Engineering d-band states of(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4)material for photocatalytic syngas production

The d-band states of catalytic materials participate in adsorbing reactive intermediate species and determine the catalytic behaviors in CO_(2)reduction reactions.However,surface d-band states relating to the photocatalytic CO_(2)reduction reactions behaviors are rarely concerned.Herein,a slightly amount of Cd^(2+)is decorated on the surface of(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4)material(Cd^(2+)/(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4))to tune the surface d-band states for improved CO_(2)+2reduction reactions.The Cd/(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4)is fabricated via the facile ions-exchange method to make that slightly Zn2+is substituted by Cd^(2+).The Cd^(2+)/(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4)exhibits much enhanced photocatalytic activity in CO_(2)reduction reactions to produce CO and water splitting to produce H_(2).Physical characterizations show that the energy band structure is not changed obviously.Density functional theory reveals that Cd^(2+)/(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4)possesses a closer shift of d-band center to Fermi level than(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4),suggesting easier adsorption of CO_(2)reduction reactive intermediates after Cd^(2+)decoration.Further calculations confirm that a relatively reduced adsorption Gibbs energy of reactive intermediates in CO_(2)reduction reaction is required on Zn atoms in Cd^(2+)/(CuGa)_(x)Zn_(1-2x)Ga_(2)S_(4)material,benefiting the photocatalytic CO_(2)reduction reactions.This work engineers surface d-band states by surface Cd^(2+)decoration,which gives an effective strategy to design highly efficient photocatalysts for syngas production.

Lithium Ion Transport Environment by Molecular Vibrations in Ion-Conducting Glasses

Controlling Li ion transport in glasses at atomic and molecular levels is key to realizing all-solid-state batteries,a promising technology for electric vehicles.In this context,Li_(3)PS_(4)glass,a promising solid electrolyte candidate,exhibits dynamic coupling between the Li^(+)cation mobility and the PS_(4)^(3-)anion libration,which is commonly referred to as the paddlewheel effect.In addition,it exhibits a concerted cation diffusion effect(i.e.,a cation-cation interaction),which is regarded as the essence of high Li ion transport.However,the correlation between the Li^(+)ions within the glass structure can only be vaguely determined,due to the limited experimental information that can be obtained.Here,this study reports that the Li ions present in glasses can be classified by evaluating their valence oscillations via Bader analysis to topologically analyze the chemical bonds.It is found that three types of Li ions are present in Li_(3)PS_(4)glass,and that the more mobile Li ions(i.e.,the Li3-type ions)exhibit a characteristic correlation at relatively long distances of 4.0-5.0A.Furthermore,reverse Monte Carlo simulations combined with deep learning potentials that reproduce X-ray,neutron,and electron diffraction pair distribution functions showed an increase in the number of Li3-type ions for partially crystallized glass structures with improved Li ion transport properties.Our results show order within the disorder of the Li ion distribution in the glass by a topological analysis of their valences.Thus,considering the molecular vibrations in the glass during the evaluation of the Li ion valences is expected to lead to the development of new solid electrolytes.

β-cyclodextrin as Lithium-ion Diffusion Channel with Enhanced Kinetics for Stable Silicon Anode

Silicon(Si)is regarded as a promising anode material for next-generation lithium-ion batteries due to its ultrahigh theoretical capacity.However,the drastic volume change and the continuous solid electrolyte interphase(SEI)formation during the lithiation/delithiation process seriously hinder its practical application as commercial anodes.Herein,macrocyclic betacyclodextrin(β-CD)has been designed as the diffusion channel for lithium ions at the molecular scale.The diameter of molecular channel is approximately comparable with the solvated lithium ions,which enables the transport of lithium ions and prevents the penetration of solvent molecules.Moreover,the addition ofβ-CD changes the formation behavior of SEI layer and stabilizes the Si nanoparticles.The enhanced electrochemical performances in terms of fast kinetics and improved stability have been achieved.The Si anode with the particularly selected lithium-ion diffusion channel and stabilized SEI layer exhibits a high reversible capability of 2562 m Ah g-1 after 50 cycles at the current density of 500 m A g-1,1944 m Ah g-1 after 200 cycles at the current density of 1 A g-1,and high rate performance.The novel strategy of molecular channel for lithium-ion diffusion offers new insights into the design of alloy-typed anode electrodes with high capacity for lithium-ion batteries.

Controllable fabrication and structure evolution of hierarchical 1T-MoS_(2) nanospheres for efficient hydrogen evolution

The layered materials have demonstrated great prospects as cost-effective substitutes for precious electrocatalysts in hydrogen evolution reaction.Research efforts have been devoted to synthesizing highly conductive MoS_(2) with the substantial cardinal plane and edge active sites.Here,we successfully synthesized a hierarchical 1T/2H–MoS_(2) with sodium ion insertion via a facile hydrothermal method.The contents of the 1T-phase can be flexibly controlled by different hydrothermal temperatures(160 ~ 200°C).And the modified uniformly dispersed 1T/2H–MoS_(2) nanospheres with different d spacings were designed to enhance the electrocatalytic efficiency by adding SiO_(2) and through the ion exchange process of Na OH and HF solution.The as-synthesized Na+intercalated 1T-MoS_(2) nanosphere with an expanded interlayer of 0.95 nm obtained at 160°C exhibits a prominent electrocatalytic performance of hydrogen evolution reaction with a comparable overpotential of 255 m V and a remarkably small Tafel slope of 44 m V/decade.Therefore,this study provides a facile and controllable strategy to yield interlayerexpanded 1T-MoS_(2) nanospheres,making it a potentially competitive hydrogen evolution catalyst for the hydrogen cell.

Schottky photodiode using submicron thick diamond epilayer for flame sensing

The sensing of a flame can be performed by using wide-bandgap semiconductors, which offer a high signal-to-noise ratio since they only response the ultraviolet emission in the flame. Diamond is a robust semiconductor with a wide-bandgap of 5.5 e V, exhibiting an intrinsic solar-blindness for deep-ultraviolet(DUV) detection. In this work, by using a submicron thick boron-doped diamond epilayer grown on a type-Ib diamond substrate, a Schottky photodiode device structure- based flame sensor is demonstrated. The photodiode exhibits extremely low dark current in both forward and reverse modes due to the holes depletion in the epilayer. The photodiode has a photoconductivity gain larger than 100 and a threshold wavelength of 330 nm in the forward bias mode. CO and OH emission bands with wavelengths shorter than 330 nm in a flame light are detected at a forward voltage of-10 V. An alcohol lamp flame in the distance of 250 mm is directly detected without a focusing lens of flame light.

Hollow spherical rare-earth-doped yttrium oxysulfate： A novel structure for upconversion

A facile biomolecule-assisted hydrothermal route followed by calcination has been employed for the preparation of monoclinic yttrium oxysulfate hollow spheres doped with other rare-earth ions （Yb3＋ and Eu3＋ or Er3＋）. The formation of hollow spheres may involve Ostwald ripening. The resulting hybrid materials were used for upconversion applications. The host crystal structure allows the easy co-doping of two different rare-earth metal ions without significantly changing the host lattice. The luminescent properties were affected by the ratio and concentration of dopant rare-earth metal ions due to energy transfer and the symmetry of the crystal field. The type of luminescent center and the crystallinity of samples were also shown to have a significant influence on the optical properties of the as-prepared products.

Emerging in-plane anisotropic two-dimensional materials

Black phosphorus(BP)is a rapidly up and coming star in two-dimensional(2D)materials.The unique characteristic of BP is its in-plane anisotropy.This characteristic of BP ignites a new type of 2D materials that have low-symmetry structures and in-plane anisotropic properties.On this basis,they offer richer and more unique low-dimensional physics compared to isotropic 2D materials,thus providing a fertile ground for novel applications including electronics,optoelectronics,molecular detection,thermoelectric,piezoelectric,and ferroelectric with respect to in-plane anisotropy.This article reviews the recent advance in characterization and applications of in-plane anisotropic 2D materials.

High-throughput screening and machine learning for the efficient growth of high-quality single-wall carbon nanotubes

It has been a great challenge to optimize the growth conditions toward structure-controlled growth of single-wall carbon nanotubes(SWCNTs).Here,a high-throughput method combined with machine learning is reported that efficiently screens the growth conditions for the synthesis of high-quality SWCNTs.Patterned cobalt(Co)nanoparticles were deposited on a numerically marked silicon wafer as catalysts,and parameters of temperature,reduction time and carbon precursor were optimized.The crystallinity of the SWCNTs was characterized by Raman spectroscopy where the featured G/D peak intensity(IG/ID)was extracted automatically and mapped to the growth parameters to build a database.1,280 data were collected to train machine learning models.Random forest regression(RFR)showed high precision in predicting the growth conditions for high-quality SWCNTs,as validated by further chemical vapor deposition(CVD)growth.This method shows great potential in structure-controlled growth of SWCNTs.

Nanometer-size Na cluster formation in micropore of hard carbon as origin of higher-capacity Na-ion battery

Development of high-energy-density anode is crucial for practical application of Na-ion battery as a post Li-ion battery.Hard carbon(HC),though a promising anode candidate,still has bottlenecks of insufficient capacity and unclear microscopic picture.Usage of the micropore has been recently discussed,however,the underlying sodiation mechanism is still controversial.Herein we examined the origin for the high-capacity sodiation of HC,based on density functional theory calculations.We demonstrated that nanometersize Na cluster with 3–6 layers is energetically stable between two sheets of graphene,a model micropore,in addition to the adsorption and intercalation mechanisms.The finding well explains the extended capacity over typical 300 mAhg^(−1),up to 478 mAhg^(−1) recently found in the MgO-templated HC.We also clarified that the MgO-template can produce suitable nanometersize micropores with slightly defective graphitic domains in HC.The present study considerably promotes the atomistic theory of sodiation mechanism and complicated HC science.

High-pressure MOCVD growth of InGaN thick films toward the photovoltaic applications

The highly efficient photovoltaic cells require the In-rich InGaN film with a thickness more than 300 nm to achieve the effective photo-electricity energy conversion.However,the InGaN thick films suffer from poor crystalline quality and phase separations by using the conventional low-pressure metal organic chemical vapor deposition(MOCVD).We report on the growth of 0.3-1μm-thick InGaN films with a specially designed vertical-type high-pressure MOCVD at the pressure up to 2.5 atms.The In incorporation is found to be greatly enhanced at the elevated pressures although the growth temperatures are the same.The phase separations are inhibited when the growth pressure is higher than atmospheric pressure,leading to the improved crystalline quality and better surface morphologies especially for the In-rich InGaN.The In 0.4 Ga 0.6 N with the thickness of 300 nm is further demonstrated as the active region of solar cells,and the widest photoresponse range from ultraviolet to more than 750 nm is achieved.

Nanotubes in a Gradient Electric Field as Revealed by STM TEM Technique

We have investigated the behavior of two nanotube systems,carbon and boron nitride,under controlled applied voltages in a high-resolution transmission electron microscope(TEM)equipped with a scanning tunneling microscope(STM)unit.Individual nanotubes(or thin bundles)were positioned between a piezo-movable gold electrode and a biased(up to±140 V)STM tip inside the pole-piece of the microscope.The structures studied include double-and multi-walled carbon nanotubes(the latter having diverse morphologies due to the various synthetic procedures utilized),few-layered boron nitride nanotube bundles and multi-walled boron nitride nanotubes(with or without functionalized surfaces).The electrical breakdown,physical failure,and electrostatic interactions are documented for each system.

Microstructure analysis and thermoelectric properties of iron doped CuGaTe_(2)

Chalcopyrite related compounds have attracted much attention in recent years due to their promising thermoelectric properties.In this research we report Fe doping in chalcopyrite-type CuGaTe_(2)and its influence on structural and thermal transport properties.We synthesized polycrystalline samples with composition CuGa_(1-x)Fe_(x)Te_(2)with x=0.0 to 0.05 by spark plasma sintering method.For structural analysis powder X-ray diffraction and electron probe micro analysis were employed.Solubility of Fe in CuGaTe_(2)was found to be very small,and other phases like FeTe_(2)and CuTe were identified.Thermal conductivity showed a significant decrease with the addition of Fe up to x=0.02,which started to increase for x≥0.03.On the other hand,the addition of Fe caused slight increase in the power factor from 1.3mW/K^(2)m for x=0.0 to 1.6 mW/K^(2)m for x=0.02 at T=770 K.As a result,ZT peak value of 0.92 is recorded for x=0.02 at 870 K,which corresponds to an enhancement of 60%from that of non-doped CuGaTe_(2).This work demonstrates that thermoelectric properties of compositematerials can be greatly improved by controlling its microstructure.

Spatial-controlled etching of coordination polymers

Nanoarchitectonics provide versatile opportunities for modifying the properties of coordination polymers(CP) other than molecular engineering.Spatial-controlled etching focuses on the controlled disassembly of the frameworks.The etching method provides an excellent opportunity for tailoring the properties and functions of the CPs.Here,we discuss the mechanism for controlled etching of the CPs and summarized the two main strategies utilized so far.Several examples are illustrated to demonstrate recent developments in this area.Moreover,advantages of the etched CPs are summarized in several important applications,including energy storage,catalysis and nanomedicine.

New insights into the effects of molecular weight and end group on the temperature-induced phase transition of poly(N-isopropylacrylamide) in water

In an attempt to clarify issues related to the molecular weight dependence of the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in water,we prepared a library of PNIPAM samples of well-controlled molecular weight (7000 to 45000 g/mol) bearing identical groups on each chain end.The polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) with a bifunctional chain tranfer agent and further end group modification.The effects of the end group chemical structure,hydroxyethyl (HE),propargyl (Pr),chloroethyl (CE),n-butyl (nBu),n-hexyl (nHe),and isobutylsulfanylthiosulfanyl (IBS) on the phase transition temperature of aqueous PNIPAM solutions were investigated by high-sensitivity differential scanning calorimetry (HS-DSC),yielding the enthalpy ΔH and the endotherm maximum temperature (T M),and turbidimetry,providing the cloud point (T CP) of each solution.The T CP and T M of the PNIPAM sample of lowest molar mass (M n 7,000 g/mol,0.5 g/L) ranged,respectively,from 38.8 to 22.5 °C and 42.2 to 26.0 °C,depending on the structure of the end-group,whereas H showed no strong end-group dependence.The phase transition of all polymers,except,-di(n-butyl-PNIPAM),exhibited a marked dependence on the polymer molar mass.

Structure search of two-dimensional systems using CALYPSO methodology

The dimensionality of structures allows materials to be classified into zero-, one-, two-, and threedimensional systems. Two-dimensional (2D) systems have attracted a great deal of attention andtypically include surfaces, interfaces, and layered materials. Due to their varied properties, 2D systemshold promise for applications such as electronics, optoelectronics, magnetronics, and valleytronics.The design of 2D systems is an area of intensive research because of the rapid development of abinitio structure-searching methods. In this paper, we highlight recent research progress on acceleratingthe design of 2D systems using the CALYPSO methodology. Challenges and perspectives for futuredevelopments in 2D structure prediction methods are also presented.