L.P. Biró

Large scale production of short functionalized carbon nanotubes

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.

Ellipsometric study of polycrystalline silicon films prepared by low-pressure chemical vapor deposition

Polysilicon layers with thicknesses between 8 and 600 nm deposited by low-pressure chemical vapor deposition at temperatures ranging from 560 to 640 °C were characterized by spectroscopic ellipsometry (SE) to determine the layer thicknesses and compositions using multilayer optical models and the Bruggeman effective-medium approximation. The dependence of the structural parameters on the layer thickness and deposition temperature have been investigated. A better characterization of the polysilicon layer is achieved by using the reference data of fine-grained polysilicon in the optical model. The amount of voids in the polysilicon layer was independently measured by Rutherford backscattering spectrometry (RBS). The SE and RBS results show a good correlation. The comparison of the surface roughness measured by SE and atomic force microscopy (AFM) shows that independently of the AFM window sizes, a good correlation of the roughness determined by SE and AFM was obtained.

Room temperature growth of single-wall coiled carbon nanotubes and Y-branches

Abstract Straight carbon nanotubes, carbon nanotube “knees,” Y-branches of carbon nanotubes and coiled carbon nanotubes were grown on a graphite substrate held at room temperature by the decomposition of fullerene under moderate heating (450 °C) in the presence of 200-nm Ni particles. The grown structures were investigated without any further manipulation by STM. The growth and the chemical stability of the carbon nanostructures containing nonhexagonal rings are discussed.

Dislocation formation and B transient diffusion in C coimplanted Si

Suppression of dislocation formation and boron transient diffusion by carbon coimplantation is studied by means of transmission electron microscopy, secondary‐ion‐mass spectrometry, photoluminescence spectroscopy, and high‐resolution x‐ray diffraction. It is shown that both the effects are due to the formation of C‐related damage which acts as a trap for Si interstitials. Quantitative simulations indicate that this damage is probably formed by coprecipitation of Si and C atoms in Si1.15C complexes. These complexes also deteriorate the electrical properties of the implanted layer. They dissolve at annealing temperatures higher than 900 °C. When this occurs, the effect of C is reduced and both B transient diffusion and dislocations, as well as the recovery of the electrical properties, are observed.

From straight carbon nanotubes to Y-branched and coiled carbon nanotubes

Abstract Straight carbon nanotubes, carbon nanotube ‘knees’, Y-branches of carbon nanotubes, and coiled carbon nanotubes were grown on a graphite substrate by the decomposition of fullerene under moderate heating (450 °C) in the presence of transition metal particles. The grown structures were investigated without any further manipulation by STM. The observed coiled carbon nanotubes are tentatively identified with the theoretically predicted haeckelite.

Selective nucleation and growth of carbon nanotubes at the CoSi2/Si interface

A patterned CoSi2/Si substrate was used for the catalytic growth of carbon nanostructures and nanotubes in the temperature range of 750–800 °C, using acetylene/N2 as a reaction mixture flowing through a quartz tube at ambient pressure. Selective nucleation confined to the CoSi2/Si interface region was achieved. Scanning electron microscopy and transmission electron microscopy were used to investigate the grown nanostructures.

Athermal effects in ion implanted layers

Defect structure and electrical characterization of boron and arsenic implanted layers has been investigated for implantation under athermal (light) excitation. This Photon Assisted (PA) implantation owes its specific properties to an additional electric field acting on charged particles including carriers and charged defects. It was shown that in case of n-type silicon this extra field draws charged vacancies and self-interstitials towards each other and, thus, diminishes transient diffusion of boron. This effect resulted in junctions which are about 20% shallower compared to conventionally processed reference wafers. Experiments using light of an Ar-ion laser and white light of a high pressure Xe are lamp were compared

Catalyst traces after chemical purification in CVD grown carbon nanotubes

For many applications, in particular for those in which transport occurs through carbon nanotubes (CNT), and for certain characterization techniques too, it is important to know whether traces of the catalyst used to grow the nanotubes are incorporated in the grown tubes. Nuclear analytical techniques (RBS, PIXE) and XRF were applied to investigate the transition metal content of CNTs after different steps of chemical purification. TEM and HRTEM were used to monitor the influence of purification process on the structure of the CNTs.

STM Investigation of Carbon Nanotubes

The general principles of scanning tunneling microscopy (STM) will be presented and their application to image interpretation will be discussed. The particular problems that may arise from the three dimensional nature and from the complexity of the tunneling system in the case of supported carbon nanotubes will be considered. An overview of the milestones of STM and scanning tunneling spectroscopy (STS) experiments performed on carbon nanotubes will be given, with particular emphasis on the questions related with atomic resolution imaging, the influence of the two tunneling gaps (tip/nanotube; nanotube/support) and point contacts during imaging. Experimental STS results on multiwall carbon nanotubes and rafts of nanotubes will be discussed and compared to computer simulations based on wave packet dynamics.

Optimization of the amount of catalyst and reaction time in single wall nanotube production

The influence of the amount of catalyst and the reaction time on the quantity and quality of catalytically grown single wall carbon nanotubes (SWNT) was investigated. The aim was to optimize some of the SWNT growth parameters using TEM and HRTEM . The thickness of catalyst layer influences the synthesis of the nanotube because the gas composi ti n can differ between top and bottom. Microscopic investigation of the grown SWNT samples showed t hat the thicker the catalyst layer the lower relative nanotube content, so the deeper pa rts of the catalyst layer are less effective. The optimum time for the reaction was found to be 10 minutes . Thi may be understood assuming that nanotube growth needs an initial incubation time while the ac ivity of the catalyst decreases steadily until the nanotube growth stops.