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Based on the interface polarization model, the two-dimensional electron gas (2DEG) at $LaInO_{3}$(LIO)/$BaSnO_{3}$(BSO) interfaces is understood to originate from a polarization discontinuity at the interface and the conduction band offset between LIO and BSO. In this scenario, the direction of polarization at the interface is determined by whether the first atomic LIO layer at the interface is LaO$^{+}$ or InO$_{2}^{-}$. We investigate the role of the terminating layer at the LIO/BSO interface in creating the 2DEG. Based on conductance measurements of our in-situ grown LIO/BSO heterostructures, we report in this work that the 2DEG only forms when the BSO surface is terminated with a SnO$_{2}$ layer. We controlled the terminating layer by additional SnO$_{2}$ deposition on the BSO surface. We show that the as-grown BSO surface has a mixed terminating layer of BaO and SnO$_{2}$ while the BSO surfaces prepared with additional SnO$_{2}$ deposition are terminated mainly with the SnO$_{2}$ layer. The terminating layer was confirmed by coaxial impact collision ion scattering spectroscopy (CAICISS). Our finding is consistent with the interface polarization model for 2DEG formation at LIO/BSO interfaces, in which the direction of the interfacial polarization in LIO is determined by the terminating layer of the BSO surface., 22 pages

Some oxide interfaces are known to exhibit unique properties such as a 2D electron gas, controlled by epitaxial strain and coherency between the two layers. Here, we study variation in the 2D electron density in the polar LaIn1-xGaxO3/Ba0.997La0.003SnO3 interface with changing x and LaIn1-xGaxO3 layer thickness. We find that the 2D electron density decreases as the gallium alloying ratio increases and the interface conductance eventually disappears, which shows that an interface with polar discontinuity is not a sufficient condition for 2D electron gas formation. The interface conductance reaches its maximum value when the LaIn1-xGaxO3 layer thickness is approximately 20 Å, beyond which conductance decreased to a constant value. Atomistic imaging reveals that dislocations start to form as the gallium ratio increases, forming away from the interface and then moving closer with increasing gallium alloying. The dislocations eventually destroy coherency in the case of LaGaO3 and suppress the formation of a 2D electron gas.

Scaling down of semiconductor devices requires high- k dielectric materials to continue lowering the operating voltage of field-effect transistors (FETs) and storing sufficient charge on a smaller area. Here, we investigate the dielectric properties of epitaxial BaHf 0.6 Ti 0.4 O 3 (BHTO), an alloy of perovskite oxide barium hafnate (BaHfO 3 ) and barium titanate (BaTiO 3 ). We found the dielectric constant, the breakdown field, and the leakage current to be 150, 5.0 megavolts per centimeter (MV cm −1 ), and 10 −4 amperes per square centimeter at 2 MV cm −1 , respectively. The results suggest that two-dimensional (2D) carrier density of more than n 2D = 10 14 per square centimeter (cm −2 ) could be modulated by the BHTO gate oxide. We demonstrate an n-type accumulation mode FET and direct suppression of more than n 2D = 10 14 cm −2 via an n-type depletion-mode FET. We attribute the large dielectric constant, high breakdown field, and low leakage current of BHTO to the nanometer scale stoichiometric modulation of hafnium and titanium.

Scaling down of semiconductor devices requires high

As the size of the semiconductor device decreases, the importance of the low resistance contacts to devices cannot be overstated. Here, we studied the contact resistance to buried nanometer thick δ-doped Ba1-xLaxSnO3 (BLSO) layers. We have used epitaxial 4% (x = 0.04) BLSO as a contact material, which has additional advantages of forming Ohmic contacts to BaSnO3 and providing thermal stability even at high temperatures. The contact resistance was measured by a modified transmission line method designed to eliminate the contribution from the resistance of the contact material. The upper bound for the contact resistance to a 12 nm thick δ-doped 1% BLSO conductive layer was measured to be 1.25 × 10−1or 2.87 × 10−7 Ω cm2. Our results show that it is possible to provide low resistance epitaxial edge contacts to an embedded nanometer-thick BLSO conductive layer using an ion-milling process. Our low resistance contact method can be easily extended to a two-dimensional electron gas at the oxide interfaces such as LaInO3/BaSnO3.

Epitaxial perovskite oxide interfaces with different symmetry of the epitaxial layers have attracted considerable attention due to the emergence of novel behaviors and phenomena. In this paper, we show by aberration-corrected transmission electron microscopy (TEM) that orthorhombic ${\mathrm{LaInO}}_{3}$ films grow in form of three different types of domains on the cubic ${\mathrm{BaSnO}}_{3}$ pseudosubstrate. Quantitative evaluation of our TEM data shows that ${c}_{\mathrm{pc}}$-oriented and ${a}_{\mathrm{pc}}/{b}_{\mathrm{pc}}$-oriented domains are present with similar probability. While continuum elasticity theory suggests that ${c}_{\mathrm{pc}}$-oriented domains should exhibit a significantly higher strain energy density than ${a}_{\mathrm{pc}}/{b}_{\mathrm{pc}}$-oriented domains, density-functional calculations confirm that ${c}_{\mathrm{pc}}$- and ${a}_{\mathrm{pc}}$-oriented domains on ${\mathrm{BaSnO}}_{3}$ have similar energies.

We investigate the transport properties of a modified interface by intentionally inserting a nanometer-scale undoped ${\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_{3}$ spacer layer at the ${\mathrm{La}\mathrm{In}\mathrm{O}}_{3}$/${\mathrm{Ba}}_{1\text{\ensuremath{-}}x}{\mathrm{La}}_{x}{\mathrm{Sn}\mathrm{O}}_{3}$ interface, thereby creating remotely doped heterostructures. Both the carrier density $({n}_{s})$ and the Hall mobility $({\ensuremath{\mu}}_{H})$ continuously decrease as the thickness of the ${\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_{3}$ spacer layer at the interface increases, indicating a changing electron-density profile as a function of the spacer thickness. We find the behavior is consistent with the recently proposed ``interface-polarization'' model by self-consistent one-dimensional Poisson-Schr\"odinger calculations. The decrease of ${n}_{s}$ makes it difficult to see the effect of the spacer layer on the mobility in the remotely doped structures due to the simultaneous decrease of $\ensuremath{\mu}$ caused by the ineffective screening of the remote Coulomb scattering from ionized donors in addition to the threading dislocation scattering. Hence, we control the band bending continuously via the field effect with a fixed spacer-layer thickness, leading to observation of enhanced mobility $({\ensuremath{\mu}}_{\mathrm{FE}})$ in the remotely doped 2DEG heterostructures in spite of high-density threading dislocations acting as the background charged impurities.

We studied the surface and electronic structures of barium stannate (${\mathrm{BaSnO}}_{3}$) thin films by low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) techniques. ${\mathrm{BaSnO}}_{3}/{\mathrm{Ba}}_{0.96}{\mathrm{La}}_{0.04}{\mathrm{SnO}}_{3}/{\mathrm{SrTiO}}_{3}$ (10 nm/100 nm/0.5 mm) samples were grown using the pulsed-laser deposition (PLD) method and were ex situ transferred from the PLD chamber to ultrahigh vacuum (UHV) chambers for annealing, LEED, and ARPES studies. UHV annealing starting from $300{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ up to $550{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, followed by LEED and ARPES measurements, show $1\ifmmode\times\else\texttimes\fi{}1$ surfaces with nondispersive energy-momentum bands. The $1\ifmmode\times\else\texttimes\fi{}1$ surface reconstructs into a $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ one at an annealing temperature of $700{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ where the ARPES data show clear dispersive bands with a valence band maximum located around 3.3 eV below the Fermi level. While the $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface reconstruction is stable under further UHV annealing, it is reversed to a $1\ifmmode\times\else\texttimes\fi{}1$ surface by annealing the sample in 400 mTorr oxygen at $600{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Another UHV annealing at $600{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, followed by LEED and ARPES measurements, suggests that LEED $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of the electronic structure of ${\mathrm{BaSnO}}_{3}$ surfaces and are suggestive of the role of oxygen vacancies in reversible $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface reconstruction.

In order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface.

In order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface.

Various δ-doped semiconductor heterostructures have been effectively used for devices at room temperature and for quantum phenomena at low temperatures. Here, we use BaSnO3 and investigate its δ-doped system, focusing on its band bending and surface boundary conditions. We measured the two-dimensional carrier density (n2D) of the δ-doped BaSnO3 system of various thicknesses and doping levels. We also studied the effect of the BaSnO3 capping layer thickness on n2D. We show that the δ-doped BaSnO3 system can be very well described by band bending with the aid of the Poisson–Schrodinger simulation. At the same time, the capping layer thickness dependence of n2D reveals how the boundary condition on the surface of La-doped BaSnO3 evolves as a function of its capping layer thickness.

We report on the electrical properties of SnO x thin films made by reactive sputtering of a Sn metal target and the performance of their field effect transistors with HfO x gate insulator on glass substrates. We investigated the electrical properties of SnO x films by controlling the oxygen partial pressure during growth. The mobility of the SnO x films on glass substrates was as high as 20.28 cm 2 V −1 s −1 after post-deposition annealing at 400 °C, while its carrier density was 4.21 × 10 18 cm −3 . Moreover, we fabricated high mobility thin film transistors using polycrystalline SnO x as the channel and the atomic-layer-deposited HfO x as the gate oxide. The field-effect mobility values were 5.01–20.15 cm 2 V −1 s −1 , the I on /I off were 10 3 ∼10 4 , and the subthreshold swing were 1.05–1.60 V dec −1 . We discuss the origins for the non-ideal performance and the future direction for improvement.

We report on thin film transistors (TFTs) based on spinel ZnGa2O4 (ZGO) that was recently spotlighted as an ultra-wide bandgap oxide semiconductor. The ZGO layers were grown in a spinel structure by pulsed laser deposition on the cubic spinel MgAl2O4 (MAO) as well as on cubic MgO substrates while changing the Zn/Ga ratio. The compressive strained epitaxial growth of ZGO on MgAl2O4 (100) and the tensile strained epitaxial growth of ZGO on MgO (100) without any misfit or threading dislocations were confirmed by the reciprocal space map and cross-sectional transmission electron microscopy. The electrical transport properties were demonstrated through TFTs based on ZGO as the channel layer, Al2O3 as the gate oxide, and Sn-doped In2O3 as the source, drain, and gate electrodes. When the Zn/Ga ratio is slightly lower than the ideal value of 0.5 on MgO substrates, the ZGO TFT showed the highest mobility of 5.4 cm2/V s. The ION/IOFF ratio and subthreshold swing (S) value are 4.5 × 108 and 0.19 V/dec, respectively.

We report on transparent thin film field effect transistors (TFTs) based on polycrystalline SnO2−x and epitaxial SnO2−x. Polycrystalline SnO2−x TFTs of the top and the bottom gate geometries exhibited high mobility values of 145.7 cm2/V s and 160.0 cm2/V s, respectively. However, our polycrystalline SnO2−x devices showed non-ideal behaviors in their output and transfer characteristics; a large hysteresis was observed along with large voltage dependence. The probable origin of these non-ideal behaviors is the barrier formation across grain boundaries of polycrystalline SnO2. To confirm this, we used SnO2−x epitaxially grown on r-plane sapphire substrates as a channel layer and compared their performance with those of polycrystalline SnO2−x based TFTs. Although the mobility of epitaxial SnO2−x TFTs was not as high as that of the polycrystalline SnO2−x TFTs, the non-ideal voltage dependence in output and transfer characteristics disappeared. We believe our direct experimental comparison clearly demonstrates the grain boundary issue in polycrystalline SnO2−x.

A wide band-gap perovskite oxide $\mathrm{BaSn}{\mathrm{O}}_{3}$ is attracting much attention due to its high electron mobility and oxygen stability. On the other hand, $\mathrm{BaHf}{\mathrm{O}}_{3}$ was recently reported to be an effective high-$k$ gate oxide. Here, we investigate the band gap and mobility of solid solutions of $\mathrm{BaS}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{H}{\mathrm{f}}_{x}{\mathrm{O}}_{3}$ ($x=0\ensuremath{-}1$) (BSHO) as a basis to build advanced perovskite oxide heterostructures. All the films were epitaxially grown on MgO substrates using pulsed laser deposition. Density functional theory calculations confirmed that Hf substitution does not create midgap states while increasing the band gap. From x-ray diffraction and optical transmittance measurements, the lattice constants and the band-gap values are significantly modified by Hf substitution. We also measured the transport properties of $n$-type La-doped BSHO films $[(\mathrm{Ba},\mathrm{La})(\mathrm{Sn},\mathrm{Hf}){\mathrm{O}}_{3}]$, investigating the feasibility of modulation doping in the $\mathrm{BaSn}{\mathrm{O}}_{3}/\mathrm{BSHO}$ heterostructures. The Hall measurement data revealed that, as the Hf content increases, the activation rate of the La dopant decreases and the scattering rate of the electrons sharply increases. These properties of BSHO films may be useful for applications in various heterostructures based on the $\mathrm{BaSn}{\mathrm{O}}_{3}$ system.

We investigate the oxygen diffusion phenomena in a Ba0.96La0.04SnO3 (BLSO) thin film on SrTiO3(001) substrate by measurements of time-dependent Hall effect at high temperatures around 500 °C under different gas atmosphere. Under the Ar (O2) atmosphere, carrier density (n) and electrical conductivity (σ) are increased (decreased) while electron mobility (µ) is slightly reduced (enhanced). This observation supports that although both n and µ are affected by the oxygen diffusion process, the change of n is a major factor of determining σ in the BLSO film. Detailed analyses of the time-dependent n exhibit fast and slow dynamics that possibly correspond to the oxygen exchange reaction at the surface and oxygen diffusion into the BLSO grains, respectively. Fitting the time dependence of n reveals that the chemical diffusion coefficient of oxygen in the BLSO grains becomes ∼10−16 cm2 s−1. This coefficient marks the lowest value among perovskite oxides around 500 °C, directly proving excellent thermal stability of oxygen in BLSO. The present results support that the donor-doped BaSnO3 system could be useful for realizing transparent semiconductor devices at high temperatures.

We investigated bipolar resistance switching (RS) behavior of a top electrode/epitaxial NiO using Al and Pt as the top electrodes (TEs) and epitaxial NiO deposited at 500 °C (NiO-500) and 700 °C (NiO-700). We found that the contact between Al and Pt TEs and NiO-500 was a high resistance insulating contact, while the contact between the two TEs and NiO-700 was a low-resistance metallic contact. We also found that only NiO-500 with the Pt TE exhibited bipolar RS after an electroforming process. This study suggests that during the formation of the Pt/NiO-500 interface, the amount and behavior of oxygen at the interface seem to play the most important role in bipolar RS behavior. In order to improve the device performance, better control of oxygen content and its movement at the interface seems necessary.

We report on the dependence of resonant response to applied tensile stress in Al and Al-CNT (carbon nanotube) nanolaminate thin-film nanomechanical beam resonators. We optically measure the dynamic flexural response, while a chip-bending method is utilized to apply a static tension along its axis. For Al thin-film resonators, large and reversible increases in the resonant frequencies are observed along with near doubling of the resonator quality factor; while, for Al-CNT, largely unaffected with a slight decrease in resonant frequencies. Such behavior gives an insight on the role of CNT as a structural reinforcement in the Al thin-film based nanolaminate.

Synchrotron X-ray absorption near edge structure (XANES) measurements of F K-edge in conjunction with first-principles calculations are used to identify the local structure of the fluorine (F) atom in F-doped ZnO. The ZnO film was grown by pulsed laser deposition with an Nd:YAG laser, and an oxyfluoridation method was used to introduce F ions into the ZnO films. The measured XANES spectrum of the sample was compared against the first-principles XANES calculations based on various models for local atomic structures surrounding F atoms. The observed spectral features are attributed to ZnF2 and FO defects in wurtzite bulk ZnO.

We investigated the electrical characteristics of MgO tunnel barriers while we add F during oxidation process of nm-thick Mg layer. Specifically we measured d I /d V and d 2 I /d V 2 data of MgO tunnel barriers as we add F. When comparing the data of magnesium oxyfluoride tunnel barriers to those of aluminum oxyfluoride data, we have found that effect of F-inclusion in MgO is different from that in AlO x ; F-inclusion in MgO barrier makes the barrier more symmetric while F-inclusion in AlO x barrier makes the barrier more asymmetric. However, the d 2 I /d V 2 data of MgO did not change much even after F-inclusion, suggesting a very small amount of F-doping can make significant change in oxidation process of nm-thick Mg layer. We believe this result from the fact the oxidation process of nm-thick Mg layer is reaction-limited while the oxidation process of Al layer is diffusion-limited.

Composites with added carbon nanotubes are known for their improved mechanical strength. Laminates of thin films of aluminium and carbon nanotubes are now used for the fabrication of micromechanical resonators with significantly enhanced mechanical properties. At micro- and nanoscales, materials with high Young’s moduli and low densities are of great interest for high-frequency micromechanical resonator devices1,2,3,4,5,6,7,8. Incorporating carbon nanotubes (CNTs), with their unmatched properties, has added functionality to many man-made composites9,10,11. We report on the fabrication of ≤100-nm-thick laminates by sputter-deposition of aluminium onto a two-dimensional single-walled CNT network12,13. These nanolaminates—composed of Al, its native oxide Al2O3 and CNTs—are fashioned, in a scalable manner, into suspended doubly clamped micromechanical beams. Dynamic flexural measurements show marked increases in resonant frequencies for nanolaminates with Al–CNT laminae. Such increases, further supported by quasi-static flexural measurements, are partly attributable to enhancements in elastic properties arising from the addition of CNTs. As a consequence, these nanolaminate micromechanical resonators show significant suppression of mechanical nonlinearity and enhanced strength, both of which are advantageous for practical applications and analogous to biological nanocomposites, similarly composed of high-aspect-ratio, mechanically superior mineral platelets in a soft protein matrix14.

We present the application of a scanning microwave microscope technique to biological samples. Since dielectric properties of most biological samples originate mainly from the water they contain, we were able to obtain microscope images of biological samples by our scanning microwave microscope technique. As a model system, we have measured the electrical properties of water in the microwave region. The high dielectric constant and the large loss tangent of water were verified. Furthermore, we have measured the properties of water with differing amounts of sodium chloride concentration ranging from de-ionized water to the saturated solution. We have observed a significant change in the resonant frequency and Q value of the resonator as a function of sodium chloride concentration. The concentration dependence of the signals shows that our scanning microwave microscope technique can be useful for investigating the local electric behavior of biological samples with a simple model of ionic conduction.

We have studied the effects of fluorine inclusion on the electrical transport characteristics and interface structure of the hafnium oxide barrier in a magnetic tunnel junction. The tunneling magnetoresistance (TMR) and resistance-area (RA) as a function of oxidation time show that the TMR ratio of the hafnium oxyfluoride barrier is higher (8.3%) than that of the hafnium oxide barrier (5.7%) at their optimum conditions, and the oxyfluoride barrier junctions maintain a high TMR ratio even when the RA product increases by three orders of magnitude. X-ray photoelectron spectroscopy analysis shows that the fluorine atoms in the oxyfluoride barrier play an important role in the formation of a barrier with uniform composition. We believe that the initial fluoride layer is causing the subsequent oxygen diffusion to slow down, resulting in the formation of a defect-free hafnium oxide layer. These results are consistent with what we have found for aluminum oxyfluoride barriers.

The electrical characteristics and the interface structure of magnetic tunnel junctions with aluminum oxyfluoride barrier were studied. Compared to conventional junctions with aluminum oxide tunnel barrier, junctions with aluminum oxyfluoride barrier exhibit larger and nearly constant tunneling magnetoresistance (TMR) values over a wide range of junction resistance and show a smaller bias dependence of TMR, a smaller temperature dependence of junction resistance, and higher effective barrier height. The cross sectional TEM image demonstrates that the junction with oxyfluoride barrier has excellent barrier flatness and smooth interfaces. X-ray photoelectron spectroscopy indicates that the fluorine forms an aluminum oxyfluoride barrier together with oxygen and that the growth of fluorine-rich oxyfluoride layer near the top surface of the barrier plays an important role in the formation of the highly insulating barrier, resulting in nearly ideal barrier/electrode interfaces without a detrimental magnetically dead layer.

We have fabricated a cross-strip-type Ni81Fe19/Co60Fe40/AlOX/Co60Fe40 magnetic tunnel junction (MTJ) and examined the changes of electrical properties through successive dielectric breakdowns. As the successive breakdowns progressed, both junction resistance and tunneling magnetoresistance (TMR) decreased and the temperature dependence of the junction resistance (R–T) shifted from insulating to metal-like behavior. These results can be explained by formation of increasingly conducting but nonmagnetoresistive channels in the barrier. These electrical properties after breakdowns can be described quantitatively with a parallel circuit model.

SrVO3 films were grown by laser molecular beam epitaxy on LaAlO3 substrates. For a 10-nm-thick film, its resistivity could be reduced by a factor of 4 by inserting a single La–O atomic layer on an oxygen-annealed LaAlO3 substrate. X-ray diffraction and x-ray photoelectron spectroscopy measurements revealed that oxygen defect concentrations could be varied significantly by controlling the substrate terminations, i.e., interface chemistry. It was suggested that the interface chemistry could influence formation of extended defects and result in changes in electrical properties.

We report measurements of the thermopower and resistivity of two superconducting ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{BiO}}_{3}$ single crystals with $x\ensuremath{\sim}0.4$ (close to optimal doping), and analyze these data together with earlier data for K concentrations that span the accessible metallic and superconducting phase $0.37lxl0.55.$ The thermopower S for temperatures below 120 K exhibits similar behavior to that seen for the cuprates close to optimal doping: the thermopower is positive for temperatures just above ${T}_{c}$ but decreases with increasing temperature. A change of slope appears in the thermopower data at T\ensuremath{\sim}120--150 K, with an increase in $dS/dT$ above this temperature. We show that all the data can be accounted for by a two-band model similar to that used by Hashimoto et al. to explain the thermopower of the related superconductor, ${\mathrm{BaPb}}_{0.75}{\mathrm{Bi}}_{0.25}{\mathrm{O}}_{3},$ and are consistent with the reported persistence of the charge-density-wave gap in the superconducting phase near the metal-semiconductor transition.

The microstructure of interface engineered ramp-edge Josephson junctions in YBCO has been studied by transmission electron microscopy (TEM). The junctions are distinctly different from the structures found in heterophase SNS junctions. This structural difference can be directly related to the improved electrical properties of interface engineered junctions. The plasma treatment used in the interface engineering method forms a continuous barrier layer of 2 to 3 nm in thickness, much thinner than the deposited heterophase layers in SNS junctions. The layer, which separates the two YBCO layers, is crystalline, but has a crystal structure different from YBCO. The main factors responsible for the improved junction properties and their good reproducibility are: small barrier thickness, small thickness variation, weak interfacial strain fields, flat and nearly defect-free barrier/YBCO interfaces and good epitaxy of the second YBCO layer with few defects. Possible mechanisms for the formation of the large junction resistance are discussed.

Using a combination of scanning probe techniques, including contact mode atomic force microscopy, electric force microscopy, piezoelectric microscopy, and scanning tunneling microscopy, the ferroelectric properties of ferroelectric/metallic oxide heterostructures (Pb(Zr 0.52 Ti 0.48 )O 3 /SrRuO 3 and Sr(Ru 0.37 Ti 0.63 )O 3 /Pb(Zr 0.2 Ti 0.8 )O 3 ) and atomically smooth epitaxial ferroelectric oxides (Pb(Zr 0.2 Ti 0.8 )O 3 and Pb(Zr 0.52 Ti 0.48 )O 3 ) have been studied. Ferroelectric domains in as-grown films were imaged with nanometer resolution, and the domain structure could be modified locally and reversibly. Using the local polarization field of the ferroelectric, nonvolatile, reversible field effects were induced in SrRuO 3 at the submicron level, changing its sheet resistance by up to 300 ohms per square in a fashion that does not require any permanent electrical contacts or associated lithographic processing.