Single crystal silicon nanowires (SiNWs) were synthesized with silane reactant using Au nanocluster-catalyzed one-dimensional growth. We have shown that under our experimental conditions, SiNWs grown epitaxially on Si(111) via the vapor-liquid-solid growth mechanism change their growth direction as a function of the total pressure. Structural characterization of a large number of samples shows that SiNWs synthesized at a total pressure of 3 mbar grow preferentially in the 111 direction, while the one at 15 mbar favors the 112 direction. Specifically by dynamically changing the system pressure during the growth process morphological changes of the NW growth directions along their length have been demonstrated.

In this letter, we report on the formation, of copper-germanide/germanium nanowire (NW) heterostructures with atomically sharp interfaces. The copper-germanide (Cu3Ge) formation process is enabled by a chemical reaction between metallic Cu pads and vapor-liquid-solid (VLS) grown Ge-NWs. The atomic scale aligned formation of the Cu3Ge segments is controlled by in situ SEM monitoring at 310 degrees C thereby enabling length control of the intrinsic Ge-NW down to a few nanometers. The single crystal Cu3Ge/Ge/Cu3Ge heterostructures were used to fabricate p-type Ge-NW field effect transistors with Schottky Cu3Ge source/drain contacts. Temperature dependent I /V measurements revealed the metallic properties of the Cu3Ge contacts with a maximum current density of 5 x 10(7) A/cm2. According to the thermoionic emission theory, we determined an effective Schottky barrier height of 218 meV.

Kinked silicon nanowires (Si-NWs) were synthesized in a well reproducible manner using gold nanocluster-catalyzed quasi-one-dimensional growth on Si(111) substrates with silane (SiH(4)) as the precursor gas. The kinking is considered to be due to the change in the growth direction induced by the sudden change of the pressure during Si-NW synthesis. Structural high resolution transmission electron microscopy (HRTEM) characterization of the sample shows that epitaxial Si-NWs synthesized on Si(111) substrates at a total pressure of 3 mbar grow along the {111} direction, while the ones at 15 mbar favour the {112} direction. By dynamically changing the system pressure during the growth process morphological changes of the NW growth directions along their length have been shown, resulting in kinked nanowires. The crystallographic orientation relation of the kinking between the 3 and 15 mbar ranges has been analysed by TEM. It is shown that no defects or grain boundaries in the intersection between the two sections of the Si-NWs are necessary to form such kinks between different wire directions.

In this paper we present the hetero-epitaxial growth of single-crystalline GaAs whiskers on Si(111)-nanowire trunks forming hierarchical star-like structures with a six-fold symmetry. These hierarchical nanostructures have been successfully formed utilizing both vapor–liquid–solid (VLS) growth by low-pressure chemical vapor deposition (LPCVD) and molecular-beam epitaxy (MBE) techniques. High-resolution transmission electron microscopy (HRTEM) studies revealed the [111] growth direction of the core Si nanowires (Si-NWs) with six {112} facet planes. The sequentially grown branches are single-crystalline hexagonal GaAs nanowhiskers which grow preferably in the [0001] direction and are perpendicular to the {112} facets of the Si-NW backbone. Photoluminescence (PL) measurements confirm the good crystalline quality of the GaAs nanowhiskers and a blueshift of about 30 meV compared to bulk zinc blende-type GaAs. The ability to prepare rotationally branched NW structures should open new opportunities for both fundamental research and applications including monolithic three-dimensional nanoelectronics and nanophotonics.

We report on the influence of the surface pretreatment for vapor-liquid-solid growth of epitaxial silicon nanowires with gold catalyst and silane precursor on Si(111) substrates. In this paper we make it obvious that a thin native oxide layer on the Si substrate-as is present under most technological conditions-or a thin layer of oxide formed on top of the catalytic gold particle restrain nucleation and nanowire growth. High resolution transmission electron microscopy, and electron energy loss spectroscopy were utilized to demonstrate Si diffusion from the substrate through the catalytic Au layer and further the formation of a thin oxide layer atop. Based on this observation we present a sample pretreatment practice, making the catalyst insensitive for further oxide formation, thereby preserving epitaxy for nanowire synthesis.