Molecular layer doping: non-destructive doping of silicon and germanium

This work describes a non-destructive method to introduce impurity atoms into silicon (Si) and germanium (Ge) using Molecular Layer Doping (MLD). Molecules containing dopant atoms (arsenic) were designed, synthesized and chemically bound in self-limiting monolayers to the semiconductor surface. Subsequent annealing enabled diffusion of the dopant atom into the substrate. Material characterization included assessment of surface analysis (AFM) and impurity and carrier concentrations (ECV). Record carrier concentration levels of arsenic (As) in Si (~5Ã 10^20 atoms/cm3) by diffusion doping have been achieved, and to the best of our knowledge this work is the first demonstration of doping Ge by MLD. Furthermore due to the ever increasing surface to bulk ratio of future devices (FinFets, MugFETs, nanowire-FETS) surface packing spacing requirements of MLD dopant molecules is becoming more relaxed. It is estimated that a molecular spacing of 2 nm and 3 nm is required to achieve doping concentration of 10^20 atoms/cm3 in a 5 nm wide fin and 5 nm diameter nanowire respectively. From a molecular perspective this is readily achievable

Rapid, low temperature synthesis of germanium nanowires from oligosilylgermane precursors

New oligosilylgermane compounds with weak Ge–H bonds have been used as precursors for the rapid synthesis of germanium (Ge) nanowires in high yields (>80%), via a solution–liquid–solid (SLS) mechanism, using indium (In) nanoparticles as a seeding agent over a temperature range between 180 and 380 °C. Even at low growth temperatures, milligram quantities of Ge nanowires could be synthesized over a reaction period of between 5 and 10 min. The speed of release of Ge(0) into the reaction environment can be tuned by altering the precursor type, synthesis temperature, and the presence or lack of an oxidizing agent, such as tri-n-octylphosphine oxide (TOPO). Energy-dispersive X-ray analysis showed that silicon atoms from the precursors were not incorporated into the structure of the Ge nanowires. As both In and Ge facilitate reversible alloying with Li, Li-ion battery anodes fabricated with these nanowires cycled efficiently with specific capacities, i.e., >1000 mAh g–

The Drosophila telomere-capping protein Verrocchio binds single-stranded DNA and protects telomeres from DNA damage response

Drosophila telomeres are sequence-independent structures maintained by transposition to chromosome ends of three specialized retroelements rather than by telomerase activity. Fly telomeres are protected by the terminin complex that includes the HOAP, HipHop, Moi and Ver proteins. These are fast evolving, non-conserved proteins that localize and function exclusively at telomeres, protecting them from fusion events. We have previously suggested that terminin is the functional analogue of shelterin, the multi-protein complex that protects human telomeres. Here, we use electrophoretic mobility shift assay (EMSA) and atomic force microscopy (AFM) to show that Ver preferentially binds single-stranded DNA (ssDNA) with no sequence specificity. We also show that Moi and Ver form a complex in vivo. Although these two proteins are mutually dependent for their localization at telomeres, Moi neither binds ssDNA nor facilitates Ver binding to ssDNA. Consistent with these results, we found that Ver-depleted telomeres form RPA and γH2AX foci, like the human telomeres lacking the ssDNA-binding POT1 protein. Collectively, our findings suggest that Drosophila telomeres possess a ssDNA overhang like the other eukaryotes, and that the terminin complex is architecturally and functionally similar to shelterin

Organo-arsenic molecular layers on silicon for high-density doping

This article describes for the first time the controlled monolayer doping (MLD) of bulk and nanostructured crystalline silicon with As at concentrations approaching 2 x 10²⁰ atoms cm⁻³. Characterization of doped structures after the MLD process confirmed that they remained defect- and damage-free, with no indication of increased roughness or a change in morphology. Electrical characterization of the doped substrates and nanowire test structures allowed determination of resistivity, sheet resistance, and active doping levels. Extremely high As-doped Si substrates and nanowire devices could be obtained and controlled using specific capping and annealing steps. Significantly, the As-doped nanowires exhibited resistances several orders of magnitude lower than the predoped materials