arXiv subjects

Sui Kong Hark

Publications and source records attributed to Sui Kong Hark.

4 recordsLinked to original sources

arXiv2017

The Evolution of Alq3 Films Exposure to Air

Small molecular solar cell becomes more stable when a thin tris-(8-hydroxyquinoline) aluminum (Alq3) buffer layer instead of bathocuproine (BCP) is inserted between the active layer and electrode. In this work, we introduce a single layer device (ITO / Alq3 / Au) exposure to air to investigate the role of Alq3 in organic solar cells. The large PL intensity and undetectable Raman peaks of 8-hydroxyquinoline (8-Hq), a degradation product of Alq3 through chemical reaction, indicate that the degradation of Alq3 is not severe even after a few hundred hours exposure. Thus the Alq3 buffer layer gives a good protection of the active layers against oxygen\water permeation comparing with BCP. However, the small quantity of degraded Alq3 products can enhance the current density (after 15 h) in single layer Alq3 device, which is reflected in the decrease of parallel resistance Rp. Therefore, due to the enhanced charge transport and the long term better protection from ambient oxygen/water, the lifetime of small molecular solar cell with Alq3 buffer layer is improved.

cond-mat.mtrl-sci↗

arXiv2017

A Saw-tooth Scaling of Work Function in Hydrogenated Graphene

The saw-tooth scaling investigations of work functions (WF) in hydrogenated graphene are theoretically performed by density functional theory. The positions of hydrogen atoms and the H/C ratios affect WF. With the comparison of different graphene structures by adsorbed two hydrogen atoms, WF is larger with less negative charges of the graphene. With different H/C ratios, WF is controlled by two parts: the graphene surface and hydrogen groups. When the ratio is smaller than 0.5, the work func-tion is more dependent on the Mulliken charge of graphene. With more hydrogen atoms, the surface of graphene is more negative, resulting in a smaller work function. When the ratio is larger than 0.5, the effect of hydrogen groups cannot be ignored. When two sides of graphene have different numbers of hy-drogen atoms, a dipole exists, making the movement of electron from Fermi level to vacuum level more difficult, thus WF is larger than that with the same hydrogen atoms of each side. Therefore the scaling of work function acts like a saw-tooth dependent on H/C ratio.

cond-mat.mtrl-sci↗

arXiv2017

The Reversible Spin Switch by External Control of Interval Distance of CuPc and C59N with the investigation of DFT

In this paper, we introduce a new kind of spin switch based on a joint system of copper phthalocyanine (CuPc) and C59N. Using density functional theory, we investigate the total magnetic moment of this system when gradually changing the interval distance between two molecules. The spin hopping happens during the critical distance with very low energy. This phenomenon shows a possible reality of reversible spin switch by external control of the interval distance. With orbital analysis and electron transfer consideration, the form of C59N+- CuPc- ion pair support this spin hopping phenomenon.

cond-mat.mtrl-sci↗

arXiv2017

Magnetic properties of quasi one-dimensional vanadium-benzene nanowire affected by gas molecules: a first-principle study

Magnetic properties of quasi one-dimensional vanadium-benzene nanowires (VBNW) are investigated theoretically with the absorption of gas molecules-NO and NO2. With the increase adsorption of NO on VBNW, the phase transition from half metal to ferromagnetic metal and last to paramagnetic semiconductor can be observed. With the increase of NO2 on VBNW, half metallic property can be enhanced at first and decreased later. Thus, the electronic and magnetic properties of VBNW can be sensitive and selective to NO and NO2, revealing the potential applications in spintronic sensors of these two kinds of molecules.

cond-mat.mtrl-sci↗