Phosphorus and hydrogen atoms on the (0 0 1) surface of silicon: A comparative scanning tunnelling microscopy study of surface species with a single dangling bond

We present a comparative scanning tunnelling microscopy (STM) study of two features on the Si(0 0 1) surface with a single dangling bond. One feature is the Si-P heterodimer—a single surface phosphorus atom substituted for one Si atom of a Si-Si dimer. The other feature is the Si-Si-H hemihydride—a single hydrogen atom adsorbed to one Si atom of a Si-Si dimer. Previous STM studies of both surface species have reported a nearly identical appearance in STM which has hampered an experimental distinction between them to date. Using voltage-dependent STM we are able to distinguish and identify both heterodimer and hemihydride on the Si(0 0 1) surface. This work is particularly relevant for the fabrication of atomic-scale Si:P devices by STM lithography on the hydrogen terminated Si(0 0 1):H surface, where it is important to monitor the distribution of single P dopants in the surface. Based on the experimental identification, we study the lateral P diffusion out of nanoscale reservoirs prepared by STM lithography.     

Doping and STM tip-induced changes to single dangling bonds on Si(0 0 1)

We have studied single Si dangling bonds on the Si(0 0 1) surface using scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations. The Si dangling bonds are created by the chemisorption of single hydrogen atoms forming a Si-Si-H hemihydride. At room temperature, the hemihydride induces static buckling on adjacent Si-Si dimers. In the STM measurements, we observe that the orientation of the static buckling pattern can be reversed with tip-sample bias and influenced by the substrate doping. Our DFT calculations yield a correlation between the electron occupancy of the hemihydride Si dangling bond and the buckling orientation around it.     

Single P and As dopants in the Si(001) surface

Using first-principles density functional theory, we discuss doping of the Si(001) surface by a single substitutional phosphorus or arsenic atom. We show that there are two competing atomic structures for isolated Si-P and Si-As heterodimers, and that the donor electron is delocalized over the surface. We also show that the Si atom dangling bond of one of these heterodimer structures can be progressively charged by additional electrons. It is predicted that surface charge accumulation as a result of tip-induced band bending leads to structural and electronic changes of the Si-P and Si-As heterodimers which could be observed experimentally. Scanning tunneling microscopy (STM) measurements of the Si-P heterodimer on a n-type Si(001) surface reveal structural characteristics and a bias-voltage dependent appearance, consistent with these predictions. STM measurements for the As:Si(001) system are predicted to exhibit similar behavior to P:Si(001).     

Infrared and ultraviolet absorptions of matrix isolated C(6)O(2)

In the course of our research into carbon chains trapped in matrices of molecular oxygen, we encountered an IR absorption line at 2180.4 cm(-1), which we tentatively assigned to linear C(6)O(2). In this article, we describe our attempts to confirm the assignment by partial isotopic substitution of carbon by (13)C and oxygen by (18)O. A detailed analysis of the IR vibration pattern allowed the unambiguous identification of the carrier of the IR absorption as C(6)O(2). The identification work was very much facilitated by the observation that it is possible to produce and destroy C(6)O(2) in a controlled fashion by suitable laser exposures. With the help of this feature, most of the confusing spectral background could be removed. Two infrared absorptions at 2180.4 (nu(5)) and 1817.7 cm(-1) (nu(6)) and ultraviolet absorption at 252 nm were assigned to the C(6)O(2) molecule--all figures are valid for oxygen matrices. The obtained spectral data are compared with results of quantum chemical calculations. DFT B3LYP/6-31G(d) and semiempirical PM3 methods were used for geometry optimization and calculation of vibrational frequencies. CIS and TD-DFT were used to calculate the electronic absorption spectrum.     

Confirmation of n-Hexane as an Inert Co-Solvent in the Production of Functionalized Silicon Nanoparticles from Reactive High-Energy Ball Milling

Alkanes such as n-hexane have been used as co-solvents in the production of functionalized semiconductor nanoparticles from alkenes and alkynes using Reactive High Energy Ball Milling (RHEBM) under the assumption that they are non-reactive under typical milling conditions. In this paper, a comparative study with two hydrocarbon solvents of comparable chain length, 1-hexyne, and n-hexane, and their milling products using three different commercially available silicon precursors, namely single crystal silicon wafers and polycrystalline particles having a nominal size of 4 µm and 1 mm, is reported. It is found that nanoparticle formation and surface functionalization in all the three silicon systems occurs only with 1-hexyne; n-hexane is non-reactive and does not lead to appreciable functionalized nanoparticle formation under the conditions studied. Nanoparticles (where formed) and microparticle byproducts of appropriate samples are characterized by Transmission electronic microscope (TEM), Fourier transform infrared  (FTIR), Photoluminiscence spectroscopy (PL), Nuclear magnetic resonance ¹H/¹³C NMR, and thermogravimetry TGA to separately confirm nanoparticle formation and surface functionalization.     

Local and non‐local ductile damage and failure modelling at large deformation with applications to engineering

The numerical analysis of ductile damage and failure in engineering materials is often based on the micromechanical model of Gurson [1]. Numerical studies in the context of the finite‐element method demonstrate that, as with other such types of local damage models, the numerical simulation of the initiation and propagation of damage zones is strongly mesh‐dependent and thus unreliable. The numerical problems concern the global load‐displacement response as well as the onset, size and orientation of damage zones. From a mathematical point of view, this problem is caused by the loss of ellipticity of the set of partial di.erential equations determining the (rate of) deformation field. One possible way to overcome these problems with and shortcomings of the local modelling is the application of so‐called non‐local damage models. In particular, these are based on the introduction of a gradient type evolution equation of the damage variable regarding the spatial distribution of damage. In this work, we investigate the (material) stability behaviour of local Gurson‐based damage modelling and a gradient‐extension of this modelling at large deformation in order to be able to model the width and other physical aspects of the localization of the damage and failure process in metallic materials.