Interlayer shear strength of single crystalline graphite

Reported values （0.2 MPa-7.0 GPa） of the interlayer shear strength （ISS） of graphite are very dispersed. The main challenge to obtain a reliable value of the ISS using conventional measuring methods was the unavailability of sufficiently large single crystalline graphite. Here we present a novel experimental method to measure the ISS, and obtain the value as -0.14 GPa. Our result can serve as an important basis for understanding mechanical behavior of graphite or graphene-based materials.

High-Quality Bi_2Te_3 Single Crystalline Films on Flexible Substrates and Bendable Photodetectors

Recently, great efforts have been made in the fabrication of arbitrary warped devices to satisfy the requirement of wearable and lightweight electronic products. Direct growth of high crystalline quality films on flexible substrates is the most desirable method to fabricate flexible devices owing to the advantage of simple and compatible preparation technology with current semiconductor devices, while it is a very challenging work, and usually amorphous, polycrystalline or discontinuous single crystalline films are achieved. Here we demonstrate the direct growth of high-quality Bi2 Te3 single crystalline films on flexible polyimide substrates by the modified hot wall epitaxy technique. Experimental results reveal that adjacent crystallites are coherently coalesced to form a continuous film, although amounts of disoriented crystallites are generated due to fast growth rate. By inserting a quartz filter into the growth tube, the number density of disoriented crystallites is effectively reduced owing to the improved spiral interaction. Furthermore, flexible Bi2 Te3 photoconductors are fabricated and exhibit strong near-infrared photoconductive response under different degrees of bending, which also confirms the obtained fexible films suitable for electronic applications.

Structural and electrical properties of single crystalline and bi-crystalline ZnO thin films grown by molecular beam epitaxy

C-oriented ZnO epitaxial thin films are grown separately on the a-plane and c-plane sapphire substrates by using a molecular-beam epitaxy technique. In contrast to single crystalline ZnO films grown on a-plane sapphire, the films grown on c-plane sapphire are found to be bi-crystalline; some domains have a 30~ rotation to reduce the large mismatch between the film and the substrate. The presence of these rotation domains in the bi-crystalline ZnO thin film causes much more carrier scatterings at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers than those of the single crystalline one. In addition, the complex impedance spectra are also studied to identify relaxation mechanisms due to the domains and/or domain boundaries in both the single crystalline and bi-crystalline ZnO thin films.

Influence of reducing anneal on the ferromagnetism in single crystalline Co-doped ZnO thin films

This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on a-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become more conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase. Compared with weak ferromagnetism （0.16 μB/Co2＋） in the Zno.95 Co0.05 O single crystalline film with reducing annealing in the absence of Zn vapour, the films annealed in the reducing atmosphere with Zn vapour are found to have much stronger ferromagnetism （0.65 μB/Co2＋） at room temperature. This experimental studies clearly indicate that Zn interstitials are more effective than oxygen vacancies to activate the high-temperature ferromagnetism in Co-doped ZnO films, and the corresponding ferromagnetic mechanism is discussed.

Fabrication and Piezoelectric Characterization of Single Crystalline GaN Nanobelts

GaN nanobelts are synthesized using the chemical vapor deposition method with the catalyst of Ni. The mi- crostrueture, composition and photoluminescence property are characterized by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectra. The results demonstrate that the single crystalline GaN nanobelts are grown with a hexagonal wurtzite structure, in width ranging from 500nm to 2μm and length up to 10-20μm. Moreover, a large piezoelectric coefficient d33 of 20pm/V is obtained from GaN nanobelts by an atomic force microscopy and the high piezoelectric property implies that the perfect single crystallinity and the freedom of dislocation for the GaN nanobelt have significant impact on the electromechanical response.

A Simple Deposition Method for Self-Assembling Single Crystalline Hybrid Perovskite Nanostructures

A sequential deposition method is developed, where the hybrid organic-inorganic halide perovskite （CH3NH3Pb （I1-xBrx）3 ） is synthesized using precursor solutions containing CH3NH3I and PbBr2 with different mole ratios and reaction times. The perovskite achieved here is quite stable in the atmosphere for a relatively long time without noticeable degradation, and the perovskite nanowires are proved to be single crystalline structure, based on transmission electron microscopy.Furthermore, strong red photoluminescence from perovskite is observed in the wavelength range from 746nm to 770nm with the increase of the reaction time, on account of the exchanges between I- ions and Br- ions in the perovskite crystal. Lastly, the influences of concentration and reaction time of the precursor solutions are discussed, which are important for evolution of hybrid perovskite from nanocuboid to nanowire and nanosheet.

In-situ construction of a thermodynamically stabilized interface on the surface of single crystalline Ni-rich cathode materials via a onestep molten-salt route

Nickel rich LiNi_(x)Co_(y)Mn_(1−x−y)O_(2)cathode materials have been studied extensively to increase the energy density of lithium-ion batteries(LIBs)due to their advantages of high capacity and low cost.However,the anisotropic crystal expansion and contraction inside the secondary particles would cause detrimental micro-cracks and severe parasitic reactions at the electrode/electrolyte interface during cycling,which severely decreases the stability of crystalline structure and cathodeelectrolyte interphase and ultimately affects the calendar life of batteries.Herein,a thermodynamically stabilized interface is constructed on the surface of single-crystalline Ni-rich cathode materials(SC811@RS)via a facile molten-salt route to suppress the generation of microcracks and interfacial parasitic side reactions simultaneously.Density functional theory calculations show that the formation energy of interface layer(−1.958 eV)is more negative than that of bulk layered structure(−1.421 eV).Such a thermodynamically stable protective layer can not only prevent the direct contact between highly reactive LiNi_(x)Co_(y)Mn_(1−x−y)O_(2)and electrolyte,but also mitigate deformation of structure caused by stress thus strengthening the mechanical properties.Raman spectra further confirm the excellent structural reversibility and reaction homogeneity of SC811@RS at particle,electrode,time scales.Consequently,SC811@RS cathode material delivers significantly improved cycling stability(high capacity retention of 92%after 200 cycles at 0.5 C)compared with polycrystalline LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(82%).

Enhancing thermodynamic stability of single-crystal Ni-rich cathode material via a synergistic dual-substitution strategy

Nickel(Ni)-rich cathode materials have become promising candidates for the next-generation electrical vehicles due to their high specific capacity.However,the poor thermodynamic stability(including cyclic performance and safety performance or thermal stability)will restrain their wide commercial application.Herein,a single-crystal Ni-rich Li Ni_(0.83)Co_(0.12)Mn_(0.05)O_(2) cathode material is synthesized and modified by a dual-substitution strategy in which the high-valence doping element improves the structural stability by forming strong metal–oxygen binding forces,while the low-valence doping element eliminates high Li^(+)/Ni^(2+)mixing.As a result,this synergistic dual substitution can effectively suppress H2-H3 phase transition and generation of microcracks,thereby ultimately improving the thermodynamic stability of Ni-rich cathode material.Notably,the dual-doped Ni-rich cathode delivers an extremely high capacity retention of 81%after 250 cycles(vs.Li/Li+)in coin-type half cells and 87%after 1000 cycles(vs.graphite/Li^(+))in pouch-type full cells at a high temperature of 55℃.More impressively,the dual-doped sample exhibits excellent thermal stability,which demonstrates a higher thermal runaway temperature and a lower calorific value.The synergetic effects of this dual-substitution strategy pave a new pathway for addressing the critical challenges of Ni-rich cathode at high temperatures,which will significantly advance the high-energy-density and high-safety cathodes to the subsequent commercialization.

Structural and optical verification of residual strain effect in single crystalline CdTe nanowires

Single crystalline CdTe nanowires have been synthesized using Au-catalyzed chemical vapor deposition. X-ray diffraction reveals the existence of non- negligible inhomogeneous compressive strain in the nanowires along the 〈111〉 growth direction. The effect of the strain on the electronic structure is manifested by the blue-shifted and broadened photoluminescence spectra involving shallow donor/acceptor states. Such residual strain is of great importance for a better understanding of the optical and electrical behaviors of various semiconductor nanomaterials as well as for device design and applications.

Anomalous anisotropic magnetoresistance in single-crystalline Co/SrTiO_(3)(001)heterostructures

The anisotropic magnetoresistances(AMRs)in single crystalline Co(6 nm)/SrTiO_(3)(001)heterostructures from 5 K to 300 K with the current direction setting along either Co[100]or Co[110]are investigated in this work.The anomalous(normal)AMR is observed below(above)100 K.With the current along Co[100]direction,the AMR shows negative longitudinal and positive transverse magnetoresistances at T<100 K,while the AMR is inverse with the current along Co[110].Meanwhile,the amplitude ratio between Co[110]and Co[100]is observed to be as large as 29 at 100 K.A crystal symmetry-adapted model of AMR demonstrates that interplay between the non-crystalline component and crossed AMR component results in the anomalous AMR.Our results may reveal more intriguing magneto-transport behaviors of film on SrTiO_(3)or other perovskite oxides.

Study of Quantitative and Qualitative Characteristics of Nickel Clusters and Semiconductor Structures

The possibility of building of clusters of impurity atoms of Ni in silicon and controlling their parameters is currently investigated in the present research article. Our group develops a special technique for doping, the so-called “low-temperature doping” of semiconductors. This method of doping is based upon the diffusion process which is carried out in stages by gradually increasing temperature ranging from room temperature to the diffusion temperature.

The effect of hierarchical single-crystal ZSM-5 zeolites with different Si/Al ratios on its pore structure and catalytic performance

Hierarchical single-crystal ZSM-5 zeolites with different Si/Al ratios(Hier-ZSM-5-x,where x=50,100,150 and 200)were synthesized using an ordered mesoporous carbon-silica composite as hard template.Hier-ZSM-5-x exhibits improved mass transport properties,excellent mechanical and hydrothermal stability,and higher catalytic activity than commercial bulk zeolites in the benzyl alcohol self-etherification reaction.Results show that a decrease in the Si/Al ratio in hierarchical single-crystal ZSM-5 zeolites leads to a significant increase in the acidity and the density of micropores,which increases the final catalytic conversion.The effect of porous hierarchy on the diffusion of active sites and the final catalytic activity was also studied by comparing the catalytic conversion after selectively designed poisoned acid sites.These poisoned Hier-ZSM-5-x shows much higher catalytic conversion than the poisoned commercial ZSM-5 zeolite,which indicates that the numerous intracrystalline mesopores significantly reduce the diffusion path of the reactant,leading to the faster diffusion inside the zeolite to contact with the acid sites in the micropores predominating in ZSM-5 zeolites.This study can be extended to develop a series of hierarchical single-crystal zeolites with expected catalytic performance.

Substrate Effects on the High-Temperature Oxidation Behavior of Thermal Barrier Coatings

The high-temperature oxidation behaviors of the NiCrAIYSi/P-YSZ thermal barrier coatings （TBCs） produced by electron beam-physical vapor deposition （EB-PVD） on directionally solidified （DS） and single crystalline （SC） Ni-based superalloy substrates were investigated. The cross-sectional microstructure investigation, isothermal and cyclic oxidation tests were conducted for the comparison of oxidation behaviors of TBCs on different substrates. Although TBC on DS substrate has a relatively higher oxidation rate, it has a longer thermal cycling lifetime than that on SC substrate. The primary factor for TBC spallation is the mismatch of thermal expansion coefficient （TEC） of the bond coat and substrate. The morphological feature of thermally grown oxide （TGO） has a strong influence on the TBC performance. By optimizing the elemental interdiffusion between bond coat and substrate, a high quality TGO layer is formed on the DS substrate, and therefore the TBC oxidation behavior is improved.

Photophysical and electrical properties of organic waveguide nanorods of perylene-3,4,9,10-tetracarboxylic dianhydride

The single crystalline nanostructure of organic semiconductors provides a very promising class of materials for applications in modern optoelectronic devices. However, morphology control and optoelectronic property modulation of high quality single crystalline samples remain a challenge. Here, we report the morphology-controlled growth of single crystalline nanorod arrays of perylene- 3,4,9,10-tetracarboxylic dianhydride （IrFCDA）. We demonstrate that, unlike FTCDA film, PTCDA nanorods exhibits optical waveguide features, enhanced absorption, and Frenkel excitation emission in the visible region. Additionally, we measured the electrical properties of PTCDA nanorods, including the conductivity along the growth direction of the nanorod, which is roughly 0.61 S-m i （much higher than that of pure crystalline PTCDA films）.

Achieving room-temperature M_(2)-phase VO_(2) nanowires for superior thermal actuation

Vanadium dioxide (VO_(2)) has emerged as a promising micro-actuator material for its large amplitude and high work density across the transition between the insulating (M_(1) and M_(2)) and metallic (R) phase. Even though M_(2)–R transition offers about 70% higher transformation stress than M_(1)–R structural phase transition, the application of the M_(2) phase in the micro-actuators is hindered by the fact that previously, M_(2) phase can only stay stable under tensile stress. In this work, we propose and verify that by synthesizing the VO_(2) nanowires under optimized oxygen-rich conditions, stoichiometry change can be introduced into the nanowires (NWs) which in turn yield a large number free-standing single-crystalline M_(2)-phase NWs stable at room temperature. In addition, we demonstrate that the output stress of the M_(2)-phase NWs is about 65% higher than that of the M_(1)-phase NWs during their transition to R phase, quite close to the theoretical prediction. Our findings open new avenues towards enhancing the performance of VO_(2)-based actuators by using M_(2)–R transition.