K Char - Academia.edu (original) (raw)
Papers by K Char
Physical Review B, 1994
Half-integral constant voltage steps were observed in many high-Tc grain-boundary Josephson junct... more Half-integral constant voltage steps were observed in many high-Tc grain-boundary Josephson junctions of YBa2Cu307-li when a microwave field was applied. Five distinct observed behaviors of the widths of both integral and half-integral steps as a function of microwave amplitude, /11de(l ae)' are reproduced by simulations of two or three junctions in parallel. This provides quantitative evidence that a single high-Tc grain-boundary junction is composed of several junctions in parallel. These junctions are formed by the overlap of superconducting filaments on either side of the grain boundary, and the spacing between ones with relatively large critical currents is-20pm.
Physical Review B, 1988
The upper critical Seld H, q and fiuctuation conductivity were measured for highly oriented thin ... more The upper critical Seld H, q and fiuctuation conductivity were measured for highly oriented thin nlHls of YBa2Cu307-. The H, 2 results demonstrate the intrinsic anisotropy in this layered superconductor. The broadening of the resistive transition under nelds is interpreted in terms of critical Buctuations. The fluctuation conductivity shows dimensional crossover as expected for quasi-two-dimensional material. Using these data we determine the intralayer and interlayer coherence lengths $, (0) end g~(0), and discuss the dimensionality af the superconductivity in this material. The recent discovery of high-T, superconductivity in metalhc oxides has generated great interest in the nature of the superconductivity in these materials. 'z Since the crystal structure is strongly anisotropic, the transport properties are expected to depend on the crystal orientation. Indeed, their anisotropic nature has been observed in resistivity, criticalwurrentMensity, and upper-criticalfield measurements. 5 s Similarly, the fluctuations above the superconducting transition are expected to reflect the degree of anisotropy. In this paper, we analyze the upper critical field, the marked broadening of the resistive transition in a field and the fluctuation conductivity above T, for highly oriented thin films of YBazCu307-". With the hypothesis of strong thermodynamic fluctuations, we can self-consistently account for all these properties and demonstrate that this material is distinctly quasi-twoMimensional with the superconductivity existing in the Cu-O (a-b) planes (possible also in the chains) and with Josephson coupling between planes. In these experiments, we used polycrystalline epitaxial thin films of YBazCu307-"with thicknesses-1 itm grown on SrTi03(100) substrates by electron-beam evaporation and magnetron sputtering. Preparation and characterization of the samples were reported elsewhere. s " The resistive transitions were measured using a four-point probe dc method and the data used to determine both the upper critical field H, z(T) and the fluctuation conductivity as described in detail below. For these resistance measurements, the samples were patterned and chemically etched into 400-pm-wide strips by standard photolithographic methods. To get a good contact, the surface is ion-milled, and then 100 A. of titanium and 1000 A of silver were evaporated sequentially on the films to form contact pads; indium was then pressed onto these pads to form the actual contact.
Physical Review B, 1989
Detailed examination of a well-ordered, high-T, Y2Ba4Cus0~6 (2:4:8) oriented thin-film sample rev... more Detailed examination of a well-ordered, high-T, Y2Ba4Cus0~6 (2:4:8) oriented thin-film sample revealed directly that the three crystallographic axes were unequal in length. Each layer of this high-T, superconductor, like the closely related superconducting YBa2Cu307-(1:2:3)phase, has structural anisotropy in the a bpla-ne. The difFerence between a (3.859~0.002 A) and b (3.874 0.002 A) in 2:4:8 is significantly smaller than in 1:2:3, so many associated strains such as those occurring during oxidation or epitaxial growth will also be smaller. Well-ordered, high-T, thin films of 2:4:8 using Er in place of Y have been produced. By comparing the x-ray-diA'raction patterns of the Y and Er 2:4:8 samples, a one-dimensional electron density map has been produced directly, without structure refinement. The result demonstrates that relative to the 1:2:3 structure, 2:4:8 contains an additional-CuOlayer. Together, the results indicate, without appeal to indirect chemical analogy, that 2:4:8 contains double-CuOlayers with interlayer vacancy ordering.
Physical Review B, 2003
We report the first application of x-rays to the measurement of the temperature dependent Bragg p... more We report the first application of x-rays to the measurement of the temperature dependent Bragg peak intensities to obtain Debye-Waller factors on high-temperature superconductors. Intensities of (0, 0, l) peaks of YBa2Cu3O7 and HgBa2CaCu2O6 thin films are measured to obtain the c-axis Debye-Waller factors. While lattice constant and some Debye-Waller factor measurements on high Tc superconductors show anomalies at the transition temperature, our measurements by x-ray diffraction show a smooth transition of the c-axis Debye-Waller factors through Tc. This suggests that the dynamic displacements of the heavy elements along the c-axis direction in these compounds do not have anomalies at Tc. This method in combination with measurements by other techniques will give more details concerning dynamics of the lattice.
Physical Review B, 1987
We report results of the study of electron tunneling into thin films of the new high-T, supercond... more We report results of the study of electron tunneling into thin films of the new high-T, superconductor La-Sr-Cu-O. Both sandwich-type tunneling with a Pb counterelectrode and pointcontact tunneling have been successfully achieved. The results show exceptionally large energy gaps in these materials (roughly 20, 30, and possibly even 60 mV), larger than previously obtained on bulk sintered powders. We interpret these results as due to large anisotropy in this material or due to the presence of a very high-T, layer near the surface of the films. The method of preparation of this new superconductor in thin film form is also discussed.
Physical Review B, 1987
We report results of a study of electron tunneling into bulk samples of the new high-T, supercond... more We report results of a study of electron tunneling into bulk samples of the new high-T, superconductor Y-Ba-Cu-0 using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 24=100 meV), implying 2hlkaT,-13. Similar values were found previously by us for La-Sr-Cu-O. We also see structure in the I-V curves similar to that seen in La-Sr-Cu-O. On the basis of the asymmetries observed in the I-V characteristics, we believe that the natural tunneling barrier on this material is of the Schottky type.
SID Symposium Digest of Technical Papers, 2010
ABSTRACT We report light-emitting diodes incorporating colloidal quantum dots as the emitters, wh... more ABSTRACT We report light-emitting diodes incorporating colloidal quantum dots as the emitters, which showed saturated red, green and blue colors mostly originating from quantum-dots (over 99%). They also showed external quantum efficiency of 1.5 % and brightness over 10,000 cd/m2, which were achieved by improving charge injection and transport layers.
ACS Macro Letters, 2014
The synthesis of dynamic covalent polymers with controllable amounts of sulfur−sulfur (S−S) bonds... more The synthesis of dynamic covalent polymers with controllable amounts of sulfur−sulfur (S−S) bonds in the polymer backbone via inverse vulcanization of elemental sulfur (S 8) and 1,3-diisopropenylbenzene (DIB) is reported. An attractive feature of the inverse vulcanization process is the ability to control the number and dynamic nature of S−S bonds in poly(sulfur-random-(1,3-diisopropenylbenzene)) (poly(S-r-DIB) copolymers by simple variation of S 8 /DIB feed ratios in the copolymerization. S−S bonds in poly(S-r-DIB) copolymers of high sulfur content and sulfur rank were found to be more dynamic upon exposure to either heat, or mechanical stimuli. Interrogation of dynamic S−S bonds was conducted in the solid-state utilizing electron paramagnetic resonance spectroscopy and in situ rheological measurements. Time-dependent rheological property behavior demonstrated a compositional dependence of the healing behavior in the copolymers, with the highest sulfur (80 wt % sulfur) content affording the most rapid dynamic response and recovery of rheological properties.
Physical Review B, 1988
An ordered defect structure in superconducting Y-Ba-Cu-0 thin films has been characterized by bot... more An ordered defect structure in superconducting Y-Ba-Cu-0 thin films has been characterized by both x-ray diffraction and transmission electron microscopy. The defect structure, which is observed growing epitaxially within the grains of normal YBa2Cu307-x structure, has the diN'raction characteristics of a distinct phase~hose volume fraction can be correlated with changes in film composition. The di8'raction characteristics are consistent with an orthorhombic unit cell (a~b 3.86 A, c 27. 19 A) with space group Antmm. These are the characteristics to be expected from a structure in which extra copper-oxygen layers create fault planes, which are inserted at every unit cell in the parent YBa2Cu307structure. The composition expected for the pure phase is Y28aqCu8020-". Preliminary transport measurements on films containing this extra phase are characterized by lo~er normal-state resistances and a lo~er Hall constant.
SID Symposium Digest of Technical Papers, 2011
ABSTRACT We provide simple and versatile QD transplanting method, which allows well-defined QD pa... more ABSTRACT We provide simple and versatile QD transplanting method, which allows well-defined QD patterns down to a few micrometers and also provides compatibility with conventional device fabrication process and device architecture. We also demonstrate red, green, and blue QLEDs with transplanted QD active layers and characterize them in systematic correlation study between QD pattern morphology and device performances.
Solid State Phenomena, 2007
We introduce a novel and versatile approach for controlling anti-reflective (AR) properties of mu... more We introduce a novel and versatile approach for controlling anti-reflective (AR) properties of multilayer films based on layer-by-layer (LbL) self-assembly (SA) method. For the fabrication of these films, blend (i.e., mixed) layers containing both polyanions (i.e., titanium precursor (TALH) and poly(sodium 4-styrenesulfonate) (PSS)) were assembled with polycation (i.e., poly(diallyldimethylammonium chloride) (PDAD)) for the formation of the high refractive index multilayers and on the other hand, the negatively charged silica particles with the diameter of about 100 nm were employed for low refractive index layer. The refractive index of TALH:PSS/PDAD multilayer was controlled by blending ratio and annealing temperature as TALH has the relatively high refractive index (n = 1.68) in comparison with that (n = 1.46) of conventional polyelectrolytes (PEs) at room temperature and furthermore these titanium precursors are partially changed into TiO2 with relatively high refractive indices...
MRS Proceedings, 2000
Processible poly(methylsilsesquioxane)s (PMSSQs) were prepared in THF solution under nitrogen atm... more Processible poly(methylsilsesquioxane)s (PMSSQs) were prepared in THF solution under nitrogen atmosphere in the presence of HCl catalyst. It was found that various reaction parameters such as concentration, temperature, reaction time, the amount of water, and the amount of acid catalyst could affect the molecular weight and the amount of functional end groups of PMSSQ samples. Thin films prepared from our PMSSQ samples by spin-coating followed by curing to 420°C exhibited a much better crack resistance than those presented in the literature, while the dielectric constant remained practically the same, i.e., ca. 2.7.
Physical Review B, 1995
We report the use of YQ 7CaQ 3Ba2Cu307 z as an epitaxial barrier between YBa2Cu307 z {YBCO)electr... more We report the use of YQ 7CaQ 3Ba2Cu307 z as an epitaxial barrier between YBa2Cu307 z {YBCO)electrodes in high-T, superconductor-normal-superconductor edge junctions. Ca-doped YBCO is an overdoped version of YBCO, and it has an excellent lattice and thermal expansion match with YBCO. We show that these junctions exhibit clean interfaces with resistances smaller than 10 ' Q cm. We present the temperature dependence of the critical current density J, and the junction resistance 8" for junc-0 tions with 200, 400, and 600 A thick barriers of YQ 7CaQ 3Ba2Cu3O7 z. As the temperature decreases, the resistance of the junction decreases faster than the resistance calculated from the resistivity of a YQ 7CaQ 38a2Cu30, z film. We analyze our data by considering various possibilities for the microstructure in the barrier region. We discuss the ideal conventional proximity effect, diffusion between the barriers and the electrodes, and doping fluctuations inside the barrier. We find that combinations of these ideas explain the observed behavior with reasonable parameter.
Applied Superconductivity, 1998
ÐWe have developed a process for fabricating YBa 2 Cu 3 O 7 thin-®lm, ramp-type edge junctions in... more ÐWe have developed a process for fabricating YBa 2 Cu 3 O 7 thin-®lm, ramp-type edge junctions in which no deposited barrier is employed. These devices display excellent RSJ-type current±voltage (I± V) characteristics with values of I c and R n tunable over a useful range for operation of digital circuits. Initial junction reproducibility and uniformity are very encouraging.
Advances in Superconductivity IV, 1992
We will report structural and electrical properties of bi-epitaxial grain boundary Josephson junc... more We will report structural and electrical properties of bi-epitaxial grain boundary Josephson junctions in YBa2Cu3O7, created at predetermined locations by controlling the in-plane epitaxy of YBa2Cu3O7 with a seea layer and a buffer layer on a base layer. Reproducibility and uniformity of the junctions is described. SQUIDs made from bi-epitaxial junctions show voltage modulation at 77 K with reasonably low noise. Complete magnetometers coupled with multi-turn flux transformers have magnetic field sensitivity at 77 K sufficient to be useful for many applications. Recent success in fabricating integrated SQUIDs by combining the SQUID and multi-turn flux transformer on a single substrate is described.
We have measured the bulk transport properties of Y_0.6Pr_0.4Ba_2Cu_2.7Co_0.3Ox thin films and ha... more We have measured the bulk transport properties of Y_0.6Pr_0.4Ba_2Cu_2.7Co_0.3Ox thin films and have fabricated edge junctions of YBa_2Cu_3O_7-delta /Y_0.6Pr_0.4Ba_2Cu_2.7Co_0.3O_x/YBa_2Cu_3O_7-delta in order to study length scale effects. The bulk transport behavior seems to be described by a variable range hopping mechanism. We will also present the behavior of the junction transport properties as a function of barrier thickness and correlate the
Physical Review B, 1994
Half-integral constant voltage steps were observed in many high-Tc grain-boundary Josephson junct... more Half-integral constant voltage steps were observed in many high-Tc grain-boundary Josephson junctions of YBa2Cu307-li when a microwave field was applied. Five distinct observed behaviors of the widths of both integral and half-integral steps as a function of microwave amplitude, /11de(l ae)' are reproduced by simulations of two or three junctions in parallel. This provides quantitative evidence that a single high-Tc grain-boundary junction is composed of several junctions in parallel. These junctions are formed by the overlap of superconducting filaments on either side of the grain boundary, and the spacing between ones with relatively large critical currents is-20pm.
Physical Review B, 1988
The upper critical Seld H, q and fiuctuation conductivity were measured for highly oriented thin ... more The upper critical Seld H, q and fiuctuation conductivity were measured for highly oriented thin nlHls of YBa2Cu307-. The H, 2 results demonstrate the intrinsic anisotropy in this layered superconductor. The broadening of the resistive transition under nelds is interpreted in terms of critical Buctuations. The fluctuation conductivity shows dimensional crossover as expected for quasi-two-dimensional material. Using these data we determine the intralayer and interlayer coherence lengths $, (0) end g~(0), and discuss the dimensionality af the superconductivity in this material. The recent discovery of high-T, superconductivity in metalhc oxides has generated great interest in the nature of the superconductivity in these materials. 'z Since the crystal structure is strongly anisotropic, the transport properties are expected to depend on the crystal orientation. Indeed, their anisotropic nature has been observed in resistivity, criticalwurrentMensity, and upper-criticalfield measurements. 5 s Similarly, the fluctuations above the superconducting transition are expected to reflect the degree of anisotropy. In this paper, we analyze the upper critical field, the marked broadening of the resistive transition in a field and the fluctuation conductivity above T, for highly oriented thin films of YBazCu307-". With the hypothesis of strong thermodynamic fluctuations, we can self-consistently account for all these properties and demonstrate that this material is distinctly quasi-twoMimensional with the superconductivity existing in the Cu-O (a-b) planes (possible also in the chains) and with Josephson coupling between planes. In these experiments, we used polycrystalline epitaxial thin films of YBazCu307-"with thicknesses-1 itm grown on SrTi03(100) substrates by electron-beam evaporation and magnetron sputtering. Preparation and characterization of the samples were reported elsewhere. s " The resistive transitions were measured using a four-point probe dc method and the data used to determine both the upper critical field H, z(T) and the fluctuation conductivity as described in detail below. For these resistance measurements, the samples were patterned and chemically etched into 400-pm-wide strips by standard photolithographic methods. To get a good contact, the surface is ion-milled, and then 100 A. of titanium and 1000 A of silver were evaporated sequentially on the films to form contact pads; indium was then pressed onto these pads to form the actual contact.
Physical Review B, 1989
Detailed examination of a well-ordered, high-T, Y2Ba4Cus0~6 (2:4:8) oriented thin-film sample rev... more Detailed examination of a well-ordered, high-T, Y2Ba4Cus0~6 (2:4:8) oriented thin-film sample revealed directly that the three crystallographic axes were unequal in length. Each layer of this high-T, superconductor, like the closely related superconducting YBa2Cu307-(1:2:3)phase, has structural anisotropy in the a bpla-ne. The difFerence between a (3.859~0.002 A) and b (3.874 0.002 A) in 2:4:8 is significantly smaller than in 1:2:3, so many associated strains such as those occurring during oxidation or epitaxial growth will also be smaller. Well-ordered, high-T, thin films of 2:4:8 using Er in place of Y have been produced. By comparing the x-ray-diA'raction patterns of the Y and Er 2:4:8 samples, a one-dimensional electron density map has been produced directly, without structure refinement. The result demonstrates that relative to the 1:2:3 structure, 2:4:8 contains an additional-CuOlayer. Together, the results indicate, without appeal to indirect chemical analogy, that 2:4:8 contains double-CuOlayers with interlayer vacancy ordering.
Physical Review B, 2003
We report the first application of x-rays to the measurement of the temperature dependent Bragg p... more We report the first application of x-rays to the measurement of the temperature dependent Bragg peak intensities to obtain Debye-Waller factors on high-temperature superconductors. Intensities of (0, 0, l) peaks of YBa2Cu3O7 and HgBa2CaCu2O6 thin films are measured to obtain the c-axis Debye-Waller factors. While lattice constant and some Debye-Waller factor measurements on high Tc superconductors show anomalies at the transition temperature, our measurements by x-ray diffraction show a smooth transition of the c-axis Debye-Waller factors through Tc. This suggests that the dynamic displacements of the heavy elements along the c-axis direction in these compounds do not have anomalies at Tc. This method in combination with measurements by other techniques will give more details concerning dynamics of the lattice.
Physical Review B, 1987
We report results of the study of electron tunneling into thin films of the new high-T, supercond... more We report results of the study of electron tunneling into thin films of the new high-T, superconductor La-Sr-Cu-O. Both sandwich-type tunneling with a Pb counterelectrode and pointcontact tunneling have been successfully achieved. The results show exceptionally large energy gaps in these materials (roughly 20, 30, and possibly even 60 mV), larger than previously obtained on bulk sintered powders. We interpret these results as due to large anisotropy in this material or due to the presence of a very high-T, layer near the surface of the films. The method of preparation of this new superconductor in thin film form is also discussed.
Physical Review B, 1987
We report results of a study of electron tunneling into bulk samples of the new high-T, supercond... more We report results of a study of electron tunneling into bulk samples of the new high-T, superconductor Y-Ba-Cu-0 using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 24=100 meV), implying 2hlkaT,-13. Similar values were found previously by us for La-Sr-Cu-O. We also see structure in the I-V curves similar to that seen in La-Sr-Cu-O. On the basis of the asymmetries observed in the I-V characteristics, we believe that the natural tunneling barrier on this material is of the Schottky type.
SID Symposium Digest of Technical Papers, 2010
ABSTRACT We report light-emitting diodes incorporating colloidal quantum dots as the emitters, wh... more ABSTRACT We report light-emitting diodes incorporating colloidal quantum dots as the emitters, which showed saturated red, green and blue colors mostly originating from quantum-dots (over 99%). They also showed external quantum efficiency of 1.5 % and brightness over 10,000 cd/m2, which were achieved by improving charge injection and transport layers.
ACS Macro Letters, 2014
The synthesis of dynamic covalent polymers with controllable amounts of sulfur−sulfur (S−S) bonds... more The synthesis of dynamic covalent polymers with controllable amounts of sulfur−sulfur (S−S) bonds in the polymer backbone via inverse vulcanization of elemental sulfur (S 8) and 1,3-diisopropenylbenzene (DIB) is reported. An attractive feature of the inverse vulcanization process is the ability to control the number and dynamic nature of S−S bonds in poly(sulfur-random-(1,3-diisopropenylbenzene)) (poly(S-r-DIB) copolymers by simple variation of S 8 /DIB feed ratios in the copolymerization. S−S bonds in poly(S-r-DIB) copolymers of high sulfur content and sulfur rank were found to be more dynamic upon exposure to either heat, or mechanical stimuli. Interrogation of dynamic S−S bonds was conducted in the solid-state utilizing electron paramagnetic resonance spectroscopy and in situ rheological measurements. Time-dependent rheological property behavior demonstrated a compositional dependence of the healing behavior in the copolymers, with the highest sulfur (80 wt % sulfur) content affording the most rapid dynamic response and recovery of rheological properties.
Physical Review B, 1988
An ordered defect structure in superconducting Y-Ba-Cu-0 thin films has been characterized by bot... more An ordered defect structure in superconducting Y-Ba-Cu-0 thin films has been characterized by both x-ray diffraction and transmission electron microscopy. The defect structure, which is observed growing epitaxially within the grains of normal YBa2Cu307-x structure, has the diN'raction characteristics of a distinct phase~hose volume fraction can be correlated with changes in film composition. The di8'raction characteristics are consistent with an orthorhombic unit cell (a~b 3.86 A, c 27. 19 A) with space group Antmm. These are the characteristics to be expected from a structure in which extra copper-oxygen layers create fault planes, which are inserted at every unit cell in the parent YBa2Cu307structure. The composition expected for the pure phase is Y28aqCu8020-". Preliminary transport measurements on films containing this extra phase are characterized by lo~er normal-state resistances and a lo~er Hall constant.
SID Symposium Digest of Technical Papers, 2011
ABSTRACT We provide simple and versatile QD transplanting method, which allows well-defined QD pa... more ABSTRACT We provide simple and versatile QD transplanting method, which allows well-defined QD patterns down to a few micrometers and also provides compatibility with conventional device fabrication process and device architecture. We also demonstrate red, green, and blue QLEDs with transplanted QD active layers and characterize them in systematic correlation study between QD pattern morphology and device performances.
Solid State Phenomena, 2007
We introduce a novel and versatile approach for controlling anti-reflective (AR) properties of mu... more We introduce a novel and versatile approach for controlling anti-reflective (AR) properties of multilayer films based on layer-by-layer (LbL) self-assembly (SA) method. For the fabrication of these films, blend (i.e., mixed) layers containing both polyanions (i.e., titanium precursor (TALH) and poly(sodium 4-styrenesulfonate) (PSS)) were assembled with polycation (i.e., poly(diallyldimethylammonium chloride) (PDAD)) for the formation of the high refractive index multilayers and on the other hand, the negatively charged silica particles with the diameter of about 100 nm were employed for low refractive index layer. The refractive index of TALH:PSS/PDAD multilayer was controlled by blending ratio and annealing temperature as TALH has the relatively high refractive index (n = 1.68) in comparison with that (n = 1.46) of conventional polyelectrolytes (PEs) at room temperature and furthermore these titanium precursors are partially changed into TiO2 with relatively high refractive indices...
MRS Proceedings, 2000
Processible poly(methylsilsesquioxane)s (PMSSQs) were prepared in THF solution under nitrogen atm... more Processible poly(methylsilsesquioxane)s (PMSSQs) were prepared in THF solution under nitrogen atmosphere in the presence of HCl catalyst. It was found that various reaction parameters such as concentration, temperature, reaction time, the amount of water, and the amount of acid catalyst could affect the molecular weight and the amount of functional end groups of PMSSQ samples. Thin films prepared from our PMSSQ samples by spin-coating followed by curing to 420°C exhibited a much better crack resistance than those presented in the literature, while the dielectric constant remained practically the same, i.e., ca. 2.7.
Physical Review B, 1995
We report the use of YQ 7CaQ 3Ba2Cu307 z as an epitaxial barrier between YBa2Cu307 z {YBCO)electr... more We report the use of YQ 7CaQ 3Ba2Cu307 z as an epitaxial barrier between YBa2Cu307 z {YBCO)electrodes in high-T, superconductor-normal-superconductor edge junctions. Ca-doped YBCO is an overdoped version of YBCO, and it has an excellent lattice and thermal expansion match with YBCO. We show that these junctions exhibit clean interfaces with resistances smaller than 10 ' Q cm. We present the temperature dependence of the critical current density J, and the junction resistance 8" for junc-0 tions with 200, 400, and 600 A thick barriers of YQ 7CaQ 3Ba2Cu3O7 z. As the temperature decreases, the resistance of the junction decreases faster than the resistance calculated from the resistivity of a YQ 7CaQ 38a2Cu30, z film. We analyze our data by considering various possibilities for the microstructure in the barrier region. We discuss the ideal conventional proximity effect, diffusion between the barriers and the electrodes, and doping fluctuations inside the barrier. We find that combinations of these ideas explain the observed behavior with reasonable parameter.
Applied Superconductivity, 1998
ÐWe have developed a process for fabricating YBa 2 Cu 3 O 7 thin-®lm, ramp-type edge junctions in... more ÐWe have developed a process for fabricating YBa 2 Cu 3 O 7 thin-®lm, ramp-type edge junctions in which no deposited barrier is employed. These devices display excellent RSJ-type current±voltage (I± V) characteristics with values of I c and R n tunable over a useful range for operation of digital circuits. Initial junction reproducibility and uniformity are very encouraging.
Advances in Superconductivity IV, 1992
We will report structural and electrical properties of bi-epitaxial grain boundary Josephson junc... more We will report structural and electrical properties of bi-epitaxial grain boundary Josephson junctions in YBa2Cu3O7, created at predetermined locations by controlling the in-plane epitaxy of YBa2Cu3O7 with a seea layer and a buffer layer on a base layer. Reproducibility and uniformity of the junctions is described. SQUIDs made from bi-epitaxial junctions show voltage modulation at 77 K with reasonably low noise. Complete magnetometers coupled with multi-turn flux transformers have magnetic field sensitivity at 77 K sufficient to be useful for many applications. Recent success in fabricating integrated SQUIDs by combining the SQUID and multi-turn flux transformer on a single substrate is described.
We have measured the bulk transport properties of Y_0.6Pr_0.4Ba_2Cu_2.7Co_0.3Ox thin films and ha... more We have measured the bulk transport properties of Y_0.6Pr_0.4Ba_2Cu_2.7Co_0.3Ox thin films and have fabricated edge junctions of YBa_2Cu_3O_7-delta /Y_0.6Pr_0.4Ba_2Cu_2.7Co_0.3O_x/YBa_2Cu_3O_7-delta in order to study length scale effects. The bulk transport behavior seems to be described by a variable range hopping mechanism. We will also present the behavior of the junction transport properties as a function of barrier thickness and correlate the