The mechanism of amine formation on Si(1 0 0) activated with chlorine atoms

The dissociation of NH₃ on a Si(1 0 0) surface activated with Cl atoms was investigated using X-ray photoelectron spectroscopy. Gas phase UV-Cl₂ (0.1-10 Torr Cl₂ for 10-600 s under 1000 W Xe lamp illumination) completely replaced the H-termination on aqueous-cleaned Si(1 0 0) with 0.82 ± 0.06 ML of Cl at 298 K. A single spin-orbit split Cl 2p doublet indicated that the Cl atoms were bound to Si dimer atoms, forming silicon monochloride (Cl-Si-Si-Cl). Exposing the Cl-terminated surface at 348 K to NH₃ (1-1000 Torr for 5-60 min) replaced one Cl atom with one N atom up to a coverage of 0.33 ± 0.02 ML. Cl atoms lowered the activation energy barrier for reaction to form a primary amine (Si-NH₂). Oxygen was coadsorbed due to competition by H₂O contamination. The presence of Cl on the surface even after high NH₃ exposures is attributed to site blocking and electrostatic interactions among neighboring Cl-Si-Si-NH₂ moieties. The results demonstrate a low temperature reaction pathway for depositing N-bearing molecules on Si surfaces.     

Charge retention in quantized energy levels of nanocrystals

Understanding charging mechanisms and charge retention dynamics of nanocrystal (NC) memory devices is important in optimization of device design. Capacitance spectroscopy on PECVD grown germanium NCs embedded in a silicon oxide matrix was performed. Dynamic measurements of discharge dynamics are carried out. Charge decay is modelled by assuming storage of carriers in the ground states of NCs and that the decay is dominated by direct tunnelling. Discharge rates are calculated using the theoretical model for different NC sizes and densities and are compared with experimental data. Experimental results agree well with the proposed model and suggest that charge is indeed stored in the quantized energy levels of the NCs.     

Charge-storage effects in a metal-insulator-semi-conductor structure containing germanium nano-crystals formed by rapid thermal annealing of an electron-beam evaporated germanium layer

Charge-storage effects in a metal-insulator-semi-conductor device containing germanium (Ge) nano-crystals were investigated. The Ge nano-crystals were formed by rapid thermal annealing (RTA) of an evaporated, ultra-thin Ge layer at 1000 °C in argon. Capacitance–voltage measurements shows that the amount of electrical charge which can be stored in the device varies with the duration of the RTA treatment. The charge shows a maximum value for 200 s RTA treatment, and then decreases with longer annealing time up to 400 s. Atomic force microscopy analysis indicates that there is a correlation between the density of Ge nano-crystals in the devices, and the amount of electrical charge stored. For an RTA treatment of 300 s, capacitance–time measurements show a time dependence, which indicates a dispersive carrier relaxation. The retention time is dependent on the applied bias, and a maximum retention time of 115 s was observed at -7 V. The value of the stored electrical charges in the device decreases with increasing ambient temperature. A possible charging/discharging mechanism for the device was discussed to explain the capacitance–time measurements and the temperature stored charge results. PACS 81.07.Ta; 81.15.Jj; 73.63.Kv; 85.35.Be; 81.40.Ef     

Electrical characteristics of a metal–insulator–semiconductor memory structure containing Ge nanocrystals

A metal–insulator–semiconductor structure device with Ge nanocrystals in SiO₂ was synthesized and the electrical characteristics were investigated. Capacitance–voltage (C–V) curves show hysteresis and the measurements indicate that the device has charge storage effects and stores more holes than electrons. For decreasing measurement frequencies from 1 MHz to 500 Hz, both branches of the C–V hysteresis shift in the positive voltage direction. The slope of the left flank of the C–V hysteresis curve becomes stretched out with decreasing frequency. The slope of the right one appears frequency independent, while there is a small hump/step on the right flank of the C–V hysteresis curve for the lower frequency cases (500 Hz and 1 kHz). The role of Si/SiO₂ interface states is discussed.     

Properties of Al2O3: nc-Si nanostructures formed by implantation of silicon ions into sapphire and amorphous films of aluminum oxide

Physics of the Solid State - Photoluminescence, infrared Fourier spectroscopy, Raman scattering, transmission electron microscopy, and electron diffraction were used to study the luminescent,...