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Heterointegration of graphene with silicon has attracted growing interest, because the resulting unique heterojunction allows for efficient collection of light generated electron–hole pairs. This study aims to understand the role of device fabrication conditions and electronic properties of chemically doped graphene on the efficiency variations and stability of graphene/silicon solar cells. We observed significant variations in the efficiency between the devices doped with metal chloride and organic molecules. A strong degradation in the hole carrier mobility by the formation of metal particles/clusters, which could act like charge puddles, accounts for the limited efficiency in the former. Molecular doping, on the other hand, offered good doping homogeneity and no mobility degradation, leading to solar cells with efficiency as high as 9.2%. Our results demonstrate that the droop in efficiency over time observed in the chemically doped devices is due to oxidation limited charge carrier separation rather than doping reversal. The prospects of molybdenum oxide (MoOx) as a multifunctional layer in improving the device stability and efficiency are also discussed based on preliminary experimental findings. [ABSTRACT FROM AUTHOR]

Research was conducted on the implications of the growth rate of a GaN buffer layer grown on a GaN epilayer. Findings show that a significant role is performed by the growth rate in the improvement of the quality of the GaN film on a sapphire substrate. Also, the optimum growth rate which yields the best quality was discovered. The promotion of the lateral growth mode illustrate the improvements in the qualities of the GaN film.

Research was conducted to examine the photoluminescence of undoped GaN grown on a sapphire substrate. The layers were grown using the rotating disk metal organic chemical vapor deposition technique. Excitonic transitions were observed from conduction band to spin-orbit split valence bands. The activation energy of the free exciton was derived and the optical band gap of GaN was deduced.

Photoluminescence measurements were performed on magnesium doped GaN epitaxial layers deposited by metal-organic chemical vapor deposition on sapphire substrate. Measurements were taken at a temperature range of 12-300 K. Several transitions related to donor to acceptor and their phonon replicas, conduction band to acceptors, and free excitons were observed. Two types of acceptors, one was deep, the other shallow, were also identified.

This study presents an optimization of the detection coil of high-Tc superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) in microtesla fields for discriminating a minimum amount of liver tumor in rats by characterizing the longitudinal relaxation rate, T1-1, of tested samples. The detection coil, which was coupled to the SQUID through a flux transformer, was optimized by varying the copper wires' winding turns and diameters. When comparing the measured NMR signals, we found that the simulated NMR signal agrees with simulated signals. When discriminating liver tumors in rats, the averaged longitudinal relaxation rate was observed to be T1-1 = 3.3 s-1 for cancerous liver tissue and T1-1 = 6.6 s-1 for normal liver tissue. The results suggest that it can be used to successfully discriminate cancerous liver tissue from normal liver tissues in rats. The minimum amount of samples that can be detected is 0.2 g for liver tumor and 0.4 g for normal liver tissue in 100 μT fields. The specimen was not damaged; it can be used for other pathological analyses. The proposed method provides more possibilities for examining undersized specimens. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the field-dependent T1-relaxation and T1-contrast imaging of ferrofluids using high-Tc superconducting quantum interference device (SQUID)-detected nuclear magnetic resonance and imaging in low magnetic fields, where T1 is the spin-lattice relaxation time. It was found that the 1/T1 of ferrofluids increases when the prepolarization field increases. We attribute this to the enhanced magnetic-field gradients generated from the induced magnetization that accelerates the T1-relaxation more in a high strength of fields in comparison to a low strength of fields. Using phantoms with different relaxation times, the T1-contrast images are demonstrated in low magnetic fields, which can be promising for discriminating tumors. [ABSTRACT FROM AUTHOR]

Shortening spin-lattice relaxation rates (1/T1) or spin-spin relaxation rates (1/T2) is the purpose of magnetic resonance imaging contrast agents. In this work, an ultralow field nuclear magnetic resonance spectrometer and imager are set up to characterize the spin relaxation rates of Fe3O4 superparamagnetic iron oxide (SPIO) for image contrast. It was found that both 1/T1 and 1/T2 increase linearly when the magnetic susceptibility χ of SPIO increases by increasing the concentration of SPIO dispersed in water. In an applied field, magnetic moments of SPIO generate microscopic field gradients that weaken the field homogeneity, in turn de-phasing the proton's nuclear spin and enhancing the relaxation rates. A T1-contrast image is demonstrated, using SPIO as the contrast agent and high-Tc superconducting quantum interference devices as the detector. T1-contrast imaging in microtesla fields might provide a potential modality for discriminating cancer. [ABSTRACT FROM AUTHOR]

In this study, we present a compact and sensitive SQUID-detected nuclear magnetic resonance spectrometer and imager (NMR/MRI) using flux coupling in microtesla fields. The pre-polarization coil, measuring coil, pulsed coil, and gradient coils were set up inside a three-layer aluminum box while the SQUID-detector was shielded with a high-Tc superconducting vessel. A compensation field was applied to improve the field homogeneity in magnetically unshielded environments. The spin precession of protons was inductively coupled to the SQUID magnetometer via a resonant flux transformer. We obtained a signal-to-noise ratio of 120 in one measurement, a spectral resolution better than 1 Hz, and a spatial resolution of 1.3 mm in the images. [ABSTRACT FROM AUTHOR]

The dislocations and the strength of a nickel bicrystal are investigated in present study. There are three kinds of crystalline orientations of the nickel bicrystal, namely (100), (110), and (111). Misfit dislocations are presented on the interface between two nickel grains when a compression process is utilized on the bicrystal. The misfit dislocations on a Ni(100) interface form a square-latticed network and those on a Ni(111) form a triangle-latticed network. When a large twist angle is applied to the Ni bicrystal, the square- and triangle-latticed unit of the misfit dislocation networks will shrink or even disappear. Thus, a plane defects distribute over the interface. If the bicrystal is compressed further, dislocations within each grain are developed from the defects on the interface between grains. The configuration of the dislocations within grains is more regular when the applied twist angle is smaller. A Ni(111) bicrystal owns the largest amount of maximal stress no matter what the twist angle is. Those of a Ni(110) bicrystal is the second and of a Ni(100) bicrystal is the smallest. [ABSTRACT FROM AUTHOR]

Superconducting quantum interference device (SQUID), which is a very sensitive magnetic sensor, has been widely used to detect the ultra-small magnetic signals in many different territories, especially in the biomagnetic measurement. In this study, a 128-channel SQUID first-order axial gradiometer system for whole-head magnetoencephalography (MEG) measurements was setup to characterize the auditory evoked magnetic fields (AEFs). A 500 Hz monaural pure tone persisting 425 ms with the sound pressure level of 80 dB was randomly applied to the left ear of subject with the inter-stimulus interval of 1.5 ∼ 2.8 s to prevent fatigue of nerves. We demonstrated the characteristic waveforms of AEFs can be accurately recorded and analyzed. Using source localization processes, the origins of AEFs were successfully calculated to be at the auditory cortices which are brain areas known for responsive to sound stimulus. A phantom experiment also proved the good localization accuracy of the established MEG system and measurement procedures. The validated performance of the SQUID system suggests that this technique can also be employed in other brain research. [ABSTRACT FROM AUTHOR]

A nuclear magnetic resonance and imaging system was constructed to study spin-lattice relaxation time T1, spin-spin relaxation time T2, and effective relaxation time T2* of gadolinium (Gd) chelates using a high-Tc superconducting quantum interference device in microtesla magnetic fields. In the presence of the magnetic contrast T2* is related to T2 by the relation: 1/T2*=1/T2+γΔB+ΓGd-chelates, where γ=42.58 kHz/mT and γΔB is the relaxation rate due to the inhomogeneity field ΔB in measuring coil at the sample position and ΓGd-chelates is the intrinsic relaxation rate of Gd chelates. It is found that T1, T2, and 1/ΓGd-chelates decay exponentially as the concentration (or magnetic susceptibility) of Gd chelates increases. The Gd chelates cause a diffusive motion of nuclear spins and hence enhance the relaxation rates. Enhanced image contrast has been demonstrated in a water phantom with Gd chelates in microtesla magnetic fields. [ABSTRACT FROM AUTHOR]

The dual first-order planar gradiometers of high transition temperature (high-Tc) superconducting quantum interference devices (SQUIDs) were designed and fabricated on a 10×10 mm2 SrTiO3 bicrystal substrate. Each gradiometer consists of four bare SQUIDs which are connected to two symmetric pickup loops. Any two of the SQUIDs can be connected in series to obtain better performance. In this study, by selecting the coupling direction of SQUID, a balance resolution of 0.08% was achieved. And, a second-order electronic planar gradiometer was composed of these two first-order gradiometers. Experimental data showed that the noise performance of the second-order electronic planar gradiometer composed of two planar first-order gradiometers can reach 15 μ[uppercase_phi_synonym]0/Hz1/2 at 1 kHz in an unshielded environment, which is comparable to the noise level of a magnetometer in a shielded environment. [ABSTRACT FROM AUTHOR]

A high-temperature superconducting (HTS) radio-frequency (rf) coil has been proposed as a promising tool in the investigation of tissue microscopy with high resolution due to its low-resistant characteristic for magnetic resonance (MR) probe design. In this work, a 200 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape HTS rf coil was built; and a signal-to-noise ratio (SNR) with the HTS tape coil having 2.22 folds higher than that of a home-made copper coil for a phantom MR study was demonstrated. Testing results were in agreement with predicted ones, and the difference between the predicted SNR gains and measured SNR gains is 0.9%. Using in vivo imaging, a SNR with the HTS tape coil having 1.95 folds higher than that of a home-made copper coil for a human hand MR study was presented. The HTS coil is expected to generate a higher SNR gain after optimization. Further applications of a functional magnetic resonance imaging system are under investigation to test the applicability of this HTS coil system in a 3T system. [ABSTRACT FROM AUTHOR]

Via immunomagnetic reduction assay, biomolecules can be quantitatively detected with aid of biofunctionalized magnetic nanoparticles, which are used as labeling markers for specific biomolecules. To achieve ultra-high sensitivity in detecting biomolecules, superconducting quantum interference device (SQUID) is a promising candidate to act as a sensor to the magnetic signal related to the concentration of detected biomolecules. In the past, we developed a single channel SQUID-based magnetosusceptometry. In order to increase the detection through-put, multichannel SQUID-based magnetosusceptometry is developed. In this work, the design and working principle of four-channel SQUID-based magnetosusceptometry are introduced. Using utilizing scanning technology, four samples can be simultaneously logged into the SQUID-based magnetosusceptometry. Notably, only single SQUID magnetometer is used in the magnetosusceptometry. The precision and sensitivity in detecting biomolecules using the four-channel SQUID-based magnetosusceptometry are investigated. [ABSTRACT FROM AUTHOR]

In this work, we present a design that improves signals produced by nuclear magnetic resonance (NMR) and magnetic resonance imaging by using optical pumping and a high-Tc superconducting quantum interference device (SQUID) magnetometer. In our design for a NMR detection system, a pickup coil is coupled to the spin procession of a 3He nucleus; the input coil is coupled to a high-Tc SQUID magnetometer; and the capacitor is connected in series to form a tank circuit resonating at the Larmor frequency of the 3He nucleus in the measuring field. A signal-to-noise ratio gain of 2.67 over a conventional Faraday detection coil was obtained with the high-Tc SQUID detection system in a measuring magnetic field equaling 0.1128 mT, at which the central frequency was 3.66 kHz for 3He nucleus. The improvement in the NMR signal for large-size, hyperpolarized 3He coupled to a high-Tc SQUID-based spectrometer in low magnetic fields at room temperature is significant compared to that without flux coupling. This result may be of interest given its potential for use in a low field imager. [ABSTRACT FROM AUTHOR]

In this paper, an overview of the current status of high-Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high-Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high IcRn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High-Tc SQUID magnetometers exhibiting magnetic field sensitivity of ∼30–50 fT/Hz1/2 or better at 100 Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high-Tc SQUIDs are addressed. [ABSTRACT FROM AUTHOR]

We report on the fabrication of organic field-effect transistors (OFETs) using perylene single crystal as the active material and their electrical characteristics. Perylene single crystals were directly grown from perylene powder in a furnace using a relatively short growth time of 1–3 h. The crystalline structure of the perylene single crystals was characterized by means of a single-crystal x-ray diffractometer. In order to place the perylene single crystal onto the Au electrodes of the field-effect transistor, a polymethlymethacrylate thin layer was spin-coated on top of the crystal surface. The OFETs fabricated using the perylene single crystal showed a typical p-type operating mode. The field-effect mobility of the perylene crystal based OFETs was measured to be ∼9.62×10-4 cm2/V s at room temperature. The anisotropy of the mobility implying the existence of different mobilities when applying currents in different directions was observed for the OFETs, and the existence of traps in the perylene crystal was found through the measurements of the temperature-dependent mobility at various operating drain voltages. [ABSTRACT FROM AUTHOR]

The parameters to optimize the measurement of longitudinal relaxation time detection using a high-Tc superconductive quantum interference device magnetometer are investigated. These parameters include the prepolarization field, Bp, the prepolarization time, TBp, and the delay time, Td, to turn on pulses after turning off the prepolarization field. Furthermore, the decreasing of magnetization with the increasing Td of the applied pulse was analyzed to determine the longitudinal relaxation time. We estimated the longitudinal relaxation time to be 2.11±0.04 s and 2.29±0.04 s, respectively, for water determined from nuclear magnetic resonance signals as a function of TBp and Td at 24 °C in a measuring field of 95 μT. The data are consistent with the derived longitudinal relaxation time of water measured from the increase of magnetization with the duration of the polarizing field. [ABSTRACT FROM AUTHOR]

We characterized the current-voltage, voltage-flux, and the field sensitivity of integrated high-Tc series superconducting quantum interference device (SQUID) magnetometers and gradiometers. The series two-SQUID magnetometers shows field sensitivities of ∼30–40 fT/Hz1/2 at 1 kHz and ∼80–100 fT/Hz1/2 at 1 Hz over that of a one-SQUID magnetometer in shielded environment. The field sensitivity of a series two-SQUID gradiometers is ∼60 fT/Hz1/2 cm, while the one-SQUID gradiometer shows a gradient sensitivity of ∼80–150 fT/Hz1/2 cm at 1 kHz in an unshielded laboratory environment. The series two-SQUID magnetometers or gradiometers show a significant improvement in flux noises over that of one-SQUID magnetometers or gradiometers. [ABSTRACT FROM AUTHOR]

In this work, we studied the engineering of high-transition-temperature superconductor Josephson junctions and superconducting quantum interference device (SQUID) by using step-edge or the bicrystal grain-boundary technologies. Serial Josephson junctions and bare SQUID array reveal high quality device characteristics. A high-Tc SQUID magnetometer exhibiting magnetic field sensitivity of 33 fT/Hz1/2 in the white regime and 80 fT/Hz1/2 at 1 Hz was demonstrated by incorporating the flux dams and serial SQUID into the pickup loop of magnetometer. Furthermore, we demonstrate the opening of the flux dams by applying an external magnetic field to induce a current higher than the critical current of the serial flux dams. We show that the serial flux dams effectively suppress the low frequency 1/f-like noises. [ABSTRACT FROM AUTHOR]

The article presents a new nuclear magnetic resonance and imaging system that can be employed for determining the relaxation rates of the protons present in gadolinium chelates. The chelates are shown to lead to the onset of a diffusive motion of the nuclear spins, hence leading to an increase in the relaxation rates.

The design and working principle of four-channel superconducting quantum interference device (SQUID)-based magnetosusceptometry which could be used as a sensor to the magnetic signal related to the concentration of detected biomolecules is reported. A study related to the precision and sensitivity of the four-channel SQUID-based magnetosusceptometry to detect biomolecules is also discussed.

A design is described that has improved the signals produced by nuclear magnetic resonance (NMR) and magnetic resonance imaging by using optical pumping and a high-[T.sub.c] superconducting quantum interference device (SQUID) magnetometer. The high sensitivity of the SQUID-based spectrometer and the high magnetization of hyperpolarized noble gas is combined to perform a high resolution magnetic resonance imaging (MRI) of [super 3]He in lung imaging.

The current status of high-[T.sub.c] superconducting quantum interference devices (SQUIDs) is discussed. High-[T.sub.c] SQUID magnetometers displaying magnetic field sensitivity of 3-50 fT/[Hz.sup.1/2] is shown by incorporating serial SQUID into the pickup loop of the magnetometers.

The characterization of different electrical properties of integrated high-[T.sub.c] superconducting quantum interference device (SQUID) magnetometers and gradiometers is presented. The series two devices are found to exhibit better flux noises than the series one devices.

The engineering of high-transition-temperature superconductor Josephson junctions and superconducting quantum interference device (SQUID) is studied using step-edge or the bicrystal grain-boundary technologies. Results reveal that serial Josephson junctions and bare SQUID array reveal high quality device characteristics.

Here, a report on diffusion tensor imaging (DTI) using a 125.3 MHz high-temperature superconducting (HTS) surface resonator for magnetic resonance imaging (MRI) is presented. A 40 mm in diameter Bi2Sr2Ca2Cu3Ox (Bi-2223) tape surface resonator was built. Using a HTS surface resonator at 77 K than a similar copper surface resonator at 300 K, the capacity to save the accuracy of DTI in a reduced scan time (11 min) was demonstrated. The standard deviation of deviation angles of DTI fiber tracking was also improved by 2.5 gains. The use of HTS surface resonator may improve the reliability of fiber tracking experiments. [ABSTRACT FROM AUTHOR]