Tunable Electronic Transport Properties Research Articles

Evolution of electrical transport properties in FeTe2-CoTe2 solid solution system for optimum thermoelectric performance

Transition metal chalcogenides have received significant attention as electronic materials owing to their tunable electronic transport properties and unique crystal structures. In this work, the electrical, thermal, and thermoelectrical transport properties of FeTe2-CoTe2 solid solution system were investigated by synthesizing a series of (Fe1–xCox)Te2 polycrystalline alloys with x = 0, 0.25, 0.5, 0.75, and 1. FeTe2 and CoTe2 exhibited identical orthorhombic structures and formed a complete solid solution. (Fe1–xCox)Te2 system exhibits wide range of electronic transport characteristics; CoTe2 exhibits metallic conduction with high electrical conductivity of ∼8000 S/cm with electron carriers, whereas FeTe2 exhibits semiconducting conduction with relatively low electrical conductivity of ∼300 S/cm with hole carriers at room temperature. The optimum carrier transport for high power factor of 1.53 mW/cmK2 at 600 K is observed for (Fe0.5Co0.5)Te2 composition. The electronic band dispersions of FeTe2, (Fe0.5Co0.5)Te2, and CoTe2 were calculated by using the density functional theory and it was found that a distinct flat band is present near the Fermi level for Fe0.5Co0.5Te2, supporting the high power factor of Fe0.5Co0.5Te2. As the lattice thermal conductivity is reduced for the solid-solution samples with additional point defect scattering, the thermoelectric figure of merit (zT) increased significantly to 0.18 for Fe0.5Co0.5Te2 compared to 0.001 for FeTe2 or 0.08 for CoTe2 at 600 K.

Study on the Thermoelectric Properties of n-Type Polycrystalline SnSe by CeCl3 Doping

SnSe is a promising medium-temperature thermoelectric material due to its extremely low thermal conductivity and tunable electronic transport properties. In this work, n-type SnSe0.95 polycrystals doped with CeCl3 are synthesized by a melting method combined with a spark plasma sintering (SPS) process. The samples have highly textured structures and anisotropic thermoelectric properties. CeCl3 doping has a favorable effect on the electronic transport above 473 K, which may benefit from the excitation of the introduced impurity energy level. Moreover, the thermal conductivity is significantly reduced due to the phonon scattering by point defects. Finally, a peak ZT value of 1.17 is obtained at 773 K in SnSe0.95–0.5 mol % CeCl3, which paves the way for improving the thermoelectric performance of n-type SnSe via rare-earth halide doping.

Effect of chemical modification on electronic transport properties of carbyne

Using density functional theory in combination with the Green’s functional formalism, we study the effect of surface functionalization on the electronic transport properties of 1D carbon allotrope—carbyne. We found that both hydrogenation and fluorination result in structural changes and semiconducting to metallic transition. Consequently, the current in the functionalization systems increases significantly due to strong delocalization of electronic states along the carbon chain. We also study the electronic transport in partially hydrogenated carbyne and interface structures consisting of pristine and functionalized carbyne. In the latter case, current rectification is obtained in the system with rectification ratio up to 50%. These findings can be useful for developing carbyne-based structures with tunable electronic transport properties.

Selective Construction of Magic Hierarchical Metal–Organic Clusters on Surfaces

Magic organic clusters, representing well-defined zero-dimensional organic clusters with identical sizes and configurations, have received increased interests in recent years. Previously, the magic clusters were mainly stabilized through van der Waals force, C–H...π interaction, hydrogen bonding, dipole interaction, etc., which yet lack thermal stability and tunable electronic transport properties for potential applications. The introduction of metal adatoms into the organic systems would be an excellent choice for facilitating more stable magic clusters as the metal adatoms could serve as a nucleation center and help for clustering of organic ligands with increased stabilities. Considering the limited coordination number of metal species, it would be of great interest to introduce multilevel interactions besides metal–organic bonding, which may provide new avenues for controllable fabrication of more complicated and larger magic clusters. Herein, we have achieved the controllable fabrication of three distinct magic metal–organic clusters, especially two hierarchical ones with different sizes on the reconstructed Au(111) and unreconstructed Ag(111) surface. The key for various unprecedented magic hierarchical clusters here is the selection of the organic ligands with only one active carboxyl (−COOH) group which possesses bonding flexibility and diversity features after dehydrogenation but avoids the usual two-dimensional network of those containing more −COOH groups.

Tunable Electronic Transport Properties of 2D Layered Double Hydroxide Crystalline Microsheets with Varied Chemical Compositions.

Transistors based on layered double hydroxides (LDH) single microcrystal are fabricated, whose conductivity of LDH can be tuned by varying metal cations or interlayer anions, but weakly affected by external electric field. The carrier mobility can reach about 1 × 10(-5) cm(2) V(-1) s(-1) , a value comparable to that of organic C60-based transistors. This work paves a way for future electrical applications of LDH.

Grain boundary barrier modification due to coupling effect of crystal polar field and water molecular dipole in ZnO-based structures

Surface water molecules induced grain boundaries (GBs) barrier modification was investigated in ZnO and ZnMgO/ZnO films. Tunable electronic transport properties of the samples by water were characterized via a field effect transistor (FET) device structure. The FETs fabricated from polar C-plane ZnO and ZnMgO/ZnO films that have lots of GBs exhibited obvious double Schottky-like current-voltage property, whereas that fabricated from nonpolar M-plane samples with GBs and ZnO bulk single-crystal had no obvious conduction modulation effects. Physically, these hallmark properties are supposed to be caused by the electrostatical coupling effect of crystal polar field and molecular dipole on GBs barrier.

Tunable Electronic Transport Properties of Metal‐Cluster‐Decorated III–V Nanowire Transistors

A metal-cluster-decoration approach is utilized to tailor electronic transport properties (e.g., threshold voltage) of III-V NWFETs through the modulation of free carriers in the NW channel via the deposition of different metal clusters with different work function. The versatility of this technique has been demonstrated through the fabrication of high-mobility enhancement-mode InAs NW parallel FETs as well as the construction of low-power InAs NW inverters.

A nanocomposite photoelectrode made of 2.2 eV band gap copper tungstate (CuWO4) and multi-wall carbon nanotubes for solar-assisted water splitting

We report on the photoelectrochemical performances of a nanocomposite photoactive material made of copper tungstate (CuWO4) and multi-wall carbon nanotubes (MWCNT). The purpose of this work was to create a light absorber/charge collector composite material with tunable electronic transport properties to minimize the bulk resistance of CuWO4 material class. Nanocomposite thin films (typically 2.0 ± 0.1 μm) were fabricated by means of spray pyrolysis using solutions containing copper acetate, ammonium metatungstate and MWCNT. Spray-deposited polycrystalline CuWO4 films were found to be porous, though crack-free, and made of CuWO4 nanoparticles with dimensions in the 10–50 nm range. Tauc plots derived from UV–visible and photocurrent spectroscopy techniques led to a consistent band gap value of 2.20 (±0.05) eV. Electrochemical impedance spectroscopy performed in pH10 buffer solution under Air Mass 1.5 global (AM1.5G) at 0.8 V vs. saturated calomel electrode (1.63V vs. reversible hydrogen electrode) pointed out a bulk resistance reduction by 30% on nanocomposites photoanodes when compared to un-modified CuWO4 control samples. It is worth mentioning that the reduction in bulk resistance was achieved with an extremely low MWCNT:CuWO4 weight ratio (1:10,000), in which MWCNT absorbed less than 2% of incoming light. Subsequent linear scan voltammetry (LSV) performed in the same conditions revealed a photocurrent density increase of 26% at 0.8 VSCE (1.63 VRHE) compared to control samples. Additional LSV and incident photon-to-current efficiency measurements demonstrated that MWCNT served as effective electron collectors distributed throughout the entire CuWO4 bulk.

Tunable electronic transport properties of silicon-fullerene-linked nanowires: Semiconductor, conducting wire, and tunnel diode

We explore the possibility of controllable tuning of the electronic transport properties of silicon-fullerene-linked nanowires by encapsulating guest atoms into their cages. Our first-principles calculations demonstrate that the guest-free nanowires are semiconductors, and do not conduct electricity. The iodine or sodium doping improves the transport properties, and makes the nanowires metallic. In the junctions of I-doped and Na-doped NWs, the current travels through the boundary by quantum tunneling. More significantly, the junctions have asymmetric $I\text{\ensuremath{-}}{V}_{b}$ curves, which could be used as rectifiers. The current-voltage curves are interpreted by band-overlapping models. Tunable electronic transport properties of silicon-fullerene-linked nanowires could find many applications such as field-effect transistors, conducting wires, and tunnel diodes.

Tunable Electronic Transport Characteristics of Surface-Architecture-Controlled ZnO Nanowire Field Effect Transistors

Surface-architecture-controlled ZnO nanowires were grown using a vapor transport method on various ZnO buffer film coated c-plane sapphire substrates with or without Au catalysts. The ZnO nanowires that were grown showed two different types of geometric properties: corrugated ZnO nanowires having a relatively smaller diameter and a strong deep-level emission photoluminescence (PL) peak and smooth ZnO nanowires having a relatively larger diameter and a weak deep-level emission PL peak. The surface morphology and size-dependent tunable electronic transport properties of the ZnO nanowires were characterized using a nanowire field effect transistor (FET) device structure. The FETs made from smooth ZnO nanowires with a larger diameter exhibited negative threshold voltages, indicating n-channel depletion-mode behavior, whereas those made from corrugated ZnO nanowires with a smaller diameter had positive threshold voltages, indicating n-channel enhancement-mode behavior.