Mixia Wang

Electronic structure of a superconducting topological insulator Sr-doped Bi2Se3

Using high-resolution angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, the atomic and low energy electronic structure of the Sr-doped superconducting topological insulators (SrxBi2Se3) was studied. Scanning tunneling microscopy shows that most of the Sr atoms are not in the van der Waals gap. After Sr doping, the Fermi level was found to move further upwards when compared with the parent compound Bi2Se3, which is consistent with the low carrier density in this system. The topological surface state was clearly observed, and the position of the Dirac point was determined in all doped samples. The surface state is well separated from the bulk conduction bands in the momentum space. The persistence of separated topological surface state combined with small Fermi energy makes this superconducting material a very promising candidate for the time reversal invariant topological superconductor.

A silicon based implantable microelectrode array for electrophysiological and dopamine recording from cortex to striatum in the non-human primate brain

Dual-mode, multielectrode recordings have become routine in rodent neuroscience research and have recently been adapted to the non-human primate. However, robust and reliable application of acute, multielectrode recording methods in monkeys especially for deep brain nucleus research remains a challenge. In this paper, We described a low cost silicon based 16-site implantable microelectrode array (MEA) chip fabricated by standard lithography technology for in vivo test. The array was 25mm long and designed to use in non-human primate models, for electrophysiological and electrochemical recording. We presented a detailed protocol for array fabrication, then showed that the device can record Spikes, LFPs and dopamine (DA) variation continuously from cortex to striatum in an esthetized monkey. Though our experiment, high-quality electrophysiological signals were obtained from the animal. Across any given microelectrode, spike amplitudes ranged from 70 to 300μV peak to peak, with a mean signal-to-noise ratio of better than 5:1. Calibration results showed the MEA probe had high sensitivity and good selectivity for DA. The DA concentration changed from 42.8 to 481.6μM when the MEA probe inserted from cortex into deep brain nucleus of striatum, which reflected the inhomogeneous distribution of DA in brains. Compared with existing methods allowing single mode (electrophysiology or electrochemistry) recording. This system is designed explicitly for dual-mode recording to meet the challenges of recording in non-human primates.

Ridge InGaAs/InP multi-quantum-well selective growth in nanoscale trenches on Si (001) substrate

Metal organic chemical vapor deposition of InGaAs/InP multi-quantum-well in nanoscale V-grooved trenches on Si (001) substrate was studied using the aspect ratio trapping method. A high quality GaAs/InP buffer layer with two convex {111} B facets was selectively grown to promote the highly uniform, single-crystal ridge InP/InGaAs multi-quantum-well structure growth. Material quality was confirmed by transmission electron microscopy and room temperature micro-photoluminescence measurements. This approach shows great promise for the fabrication of photonics devices and nanolasers on Si substrate.

Magnetically driven negative thermal expansion in antiperovskite Ga1-xMnxN0.8Mn3 (0.1 ≤ x ≤ 0.3)

Negative thermal expansion (NTE) was investigated for Ga1−xMnxN0.8Mn3 (0.1 ≤ x ≤ 0.3). As x increases, the temperature range where lattice contracts upon heating becomes broad and shifts to lower temperatures. The coefficient of linear thermal expansion beyond −40 ppm/K with a temperature interval of ∼50 K was obtained around room temperature in x = 0.2 and 0.25. Local lattice distortion which was thought to be intimately related to NTE is invisible in the X-ray pair distribution function of x = 0.3. Furthermore, a zero-field-cooling exchange bias was observed as a result of competing ferromagnetic (FM) and antiferromagnetic (AFM) orders. The concomitant FM order serves as an impediment to the growth of the AFM order, and thus broadens the temperature range of NTE. Our result suggests that NTE can be achieved in antiperovskite manganese nitrides by manipulating the magnetic orders without distorting the local structure.

Size effects on negative thermal expansion in cubic ScF3

Scandium trifluoride (ScF3), adopting a cubic ReO3-type structure at ambient pressure, undergoes a pronounced negative thermal expansion (NTE) over a wide range of temperatures (10 K–1100 K). Here, we report the size effects on the NTE properties of ScF3. The magnitude of NTE is reduced with diminishing the crystal size. As revealed by the specific heat measurement, the low-energy phonon vibrations which account for the NTE behavior are stiffened as the crystal size decreases. With decreasing the crystal size, the peaks in high-energy X-ray pair distribution function (PDF) become broad, which cannot be illuminated by local symmetry breaking. Instead, the broadened PDF peaks are strongly indicative of enhanced atomic displacements which are suggested to be responsible for the stiffening of NTE-related lattice vibrations. The present study suggests that the NTE properties of ReO3-type and other open-framework materials can be effectively adjusted by controlling the crystal size.

Simultaneous recording of brain extracellular glucose, spike and local field potential in real time using an implantable microelectrode array with nano-materials.

Glucose is the main substrate for neurons in the central nervous system. In order to efficiently characterize the brain glucose mechanism, it is desirable to determine the extracellular glucose dynamics as well as the corresponding neuroelectrical activity in vivo. In the present study, we fabricated an implantable microelectrode array (MEA) probe composed of platinum electrochemical and electrophysiology microelectrodes by standard micro electromechanical system (MEMS) processes. The MEA probe was modified with nano-materials and implanted in a urethane-anesthetized rat for simultaneous recording of striatal extracellular glucose, local field potential (LFP) and spike on the same spatiotemporal scale when the rat was in normoglycemia, hypoglycemia and hyperglycemia. During these dual-mode recordings, we observed that increase of extracellular glucose enhanced the LFP power and spike firing rate, while decrease of glucose had an opposite effect. This dual mode MEA probe is capable of examining specific spatiotemporal relationships between electrical and chemical signaling in the brain, which will contribute significantly to improve our understanding of the neuron physiology.

Scaling of reliability of gold interconnect lines subjected to alternating current

We present an investigation of damage morphologies of small-scale gold interconnect lines subjected to thermal fatigue strain generated by alternating current. Fractal dimension analysis reveals a general scaling relation between the critical strain range causing thermal fatigue damage and the ratio of the width to the thickness of the metal line. Such the scaling rule may be useful in controlling reliability of the metal interconnect lines subjected to long-term thermal cyclic strain

The electrical properties of n-ZnO/p-SnO heterojunction diodes

In the present work, n-type zinc oxide (ZnO) and p-type tin monoxide (SnO) based heterostructure diodes were fabricated on an indium-tin-oxide glass using the radio frequency magnetron sputtering technique. The prepared ZnO/SnO diodes exhibited a typical rectifying behavior, with a forward to reverse current ratio about 500 ± 5 at 2 V and turn on voltage around 1.6 V. The built-in voltage of the diode was extracted to be 0.5 V based on the capacitance-voltage (C–V) measurement. The valence and conduction band offsets were deliberated through the band energy diagram of ZnO/SnO heterojunction, as 1.08 eV and 0.41 eV, respectively. The potential barrier-dependent carrier transportation mechanism across the space charge region was also investigated.

A novel tri-axis MEMS gyroscope with in-plane tetra-pendulum proof masses and enhanced sensitive springs

This paper presents a tri-axis MEMS gyroscope design with novel tetra-pendulum proof masses for X-, Y-axis and regular proof masses for Z-axis rate sensing, which are all coupled with and embedded in a conventional tuning fork driving frame. The four pendulum proof masses are suspended via the torsional springs to a common center anchor and can be driven to swing around the anchor via the tilted transforming springs as the driving frame is oscillated in an anti-phase mode. As an X-, Y-axis angular rate is applied, the tetra-pendulum proof masses will rotate around the torsional springs in pairs for X- and Y-axis differential sensing, respectively. In particular, we investigated the relationship between the tilting angle of the transforming spring and its transforming efficiency, i.e. the amplitude ratio of the pendulums swing to the driving oscillation, which shows a straight impact on the sensitivity. By theoretical analysis and Ansys simulation, we achieved an optimal tilting angle of 22.5°, which extends along the angular bisector of the pendulums and driving mass’ moving direction and demonstrates a significant increase in transforming efficiency by about 40%, compared with the trivial tilting angle of 45°. By employing an SOI-based bulk micromachining process, the prototype device with the optimal design of the transforming spring (type I) and that with the trivial design (type II) for reference have been successfully fabricated. As expected, the testing results indicate an increase of more than 20% in the X- and Y- sensitivities, which is mainly from the enhanced sensitive transforming springs.

An implantable microelectrode array for dopamine and electrophysiological recordings in response to L-dopa therapy for Parkinson's disease

Dual-mode multielectrode recordings have become routine in rodent neuroscience research. However, robust and reliable application of acute, multielectrode recording methods in brain especially for in vivo research remains a challenge. In patients with Parkinsons disease (PD), the efficacy of L-dopa therapy depends on its ability to restore Dopamine (DA) neurotransmission in the striatum. In this paper, We describe a low cost thin film 16 sites implantable microelectrode array (MEA) chip fabricated by standard lithography technology for in vivo test. In urethane anesthetized rats, the MEA probes were implanted acutely for simultaneous recording of local field potentials, spikes, and L-dopa therapy evoked dopamine overflow on the same spatiotemporal scale. We present a detailed protocol for array fabrication, then show that the device can record Spikes, LFPs and dopamine variation in real time. Across any given microelectrode, spike amplitudes ranged from 80 to 300 μν peak to peak, with a mean signal-tonoise ratio of better than 5:1. Calibration results showed the MEA probe had high sensitivity and good selectivity for DA. Comparison with existing methods allow single mode recording, our neural probes would be useful for examining specific spatiotemporal relationships between electrical and chemical signaling in the brain.Dual-mode multielectrode recordings have become routine in rodent neuroscience research. However, robust and reliable application of acute, multielectrode recording methods in brain especially for in vivo research remains a challenge. In patients with Parkinsons disease (PD), the efficacy of L-dopa therapy depends on its ability to restore Dopamine (DA) neurotransmission in the striatum. In this paper, We describe a low cost thin film 16 sites implantable microelectrode array (MEA) chip fabricated by standard lithography technology for in vivo test. In urethane anesthetized rats, the MEA probes were implanted acutely for simultaneous recording of local field potentials, spikes, and L-dopa therapy evoked dopamine overflow on the same spatiotemporal scale. We present a detailed protocol for array fabrication, then show that the device can record Spikes, LFPs and dopamine variation in real time. Across any given microelectrode, spike amplitudes ranged from 80 to 300 μν peak to peak, with a mean signal-tonoise ratio of better than 5:1. Calibration results showed the MEA probe had high sensitivity and good selectivity for DA. Comparison with existing methods allow single mode recording, our neural probes would be useful for examining specific spatiotemporal relationships between electrical and chemical signaling in the brain.