Exploring microstencils for sub-micron patterning using pulsed laser deposition

The possibilities of sub-micron patterning by means of microstencils using pulsed laser deposition were investigated. Stencils with circular and elliptical patterns were used, with pore sizes ranging from 1 mum down to 500 nm. Strontium titanate (SrTiO3), silicon (Si) and self-assembled monolayers on gold were used as substrate materials, whereas nickel (Ni), nickel oxide (NiO) and gold (Au) have been deposited. The results show that the chosen deposition setup makes an easy and fast way for high-quality pattern creation

Large-scale extrusion processing and characterization of hybrid nylon-6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide-6 (PA-6) is achieved using a twin-screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h(-1) with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA-6 showed higher amounts of gamma-phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E-modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E' and E") increased and tan 6 decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright (C) 2004 John Wiley Sons, Ltd.</p

Spectroscopic evidence of in-gap states at the SrTiO3/LaAlO3 ultrathin interfaces

Experimental evidence of differences in the electronic properties of an insulating and a conducting SrTiO3/LaAlO3 interface is provided by soft x-ray spectroscopies. While core level photoemission measurements show that only at the conducting interface Ti ions with 3+ ionization state are present, by using resonant photoemission and x-ray absorption spectroscopies, it is shown that in both samples in-gap states with a Ti 3d character are present, but their density is higher at the conducting interface

Oxygen stoichiometry and chemical expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-&#61537; measured by in situ neutron diffraction

The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-ä (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 10-3 to 1 atm were determined by in situ neutron diffraction. BSCF has a cubic perovskite structure, space group Pm3hm, across the whole T-pO2 region investigated. The material is highly oxygen deficient with a maximum oxygen stoichiometry (3 - ä) of 2.339(12) at 873 K and a pO2 of 1 atm and a minimum of 2.192(15) at 1173 K and a pO2 of 10-3 atm. Good agreement is obtained between oxygen stoichiometry data determined by neutron diffraction and thermogravimetry. In the range covered by the experiments, the thermal and chemical expansion coefficients are 19.0(5)-20.8(6) 10-6 K-1 and 0.016(2)-0.026(4), respectivel

Phase stability and oxygen non-stoichiometry of SrCo_0.8Fe_{0.2O3&#8722;&#948;} measured by in situ neutron diffraction

The phase stability, oxygen stoichiometry and expansion properties of SrCo0.8Fe0.2O3−δ (SCF) were determined by in situ neutron diffraction\ud between 873 and 1173 K and oxygen partial pressures of 5×10−4 to 1 atm. At a pO2 of 1 atm, SCF adopts a cubic perovskite structure, space\ud group Pm3¯m, across the whole temperature range investigated. At a pO2 of 10−1 atm, a two-phase region exists below 922 K, where the cubic\ud perovskite phase coexists with a vacancy ordered brownmillerite phase, Sr2Co1.6Fe0.4O5, space group Icmm. A pure brownmillerite phase is\ud present at pO2 of 10−2 and 5×10−4 atm below 1020 K. Above 1020 K, the brownmillerite phase transforms to cubic perovskite through a twophase\ud region with no brownmillerite structure observed above 1064 K. Large distortion of the BO6 (B=Co, Fe) octahedra is present in the\ud brownmillerite structure with apical bond lengths of 2.2974(4)Å and equatorial bond lengths of 1.9737(3) Å at 1021 K and a pO2 of 10−2 atm.\ud SCF is highly oxygen deficient with a maximum oxygen stoichiometry, 3−δ, measured in this study of 2.58(2) at 873 K and a pO2 of 1 atm and a\ud minimum of 2.33(2) at 1173 K and a pO2 of 5×10−4 atm. Significant differences in lattice volume and expansion behavior between the\ud brownmillerite and cubic perovskite phases suggest potential difficulties in thermal cycling of SrCo0.8Fe0.2O3−δ membrane

Pushing the operating range of SIS mixers into the THz regime

In recent years, responding to the need of the astronomical community, superconductor-insulator-superconductor (SIS) mixers have been developed to operate at THz frequencies. Best results are obtained by using niobium-based tunnel junctions with well-matched low-loss normal metal striplines, which are found to be less lossy than niobium striplines operated above the gap-frequency of niobium (700 GHz). Niobiumnitride tunnel junctions with a magnesiumoxide tunnel barrier, although having reasonable quality current-voltage characteristics, have been found to be unsuitable due to excess shot noise resulting from pinholes in the barrier

Shot noise in NbN SIS junctions suitable for THz radiation detection

We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shot noise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q much greater than e. Using this charge enhancement mechanism we explain the junction shot noise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. The measured double side band noise temperatures are 1450 K at 600 GHz and 2800 K at 950 GHz

Fabrication and characterisation of a Nb diffusion-cooled hot electron bolometer for a 730 GHz waveguide mixer

We have fabricated Nb diffusion-cooled hot electron bolometers for a waveguide mixer around 700 GHz. The device in this work is a thin (12 nm) Nb bridge with a length and width of 220 nm and is defined by a two-step electron beam lithography process. The resistance as a function of temperature shows two transitions, which we attribute to the Nb bridge (6.1 K) and to parts of the Nb which are covered by the Au pads (5.4 K). We have measured a DSB receiver noise temperature of 2200 K at 735 GHz and a bath temperature of 3.3 K. No significant increase of the noise temperature is observed at IF frequencies between 1.1 and 1.7 GHz. The coupled LO power is estimated to be 35 nW

Integrated submm wave receiver with superconductive local oscillator

A fully superconductive integrated receiver is very promising for submm space astronomy where low weight, low power consumption, and limited volume are required. The new versions of the integrated quasioptical submm wave receiver have been designed, fabricated and tested in the frequency range of 450-700 GHz. The integrated receiver chip comprises a planar double dipole antenna, SIS-mixer and on-chip superconductive Flux-Flow Oscillator (FFO) with matching circuits. The receiver noise temperature (DSB) as low as 140 K at 500 GHz has been obtained. A light-weight and low power consuming submm imaging array is under development. Each of 9 pixels of the array is realized by an all-Nb single-chip superconductive receiver, mounted on an elliptical silicon lens with anti-reflection coating. The experimental test results of one pixel receiver are presented. A computer based system is developed to control the operation of the integrated receiver