Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user3D Nanomagnetism in Low Density Interconnected Nanowire Networks
67
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Free-standing, interconnected metallic nanowire networks with density as low as 40 mg/cm^{3} have been achieved over cm-scale areas, using electrodeposition into polycarbonate membranes that have been ion-tracked at multiple angles. Networks of interconnected magnetic nanowires further provide an exciting platform to explore 3-dimensional nanomagnetism, where their structure, topology and frustration may be used as additional degrees of freedom to tailor the materials properties. New magnetization reversal mechanisms in cobalt networks are captured by the first-order reversal curve method, which demonstrate the evolution from strong demagnetizing dipolar interactions to intersections-mediated domain wall pinning and propagation, and eventually to shape-anisotropy dominated magnetization reversal. These findings open up new possibilities for 3-dimensional integrated magnetic devices for memory, complex computation, and neuromorphics.
rate research
Read More
Nanostructured palladium foams offer exciting potential for applications in diverse fields such as catalyst, fuel cell, and particularly hydrogen storage technologies. We have fabricated palladium nanowire foams using a cross-linking and freeze-drying technique. These foams have a tunable density down to 0.1% of the bulk, and a surface area to volume ratio of up to 1,540,000:1. They exhibit highly attractive characteristics for hydrogen storage, in terms of loading capacity, rate of absorption and heat of absorption. The hydrogen absorption/desorption process is hysteretic in nature, accompanied by substantial lattice expansion/contraction as the foam converts between Pd and PdHx.
Spin-related effects in thermoelectricity can be used to design more efficient refrigerators and offer novel promising applications for the harvesting of thermal energy. The key challenge is to design structural and compositional magnetic material systems with sufficiently high efficiency and power output for transforming thermal energy into electric energy and vice versa. Here, the fabrication of large-area 3D interconnected Co/Cu nanowire networks is demonstrated, thereby enabling the controlled Peltier cooling of macroscopic electronic components with an external magnetic field. The flexible, macroscopic devices overcome inherent limitations of nanoscale magnetic structures due to insufficient power generation capability that limits the heat management applications. From properly designed experiments, large spin-dependent Seebeck and Peltier coefficients of $-9.4$ $mu$V/K and $-2.8$ mV at room temperature, respectively. The resulting power factor of Co/Cu nanowire networks at room temperature ($sim7.5$ mW/K$^2$m) is larger than those of state of the art thermoelectric materials, such as BiTe alloys and the magneto-power factor ratio reaches about 100% over a wide temperature range. Validation of magnetic control of heat flow achieved by taking advantage of the spin-dependent thermoelectric properties of flexible macroscopic nanowire networks lay the groundwork to design shapeable thermoelectric coolers exploiting the spin degree of freedom.
Bandstructure effects in the electronic transport of strongly quantized silicon nanowire field-effect-transistors (FET) in various transport orientations are examined. A 10-band sp3d5s* semi-empirical atomistic tight-binding model coupled to a self consistent Poisson solver is used for the dispersion calculation. A semi-classical, ballistic FET model is used to evaluate the current-voltage characteristics. It is found that the total gate capacitance is degraded from the oxide capacitance value by 30% for wires in all the considered transport orientations ([100], [110], [111]). Different wire directions primarily influence the carrier velocities, which mainly determine the relative performance differences, while the total charge difference is weakly affected. The velocities depend on the effective mass and degeneracy of the dispersions. The [110] and secondly the [100] oriented 3nm thick nanowires examined, indicate the best ON-current performance compared to [111] wires. The dispersion features are strong functions of quantization. Effects such as valley splitting can lift the degeneracies especially for wires with cross section sides below 3nm. The effective masses also change significantly with quantization, and change differently for different transport orientations. For the cases of [100] and [111] wires the masses increase with quantization, however, in the [110] case, the mass decreases. The mass variations can be explained from the non-parabolicities and anisotropies that reside in the first Brillouin zone of silicon.
Graphene, as a promising material of post-silicon electronics, opens a new paradigm for the novel electronic properties and device applications. On the other hand, the 2D feature of graphene makes it technically challenging to be integrated into 3D transistors with a sufficient processor capacity. Although there are many attempts to assemble 2D graphene into 3D structures, the characteristics of massless Dirac fermions cannot be well preserved in these materials for transistor applications. Here we report a high-performance graphene transistor by utilizing 3D nanoporous graphene which is comprised of an interconnected single graphene sheet and a commodious open porosity to infuse an ionic liquid for a tunable electronic state by applying electric fields. The 3D nanoporous graphene transistor, with high carrier mobility of 5000-7500 cm$^2$V$^{-1}$s$^{-1}$, exhibits two to three orders of magnitude higher electric conductance and capacitance than those of 2D graphene devices, along with preserved ambipolor electronic nature of Dirac cones. Moreover, the 3D graphene networks with Dirac fermions turn out to exhibit a unique nonlinear Hall resistance in a wide range of the gate voltages. The high quality 3D nanoporous graphene EDLT may open a new field for utilizing Dirac fermions in 3D network structures for various fundamental and practical applications.
Band gap modification for small-diameter (1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-section, the functional group used to saturate the silicon surface significantly modifies the band gap, resulting in relative energy shifts of up to an electronvolt. The band gap shifts are traced to details of the hybridization between the silicon valence band and the frontier orbitals of the terminating group, which is in competition with quantum confinement.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
