growth was affected by the off‐angle of the GaN surface, and the carrier compensation by C atoms was changed. We demonstrated that SIPM is a powerful tool for nondestructively visualizing the inhomogeneity of the carrier compensation over the wafers.

Polarity Control of GaN and Realization of GaN Schottky Barrier Diode Based on Lateral Polarity Structure

This paper reports investigation on a polarity control scheme of GaN thin films and realization of Schottky barrier diode (SBD) fabricated on a lateral-polarity-structure (LPS) GaN without intentionally doping. Specifically, Ga-polar and N-polar GaN were grown simultaneously side by side on sapphire substrate with patterned AlN buffer. Due to the surface energy difference between two polarities, N-polar regions are n-type conductive with rough surface morphology, while Ga-polar regions are semi-insulating with atomic flat surface morphology. Annealing conditions of both ohmic contact and Schottky contact were investigated. Current–voltage (I–V) characteristic revealed that the SBD fabricated on LPS GaN has higher forward current, barrier height closer to 0.7 eV, and ideality factor closer to unity compared to SBD fabricated on conventional undoped GaN. The specific on-state resistance ( ${R}_{{ \mathrm{\scriptscriptstyle ON}}})$ for the SBD based on LPS GaN is 77 $\text{m}\Omega \cdot \text {cm}^{{{{2}}}}$ lower than the SBD fabricated on conventional GaN. With oxide passivation on SBD surface, forward current exceeds 0.2 A at 10 V, while reverse current is less than 10−5 A at −10 V, respectively. The utilization of LPS in SBD demonstrates a promising approach for the development of lateral n+/n− SBD with a simple fabrication scheme.

Ex-situ atomic force microscopy on the growth mode of SrRuO3 epitaxial thin film

The functional properties of devices based on perovskite oxides depend strongly on the growth modes that dramatically affect surface morphology and microstructure of the hetero-structured thin films. To achieve atomically flat surface morphology, which is usually a necessity for the high quality devices, understanding of the growth mechanism of heteroepitaxial thin film is indispensable. In this study, we explore heteroepitaxial growth kinetics of the SrRuO3 using intermittent growth scheme of pulsed laser epitaxy and ex-situ atomic force microscopy. Two significant variations in surface roughness during deposition of the first unit cell layer were observed from atomic force microscopy indicating the possible formation of the half unit cell of the SrRuO3 before the complete formation of the first unit cell. In addition, layer-by-layer growth mode dominated during the first two unit cell layer deposition of the SrRuO3 thin film. Our observation provides underlying growth mechanism of the heteroepitaxial SrRuO3 thin film on the SrTiO3 substrate during the initial growth of the thin film.

Hydrogen production over ternary supported Ni/Al2O3-clinoptilolite-CeO2 nanocatalyst via CH4/CO2 reforming: Influence of support composition

The effect of Al2O3-Clinoptilolite-CeO2 support with different Al2O3 and clinoptilolite contents used in Ni-based Nano catalysts are studied for enhancing catalyst production costs by replacing Al2O3 with clinoptilolite. The nanocatalysts are characterized by XRD, BET, FESEM, FTIR and EDX techniques and tested for dry reforming of methane. With addition of alumina the specific surface area, NiO dispersion, surface morphology and catalytic activity of the samples are improved. However, the addition of clinoptilolite reduces specific surface area, increases crystallite size, and improves the crystallinity. CeO2 as a support promoter has positive impact on surface morphology and improves NiO particles size and activity. The Ni/Al2O3-CeO2 nanocatalyst has the best activity, highest specific surface area, proper NiO species dispersion and flat surface morphology. However, the results of Ni/Al2O3(60%)-Clinoptilolite(30%)-CeO2(10%) nanocatalyst in terms of catalytic performance and characterizations are so close to the results of the outstanding nanocatalyst (Ni/Al2O3-CeO2). Assessing similar feed conversions at high temperatures over both mentioned nanocatalysts are one of the important outcomes of this research. However, the most important result of this study is the reduction of 30 wt % of alumina consumption with achieving same results to the Ni/Al2O3-CeO2 nanocatalyst.

Transferable single-crystal GaN thin films grown on chemical vapor-deposited hexagonal BN sheets

Single-crystal gallium nitride (GaN) layers were directly grown on centimeter-scale hexagonal boron nitride (h-BN). Using chemical vapor deposition (CVD), centimeter-scale h-BN films were synthesized on a single-crystal Ni(111) and readily transferred onto amorphous fused silica supporting substrates that had no epitaxial relationship with GaN. For growing fully coalescent GaN layers on h-BN, the achievement of high-density crystal growths was a critical growth step because the sp2-bonded h-BN layers are known to be free of dangling bonds. Unlike GaN layers grown on a typical heterogeneous sapphire substrate, the morphological and microstructural results strongly suggest a high-density growth feature that is driven by the atomic cliffs inherent in the CVD-grown h-BN layers. More importantly, the GaN layers grown on CVD-grown h-BN exhibited a flat and continuous surface morphology with well-aligned crystal orientations both along the c-axis and in-plane, indicating the characteristics of GaN heteroepitaxy on h-BN.