Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 198-208). Also available via the Internet.

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In this thesis, we demonstrate in-situ scanning electron microscopy techniques for both electron beam lithography (EBL) and in-situ one dimensional nano materials electrical characterization. A precise voltage contrast image positioning for in-situ EBL to integrate nanowires into suspended structures for nanoswitch fabrication has been developed. The in-situ EBL eliminates the stage movement error and field stitching error by preventing any movements of the stage during the nanolithography process; hence, a high precision laser stage and alignment marks on the substrate are not needed, which simplifies the traditional EBL process. The ZnO piezoelectronics is also studied using nano-manipulators in scanning electron microscope. Methods to improve the contact have been demonstrated and the contacts between probe tips and the nanowires are found to have significant impact on the measurement results.

This thesis addresses the development of new gas sensor using surface acoustic wave (SAW) technology. SAW sensors detect the change in mass, modulus, and conductivity of a sensing layer material via absorption or adsorption of an analyte. The advantage of SAW sensor includes low cost, small size, high sensitivity. We investigated the use of nano-crystalline palladium film for sensing hydrogen gas. We also investigated SAW fabrication for radio frequency (RF) range operation where high signal-to-noise ratios can be achieved. A test-bed consisting of a gas dilution system, a temperature-controlled test cell, a network analyzer, and computer-based measurement system was used for evaluating the performance of SAW gas sensors at very low concentrations. Both single and dual delay line SAW devices were fabricated by means of photolithography on a lithium niobate substrate. Tests are carried to determine response speed, resolution, reproducibility, and linear characteristics, over a range of analyte concentrations.

To investigate the ultimate resolution in ion beam lithography (IBL) the resist material poly(methyl methacrylate) PMMA has been modified by single ion impacts. The latent damage tracks have been etched prior to imaging and characterisation. The interest in IBL comes from a unique advantage over more traditional electron beam or optical lithography. An ion with energy of the order of 1 MeV per nucleon evenly deposits its energy over a long range in a straight latent damage path. This gives IBL the ability to create high aspect ratio structures with a resolution in the order of 10 nm. Precise ion counting into a spin coated PMMA film on top of an active substrate enabled control over the exact fluence delivered to the PMMA from homogenously irradiated areas down to separated single ion tracks. Using the homogenous areas it was possible to macroscopically measure the sensitivity of the PMMA as a function of the developing parameters. Separated single ion tracks wer e created in the PMMA using 8 MeV F, 71 MeV Cu and 88 MeV I ions. These ion tracks were etched to create voids in the PMMA film. For characterisation the tracks were imaged primarily with atomic force microscopy (AFM) and also with scanning electron microscopy (SEM). The series of studies presented here show that the sensitivity of the resist-developer combination can be tailored to allow the etching of specific single ion tracks. With the ability to etch only the damage track, and not the bulk material, one may experimentally characterise the damage track of any chosen ion. This offers the scientific community a useful tool in the study and fabrication of etched ion tracks. Finally work has been conducted to allow the precise locating of an ion beam using a nanoscale mask and piezoelectrically driven scanning stage. This method of beam locating has been trailed in conjunction with single ion detection in an effort to test the practical limits of ion beam lithography in the single ion realm.

Electron beam lithography (EBL) and Nanoimprint Lithography (NIL) are the promising tools for today’s technology in terms of resolution capability, fidelity and cost of operation. Achieving highest possible resolution is a key concept for EBL where there is a huge request in applications of nanotechnology for sub-20 nm feature sizes. Defining features at these length scales is a challenge, and there is a large demand for resist that is not only capable of giving high resolution but also having low cost and ease of process. In this work I studied Polystyrene (PS) which is an alternative organic e-beam resist in terms of ease of process and resolution capability. I examined the process of electron-beam exposure and attempted to characterize the factors that affect the achieved resolution and sensitivity. Besides this work, I designed and fabricated a new type of mold for NIL since mold fabrication is a key factor for NIL technology. The resolution of NIL process depends on the mold features and polymer mold technology received great attention in terms of cost of fabrication and process, fidelity, and reliability. I used MD 700 Fluoropolymer as a new type of polymer mold which was believed to be a good candidate for the polymer mold of high throughput NIL.

In this thesis, we used the E-Beam lithography to fabricate a device of coupled microdisk-ring laser on the sample which was grown by molecular beam epitaxy (MBE), and analyzed the coupled effect of the device. The active layer was composed of six compressively strained InGaAs quantum dots (QDs) that were designed to support gain at 1200nm. Under the active layer, we replaced sacrificial layer by distributed bragg reflector (DBR). The purpose of the DBR was used like a mirror to reflect the particular wavelength which located at DBR¡¦s stop band, so the energy would be confined in the active layer. The device was composed of a microdisk and a ring. The diameter of the microdisk was 3£gm, and the width of the ring is 250nm. The microdisk was placed in the ring, and the gap of both was 100nm. After design, we simulated whether the device could generate coupled modes by Finite-Difference Time-Domain (FDTD). In experiment, we used the E-Beam lithography to define negative pattern on the sample which is spread with the PMMA. We also used the thermal evaporation to evaporate the metal, and lift the metal to form our pattern. Finally, we used the dry etching to transform the pattern to the epitaxial layer, and then the device was completed. In measurement, we used the micro-PL to measure our device, and got a successful result. The result showed our device generated eight resonant modes. The measured result matched the simulation result. Through simulation, the device generated three coupled modes, 1173.8nm, 1206nm, and 1214nm. We expect that the device will be used to generate terahertz source in the future.

In this thesis, we fabricate the quantum dots (QDs) micro-pillar of metal-coated by E-beam lithography, and analyze the optical and electrical properties of micro-pillar cavity devices. For the sample materials, we use S-K mode to grow 3-layer In0.75Ga0.25As QDs structures sandwiched by up and down Al0.5Ga0.5As cladding layer on GaAs substrate by molecular-beam epitaxy (MBE). 40nm GaAs spacer layers with 2nm p-modulation doping in the central barrier are adopted in this study. The micro-pillar with diameter of 2 m, metal coated on top (p-type) and down (n-type) facet are designed. The good reflectivities of metal contacts provide more energy extraction inside the cavity. We expect the device lasing while the current injection. First, we design the morphology and size of patterns by AutoCAD software. Then, we use e-beam lithography with proper exposure condition to define the patterns, and thermal evaporation to deposit metals. The superfluous metal is lifted off and the defined area metal is served as dry etching mask to transfer the pattern to the dielectric layer and epi-layer. Finally, we use SiO2 layer to prevent current leakage, and the p-n contact on each facet to complete the devices. Micro-pillar samples with/without metal coated are analyzed by micro-PL system. The emission wavelength of 1282nm and the calculated Q-value of 100 are obtained for the sample with metal coated, an increase of 500%. From the EL measurement results, the device of micro-pillar samples with metal coated generate three peaks, 1149nm, 1221nm and 1291nm. Besides, it can efficiently improve the emission intensities. The measured result matched the simulation result.

Abstract Negative index structures could be implemented through surface Plasmon polariton waves generated by nanostructures. We are interested in PMMA grating structure on curved metal surface. In order to fabricate this kind of samples, a series process parameters have been tested and also the lift-off process has been developed. Our results show superlens effect under optical microscope(OM). The sub-wavelength grating image is reconstructed in the non-grating region where the PMMA dielectric layer is not uniform. Surface Plasmon(SPP) waves generated in the grating region propagate to the non-grating region and are scattered out through the non-uniform PMMA layer. The grating information is not resolvable under OM but clear in the reconstructed region. It shows that SPP waves can show super resolution and a simple batch process should be developed in the future.

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