Density functional theory study of semiconductor bandgap regulation

The zero-band gap characteristic of graphene makes it impossible to turn off the conductivity at a specific limit. Because a certain band gap can greatly enhance the potential of graphene in a variety of applications, the widening of the graphene band gap has gained widespread attention. Silicon is the main material in the semiconductor industry. Due to the compatibility between graphene and silicon, the adsorption of graphene on silicon substrates is particularly attractive for its future applications.

The adsorption configuration, adsorption energy and band structure of graphene (including monolayer and bilayer structures) on crystalline silicon (111)/(100) with or without surface hydrogen passivation were compared in detail by density functional theory (Dmol3) calculations. It is found that the interaction between monolayer graphene and hydrogen-passivated crystalline silicon surface is very weak, and the effect on the band gap of graphene is negligible. Due to the destruction of symmetry, the band gap of double-layer graphene will be opened to a certain extent when it is adsorbed on the surface of hydrogen-passivated crystalline silicon. This study provides strong theoretical support for the design of devices based on graphene and crystalline silicon, and enhances the application potential of graphene in the field of optoelectronics.

ACS Nano 9,8562-8568 (2015)

A multistage conductive transition induced by the enhancement of intermolecular charge transfer in a memory device

The rapid development of society in the 21st century requires the development of better data storage. Organic molecules with tunable properties are expected to be used in data storage applications due to their advantages of cheap, simple, fast, low energy consumption and long data retention time. Multistage resistive memory devices based on organic molecules have received a lot of attention due to their potential to increase information storage capacity limits by indexability. The density functional theory (DFT) calculation of OZO-SO and OZA-SO is carried out using CASTEP software. The results show that for OZO-SO, the quantitative charge distribution does not change unless a high bias voltage is applied, and the corresponding current change only appears under a high bias voltage, which is reflected as a binary storage mode. For OZA-SO, the change in the illuminated charge distribution is independent of the strength of the applied bias, and two current changes can be observed, thus acting as a ternary storage mode. The findings of this study extend such research and lead to the realization of ultra-high density electron storage materials by altering the terminal electron donor groups.
Adv. Mater. 2015, 27, 5968–5973
 

Adsorption of metal atoms on nanographene

The adsorption of metal atoms on nanographene TB8C and its derivatives was completed by DMol3. In this work, it is found that the arc structure of nanographene is superior to that of intrinsic graphene in metal atom adsorption. Due to the significant increase in electron density in the central region, the amino modified TB8C greatly improves the adsorption capacity of metal atoms. The bonding interactions between 24 metal atoms and nanographenes can be divided into three types: ionic bonding, partial covalent bonding and covalent bonding. Some transition metals (V, Cr, Zr, Nb and Mo) have strong covalent bonds with nanographenes and can even be regarded as organometrical complexes. The hyperbolic configuration of nanographene also allows it to adsorb two metal atoms at the same time, especially alkali metal atoms. Most metal atoms can stably bond with nanographene, and their binding results in rich physicochemical properties, which makes the obtained M@NG complexes have great potential in alkali metal atom carrying, hydrogen storage, gas sensing and nanocatalizations.