Xiao-Chun Wang

A new class of “electro-acid/base”-induced reversible methyl ketone colour switches

Methyl ketone has been designed as a switching unit for electrically addressable molecular colour switches. A newly proposed mechanism of “electro-acid/base” (radical ions)-induced intermolecular proton transfer for the colour switch is proven clearly by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and in situ UV-Vis spectroscopy. A dramatic spectral absorption shift (about 291 nm) is observed during the switching, and blue, yellow and green colours are obtained by adjusting the substituents on the methyl ketone-bridged unit. The in situ “electro-acid/base” is far more convenient than the conventional chemical stimulus of acids or bases for the manipulation of the molecular switching properties. This new switching method and molecular structure manipulation will inspire and accelerate the further development of broad switching materials and applications in ultrathin flexible displays, etc.

Tuning the electronic and magnetic properties of penta-graphene using a hydrogen atom: a theoretical study

Herein, an isolated hydrogen atom absorbed on penta-graphene (PG) was predicted to induce magnetic moments and tune the electronic properties of penta-graphene and was systematically studied using first-principles calculations. The adsorption energy and formation energy calculations suggest that magnetic penta-graphene (M-PG) and weak magnetic penta-graphene (WM-PG) of hydrogen-absorbed PG systems are energetically the most favorable states among the possible hydrogen-absorbed configurations. The hydrogen atom adsorbed on the PG sheet can effectively tune the electronic properties of PG and change it from a semiconductor to half-metallic. In the M-PG system, this spin-polarized state is essentially localized on the three-fold coordinated C atoms in the first layer opposite to that where the hydrogen atom is chemisorbed. Through changing the bond angle and bond length of the adsorbed hydrogen atom on the PG system, we can remarkably increase the magnetic moment of the hydrogen-absorbed PG system by 137 times. This would allow us to design a magnetic nanoswitch to manipulate the magnetic state of PG. We also obtained the scanning tunneling microscopy (STM) images for future experimental identification. Our findings show that the hydrogen atom absorbed on the PG system will have exciting applications in magnetic storage technology and next-generation electronic and spintronic nanodevices.

Magnetism and piezoelectricity of hexagonal boron nitride with triangular vacancy

First-principle calculations reveal that the configuration system of hexagonal boron nitride (h-BN) monolayer with triangular vacancy can induce obvious magnetism, contrary to that of the nonmagnetic pristine boron nitride monolayer. Interestingly, the h-BN with boron atom vacancy (VB-BN) displays metallic behavior with a total magnetic moment being 0.46? B per cell, while the h-BN with nitrogen atom vacancy (VN-BN) presents a half-metallic characteristic with a total magnetic moment being 1.0? B per cell. Remarkably, piezoelectric stress coefficient e 11 of the VN-BN is about 1.5 times larger than that of pristine h-BN. Furthermore, piezoelectric strain coefficient d 11 (12.42 pm/V) of the VN-BN is 20 times larger than that of pristine h-BN and also one order of magnitude larger than the value for the h-MoS2 monolayer, which is mainly due to the spin-down electronic state in the VN-BN system. Our study demonstrates that the nitrogen atom vacancies can be an efficient route to tailoring the magnetic and piezoelectric properties of h-BN monolayer, which have promising performances for potential applications in nano-electromechanical systems (NEMS) and nanoscale electronics devices.

Linear optical properties of defective KDP with oxygen vacancy: First-principles calculations

The linear optical properties of potassium dihydrogen phosphate (KDP) with oxygen vacancy are investigated with first-principles density functional theory calculations. We use Heyd–Scuseria–Ernzerhof (HSE06) functional to calculate the linear optical properties because of its accuracy in the band gap calculation. Compared with the perfect KDP, we found that due to the defect states located at the band gap, the defective KDP with oxygen vacancy has new optical adsorption within the energy region from 4.8 eV to 7.0 eV (the corresponding wavelength region is from 258 nm to 177 nm). As a result, the oxygen vacancy can decrease the damage threshold of KDP crystal. It may give a direction to the KDP production for laser system.

Molecular dynamics simulation of structural change at metal/semiconductor interface induced by nanoindenter*

The structures of the Si/Cu heterogenous interface impacted by a nanoindenter with different incident angles and depths are investigated in detail using molecular dynamics simulation. The simulation results suggest that for certain incident angles, the nanoindenter with increasing depth can firstly increase the stress of each atom at the interface and it then introduces more serious structural deformation of the Si/Cu heterogenous interface. A nanoindenter with increasing incident angle (absolute value) can increase the length of the Si or Cu extended atom layer. It is worth mentioning that when the incident angle of the nanoindenter is between −45° and 45°, these Si or Cu atoms near the nanoindenter reach a stable state, which has a lower stress and a shorter length of the Si or Cu extended atom layer than those of the other incident angles. This may give a direction to the planarizing process of very large scale integration circuits manufacture.