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Finding promising materials that show large thermoelectricity at low temperatures is crucial for low-temperature refrigeration applications. Here, we report a significantly large thermoelectric power factor ( PF) up to 50 μW cm−1 K−2 at an extremely low temperature of ∼8 K in a quasi-one-dimensional (Q1D) antiferromagnet KMn6Bi5, in which highly electrical conductivity and dramatic enhancement of Seebeck coefficient may favor its occurrence. In addition, a giant Nernst signal has also been detected with a maximum value of 24 μV K−1 T−1 at ∼5 K. All these intriguing characteristics observed in KMn6Bi5 can be attributed to the manifestation of the unusually strong coupling among spin, charge, lattice, and one dimensionality in KMn6Bi5. Our findings provide fundamental insight into the thermal transport in Q1D antiferromagnets and should stimulate further experimental exploration of thermal transport in such Q1D family for possible thermoelectric applications at extremely low temperatures.

Spintronics is one of the most promising information technologies now, especially for nontrivial topological Dirac half-metal, which exhibits extraordinary electronic band and transport properties. In this work, we propose that 1T-CrO2 nanosheet is mechanical stable, large spin-gap, and room temperature ferromagnetic Dirac half metal. It also exhibits a desirable giant magneto band structure effect, and when the spin direction is switched from in-plane to out-of-plane with a spin orbital coupling effect, it will exhibit nontrivial topological phase transition. The topological tunable electronic band property makes it a very promising two-dimensional nanosheet for spintronics.

Graphene nanowalls (GNWs) are wall-like graphene nanosheets that are oriented vertically on a substrate. GNWs have a unique structure and special optoelectronic properties, which enables their use in photodetectors. In this paper, we use plasma-enhanced chemical vapor deposition to directly grow GNWs onto the surface of an n-type lightly doped Si substrate and to optimize the quality of the GNWs by adjusting the growth time and temperature. Furthermore, after the GNWs are lithographically patterned, we use a GNW-Si Schottky structure to develop photodetector arrays which are capable of detecting light from the visible to infrared light spectral range. Throughout the process, GNWs are directly synthesized on a Si substrate without using a catalyst or a transfer step. The process is simple and efficient. Under laser illumination at a wavelength of 792 nm, the highest on/off ratio at zero bias is approximately 105, and the specific detectivity is 7.85 × 106 cm Hz1/2/W. Under a reverse bias of 4 V, the measured responsivity of the detector reaches 1 A/W at room temperature. The device can also produce a light response in the near-infrared band. Upon laser illumination at a wavelength of 1550 nm, the detector shows a responsivity of 12 mA/W at room temperature.

We report on a prototype graphene radiation detector based on the thermoelectric effect. We used a split top gate to create a p-n junction in the graphene, thereby making an effective thermocouple to read out the electronic temperature in the graphene. The electronic temperature is increased due to the AC currents induced in the graphene from the incoming radiation, which is first received by an antenna and then directed to the graphene via the top-gate capacitance. With the exception of the constant DC voltages applied to the gate, the detector does not need any bias and is therefore very simple to use. The measurements showed a clear response to microwaves at 94 GHz with the signal being almost temperature independent in the 4–100 K temperature range. The optical responsivity reached ∼700 V/W.

Wet etching as a clean method for embedding Ag nanowires into a silicon substrate has been employed to reduce the Ag nanowires layer roughness. Close attachment of the etching holes with Ag nanowires with various diameters was obtained using a simple etching process. Finite-Difference Time-Domain (FDTD) results show that the significant enhancement in light intensity and an increase in light path are caused by the embedding of Ag nanowires into the silicon substrate. These results show that embedding of Ag nanowires into a semiconductor material by etching can simultaneously lead to significant roughness reduction, light scattering enhancement, and charge collection capacity. It is expected that the embedding process will greatly improve the transparency and conductivity of semiconductor materials and has great potential for application in light emitting diodes (LEDs) or solar cells.

Graphene encapsulated between flakes of hexagonal boron nitride (hBN) demonstrates the highest known mobility of charge carriers. However, the technology is not scalable to allow for arrays of devices. We are testing a potentially scalable technology for encapsulating graphene where we replace hBN with Parylene while still being able to make low-ohmic edge contacts. The resulting encapsulated devices show low parasitic doping and a robust Quantum Hall effect in relatively low magnetic fields

This letter reports on the realization and characterization of silicon three-terminal junction devices made in a silicon-on-insulator wafer. Room temperature electrical measurements show that the fabricated devices exhibit pronounced nonlinear electrical properties inherent to ballistic electron transport in a three-terminal ballistic junction (TBJ) device. The results show that room temperature functional TBJ devices can be realized in a semiconductor material other than high-mobility III-V semiconductor heterostructures and provide a simple design principle for compact silicon devices in nanoelectronics.

A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently "grow from below." By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000°C growth temperature.

We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.

We report a low voltage and highly transparent polymer network liquid crystal (PNLC) with submillisecond response time. By employing a large dielectric anisotropy LC host JC-BP07N, we have lowered the V2π voltage to 23 V at λ = 514 nm. This will enable PNLC to be integrated with a high resolution liquid-crystal-on-silicon spatial light modulator, in which the maximum voltage is 24 V. A simple model correlating PNLC performance with its host LC is proposed and validated experimentally. By optimizing the domain size, we can achieve V2π

The microwave noise parameters of graphene field effect transistors (GFETs) fabricated using chemical vapor deposition graphene with 1 μm gate length in the 2 to 8 GHz range are reported. The obtained minimum noise temperature (Tmin) is 210 to 610 K for the extrinsic device and 100 to 500 K for the intrinsic GFET after de-embedding the parasitic noise contribution. The GFET noise properties are discussed in relation to FET noise models and the channel carrier transport. Comparison shows that GFETs can reach similar noise levels as contemporary Si CMOS technology provided a successful gate length scaling is performed.

Quantum Hall effect (QHE) is observed in graphene grown by chemical vapour deposition using platinum catalyst. The QHE is even seen in samples which are irregularly decorated with disordered multilayer graphene patches and have very low mobility (

Ordered and dense GaN light emitting nanorods are studied with polycrystalline graphene grown by rapid chemical vapor deposition as suspended transparent electrodes. As the substitute of indium tin oxide, the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as-fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes. The suspended graphene remains electrically stable up to 300 °C in air. The graphene can be obtained at low cost and high efficiency, indicating its high potential in future applications.

In this paper, we report on a microwave characterization of the interface between Ti/Au contacts and chemical vapor deposition graphene using structures of Corbino geometry, with primary focus on extracting and modeling the capacitance associated with the contact region. It is found that with the current contact resistivity, ρc∼10^−6 Ωcm2, the contact capacitance, on the order Cc∼1 μF/cm2, has a negligible effect on microwave transmission through the contact below ∼100 GHz. Finally, a parallel plate capacitance model for the contact is presented.

We report a simple reconfigurable printing method for fabricating submillisecond-response and scattering-free polymer network liquid crystal photonic devices, such as prism, grating, and lens. To suppress light scattering in the visible region, we reduce the domain sizes by controlling polymer concentration, selecting a high viscosity liquid crystal (LC) host, and performing UV curing at a low temperature. To demonstrate the configurability, we printed a LC micro-prism array with ∼300-μm feature size and a circular lens with 1.3-mm radius without any pre-patterned templates. This reconfigurable printing technique enables fast design iterations and should have widespread applications for fabricating display and photonic devices.

An improved technique for transferring large area graphene grown by chemical vapor deposition on copper is presented. It is based on mechanical separation of the graphene/copper by H2 bubbles during H2O electrolysis, which only takes a few tens of seconds while leaving the copper cathode intact. A semi-rigid plastic frame in combination with thin polymer layer span on graphene gives a convenient way of handling- and avoiding wrinkles and holes in graphene. Optical and electrical characterizations prove the graphene quality is better than that obtained by traditional wet etching transfer. This technique appears to be highly reproducible and cost efficient.

Comment on "Mechanism of non-metal catalytic growth of graphene on silicon" [Appl. Phys. Lett. 100, 231604 (2012)]

A noncatalytic chemical vapor deposition mechanism is proposed, where high precursor concentration, long deposition time, high temperature, and flat substrate are needed to grow large-area nanocrystalline graphene using hydrocarbon pyrolysis. The graphene is scalable, uniform, and with controlled thickness. It can be deposited on virtually any nonmetallic substrate that withstands ∼1000 °C. For typical examples, graphene grown directly on quartz and sapphire shows transmittance and conductivity similar to exfoliated or metal-catalyzed graphene, as evidenced by transmission spectroscopy and transport measurements. Raman spectroscopy confirms the sp 2-C structure. The model and results demonstrate a promising transfer-free technique for transparent electrode production.

A polymer-stabilized blue-phase liquid crystal (BPLC) with microsecond response time is demonstrated using a vertical field switching cell. The measured decay time is 39 μs at room temperature (21 °C) and then decreases to 9.6 μs at 44.3 °C. Such a response time is 1-2 orders of magnitude faster than that of a typical BPLC device. The responsible physical mechanisms are the collective effects of short pitch length, strong polymer network, and low viscosity through temperature effect. The on-state voltage of our BPLC device is 44.2 V, hysteresis is below 0.7%, and contrast ratio is over 1300:1.

Dielectric dispersions on the Kerr constant of two polymer-stabilized blue phase liquid crystals (BPLCs) are investigated. An extended Cole-Cole model is proposed to fit the experimental results and good agreement is obtained. As the electric field frequency increases, Kerr constant decreases and the associated dielectric heating effect gradually increases. These results will undoubtedly affect the high frequency operation of BPLC devices.

A fast-response and scattering-free polymer network liquid crystal (PNLC) light modulator is demonstrated at λ = 1.06 μm wavelength. A decay time of 117 μs for 2π phase modulation is obtained at 70 °C, which is ∼ 650 × faster than that of the host nematic LCs. The major tradeoff is the increased operating voltage. Potential applications include spatial light modulators and adaptive optics.

Large-area uniform carbon films with graphene-like properties are synthesized by chemical vapor deposition directly on Si3N4/Si at 1000 degrees C without metal catalysts. The as deposited films are atomically thin and wrinkle- and pinhole-free. The film thickness can be controlled by modifying the growth conditions. Raman spectroscopy confirms the sp(2) graphitic structures. The films show ohmic behavior with a sheet resistance of similar to 2.3-10.5 k Omega/square at room temperature. An electric field effect of similar to 2-10% (V-G=-20 V) is observed. The growth is explained by the self-assembly of carbon clusters from hydrocarbon pyrolysis. The scalable and transfer-free technique favors the application of graphene as transparent electrodes.

A gate-defined double quantum dot with two integrated quantum point contact charge sensors is realized in an InGaAs/InP heterostructure by employing a high-kappa HfO2 thin film as gate dielectric and a polymer bridge technique. Clear honeycomb patterns are observed in the measured charge stability diagram of the double quantum dot and charge sensing signals of the quantum point contacts. It is also found that the quantum point contact charge sensors can detect the charge states in the double quantum dot even in the condition that the direct transport signal is not visible. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3409223]

Three-terminal junction devices are realized in an InGaAs/InP quantum well by focused ion beam (FIB) implantation and selective wet etching. Room temperature electrical measurements show that the fabricated devices exhibit strong nonlinear electrical properties. The results are discussed in terms of ballistic electron transport. It is demonstrated that FIB-enhanced etching processing can be exploited as a maskless, resist-free technique for fabrication of high-quality and functional nanoelectronic devices.

The elastic property and structure of dislocation in Gum Metal are investigated by anisotropic elastic theory and high-resolution transmission electron microscopy (HRTEM). The results show that the elastic energy coefficients for the 1∕2⟨111⟩ perfect dislocations nearly equal to zero as the shear modulus along ⟨111⟩{110}, {112}, {123} when the valence electron number e∕a reaches 4.2, which implies a low intrinsic critical resolved shear stress for dislocation glide. HRTEM observations further revealed 70.53° dislocations in Gum Metal after severe cold working. The substantial plastic deformation is considered to originate from the conventional dislocation mechanism, rather than from the dislocation-free mechanism in Gum Metals.

An integrated nanoelectronic circuit is fabricated from a high-mobility In0.75Ga0.25As/InP heterostructure. The manufactured device comprises two double in-plane gate transistors with a current channel of 1.1 mu m in length and 100 nm in width. The two transistors are coupled to each other in a configuration that the source of one transistor is directly connected with one in-plane gate of the other transistor. Electrical measurements reveal that this device functions as an SR (set-reset) latch (a sequential logic device) with a gain of similar to 4 in the logic swing at room temperature. The demonstrated device provides a simple circuit design for SR latches.

We have fabricated pentacene organic thin-film transistor (OTFT) driven active matrix organic light-emitting diode (OLED) displays on flexible polyethylene terephthalete substrates. These displays have 48×48 bottom-emission OLED pixels with two pentacene OTFTs used per pixel. Parylene is used to isolate the OTFTs and OLEDs with good OTFT yield and uniformity.

For the InAs/GaAs quantum-dot system, the evolution of the wetting layer (WL) with the InAs deposition thickness has been studied by reflectance difference spectroscopy (RDS) in combination with atomic force microscopy and photoluminescence. One transition related to the light hole in the WL has been observed clearly in RDS, from which its transition energy and in-plane optical anisotropy (OA) are determined. The evolution of WL with the InAs dot formation and ripening has been discussed. In addition, the remarkable changes in OA at the onsets of the dot formation and ripening have been observed, implying the mode transitions of atom transport between the WL and the dots.

We have investigated the evolution of exciton state filling as a function of excitation power density in InAs∕GaAs quantum dots (QDs). In addition to the emission bands of exciton recombination corresponding to the atom-like S, P, and D, etc. shells of quantum dots, it was observed that some extra states, P′ (between the S and P shells) and D′ (between the P and D shells), appear in the spectra with increasing number of excitons occupying the QDs. The emergence of these intershell excitonic levels is an experimental demonstration of strong exciton–exciton exchange interaction and coupling as well as state mixing and hybridization of a multiexciton system in quantum dots.