International Photonics and Optoelectronics Meetings (POEM), 2013
Sputtering process of CIGS thin film without post-selenization process. The CIGS layers were fabr... more Sputtering process of CIGS thin film without post-selenization process. The CIGS layers were fabricated by using a sputtering system with four 2-inch magnetron sputtering guns and a rotatable substrate holder with heating apparatus. Back molybdenum electrode with thickness of 1 µm was deposited onto pre-cleaned 2 × 2 cm 2 soda-lime glass (SLG) substrate by DC magnetron sputtering. CIGS films with the chalcopyrite phase were deposited by direct sputtering of a single quaternary CIGS target.
Magnesium-doped zinc oxide (MZO) films were fabricated by pulsed-laser deposition (PLD) at variou... more Magnesium-doped zinc oxide (MZO) films were fabricated by pulsed-laser deposition (PLD) at various substrate temperatures (T s ). The substitution of Mg for Zn sites (Mg Zn ) in the films was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and room-temperature photoluminescence (RTPL) measurements. Characteristic deep-level emissions (DLE) observed in the RTPL spectra further indicate the presence of Zn vacancies (V Zn ) in the MZO films. Moreover, it was found that the intensity of the blue emission corresponding to V Zn increases with increasing T s , indicating the important role played by T s on the incorporation of Mg into ZnO matrix. Hall effect measurements reveal the p-type conduction of the MZO films grown at 400°C. The p-type characteristic is attributed to the formation of nMg Zn -V Zn complex which could act as acceptor for MZO films.
Amorphous indium-tin-oxide (a-ITO) film was deposited by radio-frequency (RF) magnetron sputterin... more Amorphous indium-tin-oxide (a-ITO) film was deposited by radio-frequency (RF) magnetron sputtering at 180°C substrate temperature on the texturized p-Si wafer to fabricate a-ITO/p-Si heterojunction solar cell. The microstructural, optical and electrical properties of the a -ITO film were characterized by XRD, SEM, XPS, UV-VIS spectrophotometer, four-point probe and Hall effect measurement, respectively. The electrical properties of heterojunction were investigated by I-V measurement, which reveals that the heterojunction shows strong rectifying behavior under a dark condition. The ideality factor and the saturation current density of this diode are 2.26 and 1.58×10 4 A cm 2 , respectively. And the value of I F /I R (I F and I R stand for forward and reverse currents, respectively) at 1 V is found to be as high as 21.5. For the a-ITO/p-Si heterojunction solar cell, the a-ITO thin film acts not only as an emitter layer, but also as an anti-reflected coating film. The conversion efficiency of the fabricated a-ITO/p-Si heterojunction cell is approximately 1.1%, under 100 mW cm -2 illumination (AM1.5 condition). And the open-circuit voltage (V oc ), short-circuit current density (J SC ), filll factor (FF) are 280 mV, 9.83 mA cm 2 and 39.9%, respectively. Because the ITO film deposited at low temperature is amorphous, it can effectively reduce the interface states between ITO and p-Si. The barrier height and internal electric field, which is near the surface of p-Si, can effectively be enhanced. Thus we can see the great photovoltaic effect. amorphous indium-tin-oxide (a-ITO) film, radio-frequency (RF) magnetron sputtering, heterojunction solar cell, current-voltage (I-V) characteristics
The nano-scale deformation behaviors and indentation-induced fracture features of the (111)-orien... more The nano-scale deformation behaviors and indentation-induced fracture features of the (111)-oriented yttrium-stabilized zirconia single crystal (YSZ(111)) were investigated by Berkovich and micro-Vicker indentations, respectively. The load-displacement curves in the Berkovich nano-indentation experiments evidently exhibited indentation-induced single "pop-in" phenomenon during loading, indicating that the nano-scale deformation in the YSZ(111) crystals is due primarily to the activities of dislocation nucleation and propagation. Based on this scenario, the number of nanoindentation-induced dislocation loops giving rise to the pop-in event was estimated to be around 2×10 5 with a critical radius of ∼2nm. The hardness and Young's modulus of YSZ(111) single crystal obtained by the continuous contact stiffness measurements (CSM) mode were 22.3 ± 1.1 GPa and 270.6 ± 8.5 GPa, consistent with those reported previously in the literature. In addition, the fracture toughness of YSZ(111) single crystal was estimated to be about 1.4-1.6 MPa• m 1/2 .
This article was originally published online on 28 August 2017. Due to a production error, in the... more This article was originally published online on 28 August 2017. Due to a production error, in the originallypublished version the sentences "The measured lifetime of 2269 hrs … MDM device" (page 4, right column) contained edits which altered the intended meaning. AIP Publishing apologizes for this error. The corrected sentences are "The measured lifetime of 2269 hrs from the conventional device is related to the intrinsic emitting material of 24Ftir(acac). In fact, the lifetime is even slightly longer in the blueshifted MDM device." All online versions of the article were corrected on
In this study, the mechanical deformation behaviors of Au nanotubes (Au-NTs) under torsional stre... more In this study, the mechanical deformation behaviors of Au nanotubes (Au-NTs) under torsional stress are investigated using molecular dynamics (MD) simulations. The inter-atomic interaction is modeled using the embedded-atom potential. In particular, the effects of loading rate, thickness and length of the nanotube, as well as the thermal effects were systematically explored. The results indicated that higher loading rate, longer length and thinner wall thickness all led to a larger value of critical torsional angle (θ cr ), which signifies the onset of plastic deformation. On the other hand, θ cr decreases with increasing temperature in all simulated results. Moreover, the torsional buckling deformation behavior and geometrical instability are found to strongly depend on the length of Au-NTs, the applied strain rate and temperature with vastly different underlying mechanisms.
This article reports a nanomechanical response study of the contact-induced deformation behavior ... more This article reports a nanomechanical response study of the contact-induced deformation behavior in Al 0.16 Ga 0.84 N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy ͑XTEM͒ techniques. Al 0.16 Ga 0.84 N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young's modulus of the Al 0.16 Ga 0.84 N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young's modulus are 19.76Ϯ 0.15 and 310.63Ϯ 9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple "pop-ins" observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved.
The effects of post-annealing on the microstructures, surface morphologies and nanomechanical cha... more The effects of post-annealing on the microstructures, surface morphologies and nanomechanical characteristics of FePd thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and nanoindentation techniques. The FePd thin films were deposited on the glass substrates at room temperature by magnetron sputtering system. Postannealing was carried out at 500, 600 and 700 C, respectively, resulting in progressive increase of the average grain size and surface roughness of FePd thin films, as well as the improved film crystallinity. XRD results show that FePd thin films are predominantly (111)-oriented, indicating a well-ordered microstructure. The hardness and Young's modulus of FePd thin films measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option indicated that both mechanical properties are decreased with increasing the annealing temperature. Furthermore, the relationship between the hardness and films grain size appears to follow closely with the HallePetch equation.
Carbon‐Shielded Single‐Atom Alloy Material Family for Multi‐Functional Electrocatalysis
Advanced Functional Materials
Encapsulating metal‐based catalysts inside carbon sheaths is a frequently‐adopted strategy to enh... more Encapsulating metal‐based catalysts inside carbon sheaths is a frequently‐adopted strategy to enhance their durability under various harsh situations and improve their catalytic activity simultaneously. Such carbon encapsulation, however, imposes significant complications for directly modifying materials’ surface atomic/electronic configurations, fundamentally impeding the accurate tuning of their catalytic capabilities. Herein, a universal single‐atom alloy (SAA) strategy is reported to indirectly yet precisely manipulate the surface electronic structure of carbon‐encapsulated electrocatalysts. By versatilely constructing a SAA core inside an N‐doped carbon sheath, material's electrocatalytic capability can be flexibly tuned. The one with Ru‐SAA cores serves as an excellent bifunctional electrocatalyst for oxygen/hydrogen evolution, exhibiting minimal cell voltage of 1.55 V (10 mA cm−2) and outstanding mass activity of 1251 mA m for overall water splitting, while the one with I...
Regulating the Electronic Configuration of Supported Iron Nanoparticles for Electrochemical Catalytic Nitrogen Fixation
Advanced Functional Materials, 2022
Electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the tradition... more Electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the traditional Haber–Bosch process due to its eco‐friendly nature and capability of utilizing renewable energy. However, its low Faradic efficiency (FE), caused by the excessive adsorption and reduction of protons, has been regarded as the main challenge, which leads to low ammonia yield as well. Herein, a carbon‐supported iron electrocatalyst is reported, which is fabricated by low‐temperature (300 °C) potassium vapor reduction of FeF3‐intercalated graphite fluoride, for efficient electrochemical nitrogen reduction. The strategy enables the unique formation of exposed Fe nanoparticles uniformly anchored on graphene and in situ doped with fluorine heteroatoms. These specific features can alter the electronic configuration of the Fe nanoparticles, leading to strong surface polarization that boosts nitrogen absorption capability for eNRR, resulting in high FE (41.6%) and ammonia yield rate (53.3 μg h‐...
A series of investigations on the interrupted deposition of laser ablation strontium titanate epi... more A series of investigations on the interrupted deposition of laser ablation strontium titanate epitaxy growth were conducted. RHEED intensity recovery curves at various temperatures show a near-quadratic power law dependence on annealing time. Combined with the evidence showing the intimate correlation between the step edge density and the RHEED intensity, a diffusion Arrhenius plot with the activation energy of 1.0 eV was obtained for the kinetics of step edge migration.
By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnet... more By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnetic penetration depth k(T) in YBa2Cu3O7� d (YBCO) and Y0.7Ca0.3Ba2Cu3O7� d (Ca-YBCO) epitaxially grown thin films, the linear temperature dependence of the superfluid density qs/m* � 1/k 2 (T) was observed from the under- to the overdoped regime at the temperatures below T T c � 0:3. For the underdoped regime of YBCO and Ca-YBCO thin films, the magnitude of the slope d(1/k 2 (T))/dT is insensitive to doping, and it can be treated in the framework of projected d-density-wave model. Combining these slope values with the thermal conductivity measurements, the Fermi-liquid correction factor a 2 from the Fermi-liquid model, suggested by Wen and Lee, was revealed here with various doping levels.
Metastable ε-Fe2O3 is a unique phase of iron oxide, which exhibits a giant coercivity field. In t... more Metastable ε-Fe2O3 is a unique phase of iron oxide, which exhibits a giant coercivity field. In this work, we grew epitaxial ε-Fe2O3 films on flexible two-dimensional muscovite substrates via quasi van der Waals epitaxy. It turns out that twinning and interface energies have been playing essential roles in stabilizing metastable ε-Fe2O3 on mica substrates. Moreover, the weak interfacial bonding between ε-Fe2O3 and mica is expected to relieve the substrate clamping effect ubiquitously encountered in films epitaxially grown on rigid substrates, such as SrTiO3. It is anticipated that these flexible ε-Fe2O3 thin films can serve as a platform for exploring possible interesting emergent physical properties and eventually be integrated as flexible functional devices.
The gas discharge and photo-luminance properties of a planar lighting source featuring highly uni... more The gas discharge and photo-luminance properties of a planar lighting source featuring highly uniform light emission and mercury-free design were studied. The current density-voltage characteristics and the associated gas discharge of the devices operating with the values of the ratio of electric field to gas pressure (E/p) between 4.3 kV/Torr-cm and 35.7 kV/Torr-cm indicate that the width of the cathode fall extends over the entire gap between the two electrodes and the device is mostly in the obstructed discharge regime. The optical emission analysis confirmed the electron collision-induced gas emissions and strong effect of gas pressure on the phosphor emission when operated at constant current density, both are indicative of the primary roles played by the electron energy.
In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attenti... more In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attention because a high interface-to-volume ratio can be used to tailor or create functionalities. We have systematically investigated the magnetic properties of oxide heterostructures consisting of the CoFe 2 O 4 nanopillars embedded in the BiFeO 3 matrix using macroscopic magnetization measurements and element-selective soft X-ray absorption magnetic circular dichroism (XMCD) at the Co-and Fe-L 2,3 edge. The magnetization and XMCD data show that the total ordered magnetic moment of Co 2+ in CoFe 2 O 4 -BiFeO 3 nano-heterostructures is strongly enhanced. This study clearly indicates that the high interfaceto-volume ratio vertical nanostructure creates a strong ferromagnetic and antiferromagnetic magnetic coupling via an interface. Furthermore, the magnetic coupling can be tuned in the multiferroicferrimagnetic self-assembled heterostructures by controlling the spacing between nanopillars.
Journal of Superconductivity and Novel Magnetism, 2012
The surface impedance of Y 0.9 Ca 0.1 Ba 2 Cu 3 O 7-δ thin films was measured using the Corbino s... more The surface impedance of Y 0.9 Ca 0.1 Ba 2 Cu 3 O 7-δ thin films was measured using the Corbino spectroscopy method. This special geometry, in which the sample dimensions are well defined by a ring pattern, is ideal for broadband high frequency reflection measurements. Using the complex reflected signal, S 11 , measured by a vector network analyzer, one can find the surface impedance of the thin film, from which the complex conductivity can be deduced. In the current work we present the three-standard approach for calibration of the Corbino method and demonstrate the benefits of this approach in measuring superconducting Y 0.9 Ca 0.1 Ba 2 Cu 3 O 7-δ thin films up to 20 GHz and down to 6 K. For the data analysis the well-known generalized two-fluid model was implemented, taking into account a film thickness which is much smaller than the normal state skin depth and superconducting penetration depth.
International Photonics and Optoelectronics Meetings (POEM), 2013
Sputtering process of CIGS thin film without post-selenization process. The CIGS layers were fabr... more Sputtering process of CIGS thin film without post-selenization process. The CIGS layers were fabricated by using a sputtering system with four 2-inch magnetron sputtering guns and a rotatable substrate holder with heating apparatus. Back molybdenum electrode with thickness of 1 µm was deposited onto pre-cleaned 2 × 2 cm 2 soda-lime glass (SLG) substrate by DC magnetron sputtering. CIGS films with the chalcopyrite phase were deposited by direct sputtering of a single quaternary CIGS target.
Magnesium-doped zinc oxide (MZO) films were fabricated by pulsed-laser deposition (PLD) at variou... more Magnesium-doped zinc oxide (MZO) films were fabricated by pulsed-laser deposition (PLD) at various substrate temperatures (T s ). The substitution of Mg for Zn sites (Mg Zn ) in the films was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and room-temperature photoluminescence (RTPL) measurements. Characteristic deep-level emissions (DLE) observed in the RTPL spectra further indicate the presence of Zn vacancies (V Zn ) in the MZO films. Moreover, it was found that the intensity of the blue emission corresponding to V Zn increases with increasing T s , indicating the important role played by T s on the incorporation of Mg into ZnO matrix. Hall effect measurements reveal the p-type conduction of the MZO films grown at 400°C. The p-type characteristic is attributed to the formation of nMg Zn -V Zn complex which could act as acceptor for MZO films.
Amorphous indium-tin-oxide (a-ITO) film was deposited by radio-frequency (RF) magnetron sputterin... more Amorphous indium-tin-oxide (a-ITO) film was deposited by radio-frequency (RF) magnetron sputtering at 180°C substrate temperature on the texturized p-Si wafer to fabricate a-ITO/p-Si heterojunction solar cell. The microstructural, optical and electrical properties of the a -ITO film were characterized by XRD, SEM, XPS, UV-VIS spectrophotometer, four-point probe and Hall effect measurement, respectively. The electrical properties of heterojunction were investigated by I-V measurement, which reveals that the heterojunction shows strong rectifying behavior under a dark condition. The ideality factor and the saturation current density of this diode are 2.26 and 1.58×10 4 A cm 2 , respectively. And the value of I F /I R (I F and I R stand for forward and reverse currents, respectively) at 1 V is found to be as high as 21.5. For the a-ITO/p-Si heterojunction solar cell, the a-ITO thin film acts not only as an emitter layer, but also as an anti-reflected coating film. The conversion efficiency of the fabricated a-ITO/p-Si heterojunction cell is approximately 1.1%, under 100 mW cm -2 illumination (AM1.5 condition). And the open-circuit voltage (V oc ), short-circuit current density (J SC ), filll factor (FF) are 280 mV, 9.83 mA cm 2 and 39.9%, respectively. Because the ITO film deposited at low temperature is amorphous, it can effectively reduce the interface states between ITO and p-Si. The barrier height and internal electric field, which is near the surface of p-Si, can effectively be enhanced. Thus we can see the great photovoltaic effect. amorphous indium-tin-oxide (a-ITO) film, radio-frequency (RF) magnetron sputtering, heterojunction solar cell, current-voltage (I-V) characteristics
The nano-scale deformation behaviors and indentation-induced fracture features of the (111)-orien... more The nano-scale deformation behaviors and indentation-induced fracture features of the (111)-oriented yttrium-stabilized zirconia single crystal (YSZ(111)) were investigated by Berkovich and micro-Vicker indentations, respectively. The load-displacement curves in the Berkovich nano-indentation experiments evidently exhibited indentation-induced single "pop-in" phenomenon during loading, indicating that the nano-scale deformation in the YSZ(111) crystals is due primarily to the activities of dislocation nucleation and propagation. Based on this scenario, the number of nanoindentation-induced dislocation loops giving rise to the pop-in event was estimated to be around 2×10 5 with a critical radius of ∼2nm. The hardness and Young's modulus of YSZ(111) single crystal obtained by the continuous contact stiffness measurements (CSM) mode were 22.3 ± 1.1 GPa and 270.6 ± 8.5 GPa, consistent with those reported previously in the literature. In addition, the fracture toughness of YSZ(111) single crystal was estimated to be about 1.4-1.6 MPa• m 1/2 .
This article was originally published online on 28 August 2017. Due to a production error, in the... more This article was originally published online on 28 August 2017. Due to a production error, in the originallypublished version the sentences "The measured lifetime of 2269 hrs … MDM device" (page 4, right column) contained edits which altered the intended meaning. AIP Publishing apologizes for this error. The corrected sentences are "The measured lifetime of 2269 hrs from the conventional device is related to the intrinsic emitting material of 24Ftir(acac). In fact, the lifetime is even slightly longer in the blueshifted MDM device." All online versions of the article were corrected on
In this study, the mechanical deformation behaviors of Au nanotubes (Au-NTs) under torsional stre... more In this study, the mechanical deformation behaviors of Au nanotubes (Au-NTs) under torsional stress are investigated using molecular dynamics (MD) simulations. The inter-atomic interaction is modeled using the embedded-atom potential. In particular, the effects of loading rate, thickness and length of the nanotube, as well as the thermal effects were systematically explored. The results indicated that higher loading rate, longer length and thinner wall thickness all led to a larger value of critical torsional angle (θ cr ), which signifies the onset of plastic deformation. On the other hand, θ cr decreases with increasing temperature in all simulated results. Moreover, the torsional buckling deformation behavior and geometrical instability are found to strongly depend on the length of Au-NTs, the applied strain rate and temperature with vastly different underlying mechanisms.
This article reports a nanomechanical response study of the contact-induced deformation behavior ... more This article reports a nanomechanical response study of the contact-induced deformation behavior in Al 0.16 Ga 0.84 N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy ͑XTEM͒ techniques. Al 0.16 Ga 0.84 N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young's modulus of the Al 0.16 Ga 0.84 N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young's modulus are 19.76Ϯ 0.15 and 310.63Ϯ 9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple "pop-ins" observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved.
The effects of post-annealing on the microstructures, surface morphologies and nanomechanical cha... more The effects of post-annealing on the microstructures, surface morphologies and nanomechanical characteristics of FePd thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and nanoindentation techniques. The FePd thin films were deposited on the glass substrates at room temperature by magnetron sputtering system. Postannealing was carried out at 500, 600 and 700 C, respectively, resulting in progressive increase of the average grain size and surface roughness of FePd thin films, as well as the improved film crystallinity. XRD results show that FePd thin films are predominantly (111)-oriented, indicating a well-ordered microstructure. The hardness and Young's modulus of FePd thin films measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option indicated that both mechanical properties are decreased with increasing the annealing temperature. Furthermore, the relationship between the hardness and films grain size appears to follow closely with the HallePetch equation.
Carbon‐Shielded Single‐Atom Alloy Material Family for Multi‐Functional Electrocatalysis
Advanced Functional Materials
Encapsulating metal‐based catalysts inside carbon sheaths is a frequently‐adopted strategy to enh... more Encapsulating metal‐based catalysts inside carbon sheaths is a frequently‐adopted strategy to enhance their durability under various harsh situations and improve their catalytic activity simultaneously. Such carbon encapsulation, however, imposes significant complications for directly modifying materials’ surface atomic/electronic configurations, fundamentally impeding the accurate tuning of their catalytic capabilities. Herein, a universal single‐atom alloy (SAA) strategy is reported to indirectly yet precisely manipulate the surface electronic structure of carbon‐encapsulated electrocatalysts. By versatilely constructing a SAA core inside an N‐doped carbon sheath, material's electrocatalytic capability can be flexibly tuned. The one with Ru‐SAA cores serves as an excellent bifunctional electrocatalyst for oxygen/hydrogen evolution, exhibiting minimal cell voltage of 1.55 V (10 mA cm−2) and outstanding mass activity of 1251 mA m for overall water splitting, while the one with I...
Regulating the Electronic Configuration of Supported Iron Nanoparticles for Electrochemical Catalytic Nitrogen Fixation
Advanced Functional Materials, 2022
Electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the tradition... more Electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the traditional Haber–Bosch process due to its eco‐friendly nature and capability of utilizing renewable energy. However, its low Faradic efficiency (FE), caused by the excessive adsorption and reduction of protons, has been regarded as the main challenge, which leads to low ammonia yield as well. Herein, a carbon‐supported iron electrocatalyst is reported, which is fabricated by low‐temperature (300 °C) potassium vapor reduction of FeF3‐intercalated graphite fluoride, for efficient electrochemical nitrogen reduction. The strategy enables the unique formation of exposed Fe nanoparticles uniformly anchored on graphene and in situ doped with fluorine heteroatoms. These specific features can alter the electronic configuration of the Fe nanoparticles, leading to strong surface polarization that boosts nitrogen absorption capability for eNRR, resulting in high FE (41.6%) and ammonia yield rate (53.3 μg h‐...
A series of investigations on the interrupted deposition of laser ablation strontium titanate epi... more A series of investigations on the interrupted deposition of laser ablation strontium titanate epitaxy growth were conducted. RHEED intensity recovery curves at various temperatures show a near-quadratic power law dependence on annealing time. Combined with the evidence showing the intimate correlation between the step edge density and the RHEED intensity, a diffusion Arrhenius plot with the activation energy of 1.0 eV was obtained for the kinetics of step edge migration.
By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnet... more By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnetic penetration depth k(T) in YBa2Cu3O7� d (YBCO) and Y0.7Ca0.3Ba2Cu3O7� d (Ca-YBCO) epitaxially grown thin films, the linear temperature dependence of the superfluid density qs/m* � 1/k 2 (T) was observed from the under- to the overdoped regime at the temperatures below T T c � 0:3. For the underdoped regime of YBCO and Ca-YBCO thin films, the magnitude of the slope d(1/k 2 (T))/dT is insensitive to doping, and it can be treated in the framework of projected d-density-wave model. Combining these slope values with the thermal conductivity measurements, the Fermi-liquid correction factor a 2 from the Fermi-liquid model, suggested by Wen and Lee, was revealed here with various doping levels.
Metastable ε-Fe2O3 is a unique phase of iron oxide, which exhibits a giant coercivity field. In t... more Metastable ε-Fe2O3 is a unique phase of iron oxide, which exhibits a giant coercivity field. In this work, we grew epitaxial ε-Fe2O3 films on flexible two-dimensional muscovite substrates via quasi van der Waals epitaxy. It turns out that twinning and interface energies have been playing essential roles in stabilizing metastable ε-Fe2O3 on mica substrates. Moreover, the weak interfacial bonding between ε-Fe2O3 and mica is expected to relieve the substrate clamping effect ubiquitously encountered in films epitaxially grown on rigid substrates, such as SrTiO3. It is anticipated that these flexible ε-Fe2O3 thin films can serve as a platform for exploring possible interesting emergent physical properties and eventually be integrated as flexible functional devices.
The gas discharge and photo-luminance properties of a planar lighting source featuring highly uni... more The gas discharge and photo-luminance properties of a planar lighting source featuring highly uniform light emission and mercury-free design were studied. The current density-voltage characteristics and the associated gas discharge of the devices operating with the values of the ratio of electric field to gas pressure (E/p) between 4.3 kV/Torr-cm and 35.7 kV/Torr-cm indicate that the width of the cathode fall extends over the entire gap between the two electrodes and the device is mostly in the obstructed discharge regime. The optical emission analysis confirmed the electron collision-induced gas emissions and strong effect of gas pressure on the phosphor emission when operated at constant current density, both are indicative of the primary roles played by the electron energy.
In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attenti... more In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attention because a high interface-to-volume ratio can be used to tailor or create functionalities. We have systematically investigated the magnetic properties of oxide heterostructures consisting of the CoFe 2 O 4 nanopillars embedded in the BiFeO 3 matrix using macroscopic magnetization measurements and element-selective soft X-ray absorption magnetic circular dichroism (XMCD) at the Co-and Fe-L 2,3 edge. The magnetization and XMCD data show that the total ordered magnetic moment of Co 2+ in CoFe 2 O 4 -BiFeO 3 nano-heterostructures is strongly enhanced. This study clearly indicates that the high interfaceto-volume ratio vertical nanostructure creates a strong ferromagnetic and antiferromagnetic magnetic coupling via an interface. Furthermore, the magnetic coupling can be tuned in the multiferroicferrimagnetic self-assembled heterostructures by controlling the spacing between nanopillars.
Journal of Superconductivity and Novel Magnetism, 2012
The surface impedance of Y 0.9 Ca 0.1 Ba 2 Cu 3 O 7-δ thin films was measured using the Corbino s... more The surface impedance of Y 0.9 Ca 0.1 Ba 2 Cu 3 O 7-δ thin films was measured using the Corbino spectroscopy method. This special geometry, in which the sample dimensions are well defined by a ring pattern, is ideal for broadband high frequency reflection measurements. Using the complex reflected signal, S 11 , measured by a vector network analyzer, one can find the surface impedance of the thin film, from which the complex conductivity can be deduced. In the current work we present the three-standard approach for calibration of the Corbino method and demonstrate the benefits of this approach in measuring superconducting Y 0.9 Ca 0.1 Ba 2 Cu 3 O 7-δ thin films up to 20 GHz and down to 6 K. For the data analysis the well-known generalized two-fluid model was implemented, taking into account a film thickness which is much smaller than the normal state skin depth and superconducting penetration depth.
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Papers by Jenh-YIh Juang