W O'Neill

Carbon Nanostructure-Based Field-Effect Transistors for Label-Free Chemical/Biological Sensors

Over the past decade, electrical detection of chemical and biological species using novel nanostructure-based devices has attracted significant attention for chemical, genomics, biomedical diagnostics, and drug discovery applications. The use of nanostructured devices in chemical/biological sensors in place of conventional sensing technologies has advantages of high sensitivity, low decreased energy consumption and potentially highly miniaturized integration. Owing to their particular structure, excellent electrical properties and high chemical stability, carbon nanotube and graphene based electrical devices have been widely developed for high performance label-free chemical/biological sensors. Here, we review the latest developments of carbon nanostructure-based transistor sensors in ultrasensitive detection of chemical/biological entities, such as poisonous gases, nucleic acids, proteins and cells.

High density net shape components by direct laser re-melting of single-phase powders

Direct Metal Laser Re-Melting is a variant of the Selective Laser Sintering process, a Rapid Prototyping (RP) technology. This tool-less manufacturing technology has the potential of producing complex, high quality components from single-phase metal powders in short time scales. This is made possible by the production of consecutive two-dimensional layers. Unfortunately, finished components manufactured by this technique have their integrity and material properties dictated by the porosity within the laser re-melted structure. In order to maintain structural integrity comparable to conventionally produced components, metal components produced by the rapid prototyping method should exhibit a porosity of the order of maximum of ∼2% with corresponding bulk material properties. To achieve these objectives, process and laser parameters require optimisation for maximum densities to be attained. This paper reports on the development of a scanning strategy that produces stainless steel (316L) laser re-melted components which exhibit porosities of <1%, while maintaining the concept of rapid prototyping.

Micromachining of copper using Nd:YAG laser radiation at 1064, 532, and 355 nm wavelengths

Abstract The interaction phenomena of nanosecond time period Q-switched diode-pumped Nd:YAG laser pulses using 1064, 532 and 355 nm with 0.25 mm thick pure-copper foil was investigated at an incident laser intensity range of 0.5– 57.9 GW / cm 2 . For each sample, etch rate and surface structure were determined. Analysis of the results of the tests included scanning electron microscopy (SEM). A maximum etch rate of 13.3 μm per pulse was obtained for the etch rate tests carried out at 532 nm . The maximum etch rate obtainable for 1064 nm was 2.21 μm per pulse, and for 355 nm , 6.68 μm per pulse. The dramatic decrease in etch rate observed when processing at 1064 nm is thought to occur due the highly reflective nature of copper as the interaction wavelength is increased, plus the nature of the plasma formed above the material during the high-intensity laser–material interaction. This plasma then imparts energy to the surface of the processed area leading to surface melting of the area surrounding the hole as can be seen by the SEM photographs.

High-Quality Micromachining of Silicon at 1064 nm Using a High-Brightness MOPA-Based 20-W Yb Fiber Laser

The advances in design, performance, cost reduction, and brightness for the modern Yb fiber lasers have opened up the possibility of redefining the processing options of semiconductor materials at a wavelength of 1064 nm. The usual laser of choice for Si processing is the 355- or 266-nm diode-pumped solid-state system. The provision of a new master oscillator power amplifier (MOPA)-based high-brightness Yb-based fiber laser configuration has provided a range of pulse parameters (30-50 ns full-width at half-maximum), peak powers approaching ~2 GWmiddotcm-2, and pulse repetition rates up to 500 kHz. These processing parameters offer a broad range of material response characteristics. This paper provides a preliminary analysis of the response of Si to the new MOPA-based Yb laser operating at maximum average power of 20 W. Results presented here show no signs of the usual thermally induced deleterious effects (microcracking, heavy recast layers, and surface damage) normally associated with Si interactions at 1064 nm. Volumetric etch rates of up to 230 000 000 mum3middots-1 were observed with a high-quality percussion drilling interaction at a repetition rate of 25 kHz and an average power of 20 W.

Soft-lithographic processed soluble micropatterns of reduced graphene oxide for wafer-scale thin film transistors and gas sensors

PDMS based imprinting is firstly developed for patterning of rGO on a large area. High quality stripe and square shaped rGO patterns are obtained and the electrical properties of the rGO film can be adjusted by the concentration of GO suspension. The arrays of rGO electronics are fabricated from the patterned film by a simple shadow mask method. Gas sensors, which are based on these rGO electronics, show high sensitivity and recyclable usage in sensing NH3.

A three-dimensional analysis of gas entrainment operating during the laser-cutting process

Recent work has shown the great sensitivity of the reactive-gas-assisted laser-cutting process to impurities in the assisting gas. Process improvements have been obtained with high-purity oxygen jets and several companies have marketed a high-purity oxygen assisting gas. The role of impurities in limiting reaction energy in the laser-cutting process has aroused great interest in laser-processing laboratories, and is the subject of continuing research. In this work the authors have examined a traditional laser-cutting arrangement in order to assess the levels of impurity entrainment into the main oxygen gas jet. A three-dimensional theoretical analysis of the turbulent gas flow from a 1.5 mm diameter circular orifice through a model cut was examined in order to determine the magnitude of impurity entrainment as a function of kerf width and cut depth. Kerf widths in the range 0.4-1.4 mm and cut depths 0-20 mm were chosen as representative of possible cutting conditions. The onset of impurity entrainment at the model cut front occurred at a depth of 6.5 mm for kerf width 1.4 mm, and at a depth of 20 mm for kerf width 0.48 mm. Calculated entrainment levels are given for each combination of kerf width and cut depth within the chosen range. To examine the validity of the theoretical calculations, an experimental investigation of the benefits of using an annular jet, to protect against impurity entrainment, in conjunction with the standard cutting jet was made during CO2 laser cutting trials. Laser cuts were performed on 3, 5, 10, 16 and 20 mm thick 43A medium carbon steels with and without the anti-entrainment nozzle assembly. Cutting results support general theoretical results in that entrainment is not a significant problem for cut depths up to 10 mm thick and kerf widths less than 1 mm. A suitable anti-entrainment nozzle assembly will eliminate impurity entrainment beyond this range.

Hysteresis during field emission from chemical vapor deposition synthesized carbon nanotube fibers

Hysteresis in the field emission (FE) data of a chemical vapor synthesized carbon nanotube fiber cathode is analyzed in the regime where self-heating effects are negligible. In both the forward and reverse applied field sweeps, various FE modes of operation are identified: including Fowler-Nordheim (FN) tunneling and space-charge limited emission from the fiber tip and FN emission from the fiber sidewall. Hysteresis in the FE data is linked to the difference in the field enhancement factors in the different FE modes of operation in the forward and reverse sweeps and related to changes in the fiber morphology.

Control of Material Transport Through Pulse Shape Manipulation—A Development Toward Designer Pulses

The variety of laser systems available to industrial laser users is growing and the choice of the correct laser for a material target application is often based on an empirical assessment. Industrial master oscillator power amplifier systems with tuneable temporal pulse shapes have now entered the market, providing enormous pulse parameter flexibility in an already crowded parameter space. In this paper, an approach is developed to design interaction parameters based on observations of material responses. Energy and material transport mechanisms are studied using pulsed digital holography, post process analysis techniques and finite-difference modelling to understand the key response mechanisms for a variety of temporal pulse envelopes incident on a silicon 〈1|1|1〉 substrate. The temporal envelope is shown to be the primary control parameter of the source term that determines the subsequent material response and the resulting surface morphology. A double peak energy-bridged temporal pulse shape designed through direct application of holographic imaging data is shown to substantially improve surface quality.

The manufacture of a very high precision x-ray collimator array for rapid tomographic energy dispersive diffraction imaging (TEDDI)

A very high resolution x-ray collimator array has been constructed for use with tomographic energy dispersive diffraction imaging (TEDDI). The collimator consists of a 16 × 16 array of 50 µm diameter holes in a series of 0.1 mm tungsten plates aligned to a tolerance of ±2 µm. The minimum angular divergence of the transmitted x-ray beams through each transmission pathway in the collimator array has been designed to be 0.02°, which is equivalent to an energy dispersed resolution of 250 eV with an aspect ratio of 6000:1. The collimator array has been matched to the development of an energy sensitive x-ray detector array (Seller et al 1998 Proc. SPIE 3445 584–92) for TEDDI studies of materials. The very high tolerance of the aperture size and placement was achieved by utilizing high intensity femtosecond pulse duration laser machining from a diode pumped solid state laser (DPSS). Using a novel arrangement the laser acted as the principal alignment and cutting tool. The collimator transmission function has been tested using a uniform synchrotron radiation flood field. The transmission and spatial uniformity were found to be consistent with the design parameters for TEDDI applications and also as a diffracted beam collimator for monochromatic powder diffraction studies.

Modelling and prototyping the conceptual design of 3D CMM micro-probe

This paper details the prototyping of a novel three axial micro probe based on utilisation of piezoelectric sensors and actuators for true three dimensional metrology and measurements at micro- and nanometre scale. Computational mechanics is used first to model and simulate the performance of the conceptual design of the micro-probe. Piezoelectric analysis is conducted to understand performance of three different materials - silicon, glassy carbon, and nickel - and the effect of load parameters (amplitude, frequency, phase angle) on the magnitude of vibrations. Simulations are also used to compare several design options for layout of the lead zirconium titanate (PZT) sensors and to identify the most feasible from fabrication point of view design. The material options for the realisation of the device have been also tested. Direct laser machining was selected as the primary means of production. It is found that a Yb MOPA based fiber laser was capable of providing the necessary precision on glassy carbon (GC), although machining trials on Si and Ni were less successful due to residual thermal effects.To provide the active and sensing elements on the flexures of the probe, PZT thick films are developed and deposited at low temperatures (Lt720 degC) allowing a high quality functional ceramic to be directly integrated with selected materials. Characterisation of the materials has shown that the film has a homogenous and small pore microstructure.