Thermoelectric-cooled liquid bath chiller capable of unattended operation at -28 °C.

Using thermoelectric elements, we have developed a simple liquid bath chiller that is inexpensive and easy to fabricate. Typically, small experimental apparatus can be cooled using a liquid cold bath. These cold baths require continuous addition of a coolant such as dry ice or liquid N to maintain the desired temperature, which becomes tedious during long experiments.

Nucleation and growth of single layer graphene on electrodeposited Cu by cold wall chemical vapor deposition.

The nucleation density and average size of graphene crystallites grown using cold wall chemical vapor deposition (CVD) on 4 μm thick Cu films electrodeposited on W substrates can be tuned by varying growth parameters. Growth at a fixed substrate temperature of 1000 °C and total pressure of 700 Torr using Ar, H and CH mixtures enabled the contribution of total flow rate, CH:H ratio and dilution of the CH/H mixture by Ar to be identified. The largest variation in nucleation density was obtained by varying the CH:H ratio.

Guided VLS growth of epitaxial lateral Si nanowires.

Using the Au-seeded vapor-liquid-solid technique, epitaxial single-crystal Si nanowires (NWs) can be grown laterally along Si(111) substrates that have been miscut toward [112¯]. The ratio of lateral-to-vertical NWs increases as the miscut angle increases and as disilane pressure and substrate temperature decrease. By exploiting these trends, conditions can be identified whereby all of the deposited Au seeds form lateral NWs.

Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography.

Hole accumulation in Ge/Si core/shell nanowires (NWs) has been observed and quantified using off-axis electron holography and other electron microscopy techniques. The epitaxial [110]-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chemical vapor deposition through the vapor-liquid-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs.

Spreading of liquid AuSi on vapor-liquid-solid-grown Si nanowires.

Vapor-liquid-solid growth of high-quality Si nanowires relies on the stability of the liquid metal seed. In situ transmission electron microscopy shows that liquid AuSi seed spreads along the sidewalls of Si nanowires for some growth conditions. This liquid thin film phase separates to form solid Au clusters as the nanowire is quenched below the solidus temperature.

Kinetically induced kinking of vapor-liquid-solid grown epitaxial si nanowires.

Epitaxial Si nanowires grown from Au seeds using the vapor-liquid-solid method begin growing normal to the Si(111) substrate atop a tapered base. After a kinetically determined length, the NWs may kink away from [111] to another crystallographic direction. The smallest NWs prefer growth along 110 while larger Si NWs choose either 111 or 112 based on whether growth conditions favor Au-free sidewalls.

Kinetically suppressed ostwald ripening of Ge/Si(100) hut clusters.

Low area density Ge/Si(100) hut cluster ensembles are stable during days-long growth temperature anneals. Real-time scanning tunneling microscopy shows that all islands grow slowly at a decreasing rate throughout the anneal. Island growth depletes the Ge supersaturation that, in turn, reduces the island growth rate.

Ledge-flow-controlled catalyst interface dynamics during Si nanowire growth.

Self-assembled nanowires offer the prospect of accurate and scalable device engineering at an atomistic scale for applications in electronics, photonics and biology. However, deterministic nanowire growth and the control of dopant profiles and heterostructures are limited by an incomplete understanding of the role of commonly used catalysts and specifically of their interface dynamics. Although catalytic chemical vapour deposition of nanowires below the eutectic temperature has been demonstrated in many semiconductor-catalyst systems, growth from solid catalysts is still disputed and the overall mechanism is largely unresolved.

Strain mapping in nanowires.

A method for obtaining detailed two-dimensional strain maps in nanowires and related nanoscale structures has been developed. The approach relies on a combination of lattice imaging by high-resolution transmission electron microscopy and geometric phase analysis of the resulting micrographs using Fourier transform routines. We demonstrate the method for a germanium nanowire grown epitaxially on Si(111) by obtaining the strain components epsilon(xx), epsilon(yy), epsilon(xy), the mean dilatation, and the rotation of the lattice planes.