Suitable Substrate Material Research Articles

In-Situ Fixation of All-Inorganic Mo-Fe-S Clusters for the Highly Selective Removal of Lead(II).

The selective adsorption by suitable substrate materials is considered one of the most economical methods. In this work, an all-inorganic bimetallic Mo-Fe-S cluster is facilely achieved through in situ chemical fixation of tetrathiomolybdate (TTM) on Fe3O4 nanoparticles (NPs) at room temperature (donated as FeMoS NPs). The bimetallic building blocks on the obtained FeMoS NPs possess a monovacancy species of sulfur, endowing FeMoS NPs with a selectivity order of Zn2+, Mn2+, Ni2+ < Cd2+ ≪ Cu2+ < Pb2+ for metal-ion adsorption, a novel application for the Mo-Fe-S clusters. Particularly, with the highest selectivity for Pb2+ (Kd ≈ 107), which is about 3 × 103-1 × 106 times higher than those for other ions and has exceeded that of a series of outstanding sorbents reported for Pb2+, FeMoS NPs can efficiently reduce the concentration of Pb2+ from ∼10 ppm to an extremely low level of ∼1 ppb. This facile and rational fabrication of the Mo-Fe-S cluster with Fe3O4 represents a feasible approach to cheaply develop novel and efficient materials for the selective removal of lead(II).

Long-Term Oyster Recruitment and Growth are not Influenced by Substrate Type in China: Implications for Sustainable Oyster Reef Restoration

ABSTRACT Successful and sustainable oyster reef restoration relies on suitable substrate material that is both readily available and encourages long-term recruitment and growth of oysters. China is increasing oyster reef restoration, however, little information is available to guide sustainable practices under local conditions and on ecologically relevant time scales. This study examines the effects of four substrate materials (oyster shell, clam shell, limestone, and clay brick) on community demographics for the Kumamoto oyster (Crassostrea sikamea) and associated macrofauna over a 3-y period in Xiangshan Bay, China. During the first 2 y, oyster and clam shell had similarly high recruitment and abundance of live oysters when compared with limestone and clay bricks. All substrate types, however, ended up with similar oyster abundances and size distributions after 3 y. Similar trends existed with regard to structural complexity (weight and volume) of substrate and any differences at the onset of the experi...

Preparation and electrochemical capacitive performance of graphene/carbon nanotube composite

The development of more advanced and environmentally friendly energy storage devices is an urgent request to meet future societal and environmental needs. Supercapacitor is one of the most promising electrochemical energy storage devices owning to its long cycle life, high dynamic propagation, quickly response and low maintenance cost compared to the traditional batteries and capacitors. However, their energy density is far less batteries, which limits their application in energy storage. In order to break through the limitation, exploring novel electrode materials with both high energy densities and power densities is extremely urgent. At present, it is a hot topic to produce composite electrode materials with synergistic effect. Graphene, a one-atom-thick two dimensional single layer of sp2-bonded carbon, owning to its unique structural properties, has exhibited many advantages, such as extraordinarily high electrical and thermal conductivity, great mechanical strength and high surface area, making it a potential candidate for applications in energy storage field. Therefore, graphene based composite materials have been utilized in various practical applications, including energy storage and conversion, transparent conducting films, chemical sensors, and actuators, etc. Given the extraordinary properties of graphene, such as the low mass density, good compatibility, highly conductive, large specific surface area and excellent flexibility, it is considered as one of the most suitable substrate materials for preparing supercapacitor electrodes. In recent years, graphene composites as supercapacitor electrode material have been widely investigated. Here, three- dimensional (3D) graphene/carbon nanotube (CNT) nanocomposites were prepared by in-situ compound method using as-synthesized graphene as matrix, which prepared by chemical vapor deposition (CVD). Firstly, graphene was prepared on Ni foam by CVD method using CH4 as carbon sources and H2/Ar as buffer gas at 850°C. Then a solution carbon source was obtained by ultrasonic vibration using a mixture solution of ferrocene and dimethylbenzenes. Finally, 3D graphene/CNT nanocomposite was synthesized by CVD method using Ni foam deposited graphene as supporter substrate at 750°C for 30 min. The morphology and microstructure of the resulting samples were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the electrochemical capacitive performance of the samples were investigated using CHI 660D chemical workstation to analyze the cyclic voltammetry and AC impedance. The results indicated that large amounts of graphenes had been formed on the Ni foam and 3D graphene/CNT nanocomposites also had been synthesized. The 3D lamellar structures between graphenes formed in the synthesis process could densely upload active substance, which was very different in structure and performance with individual graphene. The cyclic voltammetry (CV) curves of 3D graphene/CNT composite exhibited that the electrochemical capacitive performance has good reversibility. The Nyquist plots also displayed that the 3D graphene/CNT composite has excellent performance of electric charge transportation and double layer capacitance. The electrochemical measurements indicated that the maximum specific capacitance of 3D graphene/CNT composite, as the supercapacitor electrode material, exhibited a maximum specific capacitance of 289.8 F/g using 1.5 mol/L Li2SO4 as the electrolyte in the system and also showed excellent high-capacity and cycling stability. The specific capacitance of the 3D graphene/CNT composite remains 92% after 2000 cycles.

Ultrathin manganese dioxide nanosheets grown on partially unzipped nitrogen-doped carbon nanotubes for high-performance asymmetric supercapacitors

In this work, N-doped carbon nanotubes (NCNTS) have been easily unzipped using a chemical oxidation method to obtain porous and multi-defective partially unzipped N-doped carbon nanotubes (PU-NCNTs), which are promising as negative electrode materials for supercapacitors and are also suitable substrate materials for the efficient loading of ultrathin manganese dioxide (MnO2) nanosheets. Herein, the PU-NCNT/MnO2 composite was synthesized through a simple microwave irradiation method. Moreover, we have fabricated an asymmetric supercapacitor (ASC) using PU-NCNT/MnO2 composite as cathode, PU-NCNTs as anode and neutral aqueous Na2SO4 as electrolyte. Because of the synergistic effects of the PU-NCNTs electrode and the high capacitance as well as good rate performance of PU-NCNT/MnO2 composite, the asymmetric cell exhibited good electrochemical performance. The optimized ASC can be worked stably in the voltage window of 0–1.8 V and exhibited a maximum energy density of 14.76 Wh kg−1 at the current density of 1 A g−1. Additionally, the PU-NCNT/MnO2//PU-NCNT ASC exhibited long cycling stability with 80.5% specific capacitance retained after 1000 cycles at a current density of 1 A g−1. These encouraging results show that PU-NCNT/MnO2 could be promising materials for commercial use of supercapacitors.

Investigation of the Direct Plating Copper (DPC) on Al2O3, BeO or AlN Ceramic Substrates for High Power Density Applications

Abstract In the high power module applications, the power increasing and the size shrinking becomes one of the major topics for the power module design. Due to both the power increasing and the size decreasing, the power density of the device will be much increased. Therefore, not only the thermal conductivity and stability of the substrate material but the long-term material reliability of the substrate have to be seriously considered. For these reasons, the ceramic PCB becomes one of the best solutions. The ceramic substrates now used are normally based on Ag-printed or direct bonding copper (DBC) technology. In the case of the Ag-printed ceramic substrate, the pattern resolution and metallization thickness are limited by the Ag-printed process. Also the combination strength of the silver and ceramic substrate by glass (which is normally mixed in the silver paste) is normally not good enough. A thermal dissipation barrier will then be formed between silver and ceramic substrate due to the poor thermal conductivity of the glass material. For the DBC ceramic substrate, DBC substrates are manufactured at 1065°C by the diffusion between ceramic and Cu/CuO layer. A thicker Cu layer thickness of normally more than 300 um is required in the thermal compressing bonding process. The Cu pattern resolution will then be limited by the thickness of the Cu layer. However, the about 5~10% of the voids exist randomly between ceramic and Cu layer is the other major issue. The resolution issues of the Ag-printed and DBC ceramic substrates make the limitation for the device density design (fine line/width and flip-chip device design become very difficult). The glass material in the Ag printed ceramic substrate and the 5~10% voids existence in DBC ceramic substrate may cause the reliability issue operating at a high power density applications. For high power density module applications, we introduce the DPC technology on the ceramic substrate. In DPC ceramic substrate system, the sputtered Ti is used as the combination material between Cu and ceramic substrate. And the first copper is then sputtered on the top of Ti layer as seed-layer for the following Cu electrode plating (second cupper layer). By the material and the sputtering process control, several ceramic substrate raw materials can be used, such as Al2O3, AlN, BeO, Si3N4 and so on. The Ti combined/buffer layer provides good adhesion strength and material stability. The second copper layer is plated by electrode casting plating to 3 to 5 oz. (100~150um) in thickness. The key technology of the metal trace plating is the material control of the sputter layers and the second copper layer stress release during plating. In the DPC system, the double layers design is available. The laser drilled via holes on the various ceramic substrates is introduced. The conducting of the front and back side is connected by the following plating process. The key technology of this process is the stability of the via-holes. We have to make sure the via-holes cleaning, impurity removing and material stability during high temperature laser drilled is well controlled. DPC ceramic substrates provide a better metal/ceramic interface uniformity and material reliability due to the stable Ti combination material and much less voids in the metal/ceramic interface. Also, the DPC ceramic substrates provide a gold pattern resolution of 50 um line space with tight tolerance of 20 um min. We believe the material characteristic make DPC a very suitable substrate material for high power module applications.

Selection of substrate material for hybrid microwave integrated circuits (HMICs)

This paper presents systematic approach of material selection for substrate material in hybrid microwave integrated circuits (HMICs). The performance of HMICs starts deteriorating at microwave frequencies because the circuit dimensions become comparable to the wavelength. So, it is important to design HMICs in such a way that its performance remains unaffected even at high frequencies. One way to fulfil this requirement is to fabricate a proper device. For this, substrate material in HMICs plays an important role. But there are different types of materials available which can be used as substrate material of HMICs. The commonly reported materials are: Silicon (Si), Gallium Arsenide (GaAs), Indium Phosphide (InP), Alumina (Al2O3), Beryllia, Fused Silica, Sapphire, Woven PTFF/ Glass, PTFE/Glass, Polyolefin, and Ferrite/Granite. As each material is having its own advantages and limitations; therefore, it is important to choose the best possible material out of all possible materials. For this purpose two decision making techniques are used. Firstly, Ashby’s approach as the Multi-Objective Decision Making (MODM) technique is used, and then the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) as the Multiple Attribute Decision Making (MADM) technique is used. Ashby’s approach provides effective material selection technique to select the best material based on their material and performance indices for better device performance. While TOPSIS approach is a decision making approach which is basically used to determine the best alternative which should have the shortest Euclidean distance (S*) from the ideal solution (A*) and the largest Euclidean distance (S-) from the negative ideal solution (A-). For MICs, the material indices considered and evaluated are surface roughness, relative dielectric constant, loss tangent, thermal conductivity, and dielectric strength. It is observed that Sapphire followed by high-purity Alumina (99.5 percent pure or better) are good candidates for substrate material in hybrid MICs. The surface roughness of Sapphire is better than that of Alumina, though the dielectric strength of both these materials is the same. A comparison between two different methods for material selection shows consistency between the two methods of material selection. Both methodologies show that Sapphire is the most suitable substrate material for hybrid MICs.

Improvement of nanoparticle filtration efficiency through synthesis of SiC whisker on graphite felt by the VS CVD mechanism

This study examines the synthesis of SiC whisker on graphite felt through the non-catalytic VS CVD (Vapor Solid Chemical Vaporized Deposition) mechanism in order to investigate its potential as a filter to replace the conventional DPF (Diesel Particulate Filer). Since the CVD process is conducted mostly in high temperature exceeding 1000°C, many restrictions exist in selecting the substrate. Graphite felt is a filter form of non-woven fabric. The graphite felt was selected as a suitable substrate material for this study based on the VS CVD mechanism due to its relatively low cost, high heat resistance, and high flexibility. The appropriate SiC whisker structure of the nanoscale was grown on the graphite felt that exhibited the fore-mentioned characteristics. This enhanced the filtration performance of the bare graphite felt filter more than two times without compromising the gas permeability. Additionally, thermal oxidation resistance was elevated by at least 200°C more than the bare graphite felt, thereby indicating the transfer of a part of the desirable chemical properties of the SiC.

Design and Implementation of Compact Coax Fed Multi Band MIMO Antenna for 4G Applications

Background/Objectives: In multimedia data communication environment a trade-off shall be opted between power, spectrum needs and wireless channel capacity in Global System for Mobile, Long Term Evaluation, and Wireless Local Area Networks applications. Multi-Input Multi-Output antenna elements display a high degree of similarity and it leads to efficacy reduction in multi user milieu. Methods: This paper investigates and presents a condensed 2-port coax fed multiband MIMO antenna for 4G applications. The proposed MIMO antenna possesses dimensions of 45mm×50mm×0.4mm 3 and comprises two layers, a rectangular patch, a pair of small-N shaped strips, two G-shaped monopole structures and L-shaped slots. An array of three resonant frequencies is opted for exciting the proposed design with the values of 1.8GHz, 2.5GHz and 5GHz. The methodology exhibits an adaptable frequency selecting with the ability to neutralize the impact of the other frequency. Findings: The implemented design accomplishes a high efficiency rates for LTE-Advanced, WiMAX and Wi-Fi applications 71.80%, 72.28% and 85.74%. Applications/Improvements: Fabrication with a suitable FR4 substrate material is used in the design of the coax fed multiband MIMO antenna. For future enhancements, the radiation pattern and reflection coefficient of an antenna shall be assessed.

Hard Coatings to Improve the Machining of Nickel Based Materials

Difficult-to-machine materials like nickel based alloys have become a key material in many branches of industry, above all in the aerospace industry. The reasons for this mainly lie in the combination of properties such as high strength at increased temperatures, a high degree of chemical resistance and high wear resistance. However, these advantages are offset by a major disadvantage: the machining, in particular milling, is very difficult. Only relatively low cutting speeds can be used and tool life is usually short. Developing tool and technology solutions aimed at obtaining an enhancement of the machining techniques used for milling of difficult-to-cut materials.The results of research, in particular with regard to the development of hard coatings in conjunction with suitable substrate materials, cutting edge preparation and finishing systems show an improvement in the performance of cutting nickel based alloys. Best results were reached by stable oxynitridic and embedded nanoscale structures. Combinations of these coating structures with optimized coating composition and improved coating adhesion were used to develop coatings with higher strength and hardness as well as an improved stability at higher temperatures. Related to ultra-fine graded solid carbide materials, sharp cutting edges (4 μm) and polished tools, hard coated tools were used for HPC milling of nickel based materials at cutting speeds up to 150 m/min. Various cutting analyses show the applicability of the developed coatings and the corresponding process chain to improve the efficiency of cutting processes.

Computed tomography of scalp embedded gravel: Differentiation between falling and kicking

Abstract In the case of a survived head injury of a 39 year old man, kick versus fall as mechanism had to be discerned. On top of conventionally used medicolegal findings, clinical computed tomography (CT) scans were evaluated. There, dense particles at the back of the head were scattered on and in the skin, around the region also likely to be the center of an impact related skull burst fracture. Experiments then were conducted to discern falling, kicking and scrubbing, based on gravel particle details, using suitable model substrate materials. Particle size and count were larger in falls without scrubbing than in kicks also because soles may not retain heavier or larger gravel particles. Based on chemical composition obtained through EDS (energy-dispersive X-ray spectroscopy), gravel particle mass attenuation coefficient was determined, linearly correlating with effective CT attenuation of scalp particles and bone and skin materials. Gravel particle size showed to be a stronger evidence in the distinction of fall versus kick than skin and brain morphology. Clinical CT can be a valuable asset in reconstructive forensic medicine.

Studies of the moisture absorption of thin carbon fiber reinforced plastic substrates for x-ray mirrors

We study a lightweight x-ray mirror with a carbon fiber reinforced plastic (CFRP) substrate for next-generation x-ray satellites. For tightly nested x-ray mirrors, such as those on the Suzaku and ASTRO-H telescopes, CFRP is the suitable substrate material because it has a higher strength-to-weight ratio and forming flexibility than those of metals. In flat CFRP substrate fabrication, the surface waviness has a root mean square (RMS) of ∼1 μm in the best products. The RMS approximately reaches a value consistent with the RMS of the mold used for the forming. We study the effect of moisture absorption using accelerated aging tests in three environments. The diffusivity of the CFRP substrate at 60°C and at relative humidity of 100% is ∼9.7×10−4 mm2·h−1, and the acceleration rate to the laboratory environment was 180 times higher. We also develop co-curing functional sheets with low water-vapor transmissivity on the CFRP substrate. Co-curing the sheets successfully reduced the moisture absorption rate by 440 times compared to the un-co-cured substrate. Details of the CFRP substrate fabrication and moisture absorption tests are also reported.

Electrochemical Separation and Purification of Astatine for Radiopharmaceutical Application

The second longest lived isotope Astatine (211At: T1/2=7.5 h), is one the most promising α-emitters for targeted cancer radiotherapy. The liquid/liquid extraction method has been shown to provide good separation of 211At from bismuth metal. However, of the liquid/liquid (L/L) extraction (separation) steps [1] used in the current manual isolation procedure presents a significant challenge due to the nature of the diisopropyl ether / hydrochloric acid (DIPE/HCl) and diisopropyl ether / sodium hydroxide (DIPE/NaOH) mixtures. The present work is focused on to evaluate the feasibility of electrochemical methods in the purification of 211At. This approach will be an alternative to hydrogen astatide (H211At) wet distillation. At the present time, Bi (III) is considered the primary contaminant from which 211At must be electrochemically purified. The initial electrochemical studies were conducted with iodine as an astatine segregate in bismuth solution. As the concentration of astatine in the original solution is much lower than micro molar levels, there are two different approaches have been adopted; (i) separation of bismuth from the original solution [Ref 1; step 4] through electrodeposition and (ii) direct extraction of iodine from the original solution [Ref 1; step 3 or 4]. Figure 1(a) shows the cyclic voltammograms (CV) for bismuth on various substrate electrodes; namely Pt, Au and glassy carbon (GC). In these, the GC substrate found to be the suitable martial than others, which could be due to surface nature of carbon. In the case second approach, initially, iodide separation was carried out without bismuth in an acidic electrolyte with various concentrations of iodide to identify the suitable substrate material and minimum separation levels. Figure 1(b) shows the model CV for iodide on Pt electrode, surprisingly iodine deposit was also observed at the working electrode. Conversely, there are no characteristic electrochemical peaks and deposits were observed for GC and Au. This study indicates iodide can be extracted with Pt electrodes and Pt catalyzes the reactions. Acknowledgements Financial support from the Department of Energy (DOE) is greatly acknowledged. Selvarani Ganesan is thankful for subcontract from the Pacific Northwest National Laboratory (Contract No. 244236; PI: Matthew J O'Hara). Reference E.R. Balkin, D.K. Hamlin, K. Gagnon, M.-K Chyan, S. Pal, S. Watanabe, and D.S. Wilbur, Appl. Sci., 3 (2013) 636-655. Figure 1

Silicane as an Inert Substrate of Silicene: A Promising Candidate for FET

Opening up a band gap without lowering high carrier mobility and finding a suitable substrate material are a challenge for designing silicon-based nanodevices. Using density functional theory calculations incorporating vdW corrections, we find that the semiconducting silicane monolayer is free of dangling bonds, providing an ideal substrate for silicene to sit on. The nearly linear band dispersion character of silicene with a sizable band gap (44–61 meV) opening is obtained in all heterobilayers (HBLs). We also find that the effective masses of electrons and holes near the Dirac point (ranging from 0.033 to 0.045m0) are very small in HBLs, and thus high carrier mobility (105cm2 V–1 s–1) of silicene is expected. These characteristics of HBLs can be flexibly modulated by applying bias voltage or strain, suitable for the high-performance FET channel operating at room temperature.

An expert-based model for selecting the most suitable substrate material type for antenna circuits

Quality and properties of microwave circuits depend on all the circuit components. One of these components is the substrate. The process of substrate material selection is a decision-making problem that involves multicriteria with objectives that are diverse and conflicting. The aim of this work was to select the most suitable substrate material type to be used in antennas in the microwave frequency range that gives best performance and reliability of the substrate. For this purpose, a model was built to ease the decision-making that includes hierarchical alternatives and criteria. The substrate material type options considered were limited to fiberglass-reinforced epoxy laminates (FR4 εr = 4.8), aluminium (III) oxide (alumina εr = 9.6), gallium arsenide III–V compound (GaAs εr = 12.8) and PTFE composites reinforced with glass microfibers (Duroid εr = 2.2–2.3). To assist in building the model and making decisions, the analytical hierarchy process (AHP) was used. The decision-making process revealed that alumina substrate material type was the most suitable choice for the antennas in the microwave frequency range that yields best performance and reliability. In addition, both the size of the circuit and the loss tangent of the substrates were found to be the most contributing subfactors in the antenna circuit specifications criterion. Experimental assessments were conducted utilising The Expert Choice™ software. The judgments were tested and found to be precise, consistent and justifiable, and the marginal inconsistency values were found to be very narrow. A sensitivity analysis was also presented to demonstrate the confidence in the drawn conclusions.

Indirect doping effects from impurities inMoS2/h-BNheterostructures

We performed density functional theory calculations on heterostructures of single layers of hexagonal BN and ${\mathrm{MoS}}_{2}$ to assess the effect of doping in the BN sheet and of interstitial Na atoms on the electronic properties of the adjacent ${\mathrm{MoS}}_{2}$ layer. Our calculations predict that $n$ doping of the boron nitride subsystem by oxygen, carbon, and sulfur impurities causes noticeable charge transfer into the conduction band of the ${\mathrm{MoS}}_{2}$ sheet, while $p$ doping by beryllium and carbon leaves the molybdenum disulphide layer largely unaffected. Intercalated sodium atoms lead to a significant increase of the interlayer distance in the heterostructure and to a metallic ground state of the ${\mathrm{MoS}}_{2}$ subsystem. The presence of such $n$ dopants leads to a distinct change of valence-band and conduction-band offsets, suggesting that doped h-BN remains a suitable substrate and gate material for applications of $n$-type ${\mathrm{MoS}}_{2}$.

Modelling of Joule heating based self-alignment method for metal grid line passivation

ABSTRACTA Joule heating based self-alignment method for solution-processable insulator structures has been modeled for the passivation of metal grid lines, for example for organic light emitting diodes or photovoltaic cells. To minimize overhang of the passivation layer from line edges, we have studied the Joule heating approach using solution-processable, cross-linkable polymer insulator films. Finite element simulations were performed to investigate the heating of the sample using glass and poly(ethylene terephthalate) (PET) substrates. The sample was at room temperature and the current was selected to induce a temperature of 410 K at the conductor. It was found that the selection of substrate material is crucial for the localization of cross-linking. For a PET substrate, the temperature gradient at the edge of the conductor is approximately twice the gradient for glass. As a result, using a glass substrate demands high selectivity from the polymer cross-linking, thus making PET a more suitable substrate material for our application. A flexible PET substrate is, in addition, compatible with roll-to-roll mass-manufacturing processes.

SmBa2NbO6Nanopowders, an Effective Percolation Network Medium for YBCO Superconductors

The percolation behavior of superconductor-insulator composite, YBa2Cu3O7–δ, and nano SmBa2NbO2synthesized by modified combustion technique was studied. Particle size of nano SmBa2NBO6was determined using transmission electron microscopy. The chemical nonreactivity of nano SmBa2NbO6with YBCO is evident from the X-Ray diffraction study which makes it a suitable nanoceramic substrate material for high temperature superconducting films. A systematic increase in the sintered density, approaching the optimum value of the insulating nanophase is clearly observed, as the vol.% of YBCO in the composite decreases. SEM micrograph showed uniform distribution of nanopowder among the large clusters of YBCO. The obtained percolation threshold is~26 vol% of YBCO in the composite. All the composites below the threshold value showedTC(0)~92 K even though the room resistivity increases with increase in vol.% of nano SmBa2NbO6. The values of critical exponents obtained matches well with the theoretically expected ones for an ideal superconductor-insulator system.

Epitaxial NiMnGa Films for Magnetic Shape Memory Alloy Microactuators

AbstractActive materials such as piezoelectrics are established in the field of microsystems application despite their low achievable strains which often require the integration of additional gear mechanisms. The ongoing search for new active materials has focused on magnetic shape memory (MSM) alloys such as NiMnGa since they combine macroscopic strains of up to 10% with a cycling frequency well above the frequencies of conventional thermal shape memory alloys. The present review focuses on preparation and analysis of NiMnGa films that can eventually be integrated in microsystems. Single crystal like films are prepared by epitaxial growth on suitable substrate materials. Since the magnetically induced reorientation of variants is blocked by a rigid substrate, we present different methods for releasing films from the substrates. We show that the sacrificial layer technology is the most promising approach. Further processing of the freestanding film requires a microtechnology which is adjusted to the film laminate structure. The properties of the freestanding films are compared with films on a rigid substrate. Although we observe stress‐induced twin boundary motion, the twinning stress is too high to be overcome by an external magnetic field. Therefore, it is necessary to develop suitable training methods to reduce the twinning stress below 2 MPa to enable the activation of the material by means of an external magnetic field.

GaN epitaxy on Cu(110) by metal organic chemical vapor deposition

We demonstrate that Cu can be a suitable substrate material for c-plane GaN epitaxy using metal organic chemical vapor deposition. By using a low temperature AlN buffer layer, Ga and Cu alloying can be prevented so that GaN layer can be grown on Cu at a temperature of 1000 °C. An epitaxial relation of GaN (0001)//Cu(110) is observed using cross-section transmission electron microscopy and electron back scatter diffraction studies. The single crystalline GaN epilayer shows a threading dislocation density of 3 × 109 cm−2 and strong band edge emission at room temperature. The site alignment between GaN (0001) and Cu(110) shows a mesh ratio of 4/3 and 5/3 in GaN [10-10] and GaN [-1100] directions, which is attributed to the epitaxial relation observed.

Hybrid Graphene and Graphitic Carbon Nitride Nanocomposite: Gap Opening, Electron–Hole Puddle, Interfacial Charge Transfer, and Enhanced Visible Light Response

Opening up a band gap and finding a suitable substrate material are two big challenges for building graphene-based nanodevices. Using state-of-the-art hybrid density functional theory incorporating long-range dispersion corrections, we investigate the interface between optically active graphitic carbon nitride (g-C(3)N(4)) and electronically active graphene. We find an inhomogeneous planar substrate (g-C(3)N(4)) promotes electron-rich and hole-rich regions, i.e., forming a well-defined electron-hole puddle, on the supported graphene layer. The composite displays significant charge transfer from graphene to the g-C(3)N(4) substrate, which alters the electronic properties of both components. In particular, the strong electronic coupling at the graphene/g-C(3)N(4) interface opens a 70 meV gap in g-C(3)N(4)-supported graphene, a feature that can potentially allow overcoming the graphene's band gap hurdle in constructing field effect transistors. Additionally, the 2-D planar structure of g-C(3)N(4) is free of dangling bonds, providing an ideal substrate for graphene to sit on. Furthermore, when compared to a pure g-C(3)N(4) monolayer, the hybrid graphene/g-C(3)N(4) complex displays an enhanced optical absorption in the visible region, a promising feature for novel photovoltaic and photocatalytic applications.