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31	Atomically controlled device fabrication using STM Ruess, Frank Joachim, Physics, Faculty of Science, UNSW January 2006 (has links) We present the development of a novel, UHV-compatible device fabrication strategy for the realisation of nano- and atomic-scale devices in silicon by harnessing the atomic-resolution capability of a scanning tunnelling microscope (STM). We develop etched registration markers in the silicon substrate in combination with a custom-designed STM/ molecular beam epitaxy system (MBE) to solve one of the key problems in STM device fabrication ??? connecting devices, fabricated in UHV, to the outside world. Using hydrogen-based STM lithography in combination with phosphine, as a dopant source, and silicon MBE, we then go on to fabricate several planar Si:P devices on one chip, including control devices that demonstrate the efficiency of each stage of the fabrication process. We demonstrate that we can perform four terminal magnetoconductance measurements at cryogenic temperatures after ex-situ alignment of metal contacts to the buried device. Using this process, we demonstrate the lateral confinement of P dopants in a delta-doped plane to a line of width 90nm; and observe the cross-over from 2D to 1D magnetotransport. These measurements enable us to extract the wire width which is in excellent agreement with STM images of the patterned wire. We then create STM-patterned Si:P wires with widths from 90nm to 8nm that show ohmic conduction and low resistivities of 1 to 20 micro Ohm-cm respectively ??? some of the highest conductivity wires reported in silicon. We study the dominant scattering mechanisms in the wires and find that temperature-dependent magnetoconductance can be described by a combination of both 1D weak localisation and 1D electron-electron interaction theories with a potential crossover to strong localisation at lower temperatures. We present results from STM-patterned tunnel junctions with gap sizes of 50nm and 17nm exhibiting clean, non-linear characteristics. We also present preliminary conductance results from a 70nm long and 90nm wide dot between source-drain leads which show evidence of Coulomb blockade behaviour. The thesis demonstrates the viability of using STM lithography to make devices in silicon down to atomic-scale dimensions. In particular, we show the enormous potential of this technology to directly correlate images of the doped regions with ex-situ electrical device characteristics. scanning tunneling microscopy silicon quantum devices nanoelectronics doping registration markers STM device fabrication quantum computer single atom electronics tunnel junctions nanowires quantum dots metal dots weak localisation strong localisation phosphine dephasing electron transport magnetotransport planar device architecture low temeperature measurements Coulomb blockade STM electron electron interactions dimensioncal crossover ultra high vacuum hydrogen resist lithography STM lithography molecular adsorption electrical dopant activation disordered electron systems electron phase coherence length photon assisted carrier generation tunnelling delta doping molecular beam epitaxy
32	Novel tools for ultrafast spectroscopy Jarvis, Thomas William 06 February 2012 (has links) Exciton dynamics in semiconductor nanostructures are dominated by the effects of many-body physics. The application of coherent spectroscopic tools, such as two-dimensional Fourier transform spectroscopy (2dFTS), to the study of these systems can reveal signatures of these effects, and in combination with sophisticated theoretical modeling, can lead to more complete understanding of the behaviour of these systems. 2dFTS has previously been applied to the study of GaAs quantum well samples. In this thesis, we outline a precis of the technique before describing our own experiments using 2dFTS in a partially collinear geometry. This geometry has previously been used to study chemical systems, but we believe these experiments to be the first such performed on semiconductor samples. We extend this technique to a reflection mode 2dFTS experiment, which we believe to be the first such measurement. In order to extend the techniques of coherent spectroscopy to structured systems, we construct an experimental apparatus that permits us to control the beam geometry used to perform four-wave mixing reflection measurements. To isolate extremely weak signals from intense background fields, we extend a conventional lock-in detection scheme to one that treats the optical fields exciting the sample on an unequal footing. To the best of our knowledge, these measurements represent a novel spectroscopic tool that has not previously been described. / text Spectroscopy Ultrafast spectroscopy Ultra-fast spectroscopy Exciton Exciton dynamics Exciton optics Excitons Four-wave mixing Four wave mixing GaAs Gallium Arsenide Quantum well Semiconductor Acousto-optic Acousto optic Acousto-optic modulation Agile frequency Direct digital synthesis Lock-in detection Lock in detection Two-dimensional Two dimensional Fourier transform Multi-dimensional Multi dimensional Coherent Dephasing Relaxation Many body Many-body Physics Correlation Plasmon Surface plasmon Polariton Surface Hybrid Coupling Mode Grating Nanostructure Nano-structure Nano structure Reflection Mode geometry Transmission Variable Angle tuning Tunable Tuned Angle-tuning Angle-tunable Beam controllable Control

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Atomically controlled device fabrication using STM

Novel tools for ultrafast spectroscopy