Epitaxial growth triggered core-shell Pd@RuP nanorods for high-efficiency electrocatalytic hydrogen evolution

Ru with Pt-like hydrogen bond strength,knockdown cost(~1/3 of Pt),and eximious stability is a competitive replacement for Pt-based catalysts towards the hydrogen evolution reaction(HER)in water splitting.The design of Ru-based catalysts via interface construction,crystal phase control,and specific light element doping to realize the impressive promotion of limited activity and stability remains challenging.Herein,we report the fabrication of Pd@RuP core-shell nanorods(NRs)via an epitaxial growth method,where ultrathin RuP shells extend the face-centered cubic(fcc)crystal structure and(111)plane of the Pd NRs core.Density functio nal theory results confirm that the core-s hell interface engineering and P doping synergistically accelerate electron transfer and moderate the d-band center to generate a suitable affinity for H*,thus optimizing HER kinetics.Compared with Pd@Ru NRs and Pt/C,the Pd@RuP NRs exhibit preferable electrocatalytic stability and superior activity with a low overpotential of 18 mV at 10 mA cm-2in the alkaline HER process.Furthermore,the integrated Pd@RuP//RuO2-based electrolyzer also displays a low operation potential of 1.42 V to acquire 10 mA cm-2,demonstrating great potential for practical water electrolysis.Our work presents an efficient avenue to design Ru-based electrocatalysts via epitaxial growth for extraordinary HER performance.

Epitaxial growth of trilayer graphene moiré superlattice

The graphene-based moiré superlattice has been demonstrated as an exciting system for investigating strong correlation phenomenon. However, the fabrication of such moiré superlattice mainly relies on transfer technology. Here, we report the epitaxial growth of trilayer graphene(TLG) moiré superlattice on hexagonal boron nitride(h BN) by a remote plasma-enhanced chemical vapor deposition method. The as-grown TLG/h BN shows a uniform moiré pattern with a period of ~ 15 nm by atomic force microscopy(AFM) imaging, which agrees with the lattice mismatch between graphene and h BN. By fabricating the device with both top and bottom gates, we observed a gate-tunable bandgap at charge neutral point(CNP) and displacement field tunable satellite resistance peaks at half and full fillings. The resistance peak at half-filling indicates a strong electron–electron correlation in our grown TLG/h BN superlattice. In addition, we observed quantum Hall states at Landau level filling factors ν = 6, 10, 14,..., indicating that our grown trilayer graphene has the ABC stacking order. Our work suggests that epitaxy provides an easy way to fabricate stable and reproducible two-dimensional strongly correlated electronic materials.

Preface to Special Issue on Towards High Performance Ga_(2)O_(3) Electronics: Epitaxial Growth and Power Devices(Ⅰ)

There is currently great optimism within the electronics community that gallium oxide(Ga_(2)O_(3)) ultra-wide bandgap semiconductors have unprecedented prospects for eventually revolutionizing a rich variety of power electronic applications. Specially, benefiting from its ultra-high bandgap of around 4.8 eV, it is expected that the emerging Ga_(2)O_(3) technology would offer an exciting platform to deliver massively enhanced device performance for power electronics and even completely new applications.

Epitaxial growth of antimony nanofilms on HOPG and thermal desorption to control the film thickness

Group-V elemental nanofilms were predicted to exhibit interesting physical properties such as nontrivial topological properties due to their strong spin-orbit coupling,the quantum confinement,and surface effect.It was reported that the ultrathin Sb nanofilms can undergo a series of topological transitions as a function of the film thickness h:from a topological semimetal(h>7.8 nm)to a topological insulator(7.8 nm>h>2.7 nm),then a quantum spin Hall(QSH)phase(2.7 nm>h>1.0 nm)and a topological trivial semiconductor(h<1.0 nm).Here,we report a comprehensive investigation on the epitaxial growth of Sb nanofilms on highly oriented pyrolytic graphite(HOPG)substrate and the controllable thermal desorption to achieve their specific thickness.The morphology,thickness,atomic structure,and thermal-strain effect of the Sb nanofilms were characterized by a combination study of scanning electron microscopy(SEM),atomic force microscopy(AFM),and scanning tunneling microscopy(STM).The realization of Sb nanofilms with specific thickness paves the way for the further exploring their thickness-dependent topological phase transitions and exotic physical properties.

Effect of Oxygen Partial Pressure on Epitaxial Growth and Properties of Laser-Ablated AZO Thin Films

Al-doped ZnO（AZO） thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures（P_（O2））.The effect of P_（O2） on the crystal structure,preferred orientation as well as the electrical and optical properties of the films was investigated.The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure,showing a significant c-axis orientation.The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P_（O2）.At the optimum oxygen partial pressures of 10- 15 Pa,the AZO thin films were epitaxially grown on c-sapphire substrates with the（0001） plane parallel to the substrate surface,i e,the epitaxial relationship was AZO（000 1） // A1_2O_3（000 1）.With increasing P_（O2）,the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly,which led to an enhancement in electrical conductivity of the AZO thin films.All the films were highly transparent with an optical transmittance higher than 85%.

Fast High Order and Energy Dissipative Schemes with Variable Time Steps for Time-Fractional Molecular Beam Epitaxial Growth Model

In this paper,we propose and analyze high order energy dissipative time-stepping schemes for time-fractional molecular beam epitaxial(MBE)growth model on the nonuniform mesh.More precisely,(2−α)-order,secondorder and(3−α)-order time-stepping schemes are developed for the timefractional MBE model based on the well known L1,L2-1σ,and L2 formulations in discretization of the time-fractional derivative,which are all proved to be unconditional energy dissipation in the sense of a modified discrete nonlocalenergy on the nonuniform mesh.In order to reduce the computational storage,we apply the sum of exponential technique to approximate the history part of the time-fractional derivative.Moreover,the scalar auxiliary variable(SAV)approach is introduced to deal with the nonlinear potential function and the history part of the fractional derivative.Furthermore,only first order method is used to discretize the introduced SAV equation,which will not affect high order accuracy of the unknown thin film height function by using some proper auxiliary variable functions V(ξ).To our knowledge,it is the first time to unconditionally establish the discrete nonlocal-energy dissipation law for the modified L1-,L2-1σ-,and L2-based high-order schemes on the nonuniform mesh,which is essentially important for such time-fractional MBE models with low regular solutions at initial time.Finally,a series of numerical experiments are carried out to verify the accuracy and efficiency of the proposed schemes.

Epitaxial growth and cracking of highly tough 7YSZ splats by thermal spray technology

Thermally sprayed coatings are essentially layered materials and contain large numbers of lamellar pores. It is thus quite necessary to clarify the formation mechanism of lamellar pores which significantly influence coating performances. In the present study, to elaborate the formation mechanism of lamellar pores, the yttria-stabilized zirconia(ZrO_2–7 wt% Y_2O_3, 7YSZ) splats, which have high fracture toughness and tetragonal phase stability, were employed. Interestingly, anomalous epitaxial growth occurred for all deposition temperatures in spite of the extremely high cooling rate,which clearly indicated chemical bonding and complete contact at splat/substrate interface before splat cooling. However, transverse spallation substantially occurred for all deposition temperatures in spite of the high fracture toughness of 7YSZ, which revealed that the lamellar pores were from transverse cracking/spallation due to the large stress during splat cooling. Additionally, fracture mechanics analysis was carried out, and it was found that the stress arose from the constraint effect of the shrinkage of the splat by locally heated substrate with the value about 1.97 GPa. This clearly demonstrated that the stress was indeed large enough to drive transverse cracking/spallation forming lamellar pores during splat cooling. All of these contribute to understanding the essential features of lamellar bonding and further tailoring the coating structures and performance.

Epitaxial growth of large-area and highly crystalline anisotropic ReSe2 atomic layer

The anisotropic two-dimensional （2D） layered material rhenium disulfide （ReSe2） has attracted considerable attention because of its unusual properties and promising applications in electronic and optoelectronic devices. However, because of its low lattice symmetry and interlayer decoupling, anisotropic growth and out-of-plane growth occur easily, yielding thick flakes, dendritic structure, or flower-like structure. In this stud34 we demonstrated a bottom-up method for the controlled and scalable synthesis of ReSe2 by van der Waals epitaxy. To achieve controllable growth, a micro-reactor with a confined reaction space was constructed by stacking two mica substrates in the chemical vapor deposition system. Within the confined reaction space, the nucleation density and growth rate of ReSe2 were significantly reduced, favoring the large-area synthesis of ReSe2 with a uniform monolayer thickness. The morphological evolution of ReSe2 with growth temperature indicated that the anisotropic growth was suppressed at a low growth temperature （〈600 ℃）. Field-effect transistors employing the grown ReSe2 exhibited p-type conduction with a current ON/OFF ratio up to 10s and a hole carrier mobility of 0.98 cm^2/（V·s）. Furthermore, the ReSe2 device exhibited an outstanding photoresponse to near-infrared light, with responsivity up to 8.4 and 5.1 A/W for 850- and 940-nm light, respectively. This work not only promotes the large-scale application of ReSe2 in high-performance electronic devices but also clarifies the growth mechanism of low-lattice symmetry 2D materials.

Effect of substrate cooling on the epitaxial growth of Ni-based single-crystal superalloy fabricated by direct energy deposition

The columnar-to-equiaxed transition(CET)or the formation of stray grains in the laser melting deposition is the least desirable for the repair of single-crystal blades.In this work,the forced water-cooling was conducted on a single-crystal Rene N5 substrate during the direct energy deposition(DED).The single track remelting,one-layer,two-layer,and eight-layer depositions were investigated to explore the grain growth mechanism.The solidification conditions of the DED process,including temperature field,temperature gradient,and solidification speed,were numerically analyzed by a finite element model.The single-track remelting results showed that the fraction of columnar crystal regions increases from55.81%in the air-cooled sample to 77.14%in the water-cooled one.The single-track deposits of one-and two-layer have the same trend,where the proportion of columnar crystal height was higher under the forced water-cooled condition.The electron backscattered diffraction(EBSD)grain-structure maps of an eight-layer deposit show that the epitaxial growth height increases from 1 mm in the air-cooling sample to 1.5 mm in the water-cooling one.The numerical results showed that the tempe rature gradient in[0011 direction was significantly increased by using forced water-cooling.In conclusion,the in-situ substrate cooling can become a potential method to promote epitaxial growth during DED via the influence on CET occurrence.

Vapor-assisted epitaxial growth of porphyrin-based MOF thin film for nonlinear optical limiting

Fabrication of metal-organic frameworks(MOFs)thin films has been an efficient way to expand their functionalities and applications.Here,we use the vapor-assisted deposition(VAD)method to epitaxially grow a porphyrin-based MOF PCN-222 film.That is,vapor source assists to deposit pre-treated precursor solution on quartz substrate to form a continuous PCN-222 film.Furthermore,utilizing the post-treated encapsulation of functional carbon-based nanoparticles,the carbon nanodots(CND)and Pt doped CND(Pt/CND)are well loaded into the pores of PCN-222 film,the size(~3.1 nm)of which is highly close to the pore size of the corresponding MOF(~3.7 nm).The Z-scan results reveal that PCN-222 film exhibits high reverse saturable absorption.In addition,encapsulation of carbon based nanodots into PCN-222 film could enhance the nonlinear optical limiting effect benefiting from the host-guest combination.This study serves to present both the available toolbox of thin film preparation and high potential for precise synthetic nanocomposite films in optical limiting devices.

Variation of crystal orientation during epitaxial growth of dendrites by laser deposition

A nickel-based superalloy was deposited onto a single crystal substrate based on epitaxial laser metal forming （E-LMF）. The microstructure development in two depositions has been researched. For the first time, the crystal orientation of dendrites varying beyond 20° was found when the dendrites deflected in deposition. In addition, a new grain boundary was found between different orientation dendrites in a grain, and the detected grain boundary angle was 23°. The result shows that flowing field in laser pool is responsible for this phenomenon.

Epitaxial growth of large area ZrS_(2)2D semiconductor films on sapphire for optoelectronics

Recently,group-IVB semiconducting transition metal dichalcogenides(TMDs)of ZrS_(2) have attracted significant research interest due to its layered nature,moderate band gap,and extraordinary physical properties.Most device applications require a deposition of high quality large-area uniform ZrS_(2) single crystalline films,which has not yet been achieved.In this work,for the first time,we demonstrate the epitaxial growth of high quality large-area uniform ZrS_(2) films on c-plane sapphire substrates by chemical vapor deposition.An atomically sharp interface is observed due to the supercell matching between ZrS_(2) and sapphire,and their epitaxial relationship is found to be ZrS_(2)(0001)[1010]||Al_(2)O_(3)(0001)[1120].The epitaxial ZrS_(2) film exhibits n-type semiconductor behavior with a room temperature mobility of 2.4 cm^(2)·V^(−1)·s^(−1),and the optical phonon is the dominant scattering mechanism at room temperature or above.Furthermore,the optoelectronic applications of ZrS_(2) films are demonstrated by fabricating photodetector devices.The ZrS_(2) photodetectors exhibit the excellent comprehensive performance,such as a light on/off ratio of 106 and a specific detectivity of 2.6×10^(12) Jones,which are the highest values compared with the photodetectors based on other group-IVB two-dimensional TMDs.

Epitaxial growth of CsPbBr_(3)-PbS vertical and lateral heterostructures for visible to infrared broadband photodetection

Owing to their excellent optoelectronic properties, halide perovskite is very promising for photodetectors and other optoelectronic devices. Perovskite heterostructures are considered to be the key components for these devices. However, it is challenging to rationally synthesize those heterostructures. Here, we demonstrate that perovskite can be epitaxially grown on PbS by vapor transport, thereby creating an interesting CsPbBr_(3)-PbS heterostructure. Remarkably, photodetectors based on CsPbBr_(3)-PbS heterostructures exhibit visible to infrared broadband response with room temperature operation up to 2 μm. The room temperature detectivity higher than 1.0 × 10^(9) Jones was obtained in the 1.8- to 2-μm range. Furthermore, the p-n heterojunction exhibits a clear rectifying characteristic and enables detector to operate at zero-bias. Our study provides fundamentally contributes to establish the epitaxial growth perovskite heterostructures and demonstrate a materials platform for efficient perovskite-based optoelectronic devices.

Above 700 V superjunction MOSFETs fabricated by deep trench etching and epitaxial growth

Silicon superjunction power MOSFETs were fabricated with deep trench etching and epitaxial growth,based on the process platform of the Shanghai Hua Hong NEC Electronics Company Limited.The breakdown voltages of the fabricated superjunction MOSFETs are above 700 V and agree with the simulation.The dynamic characteristics, especially reverse diode characteristics,are equivalent or even superior to foreign counterparts.

Review of a direct epitaxial approach to achieving micro-LEDs

There is a significantly increasing demand of developing augmented reality and virtual reality(AR and VR) devices,where micro-LEDs(μLEDs) with a dimension of ≤ 5 μm are the key elements. Typically, μLEDs are fabricated by dry-etching technologies, unavoidably leading to a severe degradation in optical performance as a result of dry-etching induced damages. This becomes a particularly severe issue when the dimension of LEDs is ≤ 10 μm. In order to address the fundamental challenge, the Sheffield team has proposed and then developed a direct epitaxial approach to achievingμLEDs, where the dry-etching technologies for the formation of μLED mesas are not needed anymore. This paper provides a review on this technology and then demonstrates a number of monolithically integrated devices on a single chip using this technology.

Epitaxial growth and characterization of Gd_2O_3-doped HfO_2 film on Ge(001) substrates with zero interface layer

The GHO （Gd2O3-doped HfO2） films were epitaxially grown on Ge （001） substrates adopting cube-on-cube mode with zero interface layer using pulsed laser deposition （PLD）. Reflection high-energy electron diffraction （RHEED） and high-resolution transmission electron microscopy （HRTEM） observation revealed a sharp interface of GHO/Ge and orientation relationship corre-sponding to （001）GHO//（001）Ge and [011] GHO//[011]Ge. The band offset for GHO/Ge stack was evaluated to be 3.92 eV for va-lence band and 1.38 eV for conduction band by X-ray photoelectron spectrum. Small equivalent oxide thickness （0.49 nm） and inter-face state density （7×1011 cm-2） were achieved from Au/Ti/GHO/Ge/Al capacitors.

Heteroepitaxial growth of InP/GaAs(100) by metalorganic chemical vapor deposition

Using two-step method InP epilayers were grown on GaAs（100） substrates by low-pressure metalorganic chemical vapor deposition （LP-MOCVD）. X-ray diffraction （XRD） and room-temperature （RT） photolu- minescence （PL） were employed to characterize the quality of InP epilayer. The best scheme of growing InP/GaAs（100） heterostructures was obtained by optimizing the initial low-temperature （LT） InP growth conditions, investigating the effects of thermal cycle annealing （TCA） and strained layer superlattice （SLS） on InP epilayers. Compared with annealing, 10-periods Ga0.1In0.9P/InP SLS inserted into InP epilayers can improve the quality of epilayers dramatically, by this means, for 2.6-#m-thick heteroepitaxial InP, the full-widths at half-maximum （FWHMs） of XRD ω and ω-28 scans are 219 and 203 arcsec, respectively, the RT PL spectrum shows the band edge transition of InP, the FWHM is 42 meV. In addition, the successful growth of InP/In0.53Ga0.47As MQWs on GaAs（100） substrates indicates the quality of device demand of InP/GaAs heterostructures.

Epitaxial growth on 4H-SiC by TCS as a silicon precursor

Epitaxial growth on n-type 4H-SiC 8° off-oriented substrates with a size of 10 × 10 mm^2 at different temperatures with various gas flow rates has been performed in a horizontal hot wall CVD reactor, using trichlorosilane （TCS） as a silicon precursor source together with ethylene as a carbon precursor source. The growth rate reached 23 μm/h and the optimal epilayer was obtained at 1600℃ with a TCS flow rate of 12 sccm in C/Si of 0.42, which has a good surface morphology with a low RMS of 0.64 nm in an area of 10 x 10 pm2. The homoepitaxial layer was obtained at 1500℃ with low growth rate （〈 5 μm/h） and the 3C-SiC epilayers were obtained at 1650 ℃ with a growth rate of 60-70 μm/h. It is estimated that the structural properties of the epilayers have a relationship with the growth temperature and growth rate. Silicon droplets with different sizes are observed on the surface of the homoepitaxial layer in a low C/Si ratio of 0.32.

Epitaxial Growth of YBCO Thin Films on LaAlO_3 Substrate with CeO_2 Buffer Layer

By the r. f. magnetron sputtering method, the CeO_2 buffer layers were prepared on (100) LaAlO_3 sub-strates. The results of X-ray diffraction and Ф-scan indicated that the CeO_2 films were unique ( 100)-orientedand epitaxial. The YBa_2Cu_3O_(7-6)(YBCO) films, which were deposited on the CeO_2/LaAlO_3 by d. c. magnetronsputtering, exhibited transition temperatures of 89～91 K,and had critical current densities exceeding 10￣6 A/cm￣2 at 77 K in zero magnetic field.

Novel two-dimensional transition metal chalcogenides created by epitaxial growth

Two-dimensional(2D) materials have been a very important field in condensed matter physics, materials science, chemistry, and electronics. In a variety of 2D materials, transition metal chalcogenides are of particular interest due to their unique structures and rich properties. In this review, we introduce a series of 2D transition metal chalcogenides prepared by epitaxial growth. We show that not only 2D transition metal dichalcogenides can be grown, but also the transition metal chalcogenides that do not have bulk counterparts, and even patterned transition metal chalcogenides can be fabricated. We discuss the formation mechanisms of the novel structures, their interesting properties, and potential applications of these 2D transition metal chalcogenides. Finally, we give a summary and some perspectives on future studies.