The ability of Mercuric Iodide (HgI2) to function as a highly efficient radiation detector at room temperature has generated great interest and has triggered further studies on this difficult material. This property is expected to enable significant enhancements to a far-ranging variety of applications and systems. HgI2 devices have shown superior performance at room temperature compared to elemental Si or Ge devices, which require to be cooled down to liquid nitrogen temperature when used as nuclear radiation detectors. While substantial studies have been conducted on single crystal HgI2, polycrystalline HgI2 remains a comparatively less studied form of this material. The primary use of HgI2 is as a direct radiation detector. It can also be used in applications with a scintillator intermediate to generate visible light from incident nuclear radiation. Hence its response to visible light can be used to study the electronic properties of HgI2 polycrystalline films. The films are deposited on TEC-15 LOF glass with a Tin Oxide(Sn02) coating which acts as the growth surface. It also acts as the front contact with Palladium (Pd) being the back contact. Wire leads are attached to the palladium for electrical contact. The deposited films are circular in shape with a diameter of 2.5cm with thickness ranging from 50 to 600µm. A maximum of 7 devices are contacted at various points on every film. For the measurements documented in this thesis, a tungsten-halogen lamp and an Oriel 1/4m grating monochromator are used as a light source. The incident flux on the sample is determined using a Si photodiode as reference. Device performance for both single crystal as well as polycrystalline films is documented. We have attempted to identify a set of optimum growth parameters using these measurements. For a film to be considered favorably, not only should the individual devices show high quantum efficiencies and low dark currents, but the response of all devices on the same film should be uniform. A number of films are studied and the optimum film deposition conditions are commented upon. A powerful semiconductor device simulation tool, MEDICItm, is used to simulate the photoresponse of these films. The simulations are compared to the measurements and the transport and light absorption parameters of the polycrystalline films are determined.

Studies of light-matter interactions in organic semiconductors and in optical tweezer trapping of nanoparticles are presented. In the research related to organic semiconductor materials, a variety of novel materials and their composites have been characterized, and physical mechanisms behind their optoelectronic properties have been established. Three novel functionalized hexacene derivatives were deemed sufficiently stable to enable characterization of these materials in devices. From dark current and photocurrent measurements of the hexacene thin-films, it was determined that all three derivatives are photoconductive in the near-infrared, and space charge limited mobility values were obtained. In addition, physical mechanisms behind charge transfer, charge carrier photogeneration, and charge transport in small-molecule donor/acceptor composite films have been systematically studied. In these studies, it was determined that the charge transfer from the donor to the acceptor molecule can result in either an emissive charge transfer exciton (exciplex) or a non-emissive charge transfer exciton formation, depending on the energy difference between LUMO of the donor and the acceptor. However, the most dramatic trends in photoluminescent and photoconductive properties of the donor/acceptor composites were correlated with the separation between the donor and acceptor molecules at the donor/acceptor interface. In particular, composite films with larger separations exhibited electric field-assisted charge transfer exciton dissociation, which contributed to nanosecond time-scale photocurrents under a 500 ps pulsed photoexciation. Large donor/acceptor separation also resulted in reduced charge carrier recombination, which led to a factor of 5-10 increase in continuous wave photocurrents in certain donor/acceptor composites, as compared to those in pristine donor films. In the optical tweezer based studies, work towards the development of high spatial resolution optical tweezer controlled nanoprobes is presented. In particular, the possibility of exploiting the optical resonance of a particle to increase the optical tweezer forces acting on it within the trap has been investigated. Such an increase in the force would improve the potential spatial resolution of an optical tweezer controlled probe. Experimental results and numerical simulations on micron sized resonant dielectric particles showed a small increase in the optical forces that confine such particles within the trap, when tweezer trapping is conducted at wavelengths on the red-side of the optical resonance. Preliminary work on optical tweezer controlled ion/pH sensitive probes and on surface charge measurements is also reported. / Graduation date: 2012

This paper presents a new technique for the monolithic heterogeneous integration of compound semiconductor devices with silicon integrated circuits, and establishes the theoretical foundation for a key element of the process, tailored magnetic attraction and retention. It is shown how a patterned thin film of hard magnetic material can be used to engineer the attraction between the film and nanopills covered with a soft magnetic material. With a suitable choice of pattern, it is anticipated that it will be possible to achieve complete filling of recesses in the surface of fully-processed integrated circuit wafers, preparatory to subsequent processing to fabricate the nanopills into heterostructure devices integrated monolithically with the pre-existing electronics. / Singapore-MIT Alliance (SMA)

Charge transport dynamics through molecular scale materials is of common interest to both scientific and engineering disciplines. Putting molecules on nanoscale break junctions is the most straightforward setup to study charge transport dynamics through single molecules. Electromigration process can provide a simple and easy method of forming metallic oxide nanogap junctions. By using silver oxide thin films to form such nanogap junctions, silver nanoclusters (Ag2~Ag8) are also formed in-situ within the junctions. Formed silver nanoclusters strongly and stably electroluminesce under DC, AC, and customized pulse train excitation. By detecting extremely sensitive feedback, i.e. photons, two interesting behaviors of single molecule charge transport dynamics were revealed: 1) asymmetric charge transport and 2) discrete energy level tunneling. The discrete energy level tunneling of field emitted electrons yields negative differential resistance (NDR). Combined with photoconductivity and optical reduction of silver oxide to form silver nanoclusters, junction-asymmetry and NDR can be very useful in both electronic and optoelectronic applications such as on-demand electronics fabrication, single photon sources, and nanoscale photon detectors.

Full field characterization is an important issue for ultrafast optoelectronics. By suitable nonlinear constrain, several approaches, such as FROG, SPIDERS, MIIPS and so on, have been developed for providing detail information of optical pulses. However, phase matching bandwidth of nonlinear material limit the functionality for broadband signal. In this thesis, linear approach without limitation of phase matching bandwidth is proposed. Theoretically, we successfully demonstrated the feasibility of proposed method. We analyzed the limitation and discussed the pulse compression power with the proposed method. Besides, we also proposed experimental method for this method.

Indium tin oxide (ITO) thin films were formed on glass substrates by sol-gel method. Coating sols were prepared using indium chloride tetrahydrate (InCl3&bull / 4H2O) and tin-chloride pentahydrate (SnCl4&bull / 5H2O) stabilized in organic solvents (acetylacetone and ethanol). First attempt was to synthesize ITO thin films using standard/unmodified coating sols. The effect of calcination treatment in air (300 &ndash / 600 &deg / C) and number of coating layer(s) (1, 4, 7 or 10) on optoelectronic properties (electrical conductivity and optical transparency), crystal structure and microstructure of ITO thin films were investigated. In addition, single-layer ITO thin films with optoelectronic properties comparable to multi-layered films were prepared by employing organically modified coating sols. Oxalic acid dihydrate (OAD) &ndash / a drying/microstructure control agent&ndash / addition to standard sol formulation was achieved. The rationale was to improve the optoelectronic properties of ITO films through enhancement in microstructure and chemical characteristics upon OAD addition. The effects of OAD content in the sol formulation and post-coating calcination treatment on electrical/optical properties of ITO films have been reported. Finally, the effects of post coating drying temperature (100 &ndash / 200 &deg / C) and time (10 &ndash / 60 min) on optoelectronic and microstructural properties of OAD-modified ITO thin films were discussed. Thin films have been characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD),x-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-Vis) spectroscopy, fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and four-point probe measurement techniques. It was shown that film formation efficiency, surface coverage and homogeneity were all enhanced with OAD addition. OAD modification also leads to a significant improvement in electrical conductivity without affecting the film thickness (45&plusmn / 3 nm). Highly transparent (98 % transmittance in visible region) ITO thin films with a sheet resistance as low as 3.8&plusmn / 0.4 k&Omega / /sqr have been obtained by employing coating sols with optimized OAD amount (0.75 M). The optimum post-coating drying temperature (100 &deg / C) and drying time (10 min) was also determined for 0.75 M OAD-modified ITO thin films.

Microresonators are devices that confine light in small volumes through total internal reflection. Introducing an emissive species into a microresonator allows for resonance enhanced emission at frequencies where the spectrum of the emissive species overlaps with the resonant frequencies of the microresonator. Previous research has led to a good understanding of these phenomena in 1D and 2D microresonators, but many 3D microresonator geometries have not yet been investigated. This work details the successful creation and demonstration of a cubic polymeric optical microresonator.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007. / Committee Chair: A. Rahman Zaghloul ; Committee Members: W. Russell Callen and Doug Yoder. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19096号 / エネ博第320号 / 新制||エネ||65 / 32047 / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 松田 一成, 教授 岸本 泰明, 教授 大垣 英明 / 学位規則第4条第1項該当

EEV buried channel charge coupled devices (BC CDs) with technological variations have been studied with respect to their response to 70kVp X-rays. Process variations considered are the conventional BCCD, scintillator coated BCCDs (Gadox(Eu) and Csl(Tl)) and the inversion mode device. The work was made necessary by the use of these CCDs for dental X-ray imaging. Effects investigated include changes in device operating voltages and dark current. The dark current buildup has been characterised in terms of a prompt component seen immediately following irradiation, and a time dependent component which occurs gradually. A major part of this work was the determination of the location and concentration of the energy states responsible for this dark current buildup. Also a novel aspect of the work was the derivation of an expression describing the time dependent component as a function of time and temperature. Effects associated with the bias dependence of the BCCD have also been considered, with particular regard to the effect of a negative substrate bias, and the theoretical explanation has been developed. The findings of this work have demonstrated the suitability of these devices for the commercial application of imaging X-rays for dentistry.