Adiabatic focusing of cold atoms in a blue-detuned laser standing wave

Adiabatic focusing of cold atoms in a blue-detuned laser standing wave is analyzed. It is shown that using repulsive light forces that push atoms towards dark regions and thus minimizes heating, cold atoms can be adiabatically compressed by more than an order of magnitude to yield background-free sub-10-nm (rms) spots. The optimal parameters for the atomic lens and the maximal compression ratio are predicted using an analytic model and found to be in agreement with the exact results of our Monte Carlo simulations. A combined adiabatic-coherent scheme is proposed and shown to yield 8.8 nm spot size even for a thermal atomic beam. Received: 1 October 1999 / Revised version: 13 December 1999 / Published online: 5 April 2000     

Perfect alignment of self-organized Ge islands on pre-grown Si stripe mesas

Self-organized Ge islands grown on patterned Si(001) substrates have been investigated. Selective epitaxial growth (SEG) of Si is carried out with gas-source molecular beam epitaxy to form Si stripe mesas followed by subsequent Ge island growth. Self-aligned Ge islands with regular spacing are formed on the <110>-oriented ridges of the Si mesas. The regular spacing is driven by the repulsive interaction between the neighbor islands through the substrates. A mono-modal distribution of the islands has been observed on the ridges of the Si mesas. The spatial confinement as well as the preferential nucleation is believed to be the mechanism of this alignment of the self-organized Ge islands. Received: 16 July 1999 / Accepted: 6 August 1999 / Published online: 24 March 2000     

Image contrast enhancement in field-emission scanning electron microscopy of single-walled carbon nanotubes

The image contrast enhancement in scanning electron microscopy of single-walled carbon nanotubes (SWNTs) on SiO₂ surfaces was experimentally investigated using a field-emission scanning electron microscope (FESEM) using a wide range of primary electron (PE) voltages. SWNT images of different contrasts were obtained at different PE voltages. Image contrast enhancement of SWNTs was investigated by charging SiO₂ surfaces at different PE voltages. The phenomena are ascribed to the surface potential difference and charge injection between SWNTs and SiO₂ substrates induced by the electron-beam irradiation.     

Controlled synthesis of ZnO nanowires or nanotubes via sol-gel template process

ZnO nanowires and nanotubes have been rationally fabricated within the nanochannels of porous anodic alumina templates by an improved sol-gel template process. X-ray diffraction and selected area electronic diffraction demonstrate that the as-obtained ZnO nanowires and nanotubes can be indexed to hexagonal wurtzite polycrystalline. In this method, zinc nitrate and urea are used as precursors, zinc nitrate serve as zinc ions source, and urea offered a basic medium through its hydrolysis. ZnO nanowires or ZnO nanotubes can be obtained easily by controlling hydrolysis time. The formation mechanism of ZnO nanowires and nanotubes was also discussed.     

Inexpensive two-tip nanomanipulator for a SEM

One of the major obstacles for nanotechnology progress is the lack of effective tools and processes to build, characterize and manipulate nanosystems. Here, we present the development of a low-cost nanomanipulator with two probe tips that operates inside a scanning electron microscope. This manipulation system is based on parallel-guiding-plate-spring mechanism and inexpensive materials. The movements are divided on coarse and fine displacements, which are based on picomotors and piezoelectric elements, respectively. The nanomanipulator was applied to transport and manipulate nanotubes and semiconductor nanowires. The probe tips have independent electrical contacts, so that electrical two point measurements can be performed in situ. The system is expected to be a valuable tool for research laboratories working with nanostructures.     

Controllable off-plane deflection of cantilevers for multiple scanning proximity probe arrays

The presented work reports the fabrication of 4×32 arrays of fully addressable proximity probes, which are initially and controllably off-plane deflected (bent). Such a deflection is required for the simultaneous approach and scanning of all cantilevers. It is realized by deposition of the silicon cantilevers with Si₃N₄ film inducing tensile stress. ANSYS simulations are used to calculate the off-plane deflection for different thickness of the cantilever and the Si₃N₄ layer and compared with experimentally obtained values. Cantilever arrays with set bending up to 50 μm, employing LPCVD silicon nitride film with a tensile stress of 750 MPa are fabricated.     

Monodispersive CoPt Nanoparticles Synthesized Using Chemical Reduction Method

Monodispersive CoPt nanopaxticles in sizes of about 2.2 nm axe synthesized by superhydride reduction of COCl2 and PtCl2 in diphenyl ether. The as-prepared nanoparticles show a chemically disordered Al structure and axe superpaxamagnetic. Thermal annealing transforms the Al structure into chemically ordered Llo structure and the particles are ferromagnetic at room temperature.     

Organisation of carbon and boron nitride layers in mixed nanoparticles and nanotubes synthesised by arc discharge

2 bonds attests for the presence of ordered BN domains and of carbon domains; (ii) the elemental profiles show that BN layers and carbon layers are immiscible with a radial organisation into two to five domains; and (iii) the sets of layers at free surfaces – including the inner surfaces of tubes – are always made of carbon. The origin of this chemical organisation, which is most likely obtained during the growth, is discussed. For the hafnium-boride metallic particles coated by C/BN envelopes, a model based on the solidification from the outside to the inside of isolated liquid-like droplets is proposed: the carbon phase solidifies first according to theoretical phase diagrams, and forms the outer shells. For the tubes, a directional eutectic solidification process is shown to account for the observed C/BN/C sequence, in a vapour–liquid–solid scheme, with an hafnium-rich liquid-like particle at the tip of the tube. Received: 26 November 1998 / Accepted: 14 January 1999     

Bias voltage influence on the shape of cobalt-silicide nanowires

We have fabricated cobalt-silicide nanowires on silicon by removing hydrogen from a passivated Si(001)2×1 surface with a scanning tunnelling microscope, followed by evaporation of cobalt. The apparent shape of the wires depends on the bias applied to the tip. This is due to the Fermi level pinning close to the valence edge by the high work function Pt-Ir tips, and the Co acceptor levels 0.35 eV above the valence band. Moreover, the decrement in the image contrast with increasing bias voltage is related to decrement in the local density of states, which is in qualitative agreement with former studies of nanosized cobalt disilicide islands.     

Strain-driven self-organization of nanostructures on semiconductor surfaces

Received: 14 April 1998/Accepted: 23 October 1998