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This thesis describes the fabrication of a variety of \nanotool" structures which are fabricated on Atomic Force Microscope (AFM) probe tips. The structures are fabricated on standard AFM probes using a method of electron beam induced deposition (EBID), forming an amorphous carbon structure on the probe tip. Experiments are described which demonstrate the successful application of these probes for a variety of di�erent manipulation applications, focussing on the nanomanipulation of biological cells. A variety of tools are described, including \nanoscalpel" probes able to cut and section biological materials on very small scales, \nanoneedles" which function as high aspect ratio AFM probes or as probes of intracellular structures, \nanotweezers" and a \nanotome" which can be used to remove thin layers of material from a biological sample. A variety of techniques to fabricate complex nanotool structures and to strengthen the structures against large applied forces are described. Using these tools, the investigation of a variety of cell types including smooth muscle cells, megakaryocytes and corneocytes has been performed. Results are presented showing the \nanodissection" of these cells to expose their internal structures for in situ AFM imaging, and the detection of the mechanical properties of intracellular structures by indentation using nanoneedle probes. Extraction of samples from the outer corni�ed envelope of corneocyte cells using a nanoneedle probe is also demonstrated. The mechanical properties of the amorphous carbon making up these nanotools are also characterised using AFM manipulation, and their elastic bending modulus determined using models based on the Euler-Bernoulli beam bending equation. The structures are shown to be highly exible, with thin nanoneedle structures able to buckle elastically under large tip-sample forces in a manner similar to the high aspect ratio carbon nanotubes which are currently used as AFM probes.

An investigation is carried out into the relation between impact ionization threshold positions and the detailed band structure of a number of semiconductors. The band structures of the semiconductors investigated are reproduced, from the data published by previous workers, by the Empirical Pseudopotential Method (EPM). From these detailed band structures, the impact ionization threshold positions are calculated by a method developed in the present work, referred to as the Envelope Method, and are compared with the values calculated by using two different approximate band structure models. From the EPM, the plane-wave expansions of the wavefunctions of the electron states involved in each impact ionization threshold are then calculated. These wavefunctions are then used to evaluate the sizes of the matrix element (overlap integral) of the coulomb interaction corresponding to each threshold position determined. The relative significance of the threshold positions, particularly the lowest threshold positions, are compared with each other to determine the lowest significant threshold position. It is shown that it is dangerous to rely on impact ionization threshold values determined by approximate band structure models, and that realistic band structures should be used which are in substantial agreement with experimental data. It is also shown that it is necessary to consider the sizes of the matrix element of the coulomb interaction, since many impact ionization threshold positions have corresponding matrix element sizes which are insignificant.

The III-V semiconductor GaN is of technological interest because of its high band gap (3.44 eV at 300 K). The impurities K, Ca, Zn, B, Al, C, Si, P, As, S, F, and Cl have been implanted into GaN. After annealing the optical spectra of the implanted material were investigated. Studies were also made of neutron irradiated GaN and some Ga1-xAlxN alloys. Broad emission bands at 2.9, 2.85, and 2.58 eV were identified with the impurities Zn, P, and As respectively. Sharper emissions near 3.5 and 3.3 eV were seen in the Al implant. Peaks near 3.27 eV, associated with DA pair transitions in purer GaN, were seen in the B, Al, F and Cl implants. The intrinsic luminescence of most samples is reduced by an amount dependent on the damage introduced during implantation. A broad band near 2.2 eV is associated with defects introduced by implantation and by the dissociation of GaN during high temperature annealing. A reduction in efficiency of implanted luminescence centres is also associated with high temperature annealing.

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