Previous work has shown that laser-induced desorption (LID) can prove useful for the determination of surface contamination. However, because of the nature of small-spot sampling utilized in the previous work, it proved rather difficult to gather statistically significant data. A solution to this problem that still allowed sampling the surface with small focused laser spots was to automate the sample manipulation, laser control, and data acquisition of the system. With the automation of the LID facility in place, a detailed study of the LID of water/heavy water (H₂O/D₂O) was undertaken. As in the earlier work, samples were irradiated with a hydrogen fluoride/deuterium fluoride (HF/DF) laser beam focused inside an ultrahigh vacuum (UHV) chamber. The molecules desorbed from the sample surface were partially contained in a glass envelope that also contained a quadrupole mass analyzer. Samples consisted of bulk-etched CaF₂ and optical thin-film coatings of CaF₂--undosed or H₂O/D₂O dosed--on a variety of substrates. Some analysis was performed on cleaved, single-crystal alkali halides. The focused laser spot size was 155 μm (l/e² diameter) for the HF laser and 138 μm (l/e² diameter) for the DF laser. Between 400 and 800 sites per sample were tested for each desorption onset analysis. A study was also performed to test the possibility of correlation between (1) laser-induced damage and defects and (2) laser-induced desorption and adsorption sites for some of the samples listed above. Attempts to deuterate and hydrate CaF₂ thin films met with limited success as laser-induced desorption samples. Other analysis techniques showed that dosing during the coating process produced a more ordered coating; in fact, dosing with H₂O reduced the optical absorption in the "H₂O" band, modified the damage morphology, and, along with a low temperature bakeout, raised the laser-damage threshold.

Spectrally selective designs (SSDs), which selectively reflect, transmit, absorb or radiate light depending on the wavelength, impact our lives in many ways. For instance, precisely designed metasurfaces on silicon offer unprecedented control of light in the visible and infrared wavelengths. A less sophisticated example, white paints, simultaneously reflect sunlight and radiate heat to passively cool buildings. SSDs like these are meaningful scientific pursuits as well as socially impactful in their applications. However, the latter is not always the case, as prioritization of novelty and performance in research have often led to SSDs whose sophistication and cost restricts their use. Furthermore, given increasing concerns about cost, eco-friendliness and applicability in the developing world, designs that overcome such issues are becoming increasingly sought-after. The works presented here aim to address this gap between high performance and applicability by combining scientific principles with the use of common materials and simple techniques to create SSDs for optical and energy applications. The work is categorized under three chapters. The first of these involve solution-derived nanostructured metal surfaces as a plasmonic platform for solar, thermal and optical applications. The second is concerned with porous polymers for passive daytime radiative cooling. The third and last chapter involves porous polymer coatings for switchable optical and thermal management. Prior to these sections, a general introduction to the fundamentals related to the topics – e.g. solar and thermal radiation, plasmon resonances in nanoparticles and electromagnetic scattering of light – are presented. The works in the three aforementioned sections are briefly summarized below. For the work on plasmonic nanostructured metal surfaces, a galvanic-displacement-reaction-based, room-temperature “dip-and-dry” technique is demonstrated for fabricating plasmonic-nanoparticle-coated foils (PNFs). The technique involves simply dipping a metal (M1) foil onto an aqueous salt of a less reactive metal (M2), and allowing the spontaneously resulting chemical reaction to form plasmonic nano or microparticles of M2 to form on M1. By controlling reaction parameters such as time, temperature and salt concentration, the reflectance spectrum of the PNFs can be tuned across the solar to far infrared wavelengths (0.35 – 20 μm). Consequently, the technique can tune the PNFs solar absorptance (~0.35 to 0.98) and thermal emittance (~0.05 to ~0.95). This is promising for applications such as selective solar absorption, selective thermal infrared emission, super-broadband thermal absorbers and emitters, and radiative cooling. The potential for selective solar absorption is investigated in detail, with the technique tuned to yield copper nanoparticle-coated Zinc substrate with excellent, wide-angle solar absorptance (0.96 at 15°, to 0.97 at 35°, to 0.79 at 80°), and low hemispherical thermal emittance (< 0.10). Issues important for applications, such as mechanical and thermal stability of the PNFs, are also investigated. The work on porous polymers for radiative cooling investigates the effect of porosity on the optical properties of polymers. Typically, polymers are intrinsically non-absorptive in the solar (0.35-2.5 μm), and emissive in one or more bands within the thermal infrared (2.5-20 μm) wavelengths. When made porous, the voids within the polymer can lead to different optical behaviors depending on their size. For instance, air voids with sizes (~1 μm) similar to solar wavelengths scatter sunlight due to the refractive index contrast between the polymer and air, leading to a high solar reflectance. Nanoscale (~0.1 μm) air voids, which are much smaller than longer thermal wavelengths (> 2.5 μm), lower the effective refractive index of the polymer in those wavelengths and increase thermal emittance. Porous polymer coatings (PPCs) with such air voids and optical properties can be made by scalable, solution-based and paint-like processes such as phase inversion. For example, phase-inverted poly(vinylidene fluoride-co-hexafluoropropene) (P(VdF-HFP)) exhibit an exceptional solar reflectance of up to 0.99 and hemispherical long-wave infrared emittance ~ 0.97. This allows the P(VdF-HFP) PPCs to achieve a net heat loss and reach sub-ambient temperatures of 6˚C even at noon. This passive radiative cooling performance, which surpasses those of notable designs in the literature, is obtained with a paint like convenience – making it promising as a sustainable cooling solution for buildings. The work on switchable optical and thermal management is related to the work above, and shows that optical performance of PPCs can also be altered by replacing the air in the pores with commonly available liquids. For instance, wetting PPCs with a liquid having the same solar refractive index as the polymer reduces optical scattering and turns the PPCs from white to transparent. Thermally transparent PPCs, meanwhile, turn absorptive or emissive when wetted with infrared-absorptive liquids. Both of these transitions can be reversed by drying – yielding a scalable and low-cost optical switching paradigm for solar and thermal wavelengths. The switchable optical transmittance can be useful in a wide variety of applications, such as controlling daylight in buildings, tunable solar heating and radiative cooling, water responsive systems and thermal camouflage. The works presented above attempt to achieve a desirable balance between scientific novelty, performance, simplicity and cost, with the intention of bringing high-performing optical designs to low-resource settings in the developing world. While this dissertation is a small step towards that goal, the author hopes that the readers will find the content to be of value.

Cheng, Zhenzhou. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Microfluidic device construction uses certain critical structures throughout many different applications. The valve structure remains one of the primary structures that present a barrier to miniaturization and portability. The extensive support devices required to power common microfluidic valves remove a significant amount of freedom from microfluidic device design. Moving to electrostatic methods of actuation could reduce the overall footprint of the microfluidic valve. This thesis covers three concept prototypes. Concept I presents an attempt at inlaying gold electrodes into polydimethylsiloxane substrates. Concept II attempts to use liquid silver injected into channels as electrode materials. Concept III uses aluminum sputtering to fabricate valve electrodes. Each device encountered complications during fabrication which led to improved fabrication guidelines for future devices. Designing and fabricating these concept devices required the development of several new processes in the clean room, including RIE Plasma bonding, PDMS sputtering techniques, and multilayer PDMS thin film fabrication. The PDMS sputtering technique in particular allows profilometry measurement of PDMS surfaces without risk of damaging the profilometer tip, a development that could allow for much more control over PDMS film thicknesses in future projects.

When porous silicon is plated with a catalytic metal, the two materials can act together as a single entity whose electrical properties are sensitive to its environment – the sensing component of an electrochemical gas sensor. Etching pores into silicon is an electrochemical process; and which type of doped silicon used is one of its key parameters. For nearly all reported porous silicon gas sensors, the silicon has been of the p-doped variety – because p-doped porous etching is better understood and the layers that result from it are more predictable – despite n-doped silicon having potentially significant benefits in ease of fabrication and being more conducive to plating by a catalyst. This experiment is an attempt at creating a palladium plated n-doped porous silicon layer, and an examination into what differentiates this fabrication process and the layers that result from the traditional p-doped type. The porous layers to be plated are to be the same and would ideally have properties that are a close approximation to what a functional gas sensor would require. This experiment defined a process that fabricated this “ideal” layer out of N-type, , double polished silicon wafers with a resistance of 20 Ω cm. The wafers were subjected to the anodic etching method with an HF/ethanol mixture as the electrolyte; and only two (of among many) fabrication parameters were varied: HF concentration of the electrolyte and total etching time. We find that a concentration of 12% HF (by volume) and an etching time of 6 hours result in layers most appropriate to carry into plating. The anodization current density is 15 mA cm-2. Deposition of the catalyst, palladium, is done using the electroless method by immersing the porous layer in a .001M PdCl2 aqueous bath. Characterization of this Pd/Porous Silicon layer was done by measuring resistivity by four point probe and imaging through Scanning Electron Microscopy. It was found that layers of a maximum average of 63 ± 6% porosity were created using our fabrication method. There is evidence of palladium deposition, but it is spotty and irregular and is of no improvement despite the n-doping wafer makeup. Resistivity in well-plated regions was measured to be 7-10 Ωcm, while resistivity in regions not well-plated was measured to be 70-140 Ω cm. This is comparable to previous literature values, indicating n-silicon porous silicon can be fabricated and still have potential as a catalytic layer, should metal deposition methods improve.

The emphasis of this work has been in two areas of optical materials - the crystal-chemical development of new optical frequency converters and the synthesis and study of new hosts for Cr����� luminescence and lasing. A simple method has been developed to identify promising frequency-doubling materials containing triangular oxoanions by estimation of nonlinear susceptibilities. Implementation of this method and its results have generated predictive capabilities in determining the relationships among crystal structure, nonlinear properties, and threshold powers. The new noncentrosymmetric borate SrLiB���O������ is discussed; its structure is built from a 3-dimensional condensation of B���0��� units with channels alternately filled with Sr and Li atoms. From these studies, a prescription for new pyroborate frequency converters has been developed. The material CdC������C���H7NO���, has been synthesized and structurally characterized by single-ciystal X-ray diffraction. Three new alkaline-earth beryllium borates, built from unique 2- and 3- dimensional networks and frameworks, have been identified. The structure of SrBe���(B0���)��� consists of layers of composition [Be���(BO���)���] interleaved by Sr atoms. CaBeB���O��� is constructed from a Ca0��� polyhedral network and a beryllium borate network. In BaBe���(B0���)��� the structure is composed of a beryllium borate framework intermingled with a Ba-centered dodecahedral framework. Several materials with potential as hosts for Cr����� lasing have been analyzed. The structural study of the laser host LiSrAIF6 revealed the distortions at the Al site that contribute to the unique optical properties of the Cr����� -doped crystals. The family of solid state oxide A���MM'(B0���)��� is one of the largest families of oxide reported to date. Metal site preferences, disorder, solid solubility, and the interrelationship between this structure and the layered structure type of Ba���Sc(B0���)��� are detailed. An optimal synthetic procedure has been developed for these materials to provide pure, highly crystalline phases. Also, the structural and optical features of (Cr�����:) Sr���In(B0���)��� with A= Sr and M=M'= In have been studied. The material Sr���LilnB���O������, was discovered while searching for a suitable lithium borate flux for crystal growth of the compound Sr���In(B0���)���. / Graduation date: 1993

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No description available.

D.Ing. (Electrical And Electronic Engineering ) / Please refer to full text to view abstract

With sub-micrometric form accuracy and nanometer scale surface roughness, the diamond turning process provides a great solution of fast prototyping optical systems with aspheric or freeform surfaces. On the other hand, with relatively lower cost and lighter weight, optical plastics are now widely used in consumer products. To study and optimize the cutting parameters of the diamond turning process on optical plastics, a series of tests with different cutting parameters settings are conducted on seven different optical plastic materials: E48R, OKP1, OKP4, OKP4HT, PC, PMMA, and Rexolite 1422. The relationship between the surface roughness and optical plastic materials is found, and the optimized cutting parameters are recommended.