Theoretical investigation of the interaction of CH4 with Al2 and Al3 neutral and charged clusters

Post-annealing effect of low temperature atomic layer deposited Al2O3on the top gate IGZO TFT

Electronical properties of top gate amorphous InGaZnO4thin film transistors (TFTs) could be controlled by post-annealing treatment, which has a great impact on the Al2O3insulator. To investigate the effect of post-annealing on Al2O3, Al/Al2O3/p-Si MOS capacitoras with Al2O3films treated under various post-deposition annealing (PDA) temperature were employed to analysis the change of electrical properties, surface morphology, and chemical components by electrical voltage scanning, atomic force microscope (AFM), and x-ray photoelectron spectroscopy (XPS) technologies. After PDA treatment, the top gate TFTs had a mobility about 7 cm2V-1s-1and the minimum subthreshold swing (SS) about 0.11 V/dec, and the threshold voltage (Vth) shifted from positive direction to negative direction as the post-annealing temperature increased. Electrical properties of MOS capacitors revealed the existence of positive fixed charges and the variation of trap state density with increasing PDA temperature, and further explained the change of negative bias stress (NBS) stability in TFT. AFM results clarified the increased leakage current, degraded SS, and NBS stability in MOS capacitors and TFTs, respectively. XPS results not only illuminated the origin of fixed charges and the trap density variation with PDA temperatures of Al2O3films, but also showed the O and H diffusion from Al2O3into IGZO during post-annealing process, which led to the deviation ofVth, the change of current density, and the negativeVthshift after positive bias stress in TFTs.

Adsorption and dissociation of gas-phase HCl molecules on Al17q (q = -2 - +3) ions

Al₁₇ clusters exhibit apparent changes in curvature, which resemble macroscopic metal tips. Here, we show, using the density functional theory method, how surface charges of Al₁₇^q (q = -2  to +3) ions affect the adsorption and dissociation behavior of HCl molecules. Geometries, adsorption energies, vibrational frequencies, Mulliken population analysis and transition states of (Al₁₇HCl)^q (q = -2  to +3) adsorption complexes were studied. The results revealed that HCl molecules tend to locate on tip sites of the Al₁₇^q (q = -2  to  +3) ions. Anionic adsorption complexes are prone to H affinity adsorption, whereas cationic adsorption complexes favor Cl-affinity adsorptions. These adsorption behaviors look quite like macroscopic tip effects. H-Cl bonds of the adsorption complexes weaken with an increase in either positive or negative charge. Dissociation barriers of the H-Cl bonds exhibit binding energies that are 2 orders of magnitude smaller than those of an isolated HCl molecule. Considering adsorption energies and dissociation barriers comprehensively, HCl molecules should dissociate spontaneously for all the models considered. Generally, the more negative charges the clusters carry, the more energy the reaction will release. Graphical abstract Dissociation barriers of the H-Cl bonds in Al₁₇^q (q = -2 - +3) cluster ions exhibit energy barriers ~2 orders of magnitude smaller than isolated HCI molecules.