Yu. B. Gorbatov

Superconductivity in Ropes of Single-Walled Carbon Nanotubes

We report measurements on ropes of single-walled carbon nanotubes (SWNT) in low-resistance contact to nonsuperconducting (normal) metallic pads, at low voltage and at temperatures down to 70 mK. In one sample, we find a 2 orders of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic field of the order of 1 T, or by a dc current greater than 2.5 microA. These features strongly suggest the existence of superconductivity in ropes of SWNT.

Acoustoelectric Effects in Carbon Nanotubes

We show that it is possible to detect mechanical bending modes on 1µm long ropes of single walled-carbon nanotubes suspended between 2 metallic contacts. This is done by measuring either their dc resistance in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. The vibrations are excited by a radio-frequency electric field produced by an antenna located in the vicinity of the sample. We analyze the mechanism of detection of the mechanical resonances in terms of heating and phase breaking effects.

Formation of two-dimensional photonic-crystal structures in silicon for near-infrared region using fine focused ion beams

One of the two variants of producing two-dimensional photonic crystals in silicon is the formation of ordered macropore structures in a silicon substrate. The characteristic pore dimensions (the diameter and the wall thickness between pores) determine the wavelength range in which such a pore structure exhibits the properties of a photonic crystal. For the near-infrared region, these dimensions approach 1 µm or fall in a submicron region. An ordered structure of macropores with such dimensions is formed in this work using fine focused ion beams to provide the stimulating effect of implanted ions on pore nucleation in given sites on the silicon substrate surface. Pores are shown to nucleate at sites subjected to ion irradiation even at a low implantation dose (2×1013 ion/cm2). A model describing the orienting effect of ion irradiation on pore nucleation is proposed.

Local dielectric layers formation in Si and SiGe using focused ion beam implantation

25 kev Ga/sup +/ focused ion beam implantation of various structures has been used to provide local dielectric isolation of devices. Stain etching in HF:H/sub 2/O solution following the implantation step transforms the implanted areas in a porous state. Low thermal budget oxidation of the treated samples results in selective oxidation of these areas. Electrical measurements made on the test transistors structures reveal high resistive region in between the single transistors. SIMS, TEM and optical measurements were used to describe phenomena observed.

TWO-DIMENSIONAL ORDERED POROUS STRUCTURES FOR PHOTONIC CRYSTALS OBTAINED USING DEEP ANODIC ETCHING AND FOCUSED ION BEAM TECHNIQUES

Photonic crystals are the very promising novel materials for micro- and nanophotonics for visible region. To produce photonic crystals for this region of light, artificial structures with characteristic sizes less than 1 μm have to be manufactured. Electrochemical deep anodic etching and plasma etching techniques is normally used to produce such structures in silicon wafers. However, standard way of deep anodic etching realization is not suitable for sub-micrometer porous silicon formation. In the present work combination of the deep anodic etching and focused ion beam techniques is used to produce ordered structure of macropores in silicon.

Superconductivity in molecular wires

We show experimental evidence of a proximity-induced superconducting transition in individual single-walled carbon nanotubes with normal state resistance much large than the quantum of resistance. The critical current of samples is extensively studied as a function of temperature and magnetic field. We also studied an influence of electron and ion beams radiation on the superconducting properties of carbon nanotubes.

Formation of local insulating regions in Si/Si—Ge structures by ion implantation with subsequent stain etching

It is suggested to use amorphous porous films obtained by stain etching for device isolation. The characteristics of the isolations, as applied to heteroepitaxial transistor structures, are compared with those obtained by trench isolation.

Magnetoresistance of nanobridges of lanthanum-strontium manganite

Nanobridges are fabricated from lanthanum-strontium anganite deposited on Si3N4 membranes perforated by a focused ion beam. The magnetoresistance is ≈9% in fields of ∼ kOe. Nonlinearity of the current-voltage characteristic of the bridges is observed, and it is found that the maximum of the resistance is shifted to lower temperatures from that of a control film sample of composition La0.8Sr0.2MnO3.