Philip D. Prewett

Temperature dependent electrical resistivity of a single strand of ferromagnetic single crystalline nanowire

We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of diameter 55 nm using a four-probe method in the temperature range 3–300 K. The wire used is chemically pure and is a high quality oriented single crystalline sample in which the temperature independent residual resistivity is determined predominantly by surface scattering. Precise evaluation of the temperature dependent resistivity (ρ) allowed us to identify quantitatively the electron-phonon contribution (characterized by a Debye temperature θR) as well as the spin-wave contribution, which is significantly suppressed upon size reduction.

Liquid-like instabilities in gold nanowires fabricated by focused ion beam lithography

Observation of liquid-like instabilities is reported in Au nanowires formed by nanopatterning of Au films using focused ion beam (FIB) on different types of Si substrates including those passivated with SiO2 or Si3N4 surfaces. The onset of the instability, which can ultimately lead to break up of the FIB patterned nanowires into gold islands, occurs when the diameter of the nanowire is below a critical range, which depends on the conductivity of the substrate and the extent of native oxide present on it. We also observe the formation of Taylor cones on very narrow nanowires grown on insulating substrates at the onset of instabilities. This effect is further strong evidence of liquid behaviour and is the result of charging of the wires during FIB nanofabrication.

MOXI: a novel microfabricated zoom lens for x-ray imaging

Conventional x-ray optics have low optical efficiency and wavelength dependent focusing. The use of grazing incidence reflective optics overcomes these problems and significant progress has been made using polycapillary systems based on commercial microchannel plates originally designed as electron multipliers. Microfabrication techniques, under development for microelectromechanical systems (MEMS), provide a means of making arrays of microchannels with radial symmetry for a wide range of x-ray optical applications. The focal length of such micro-optical arrays may be varied to provide a zoom lens capability.

Stop grating for perfect replication of micro Fresnel lens by thermal imprinting

A stop grating concept is proposed to improve polymer filling in the thermal imprinting of a micro Fresnel lens structure. The stop grating consists of line and space structures outside the Fresnel lens pattern zone area. The experimental results have proved that the stop grating can help to achieve the complete filling of a mold, at the same time acting as a stop to prevent possible damage to the mold surface relief structures during imprinting press. A computer simulation was carried out to identify the phenomena of micro-holes at the edge of imprinted pattern. By removing the cavity between the pattern area and stop grating, perfect imprinting results have been achieved.

Research and evaluation of a high temperature pressure sensor chip

In order to solve the pressure measurement problem in the harsh environment, such as high temperature above 200°C, a special piezoresistive pressure sensor chip has been developed. Based on the MEMS (Micro Electro-Mechanical System) and SIMOX (Separation by Implantation of Oxygen) technology, the piezoresistive pressure sensor chip was constituted by silicon substrate, a thin buried silicon dioxide layer by SIMOX, an optimized boron ion implantation doping layer, photolithographically patterned on a Wheatstone bridge configuration, stress matching layer with silicon nitride, and beam lead layer (Ti-Pt-Au) for bonding the gold wires. A special buried silicon dioxide layer with the thickness 367nm, which used to isolate the upper measuring circuit layer from the silicon substrate, was fabricated by the SIMOX technology with the oxygen ion dose of 1.4×1018/cm2 and implantation energy of 200keV, so the leak-current between the upper measuring circuit layer and the silicon substrate was avoided. Utilizing the developed sensor chip and high temperature packaging process, a pressure sensor was fabricated with the range of 0∼25MPa, the experimental results showed that this pressure sensor had good performances under the high temperature of 200°C, such as accuracy of 0.114%FS and natural frequency of about 694.4 kHz.

A focused-ion-beam-fabricated micro-paddle resonator for mass detection

An experimental microelectromechanical system paddle resonator was made using focused ion beam fabrication from a 200 nm thick silicon nitride membrane and investigated using a laser vibrometer for resonant frequency detection. The fundamental mode was found to be torsional, as required, with a resonant frequency of 1.38 MHz and Q of 1070 at a test pressure of 20 μbar. The mass sensitivity was 55 ag Hz−1, close to the results of analytical and finite element analysis modeling, demonstrating proof of principle.

The development of a novel Bio-MEMS filtration chip for the separation of specific cells in fluid suspension.

Abstract In the clinical/microbiological laboratory there are currently several ways of separating specific cells from a fluid suspension. Conventionally cells can be separated based on size, density, electrical charge, light-scattering properties, and antigenic surface properties. Separating cells using these parameters can require complex technologies and specialist equipment. This paper proposes new Bio-MEMS (microelectromechanical systems) filtration chips manufactured using deep reactive ion etching (DRIE) technology that, when used in conjunction with an optical microscope and a syringe, can filter and grade cells for size without the requirement for additional expensive equipment. These chips also offer great versatility in terms of design and their low cost allows them to be disposable, eliminating sample contamination. The pumping mechanism, unlike many other current filtration techniques, leaves samples mechanically and chemically undamaged. In this paper the principles behind harnessing passive pumping are explored, modelled, and validated against empirical data, and their integration into a microfluidic device to separate cells from a mixed population suspension is described. The design, means of manufacture, and results from preliminary tests are also presented.

Characterization of line edge roughness and line width roughness of nano-scale typical structures

Two kinds of nano-scale typical structures were fabricated for characterizing line edge roughness(LER) and line width roughness(LWR). With Cr and Si3N4 thin films alternately deposited on a silicon substrate and electronic beam lithography employed on a positive resist ZEP520 layer, a nano-scale multiple linewidth standard and a nano-scale grating structure were processed respectively. In regard to the nano-scale multiple linewidth standards, an offline image analysis algorithm of Scanning Electron Microscopy (SEM) image and a random error analysis method were employed to characterize its LER and LWR, including standard deviations 3 σLER and 3 σLWR. With respect to the nano-scale grating structure, sampling and evaluation length, amplitude standard deviation, skewness, kurtosis, auto-correlation function as well as power spectral density function of the nano-scale grating structure were analyzed based on stochastic process analysis to show LER characteristics. Similarly Motif parameters-based analysis also was introduced to get LER characteristics of the nano-scale grating structure.

RECENT STUDY ON THE RELATED PROBLEMS IN EVALUATION OF MECHANICAL PROPERTIES FOR MEMS MATERIALS

In order to obtain reliable evaluation result by nanoindentation, the related problems during measurement of the hardness and elastic modulus are investigated. Two quantitative approaches, i.e. calculating actual contact area and correcting contact depth errors, are proposed to deal with the significant pile-up errors for indentation on those ductile soft materials, especially thin soft metal films on hard substrates. The various influence factors during indentation are analyzed, and a new method for uncertainty estimation in hardness and elastic modulus is provided based on the random-fuzzy variables. Through the illustration of Au/glass-ceramic and Al/7059 glass, both the quantitative approaches are suitable for the elastically matching film-substrate systems. The measurement uncertainties in hardness and elastic modulus of Si(100) are effectively estimated, and all possible influencing effects on uncertainty can be involved.

Design and fabrication of a micro optical system for x-ray analysis of biological cells

X-ray technology provides a number of powerful tools used in many different areas of science and industry. The ability to focus x-rays is the key to a wide range of applications including medicine (diagnosis and therapy), industrial applications (lithography and inspection), astronomy (space telescopes) and x-ray imaging (microscopy and analysis). This work presents the design and microfabrication of a novel x-ray micro optical system for use in an x-ray microprobe for analysis of biological cells. A reflective micro-optical system capable of focusing a wide range of wavelengths is at an advanced stage of development. The lens system consists of a pair of microfabricated optical elements, one of which has variable curvature providing a unique mechanically-actuated zoom focusing capability. Experiments have been carried out to measure the changes of the focal length (lens curvature) and sensor calibration.