Huijun Yao

Electrochemical fabrication of single-crystalline and polycrystalline Au nanowires : the influence of deposition parameters

We report the electrochemical growth of gold nanowires with controlled dimensions and crystallinity. By systematically varying the deposition conditions, both polycrystalline and single-crystalline wires with diameters between 20 and 100 nm are successfully synthesized in etched ion-track membranes. The nanowires are characterized using scanning electron microscopy, high resolution transmission electron microscopy, scanning tunnelling microscopy and x-ray diffraction. The influence of the deposition parameters, especially those of the electrolyte, on the nanowire structure is investigated. Gold sulfite electrolytes lead to polycrystalline structure at the temperatures and voltages employed. In contrast, gold cyanide solution favours the growth of single crystals at temperatures between 50 and 65 °C under both direct current and reverse pulse current deposition conditions. The single-crystalline wires possess a [110] preferred orientation.

Controlled crystallinity and crystallographic orientation of Cu nanowires fabricated in ion-track templates.

The hallmark of materials science is the ability to tailor the structures of a given material to provide a desired response. In this work, the structures involving crystallinity and crystallographic orientation of Cu nanowires electrochemically fabricated in ion-track templates have been investigated as a function of fabrication condition. Both single crystalline and polycrystalline nanowires were obtained by adjusting applied voltages and temperatures of electrochemical deposition. The anti-Hall-Petch effect was experimentally evidenced in the polycrystalline nanowires. The dominant crystallographic orientations of wires along [111], [100], or [110] directions were obtained by selecting electrochemical deposition conditions, i.e., H(2)SO(4) concentration in electrolyte, applied voltage, and electrodeposition temperature.

Optical and electrical properties of gold nanowires synthesized by electrochemical deposition

Gold nanowire arrays with different sizes were fabricated by electrochemical deposition in etched ion-track templates. The diameter of the gold nanowires between 30 and 130 nm could be well adjusted by pore sizes in the templates through etching time. Single-crystalline nanowires were achieved by changing the parameters of electrochemical deposition. The morphology and crystal structure of the fabricated gold nanowires were characterized by means of scanning electron microscopy and transmission electron microscopy. The optical properties of the gold nanowire arrays embodied in templates were systematically measured by absorption spectra with a UV/Vis/NIR spectrophotometer. Due to the surface plasmon resonance effect, the extinction peaks of gold nanowire arrays possessed a red-shift with increasing wires diameter and a blue-shift with decreasing angle between incident light and nanowire arrays. The failure current density of the single gold nanowire as a function of diameter was determined and the failure...

Phase coherent transport in InSb nanowires

Comprehensive electrical transport studies are performed on InSb nanowires by varying temperature, gate voltage, and magnetic field. The 3-dimensional bulk conduction is found to dominate in the nanowire channel after investigating a large number of nanowires with different diameters, which show approximately a linear relation between the conductance normalized to the length and the wire cross section. At low temperatures, universal conductance fluctuations are observed. From the amplitude and the correlation voltage of the conductance fluctuations, the phase-coherence length in InSb nanowires is determined at various temperatures.

An embryo of protocells: The capsule of graphene with selective ion channels

The synthesis of artificial cell is a route for searching the origin of protocell. Here, we create a novel cell model of graphene capsules with selective ion channels, indicating that graphene might be an embryo of protocell membrane. Firstly, we found that the highly oxidized graphene and phospholipid-graphene oxide composite would curl into capsules under a strongly acidic saturated solution of heavy metallic salt solution at low temperature. Secondly, L-amino acids exhibited higher reactivity than D-amino acids on graphene oxides to form peptides, and the formed peptides in the influence of graphene would be transformed into a secondary structure, promoting the formation of left-handed proteins. Lastly, monolayer nanoporous graphene, prepared by unfocused 84Kr25+, has a high selectivity for permeation of the monovalent metal ions ( Rb+ > K+ > Cs+ > Na+ > Li+, based on permeation concentration), but does not allow Cl- go through. It is similar to K+ channels, which would cause an influx of K+ into capsule of graphene with the increase of pH in the primitive ocean, creating a suitable inner condition for the origin of life. Therefore, we built a model cell of graphene, which would provide a route for reproducing the origin of life.

Investigation of Threshold Ion Range for Accurate Single Event Upset Measurements in Both SOI and Bulk Technologies

Experimental evidences are presented showing obvious differences in threshold ion range for silicon-on-insulator (SOI) and bulk static random access memories (SRAMs). Single event upset (SEU) cross sections of SOI SRAMs start to decline off the Weibull curve at ion ranges of 20.7 μm to 40.6 μm, depending on the ion species and also the thickness of metallization layers. Whereas for the bulk SRAMs, threshold range of Bismuth beam is unexpectedly larger than 60.4 μm. Underlying mechanisms are further revealed by Monte Carlo simulations and in-depth analysis. The relative location of ions Bragg peak to the sensitive region and also the position of ion LET in the σ-LET curve of test device turn out to be two key parameters in determining the threshold ion range which can explain the experimental results. Significant discrepancies are observed in the deposited energy spectrums in sensitive regions of bulk SRAM by ions at different sides of the Bragg peak, but with almost the same LET at die surface (all with ion range larger than 30 μm). Energy straggling of incident ions at the die surface is considered by Monte Carlo calculations. Implications for hardness assurance testing are also discussed. A formula is proposed for calculating the “worst case” threshold ion range.

Large energy-loss straggling of swift heavy ions in ultra-thin active silicon layers

Monte Carlo simulations reveal considerable straggling of energy loss by the same ions with the same energy in fully-depleted silicon-on-insulator (FDSOI) devices with ultra-thin sensitive silicon layers down to 2.5 nm. The absolute straggling of deposited energy decreases with decreasing thickness of the active silicon layer. While the relative straggling increases gradually with decreasing thickness of silicon films and exhibits a sharp rise as the thickness of the silicon film descends below a threshold value of 50 nm, with the dispersion of deposited energy ascending above ±10%. Ion species and energy dependence of the energy-loss straggling are also investigated. For a given beam, the dispersion of deposited energy results in large uncertainty on the actual linear energy transfer (LET) of incident ions, and thus single event effect (SEE) responses, which pose great challenges for traditional error rate prediction methods.

Temperature- and Angle-Dependent Magnetic Properties of Ni Nanotube Arrays Fabricated by Electrodeposition in Polycarbonate Templates

Parallel arrays of Ni nanotubes with an external diameter of 150 nm, a wall thickness of 15 nm, and a length of 1.2 ± 0.3 µm were successfully fabricated in ion-track etched polycarbonate (PC) templates by electrochemical deposition. The morphology and crystal structure of the nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Structural analyses indicate that Ni nanotubes have a polycrystalline structure with no preferred orientation. Angle dependent hysteresis studies at room temperature carried out by using a vibrating sample magnetometer (VSM) demonstrate a transition of magnetization between the two different magnetization reversal modes: curling rotation for small angles and coherent rotation for large angles. Furthermore, temperature dependent magnetic analyses performed with a superconducting quantum interference device (SQUID) magnetometer indicate that magnetization of the nanotubes follows modified Bloch’s law in the range 60–300 K, while the deviation of the experimental curve from this law below 60 K can be attributed to the finite size effects in the nanotubes. Finally, it was found that coercivity measured at different temperatures follows Kneller’s law within the premises of Stoner–Wohlfarth model for ferromagnetic nanostructures.

Cyanide-free preparation of gold nanowires: controlled crystallinity, crystallographic orientation and enhanced field emission

The environmentally friendly preparation of nanomaterials with controlled structural features represents a development trend of nanoscience and nanotechnology. In this work, using a cyanide-free bath, gold nanowires with controlled crystallinity and preferred crystallographic orientation have been prepared by electrochemical deposition in home-made polycarbonate ion track-etched templates. Single-crystal and polycrystal gold nanowires with preferred orientations along the [111] and [100] directions have been obtained by selecting fabrication parameters. The influence mechanisms of nanopore diameter, applied voltage, and deposition temperature on structural properties are proposed. In addition, single-crystal nanowires with [100] preferred orientation show enhanced field emission, which may be attributed to their single-crystal structure and the lower work function of loosely packed crystal planes.

Supply voltage dependence of single event upset sensitivity in diverse SRAM devices

Experimental evidences are presented showing the variety of supply voltage dependence of single event upset (SEU) sensitivity in diverse SRAM devices. Devices under test (DUTs) from Alliance Memory, ISSI and IDT companies with different technologies were irradiated by several kinds of heavy ions at Heavy ion Research Facility in Lanzhou (HIRFL) cyclotrons. For the Alliance 256 kb SRAM device, SEU cross section increases by more than one order of magnitude as supply voltage decreases from 5.0 V to 3.0 V. SEU data of Alliance 64 kb SRAM also exhibits significant supply voltage dependence. The reduction of critical charge is the predominant factor worsening the device performance. While for the Alliance 8 Mb, ISSI 2 Mb and IDT 256 kb SRAM devices, no obvious trend was observed, which is attributed to the negligible net contribution of competing mechanisms. Those results suggest that the worst-case supply voltage for evaluation of SEU sensitivity depends on the test devices.