Xuefen Song

Wearable temperature sensor based on graphene nanowalls

We demonstrate an ultrasensitive wearable temperature sensor prepared using an emerging material, graphene nanowalls (GNWs), and its ease of combination with polydimethylsiloxane (PDMS). Fabrication of the sensor allows for a polymer-assisted transfer method making it considerably facile, biocompatible and cost effective. The resultant device exhibits a positive temperature coefficient of resistivity (TCR) as high as 0.214 °C−1, which is three fold higher than that of conventional counterparts. We attribute this to the excellent stretchability and thermal sensitivity of GNWs together with the large expansion coefficient of PDMS. Moreover, the sensor is capable of monitoring body temperature in real time, and it presents a quite fast response/recovery speed as well as long term stability. Such wearable temperature sensors could constitute a significant step towards integration with the next frontier in personalized healthcare and human–machine interface systems.

Al2O3 coated α-Fe solid solution nanocapsules prepared by arc discharge

Al2O3 coated alpha-Fe solid solution nanocapsules are prepared by arc-discharging a bulk AlNiCo permanent magnet. The size of the nanocapsule is in range of 3-300 nm and the thickness of the shell is 1-6 nm. Al atoms in the AlNiCo magnet form the shell of amorphous Al2O3 to prevent the nanocapsules from further oxidation. The magnetic properties of saturation magnetization J(s) = 85 A m(2)/kg and coercive force H-j(c) = 27.5 kA/m are achieved for the nanocapsules

Composition anisotropy compensation and spontaneous magnetostriction in Tb0.2Dy0-8-xPrx(Fe0.9B0.1)1,93 alloys

The possibility of the composition anisotropy compensating in Dy1-xPrxFe2 is discussed phenomenologically, based on a single ion approach. The crystal structure, the easy magnetization direction, and the spontaneous magnetostriction of Tb0.2Dy0.8-xPrx(Fe0.9B0.1)(1.93) (0less than or equal toxless than or equal to0.7) alloys are studied. Single-phase Tb0.2Dy0.8-xPrx(Fe0.9B0.1)(1.93) with cubic MgCu2-type structure forms up to x=0.4 and the magnetostrictive phase exists in all the alloys studied. A single (440) peak of x-ray diffraction of the Laves phase exists when 0less than or equal toxless than or equal to0.3, but becomes doubly split when 0.4less than or equal toxless than or equal to0.7 because of a large spontaneous magnetostriction along its easy magnetization direction . Composition anisotropy compensation is realized in Tb0.2Dy0.8-xPrx(Fe0.9B0.1)(1.93) alloys. Tb0.2Dy0.4Pr0.4(Fe0.9B0.1)(1.93) alloy with the single Laves phase has a large magnetostriction (lambda(111)approximate to1200 ppm) and a low anisotropy, which may be a good candidate material for magnetostriction application

Direct Growth of Graphene Films on 3D Grating Structural Quartz Substrates for High-Performance Pressure-Sensitive Sensors.

Conformal graphene films have directly been synthesized on the surface of grating microstructured quartz substrates by a simple chemical vapor deposition process. The wonderful conformality and relatively high quality of the as-prepared graphene on the three-dimensional substrate have been verified by scanning electron microscopy and Raman spectra. This conformal graphene film possesses excellent electrical and optical properties with a sheet resistance of <2000 Ω·sq(-1) and a transmittance of >80% (at 550 nm), which can be attached with a flat graphene film on a poly(dimethylsiloxane) substrate, and then could work as a pressure-sensitive sensor. This device possesses a high-pressure sensitivity of -6.524 kPa(-1) in a low-pressure range of 0-200 Pa. Meanwhile, this pressure-sensitive sensor exhibits super-reliability (≥5000 cycles) and an ultrafast response time (≤4 ms). Owing to these features, this pressure-sensitive sensor based on 3D conformal graphene is adequately introduced to test wind pressure, expressing higher accuracy and a lower background noise level than a market anemometer.

Direct growth of graphene nanowalls on the crystalline silicon for solar cells

We developed a simple approach to fabricate graphene/Si heterojunction solar cells via direct growth of graphene nanowalls on Si substrate. This 3D graphene structure was outstanding electrode network and could form fine interface with Si substrate. Moreover, direct growth method not only simplified manufacturing process, but also avoided damages and contaminants from graphene transfer process. The short-circuit current (Jsc) increased greatly and could reach 31 mA/cm2. After HNO3 doping, the energy conversion efficiency was increased up to 5.1%. Furthermore, we investigated the influence of growth time on the cell performance.

High-efficiency, stable and non-chemically doped graphene–Si solar cells through interface engineering and PMMA antireflection

In graphene–Si (Gr–Si) solar cells, chemical doping could remarkably enhance the performance of the cells, but weakens their stability, which limits their further application. However, in terms of the efficiency of pristine cells, the interfacial defect states and the increased thickness of the oxide layer in air also make high-efficiency and stable cells more difficult to achieve. Here we directly grew carbon nanowalls (CNWs) as a passivation layer onto the Si surface, which could obviously increase the efficiency. On the other hand, a poly(methyl-methacrylate) (PMMA) film was retained after transferring graphene, which could not only keep the graphene intact, but could also serve as an efficient antireflection layer for greater light absorption of the Si. A maximum PCE of 8.9% was achieved for a PMMA-bilayer Gr-CNWs-Si solar cell. Our cell’s efficiency showed a slight degradation after being stored in air for 4 months. This result is far superior to other previously reported stability data for chemically doped Gr–Si solar cells. The PMMA-Gr-CNWs-Si solar cell, with high efficiency and stability, possesses important potential for practical photovoltaic applications.

Structure and magnetostriction of Tb1−xPrxFe1.93B0.15 alloys

Structure, magnetic properties and magnetostriction of Tb1-x,PrxFe1.93B0.15 (0 less than or equal to x less than or equal to 0.8) alloys are investigated. Addition of a small amount of boron and extra rare earth is beneficial to the formation of a single Laves phase. Single phase Tb1-xPrxFe1.93B0.15 with cubic MgCu2-type structure forms up to x = 0.3 as determined by X-ray diffraction. In the range of high Pr content, the boron atoms preferentially combine with rare-earth atoms to form the Nd2Fe14B-type phase. The results of lattice parameter and Curie temperature show that the Pr solubility limit for Tb1-xPrxFe1.93B0.15 is reached in the range of x from 0.3 to 0.5. Large spontaneous magnetostriction of chi(111) > 2100ppm is observed for the Laves phases in the Tb1-x,PrxFe1.93B0.15 alloys with 0 less than or equal to x less than or equal to 0.3. Linear magnetostriction at room temperature of the single phase Tb1-x,PrxFe1.93B0.15 alloys decreases with increasing Pr content

Composite Transparent Electrode of Graphene Nanowalls and Silver Nanowires on Micropyramidal Si for High-Efficiency Schottky Junction Solar Cells

The conventional graphene-silicon Schottky junction solar cell inevitably involves the graphene growth and transfer process, which results in complicated technology, loss of quality of the graphene, extra cost, and environmental unfriendliness. Moreover, the conventional transfer method is not well suited to conformationally coat graphene on a three-dimensional (3D) silicon surface. Thus, worse interfacial conditions are inevitable. In this work, we directly grow graphene nanowalls (GNWs) onto the micropyramidal silicon (MP) by the plasma-enhanced chemical vapor deposition method. By controlling growth time, the cell exhibits optimal pristine photovoltaic performance of 3.8%. Furthermore, we improve the conductivity of the GNW electrode by introducing the silver nanowire (AgNW) network, which could achieve lower sheet resistance. An efficiency of 6.6% has been obtained for the AgNWs-GNWs-MP solar cell without any chemical doping. Meanwhile, the cell exhibits excellent stability exposed to air. Our studies show a promising way to develop simple-technology, low-cost, high-efficiency, and stable Schottky junction solar cells.

Three-dimensional conformal graphene microstructure for flexible and highly sensitive electronic skin

We demonstrate a highly stretchable electronic skin (E-skin) based on the facile combination of microstructured graphene nanowalls (GNWs) and a polydimethylsiloxane (PDMS) substrate. The microstructure of the GNWs was endowed by conformally growing them on the unpolished silicon wafer without the aid of nanofabrication technology. Then a stamping transfer method was used to replicate the micropattern of the unpolished silicon wafer. Due to the large contact interface between the 3D graphene network and the PDMS, this type of E-skin worked under a stretching ratio of nearly 100%, and showed excellent mechanical strength and high sensitivity, with a change in relative resistance of up to 6500% and a gauge factor of 65.9 at 99.64% strain. Furthermore, the E-skin exhibited an obvious highly sensitive response to joint movement, eye movement and sound vibration, demonstrating broad potential applications in healthcare, body monitoring and wearable devices.

Flexible electrochemical biosensors based on graphene nanowalls for the real-time measurement of lactate

We demonstrate a flexible biosensor for lactate detection based on l-lactate oxidase immobilized by chitosan film cross-linked with glutaraldehyde on the surface of a graphene nanowall (GNW) electrode. The oxygen-plasma technique was developed to enhance the wettability of the GNWs, and the strength of the sensors oxidation response depended on the concentration of lactate. First, in order to eliminate interference from other substances, biosensors were primarily tested in deionized water and displayed good electrochemical reversibility at different scan rates (20-100 mV s-1), a large index range (1.0 μM to 10.0 mM) and a low detection limit (1.0 μM) for lactate. Next, these sensors were further examined in phosphate buffer solution (to mimick human body fluids), and still exhibited high sensitivity, stability and flexibility. These results show that the GNW-based lactate biosensors possess important potential for application in clinical analysis, sports medicine and the food industry.