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As a new type of energy-storage devices, lithium-ion capacitors (LICs) are designed to deliver high energy densities, high power densities, and long lifespan by integrating the battery-type anodes and capacitor-type cathodes. Achieving high energy and power density simultaneously is the challenge of LICs, which is mainly determined by the cathode and anode materials. In this mini-review, basing on the working principles of LICs, we discuss the categories and electrochemical performance as well as the matching strategies of the cathodes and anodes. In anodes, we focus on summarizing the structural design of the prelithiation transition-metal compounds based materials. In cathodes, we emphasize discussing the fabrication and morphology adjustment of the low dimensional carbon materials. Finally, the prospects and challenges confronting future research and development of LICs are provided.

Flexible supercapacitors (SCs) are desirable for elastic and clothing electronic products owning to their considerable safety, high foldability and outstanding power density. Herein, multilayered films composed of alternating mesoporous Nb4N5 nanobelts and rGO nanosheets (Nb4N5/rGO) are designed and fabricated exhibiting good flexibility. The folding Nb4N5/rGO film electrode reveals an areal capacitance of 141 mF cm-2 (at 1 mA cm-2) along with remarkable cycling stability (the capacitance retention is 90% after 6,000 cycles). The flexible SCs devices were constructed by interlayer couple films of Nb4N5/rGO electrodes with PVA/H2SO4 gel as the electrolyte, which exhibited huge volumetric capacitance of 19 F cm-3 (at 0.1 A cm-3) and a considerable energy density of 0.98 mW h cm-3 with a power density of 0.029 W cm-3. Additionally, the as-obtained folding devices bode outstanding cycling stability with capacitance retention of 89% after 4,000 cycles measured by cyclic voltammetry method (at 100 mV s-1). Above results about niobium nitride based flexible electrodes and devices exploit a platform for wearable electronics and flexible devices.

The cellular biocompatibility of two types of nanophase hydroxyapatites including nanophase standard hydroxyapatite (n-HA) and nanophase calcium deficient hydroxyapatite (n-CDHA) synthesized by a wet chemical method were assessed using primary cultured osteoblasts. Cytotoxicity of both materials was investigated with L929 cell line. The MTT method was used to evaluate the proliferation of osteoblasts on the third day and ALP activity assay was carried out on the fifth day. SEM was used to observe the morphology of the osteoblasts on the third day. Two types of nanophase hydroxyapatite both showed no cytotoxicity. Higher cell proliferation was observed on n-CDHA than n-HA. At the same time, cells spread more actively on the n-CDHA group. The ALP level of n-CDHA was also significantly higher on the former. Our results show that the n-CDHA is more suitable for osteoblasts growth and is also helpful for ALP synthesis.

We present the enhanced wet etching of GaN epilayer implanted with Au+ ion. Patterned GaN with 2 microm-wide sink-like strips was achieved by using 500 keV Au+ ion implantation and KOH etching. The Dependence of etching depth on etching time for the implantation at different ion fluences was investigated. The experiment showed that the damaged GaN area could be almost etched out at high ion fluence, and the etching depth could exceed the project range of incident 500 keV Au+ ion. The etch pits could be observed at the bottom of the etched area. The -400 nm depth etching could be achieved with high fluence implantation after a long etching time, and the edge of etched area could remain clear until the etching process had passed 40 min. As-deposited SiO2 spheres were used to mask the GaN sample in implantation process to investigate the etching effect. -70 nm wave of the GaN surface was observed. The results of our experiments may suggest an approach to the fabricating of GaN devices.

Titanium oxide nanotube arrays (TiO2-NTAs) with different diameters and lengths are prepared by anodization of titanium foils in a water/ethylene glycol solution (5:95 V/V) containing 0.3 wt% NH4F. The effects of the diameters, lengths and crystalline phases of the NTAs on the photocatalytic (PC) activity are systematically evaluated. Larger pore diameter results in higher PC activity. The PC activity increases initially and then decreases with lengths for TiO2-NTAs and the optimal length that yields the highest PC activity is observed to be 6.2 microm. The crystalline phase and corresponding PC activity depend on the calcination temperature and their relationship is also investigated. The amorphous-to-anatase and anatase-to-rutile phase transitions initially occur at 300 and 500 degrees C, respectively. The PC activity of TiO2-NTAs initially increases with calcination temperature from 250 to 500 degrees C and then decreases at higher calcination temperature. The enhanced PC activity observed from the samples annealed at 250-450 degrees C is attributed to the better anatase crystalline structure at higher calcination temperature. The highest PC activity with regard to photodecomposition of methyl orange is observed from TiO2-NTAs calcined at 500 degrees C, which coincides with the anatse-to-rutile phase transformation. The synergistic effect of the anatase TiO2-NTAs and rutile barrier layers facilitate interfacial electron transfer consequently enhancing the PC activity. Further elevation of the calcination temperatures to 550 and 600 degrees C exhibits diminished PC activity because the NTs become shorter due to conversion of the bottom of anatase NTs into rutile film.

To conduct grain refinement induced by plastic deformation, NiTi shape memory alloy is processed by surface mechanical attrition treatment. The process leads to surface nanocrystallization and consequently surface hardening. The cross sectional microhardness of the treated NiTi is measured and compared to those of annealed NiTi specimens with residual stress relaxation and recrystallization. Our results show that surface nanocrystallization induced by surface mechanical attrition treatment is an effective method to enhance the surface hardness and anti-wear properties of NiTi shape memory alloy for the biomedical application.

Various silicon-based microchannels with different internal surface morphologies were investigated to improve the growth of carbon nanotubes on the inner surface of the pore wall. The morphology of the samples prepared under different conditions was characterized by scanning electron microscopy. Parameters such as concentration of hydrofluoric acid, potential, current density, temperature and so on were found to affect the inner surface of the pore wall. Experiments showed that certain etchant concentration, current density and temperature were important to the fabrication of samples with the regular structure and good morphology. By considering these factors, samples with the proper internal pore surface could be fabricated. Nickel was adopted as the metallic catalyst during electroless deposition onto the surface of the pore wall and bottom. The nickel/silicon microchannels were characterized and found to be suitable for the fabrication of carbon nanotubes by thermal chemical vapor deposition.

Carbon nanotubes including single wall and multi wall carbon nanotubes (SWNT and MWNT) are attractive nanomaterials with great promise in industrial and medical applications. However, little is known about the role of p21 and hus1 gene in the toxic response of SWNT and MWNT to mammalian cells. The aim of this study is to investigate the role of the p21 and hus1 genes in the toxicity of carbon nanotubes. Comparison of micronucleus fraction between the wild type and p21 -/- , hus1 +/+ mouse embryo fibroblast (MEF) cells was performed experimentally. Our results show that the yield of the micronucleus ratio in p21 gene knock-out MEF cells is lower than that in the wild type counterpart, indicating that p21 may play as anti-apoptosis factor during the signal transduction of DNA damage caused by carbon nanotubes in mammalian cells.

Surface nanomechanical behavior under nanoindentation of ZrN and ZrCN film on NiTi substrate was studied. The surface hardness and modulus of the films increase initially with larger nanoindentation depths and then reach their maximum values. Afterwards, they diminish gradually and finally reaching plateau values which are the composite modulus and composite hardness derived from the ZrN/ZrCN film and NiTi substrate. They are higher than those of electropolished NiTi SMA due to the properties of ZrN and ZrCN. In comparison, the surface nanomechanical properties of electropolished NiTi exhibit a different change with depths.

Crystalline core/shell Si/SiO2 nanotubes (NTs) with outer diameters of 130-220 nm and lengths of approximately 1 microm have been synthesized using thermal evaporation. High resolution scanning electron microscopy reveals that the NT formation stems from the intrinsic interfacial stress imbalance in the strained Si/SiO2 bilayered film, consequently leading to NTs with different orifice levels. The NT diameters depend strongly on the bilayer film thicknesses and crystal orientations of the Si and SiO2 layers. A modified Timoshenko formula is derived to calculate the dependence of the tube diameter on the bilayer film thickness. The obtained results are consistent well with experimental data.

Single-crystalline mullite (3Al2O3 2SiO2) nanowires have been produced in large quantities by a low cost and environmentally benign molten salt synthesis (MSS) method. The raw materials, Al2(SO4)3 and SiO2 powders, react in molten Na2SO4 at 1000 degrees C to produce mullite nanowires without the use of surfactants or templates. After the synthesis, the remaining salts can be easily separated from the products by washing with water. The final products are characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, selected-area electron diffraction, and inductively coupled plasma-atomic emission spectrometry. The thermal and chemical behavior of the raw materials is investigated by heating at a rate of 10 degrees C/min up to 1200 degrees C in air followed by thermogravimetric and differential scanning calorimetry analyses. The single-crystalline mullite nanowires have diameters of 30-80 nm and lengths from several hundreds of nanometers to micrometers and the growth mechanism is discussed.

Well-aligned ZnO nanorod arrays with uniform diameters and lengths have been fabricated on a Si substrate by simple thermal evaporation of Cu-Zn alloy powders in the presence of oxygen without using a template, catalyst, or pre-deposited ZnO seed layer. The ZnO nanorods are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy and the growth mechanism is suggested. The nanorods have a single-crystal hexagonal structure and grow along the (0001) direction. Their diameters range from 200 to 400 nm and the lengths are up to several micrometers. The photoluminescence (PL) and Raman spectra disclose the optical properties of the products. The PL spectra show intense near-band ultraviolet emission at 378 nm from the nanorod arrays. The well-aligned ZnO nanorod arrays have a low turn-on field of 6.1 V/microm, suggesting good field emission properties. The simple synthesis methodology in conjunction with the good field emission and optical properties make the study both scientifically and technologically interesting.

Nanomaterial for lithium batteries can decrease mechanical strain upon lithium intercalation/ deintercalation from lattice, and lead to high rate capability. The currently available microwave technology permits the development and implantation of a temperature-controlled microwave-assisted hydrothermal synthesis (TCMH) of nano-sized cathode material for lithium batteries. Unlike in previous reported traditional hydrothermal synthesis of cathode material LiFePO4, the pure phase of LiFePO4 can be simply and rapidly synthesized for 5 minutes in water under hydrothermal treatment with microwave irradiation. The homogeneous effects induced by microwave irradiation could create a uniform seeding condition. The colloid precursor Li3PO4 plays the key role to be the nucleation center for the new phase while the formation energy for LiFePO4 would be decreased during the following microwave irradiation. The as-prepared pristine LiFePO4 without carbon coating are characterized by X-ray diffraction, Raman, scanning and transmission electron microscopy, and tested as the cathode in lithium batteries. The particle sizes of pristine LiFePO4 are dependent on hydrothermal and microwave-assisted hydrothermal condition and the electrochemical performance are relatively determined.

Cubic silicon carbide (3C-SiC) nanostructures such as needle- and Y-shaped nanowhiskers, smooth and pagoda-shaped nanorods are synthesized on a large scale from activated carbon and silicon powders at 1250 degrees C under atmospheric pressure. The use of ball-milled silicon powders results in the formation of nanowires and nanowhiskers, whereas non-milled silicon powders lead to nanorods together with unreacted silicon powders. Residual oxygen in the growth chamber initiates the carburization reactions which can proceed without further oxygen consumption. The size and morphology of the as-synthesized 3C-SiC nanostructures are observed to be related to the size and morphology of the starting silicon particles. An oxygen-assisted gas-solid model is proposed to explain the observed nanostructures.

Large quantities of cubic silicon carbide (3C-SiC) nanospheres are synthesized on silicon wafer using zinc sulphide (ZnS) and activated carbon powder. The synthesized nanospheres have smooth surfaces and their diameters range from 20 to 430 nm. The growth of these nanospheres can be explained by a gas-solid model. ZnS powder plays a key role in the formation of activated Si and SiOx. Carburization of the activated Si and SiOx by CO gas leads to the formation of the 3C-SiC nanospheres. Special three-dimensional structure of the product is related to high concentrations of the reactants.

Large-area and uniform ZnO nanowires have been produced directly on a conducting brass substrate by annealing a Cu0.66Zn0.34 foil under a mixture of argon and oxygen. The morphology, structure, and composition of the ZnO nanowires are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. The ZnO nanowires with diameters of about 40-70 nm and lengths up to micrometers grow preferentially along the [001] direction. Since the Cu0.66Zn0.34 foil serves as both the Zn source and substrate, the synthesis and assembly of the ZnO nanowires on a conducting substrate is accomplished in one step, and good intrinsic adhesion and robust electrical contact between the ZnO nanowires and conducting substrate are realized. This ZnO configuration forms an ideal field emitter and good field emission properties are corroborated in this study. Photoluminescence studies indicate that these ZnO nanowires have good optical quality exhibiting strong ultraviolet (UV) emission at 383 nm and a weak visible emission band centered around 485 nm at room temperature. The good field emission and optical properties suggest that ZnO nanowires fabricated by this method have promising applications in nano-optoelectronic and field emission devices.

Plasma immersion ion implantation (PIII) is an effective method to increase the corrosion resistance and inhibit nickel release from orthopedic NiTi shape memory alloy. Nitrogen was plasma-implanted into NiTi using different pulsing frequencies to investigate the effects on the nano-scale surface morphology, structure, wettability, as well as biocompatibility. X-ray photoelectron spectroscopy (XPS) results show that the implantation depth of nitrogen increases with higher pulsing frequencies. Atomic force microscopy (AFM) discloses that the nano-scale surface roughness increases and surface features are changed from islands to spiky cones with higher pulsing frequencies. This variation in the nano surface structures leads to different surface free energy (SFE) monitored by contact angle measurements. The adhesion, spreading, and proliferation of osteoblasts on the implanted NiTi surface are assessed by cell culture tests. Our results indicate that the nano-scale surface morphology that is altered by the implantation frequencies impacts the surface free energy and wettability of the NiTi surfaces, and in turn affects the osteoblast adhesion behavior.

Hierarchical tree-like and jellyfish-like SiOx nanostructures have been synthesized by annealing a mixture of carbon coated Ni nanoparticles (Ni@C) and SiO2 powers under argon atmosphere at 1400 degrees C. The synthesized products were characterized by electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The tree-like SiOx nanostructures consisting of the trunks and many branches and subbranches with diminishing diameters have been observed for the first time. The diameters of the trunks are about 150-1000 nm, and the branches become more slender for each branching, ultimately to 20-40 nm in diameter for the ends. The jellyfish-like SiOx nanostructures are constructed by the catalyst heads with sizes of about 1-10 microm and many connected quasi-aligned SiOx nanowires with diameters about 20-40 nm. The Ni species of the Ni@C nanoparticles acts as the catalyst and the surface carbon as the reducing agent for carbothermal reduction of SiO2. The experimental results suggest that the formation of different SiOx nanostructures mainly depend on the dimensions of the congregated Ni catalyst droplets during the reaction process and the growth mechanism is reasonably discussed.

Uniform hexagonal Cd(OH)2 nanoplates have been produced directly on Cd substrates by a hydrothermal process in alkaline solution containing (NH4)2S2)8 without the use of templates or surfactants. The Cd foil serves as both the Cd source and substrate. The morphology, structure, and composition of the Cd(OH)2 nanoplates are characterized by X-ray diffraction, electron microscopy, selected area electron diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The Cd(OH)2 nanoplates are single-crystalline and possess a well defined hexagonal shape. The thicknesses of hexagonal Cd(OH)2 nanoplates range from 30 to 80 nm and the lateral lengths are about 80-200 nm. The growth mechanism is also discussed.

Large-area and uniform quasi-aligned titanium oxide (TiO2) nanowire arrays have been produced in situ on a titanium (Ti) foil by a simple high-temperature oxidation process with acetone as the oxidant. The products are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The TiO2 nanowires have a rutile single-crystalline structure. The typical diameters range from 20 to 50 nm and lengths are up to a few micrometers. Since the Ti foil serves as both the source of Ti and substrate, direct synthesis and assembly of TiO2 nanowire arrays on a conductive Ti substrate is accomplished in a single step. Consequently, good intrinsic adhesion and electrical contact are achieved naturally between the nanowires and metal substrate. Such TiO2 nanowire arrays exhibit good field emission properties with a low turn-on field of 4.1 V/microm boding well for applications in vacuum microelectronics.

Quasi-aligned ultrafine ZnS nanowire arrays have been grown directly on zinc substrates via a simple hydrothermal method. The morphology, structure, and composition are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The single-crystalline ultrafine ZnS nanowires have a hexagonal structure with typical diameters of 5-15 nm and lengths of up to micrometers. A possible growth mechanism is proposed. Since the Zn foil serves as both the Zn source and substrate, direct synthesis and assembly of ZnS nanowires on an electrically conductive Zn substrate are accomplished in one step. Optical properties of the product are studied by photoluminescence. Field emission measurements disclose that the synthesized nanostructures possess good electron emission properties with a low turn-on field of about 5.4 V/microm at a current density of 10 microA/cm2. The materials are potentially useful as cathode materials in field emission devices.