Charged Exciton Generation by Curvature-Induced Band Gap Fluctuations in Structurally Disordered Two-Dimensional Semiconductors.

Curvature is a general factor for various two-dimensional (2D) materials due to their flexibility, which is not yet fully unveiled to control their physical properties. In particular, the effect of structural disorder with random curvature formation on excitons in 2D semiconductors is not fully understood. Here, the correlation between structural disorder and exciton formation in monolayer MoS on SiO was investigated by using photoluminescence (PL) and Raman spectroscopy.

Anomalous Conductance near Percolative Metal-Insulator Transition in Monolayer MoS at Low Voltage Regime.

Conductivity of the insulating phase increases generally at an elevated drain-source voltage due to the field-enhanced hopping or heating effect. Meanwhile, a transport mechanism governed by percolation in a low compensated semiconductor gives rise to the reduced conductivity at a low-field regime. Here, in addition to this behavior, we report the anomalous conductivity behavior to transform from a percolative metallic to an insulating phase at the low voltage regime in monolayer molybdenum disulfide (MoS).

Correction: Thickness-dependent in-plane thermal conductivity of suspended MoS grown by chemical vapor deposition.

Correction for 'Thickness-dependent in-plane thermal conductivity of suspended MoS2 grown by chemical vapor deposition' by Jung Jun Bae et al., Nanoscale, 2017, 9, 2541-2547.

Electrothermal Local Annealing via Graphite Joule Heating on Two-Dimensional Layered Transistors.

A simple but powerful device platform for electrothermal local annealing (ELA) via graphite Joule heating on the surface of transition-metal dichalcogenide, is suggested here to sustainably restore intrinsic electrical properties of atomically thin layered materials. Such two-dimensional materials are easily deteriorated by undesirable surface/interface adsorbates and are screened by a high metal-to-semiconductor contact resistance. The proposed ELA allows one to expect a better electrical performance such as an excess electron doping, an enhanced carrier mobility, and a reduced surface traps in a monolayer molybdenum disulfide (MoS)/graphite heterostructure.

Soft Coulomb gap and asymmetric scaling towards metal-insulator quantum criticality in multilayer MoS.

Quantum localization-delocalization of carriers are well described by either carrier-carrier interaction or disorder. When both effects come into play, however, a comprehensive understanding is not well established mainly due to complexity and sparse experimental data. Recently developed two-dimensional layered materials are ideal in describing such mesoscopic critical phenomena as they have both strong interactions and disorder.

Junction-Structure-Dependent Schottky Barrier Inhomogeneity and Device Ideality of Monolayer MoS Field-Effect Transistors.

Although monolayer transition metal dichalcogenides (TMDs) exhibit superior optical and electrical characteristics, their use in digital switching devices is limited by incomplete understanding of the metal contact. Comparative studies of Au top and edge contacts with monolayer MoS reveal a temperature-dependent ideality factor and Schottky barrier height (SBH). The latter originates from inhomogeneities in MoS caused by defects, charge puddles, and grain boundaries, which cause local variation in the work function at Au-MoS junctions and thus different activation temperatures for thermionic emission.

Thickness-dependent in-plane thermal conductivity of suspended MoS grown by chemical vapor deposition.

The in-plane thermal conductivities of suspended monolayer, bilayer, and multilayer MoS films were measured in vacuum by using non-invasive Raman spectroscopy. The samples were prepared by chemical vapor deposition (CVD) and transferred onto preformed cavities on a Au-coated SiO/Si substrate. The measured thermal conductivity (13.

Indirect Bandgap Puddles in Monolayer MoS by Substrate-Induced Local Strain.

An unusually large bandgap modulation of 1.23-2.65 eV in monolayer MoS on a SiO /Si substrate is found due to the inherent local bending strain induced by the surface roughness of the substrate, reaching the direct-to-indirect bandgap transition.

Electrical Transport Properties of Polymorphic MoS2.

The engineering of polymorphs in two-dimensional layered materials has recently attracted significant interest. Although the semiconducting (2H) and metallic (1T) phases are known to be stable in thin-film MoTe2, semiconducting 2H-MoS2 is locally converted into metallic 1T-MoS2 through chemical lithiation. In this paper, we describe the observation of the 2H, 1T, and 1T' phases coexisting in Li-treated MoS2, which result in unusual transport phenomena.

Photochemical Reaction in Monolayer MoS2 via Correlated Photoluminescence, Raman Spectroscopy, and Atomic Force Microscopy.

Photoluminescence (PL) from monolayer MoS2 has been modulated using plasma treatment or thermal annealing. However, a systematic way of understanding the underlying PL modulation mechanism has not yet been achieved. By introducing PL and Raman spectroscopy, we analyze that the PL modulation by laser irradiation is associated with structural damage and associated oxygen adsorption on the sample in ambient conditions.

Sensitive photo-thermal response of graphene oxide for mid-infrared detection.

This study characterizes the effects of incident infrared (IR) radiation on the electrical conductivity of graphene oxide (GO) and examines its potential for mid-IR detection. Analysis of the mildly reduced GO (m-GO) transport mechanism near room temperature reveals variable range hopping (VRH) for the conduction of electrons. This VRH behavior causes the m-GO resistance to exhibit a strong temperature dependence, with a large negative temperature coefficient of resistance of approximately -2 to -4% K(-1).

Hollow carbon nanospheres/silicon/alumina core-shell film as an anode for lithium-ion batteries.

Hollow carbon nanospheres/silicon/alumina (CNS/Si/Al₂O₃) core-shell films obtained by the deposition of Si and Al₂O₃ on hollow CNS interconnected films are used as the anode materials for lithium-ion batteries. The hollow CNS film acts as a three dimensional conductive substrate and provides void space for silicon volume expansion during electrochemical cycling. The Al2O3 thin layer is beneficial to the reduction of solid-electrolyte interphase (SEI) formation.

Transition from direct to Fowler-Nordheim tunneling in chemically reduced graphene oxide film.

We investigate charge transport in a chemically reduced graphene oxide (RGO) film of sub-micron thickness. The I-V curve of RGO film shows current switching of the order of ∼10(5) above the threshold voltage. We found that the observed I-V curve is consistent with quantum tunnelling based charge transport.

TLM-PSD model for optimization of energy and power density of vertically aligned carbon nanotube supercapacitor.

Electrochemical capacitors with fast charging-discharging rates are very promising for hybrid electric vehicle industries including portable electronics. Complicated pore structures have been implemented in active materials to increase energy storage capacity, which often leads to degrade dynamic response of ions. In order to understand this trade-off phenomenon, we report a theoretical model based on transmission line model which is further combined with pore size distribution function.

Transferred wrinkled Al2O3 for highly stretchable and transparent graphene-carbon nanotube transistors.

Despite recent progress in producing transparent and bendable thin-film transistors using graphene and carbon nanotubes, the development of stretchable devices remains limited either by fragile inorganic oxides or polymer dielectrics with high leakage current. Here we report the fabrication of highly stretchable and transparent field-effect transistors combining graphene/single-walled carbon nanotube (SWCNT) electrodes and a SWCNT-network channel with a geometrically wrinkled inorganic dielectric layer. The wrinkled Al2O3 layer contained effective built-in air gaps with a small gate leakage current of 10(-13) A.

Synthesis of multilayer graphene balls by carbon segregation from nickel nanoparticles.

Three-dimensional (3D) structured graphene is a material of great interest due to its diverse applications in electronics, catalytic electrodes, and sensors. However, the preparation of 3D structured graphene is still challenging. Here, we report the fabrication of multilayer graphene balls (GBs) by template-directed carbon segregation using nickel nanoparticles (Ni-NPs) as template materials.

Influence of copper morphology in forming nucleation seeds for graphene growth.

We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film.

Graphene/carbon nanotube hybrid-based transparent 2D optical array.

Graphene/carbon nanotube (CNT) hybrid structures are fabricated for use as optical arrays. Vertically aligned CNTs are directly synthesized on a graphene/quartz substrate using plasma-enhanced chemical vapor deposition (PECVD). Graphene preserves the transparency and resistance during CNT growth.

Reduction-controlled viologen in bisolvent as an environmentally stable n-type dopant for carbon nanotubes.

Various viologens have been used to control the doping of single-walled carbon nanotubes (SWCNTs) via direct redox reactions. A new method of extracting neutral viologen (V(0)) was introduced using a biphase of toluene and viologen-dissolved water. A reductant of sodium borohydride transferred positively charged viologen (V(2+)) into V(0), where the reduced V(0) was separated into toluene with high separation yield.

Fermi level engineering of single-walled carbon nanotubes by AuCl3 doping.

We investigated the modulation of optical properties of single-walled carbon nanotubes (SWCNTs) by AuCl 3 doping. The van Hove singularity transitions (E 11 (S), E 22 (S), E 11 (M)) in absorption spectroscopy disappeared gradually with an increasing doping concentration and a new peak appeared at a high doping concentration. The work function was downshifted up to 0.