Xiaoqing Tian

Band Gap Opening of Bilayer Graphene by F4-TCNQ Molecular Doping and Externally Applied Electric Field

The band gap opening of bilayer graphene with one side surface adsorption of F4-TCNQ is reported. F4-TCNQ doped bilayer graphene shows p-type semiconductor characteristics. With a F4-TCNQ concentration of 1.3 x 10(-10) mol/cm(2), the charge transfer between each F4-TCNQ molecule and graphene is 0.45e, and the built-in electric field, E(bi), between the graphene layers could reach 0.070 V/A. The charge transfer and band gap opening of the F4-TCNQ-doped graphene can be further modulated by an externally applied electric field (E(ext)). At 0.077 V/A, the gap opening at the Dirac point (K), DeltaE(K) = 306 meV, and the band gap, E(g) = 253 meV, are around 71% and 49% larger than those of the pristine bilayer under the same E(ext).

Engineering of the interactions of volatile organic compounds with MoS2

We investigate the interactions between volatile organic compounds (VOCs, including ethanol, acetone and propanal) and pristine, defective and transition metal-functionalized MoS2 using the first-principles method. The sensitivity of MoS2-based chemical gas sensors could be drastically improved by transition metal functionalization. The VOCs exhibit physical adsorption on pure and sulfur-vacancy-defective MoS2 but stronger chemisorption on transition metal (TM) (Fe, Co, Pd) functionalized MoS2 together with larger adsorption energy and charge transfer. The band gaps of defective and transition metal functionalized MoS2 are smaller than that of perfect monolayer MoS2 and there are a few localized states inside. This also favors the adsorption of VOCs. The VOCs have the largest adsorption energies on the Fe functionalized MoS2 substrate. The adsorption of VOCs will reduce the total magnetic moments of the Fe and Co functionalized MoS2 substrates. Moreover the magnetic exchange coupling energies are variable in response to the adsorption of VOCs. The ferromagnetic coupling can be even reversed to anti-ferromagnetic coupling. This ferromagnetic to antiferromagnetic transition can be detected by a magnetic force microscope. Our work strongly suggests that MoS2 is a compelling and feasible candidate as a magnetic sensor for VOCs.

Unusual electronic and magnetic properties of lateral phosphorene–WSe2 heterostructures

The unusual electronic and magnetic properties of in-plane phosphorene/WSe2 heterostructures are theoretically investigated. Due to strong spin–orbit-coupling (SOC), a giant magnetocrystalline anisotropy energy with an easy out-of-plane magnetization is realized in the lateral phosphorene/WSe2 heterostructures. The heterostructures can be either half-metallic or metallic dependent on their edges and sizes. In light of these results, it is expected that in-plane heterostructures of phosphorene/graphene will provide abundant opportunities for applications in spintronic and electronic devices.

Configuration-dependent electronic and magnetic properties of graphene monolayers and nanoribbons functionalized with aryl groups.

Graphene monolayers functionalized with aryl groups exhibit configuration-dependent electronic and magnetic properties. The aryl groups were adsorbed in pairs of neighboring atoms in the same sublattice A (different sublattices) of graphene monolayers, denoted as the M2 (AA) (M2 (AB)) configuration. The M2 (AA) configuration behaved as a ferromagnetic semiconductor. The band gaps for the majority and minority bands were 1.1 eV and 1.2 eV, respectively. The M2 (AB) configuration behaved as a nonmagnetic semiconductor with a band gap of 0.8 eV. Each aryl group could induce 1 Bohr magneton (μB) into the molecule-graphene system. Armchair graphene nanoribbons (GNRs) exhibited the same configuration-dependent magnetic properties as the graphene monolayers. The net spin of the functionalized zigzag GNRs was mainly localized on the edges demonstrating an adsorption site-dependent magnetism. For the zigzag GNRs, both the M2 (AA) and M2 (AB) configurations possibly had a magnetic moment. Each aryl group could induce 1.5-3.5 μB into the molecule-graphene system. There was a metal-to-insulator transition after adsorption of the aryl groups for the zigzag GNRs.

UV-Enhanced Ethanol Sensing Properties of RF Magnetron-Sputtered ZnO Film

ZnO film was deposited by the magnetron sputtering method. The thickness of ZnO film is approximately 2 μm. The influence of UV light illumination on C2H5OH sensing properties of ZnO film was investigated. Gas sensing results revealed that the UV-illuminated ZnO film displays excellent C2H5OH characteristics in terms of high sensitivity, excellent selectivity, rapid response/recovery, and low detection limit down to 0.1 ppm. The excellent sensing performance of the sensor with UV activation could be attributed to the photocatalytic oxidation of ethanol on the surface of the ZnO film, the planar film structure with high utilizing efficiency of UV light, high electron mobility, and a good surface/volume ratio of of ZnO film with a relatively rough and porous surface.

Zinc oxide–black phosphorus composites for ultrasensitive nitrogen dioxide sensing

Multi-layer black phosphorus (m-BP) has been successfully incorporated in zinc oxide (ZnO) hollow spheres, thus forming hetero-structured ZnO-BP composites; a study performed on their properties reveals that the BP environmental stability can be significantly enhanced by the introduction of ZnO, and the sensors based on ZnO-BP composites exhibit high response, fast response behavior, outstanding selectivity, and ultralow detection limit of 1 ppb towards NO2 gas molecules. The ultrasensitive sensing performance is suggested to be due to the large surface area, excellent carrier mobility, and enhanced charge transfer of ZnO-BP in the presence of BP. Moreover, the mechanism of NO2 sensing with ZnO-BP is confirmed by the calculations obtained from the first-principle studies.

Highly Tunable Electronic Structures of Phosphorene/Carbon Nanotube Heterostructures through External Electric Field and Atomic Intercalation

Black phosphorene (BP)/carbon nanotube (CNT) heterostructures can be classified as either type I or II, depending on the size of the CNTs. An external electric field (Eext) can modulate the interfacial electronic structures and separate the electron and hole carriers of the BP/CNT heterostructures. The giant Stark effect is observed, and the band gap of the semiconducting heterostructures can vary several-fold. The intercalation of 3d transition metals can strongly bond BP and CNTs together. Furthermore, strong ferromagnetism with Curie temperature (TC) above room temperature is predicted. It is expected that these BP/CNT heterostructures will provide new opportunities and applications in the fields of optoelectronics and electronics as well as spintronics.

Correction: Unusual electronic and magnetic properties of lateral phosphorene–WSe2 heterostructures

Correction for ‘Unusual electronic and magnetic properties of lateral phosphorene–WSe2 heterostructures’ by Xiao-Qing Tian et al., J. Mater. Chem. C, 2016, DOI: 10.1039/c6tc01978a.