Low-temperature Growth Technique Research Articles

Development of Novel Ternary Alloy of CSiSn for Low-Cost Next Generation Photovoltaics

The growing need for highly efficient solar cells calls for significant advancements in the development of a new material system to meet the needs of low-cost and low-cost production. Current multi-junction solar cell alternatives are more costly to produce. This research showcases the development and analysis of a novel ternary material system, The CSiSn (CST) alloy, which shows potential for creating low-cost material with high absorption in of solar spectrum. In this work, the following aspects regarding the CST material are investigated: 1) Material modeling using density functional theory, 2) electronic band structure estimations, 3) low-temperature material growth technique via Plasma Enhanced Chemical Vapor Deposition (PE-CVD) system; 4) advanced material and optical characterizations of CST alloys.

The growth aspects and experimental techniques for the characterization of amino acid L-histidine hybrid crystals for nonlinear optical device applications

The development of crystal growth and measurement methods opens new possibilities for studying materials with remarkable nonlinear optical features. The development of bulk crystals is a constant concern to be beneficial for device applications. This study focuses on the development of nonlinear optical crystals of l-histidine complexes, characterization approaches, and prospective applications. The solution growth approach, a straightforward, inexpensive, and low-temperature growth technique, was adopted broadly. Recent studies show that l-histidine derivatives have potential optical, SHG, thermal, dielectric, and mechanical properties, making them an excellent choice for nonlinear optical devices. In this work, structural, spectroscopic, chemical composition, linear and nonlinear optical analyses, thermal, and dielectric characterizations of l-histidine derivatives were conducted. Most of the l-histidine complexes were found to be crystallized in orthorhombic and monoclinic crystal systems with P212121 and P21 space groups. The crystalline perfections of the samples were analyzed by the HR-XRD method. The energy-dispersive X-ray (EDX) spectroscopic technique was applied to evaluate the chemical content of the compounds. FT-IR and FT-Raman techniques were used to recognize the molecular vibrations and functional groups of the l-histidine derivatives. The UV-visible and photoconductivity studies were done to examine the optical behaviors of the developed crystals. Most of the crystals were found to have excellent optical transparency and wide bandgaps. It has been observed that l-histidine hydro-fluoride dehydrate and l-histidine tetrafluoroborate are found to have the highest second harmonic generation (SHG) efficiencies. The dielectric analyses were utilized to study the dielectric constant and dielectric loss variations with the applied frequency. According to the thermal analyses, most of the crystals were found to have substantial thermal stabilities suitable for device applications.

Low-Temperature Vapor-Phase Growth of 2D Metal Chalcogenides.

2D metal chalcogenides (MCs) have garnered significant attention from both scientific and industrial communities due to their potential in developing next-generation functional devices. Vapor-phase deposition methods have proven highly effective in fabricating high-quality 2D MCs. Nevertheless, the conventionally high thermal budgets required for synthesizing 2D MCs pose limitations, particularly in the integration of multiple components and in specialized applications (such as flexible electronics). To overcome these challenges, it is desirable to reduce the thermal energy requirements, thus facilitating the growth of various 2D MCs at lower temperatures. Numerous endeavors have been undertaken to develop low-temperature vapor-phase growth techniques for 2D MCs, and this review aims to provide an overview of the latest advances in low-temperature vapor-phase growth of 2D MCs. Initially, the review highlights the latest progress in achieving high-quality 2D MCs through various low-temperature vapor-phase techniques, including chemical vapor deposition (CVD), metal-organic CVD, plasma-enhanced CVD, atomic layer deposition (ALD), etc. The strengths and current limitations of these methods are also evaluated. Subsequently, the review consolidates the diverse applications of 2D MCs grown at low temperatures, covering fields such as electronics, optoelectronics, flexible devices, and catalysis. Finally, current challenges and future research directions are briefly discussed, considering the most recent progress in the field.

Recent progress in low-temperature CVD growth of 2D materials

Abstract Two-dimensional (2D) materials have emerged as a promising class of materials with unique physical and chemical properties that offer exciting prospects for various applications. Among all the synthesis methods, chemical vapor deposition (CVD) techniques have demonstrated great advantages in the large-scale production of 2D materials with a controlled thickness. One of the main challenges in the growth of 2D materials is the need for high temperatures and crystalline substrates, which restrict the scalability and compatibility of 2D materials with existing manufacturing processes, due to the high thermal budget and the necessity to transfer the 2D films to secondary substrates. Low-temperature growth methods for 2D materials have the potential to overcome this challenge and enable the integration of 2D materials into a wide range of devices and applications. In recent years, there have been substantial efforts to develop low-temperature growth techniques for different 2D materials, including graphene, hexagonal boron nitride and transition metal dichalcogenides. These methods include thermal CVD, plasma-enhanced CVD, atomic layer deposition and metal-organic chemical vapor deposition. This review not only discusses the progress in the growth but also highlights the applications of low-temperature-grown 2D materials in various fields, such as field effect transistors, sensors, photodetectors, catalysts, batteries and supercapacitors.

Investigational studies of crystalline, optical, dielectric, thermal, mechanical, second besides third order nonlinear optical properties of urea itaconic acid solitary material

In this research work, we used low temperature growth technique (Slow cooling method) for the growth of nonlinear optical and antimicrobial activity of fully-fledged organic Urea Itaconic acid (UITA) crystal. The model was crystallised with a monoclinic crystal structure in the centrosymmetric space group P21/c. The single crystal X-ray diffraction (SXRD) method was used to determine the crystal characteristics of the compounds. To validate the presence of separate functional groups, a Fourier transform infra-red test is utilised. The crystallinity and phase purity of the entire crystal is confirmed by the X-ray diffraction pattern of the detected Bragg peaks. The optical transmission window and shorter UITA wavelength cut-off were established using UV-Vis-NIR studies. Defects were also analysed by the dielectric loss, dielectric constant and AC conductivity studies. The mechanical stability of growing crystal was required to identify using Vickers microhardness analysis and by the Hays-Kendall approach, the effect of hole size (ISE) and the proportional stability model (PSRM) was adequately explained. Using energy dispersion spectrometry, the presence of urea and itaconic acid was confirmed. The differential thermal analysis (DTA) and thermogravimetric (TG) technique were studied by thermal effects of crystal. Using Z scan method the good third order nonlinear response for different planes (1 0 0), (0 0 1) and (1 1 − 1) of the UITA crystal sample were determined. Potentially threatening microbe’s activity utilised to analysis antimicrobial chattels. UITA sample were taken into the solubility and width of the metastable region. The good crystal perfection is showed that the grown crystals using by HRXRD and etching studies. Using on classical nucleation theory, the final nucleation constraints such as phase to phase strain, Gibbs free energy transformation, critical radius, molecular count in the critical nucleus and nucleation rate were calculated for the UITA sample. Second Order NLO behaviour of the grown crystals were confirmed by Kurtz powder procedure.

Crystal Growth Simulation of BMO Nanorods in BMO-Doped REBCO Films With Seed layers

The self-organization of BaMO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BMO) nanorods in 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> films is important for enhancing the superconducting properties in magnetic fields. We previously reported the control of BMO self-organization using the seed layer technique, which included the low-temperature growth (LTG) technique. The LTG technique can achieve a high number density of BMO nanorods and excellent critical current density in magnetic fields at 4.2 K. To clarify the self-organization mechanism of BMO nanorods, we develop a three-dimensional Monte Carlo simulation and investigate the effect of the seed layer technique on the growth of BMO nanorods. Results show that the number density of BMO nanorods is affected by the seed layer deposited at a low deposition rate (v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DR</sub> ) and/or high substrate temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ). Moreover, we propose a growth kinetic factor (R) that includes v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DR</sub> , T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , and BMO volume fraction. Our simulation results of the number density are affected by R; therefore, Ris useful for predicting the number density of BMO nanorods.

High-quality Ge film grown on Si substrate and its thermodynamic mechanism

By right of the prominent properties, Ge film grown on Si substrate plays an important role in the field of optoelectronic devices. However, the dislocation density of Ge film grown on Si substrate is still high due to the relatively large lattice mismatch between Ge and Si of ~4.18% that hinders the further development of devices. In this work, high-quality Ge film grown on Si substrate has been obtained based on study of the thermodynamic mechanism. On the one hand, the thermodynamic mechanism of Ge film on Si substrate by First-principle calculation based on density functional theory; and then high-quality Ge films were achieved on Si substrate by the low temperature and high temperature two-step growth technique by molecular beam epitaxy accordingly. The as-grown 2.0 μm-thick Ge film show high quality with a full-width at half-maximums for Ge(004) of 110 arcsec and very smooth surface with a root-mean-square roughness of 0.2 nm. The Ge film achieved in this work is a promising candidate for the fabrication of optoelectronic devices.

Growth and Characterizations of GeSn Films with High Sn Composition by Chemical Vapor Deposition (CVD) Using Ge2H6 and SnCl4 for Mid-IR Applications

Epitaxial GeSn films present several advantages which can provide the semiconductor devices with higher frequency operation [1-2]. GeSn films have been theoretically and experimentally shown to become direct bandgap materials with about 6-10% of Sn composition [3-7]. This opens the room for potential optoelectronic applications such as amplifiers, lasers, photodetectors [8-13]. The red shift in the absorption due to the reduction of band-gap of the GeSn film enables the optoelectronic devices to operate in the mid-infrared (MIR) region [14-16]. However, it is very challenging to incorporate Sn into Ge crystal lattice due to the extremely limited solid solubility of Sn [17]. Therefore, low temperature growth techniques were developed to create non-equilibrium growth conditions so as to incorporate higher Sn content in high quality GeSn layer. In this work, the epitaxial growth of GeSn alloys with Sn content varying from 3.4 to 11% using Ge2H6 and SnCl4 as precursors in a CVD system under reduced pressure condition is reported in detail. Characterisation results are also presented. High quality GeSn film with Sn content as high as 11% has been achieved.The growth process consists of Ge buffer layer growth followed by GeSn epitaxial growth: 1 µm of Ge buffer layer was grown on 6“ Si wafers in the CVD reactor. Prior to actual growth of Ge, the wafer was baked in H2 at 1000°C for 2 min to remove the native oxide. 10% Ge2H6 diluted in H2 was used as Ge precursor, and H2 worked as the carrier gas. The Ge growth was then carried out at 400°C for ~10 min to target a thickness of 1 µm. The wafers were annealed soon after growth at ~850°C for another 20 min in H2 environment to reduce the threading dislocation density (TDD). Subsequently, SnCl4 was introduced into the chamber. The chamber temperature was kept below 350°C. Table I summarizes the growth conditions for some of the grown GeSn films. GeSn film with Sn content as high as 11% has been achieved successfully.Atomic force microscope (AFM) images in Figure 1(a)-(d) show that the RMS value of the surface roughness of the GeSn films is 0.52, 1.09, 0.95 and 0.91 nm for sample 1 to 4, respectively. The comprehensive studies showed that higher SnCl4flow rate, lower Ge2H6flow rate or higher growth temperature resulted in higher surface roughness (Figure 1(e)-(g)). Secondary ion mass spectrometry (SIMS) results shown in Figure 2 confirm the existence of Sn element and the Sn content. For sample 1 to 4, the Sn content is 3.4, 8, 10 and 11%, respectively.The X-Ray Diffraction (XRD) results of GeSn films are shown in Figure 3(a). It revealed that the growth temperature played the most important role in varying the Sn content in the GeSn film. The Sn content value extracted from rocking curve aligned well with the SIMS data. From the RSM mapping shown in Figure 3(b), sample 3 has a film relaxation of ~49% and compressive strain of ~0.7% based on models reported in the literatures [18-20].Etching pits density (EPD) measurements were carried out to study the threading dislocation density (TDD) of the GeSn films. Figure 4(a) shows the scanning electron microscope (SEM) image of sample 3 (Ge0.9Sn0.1) after EPD. The TDD of Ge0.9Sn0.1 is ~3.33 x 107cm-2. Figure 4(b) summarised that the TDD increases as Sn content increases which is due to the increased lattice mismatch, moreover, rapid thermal annealing (RTA) does not effectively reduce the TDD of the GeSn film.Raman analysis results are shown in Figure 5. The peak position of sample 3 (Ge0.9Sn0.1) is at 293.7 cm-1. Sn content and compressive strain were calculated to be 10 and 0.7%, respectively, by using the models in literature [21]. The values are consistent with those from XRD RSM and SIMS results. Figure 6 shows the absorption coefficient of GeSn films from ellipsometry analysis. Sn-induced red shift is observed. The cut off wavelength of the absorption extends from ~1,500 nm for bulk Ge to ~2,175 nm for sample 2 (Ge0.92Sn0.08), and it enables the devices fabricated to work in the MIR region.High resolution transmission electron microscopy (HRTEM) images in Figure 7(a)-(b) confirm that Ge buffer layer has a thickness of ~916.4 nm, while the thickness of GeSn film in sample 3 is ~175.9 nm. Figure 7(c) shows the selected area electron diffraction (SAED) pattern of the GeSn film and it concludes that the film is single crystalline.We would like to acknowledge support from the National Research Foundation Singapore under the Competitive Research Program (NRF-CRP19-2017-01). Figure 1

Effect on SmBa2Cu3Oy films of lattice strain induced by BaHfO3 nanorods

BaMO3 (BMO, M=Zr, Sn, Hf, etc.) is well known to undergo self-organisation into many nanorods in a REBCO film grown by vapour phase epitaxy. However, REBCO experiences strain resulting from the BMO nanorods and this strain causes the superconducting properties to deteriorate. In this study, we prepared SmBCO films containing 16 vol% BaHfO3 (BHO) using a pulsed laser deposition method. Deposition was accomplished by using a low-temperature growth (LTG) technique to grow the films even at low substrate temperatures. By decreasing the substrate temperature, the number density of the BHO nanorods, which is estimated from the critical current density in magnetic fields and the irreversibility line, increased and their diameter decreased. The lattice strain exerted upon SmBCO and BHO could conveniently be evaluated by conventional X-ray diffraction owing to the substantial BHO content. This evaluation indicated that, as the substrate temperature decreased, the tensile strain exerted upon SmBCO decreased, whereas the compressive strain experienced by BHO increased. These results indicate that the effect of stress exercised by the narrow nanorods on REBCO is small. Our findings suggest LTG to be an effective technique to prepare REBCO films with a high number density of BMO nanorods owing to the small amount of stress induced by these nanorods.

Optical characteristics of highly conductive n-type GaN prepared by pulsed sputtering deposition

We have characterized highly conductive Si-doped GaN films with a high electron mobility of 112 cm2V−1s−1 at an electron concentration of 2.9 × 1020 cm−3, prepared using pulsed sputtering deposition (PSD). With an increase in the doping concentration, the absorption edge was found to shift toward a higher energy level, owing to the Burstein-Moss effect, thus making this material suitable for the transparent conductive tunneling electrodes of visible and ultraviolet-A light-emitting diodes. The full width at half maximum value of the near-band-edge (NBE) emissions in a photoluminescence spectrum measured at 77 K was as small as 185 meV, even for the sample with the highest electron concentration of 2.9 × 1020 cm−3. Such sharp NBE emissions from PSD-grown heavily Si-doped GaN films can be explained by an analytical model with a low compensation ratio θ of around 0.1, which is consistent with the exceptionally high observed electron mobility. These results indicate the strong potential of the low-temperature PSD growth technique for the formation of high-quality, heavily Si-doped GaN.

Metalorganic vapor phase epitaxy growth and characterization of quaternary (Ga,In)(As,Bi) on GaAs substrates

The incorporation of dilute amounts of Bi into the host lattice of a III/V semiconductor has a strong influence on its electronic properties. The bandgap is strongly redshifted which makes these materials interesting for application in the near- to mid-infrared regime. Furthermore, the spin-orbit splitting is increased resulting in suppression of hot-hole producing Auger recombination, which makes the fabrication of highly efficient optical devices feasible. However, for ternary Ga(As,Bi) grown using metalorganic vapor phase epitaxy (MOVPE), it has proven difficult to achieve the desired composition of the ternary material. Therefore, the additional incorporation of indium (In) into Ga(As,Bi), which should induce a further redshift of the bandgap, is investigated and summarized in this paper. For deposition of quaternary (Ga,In)(As,Bi), two different low temperature growth techniques using MOVPE are conducted. The strain and photoluminescence peak positions of the samples are correlated to estimate the composition of the (Ga,In)(As,Bi) layers. It was found that the trimethylindium and tertiarybutylarsine supplies need to be carefully adjusted to grow high quality bulk materials and that the incorporation of indium is inversely related to the amount of incorporated Bi.

Epitaxial Ge0.81Sn0.19 Nanowires for Nanoscale Mid-Infrared Emitters.

Highly oriented Ge0.81Sn0.19 nanowires have been synthesized by a low-temperature chemical vapor deposition growth technique. The nanostructures form by a self-seeded vapor-liquid-solid mechanism. In this process, liquid metallic Sn seeds enable the anisotropic crystal growth and act as a sole source of Sn for the formation of the metastable Ge1-xSnx semiconductor material. The strain relaxation for a lattice mismatch of ε = 2.94% between the Ge (111) substrate and the constant Ge0.81Sn0.19 composition of nanowires is confined to a transition zone of <100 nm. In contrast, Ge1-xSnx structures with diameters in the micrometer range show a 5-fold longer compositional gradient very similar to epitaxial thin-film growth. Effects of the Sn growth promoters' dimensions on the morphological and compositional evolution of Ge1-xSnx are described. The temperature- and laser power-dependent photoluminescence analyses verify the formation of a direct band gap material with emission in the mid-infrared region and values expected for unstrained Ge0.81Sn0.19 (e.g., band gap of 0.3 eV at room temperature). These materials hold promise in applications such as thermal imaging and photodetection as well as building blocks for group IV-based mid- to near-IR photonics.

Hexagonal germanium formation at room temperature using controlled penetration depth nano-indentation

Thin Ge films directly grown on Si substrate using two-step low temperature growth technique are subjected to low load nano-indentation at room temperature. The nano-indentation is carried out using a Berkovich diamond tip (R ~ 20 nm). The residual impressions are studied using ex-situ Raman Micro-Spectroscopy, Atomic Force Microscopy combined system, and Transmission Electron Microscopy. The analysis of residual indentation impressions and displacement-load curves show evidence of deformation by phase transformation at room temperature under a critical pressure ranging from 4.9GPa–8.1GPa. Furthermore, the formation of additional Ge phases such as r8-Ge, hd-Ge, and amorphous Ge as a function of indentation depth have been realized. The inelastic deformation mechanism is found to depend critically on the indentation penetration depth. The non-uniform spatial distribution of the shear stress depends on the indentation depth and plays a crucial role in determining which phase is formed. Similarly, nano-indentation fracture response depends on indentation penetration depth. This opens the potential of tuning the contact response of Ge and other semiconductors thin films by varying indentation depth and indenter geometry. Furthermore, this observed effect can be reliably used to induce phase transformation in Ge-on-Si with technological interest as a narrow band gap material for mid-wavelength infrared detection.

Topological insulator Bi2Se3 films on rare earth iron garnets and their high-quality interfaces

The integration of quantum materials like topological insulators (TIs) with magnetic insulators (MIs) has important technological implications for spintronics and quantum computing. Here, we report excellent crystallinity of c-axis oriented epitaxial TI films of Bi2Se3 grown on MI films, a rare earth iron garnet (ReIG), such as thulium iron garnet (Tm3Fe5O12, TmIG), by molecular beam epitaxy using Se-buffered low-temperature growth technique. Strained-TmIG films with robust perpendicular magnetic anisotropy were deposited by off-axis sputtering. We demonstrated a streaky reflection high-energy electron diffraction pattern starting from the very first quintuple layer of Bi2Se3, indicating the high-quality interface between TmIG and Bi2Se3, a prerequisite for studying interfacial exchange coupling effects. The strong interfacial exchange interaction was manifested by the observation of an anomalous Hall effect in the Bi2Se3/TmIG bilayer and a shift of the ferromagnetic resonance field of TmIG induced by Bi2Se3. We have reproducibly grown high-quality Bi2Se3/ReIG and interfaces using this TI growth method, which may be applied to grow other types of van der Waals hetero-structures.

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model.

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 °C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (≤150 °C) growth of ultrathin films (100-1000 Å) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films' optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 °C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (≤150 °C) growth of ultrathin films (100-1000 Å) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films' optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Effect of Surface and Defect Chemistry on the Photocatalytic Properties of Intentionally Defect-Rich ZnO Nanorod Arrays.

Due to the abundance of intrinsic defects in zinc oxide (ZnO), the material properties are often governed by same. Knowledge of the defect chemistry has proven to be highly important, especially in terms of the photocatalytic degradation of pollutants. Given the fact that defect-free materials or structures exhibiting only one type of defect are extremely difficult to produce, it is necessary to evaluate what influence various defects may have when present together in the material. In this study, intentionally defect-rich ZnO nanorod (NR) arrays are grown using a simple low-temperature solution-based growth technique. Upon changing the defect chemistry using rapid thermal annealing (RTA) the material properties are carefully assessed and correlated to the resulting photocatalytic properties. Special focus is put on the investigation of these properties for samples showing strong orange photoluminescence (PL). It is shown that intense orange emitting NR arrays exhibit improved dye-degradation rates under UV-light irradiation. Furthermore, strong dye-adsorption has been observed for some samples. This behavior is found to stem from a graphitic surface structure (e.g., shell) formed during RTA in vacuum. Since orange-luminescent samples also exhibit an enhancement of the dye adsorption a possible interplay and synergy of these two defects is elucidated. Additionally, evidence is presented suggesting that in annealed ZnO NRs structural defects may be responsible for the often observed PL emission at 3.31 eV. However, a clear correlation with the photocatalytic properties could not be established for these defects. Building on the specific findings presented here, this study also presents some more general guidelines which, it is suggested, should be employed when assessing the photocatalytic properties of defect-rich ZnO.

Flux pinning landscape up to 25 T in SmBa2Cu3Oy films with BaHfO3 nanorods fabricated by low-temperature growth technique

REBa2Cu3Oy superconducting tapes are appropriate for high field magnet applications at low temperatures (i.e. below liquid nitrogen temperature). To clarify the morphology and the volume of the effective pinning center at low temperatures, we used a low-temperature growth technique to fabricate SmBa2Cu3Oy (SmBCO) films with various amounts of BaHfO3 (BHO) nanorods onto MgO-buffered metal substrates produced by ion-beam-assisted deposition; we investigated their flux pinning properties using a 25 T cryogen-free superconducting magnet that was recently developed at Tohoku University. According to the microstructural analysis using transmission electron microscopy, the BHO nanorods have a content-dependent morphology and are aligned for the higher content. The inclined and discontinuous BHO nanorods were observed in SmBCO films with BHO contents up to 3.8 vol%; they show an excellent flux pinning force density (1.5 TN m−3 at 21 T and 4.2 K) even when the magnetic field is perpendicular to the films. Based on the effective mass model for the flux pinning, the random pinning centers are dominant at low temperatures. The correlated flux pinning is stronger for aligned nanorods; however, the random pinning center becomes weaker in the 4.5 vol% BHO-doped films. Therefore, the optimal BHO doping level is approximately 3.8 vol% in terms of the amplitude of the critical current density and the anisotropy from 4.2 K to 20 K because this provides the best mixture of correlated and random flux pinning centers.

Low-temperature growth of fully epitaxial CoFe/Ge/Fe3Si layers on Si for vertical-type semiconductor spintronic devices

We develop a low-temperature growth technique of epitaxial Ge layers on a body-centered-cubic ferromagnetic metal (bcc-FM), Fe3Si, by combining solid phase epitaxy (SPE) and molecular beam epitaxy (MBE). The insertion of an SPE-grown Ge layer enables two-dimensional epitaxial growth of Ge layers by MBE even at a growth temperature of ∼175 C. Thanks to the relatively flat surface of the Ge epilayers, we can obtain an epitaxial CoFe (bcc-FM) layer on top of the Ge layers, leading to the all-epitaxial CoFe/Ge/Fe3Si trilayer with a reasonable magnetization reversal process. We believe that the all-epitaxial CoFe/Ge/Fe3Si trilayer has great potential to be utilized as novel vertical-type Ge-channel spintronic devices.

Unique optical properties of Eu3 + doped l-histidine hydrochloride mono hydrate single crystals from low temperature growth technique

A low-temperature solution method was utilized to grow single crystals of Eu3+doped l-histidine hydrochloride monohydrate. The quality of the crystals was confirmed by high-resolution X-ray diffraction measurements with full width at half maximum (FWHM) of rocking curve at 8arc per sec. The incorporation of Eu3+ ions into the lattice was confirmed by functional group analysis using Fourier Transform Infrared (FTIR) spectroscopy. The amount of Eu3+ ions was found to be 0.08 weight (%) using energy dispersive X-ray analysis. The crystal's thermal and mechanical properties were tested as well. The unique spectral properties such as UV–Vis transmittance, nonlinear optical efficiency (NLO), photoluminescence (PL) and its lifetime were measured. The PL study revealed that the intensity of 5D0→7F2 emission of Eu3+ is stronger than that of 5D0→7F1 emission and the decay measurement showed a life time of 7.2410μs. The photoluminescence results prove that l-histidine hydrochloride monohydrate is a new, highly efficient host material for europium ion red emissions.