All-optical manipulation of photonic membranes

Optical tweezers have allowed us to harness the momentum of light to trap, move, and manipulate microscopic particles with Angstrom-level precision. Position and force feedback systems grant us the ability to feel the microscopic world. As a tool, optical tweezers have allowed us to study a variety of biological systems, from the mechanical properties of red blood cells to the quantised motion of motor-molecules such as kinesin. They have been applied, with similar impact, to the manipulation of gases, atoms, and Bose-Einstein condensates. There are, however, limits to their applicability. Historically speaking, optical tweezers have only been used to trap relatively simple structures such as spheres or cylinders. This thesis is concerned with the development of a fabricational and optical manipulation protocol that allows holographical optical tweezers to trap photonic membranes. Photonic membranes are thin, flexible membranes, that are capable of supporting nanoplasmonic features. These features can be patterned to function as metamaterials, granting the photonic membrane the ability to function as almost any optical device. It is highly desirable to take advantage of these tools in a microfluidic environment, however, their extreme aspect ratios mean that they are not traditionally compatible with the primary technology of microfluidic manipulation: optical tweezers. In line with recent developments in optical manipulation, an holistic approach to optical trapping is used to overcome these limitations. Full six-degree-of-freedom control over a photonic membrane is demonstrated through the use of holographical optical tweezers. Furthermore, a photonic membrane (PM)-based surface-enhanced Raman spectroscopy sensor is presented which is capable of detecting rhodamine dye from a topologically undulating sample. This work moves towards marrying these technologies such that photonic membranes, designed for bespoke applications, can be readily deployed into a microfluidic environment. Extending the range of tools available in the microfluidic setting helps pave the way toward the next set of advances in the field of optical manipulation

A testbed for optimal coating selection for micromilling of biomedical grade TI-6AL-4V.

One of the biggest challenges in precision micro-machining of titanium alloys is the tool wear as titanium is characterised as a “difficult to cut” material. Tool coatings provide a promising solution for the problem of tool wear while offering a low cost high value machining route. This project aims to explore the design of engineering material systems along with machining parameters to guide the choice of tool coating while machining biomedical grade Ti-6Al-4V. The overarching aim is to identify a low cost tooling such as WC coated with the right coating composition together with the appropriate machining parameters. The research methodology applied to work towards this aim employs a design of experimental approach using the Taguchi method such that the spindle speed, feed rate and coating would be varied. Both qualitative and quantitative analysis of the machining process was carried out to qualify the machining performance. During the machining trials, data was gathered and analysed to study the effect of cutting parameters on the specific cutting energy, material removal rate and surface roughness.PhD in Manufacturin

Institute of Ion Beam Physics and Materials Research: Annual Report 2001

Summary of the scientific activities of the institute in 2001 including selected highlight reports, short research contributions and an extended statistics overview

Nitrogen in diamond

Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methods—high pressure high temperature (HPHT) growth and chemical vapor deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g., by implantation or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamond—alone and in association with vacancies, hydrogen, and transition metal atoms. Among these, the negatively charged nitrogen-vacancy (NV–) defect in diamond is attracting particular current interest in account of the many new and exciting opportunities it offers for, for example, quantum technologies, nanoscale magnetometry, and biosensing

Aspects on Fundaments and Applications of Conducting Polymers

Since the establishment of the conductive properties of intrinsic conductive polymers, a huge variety of basic and applied research has been carried out, involving different polymers, copolymers, blends, mixtures and composites. Thus, fundamental understanding of physical and chemical properties of these materials has been sought, while the applied aspects have advanced very rapidly, crossing the boundaries between disciplines. Today, the applications of conducting polymers in various fields such as neuroscience, nanotechnology and green chemistry, are easily found. This development is dynamic and it needs to be updated and hence the motivation for the set of results presented in this book; which provides information about the development of fundamentals, and about some applications of conductive polymers

Consolidation of WC-Co nanocomposites synthesised by mechanical alloying

The influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Micro Heat Exchangers by Selective Laser Melting

Selective Laser Melting (SLM), a layer-based Solid Freeform Fabrication (SFF) process, was used to fabricate micro cross-flow heat exchangers from 316L stainless steel, bronze (Cu 90%, Sn 10%) and Inconel 718 powder. Their mechanical and thermal properties were determined using solid blocks of SLM material prior to the fabrication of the micro cross flow heat exchangers. Initially the process parameters for the fabrication of high density (>97%) parts for the different materials were defined. The mechanical and thermal properties of SLM parts were then measured. The tensile test results exhibited yield strength values superior to the parent metals, but also showed low tensile strength and ductility as a result of the inherent residual porosity (2-4%). Results obtained from the thermal conductivity of the stainless steel material system were in good agreement with the bulk material values. The heat transfer performance of the heat exchangers with either micro channels or lattice structures as heat exchange surfaces was investigated experimentally and the results were evaluated in terms of geometry and materials. The performance of the micro heat exchangers was found to be dependent not only on the choice of material but also on the heat exchanger media geometry

A study on the performance of microinjection moulds obtained using additive manufacturing

Tese de doutoramento em Ciência e Engenharia de PolímerosThe development of smaller and more effective microsystems for medical, electronic and automotive applications is driving the industry and research institutions to the development of new manufacturing processes. In the last two decades several techniques were developed complying with the requirements of micromanufacturing. Considering their specific nature and purpose, microreplication processes such as microinjection are the most suitable for high production levels. Nevertheless, microinjection moulding is still a relatively unknown process considering polymer flow behaviour at the microscale. Therefore, experimental studies and numerical analyses were required to enable process optimization. Microscale effects such as wall-slip and heat transfer can have a significant influence on microinjection processing conditions as well as on the quality of the moulded parts. Therefore, these effects must be accounted for a numerical simulation with accurate results. For that purpose, tests on an instrumented micromould were carried out to obtain suitable data to be compared with filling and packing simulation results. Furthermore, when considering the use of moulding blocks manufactured by additive technologies such as stereolithography (SLA) and selective laser melting (SLM), it is important to evaluate their mechanical behaviour after the experimental tests have been performed. The use of this type moulding blocks decisively contributes for the time-to-market decrease of plastic microcomponents obtained through microinjection moulding.O desenvolvimento de microsistemas cada vez mais pequenos e eficazes para aplicações médicas, electrónica e automóvel está a conduzir a indústria e centros de investigação para o desenvolvimento de novos processos de fabrico. Foram desenvolvidas diversas técnicas nas últimas duas decadas orientadas para o cumprimento dos requisitos da microfabricação. Considerando a sua natureza específica e objectivos, os processos de microreplicação como a microinjecção revelam-se como os mais adequados para elevados níveis de produção. Contudo, a moldação por microinjecção é ainda um processo relativamente pouco dominado considerando o comportamento do escoamento de polímero à microescala. Assim sendo, é fundamental a realização de estudos experimentais e de simulações numéricas para optimizar o processo. Efeitos de escoamento à microescala, tais como o escorregamento e a transferência de calor podem ter uma influência significativa nas condições de processamento da microinjecção assim como na qualidade das peças moldadas. Estes efeitos devem assim ser contabilizados para que se possa realizar uma simulação numérica que produza resultados precisos. Para esse efeito, foram realizados testes de microinjecção num micromolde instrumentado com o objectivo de retirar dados comparáveis com os resultados numéricos do enchimento e da compactação. Adicionalmente, considerando a utilização de blocos moldantes fabricados por tecnologias aditivas tais como a estereolitografia (SLA) e a fusão selectiva por laser (SLM), revela-se importante a avaliação do seu comportamento mecânico apoós a realização dos testes experimentais. A utilização deste tipo de blocos moldantes contribui decisivamente para o decréscimo do time-to-market para microcomponentes plásticos obtidos por micromoldação por injecção.Fundação para a Ciência e a Tecnologia (FCT) - bolsa SFRH/BD/36982/2007