Kinetic study of H-terminated silicon nanowires oxidation in very first stages

Oxidation of silicon nanowires (Si NWs) is an undesirable phenomenon that has a detrimental effect on their electronic properties. To prevent oxidation of Si NWs, a deeper understanding of the oxidation reaction kinetics is necessary. In the current work, we study the oxidation kinetics of hydrogen- terminated Si NWs (H-Si NWs) as the starting surfaces for molecular functionalization of Si surfaces. H-Si NWs of 85-nm average diameter were annealed at various temperatures from 50°C to 400°C, in short-time spans ranging from 5 to 60 min. At high temperatures (T ≥ 200°C), oxidation was found to be dominated by the oxide growth site formation (made up of silicon suboxides) and subsequent silicon oxide self-limitation. Si-Si backbond oxidation and Si-H surface bond propagation dominated the process at lower temperatures (T < 200°C)

Evolution of Optoelectronic and Texture Properties

We show a simple room temperature surface functionalization approach using iodine vapour to control a surface phase transition from cubic silver (Ag) of thin films into wurtzite silver-iodid (β-AgI) films. A combination of surface characterization techniques (optical, electronical and structural characterization) reveal distinct physical properties of the new surface phase. We discuss the AgI thin film formation dynamics and related transformation of physical properties by determining the work-function, dielectric constant and pyroelectric behavior together with morphological and structural thin film properties such as layer thickness, grain structure and texture formation. Notable results are: (i) a remarkable increase of the work- function (by 0.9 eV) of the Ag thin layer after short a iodine exposure time (≤60 s), with simultaneous increase of the thin film transparency (by two orders of magnitude), (ii) pinning of the Fermi level at the valance band maximum upon iodine functionalization, (iii) 84% of all crystallites grain were aligned as a result of the evolution of an internal electric field. Realizing a nano-scale layer stack composed of a dielectric AgI layer on top of a metallic thin Ag layer with such a simple method has some technological implications e.g. to realize optical elements such as planar optical waveguides

Attosecond-fast internal photoemission

International audienceThe photoelectric effect has a sister process relevant in optoelectronics called internal photoemission1,2,3. Here an electron is photoemitted from a metal into a semiconductor4,5. While the photoelectric effect takes place within less than 100 attoseconds (1 as = 10−18 seconds)6,7, the attosecond timescale has so far not been measured for internal photoemission. Based on the new method CHArge transfer time MEasurement via Laser pulse duration-dependent saturation fluEnce determinatiON—CHAMELEON—we show that the atomically thin semimetal graphene coupled to bulk silicon carbide, forming a Schottky junction, allows charge transfer times as fast as (300 ± 200) as. These results are supported by a simple quantum mechanical model simulation. With the obtained cut-off bandwidth of 3.3 PHz (1 PHz = 1015 Hz) for the charge transfer rate, this semimetal/semiconductor interface represents a functional solid-state interface offering the speed and design space required for future light-wave signal processing

Polarization doping of graphene on silicon carbide

The doping of quasi-freestanding graphene (QFG) on H-terminated, Si-face 6H-, 4H-, and 3C-SiC is studied by angle-resolved photoelectron spectroscopy (ARPES) close to the Dirac point. Using semi-insulating as well as n-type doped substrates we shed light on the contributions to the charge carrier density in QFG caused by i) the spontaneous polarization of the substrate, and ii) the band alignment between the substrate and the graphene layer. In this way we provide quantitative support for the previously suggested model of polarization doping of graphene on SiC [Phys. Rev. Lett. 108, 246104 (2012)]

Gateless patterning of epitaxial graphene by local intercalation

We present a technique to pattern the charge density of a large-area epitaxial graphene sheet locally without using metallic gates. Instead, local intercalation of the graphene–substrate interface can selectively be established in the vicinity of graphene edges or predefined voids. It provides changes of the work function of several hundred meV, corresponding to a conversion from n-type to p-type charge carriers. This assignment is supported by photoelectron spectroscopy, scanning tunneling microscopy, scanning electron microscopy and Hall effect measurements. The technique introduces materials contrast to a graphene sheet in a variety of geometries and thus allows for novel experiments and novel functionalities

From strong-field physics in and at nanoscale matter to photonics-based laser accelerators

New ways of controlling quasi-free and free electrons by means of phase-controlled ultrashort laser pulses are demonstrated: from strong-field physics in the conducting 2-d material graphene and at the surface of nanostructures, to laser acceleration of free electrons with a nanophotonic structure, and the demonstration of the longitudinal Kapitza-Dirac effect

From strong-field physics in and at nanoscale matter to photonics-based laser accelerators

New ways of controlling quasi-free and free electrons by means of phase-controlled ultrashort laser pulses are demonstrated: from strong-field physics in the conducting 2-d material graphene and at the surface of nanostructures, to laser acceleration of free electrons with a nanophotonic structure, and the demonstration of the longitudinal Kapitza-Dirac effect