Patterning of high T c superconducting thin films by copper-vapour laser

The projection microscope, based on a copper-vapour laser (CVL), is a unique system which combines the capabilities of a high magnification optical microscope and the performance of a high quality laser. The system performance with respect to high T _c superconducting (HTSC) device technology was studied using a scanning electron microscope. CVL patterning of YBaCuO films was demonstrated down to less than 2 μm. The thin films could be partially etched in depth just by controlling the laser pulse power density. In addition in HTSC device applications it could remove layers from thin films up to a complete etching.     

Loss due to transverse thermoelastic currents in microscale resonators

In order to understand the loss mechanisms associated with microscale resonators we have studied the importance of thermoelastic (TE) damping due to transverse thermal currents. In the work presented here, we study this damping mechanism as it applies to structures involving torsional vibration, or in general possessing a non-trivial mode shape such as those associated with microelectromechanical systems (MEMS) devices. A model of thermoelastic dissipation is presented that is based on the observation that the resonant modes of elastic structures almost always contain some flexural component. We determine a flexural energy participation factor and apply this to Zener’s model for damping of a simple reed in pure bending. Predictions agree well with internal friction measurements for a macroscale single-crystal silicon double paddle oscillator (300 μm thick) at temperatures from 130 to 300 K. The approach has also been successfully applied to predict microscale oscillator (1.5 μm thick) internal friction measurements at room temperature. Our results indicate that the internal friction arising from this mechanism is strong and can be quite significant for silicon-based MEMS (Q<10⁴) and persists down to 50 nm scale structures even for nominally torsional or even slightly asymmetric compressional devices which one might conclude have no loss. The importance of the thermoelastic mechanism is examined as a function of material properties. From this perspective, diamond possesses desirable thermal expansivity and diffusivity that is examined with our model.     

A novel gamma-ray imaging concept using “edge-on” microchannel plate detector

The “edge-on” illuminated microchannel plate (MCP) position-sensitive detector (PSD) is used for gamma-ray imaging for the first time. The superior position resolution of the MCP is combined with high detection efficiency due to the “edge-on” illumination mode. The results of imaging a 15 μCi ¹³⁷Cs source (662 keV quantum energy) are presented.     

A single-layer flat-coil-oscillator (SFCO)-based super-broadband position sensor for nano-scale-resolution seismometry

A new class super-broadband, nano-scale-resolution position sensor is tested. It is used as an additional sensor in seismograph. It enables to extend the band and enhance the sensitivity of the available technique by at least an order of magnitude. It allows transferring of mechanical vibrations of constructions and buildings, with amplitudes over 1 nm, into detectable signal in a frequency range starting practically from quasi-static movements. It is based on detection of position changes of a vibrating normal-metallic plate placed near the flat coil—being used as a pick-up in a stable tunnel diode oscillator. Frequency of the oscillator is used as a detecting parameter, and the measuring effect is determined by a distortion of the MHz-range testing field configuration near a coil by a vibrating plate, leading to magnetic inductance changes of the coil, with a resolution 10 pH. This results in changes of oscillator frequency. We discuss test data of such a position sensor, installed in a Russian SM-3 seismometer, as an additional pick-up component, showing its advantages compared to traditional techniques. We also discuss the future of such a novel sensor involving substitution of a metallic coil by a superconductive one and replacement of a tunnel diode by an S/I/S hetero-structure-as much less-powered active element in the oscillator, compared to tunnel diode. These may strongly improve the stability of oscillators, and therefore enhance the resolution of seismic techniques.     

Effect of microarc oxidised layer thickness on plain fatigue and fretting fatigue behaviour of Al–Mg–Si alloy

The objective of this work was to investigate the performance of microarc oxide coatings of two different thicknesses (40 and 100 μm) on Al–Mg–Si alloy samples under plain fatigue and fretting fatigue loadings. Tensile residual stress present in the substrate of 40 μm thick coated samples induced early crack initiation in the substrate and so their plain fatigue lives were shorter than those of untreated specimens. Presence of more pores and tensile surface residual stress in 100 μm thick coated samples caused early crack initiation at the surface leading to their inferior plain fatigue lives compared with 40 μm thick coated samples. While the differences between the lives of coated and uncoated specimens were significant under plain fatigue loading, this was not the case under fretting fatigue loading. This may be attributed to relatively higher surface hardness of coated specimens. The performance of 40 μm thick coated samples was better than that of 100 μm thick coated specimens under both plain fatigue and fretting fatigue loadings.     

X-ray imaging with “edge-on” microchannel plate detector: first experimental results

A novel scanning slit X-ray imaging system based on an “edge-on” microchannel plate detector was developed and tested. Images were acquired at 50 kV(p) X-ray tube voltage with a limiting spatial resolution of 7 lp/mm. The pixel noise was measured to be 0.3 count/pixel/s for a 50×70 μm² pixel size. This photon counting detector can be considered to be virtually noise free.     

Young’s modulus and interlaminar fracture toughness of SU-8 film on silicon wafer

SU-8 cantilever beams deposited on the polished sides or unpolished sides of silicon wafers were fabricated by MEMS and bulk micro-machining techniques. Bending tests were conducted to measure the Young’s modulus and interface fracture toughness. The results indicate that the Young’s modulus is increasing as the width of specimens is increasing because the specimen quality becomes better. When the width of SU-8 cantilever beam is 400 μm, the Young’s modulus is about 3.5 GPa. On the other hand, since the interface between SU-8 and silicon wafer does not suffer the attack of etchant, the measured interface fracture toughness has no clear dependence on the specimen width. The averaged interface fracture toughness is about 25–30 J/m² for the polished interface and 15–20 J/m² for the unpolished interface.     

3D-Modeling Numerical Solutions of Electromagnetic Behavior of HTSC Bulk above Permanent Magnetic Guideway

This paper presents a 3D-modeling numerical method using finite element method (FEM) to simulate the electromagnetic behavior of high-temperature superconductors (HTSC). The models are formulated by the magnetic field vector method (H-method). The resolving code was written by FROTRAN language. The electromagnetic properties of HTSC are described though Kim critical-state model. The magnetic fields and current distribution in the bulk HTSC in the applied non-uniform external magnetic fields generated by the permanent magnetic guideway (PMG) are obtained using the proposed method. The magnetic levitation forces by the interaction between the bulk HTSC and the PMG are calculated. In order to validate the method, measurement of the vertical force between a bulk YBaCuO(YBCO) and a PMG is obtained. The measurement and simulation results show good matching. This method could be used in the HTSC magnetic levitation transportation system optimization design.      

CHICSi—a compact ultra-high vacuum compatible detector system for nuclear reaction experiments at storage rings. II. Detectors

We describe the detectors for identification of charged particles and fragments in CHICSi, a large solid angle multi-telescope system mounted inside an ultra-high vacuum (UHV), cluster-jet target chamber. CHICSi performs nuclear reaction experiments at storage rings. The telescopes consist of a first very thin, 10–14 μm Si detector, a second 300 μm (or possibly 500 μm) ion implanted Si detector supplemented by a 6 mm GSO(Ce) scintillator read out by a photodiode (PD) or by a third 300 μm Si detector. The telescopes provide full charge separation up to Z=17 and mass resolution up to A=9 in the energy range 0.7–60A MeV. The thin p-i-n diode detector, etched out from a 280 μm Si wafer, and the GSO/PD detector, both exclusively developed for CHICSi, provide an energy resolution 8%, while the standard 300 μm detectors have 2% energy resolution. Radiation stability of the Si detectors is confirmed up to an integrated flux of 10¹⁰ alpha particles. The GSO detector has 70% light collection efficiency with the optical coupling to the PD a simple open, 0.2 mm, gap. A new method, developed to perform absolute energy calibration for the GSO/PD detector is presented.     

Prospects for charge sensitive amplifiers in scaled CMOS

Due to its low cost and flexibility for custom design, monolithic CMOS technology is being increasingly employed in charge preamplifiers across a broad range of applications, including both scientific research and commercial products. The associated detectors have capacitances ranging from a few tens of fF to several hundred pF. Applications call for pulse shaping from tens of ns to tens of μs, and constrain the available power per channel from tens of μW to tens of mW. At the same time a new technology generation, with changed device parameters, appears every 2 years or so. The optimum design of the front-end circuitry is examined taking into account submicron device characteristics, weak inversion operation, the reset system, and power supply scaling. Experimental results from recent prototypes will be presented. We will also discuss the evolution of preamplifier topologies and anticipated performance limits as CMOS technology scales down to the 0.1 μm/1.0 V generation in 2006.     

Ion formation by high velocity impacts on porous metal targets

In impact ionization studies the target normally consists of a metal surface of compact solid density. In the present experiments, we investigate the use of a layer of a highly porous structure of nanometre-sized grains, sometimes also called “metal black”, as an alternative target. In our comparative experiments, spherical iron particles (0.1<d_p<1.5 μm) were shot with velocities 2–30 km/s onto both a compact solid silver plate and a silver metal black layer of about 7 μm thickness (grain size 20–40 nm, mean density ≈1 g/cm³), deposited on a compact solid gold plate. Impact generated ions were analysed by means of time-of-flight mass spectrometry. The results reveal important advantages of the porous black layer, such as better mass resolution and a larger amount of ions from the impacting particle. Therefore metal blacks may be very suitable targets for the purposes of identification and characterisation of the impacting particle's composition. An attempt is made to give a physical explanation of the results in the frame of existing empirical ionization models. The study is part of a programme to improve devices for in-situ analysis of fast moving cosmic dust particles.     

EBSD analysis of a Ti-IF steel subjected to hot torsion in the ferritic region

The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial free steel was investigated using hot torsion. Tests were performed at temperatures between 765 °C and 850 °C at strain rates between 0.003 s⁻¹ and 1 s⁻¹ for samples with grain sizes of 25 μm, 75 μm and 150 μm. The structures were observed using EBSD analysis and are consistent with those expected for materials dominated by dynamic recovery. Some evidence was found for small amounts of thermally induced migration of pre-existing boundary (bulging) and for the generation of new segments of high angle boundaries by continuous dynamic recrystallization. The early onset of a steady-state flow stress in the finer grained samples is attributed to one or a combination of thermally induced boundary migration and enhanced rates of recovery near subgrain (and grain) boundaries.     

Q-switch Nd:YAG laser welding of AISI 304 stainless steel foils

Conventional fusion welding of stainless steel foils (<100 μm thickness) used in computer disk, precision machinery and medical device applications suffer from excessive distortion, formation of discontinuities (pore, void and hot crack), uncontrolled melting (melt-drop through) and poor aesthetics. In this work, a 15 ns pulsed, 400 mJ Nd:YAG laser beam was utilized to overcome these barriers in seam welding of 60 μm thin foil of AISI 304 stainless steel. Transmission electron microscopy was used to characterize the microstructures while hardness and tensile-shear tests were used to evaluate the strengths. Surface roughness was measured using a DekTak profilometer while porosity content was estimated using the light microscope. Results were compared against the data obtained from resistance seam welding. Laser welding, compared to resistance seam welding, required nearly three times less heat input and produced welds having 50% narrower seam, 15% less porosity, 25% stronger and improved surface aesthetics. In addition, there was no evidence of δ-ferrite in laser welds, supporting the absence of hot cracking unlike resistance welding.     

Fluoride compound targets for the sputter deposition of thin films of high-T c superconductors

A new method has been developed for the preparation of sputter targets from a mixture of fluorides of the elements entering into the composition of high-temperature superconductors (HTSC). The composition and structure of the proposed targets, the parameters of their magnetron sputtering, and the properties of obtained HTSC films have been determined. It is established that the YBaCuO films obtained by the magnetron sputtering of YF₃-BaF₂-Cu targets exhibit stable transition into the superconducting state at T _c = 82 K, with the phase transition width not exceeding 3 K.     

Measurements on a GaAs microstrip detector with 50 GeV/c electrons

A microstrip gallium arsenide detector (thickness 508 μm, strip width 100 μm, strip pitch and readout pitch 200 μm) has been tested in a 50 GeV/c electron beam at CERN. Using the low noise Viking preamplifier chip (shaping time 1.5 μs) signal to noise ratios up to 25 were measured depending on bias voltage and angle of incidence. Applying the so-called η-algorithm (using the impact position-sensitive charge sharing between adjacent strips) a resolution down to σ 20 μm could be obtained.     

Edge sensitivity of “edgeless” silicon pad detectors measured in a high-energy beam

We report measurements in a high-energy beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors. The edgeless side of these rectangular diodes is formed by a cut and break through the contact implants. A large surface current on such an edge prevents the normal reverse biasing of this device above the full depletion voltage, but we have shown that the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at a low temperature. A pair of these edgeless silicon diode pad sensors was exposed to the X5 high-energy pion beam at CERN, to determine the edge sensitivity. The signal of the detector pair triggered a reference telescope made of silicon microstrip detector modules. The gap width between the edgeless sensors, determined using the tracks measured by the reference telescope, was then compared with the results of precision metrology. It was concluded that the depth of the dead layer at the diced edge is compatible with zero within the statistical precision of ±8 μm and systematic error of ±6 μm.     

Gas pixel detectors for X-ray polarimetry applications

We discuss a new class of micro pattern gas detectors, the gas pixel detector (GPD), in which a complete integration between the gas amplification structure and the read-out electronics has been reached. An application-specific integrated circuit (ASIC) built in deep sub-micron technology has been developed to realize a monolithic device that is, at the same time, the pixelized charge collecting electrode and the amplifying, shaping and charge measuring front-end electronics. The CMOS chip has the top metal layer patterned in a matrix of 80 μm pitch hexagonal pixels, each of them directly connected to the underneath electronics chain which has been realized in the remaining five layers of the 0.35 μm VLSI technology. Results from tests of a first prototype of such detector with 2 k pixels and a full scale version with 22 k pixels are presented. The application of this device for Astronomical X-ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation is shown. Results from a full MonteCarlo simulation for two astronomical sources, the Crab Nebula and the Hercules X1, are also reported.     

Synthesis of hydroxyapatite on titanium coated with organic self-assembled monolayers

The work focuses the formation of hydroxyapatite (HA) layers from simulated body fluids (SBF) onto titanium coated with NH₂-, SH-, and SO₃H-SAMs, respectively, at room temperature and 37 °C as well as pH values of SBF of 7.4, 8, and 8.4. At an upside up arrangement of the samples in the SBF, the formation of sufficient thick HA layers with a pillow like structure onto all SAMs were observed, which is believed to be caused by combined homogeneous and heterogeneous precipitation of HA from the SBF. These layers do not show sufficient adhesive strength. An upside down arrangement of the samples result in the formation of up to 5–10 μm thick flat HA layers with a much higher adhesive strength, which is believed to be due to formation of HA from the SBF only by heterogeneous precipitation. Also HA layers were obtained onto all studied SAMs, SH-SAM appears to favour the formation of HA resulting in a layer with a thickness of about 10 μm and an almost stoichiometric Ca/P-ratio of the layer of 1.72. All other layers exhibit much lower ratios.     

Replication of metal microstructures by micro powder injection molding

In this paper, a study on the production of 316L stainless steel microstructures by μPIM (powder injection molding) is presented. Two types of mold inserts were used and the molding was conducted on a conventional injection molding machine. Based on the characteristics of the mold inserts and the feedstock, suitable processing parameters were selected. Some requirements for the production of the microstructures are discussed. For example, a relatively high mold temperature, high injection pressure and holding pressure were required. The study showed that 316L stainless steel microstructures of φ100 × 200 μm can be injection molded, but there were incomplete filling and demolding problem in the case of smaller microstructures of φ60 × 191 μm. The molded parts were successfully debound and sintered.     

Design, fabrication and optical characterization of cerium oxide-magnesium fluoride double layer antireflection coatings on monocrystalline silicon substrates

Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF₂–CeO₂–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO₂ layer of a thickness of 16 nm is formed onto Si substrates.