W. Zander

Microstructure of epitaxial YBa2Cu3O7 films on step-edge SrTiO3 substrates

Abstract The microstructure of YBa 2 Cu 3 O 7 films epitaxially grown on step-edge (100) SrTiO 3 substrates has been characterized by means of high resolution transmission electron microscopy. The results indicate a relationship between the microstructure of the film acreoss a step and the angle step makes with the substrate plane. On a steep, high-angle step, the film grows with its c -axis perpendicular to that of the film on the substrate surface so that two grain boundaries are formed. On a low-angle step, the film grows without any change in c -axis orientation across the step and without grain boundaries. Epitaxial second phases intergrowths across the steps have been found in some cases which may act as barrier layers when they cut through th YBa 2 Cu 3 O 7 film.

Structural and optical characterization of epitaxial waveguiding BaTiO3 thin films on MgO

Epitaxial waveguide structures of c-axis oriented BaTiO3 thin films on MgO(001) have been grown by pulsed laser deposition. The structural properties of the samples have been characterized by Rutherford backscattering spectrometry/ion channeling (RBS/C), x-ray diffraction, and atomic force microscopy. We found excellent crystalline quality even up to thicknesses of a few microns. This has been confirmed by RBS/C minimum yield values of 2%–3%, a full width at half maximum of 0.36° of the BaTiO3 (002) rocking curve, and a rms roughness of 1.1 nm for a 950 nm BaTiO3 film. The out-of-plane refractive index was measured to be close to the extraordinary bulk value with the birefringence being about one third of the bulk value. Waveguide losses of 2.9 dB/cm have been demonstrated.

Development of multisensor systems based on chalcogenide thin film chemical sensors for the simultaneous multicomponent analysis of metal ions in complex solutions

Abstract A new type of thin film chemical microsensors based on chalcogenide glass-sensitive materials was developed by means of silicon planar technology and pulsed laser deposition technique. These miniaturised ion-selective electrodes (ISEs) exhibit Nernstian responses over five concentration decades with detection limits of 1×10 −7 mol/l towards the primary ions Cu and Pb, and 4×10 −7 and 3×10 −5 mol/l towards Cd and Tl, respectively. The thin film microsensors have been shown to be perspective instruments for the simultaneous multicomponent analysis of complex liquid media based on the principles of an ‘electronic tongue’ device. Incorporating the thin film sensors into a sensor array allowed the multicomponent analysis of heavy metal-ion species (Pb 2+ , Cd 2+ , Zn 2+ and Fe 3+ ). The concentrations of Pb 2+ -, Cd 2+ - and Zn 2+ -ions can be determined simultaneously by direct potentiometric measurements using a sensor array of seven all-solid-state thin film chemical microsensors with an accuracy of 15–30%. The sensor array allows overcoming the problem of an insufficient selectivity of single sensors. The suggested microsystem-compatible fabrication technique favours a further miniaturisation, aimed to a fully integrated electrochemical microsystem.

The microstructure of epitaxial YBa2Cu3O7 films on steep steps in LaAlO3 substrates

Abstract The microstructure of YBa 2 Cu 3 O 7 grown on steep steps in (001 pseudocubic LaAlO 3 substrates was studied by high-resolution electron microscopy of cross-sectional and plan-view samples. Steps with angles of about 80° were obtained by ion milling. On the substrate plane, the films grew with the c -axis parallel to [001] while on the flank of a step the c -axis was parallel to the [100] direction of the substrate. As a result, two [010] tilt axis grain boundaries were formed at which the YBa 2 Cu 3 O 7 lattice changed orientation by approximately 90°. In the upper grain boundary, a [100] tilt axis and, on the average, a (013) habit plane alternated with a [010] tilt axis and a (1 0 3) habit plane. This alternating structure was caused by twinning in the orthorhombic film structure. The lower grain boundaries were found to be rather irregular and consisted of a chain of (0 1 3)(0 1 3) and (0 1 0)(0 0 1) type segments exhibiting a tendency to tilt the whole habit plane toward the a-b plane of the flank film. Dislocations, stacking faults and misfit strains were also observed in or close to the boundaries. Grain boundary modeling indicated a good agreement with the experimental image and permitted us to determine the atomic plane of a boundary.

Sensitive RF-SQUIDs and magnetometers operating at 77 K

Large 6-mm*6-mm and 8-mm*8-mm flux-focusing washer structures with inductances L/sub S/ between 25 pH and 500 pH were fabricated from epitaxial, c-axis YBa/sub 2/Cu/sub 3/O/sub 7/ films. Double step-edge junctions having a low 1/f noise were incorporated in these washers to form RF-SQUIDs (superconducting quantum interference devices). A high tank circuit frequency near 150 MHz was chosen to reduce noise and improve the sensitivity of the SQUIDs. At 77 K, a transfer function exceeding 100 mu V/ Phi /sub 0/ and a white flux noise of 3*10/sup -5/ Phi /sub 0// square root Hz down to below 0.3 Hz were attained with L/sub S/=25 pH. A magnetometer with L/sub S/=190 pH was demonstrated. The best magnetic field and energy resolutions were 170 fT/ square root Hz and 5*10/sup -29/ J/Hz respectively, over a signal frequency range to below 1 Hz. The magnetometer was used to record human magnetocardiograms and auditory evoked human brain responses.<<ETX>>

High quality epitaxy of YBa2Cu3O7−x on silicon‐on‐sapphire with the multiple buffer layer YSZ/CeO2

High quality YBa2Cu3O7−x films on silicon‐on‐sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO2. Ion channeling reveals the high crystalline perfection of the YBa2Cu3O7−x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical temperatures above 90 K, with transition widths down to 0.5 K, critical current densities above 2×106 A/cm2 at 77 K and surface resistance values of 1.4 mΩ at 18.9 GHz and 77 K confirm the high quality of the YBa2Cu3O7−x films. These results are very promising for integrated superconductor and semiconductor applications.

A highly long-term stable silicon-based pH sensor fabricated by pulsed laser deposition technique

Abstract A highly long-term stable pH sensor based on a capacitive electrolyte insulator semiconductor heterostructure has been developed. The pH-sensitive gate insulator material Al2O3 has been deposited by means of the pulsed laser deposition technique. The basic characteristics of the sensor device, such as pH sensitivity, stability, selectivity, sensor drift and response time have been investigated using capacitance/voltage measurements. Furthermore the physical structure and the stoichiometric composition of the deposited Al2O3 layers have been studied by Rutherford backscattering spectrometry, ion channeling and transmission electron microscopy. According to the results obtained during a measurement period of more than 600 days, the sensor possesses a high pH sensitivity of about 56 mV/pH including a small baseline drift of the sensor signal of less than 1 mV per day.

Characterization of YBa2Cu3O7 step-edge Josephson junctions

The authors have fabricated and characterized thin film YBa2Cu3O7 step-edge microbridges for application in SQUIDS. Epitaxial YBCO films were pulsed-laser-deposited on SrTiO3 and had Tcs of 88-90 K. Sharp steps in SrTiO3 were obtained by photolithographic techniques and Ar ion milling with step heights (h) between 100 and 250 mm. They investigated step-edge junctions (SEJ) with different film thicknesses (d) from 100 to 250 mm but with a constant ratio d/h=1. The width of the microbridges was 2-2.5 mu m. The Tcs of the bridges were 65-85 K, depending on film thickness and the duty cycle during ion milling. The I-V curves were RSJ-like and clear Shapiro steps were observed. The junction normal resistance was independent of temperature. With applied magnetic field the critical current Ic showed a T-dependent modulation, indicating that there was self-shielding and Ic non-uniformity in the junctions. Low-frequency noise measured in RF SQUIDS was relatively low. They showed that it was generated predominantly in the junctions.

Thin film sensors on the basis of chalcogenide glass materials prepared by pulsed laser deposition technique

Abstract Potentiometric thin film sensors on the basis of the two different chalcogenide glass materials Ag–As–S and Cu–Ag–As–Se–Te have been prepared by means of the pulsed laser deposition (PLD) technique onto Si/SiO2 substrates with an additional contact layer of Cr/Au and Ti/Pt, respectively. The physical layer structure and the stoichiometric composition of the deposited glass materials have been investigated by means of Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Depending on the material systems used, in a conventional “two-electrodes” measuring set-up, these novel thin film sensors possess a high sensitivity towards lead (23–25 mV/pPb), copper (29–31 mV/pCu), cadmium (23–27 mV/pCd) and silver (about 54 mV/pAg) over a measuring period of more than 60 days. The obtained results are in good accordance when comparing them to measurements performed with conventional bulk ion-selective electrodes, built-up of the same layer composition.

Copper, cadmium and thallium thin film sensors based on chalcogenide glasses

All-solid-state copper, cadmium and thallium sensors based on chalcogenide thin film layers prepared by means of the pulsed laser deposition (PLD) technique have been developed. The sensitive layers have been investigated using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The electrochemical behaviour of the sensors in terms of ionic sensitivity, limit of detection, Nernstian response interval, the effect of the pH, selectivity coefficients, dynamic response time and drift has been evaluated. The results of copper, cadmium and nickel analysis in industrial solutions using the developed sensors are presented.