Alois Weidinger

Buckminsterfullerene C60: a chemical Faraday cage for atomic nitrogen

Abstract N@C 60 (atomic nitrogen in C 60 , produced by ion implantation) is the first member of a new class of endohedral fullerenes in which a highly reactive atom in its atomic ground state is enclosed in C 60 . Nitrogen in C 60 is chemically inert and stable under ambient conditions. The atomic states of nitrogen in C 60 can be slightly tuned by cage distortions caused by exohedral additions to N@C 60 . In this Letter, a new and simple production method for N@C 60 is described and the effect of cage distortions on the atomic states of nitrogen is discussed.

Hydrogen implantation and diffusion in silicon and silicon dioxide

Depth profiles of hydrogen implanted into crystalline silicon in random direction at different fluences have been measured by the15N technique and by SIMS. Whereas hydrogen implanted at a fluence of 1015 ions/cm2 shows some limited mobility, no such mobility is observed for higher implantation fluences. In these cases, ballistic computer codes describe the depth distributions well, within the ranges of both experimental and theoretical accuracy. Annealing up to 510 K does not change the hydrogen distributions.Furthermore, high-fluence hydrogen implantation into silicon dioxide has been examined. There is some indication for radiation-enhanced diffusion during the implantation process. Upon subsequent thermal annealing, the hydrogen is found to diffuse, probably via a trapping/detrapping mechanism associated with an OH/H2 transformation of the hydrogen bonding.

Properties of endohedral N@C60

Abstract Endohedral N@C 60 (atomic nitrogen inside C 60 ) is produced by ion implantation. N@C 60 is soluble in organic solvents and stable in air. A special feature is that it gives a very clear hyperfine split EPR signal with sharp lines even in the solid. This makes it an ideal probe for monitoring chemical reactions of C 60 via changes of the EPR signal. As an example, the formation of the monoadduct of diethyl malonate on C 60 will be discussed. In general, N@C 60 can be used as a probe or tracer for monitoring reactions or the transport of C 60 . We show that C 60 is an ideal trap for atomic nitrogen. Nitrogen is in the center of C 60 and keeps its atomic structure. In a first experiment, the vibrations of nitrogen in C 60 were studied.

Group V Endohedral Fullerenes: N@C60, N@C70, and P@C60

In this article, the production and the properties of endohedral fullerenes N@C60, P@C60 and N@C70 are described. The distinct feature of these systems is that the enclosed nitrogen and phosphorous atoms keep their atomic ground state configuration and are localized in the center of the fullerenes. The atoms are almost freely suspended in these molecular cages and exhibit properties resembling those of ions in electromagnetic traps, i.e. sharp spectroscopic transitions and long life times. Since the fullerene shell can be easily manipulated, a large variety of different physical or chemical modifications can be realized.

Self-aligned nanostructures created by swift heavy ion irradiation

In tetrahedral amorphous carbon (ta-C) swift heavy ions create conducting tracks of about 8 nm in diameter. To apply these nanowires and implement them into nanodevices, they have to be contacted and gated. In the present work, we demonstrate the fabrication of conducting vertical nanostructures in ta-C together with self-aligned gate electrodes. A multilayer assembly is irradiated with GeV heavy ions and subsequently exposed to several selective etching processes. The samples consist of a Si wafer as substrate covered by a thin ta-C layer. On top is deposited a SiNx film for insulation, a Cr layer as electrode, and finally a polycarbonate film as ion track template. Chemical track etching opens nanochannels in the polymer which are self-aligned with the conducting tracks in ta-C because they are produced by the same ions. Through the pores in the polymer template, the Cr and SiNx layers are opened by ion beam sputtering and plasma etching, respectively. The resulting structure consists of nanowires embed...

Highly conductive ion tracks in tetrahedral amorphous carbon by irradiation with 30 MeV C60 projectiles

Electrically conducting ion tracks are produced when high-energy heavy ions pass through a layer of tetrahedral amorphous carbon (ta-C). The tracks are embedded in the insulating ta-C matrix and have a diameter of about 8u2009nm. Earlier studies showed that the electrical currents through individual tracks produced with Au and U projectiles exhibit rather large track-to-track fluctuations. In striking contrast, 30u2009MeV C60 cluster ions are shown to generate conducting tracks of very narrow conductivity distributions. Their current-versus-voltage curves are linear at room temperature. We also investigated ta-C films doped with B, N, Cu and Fe at a concentration of 1 or 2u2009at.%. In particular, Cu- and Fe-doped samples show increased ion track conductivity.

Effects of post-deposition treatment on the PL spectra and the hydrogen content of CuInS2 absorber layers

Abstract CuInS 2 absorber layers for thin-film solar cells are examined in this work. The influence of post-deposition annealing in hydrogen and oxygen atmosphere is studied by means of photoluminescence (PL) and nuclear reaction analysis (NRA). The intensity of a PL peak at 1.445 eV can be drastically influenced by post-deposition treatments. This transition is ascribed to the donor-acceptor pair recombination between a sulfur vacancy and a copper vacancy. From the measurements, a simple defect model is deduced which assumes the occupation of sulfur vacancies by oxygen. The sulfur vacancy can be activated by hydrogen annealing and passivated by oxygen annealing.

Magnetic interaction in diluted N@C60

Nitrogen in C60 is a paramagnetic atom with a magnetic moment corresponding to the S=3/2 electronic spin. The dipolar interaction of two N@C60 at closest distance, i.e. 1 nm apart, reaches a maximum value of 1.85 mT or 52 MHz, more than three times larger than the hyperfine interaction with the nuclear spin. For diluted N@C60 in a C60 matrix, the distribution of interactions leads to a line broadening in EPR experiments. We report here on a EPR line width measurement for N@C60 in C60 with concentrations varying by a factor of 1000. For the first time a concentration in the percent range was reached by repeated HPLC enrichment. A surprising and completely unexpected result is that sharp lines appear superimposed on the broad lines. We attribute the sharp line to motional narrowing of N@C60 diffusing on the surface of C60 grains. It can be assumed that the diffusion seen here is a general phenomenon of C60, the doped fullerene being just the indicator.

Hydrogen diffusion in chalcopyrite solar cell materials

Hydrogen diffusion in CuInSe{sub 2} single crystals and CuInS{sub 2} thin films was studied by measuring the spreading of implantation profiles upon annealing. Deep implantation with an ion energy of 10 keV and sub-surface implantation with 300 eV were applied. The diffusion coefficients in both materials were found to be in the order of 10{sup {minus}14} to 10{sup {minus}13} cm{sup 2}/s in the temperature range between 400 and 520 K. These fairly low diffusivities are typical for a trap and release transport process rather than intrinsic diffusion of interstitial hydrogen. In the polycrystalline CuInS{sub 2} films, hydrogen leaves the sample through the grain boundaries.

Influence of atomic hydrogen on intrinsic defects in CuInSe 2

Hydrogen with an energy of 300 eV was implanted into single crystalline CuInSe 2 samples at temperatures of 200 °C and 300 °C during implantation. We found that the hydrogen is not limited to the expected implantation depth but diffuses into the bulk of the sample. The hydrogen concentration ranges from 10 19 H/cm 3 in a depth of about 300 nm up to some 10 21 H/cm 3 next to the surface and resembles a diffusion profile. The hydrogen induced change of composition was not only at the surface, but also up to a depth of about 200 nm similar to that of the hydrogen profile. Mainly a Cu deficiency after hydrogen implantation could be observed and is explained as the passivation of V Cu by hydrogen and the additional production of V Cu by the induced band-bending.