Search

κ-Ga2O3 has been predicted to be a potential ferroelectric material. In this work, undoped Ga2O3 films were grown by either plasma-enhanced atomic layer deposition (PEALD) or metal organic chemical vapor deposition (MOCVD) on platinized sapphire substrates. 50 nm thick PEALD films with a mixture of κ-Ga2O3 and β-Ga2O3 had a relative permittivity of ∼27, a loss tangent below 2%, and high electrical resistivity up to ∼1.5 MV/cm. 700 nm thick MOCVD films with predominantly the κ-Ga2O3 phase had relative permittivities of ∼18 and a loss tangent of 1% at 10 kHz. Neither film showed compelling evidence for ferroelectricity measured at fields up to 1.5 MV/cm, even after hundreds of cycles. Piezoresponse force microscopy measurements on bare κ-Ga2O3 showed a finite piezoelectric response that could not be reoriented for electric fields up to 1.33 MV/cm. [ABSTRACT FROM AUTHOR]

Phase transitions in metastable α-, κ(ε)-, and γ-Ga2O3 films to thermodynamically stable β-Ga2O3 during annealing in air, N2, and vacuum have been systematically investigated via in situ high-temperature x-ray diffraction (HT-XRD) and scanning electron microscopy (SEM). These respective polymorphs exhibited thermal stability to ∼471–525 °C, ∼773–825 °C, and ∼490–575 °C before transforming into β-Ga2O3, across all tested ambient conditions. Particular crystallographic orientation relationships were observed before and after the phase transitions, i.e., (0001) α-Ga2O3 → ( 2 ¯ 01) β-Ga2O3, (001) κ(ε)-Ga2O3 → (310) and ( 2 ¯ 01) β-Ga2O3, and (100) γ-Ga2O3 → (100) β-Ga2O3. The phase transition of α-Ga2O3 to β-Ga2O3 resulted in catastrophic damage to the film and upheaval of the surface. The respective primary and possibly secondary causes of this damage are the +8.6% volume expansion and the dual displacive and reconstructive transformations that occur during this transition. The κ(ε)- and γ-Ga2O3 films converted to β-Ga2O3 via singular reconstructive transformations with small changes in volume and unchanged surface microstructures. [ABSTRACT FROM AUTHOR]

Phase and microstructural evolution of gallium oxide (Ga2O3) films grown on vicinal (0001) sapphire substrates was investigated using a suite of analytical tools. High-resolution transmission electron microscopy and scanning transmission electron microscopy of a film grown at 530 °C revealed the initial pseudomorphic growth of three to four monolayers of α-Ga2O3, a 20–60 nm transition layer that contained both β- and γ-Ga2O3, and a top ∼700 nm-thick layer of phase-pure κ-Ga2O3. Explanations for the occurrence of these phases and their sequence of formation are presented. Additional growths of Ga2O3 films in tandem with x-ray diffraction and scanning electron microscopy investigations revealed that the top layer varied in phase composition between ∼100% κ-Ga2O3 and ∼100% β-Ga2O3; the surface microstructure ranged from poorly coalesced to completely coalesced grains as a function of growth temperature, growth rate, or diluent gas flow rate. In general, it was found that the κ-phase is favored at lower growth temperatures and higher triethylgallium flow rates (low VI/III ratios). The growth of nominally single-phase κ-Ga2O3 within the top layer was observed in a temperature range between 500 and 530 °C. Below 470 °C, only amorphous Ga2O3 was obtained; above 570 °C, only the β-phase was deposited. [ABSTRACT FROM AUTHOR]

A near-ideal and homogeneous β-Ga2O3 Schottky diode with Co contact for a doping level of ∼4.2 × 1017 cm−3 in the drift layer where the Boltzmann approximation is valid is reported. Unlike Si or GaN, thermionic emission is shown to be the dominant current conduction mechanism in the β-Ga2O3 Schottky diode at this doping level. A wide depletion region appended with a large built-in potential is observed to limit the thermionic field emission current, which is otherwise evident in narrower bandgap semiconductor (such as Si or GaN) Schottky diodes having a similar carrier concentration in the drift region. The results shown in this study can be used to identify the theoretical limits of drift layer doping beyond which the ideality factor and reverse leakage current should start deteriorating in ultra-wide bandgap semiconductor based Schottky diodes. [ABSTRACT FROM AUTHOR]

Nominally phase-pure γ-Ga2O3 was deposited on (100) MgAl2O4 within a narrow temperature window centered at ∼470 °C using metal-organic chemical vapor deposition. The film deposited at 440 °C exhibited either poor crystallization or an amorphous structure; the film grown at 500 °C contained both β-Ga2O3 and γ-Ga2O3. A nominally phase-pure β-Ga2O3 film was obtained at 530 °C. Atomic-resolution scanning transmission electron microscopy (STEM) investigations of the γ-Ga2O3 film grown at 470 °C revealed a high density of antiphase boundaries. A planar defect model developed for γ-Al2O3 was extended to explain the stacking sequences of the Ga sublattice observed in the STEM images of γ-Ga2O3. The presence of the 180° rotational domains and 90° rotational domains of β-Ga2O3 inclusions within the γ-Ga2O3 matrix is discussed within the context of a comprehensive investigation of the epitaxial relationship between those two phases in the as-grown film at 470 °C and the same film annealed at 600 °C. The results led to the hypotheses that (i) incorporation of certain dopants, including Si, Ge, Sn, Mg, Al, and Sc, into β-Ga2O3 locally stabilizes the "γ-phase" and (ii) the site preference(s) for these dopants promotes the formation of "γ-phase" and/or γ-Ga2O3 solid solutions. However, in the absence of such dopants, pure γ-Ga2O3 remains the least stable Ga2O3 polymorph, as indicated by its very narrow growth window, lower growth temperatures relative to other Ga2O3 polymorphs, and the largest calculated difference in Helmholtz free energy per formula unit between γ-Ga2O3 and β-Ga2O3 than all other polymorphs. [ABSTRACT FROM AUTHOR]

Atomic resolution scanning/transmission electron microscopy (S/TEM) and energy-dispersive x-ray (EDX) analysis were used to determine the effects of annealing at 800–1000 °C in air on Ga2O3 films grown on (100) MgAl2O4 at 650 °C via metal-organic chemical vapor deposition. Annealing resulted in the diffusion of Mg and Al into the films concomitantly with the transformation of β-Ga2O3 to γ-Ga2O3 solid solutions. The minimum atomic percent of Al + Mg that corresponded with the transformation was ∼4.6 at. %. Analyses of atomic-scale STEM images and EDX profiles revealed that the Al and Mg atoms in the γ-Ga2O3 solid solutions occupied octahedral sites; whereas the Ga atoms occupied tetrahedral sites. These site preferences may account for the stabilization of the γ-Ga2O3 solid solutions. [ABSTRACT FROM AUTHOR]

Importance: Adolescents and adults report that their sensory integration and processing differences affect their occupational performance and quality of life, thus requiring effective sensory-focused interventions. Researchers have yet to investigate this population's experience of occupational therapy interventions designed to remediate these challenges. Objective: To explore the perceived experience of adolescents and adults with respect to (1) response to intervention, (2) strategies offered to manage sensory differences, and (3) need for services on completion of an intervention. Design: Retrospective, qualitative study. Setting: Zoom or phone call. Participants: Eleven adolescents and adults with sensory integration and processing differences who had previously completed occupational therapy interventions. Intervention: Sensory-based intervention based on the principles of Ayres Sensory Integration® (ASI) and the Sensory Therapies and Research Frame of Reference. Outcomes and Measures: A semistructured interview to obtain data, followed by an in-depth analysis using an inductive coding process to group initial open codes into themes and common subthemes Results: Open codes were grouped into three core themes: (1) therapist-related factors (what the therapist did in treatment); (2) client-related factors (what the client experienced); and (3) follow-up (future needs of the clients). Four main subthemes of the client–therapist relationship emerged: (1) therapeutic alliance; (2) education and knowledge; (3) strategies, tools, and resources; and (4) future needs. Conclusions and Relevance: This study provides a perspective on the experience of adolescents and adults specific to the impact of a sensory-focused occupational therapy intervention on their daily lives. This will help occupational therapists when designing interventions for current and future clients. What This Article Adds: This study highlights the need for further research addressing effective sensory-based interventions for adolescents and adults. It also captures which components of intervention clients deemed helpful and identifies potential targets for future intervention. This study highlights the need for further research that addresses effective sensory-based occupational therapy interventions for adolescents and adults. It also captures which components of intervention clients deemed helpful and identifies potential targets for future intervention. [ABSTRACT FROM AUTHOR]

Ga2O3 films were deposited on (100) MgAl2O4 spinel substrates at 550, 650, 750, and 850 ° C using metal-organic chemical vapor deposition and investigated using x-ray diffraction and transmission electron microscopy. A phase-pure γ-Ga2O3-based material having an inverse spinel structure was formed at 850 °C; a mixture of the γ-phase and β-Ga2O3 was detected in films grown at 750 ° C. Only β-Ga2O3 was determined in the films deposited at 650 and 550 ° C. A β- to γ-phase transition occurred from the substrate/film interface during growth at 750 ° C. The growth and stabilization of the γ-phase at the outset of film growth at 850 ° C was affected by the substantial Mg and Al chemical interdiffusion from the MgAl2O4 substrate observed in the energy-dispersive x-ray spectrum. Atomic-scale investigations via scanning transmission electron microscopy of the films grown at 750 and 850 ° C revealed a strong tetrahedral site preference for Ga and an octahedral site preference for Mg and Al. It is postulated that the occupation of these atoms in these particular sites drives the β-Ga2O3 to γ-phase transition and markedly enhances the thermal stability of the latter phase at elevated temperatures. [ABSTRACT FROM AUTHOR]

Thin (40–150 nm), highly doped n+ (1019–1020 cm−3) Ga2O3 layers deposited using pulsed laser deposition (PLD) were incorporated into Ti/Au ohmic contacts on (001) and (010) β-Ga2O3 substrates with carrier concentrations between 2.5 and 5.1 × 1018 cm−3. Specific contact resistivity values were calculated for contact structures both without and with a PLD layer having different thicknesses up to 150 nm. With the exception of a 40 nm PLD layer on the (001) substrate, the specific contact resistivity values decreased with increasing PLD layer thickness: up to 8× on (001) Ga2O3 and up to 16× on (010) Ga2O3 compared with samples without a PLD layer. The lowest average specific contact resistivities were achieved with 150 nm PLD layers: 3.48 × 10−5 Ω cm2 on (001) Ga2O3 and 4.79 × 10−5 Ω cm2 on (010) Ga2O3. Cross-sectional transmission electron microscopy images revealed differences in the microstructure and morphology of the PLD layers on the different substrate orientations. This study describes a low-temperature process that could be used to reduce the contact resistance in Ga2O3 devices. [ABSTRACT FROM AUTHOR]

We have investigated the thermal stability of Co/Au and Ni/Au Schottky contacts to Sn-doped ( 2 ¯ 01) β-Ga2O3 substrates. Current–voltage (I–V) and capacitance–voltage (C–V) measurements were conducted after sequential annealing treatments totaling > 400 h at 300°C and > 150 h at 500°C in vacuum. For both sets of contacts, the average Schottky barrier heights (SBHs) calculated from the I–V measurements displayed no significant changes and remained within a narrow range throughout the anneals at 300°C. The SBHs calculated from the C–V measurements also remained largely constant for 300°C anneals, except for a modest increase for both contacts for anneal times > 350 h. For 500°C anneals, the I–V characteristics for Ni/Au and Co/Au contacts displayed continual degradation in the electrical behavior after 12 h and 24 h, respectively. Characterizations using scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and scanning electron microscopy of the samples annealed at 500°C revealed considerable changes in film morphology, interdiffusion, and phase segregation within the contacts. The results suggest the potential for Co/Au or Ni/Au Schottky contacts to be used in Ga2O3 devices at temperatures below, or possibly up to, 300°C, whereas higher temperatures will require modified metallization schemes. [ABSTRACT FROM AUTHOR]

Importance: Parent training is an essential part of occupational therapy intervention for children with sensory processing and sensory integration (SP–SI) challenges, and parents' learning needs should be considered. Objective: To identify the extent to which adult learning needs are considered in occupational therapy literature addressing parent training as a part of intervention for children with SP–SI challenges. Data Sources: Searches were performed of the following databases: MEDLINE, PsycINFO, CINAHL, Web of Science, EMBASE, and ERIC. The date range was limited to 1990 to 2019 to capture literature focused on family-centered care. Study Selection and Data Collection: Using Arksey and O'Malley's framework for scoping reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews Checklist, the following criteria were used to guide the literature searches: population (parents and families of children with SP–SI challenges), intervention (parent training), outcomes (parent learning needs), and concept (parents as adult learners). Findings: Searches produced 133 peer-reviewed articles, and 5 met the criteria for inclusion. Qualitative thematic analysis, including stakeholder interviews, revealed two themes: (1) Parents focus on children's needs, not their own, and (2) parents benefit from connection with peers and learn through shared experiences. Conclusions and Relevance: Parent training is an essential component of occupational therapy; however, there is limited occupational therapy evidence examining parents' learning needs, specifically parents of children with SP–SI challenges. Future studies should investigate parents' learning needs in relation to occupational therapy intervention for families of children with SP–SI challenges. What This Article Adds: Parents' learning needs are both rarely considered in the occupational therapy literature and important for best practice in pediatric therapy for children with SP–SI challenges. The results of this scoping review point to the need for further investigation of parent training programs specifically examining parents as adult learners. The results of this scoping review identify the limited extent to which adult learning needs are considered in occupational therapy literature, specifically for parents of children with sensory processing and sensory integration (SP–SI) challenges, and point to the need for further investigation of parents' learning needs in relation to occupational therapy intervention. [ABSTRACT FROM AUTHOR]

Cardiac ATP-sensitive [K.sup.+] ([K.sub.ATP]) channels are formed by Kir6.2 and SUR2A subunits. We produced transgenic mice that express dominant negative Kir6.x pore-forming subunits (Kir6.1-AAA or Kir6.2-AAA) in cardiac myocytes by driving their expression with the [alpha]-myosin heavy chain promoter. Weight gain and development after birth of these mice were similar to nontransgenic mice, but an increased mortality was noted after the age of 4-5 mo. Transgenic mice lacked cardiac [K.sub.ATP] channel activity as assessed with patch clamp techniques. Consistent with a decreased current density observed at positive voltages, the action potential duration was increased in these mice. Some myocytes developed EADs after isoproterenol treatment. Hemodynamic measurements revealed no significant effects on ventricular function (apart from a slightly elevated heart rate), whereas in vivo electrophysiological recordings revealed a prolonged ventricular effective refractory period in transgenic mice. The transgenic mice tolerated stress less well as evident from treadmill stress tests. The proarrhythmogenic features and lack of adaptation to a stress response in transgenic mice suggest that these features are intrinsic to the myocardium and that [K.sub.ATP] channels in the myocardium have an important role in protecting the heart from lethal arrhythmias and adaptation to stress situations. potassium channels; ATP-sensitive [K.sup.+] channel; heart; ventricle; stress responses doi:10.1152/ajpheart.00051.2006

Date Presented 03/23/24 This qualitative study explores the experience of eleven adults and adolescents with sensory integration/processing differences through semi-structured interviews after completion of intervention. Implications relate to better targeted intervention. Primary Author and Speaker: Dana Miller Additional Authors and Speakers: Sarah A. Schoen, Carolyn M. Schmitt, Lisa M. Porter [ABSTRACT FROM AUTHOR]

A study was conducted on the role of QLS motif in transmembrane helix VII of the glucose transporter family. The findings indicate that the QLS motif in helix VII functions as a molecular filter that dictates the ability of GLUTs 1, 3 and 4 to transport glucose. Moreover, this region of helix VII plays a key role in substrate recognition at the exofacial substrate binding site by interaction with the C-1 position of the incoming sugar molecule.

Alanine-scanning mutagenesis of putative transmembrane helix VIII and an investigation of the role of proline residues in transport catalysis were conducted to understand the structure-function of the brain-type glucose transporter, GLUT3. Results reveal that no individual amino acid within the helix is required for transport catalysis. Results also suggest that the role of the helix is to provide a framework for structural packing within the transporter molecule.

A range of chimeric glucose transporters composed of regions of liver-type (GLUT2) and brain-type (GLUT3) human facilitative glucose transporters were produced to determine the regions of the transporter which are involved in substrate recognition and binding. Findings indicate a model in which the seventh putative transmembrane-spanning helix is intimately involved in the selection of transported substrate and in which this region plays a critical role in determining the K(sub m) for 2-deoxyglucose.

Chemical and electrical measurements of Ti/(010) β-Ga2O3 and Ti/(001) β-Ga2O3 interfaces were conducted as a function of annealing temperature using x-ray photoelectron spectroscopy (XPS), current density–voltage (J–V), and capacitance–voltage (C–V) measurements. XPS revealed partial Ti oxidation at both interfaces in the as-deposited condition, with more Ti oxidation on the (001) β-Ga2O3 epilayer surface than the (010) β-Ga2O3 substrate surface. The amount of oxidized Ti increased with annealing temperature. The Schottky barrier heights for as-deposited (unannealed) Au/Ti/(010) β-Ga2O3 and Au/Ti/(001) β-Ga2O3 contacts as determined from J–V and C–V measurements were between 0.64 and 0.83 eV. Shifts in XPS core level peaks for Ti/(010) β-Ga2O3 suggest that the Schottky barrier height decreases with temperature up to 350 °C for 10-min anneals and increases for 10-min anneals ≥460 °C. Taken together, the results suggest a strong dependence of Ti reactivity on the β-Ga2O3 surface, which can affect the electrical performance and stability of Ti/β-Ga2O3 ohmic contacts at elevated temperatures. [ABSTRACT FROM AUTHOR]

The Schottky barriers of Ti, Mo, Co, Ni, Pd, and Au on (100) β-Ga2O3 substrates were analyzed using a combination of current-voltage (J-V), capacitance-voltage (C-V), and current-voltage-temperature (J-V-T) measurements. Near-ideal, average ideality factors for Ti, Mo, Co, and Ni were 1.05–1.15, whereas higher ideality factors (∼1.3) were observed for Pd and Au contacts. Barrier heights ranging from 0.60 to 1.20 eV were calculated from J-V measurements for the metals with low ideality factors. C-V measurements of all Schottky metals were conducted and yielded average barrier heights ranging from 0.78 to 1.98 eV. J-V-T measurements of Ti and Co diodes yielded barrier heights of 0.81 and 1.35 eV, respectively. The results reveal a strong positive correlation between the calculated Schottky barrier heights and the metal work functions: the index of interface behavior, S = 0.70, 0.97, and 0.81 for J-V, C-V, and J-V-T data, respectively. [ABSTRACT FROM AUTHOR]

Nanocrystalline tin sulfide (SnS) thin films were deposited by electron-beam evaporation at growth temperatures ranging from room temperature to 300 °C and characterized prior to and after annealing at 300 °C in high vacuum. X-ray diffraction and Raman spectroscopy results indicated that SnS films deposited at 100 and 200 °C contained predominately a mixture of orthorhombic α-SnS and cubic π-SnS phases, whereas only α-SnS was detected in SnS films deposited at 300 °C. Contacts with a range of work functions were deposited onto p-type α-SnS films. All of the contacts investigated (Ti/Au, Ru/Au, Ni/Au, and Au) were ohmic as-deposited and yielded average specific contact resistance values that decreased with increasing metal work function, suggesting that the barrier height has at least a partial dependence on the work functions of the metals. Annealing at 350 °C for 5 min in Ar reduced the specific contact resistance value for Ru/Au contacts, resulting in the lowest value (1.9 × 10−3 Ω cm2) of contacts investigated to SnS thin films. [ABSTRACT FROM AUTHOR]

Heteroepitaxial films of Ga2O3 were grown on c-plane sapphire (0001). The stable phase β-Ga2O3 was grown using the metalorganic chemical vapor deposition technique, regardless of precursor flow rates, at temperatures between 500°C and 850°C. Metastable α- and ε-phases were grownwhen using the halide vapor phase epitaxy (HVPE) technique, at growth temperatures between 650°C and 850°C, both separately and in combination. XTEM revealed the better lattice-matched α-phase growing semi-coherently on the substrate, followed by ε-Ga2O3. The epitaxial relationship was determined to be [1100] ε-Ga2O3 || [1120] α-Ga2O3 || [1120] α-Al2O3. SIMS revealed that epilayers forming the ε-phase contain higher concentrations of Cl introduced during HVPE growth. [ABSTRACT FROM AUTHOR]

Schottky diodes based on (–201) b-Ga2O3 substrates and (010) b-Ga2O3 homoepitaxial layers were formed using five different Schottky metals: W, Cu, Ni, Ir and Pt. Based on a comparison of the effects of different wet chemical surface treatments on the Ga2O3 Schottky diodes, it was established that a treatment with an organic solvent, cleaning with HCl and H2O2 and rinsing with deionized water following each step yielded the best results. Schottky barrier heights calculated from current-voltage (I-V) and capacitance-voltage (C-V) measurements of the five selected metals were typically in the range of 1.0-1.3 and 1.6-2.0 eV, respectively and showed little dependence on the metal work function. Several diodes also displayed inhomogeneous Schottky barrier behavior at room temperature. The results indicate that bulk or near-surface defects and/or unpassivated surface states may have a more dominant effect on the electrical behavior of these diodes compared to the choice of Schottky metal and its work function. [ABSTRACT FROM AUTHOR]

Calculated frequency distributions of atom probe tomography reconstructions (~80nm field of view) of very thin AlxGa1- xN (0.18=x=0.51) films grown via metalorganic vapor phase epitaxy on both (0001) GaN/AlN/SiC and (0001) GaN/sapphire heterostructures revealed homogeneous concentrations of Al and chemically abrupt AlxGa1- xN/GaN interfaces. The results of scanning transmission electron microscopy and selected area diffraction corroborated these results and revealed that neither superlattice ordering nor phase separation was present at nanometer length scales. [ABSTRACT FROM AUTHOR]

In0.20Ga0.80N/GaN multiquantum wells (MQWs) grown on [0001]-oriented GaN substrates with and without an InGaN buffer layer were characterized using three-dimensional atom probe tomography. In all samples, the upper interfaces of the QWs were slightly more diffuse than the lower interfaces. The buffer layers did not affect the roughness of the interfaces within the quantum well structure, a result attributed to planarization of the surface of the first GaN barrier layer, which had an average root-mean-square roughness of 0.18 nm. The In and Ga distributions within the MQWs followed the expected distributions for a random alloy with no indications of In clustering. High resolution Rutherford backscattering characterizations showed the ability to resolve the MQWs, and the resulting compositions and widths corroborated those determined from the atom probe analyses. [ABSTRACT FROM AUTHOR]

Nanostructured carbon (ns-C) films fabricated by stabilization and pyrolysis of diblock copolymers are of interest for a variety of electrical/electronic applications due to their chemical inertness, high-temperature insensitivity, very high surface area, and tunable electrical resistivity over a wide range [Kulkarni et al., Synth. Met. 159, 177 (2009)]. Because of their high porosity and associated high specific surface area, controlled surface cleaning studies are important for fabricating electronic devices from these films. In this study, quantification of surface composition and surface cleaning studies on ns-C films synthesized by carbonization of diblock copolymers of polyacrylonitrile-b-poly(n-butyl acrylate) at two different temperatures were carried out. X-ray photoelectron spectroscopy was used for elemental analysis and to determine the efficacy of various surface cleaning methods for ns-C films and to examine the polymer residues in the films. The in-situ surface cleaning methods included HF vapor treatment, vacuum annealing, and exposure to UV-ozone. Quantitative analysis of high-resolution XPS scans showed 11 at. % nitrogen was present in the films pyrolyzed at 600 °C, suggesting incomplete denitrogenation of the copolymer films. The nitrogen atomic concentration decreased significantly for films pyrolyzed at 900 °C confirming extensive denitrogenation at that temperature. Furthermore, quantitative analysis of nitrogen subpeaks indicated higher loss of nitrogen atoms residing at the edge of graphitic clusters relative to that of nitrogen atoms within the graphitic clusters, suggesting higher graphitization with increasing pyrolysis temperature. Of the surface cleaning methods investigated, in-situ annealing of the films at 300 °C for 40 min was found to be the most efficacious in removing adventitious carbon and oxygen impurities from the surface. [ABSTRACT FROM AUTHOR]

Cardiac ATP-sensitive K+ (KATP) channels are formed by Kir6.2 and SUR2A subunits. We produced transgenic mice that express dominant negative Kir6.x pore-forming subunits (Kir6.1-AAA or Kir6.2-AAA) in cardiac myocytes by driving their expression with the α-myosin heavy chain promoter. Weight gain and development after birth of these mice were similar to nontransgenic mice, but an increased mortality was noted after the age of 4–5 too. Transgenic mice lacked cardiac KATP channel activity as assessed with patch clamp techniques. Consistent with a decreased current density observed at positive voltages, the action potential duration was increased in these mice. Some myocytes developed EADs after isoproterenol treatment. Hemodynamic measurements revealed no significant effects on ventricular function (apart from a slightly elevated heart rate), whereas in vivo electrophysiological recordings revealed a prolonged ventricular effective refractory period in transgenic mice. The transgenic mice tolerated stress less well as evident from treadmill stress tests. The proarrhythmogenic features and lack of adaptation to a stress response in transgenic mice suggest that these features are intrinsic to the myocardium and that KATP channels in the myocardium have an important role in protecting the heart from lethal arrhythmias and adaptation to stress situations. [ABSTRACT FROM AUTHOR]

Introduction: ATP-sensitive K+ channels (KATP) are expressed abundantly in cardiovascular tissues. Blocking this channel in experimental models of ischemia can reduce arrhythmias. We Investigated the acute effects of amiodarone on the activity of cardiac sarcolemmal KATP channels and their sensitivity to ATP. Methods and Results: Single KATP channel activity was recorded using inside-out patches from rat ventricular myocytes (symmetric 140 mM K+ solutions and a pipette potential of +40 mV). Amiodarone inhibited KATP channel activity in a concentration-dependent manner. After 60 seconds of exposure to amiodarone, the fraction of mean patch current relative to baseline current was 1.0 ± 0.05 (n = 4), 0.8 ± 0.07 (n = 4), 0.6 ± 0.07 (n = 5), and 0.2 ± 0.05 (n = 7) with 0, 0.1, 1.0, or 10 μM amiodarone, respectively (IC50 = 2.3 μM). ATP sensitivity was greater in the presence of amiodarone (EC50 = 13 ± 0.2 μM in the presence of 10 μM amiodarone vs 43 ± 0.1 μM in controls, n = 5; P < 0.05). Kinetic analysis showed that open and short closed intervals (bursting activity) were unchanged by 1 μM amiodarone, whereas interburst closed intervals were prolonged. Amiodarone also inhibited whole cell KATP channel current (activated by 100 μM bimakalim). After a 10-minute application of amiodarone (10 μM), relative current was 0.71 ± 0.03 vs 0.92 ± 0.09 in control (P < 0.03). Conclusion: Amiodarone rapidly inhibited KATP channel activity by both promoting channel closure and increasing ATP sensitivity. These actions may contribute to the antiarrhythmic properties of amiodarone. [ABSTRACT FROM AUTHOR]

Thermal conductivities (k) of the individual layers of a GaN-based light emitting diode (LED) were measured along [0001] using the 3-omega method from 100-400 K. Base layers of AlN, GaN, and InGaN, grown by organometallic vapor phase epitaxy on SiC, have effective k much lower than bulk values. The 100 nm thick AlN layer has k = 0.93 ± 0.16 W/mK at 300 K, which is suppressed >100 times relative to bulk AlN. Transmission electron microscope images revealed high dislocation densities (4 × 1010 cm-2) within AlN and a severely defective AlN-SiC interface that cause additional phonon scattering. Resultant thermal resistances degrade LED performance and lifetime making layer-by-layer k, a critical design metric for LEDs. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial hexagonal YMnO3 (h-YMnO3) films having sharp (00l) X-ray diffraction peaks were grown above 700 °C in 5 mTorr O2 via pulsed laser deposition both on as-received wurtzite GaN/AlN/6H-SiC(001) (w-GaN) substrates as well as on w-GaN surfaces that were etched in 50% HF solution. High-resolution transmission electron microscopy revealed an interfacial layer between film and the unetched substrate; this layer was absent in those samples wherein an etched substrate was used. However, the substrate treatment did not affect the epitaxial arrangement between the h-YMnO3 film and w-GaN substrate. The epitaxial relationships of the h-YMnO3 films with the w-GaN(001) substrate was determined via X-ray diffraction to be (001)YMnO3 ‖(001)GaN :[11¯0]YMnO3 ‖[110]GaN; in other words, the basal planes of the film and the substrate are aligned parallel to one another, as are the most densely packed directions in planes of the film and the substrate. Interestingly, this arrangement has a larger lattice mismatch than if the principal axes of the unit cells were aligned. [Copyright &y& Elsevier]

We have examined the growth of thin Pt films on the polar SrTiO3(1 1 1) surface using both experimental and theoretical methods. Pt films were grown on both as-received and treated substrates using electron-beam evaporation, and then were characterized with X-ray and low-energy electron diffraction and atomic force microscopy. The nature of the substrate surface strongly influences the crystallinity and microstructure of the Pt films. We find that for well-treated, crystalline SrTiO3(1 1 1) substrates we obtain crystalline Pt(1 1 1) films. In addition, the first few layers strongly replicate the surface structure of the substrate. XRD results demonstrate that even the best films exhibit two distinct in-plane domains separated by 60°, equivalent to the existence of inversion domains. Density functional theory (DFT) calculations were performed for 1–4 monolayers of Pt on both terminations of SrTiO3(1 1 1). These calculations find that two energetically equivalent stacking sequences are possible for the second monolayer of Pt, corresponding to the observed 60° domains. We propose that these stacking faults are the source of the observed domains in crystalline Pt(1 1 1) films grown on polar SrTiO3(1 1 1) surfaces. Finally, the DFT calculations corroborate the observation that the structures and growth modes of the first few monolayers are coupled strongly to the substrate, yet the films quickly relax to bulk-like Pt arrangements and homoepitaxial growth modes. [Copyright &y& Elsevier]