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InGaN nanowires (NWs) are grown on pyramid textured Si substrates by stationary plasma-assisted molecular beam epitaxy (PA-MBE). The incidence angles of the highly directional source beams vary for different pyramid facets, inducing a distinct inter-facet modulation of the In content of the InGaN NWs, which is verified by spatial element distribution analysis. The resulting multi-wavelength emission is confirmed by photoluminescence (PL) and cathodoluminescence (CL). Pure GaN phase formation dominates on certain facets, which is attributed to extreme local growth conditions, such as low active N flux. On the same facets, InGaN NWs exhibit a morphology change close to the pyramid ridge, indicating inter-facet atom migration. This cross-talk effect due to inter-facet atom migration is verified by a decrease of the inter-facet In content modulation amplitude with shrinking pyramid size. A detailed analysis of the In content variation across individual pyramid facets and element distribution line profiles reveals that the cross-talk effect originates mainly from the inter-facet atom migration over the convex pyramid ridge facet boundaries rather than the concave base line facet boundaries. This is understood by first-principles calculations showing that the pyramid baseline facet boundary acts as an energy barrier for atom migration, which is much higher than that of the ridge facet boundary. The influence of the growth temperature on the inter-facet In content modulation is also presented. This work gives deep insight into the composition modulation for the realization of multi-color light-emitting devices based on the monolithic growth of InGaN NWs on pyramid textured Si substrates.

Supercapacitors that store energy through dual electrochemical layer capacitance or surface faradaic redox reactions are characterized by their fast charging/discharging capability, high power densities, and long cycling lifetime. However, the low energy density of supercapacitors seriously inhibits their practical applications. Herein, a dual-ion hybrid energy storage system using expanded graphite (EG) as the anion-intercalation supercapacitor-type cathode and graphite@nano-silicon@carbon (Si/C) as the cation intercalation battery-type anode is designed for efficient energy storage. The Si/C anode, synthesized by interfacial adhesion between nanosilicon and graphite with the help of pitch, demonstrates high specific capacity, remarkable cycling stability, and enhanced rate capability. Meanwhile, the EG cathode, which stores energy based on electrochemical double layer capacitance through its unique faradaic pseudocapacitive negative anion intercalation behaviour, demonstrates high energy densities of 462.9–356.5 W h kg−1 at power densities of 403–7130 W kg−1. The resulting Si/C//EG hybrid system delivered highly attractive energy densities of 252–222.6 W h kg−1 at power densities of 215–5420 W kg−1, which are superior to those of conventional electrochemical double layer capacitors and lithium-ion capacitors, making the dual-ion hybrid system a new type of energy storage device capable of achieving fast and efficient energy storage.

We introduce a novel concept for the design of functional surfaces of materials: Spatial surface charge engineering. We exploit the concept for an all-solid-state, epitaxial InN/InGaN-on-Si reference electrode to replace the inconvenient liquid-filled reference electrodes, such as Ag/AgCl. Reference electrodes are universal components of electrochemical sensors, ubiquitous in electrochemistry to set a constant potential. For subtle interrelation of structure design, surface morphology and the unique surface charge properties of InGaN, the reference electrode has less than 10 mV/decade sensitivity over a wide concentration range, evaluated for KCl aqueous solutions and less than 2 mV/hour long-time drift over 12 hours. Key is a nanoscale charge balanced surface for the right InGaN composition, InN amount and InGaN surface morphology, depending on growth conditions and layer thickness, which is underpinned by the surface potential measured by Kelvin probe force microscopy. When paired with the InN/InGaN quantum dot sensing electrode with super-Nernstian sensitivity, where only structure design and surface morphology are changed, this completes an all-InGaN-based electrochemical sensor with unprecedented performance.

The heterostructuring and doping concepts have proved to obtain a novel n-InGaN/p-Cu2O nanowire (NW) photoanode by strong enhancement of the photocurrent compared to a bare InGaN NW photoanode in solar water splitting. The large photocurrent is due to the maximized photocarrier separation and hole transfer to the surface in the depletion zone of the p–n heterojunction established by the p-Cu2O layer, forming a thin, uniform shell-layer around the n-InGaN NW core by electrodeposition. For sufficiently thin Cu2O layers, the upward energy band bending in the depletion zone extends up to the surface for optimized hole transport and surface reaction. Thick Cu2O layers on top of the InGaN NWs act as common photocathodes. The functional InGaN/Cu2O heterostructure core-shell NW photoanode is chemically self-stabilized at positive applied voltage by a thin CuO surface layer. Final deposition of the earth-abundant NiOOH co-catalyst boosts the photocurrent of the InGaN/Cu2O/NiOOH complete NW photoanode into the competitive mA/cm2 range.

Si-based anode with hierarchical protective function and hollow ring-like carbon matrix has been successfully designed and prepared by a simple one-step spray drying method. Nano-Si particles are coated by carbon layer and then encapsulated in a strong carbon matrix with hollow ring-like structure composed of carbon nanotubes and wrinkled graphene sheets. The Si-based anode, nano-Si@carbon/carbon nanotubes@graphene sheets, exhibits excellent electrochemical performance including high initial coloumbic efficiency, favorable cyclic stability and outstanding rate capability. The composite delivers an initial discharge/charge capacity of 2891.7/2533.3 mAh g−1 with a high initial coloumbic efficiency of 87.6%, high capacity of 1524.3 mAh g−1 after 130 cycles with high capacity retention of 92.4% (vs. 1618.4 mAh g−1 for the 100 cycles), and high capacity maintaining at 1073.2/1016.2 mAh g−1 at a large current density of 1.6 A g−1. Furthermore, the scanning electron microscopy and transmission electron microscopy images of the composite electrode after several operating cycles also indicate that composite electrode exhibits structural stability and nano-Si particles are still wrapped by the carbon matrix material. Therefore, the composite is very promising anode for lithium ion batteries.

An anisotropic piezoelectric response is demonstrated from InGaN nanowires (NWs) over a pyramid-textured Si(100) substrate with an interfacet composition and topography modulation induced by stationary molecular beam epitaxy growth conditions, taking advantage of the unidirectional source beam flux. The variations of InGaN NWs between the pyramid facets are verified in terms of morphology, element distribution, and crystalline properties. The piezoelectric response is investigated by electrical atomic force microscopy (AFM) with a statistic analyzing method. Representative pyramids from the ensemble, on top of which InGaN NWs grown with a substrate held at an oblique angle, were characterized for understanding and confirming the degree of anisotropy. The positive deviated oscillation of the peak force error is identified as a measure of the effective AFM tip/NW interaction with respect to the electrical contact and mechanical deformation. The Schottky contact between the metal-coated AFM tip and the NWs on the different facets reveals distinctions consistent with the interfacet composition variation. The interfacet variation of the piezoelectric response of the InGaN NWs is first evaluated by electrical AFM under zero bias. The average current monotonically depends on the scan frequency, which determines the average peak force error, that is, mechanical deformation, with a facet characteristic slope. A piezoelectric nanogenerator device is fabricated out of a sample with an ensemble of pyramids, which exhibits anisotropic output under periodic directional pressing. This work provides a universal strategy for the synthesis of composite semiconductor materials with an anisotropic piezoelectric response.

We demonstrate multi-wavelength light emission from InGaN nanowires (NWs) monolithically grown on pyramid-textured Si(100) substrates by plasma-assisted molecular beam epitaxy (MBE) under stationary conditions. Taking advantage of the highly unidirectional source material beam fluxes, the In content of the NWs is tuned on the different pyramid facets due to varied incidence angle. This is confirmed by distinct NW morphologies observed by scanning electron microscopy (SEM) and by energy-dispersive X-ray (EDX) element mapping. Photoluminescence and cathodoluminescence (CL) reveal multiple lines originating from InGaN NWs on the different pyramid facets. The anomalous temperature dependence of the emission wavelength results from carrier redistribution between localized or confined states, spontaneously formed within the NWs due to composition fluctuations, verified by high-resolution EDX elemental analysis. First-principles calculations show that the pyramid facet edges act as a barrier for atom migration and enhance atom incorporation. This leads to uniform composition within the facets for not too high a growth temperature, consistent with the SEM, EDX and CL results. At elevated temperature, InGaN decomposition and In desorption are enhanced on facets with low growth rate, accompanied by Ga inter-facet migration, leading to non-uniform composition over the Ga migration length which is deduced to be around 580 nm. Our study presents a method for the fabrication of multi-wavelength light sources by highly unidirectional MBE on textured Si substrates towards color temperature-tunable solid-state lighting and RGB light-emitting diode displays.

Layered Li-rich cathode materials Li1.2Mn0.534Ni0.133Co0.133O2 (LNCMN-0) and Na doping Li1.1Na0.1Mn0.534Ni0.133Co0.133O2 (LNCMN-0.1) are prepared successfully by a co-precipitation method and several consecutive calcination treatments. Besides, the phase structure, morphology, and electrochemical properties of the four samples are studied in detail using X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge-discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Although the discharge capacity of spherical LNCMN-0.1 decreases slightly at 0.1 C (1 C = 250 mA g−1), compared to the pristine LNCMN-0, it is noteworthy that the LNCMN-0.1 matched with dual Li+/Na+ electrolyte exhibit superior stability performance at 1 C, as well as enhanced rate capability. The LNCMN-0.1 (Li+/Na+) delivers an initial discharge specific capacity of 267.61 mAh g−1 at 0.1 C between 2.0 and 4.8 V at room temperature and initial coulombic efficiency of 83.51%, which is higher than the LNCMN-0 samples (76.42 and 81.54%). The experimental results verify that Na doping combined with dual Li+/Na+ electrolyte can generate a synergistic effect, which is a promising idea to ameliorate the electrochemical performance for this material.

To reduce the influence from volume expansion of silicon during lithium lithiation/delithiation, milled flake graphite/plasma nano-silicon@carbon (MFG/PNSi@C) composite with void sandwich structure is synthesized by assembling thin MFG (thickness of 150 nm) sheets loading with carbon-coated PNSi (plasma nano-silicon) via a facile spray drying method. The MFG/PNSi@C composite, as lithium ion battery anode, exhibits excellent electrochemical performance at room temperature and displays an outstanding cyclic property even at high temperature. The MFG/PNSi@C electrode delivers reversible capacity of 1141 mAh g−1, and high initial Coulombic efficiency of 84.4%, and capacity retention of 84.1% after 200 cycles at a current density of 0.1 A g−1. Even at the current density of 0.2 and 0.4 A g−1, the reversible capacities of 1168 and 1102 mAh g−1 can be achieved respectively, with the capacity retention of 68.9% and 63.9% after 200 cycles. Even the work temperature goes up 60 °C, the discharge/charge capacities of 832/808 mAh g−1 can be obtained at a current density of 0.1 A g−1. The stable cyclic performance is mainly due to the void sandwich structure of the MFG/PNSi@C composite, which dramatically shortens lithium ion diffusion path and pitch carbon shell can buffer huge volume expansion.

In this work, a graphene-decorated Li2S cathode has been prepared via spray drying method using Li2SO4, graphene oxide and sucrose as raw materials. During spray drying, sucrose melts and embeds Li2SO4 when Li2SO4 were sprayed out with graphene oxide and sucrose, and becomes sphere particles. The as-prepared Li2S composite was received after a heat treatment under nitrogen atmosphere. X-ray diffraction patterns confirm the cubic structure of Li2S and scanning electron microscope images reveal that Li2S and carbon components stay in sphere structure with diameter around 20 μm. The sphere Li2S composite shows enhanced performance when acts as cathode. Under current density of 100 mA g−1, a specific discharge capacity of 778 mAh g−1 has been achieved and the battery cycled over 60 rounds. Furtherly, the sphere composite was coupled with silicon/graphite anode to construct full cell system, suggesting large possibility to work with the current lithium-ion battery anodes.

Silicon with high theoretical specific capacity is a promising anode material, but the poor electronic conductivity and excessive volume expansion hinder its practical application. In order to solve this problem, a novel double core-shell structure composite Si/G/C-CVD coated by pitch pyrolysis and CVD (Chemical Vapor Deposition) carbon has been prepared. In the Si/G/C-CVD composite, nano-silicon particles and pitch particles are embedded on the surface of graphite particles, then the second carbon layer via CVD is added. The double carbon layer can protect nano-silicon particles from direct exposure to the electrolyte and enhance the electrochemistry performance during the lithium intercalation/extraction process. The as-prepared Si/G/C-CVD composite demonstrates superior electrochemical performance, with enhanced specific reversible capacity (688.44 mAh g−1 at 100 mA g− 1), excellent rate performance (261.66 mAh g−1 even at the specific current of 1.6A g− 1) and good cycle performance with little fading (91% after 155 cycles).

Direction sensitive piezoelectric response is demonstrated from a nanogenerator based on an InGaN nanowires array on a ridge textured Si (1 1 0) substrate with inter-facet topography modulation. Under stationary molecular beam epitaxy, distinct variations of the inclination orientation of the InGaN nanowires are created due to the different beam flux incidence angle between the facets, which act as the primary factor for the asymmetric piezoelectric output. The piezoelectric properties were first studied using an electrical atomic force microscope (AFM) in contact scan mode at zero bias. The InGaN NWs on opposite ridge facets show different piezoelectric output distribution under the same scanning geometry. The difference of the tangential force component due to the varied NWs tilting angle, applied on the NWs by the AFM probe tip, explains the non-uniform piezoelectric signal distribution. A capacitor type piezoelectric nanogenerator (PNG) device was fabricated, which exhibits pronounced direction sensitive piezoelectric response under rotated external pressure. This work gives a universal strategy on synthesis of composite semiconductor materials with anisotropic piezoelectric response in terms of a self-powered force direction sensitive angle sensor piezoelectric nanogenerator device.

We study Ⅲ-nitride nanowire (NW) anti-reflection structures employed as photoelectrocatalyst for solar water splitting. We found that 1D vertical InGaN NW arrays tilted by 73° exhibit maximized photocurrent. Therefore, we grow 3D InGaN NW arrays on the facets of oblique pyramid-textured Si (311) (OPSi/InGaN) by plasma-assisted molecular beam epitaxy, exhibiting facets tilted by 73°. In addition, using finite difference time domain simulations we find the crucial impact of the asymmetry of the oblique pyramid InGaN NW arrays on the light trapping. Compared with InGaN NWs grown on a planar Si substrate (Si/InGaN), the OPSi/InGaN photoanode exhibits ~500% enhancement of the photocurrent due to various light trapping effects attributed to: 1D vertical NW arrays, their tilt, 3D arrangement and asymmetry. Decorated with NiOOH co-catalyst, the OPSi/InGaN photoanode exhibits photocurrent densities in the mA cm−2 range. The present research provides a rational design for the fabrication of nanostructured photoelectrocatalyst with enhanced light absorption.

Carbon-coated core-shell structure artificial graphite@plasma nano-silicon@carbon (AG@PNSi@C) composite, applying as lithium ion battery anode material, has been prepared via spray drying method. The plasma nano-silicon (

Porous ZnFe2O4 nanorods have been successfully prepared by a simple spray-drying process followed by sintering. The structure and morphology of the samples were characterized by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. The porous structured ZnFe2O4 materials are successfully used as potential anode material for lithium-ion batteries. Electrochemical results show that the anodes exhibit good cycling performance and rate capability. The anode exhibits initial discharge capacity of approximately 1459 mAh g−1 with an initial coulombic efficiency of 77.8% at a constant density of 100 mA g−1. The discharge capacity of the ZnFe2O4 retained 1458 mA h g−1 after 120 cycles at the current rate of 100 mA g−1 and 456 mA h g−1 could be obtained at the current density of 5000 mA g−1 after 200 cycles. The discharge capacities can still be as high as 778 mAh g−1 at a high rate of 3000 mA g−1. Such remarkable electrochemical properties could be ascribed to the unique porous morphology with large surface area and porosity that were beneficial to facilitate the diffusion of Li ions and electrolyte into the electrodes, meanwhile prevent volume expansion/contraction during lithiation/dislithiation processes.

Si@carbon composites have been successfully prepared via spray drying and subsequent calcination using PSA microspheres, nano-silicon and natural graphite as raw materials. Nano-silicon with a 20–100 nm particle size is prepared by radio-frequency electromagnetic induction. Such small nano-silicon particles can effectively accommodate the volume expansion of the Si@carbon anode. Additionally, the unique core–shell structure of Si@carbon composites can effectively alleviate the agglomeration of nano-silicon particles. Electrochemical tests show that the Si/carbon electrode delivers a high initial discharge capacity of approximately 1404.27 mAh g−1 with an initial coulombic efficiency of 82.4 %. The discharge specific capacity remains as high as 73.6 % after 100 charging-discharging cycles, demonstrating the electrode material’s good cycle stability. In addition, the corresponding specific capacity of the Si@carbon composites electrode remains at around 1150 mAh g−1 at a current density of 1 A g−1. And when the current density is 0.1 A g−1, its specific capacity can still remain at around 920 mAh g−1, indicating excellent capacity reversibility. Therefore, Si@carbon composites are superior anode materials for high-performance Li-ion batteries.