Low-temperature Growth Technique Research Articles

Erratum: “Epitaxial growth of GaN films on nearly lattice-matched hafnium substrates using a low-temperature growth technique” [APL Mater. 4, 076104 (2016)

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Delocalization of vortex in SmBa2Cu3O7−δ superconducting films with BaHfO3 nano-rods

Transport measurements revealed flux pinning properties and vortex phases in SmBa2Cu3O7−δ (Sm123) superconducting films with BaHfO3 nano-rods on LaAlO3 substrates. The films have large matching fields BΦ up to 9.9 T, nano-rod diameters of ∼6 nm, and a slight Tc degradation with Tc ∼ 91.8 K by using the low temperature growth technique. According to the transport results, a small critical exponent ∼4 indicates the presence of a Bose-glass phase in the films. Double peaks of the flux pinning force density are unexpectedly observed at high temperatures over 80 K, which is accompanied by steep drops of the crossover magnetic fields between the single vortex pinning and the collective pinning states. The drops are explained by the delocalization of the vortex where the vortex is pinned by many nano-rods in the single vortex pinning state. From the viewpoint of the vortex delocalization, we conclude that BΦ should be less than 11 T for applications at liquid nitrogen temperature.

Model for Low-Temperature Growth of Gallium Nitride

A low growth temperature is essential to realize low-cost and large-area GaN-based lighting and display. In this work, through detailed investigation under plasma-assisted molecular beam epitaxy, a physical model for low-temperature growth of GaN under N-rich conditions is proposed based on the fact that the desorption process of Ga adatoms can be ignored and the energy for lattice incorporation of Ga adatoms comes only from active N species. A normalized diffusion length (NDL, a dimensionless parameter) is also introduced to provide further insight: the diffusion rate and diffusion time of Ga adatoms are determined by the growth temperature and N flux, respectively; meanwhile the average distance between Ga adatoms is affected by both Ga flux and N flux. Excellent agreement between theoretical predictions and experimental results validates this model and demonstrates the importance of NDL in optimizing the growth condition. The model and NDL could be applied in growing III-nitrides under N-rich conditions by various low-temperature growth techniques where group-III adatoms are unable to incorporate into the lattice by their own kinetic energy.

(Invited) Low-Temperature Growth of Orientation-Controlled Large-Grain Ge-Rich SiGe on Insulator at Controlled-Position for Flexible Electronics

A technique for low-temperature (≤300°C) formation of large-grain (≥10 μm) Ge-rich SiGe crystals on insulator, whose orientation and position are controlled, should be developed to realize flexible electronics. To achieve this, the gold-induced layer-exchange crystallization technique using a-SiGe/Au stacked structures has been investigated. By introduction of diffusion control layers into the a-SiGe/Au interface, (111)-oriented large-grain Ge-rich SiGe crystals are achieved on insulating substrates at low temperatures (≤300°C). Moreover, position control of large-grain crystals becomes possible by patterning the diffusion control layers. This low-temperature growth technique is expected to be useful to realize flexible electronics.

Epitaxial growth of GaN films on nearly lattice-matched hafnium substrates using a low-temperature growth technique

We demonstrated epitaxial growth of GaN (0001) films on nearly lattice-matched Hf (0001) substrates by using a low-temperature (LT) epitaxial growth technique. High-temperature growth of GaN films results in the formation of polycrystalline films due to significant reaction at GaN/Hf heterointerfaces, while LT-growth allowed us to suppress the interfacial reactions and to obtain epitaxial GaN films on Hf substrates with a GaN112̄0//Hf112̄0 in-plane orientation. LT-grown GaN films can act as buffer layers for GaN growth at high temperatures. The interfacial layer thickness at the LT-GaN/Hf heterointerface was as small as 1 nm, and the sharpness of the contact remained unchanged even after annealing up to approximately 700 °C, which likely accounts for the dramatic improvement in GaN crystalline quality on Hf substrates.

Clarification and mitigation of marked Jc decrease at low magnetic fields of BaHfO3-doped SmBaCuO3 thin films deposited on seed layer

In accordance with the results of our previous research, a low-temperature growth (LTG) technique is effective for expanding the lower growth temperature region of c-axis-orientated SmBa2Cu3Oy (SmBCO) thin films. However, BaHfO3 (BHO)-doped LTG films show a marked decrease in Jc at low magnetic fields compared with conventional PLD films. In this study, we aimed to clarify the mechanism of Jc decrease and investigated the thickness dependence of the seed layer on the (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (100) single crystal. The obtained results indicate that Jc decreased at low magnetic fields as the thickness of the seed layer increased. It is suggested that flux line kinks produced by flux motion in the seed layer would lead to the depinning of flux lines from BHO nanorods in the upper layer. Thus, we added Y2O3 into the seed layer to trap flux lines in the seed layer. Consequently, we improved Jc in the low magnetic field region even in the films prepared by using the LTG technique.

Vortex pinning at low temperature under high magnetic field in SmBa2Cu3Oy superconducting films with high number density and small size of BaHfO3 nano-rods

We have fabricated 5.6 vol.% BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) films at a low substrate temperature of 750 °C by using the low temperature growth (LTG) technique with a seed layer. Using the LTG technique, we can obtain a purely c-axis oriented SmBCO film even at low growth temperatures. The LTG technique also greatly increases the number density of BHO nanorods. The size and matching field of the BHO nanorods in the films were 5.4 nm and 9.9 T. Transport measurements were carried out, and a high irreversibility field (Birr) and strong flux pinning force density (Fp) were obtained. The Birr was 15.1 T at 77 K for B//c. The maximum Fp of 407 GN m−3 in 10 T at 40 K and 770 GN m−3 from 9 to 17 T at 20 K have been measured. We believe that the LTG technique can be considered as important for improving of flux pinning performance in BaMO3 (BMO: M = Zr, Sn and Hf)-doped SmBCO coated conductors.

(Invited) Gold-Induced Low-Temperature (

A low-temperature (¡Ü300¡ãC) growth technique of quasi-single crystal, i.e., orientation-controlled large-grain (¡Ý10 ¦Ìm), Ge-related semiconductors, on insulator is desired for realization of advanced flexible electronics. To achieve this, we have developed the gold-induced layer-exchange crystallization technique using a-SiGe/Au stacked structures. By introduction of diffusion barrier with appropriate thickness into the a-SiGe/Au interface, (111)-oriented quasi-single crystal SiGe is achieved on insulating substrates at low temperatures (~300¡ãC). Based on these results, this technique is developed to formation of quasi-single crystal Ge on flexible plastic sheets. The grown layers have high carrier mobility, because residual Au hardly deteriorates the electrical properties of grown layers due to low solubility of Au in Ge. This technique will facilitate realization of advanced flexible electronics.

Superconducting Properties in SmBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> Films With High Density of BaHfO<sub>3</sub> Nanorods Fabricated With a Seed Layer

A high density of BaMO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BMO) nanorods within a REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (REBCO) film can be generated by heavy doping of the BMO. This is very effective in improving superconducting properties in high magnetic fields. However, heavy doping causes a significant T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> reduction. Introduction of a high density of BMO nanorods into REBCO films without reduction in T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is required. To this end, we deposited SmBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (SmBCO) films with various amount of BaHfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BHO) by a pulsed laser deposition (PLD) method using a seed-layer technique and a low-temperature growth (LTG) technique. Using this technique, we can fabricate a purely c-axis-oriented SmBCO film even at low substrate temperatures T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The SmBCO films with BHO were fabricated at low T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> of 750 °C without heavy doping of BHO. As a result, the BHO nanorods became thinner and denser than those within SmBCO films fabricated by conventional PLD methods at high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The maximum density was 4780/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">φ</sub> of the film reached 9.9 T. These samples showed high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (> 90 K). We have therefore successfully fabricated high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> SmBCO films with high densities of BHO nanorods using the LTG technique.

Fast and low temperature growth of electron transport layers for efficient perovskite solar cells

A fast, simple and low temperature growth technique is described for the preparation of high structural and optical quality ZnO layers. These layers are shown to act as efficient selective contacts in perovskite solar cells.

Flux pinning properties and microstructures of a SmBa2Cu3Oy film with high number density of BaHfO3 nanorods deposited by using low-temperature growth technique

To enhance Jc in high magnetic fields, we fabricated a SmBa2Cu3Oy (SmBCO) film with a high number density (2830/µm2) of BaHfO3 (BHO) nanorods by pulsed laser deposition (PLD) adopting a low-temperature growth (LTG) technique (LTG-SmBCO + BHO). The LTG technique consists of seed layer deposition and subsequent film deposition at a lower temperature. The number density of BHO nanorods in the film was approximately 4 times higher than that in a BHO-doped SmBCO film fabricated by conventional PLD without a seed layer. The flux pinning performance of the LTG-SmBCO + BHO film (Fp = 23.8 GN/m3 at 77 K under 4.5 T) was comparable to the reported record high value of 28.3 GN/m3 at 77 K.

Improvement of critical current densities in SmBa2Cu3Oy, films with BaHfO3 nano-rods using low temperature growth technique

We studied growth substrate temperature dependent morphologies of BaHfO3 (BHO) nano-rods for SmBa2Cu3Oy, (SmBCO) films with BHO fabricated by pulsed laser deposition (PLD) method. The morphology of BHO nano-rods within the SmBCO matrix could be controlled by changing substrate temperatures adoping a Low Temperature Growth (LTG) technique. Using the LTG technique, we could fabricate SmBCO films showed c-axis orientation even at low substrate temperature during deposition without a degradation of superconducting properties, which is one of the most advantages of the LTG technique. In this study, we found an optimal morphology of the BHO nano-rods and the morphology was fine, straight and various growth directions. The BHO nano-rods were more effective to improve the Jc in a magnetic field than other morphologies of the BHO nano-rods.

AlGaN/GaN heterostructure prepared on a Si (110) substrate via pulsed sputtering

GaN films were grown on Si (110) substrates using a low-temperature growth technique based on pulsed sputtering. Reduction of the growth temperature suppressed the strain in the GaN films, leading to an increase in the critical thickness for crack formation. In addition, an AlGaN/GaN heterostructure with a flat heterointerface was prepared using this technique. Furthermore, the existence of a two dimensional electron gas at the heterointerface with a mobility of 1360 cm2/Vs and a sheet carrier density of 1.3 × 1013 cm−2 was confirmed. Finally, the use of the AlGaN/GaN heterostructure in a high electron mobility transistor was demonstrated. These results indicate that low-temperature growth via pulsed sputtering is quite promising for the fabrication of GaN-based electronic devices.

Low temperature growth of carbon nanotubes on carbon fibre to create a highly networked fuzzy fibre reinforced composite with superior electrical conductivity

We report a method for the growth of carbon nanotubes on carbon fibre using a low temperature growth technique which is infused using a standard industrial process, to create a fuzzy fibre composite with enhanced electrical characteristics. Conductivity tests reveal improvements of 510% in the out-of-plane and 330% in the in-plane direction for the nanocomposite compared to the reference composite. Further analysis of current–voltage (I–V) curves confirm a transformation in the electron transport mechanism from charge – hopping in the conventional material, to an Ohmic diffusive mechanism for the carbon nanotube modified composite. Single fibre tensile tests reveal a tensile performance decrease of only 9.7% after subjecting it to our low temperature carbon nanotube growth process, which is significantly smaller than previous reports. Our low-temperature growth process uses substrate water-cooling to maintain the bulk of the fibre material at lower temperatures, whilst the catalyst on the surface of the carbon fibre is at optimally higher temperatures required for carbon nanotube growth. The process is large-area production compatible with bulk-manufacturing of carbon fibre polymer composites.

The formation and UV-blocking property of flower-like ZnO nanorod on electrospun natural cotton cellulose nanofibers

We report a simple and effective route to fabricate branched hierarchical flower-like nanostructures of ZnO on natural cotton cellulose fiber by combining electrospinning and the low-temperature hydrothermal growth technique. First, natural cotton cellulose nanofibers were prepared by electrospinning cotton cellulose /LiCl/DMAc solution. The electrospun cotton cellulose nanofibers served as flexible substrate, on which the branched, highly uniform, and dense flower-like ZnO were hydrothermally grown. The as-prepared cotton cellulose/ZnO nanocomposite fibers were characterized by SEM, HRTEM, EDS, TG, and UV-vis spectrophotometry. The modified cotton cellulose nanocomposite fibers were not only exhibiting dispersed uniformly, but also rendered excellent protection against UV radiation because of the incorporation of flower-like ZnO nanostructures. Therefore, the as-prepared nanocomposite fibers demonstrate a significant performance in ultraviolet protection and provide a potential application for ultraviolet detection.

LTG 法を用いて作製したBaHfO&lt;sub&gt;3 &lt;/sub&gt;添加SmBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;i&gt;&lt;sub&gt;y &lt;/sub&gt;&lt;/i&gt;薄膜の 超伝導特性及び微細構造観察

We have proposed a low-temperature growth (LTG) technique which makes it possible to fabricate SmBa2Cu3Oy (SmBCO) films with c-axis orientation in a wide range of growth temperatures without the degradation of superconducting properties. In this study, using the LTG technique, we fabricated SmBa2Cu3Oy (SmBCO) films with BaHfO3 (BHO) nano-rods at low substrate temperatures using the pulsed laser deposition (PLD) method. The effect of low substrate temperatures on BHO nano-rods in SmBCO films are discussed in terms of their microstructures and superconducting properties. The nano-rods were observed clearly in transmission electron microscopic (TEM) images of the films. We found that the morphologies of the nanorods were small in diameter, had high densities and inclined along the c-axis of SmBCO. In the case of the substrate temperature of 750°C, the diameter and density of nano-rods with 2.7 vol.% BHO-doping were 5.7 nm and 2300 /μm2, respectively. The film showed high flux pinning force, Fp, of 25 GN/m3 (77 K, B//c) in a high field, 4 T. Furthermore, in the film, the angular dependence of Jc showed a broad peak at B//c, due to the flux pinning by nano-rods growing in various directions.

The influence of unintentional Au impurities on the doping properties of Si nanowires

Gold is the most commonly used catalyst for the growth of silicon nanowires. During the growth process, Au atoms are inevitably incorporated into the nanowire. In this study, the impact of Au impurities on the doping of silicon nanowires is systematically studied based on first-principles calculations. Our calculations demonstrate that the Au impurity prefers to occupy the substitutional site in the centre of nanowire, which results in midgap deep defect levels, forming a carrier combination centre. Further analysis indicates that both n- and p-type doping efficiencies are strongly inhibited by the unintentional Au impurity in the nanowire. Our results suggest that effective methods should be adopted to reduce the concentration of Au impurities in silicon nanowires, such as low-temperature growth and self-catalysed growth techniques.

ZnO/ZnS–PdS core/shell nanorods: Synthesis, characterization and application for photocatalytic hydrogen production from a glycerol/water solution

The composite photocatalysts comprised of ZnO nanorods core and ZnS–PdS heterostructural shell layer with different PdS/ZnS molar ratios were prepared via the combination of a low-temperature hydrothermal growth and cation exchange technique. The SEM and TEM results reveal that the ZnO nanorods, with the diameters of about 150nm and the lengths of ranging from a few hundred nanometers to several micrometers, were coated by a layer of ZnS and PdS composite shell mainly consisting of nanocrystal in size of 5–8nm. The molar ratios of PdS/ZnS in shell layer strongly affect the morphology, distribution of components, photo absorption and photocatalytic activity of the ZnO/ZnS–PdS core/shell nanorods. With coupling low band gap PdS, the ZnO/ZnS–PdS nanorods have a much higher light absorption capability than ZnO/ZnS. As a result, the as-prepared ZnO/ZnS–PdS nanocomposites exhibited much higher catalytic efficiency for the hydrogen production from glycerol aqueous solution. The superior photo absorption properties and photocatalytic performance of the ZnO/ZnS–PdS core/shell nanorods may be ascribed to the heterostructure, which enhanced the separation of photoinduced electron–hole pairs and improved the charge transfer ability and meanwhile, efficiently inhibited the recombination of photoinduced electron–hole pairs.

Synthesis, characterization and enhanced photocatalytic performance of Ag2S-coupled ZnO/ZnS core/shell nanorods

A series of composite photocatalysts comprised of ZnO nanorods core and ZnS–Ag2S heterostructural shell layer with different Ag2S/ZnS molar ratios have been synthesized via the combination of a low-temperature hydrothermal growth and cation exchange technique. The core/shell nanorods, with the diameters of about 150nm and the lengths of ranging from a few 100nm to several micrometers, were fabricated by coating the ZnO nanorods with a layer of ZnS and Ag2S composite shell mainly consisting of nanocrystals with the diameters of about 5–8nm. The characterization from SEM, TEM, EDX, XPS, and UV–Vis DRS reveals that the molar ratio of Ag2S/ZnS in shell layer strongly affects the morphologies, distribution of components, photo absorption, and photocatalytic performance of the ZnO/ZnS–Ag2S core/shell nanorods. Due to the coupling with low bandgap material Ag2S, the ZnO/ZnS–Ag2S nanorods have a much higher solar-simulated light absorption capability than that of ZnO/ZnS. As a result, the as-prepared ZnO/ZnS–Ag2S nanocomposites exhibited much higher catalytic efficiency for the hydrogen production from glycerol aqueous solution. The superior photo absorption properties and photocatalytic performance of the ZnO/ZnS–Ag2S core/shell nanorods may be ascribed to the heterostructure, which enhanced the separation of photo-induced electron–hole pairs.

Systematic Study of the Structure–Property Relationships of Branched Hierarchical TiO2/ZnO Nanostructures

We report a simple and effective route for fabricating branched hierarchical nanostructures of TiO(2)/ZnO by combining electrospinning and the low-temperature hydrothermal growth technique. First, TiO(2) nanofibers were prepared by electrospinning polystyrene (PS)/titanium tetraisopropoxide (Ti(OiPr)(4)) solutions onto glass substrates followed by calcination at 500 °C. The electrospun TiO(2) nanofibers served as a 3D primary platform upon which the branched, highly uniform, and dense secondary ZnO nanorods were hydrothermally grown. We observed that the concentration of Ti(OiPr)(4) in the polystyrene solution has a significant effect on the surface roughness and areal material ratio of the electrospun fibers. Most significantly, the morphology of the branched secondary ZnO nanorods and the overall charge transfer capacity of the nanoheterostructured systems are controlled by the density of the TiO(2) platform. This study demonstrates that, by properly choosing the synthesis parameters, it is possible to fine-tune the microscopic and macroscopic properties of branched hierarchical metal-oxide systems. The presented approach can be applied to the development of controlled, reproducible, miniaturized, and robust high-performance metal-oxide photovoltaic and photocatalytic systems.