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Here we present an original CMOS compatible technique for fabrication a sensor system based on field-effect transistors with a nanowire channel and its application for the quantitative determination of thyroid-stimulating hormone (TSH) in model blood serum. The fabrication process is based on the reactive-ion etching of the upper layer of silicon on insulator through a mask formed by electron beam lithography. The detection is based on the registration the change in the conductivity of the transistor during the selective interaction of the analyte with specific biomolecules on its surface. There were fabricated field-effect transistors with a nanowire channel of $$70{-}90\text{nm}$$ wide and $$3{-}5 \mu\text{m}$$ in long and a contact leads completely insulated from the analyte fluid. As the model antigen protein TSH of the pituitary gland, and as the recognition biomolecules - the specific to TSH fragments of antibodies were used, which were oriented immobilized on the nanowires surface. We carefully studied the conditions for biospecific interaction of antibodies with TSH. The detection limit of TSH was found to be $$1\times 10^{-4}\mu\text{IU}/\text{mL}$$ , which is significantly lower in comparison with currently used methods of standard enzyme-linked immunosorbent assay.

In this work, we present a nanoscale solid state structure, which is a 3D-array of tunnel-coupled arsenic dopants in silicon with a system of metallic electrodes leading to them. The structures of eight metal electrodes were fabricated on the inhomogeneously in depth doped with arsenic silicon surface, four of which converge to a region 50 nm in diameter, and four to a region of 200 nm. After removal of a thin highly conducting upper silicon layer, single-electron transport in an array (reservoir) of arsenic impurity atoms located between the electrodes is demonstrated. The Coulomb blockade was $${\sim}100$$ mV at a temperature of 4.2 K. The proposed structure can be used as a reservoir neural network, where single impurity atoms act as neurons, and electrodes will act as input and output terminals of the device, and also be used to configure the neural network. The operating temperature of such devices can be significantly increased due to the relatively small effective size of impurity arsenic atoms in silicon (3–5 nm).

The characteristics of a SQUID magnetometer-based readout system for a superconducting gyroscope-based inertial navigation system (INS) are investigated. The transformation function of the rotation angle of the gyroscope simulator to the voltage at the magnetometer output with a value close to 6.5 mV/deg is calculated and measured. This value corresponds to 4.1 V/deg for a superconducting gyroscope with a rotor diameter of 30 mm. Zero voltage drifts with a duration of up to 8 h are measured on the SQUID magnetometer. A drift of $$10^{-6}$$ deg/h was detected.

We present an investigation of the superconducting properties of thin YBa2Cu3O7-x (YBCO) films grown on [001] single-crystalline quartz substrates by pulsed laser deposition (PLD) technique. The growth of YBCO on quartz is challenging due to large crystal lattice mismatch between YBCO and quartz. We obtained highly c-oriented textured films with superconducting transition at about 85 K, transition width of 1 K, and critical current density jc ≈ 104 A cm−2 at 77 K. Analysis of the temperature dependences of the resistivity and current-voltage characteristics has shown the presence of the thermally-assisted flux flow at temperatures above 70 K. From the temperature and magnetic field dependences of critical current, vortex activation energy, U0(H), was estimated for both parallel and perpendicular orientation of magnetic field. Second critical field, Hc2(0), was estimated from extrapolation of the Hc2(T) dependences. The obtained results are an important step towards realization of YBCO thin films on amorphous silica fibers for the third generation (3 G) of the HTS long wire with low losses in alternative current applications.

Here we present CMOS compatible fabrication methods and the results of an experimental study of single-atom single-electron transistors made from silicon on insulator and based on various dopant atoms. Transistors with channels doped with arsenic (As), phosphorus (P), gold (Au) and potassium (K) atoms were fabricated and studied. Two methods for fabricating of experimental transistor structures are presented. The first method (As, P transistors) used a inhomogeneously doped in depth silicon layer and controlled reduction of the size of the transistor channel in several cycles of isotropic reactive-ion etching. The second method (Au and K transistors) used an undoped silicon layer and the subsequent implantation of dopant atoms into a preformed transistor channel. Dopant electron and hole levels of Au and K atoms in silicon are located near the middle of the silicon band gap, which provides a small effective size of the dopant charge center and, as a result, a high value of the charge energy and operating temperature of the transistor compared to the traditional dopants (P, As, Sb, B). The values of the charge energy of the Au and K transistors, which were estimated from the measurements (Ec ≥ 150 meV), are much higher than those of the As and P transistors (Ec < 30 meV). Important advantages of the proposed methods are: controlled implantation of various impurities and possibility to combine etching and implantation cycles during sample preparation.

Results of investigations using X-ray diffraction and scanning electron microscopy of composite materials made from YBa2Cu3O y films sputtered (using various regimes) onto a substrate of amorphous quartz with a platinum buffer layer, have been given.

We present the results of an experimental study of electron transport through individual phosphorus dopants implanted into a silicon crystal. We developed an original technique for single-electron transistor fabrication from silicon-on-insulator material with an island formed by single phosphorus atoms. The proposed method is based on well-known CMOS compatible technological processes that are standard in semiconductor electronics and may be used in most research groups. The large Coulomb blockade energy value of the investigated single-electron transistor (∼20 meV) allows one to observe single-electron effects in a wide temperature range up to 77 K. We measured and analyzed stability diagrams of fabricated experimental structures. We demonstrated a single-electron transistor with controllable electron transport through two to three phosphorus dopants only.

The binding to Lon protease through biotinylated aptamers whose structures contain G-quadruplex fragments with magnetic nanoparticles (MNPs) functionalized by streptavidin was investigated. The conditions of binding of target aptamers to MNPs are met. The resulting complexes are proposed for detection of Lon protease in different biological sources and for constructing a novel biomagnetic nanosensor immunoassay system.

A composite superconductor SiO2/YSZ/CeO2/YBa2Cu3O y with a critical current density of 7 × 104 A/cm2 has been prepared by laser ablation. Small hills enriched in copper and oxygen on the surface of the deposited films have been detected using scanning electron microscopy. A grain structure (sizes of 0.2–0.3 μm) and a system of twins ~400 A in width have been detected in the superconducting film using transmission electron microscopy. Such a structure and high (001) texture of the film provide the noted critical current density.

The internal structure and orientation of thin (150–300 μm) flexible Al2O3 fibers used as substrates for third-generation high-temperature superconducting wires are studied by different methods. It is shown that using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction, one can reliably determine the position of the \((1\bar 102)\) plane, on which good YBa2Cu3Oy films can be grown.

We used aptamers, which are functional equivalents of antibodies, in order to develop a nanosensor immunoassay system based on magnetic nanoparticles and a SQUID magnetometer. Selection was used to obtain DNA aptamers to interleukin-6; their affinity to the target protein was characterized by surface plasmon resonance. It was shown that the biotinylated aptamer binds to magnetic nanoparticles that were functionalized with streptavidin.

The problem of the fabrication of third-generation high-temperature superconductors (HTSCs) that are designed for the transmission of electric energy and the creation of nanoelectronic devices is studied in this work. The issues of the fabrication of dielectric substrates for the third generation wires are considered. The technology of HTSC film deposition on the quartz substrates is presented. Complex studies of sputtering of the buffer and superconducting YBa2Cu3O7 − δ (YBCO) layers were performed. The results of studies of electrophysical properties of the HTSC films on the quartz substrates are discussed.

The simple variant of the SQUID-based readout system for a strap-down gyroscopic inertial navigation system was created and tested. A voltage-to-angle transfer function close to 6 V/deg was measured. A drift rate less than 4 mV during 450 s was observed in the developed experimental stand. A noise level is strongly influenced by gyroscope's electrostatic support plates.

An electron transport through the extremely small gaps (1–5 nm wide) formed in narrow and thin gold nanowires by the electromigration method is studied in this work at various temperatures. A careful investigation of the final stage of a gap formation has shown a quantum character of a nanowire conductivity on this stage. Analysis of the electron transport characteristics through the resulting gaps was carried out. It shows that regimes of both a direct tunneling between electrodes and a “cold” emission into a barrier region were realized. Significant reduction of electron work function for gold electrodes of prepared gaps is revealed.

We propose an analytical parametric model for defining energy spectra of nanoparticles with a number of atoms of up to 3,300. This allows us to perform Monte- Carlo simulations for single-electron transistor (SET) based on gold nanoparticles with a size of up to 5.2 nm at tem- peratures from 0.1 to 300 K. At the first step, energy spectra were calculated for isomers of gold nanoparti- cles, consisting of up to 33 gold atoms using methods of quantum mechanics: density functional theory (DFT) with LANL2DZ basis set for "geometry" optimization; unre- stricted Hartree-Fock method (UHF)x with SBKJC basis set to evaluate energy parameters of nanoobjects, which include gold atoms with many electrons. It was found that the general structure of the energy spectra changes unsignif- icantly if the number of atoms is greater than 27. Moreover, the size of the energy gap and the position of energy levels in it are linear functions of one parameter—the total electric charge of the nanoparticle. These features of energy spectra allowed us to perform calculations of the transport charac- teristics for a real SET using gold nanoparticle as a central conducting island.

The Y3d, Ba3d 5/2, Cu2p 3/2, and O1s X-ray photoelectron spectra of thick (600 nm) superconducting YBa2Cu3O7 − δ films deposited on textured Ni-W substrates with Y2O3 + ZrO2 and CeO2 buffer layers have been studied. It has been established that, after the mechanical removal of surface layers with a diamond scraper (and as the analyzed region of the film approaches the interface), a decrease in the oxygen content leads to a decrease of the orthophase fraction and an increase of the tetraphase and Cu+ ion fractions. This is caused by the presence of elastic stresses in the superconducting film due to the lattice misfit between the phases making up a composite sample. These stresses prevent oxygen diffusion involved in oxidizing annealing. The spectra of the superconducting film have not revealed signals generated by elements of the substrate and buffer layers.

The degradation processes of YBa2Cu3O6.77(3) films 600 nm thick deposited on substrates from a textured (100) foil of the Ni-W alloy with the YSZ (Y2O3 + ZrO2) (100 nm) and CeO2 (50 nm) buffer layers at 200°C in air have been investigated. It has been shown that the degradation proceeds in the same manner as in the bulk ceramic materials with the same oxygen content, namely, initially the single-phase material with the orthorhombic structure laminates into the fractions depleted (the main fraction) and enriched with oxygen. After holding for more than 20 h, the oxygen-depleted fraction is first subjected to the structural phase transformation with the transition of the orthorhombic structure into the cubic one, which is associated with the redistribution of barium and yttrium atoms over their sites in the presence of water vapors.

The structure of buffer layers and deposited YBa2Cu3O x (Y123) films with a high critical current density (∼106 A/cm2) has been investigated by different methods. These superconducting films and buffer layers are found to have a fine-grained structure, which, along with the high texture of Y123 films of the (001) type, is believed to be responsible for the high critical current density. An unusual texture is revealed in buffer layers, which differs from that of substrates and Y123 films. The superconducting films deposited on buffer CeO2 layers exhibit a system of orthogonal lines; in the case under consideration, this is a manifestation of a domain structure with Y123 particles at boundaries.

The growth of the hightemperature supercondu ctors (HTSCs) on flexible films for the fabrica� tion of nanoelectronic devices is considered. A method for the creation of the HTSC films on the nickel- tungsten substrates is proposed. The deposition of the CeO2 and YBCO epitaxial films that are grown on short substrates made of flexible nickel-tungsten ribbon manufactured using the RABiTS technology is compre� hensively analyzed, and the properties of the resulting HTSC films are studied. The electrophysical properties of the HTSC films on flexible substrates are demonstrated.

Electroluminescence intensity of single CdSe nanocrystals (NCs) excited by the tunnel current of a scanning tunneling microscope (STM) was measured. Samples with NCs do not exhibit plasmon emission. This enables one to measure pure emission from a single NC. Electroluminescence, measured in time, differs considerably from that of photoluminescence in similar NCs. This difference in temporal behavior results from the difference in physical conditions of experiments on photo- and electroluminescence.

A method for determination of the mutual effective capacitance for molecules, molecular clusters, and nanoparticles on the basis of the quantum-mechanical calculation of the interaction energy of nanoscale charged objects is proposed. The mutual effective capacitance for pairs of similar molecules (carborane C2B10H12, fullerene C60, and molecular cluster Pt5(CO)6(PPh3)4) with a size of 0.3 to 0.7 nm is calculated for distances between these molecules from 2 to 20 nm. It is demonstrated that this method makes it possible to determine the scale of distances between nanoobjects for which it is necessary to take into account quantum corrections.

In our study, we constructed a ultra-low field (ULF) nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI) system employing a high-temperature superconductor (HTS)-rf-SQUID and room-temperature coils. In the system, we employed a pulsed polarizing field Bp perpendicular to a measurement field Bm; a high-speed switching circuit with an optical FET was used to switch off Bp of approximately 30 mT. When a field gradient dBz/dz of approximately 10 nT/cm was applied to a sample, which was designed to contain water in two compartments, a 1H-NMR spectrum with two peaks was observed. The frequency difference between the two peaks roughly corresponded to the distance between each center of the water in the two parts. We measured the 1H -NMR signals for water and mineral oil and found a clear difference in their signal amplitudes owing to their different molecular compositions. The longitudinal relaxation times T1 of water and the oil were also estimated by changing the polarizing time of Bp. From these results, it was confirmed that 1H- and T1-weighted contrast imaging could be realized by using this system.

We constructed and studied an ultra low-field nuclear magnetic resonance imaging system using a HTS rf SQUID and room-temperature coils. We recorded the free induction decay signals of 1H by employing a measuring field, Bm, of 44.8 μT and a polarizing field, Bp, of 36.8 mT; in the presence of ∂BZ/∂z and ∂BZ/∂y gradients of the order of 0.8 μT/m, we were able to obtain a quasi two-dimensional 4-pixels image of a simple water phantom.

Gaps with a size of less than 5 nm have been fabricated in 15-nm-thick and 200-nm-wide gold strips deposited on sapphire substrates. Preparation conditions providing a sufficient adhesion of such electrodes as well as the parameters for the electromigration process used to fabricate the gaps have been found which allow a successful gap implementation. Such gaps transform gold strips to the source-drain electrodes of planar single electron transistors based on nanoparticles or molecules.

An operating prototype model of an electronic gradiometric system based on three high-sensitivity high-Tc (HTS) SQUID magnetometers is developed, fabricated, and studied. A dynamic range of 140 dB implemented in the system provides its stable operation in an unshielded space with a sensitivity level of about 8 fT/cm2 Hz1/2. The ultimate sensitivity of the system, which can be attained either at large distances from man-made noises or in a weakly shielded space, is 4 fT/cm2 Hz1/2. This value is equivalent to 100 fT/Hz1/2 reduced to the sensitivity of a single SQUID magnetometer. The operating frequency band of the system is from 1 Hz to 15 kHz. The developed system, which is based on three HTS SQUIDs, can be successfully used in its present configuration in geophysical studies performed under field conditions and in magnetometric methods of nondestructive evaluation of materials.

The new variant of DC SQUID modulation electronics for functioning with HTS DC SQUID magnetometers in the unshielded environment, was designed, manufactured and tested. The electronics was optimized for operation with new ultrasensitive HTS DC SQUID magnetometer providing magnetic field resolution of about 15 fT/radicHz at frequencies above 10 Hz and 30 fT/radicHz at 1 Hz. The central commutation core of electronics was based on a complex programmable logic device (CPLD). It has allowed to include into the SQUID-electronics the flexible system of a bias reversal which provides a stable magnetometer operation for various configurations of wiring in the cryostat and various HTS DC SQUID topologies. The electronics was manufactured in one compact box with size 110 mm times60 mm times 15 mm. The channel has standard bandwidth of about 100 kHz with greatly increased dynamic range due to high coupling (8 mV/Phi0) of feedback signal with main SQUID's loop.

The method of SQUID-based relaxometric diagnostics has been applied to the ensembles of non-interacting near-spherical Fe3O4 and Co nanoparticles in order to reveal the behavior of the anisotropy constant upon varying the molecular surrounding of nanoparticles by using different polymer matrices. The transmission electron microscopy (TEM) and X-ray diffraction techniques have been employed to obtain the structural information about objects of study. The relaxation curves measured with the SQUID-relaxometer in the time range from about 50 s to several tens of seconds after application of a pulse of low dc magnetizing field have been approximated by theoretical dependences calculated within the framework of activation Néel–Arrhenius law with account for the size distribution functions retrieved from TEM data. From results of approximations, the values of anisotropy constant have been determined.

SQUID electronics optimized for operation in unshielded space with dc high-Tc superconducting quantum interference devices (HTS SQUIDs) are developed, manufactured, and studied. The dynamic characteristics of the SQUID electronics are studied with two magnetic-field sensors based on the HTS SQUIDs: a conventional SQUID sensor with a resolution of 100 fT/Hz1/2 and a supersensitive SQUID sensor with a resolution of 15 fT/Hz1/2 at frequencies exceeding 10 Hz and a resolution of 30 fT/Hz1/2 at a frequency of 1 Hz. Stable operation of the magnetometric channel is demonstrated with both SQUID sensors under urban conditions. On the basis of a complex programmable logic device (CPLD), an ac bias can be realized in the SQUID and the modulation signal can be compensated in the feedback, bias-current, and desired-signal circuits. Such a compensation system is the most appropriate and versatile means of providing stable operation of the magnetometric channel in the presence of the SQUID ac bias, regardless of the type of high-temperature sensor and the configuration of the input contacts in the measurement probe.

A laboratory prototype RF amplifier for the frequency range 1–10 GHz is designed, created, and tested. The device is based on high-temperature superconducting quantum interference filters (SQUIFs) and the technology of bicrystalline substrates. The main characteristics of the prototype SQUIF amplifier are numerically simulated and measured.

We have developed a new method for the determination of the anisotropy constant and saturation magnetization of magnetic nanoparticles. This method deals with the approximation of magnetization relaxation curves measured upon application and further fast switching off the dc magnetizing field. The relaxation process is registered in the time interval from 6 μs to several minutes by using a scanning high-T C SQUID-microscope equipped with a specially designed electronic circuit composed of a fast solid-state switch and a low-inductance magnetizing coil. The algorithm for calculating the approximation data is based on the activation Neel–Arrhenius law and takes into account the size distribution of the nanoparticles and the angular distribution of their easy axes. The performance of the method is demonstrated on dilute (∼0.2 vol%) ensembles of near-spherical Fe3O4 nanoparticles with a mean size of 7.7 nm and a standard deviation of 45% as determined from transmission electron microscopy data.

The superconducting quantum interference filter (SQIF) is a new type of superconducting device which has been recently proposed for highly sensitive magnetometers for absolute magnetic field measurements. It benefits of very high voltage-to-field response, which is, in contrast conventional dc SQUIDs, not periodical. The SQIF can also be used as a radiofrequency amplifier in a similar way as the dc SQUID that can operate in a gigahertz frequency range. We designed a series type of SQIF amplifier that is compatible to conventional YBa2Cu3O7 (YBCO) technology on bicrystal substrates. We present analytical, numerical and scale modeling as well as first electrical measurements results at frequencies up to 10 GHz. The SQIF array consists of 50 loops with randomly distributed areas from 0.5 to 1.5 times of . We also compared it to the regular array of conventional SQUIDs with the same loop areas. We have additional dc contacts to each 5-th SQUIDs and the SQIFs for control and comparison. Devices are fabricated using Josephson junctions with 3 mum width formed in YBCO over 24/24 and 12/12 degrees grain boundaries in yttrium-stabilized zirconia (YSZ) bicrystal substrates.

An optimized picoamperemeter based on a superconducting quantum interferometer device (SQUID) for a metal cold-electron bolometer is fabricated and experimentally studied. The intrinsic SQUID current noise caused by the input coil is estimated to be less than 1 pA/Hz1/2. Owing to the application of modulation electronics, current sensitivity in the input coil reaches 5 pA/Hz1/2 in the frequency band from 10 Hz to 10 kHz.

High- T C scanning SQUID magnetometer is applied for measuring the magnetization relaxation of the ensembles of spherical colloidal Fe 3 O 4 nanoparticles dispersed in the rigid polymer matrix preventing nanoparticles from agglomeration. According to the transmission electron microscopy data, the size distribution of nanoparticles is well described by the Gaussian profile with the mean size and the dispersion of about 7.5 and 2.3 nm, respectively. High sensitivity of SQUID magnetometer allows us to study samples at low contents of the magnetic component (0.1–1.0 vol%) magnetized in low magnetic field (∼10 –4 T) produced by a low-inductance coil with short switching time (12 μs). A low content of the magnetic component provides the absence of interparticle dipolar interactions, thus simplifying significantly the theoretical description of the magnetization relaxation process. The measured magnetization relaxation curves are found to be in reasonable agreement with the numerical simulation data.

HTS SQUID microscopy is applied for measuring the magnetization relaxation of the ensembles of noninteracting Fe/sub 3/O/sub 4/ nanoparticles dispersed in rigid polymer matrix preventing nanoparticles from agglomeration. Transmission electron microscopy (TEM) is used to determine the size distribution of magnetic nanoparticles and to control the homogeneity of their spatial distribution in the matrix. High sensitivity of SQUID microscope allows us to study samples at low contents of the magnetic component (0.1-0.5 vol%) magnetized in low magnetic field (/spl sim/10/sup -4/ T) produced by a low-inductance coil with short switching time (20 /spl mu/s). A low content of the magnetic component provides the absence of interparticle dipolar interactions, thus simplifying significantly the theoretical description of the magnetization relaxation process. The detection of magnetization relaxation starts after the external magnetizing field is switched off and proceeds for several minutes. A series of samples with a mean size of nanoparticles of about 7 nm possessing relaxation times less than 5 min was measured at a temperature of 77 K. The calculation formula based on the Stoner-Wohlfarth model for single-domain particles with a size distribution as determined from the TEM images will enable to obtain reliable data on the anisotropy constant and the saturation magnetization of Fe/sub 3/O/sub 4/ nanoparticles studied.

We have developed a program running on the Windows platform which enhances the quality of two-dimensional images acquired by a scanning SQUID microscope. The program can also be used for image processing of data from other SQUID based systems, such as eddy current SQUID NDE systems. A general description of the program and the incorporated additional digital filters for removing image artifacts in the Fourier space is given. The user interface is presented as well as several examples of this software applications to real images.

A technique for the calculation of current-to-voltage curves and control curves of a molecular single-electron transistor with a discrete energy spectrum has been developed. The effective recursive methods for quick computation of the Gibbs canonical distribution of electrons between energy levels, as well as techniques for the fast calculation of the distribution function for a slow relaxation process have been found. Characteristics of the single-electron transistor in the cases of different types of molecule's energy spectrum, fast and slow energy relaxations have been compared.

Electroluminescence from a single CdSe nanocrystal (NC) excited by the tunneling current of a scanning tunneling microscope (STM) is measured. Such samples produce no plasmon emissions. This allows us to measure pure signals from nanocrystals. The time dependence of electroluminescence differs from the photoluminescence of an identical nanocrystal because of different physical processes of excitation.

We have developed a technological process for fabrication of YBa 2 Cu 3 O x (YBCO) submicron wide Josephson junctions (JJ) on bicrystal substrates. This process is based on e-beam lithography and ion beam etching of YBCO films through carbon masks. A series of JJ with 0.4–1 μm width have been fabricated on SrTiO 3 bicrystal substrates with misorientation angles θ =24° and 36.8° using this process. The analysis of the current–voltage characteristics of the fabricated junctions at high bias currents supports the model of electrons tunneling through the localized states (LS) formed in the barrier region. The approximation of experimental data on white noise of the junctions by theoretical formula, which represents the contribution of thermal noise as well as shot noise, shows that tunnel mechanism of electrons transport through the LS greatly dominates a normal metallic one.

A scanning HTS SQUID microscope for magnetic imaging samples at room temperature and atmospheric pressure has been developed. A sensor for the microscope was completed by a bicrystal dc SQUID and a needle made of soft magnetic material, which serves as a magnetic flux guide (MFG). This sensor has allowed magnetic imaging of the warm samples with spatial resolution of the order of 100 μm. Line scans of magnetic field produced by the current-carrying wires are measured and compared with results of a numerical modeling. The influence of the MFG on the image details has been studied.

An experimental investigation of high-temperature dc SQUID amplifier connected in series with a high-Tc superconductor (HTS) thin-film band-pass filter is presented. The SQUID amplifiers are designed with microstrip input coils and fabricated on bicrystal substrates of zirconia and sapphire with different misorientation angles of 24 and 37. SQUID parameters are optimized to attain 50-X input impedance for the 1500 MHz central frequency range. The maximum power gain of the amplifier with six turn input coil was measured to be 6 dB at 800 MHz and 4.5 dB at 1750 MHz. Thin-film HTS YBCO filters are based on a band-pass quasi-elliptic prototype consisting of a set of parallel tank circuits connected to a shunt and separated by admittance inverters. The central frequency of the band-pass filter was adjusted close to 1750 MHz amplifier frequency with 4% bandwidth. The natural combination of a high-Tc SQUID amplifier with a HTS band-pass filter allows the reduction of out-of-band noise and optimization of amplifier performance,and demonstrates compatibility with practical components of front-end receiver subsystems. 2001 Elsevier Science B.V. All rights reserved.

Magnetic properties of amorphous ferromagnetic wires serving as a magnetic flux guide for the high- T c SQUID microscope are investigated. A mathematical model of a flux guide operation was developed on the base of integral equation methods. It is shown that when the flux guide is used in combination with the SQUID the integral of magnetic potential along the flux guide is the main measured value. Experimental results received with the use of the scanning high- T c SQUID microscope for liquid-nitrogen cooled samples are in good agreement with the proposed model.

Magnetic, structural and electronic properties of Langmuir–Blodgett films with incorporated Gd 3+ ions has been detected using a scanning DC SQUID microscope, scanning electron microscope and X-ray diffraction. The magnetic images of 28 and 50 layer thick films at 77 K have been obtained after in-plane and out-of-plane pre-magnetization in a field of 1.4 T at 300 K. Randomly placed “magnetic volcanos” with a remanent magnetic moment of the order of 10 −13 A m 2 was observed. A decay of the remanent magnetization with a characteristic time of about 120 h was observed. It is suggested that the magnetic order is relatively long ranged, and that topological defects (vortices) lead to the observed out-of-plane field lines, and are responsible for the magnetic volcanos. Finally, it is hypothesized that a similar topology of field lines is responsible for superconductivity as observed in ceramic high- T C superconductors.

A description is given of the design, fabrication technology, and characteristics of a sensor for a scanning magnetic microscope using a thin-film dc SQUID with Nb/Al2O3/Nb shunted Josephson tunnel junctions. It is shown that at a sample temperature of 4.2 K the spatial resolution of this detector is 10 µm with a field resolution of 70 pT/Hz1/2.

We have applied a dc SQUID based microscope to study surface magnetization of a Ho single crystal at 77 K in parallel (up to 0.4 kA/m) and perpendicular (up to 0.1 kA/m) magnetic fields. Magnetization curves and the topographic maps of the magnetic field distribution near the polished surface [0001] of the crystals have been recorded with a spatial resolution better than 50 /spl mu/m. Qualitative evidence for ferromagnetic ordering at the [0001] surface have been found.

A method is presented for the deposition of smooth epitaxial high-T c superconducting films using a pulsed infrared YAG: Nd3+ laser and velocity filtration. This method is based on the removal of drops and solid particles from the flow of deposited substance with a fast shutter made of a rotating disk. The deposited smooth homogeneous YBa2Cu3O7−δ films have a critical temperature T c > 90 K. The surface concentration of drops is less than 3 × 102 cm−2, and their amount is decreased by more than six orders of magnitude.

The magnetic properties of Au/Ni/Si(100) films with Ni thicknesses of 8–200 A are studied at T=77 K using a scanning magnetic microscope with a thin-film high-temperature dc SQUID. It is found that the Ni films, with an area of 0.6×0.6 mm, which are thicker than 26 A have a single-domain structure with the magnetic moment oriented in the plane of the film and a saturation magnetization close to 0.17 MA/m. For films less than 26 A thick, the magnetization of the film is found to drop sharply.

A technique for quantitative determination of the ultrathin films volume magnetization in the in-plane magnetizing field up to 10 4 A/m has been developed. This technique uses a scanning SQUID microscope with the YBCO thin film bicrystal dc SQUID and allows us also to reveal the orientation of the sample magnetization. A spatial resolution of about 100 μ m and a field of view of 8×8 mm 2 have been obtained. The resolution in terms of the magnetic moment of the studied film was close to 10 −15 Am 2 /Hz 1/2 at 1 Hz.

The integrated version of a two stage dc SQUID-based low frequency amplifier has been designed, fabricated and tested. The value of the gain of the applied flux d/spl Phi//sub SQ2//d/spl Phi//sub SQ1/ in the range 30-70 and an overall flux-to-voltage transfer factor d/spl Phi//sub SQ2//d/spl Phi//sub SQ1/ as high as 3 mV//spl Phi//sub 0/ have been obtained. An effective input inductance L/sub IN/ equal to 1.8 /spl mu/H, a current sensitivity 1.33 /spl mu/A//spl Phi//sub 0/, and an effective coupling coefficient k/sup 2//sub IN/ close to 0.1 have been found in the accordance with the design.

Scanning SQUID microscopy has been extended to record current-induced magnetic field maps of superconductor topologies based on YBCO film structures. The technique described can be used as a powerful tool for the diagnostics of superconductor integrated circuits and highly sensitive bolometers. This kind of diagnostics predicts the degree of integration which can be achieved at the modern level of HTSC microelectronics technology. One would expect an overall yield of 100-element chips at a level of in the production of superconducting YBCO/MgO bolometers.

A low-volume, high-performance, direct-coupled electronic system for high-T/sub c/ dc SQUID magnetometers has been developed and tested. This system is based on a liquid nitrogen-cooled amplifier and a modified integrator. The amplifier has a white noise voltage level close to 0.25 nVHz/sup - 1/2 /, a current noise of the order of 3 pAHz/sup - 1/2 /, a gain equal to 3000, a 3 dB bandwidth of about 370 kHz, and a package volume less than 3 cm/sup 3/. The modified integrator has an input resistance of the order to 10 k/spl Omega/ and a considerably high output drive current of about 30 mA. This unique combination results in the typical electronic 3 dB bandwidth of about 1 MHz, a dynamic range of /spl plusmn/5/spl times/10/sup 6/ Hz/sup - 1/2 / for frequencies up to 1.6 kHz, and a slew rate of 1/spl times/10/sub 6/ flux quanta/s in a wide signal frequency range for a middle-quality high-T/sub c/ dc SQUID sensor.