Search

Results of viscosity measurement for the as-cast (a) Mg65Cu7.5Ni7.5Zn5Ag5Y10 and (b) Mg65Cu7.5Ni7.5Zn5Ag5Y5Gd5 BMG plate samples with 1 mm thickness using the TMA technique (heating rate: 0.333 K/s). The inset shows a schematic diagram of the cone-shaped copper mold including the positions (top, middle, and bottom) of the inserted thermocouples. Results of viscosity measurement for the as-cast Mg65Cu7.5Ni7.5Zn5Ag5Y5Gd5 BMG sample with different diameters (d = 3, 6, 9, and 12 mm) using the TMA technique (heating rate: 0.333 K/s). [Extracted from the article]

We report on the anisotropic structural properties of periodically polarity-inverted (PPI) ZnO structures grown on patterned templates. The etching and growth rates along [formula] direction of ZnO structures are higher than those of [formula] direction of ZnO films. From the strain evaluation by Raman spectroscopy, compressive strains are observed in all PPI ZnO samples with different stripe pattern size and the smaller pattern size is more effective to residual stress relaxation. The detailed structures at transition region show relationship with the anisotropic crystal quality. [ABSTRACT FROM AUTHOR]

A correlation between the kinetic fragility index (m) and enhanced plasticity is presented in Mg-based bulk metallic glasses (BMGs) with modulated heterogeneity by both suitable minor addition and optimal cooling rate. As case study, with minor addition of Gd in Mg65Cu7.5Ni7.5Zn5Ag5Y10-xGdx BMG, plasticity as well as glass-forming ability improves in a wide composition range (2.5≤x≤7.5 at. %). Furthermore, the cooling rate can affect the structural heterogeneity and the deformability of BMGs. With increasing diameters for the alloy x=5, the compressive fracture strain increases from 2.97% at d=1 mm up to 3.74% at d=2 mm and then largely decreases. In particular, the variation of heterogeneity, which can directly affect in the property of BMG, can be evaluated by comparing the m values reflecting the inherent structure of BMGs. This concept can be used as a means of guiding alloy design and processing to alleviate brittleness of BMGs. [ABSTRACT FROM AUTHOR]

The x-ray diffraction patterns, transmission electron microscopy images, and selected-area electron diffraction patterns for the ZnO/Si heterostructures annealed at 900 °C showed that orthorhombic ZnSiO3 nanoparticles were formed in the amorphous layer between the ZnO film and the Si substrate, resulting from the interdiffusion between the ZnO film and the Si substrate due to thermal treatment. Auger electron spectroscopy depth profiles for the ZnO/Si heterostructures annealed at 900 °C demonstrated the formation of amorphous Zn2xSi1-xO2, an interfacial layer. A formation mechanism for the orthorhombic ZnSiO3 nanoparticles embedded in the amorphous Zn2xSi1-xO2 layer is described on the basis of the experimental results. [ABSTRACT FROM AUTHOR]

High-resolution transmission electron microscopy (HRTEM) images, selected-area electron diffraction (SAED) patterns, and energy dispersive x-ray spectroscopy (EDS) profiles showed that P atoms accumulated due to thermal treatment on the top sides and in the heterointerface layers of ZnO thin films grown on p-InP (100) substrates, resulting in the formation of amorphous ZnO layers in the ZnO thin films. The formation mechanisms of the ZnO amorphous layers due to thermal treatment are described on the basis of the HRTEM, the SAED, and the EDS measurements. [ABSTRACT FROM AUTHOR]

This is a report on the fabrication and electrical characteristics of an all-organic-based thin film transistor that uses conducting poly(3,4-ethylenedioxythiophene) (PEDOT) as electrodes. The conducting PEDOT layers as source, drain, and gate electrodes were patterned by using photolithography. The poly(vinyl cinnamate) (PVCN) was spin coated and cross-linked as a gate insulator. The pentacene as an active layer was vapor deposited onto the PVCN layer. In order to compare the characteristics of the pentacene-based organic thin film transistor (OTFT) with PEDOT electrodes, we fabricated another pentacene-based OTFT using a Si-based pattern with Au electrodes. The electrical characteristics of the devices, such as charge carrier mobility (μ), threshold voltage (Vth), and on/off current ratio (Ion/off), were measured from its current-voltage (I-V) characteristic curves. The μ, Vth, and Ion/off of the pentacene-based OTFT with PEDOT electrodes were ∼2.3×10-3 cm2/V s, 4 V, and ∼100, respectively. We evaluated the activation energy (Ea) of the pentacene layer of the OTFT devices by analyzing the transfer characteristic curves measured in a temperature range from 10 to 300 K based on the multitrap and release model. The Ea of the OTFT with PEDOT electrodes was measured to be ∼0.33 eV, in the saturation region. This energy was larger than that of the OTFT with Au electrodes which was measured to be ∼0.13 eV. However, the μ’s of both OTFTs were almost the same, in spite of the relatively lower electrical conductivity of the PEDOT and the larger Ea of the OTFT with the PEDOT electrodes. From the results of temperature dependence of current density based on the Schottky emission model, we analyze that the lower barrier height between the PEDOT electrode and the pentacene active layer resulted in easier charge injection from the PEDOT electrode into the active layer. [ABSTRACT FROM AUTHOR]

X-ray diffraction patterns showed that crystallinity of the annealed ZnO films was improved by thermal annealing. Transmission electron microscopy images showed that columnar structures were preferentially formed in ZnO thin films due to thermal annealing, and electron energy loss spectroscopy images showed that annealing caused O2 atoms to diffuse out from the upper region in the ZnO thin film. The effects of thermal treatment on the formation of the columnar structures in ZnO thin films grown on Si (100) substrates are described on the basis of the experimental results. [ABSTRACT FROM AUTHOR]

The coexistence of a phase separation and an ordered structure in CdxZn1-xTe epilayers grown on GaAs(001) substrates by using molecular beam epitaxy was investigated. The results of selected-area electron diffraction pattern and transmission electron microscopy measurements showed that ordered structures, such as CuPt-type and CuAu-I-type ordered structures, together with a spinodal-like phase separation were formed in the CdxZn1-xTe/GaAs heteroepitaxial layers. The coexistence of the phase separation and the ordered structures is discussed. [ABSTRACT FROM AUTHOR]

The Ge2Sb2Te5 thin films deposited by a sputtering method on SiO2/Si substrates were annealed through a rapid thermal annealing process and performed a high-resolution transmission electron microscopy study in order to investigate the atomic arrangement of the metastable Ge2Sb2Te5. The metastable rocksalt structure having face-centered-cubic lattice was confirmed by high-resolution transmission electron microscopy images and simulated images on the directions of <100>, <110>, and <211> zone axes. According to the position of Ge and Sb in the metastable rocksalt structure, the atomic distribution alters when observed in different direction and this causes change in the charge-density distribution, resulting in different images in a high-resolution transmission electron microscopy. It is expected that as the crystallization proceeds, the Ge and Sb atoms tend to position themselves on a specific plane. From this aspect, the ordered structure model of the metastable Ge2Sb2Te5 was proposed by varying the position of the Ge and Sb atoms. [ABSTRACT FROM AUTHOR]

Microstructural and atomic structure studies of GaN/sapphire and AlxGa1-xN/AlN/GaN heterointerfaces have been performed by using bright-field transmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements. TEM and SADP results from the GaN/sapphire and the Al0.4Ga0.6N/AlN/GaN/sapphire heterointerfaces showed that GaN epilayers and Al0.4Ga0.6N, AlN, and GaN active layers, respectively, had been grown on the sapphire substrates. The values of the strain and the stress in the Al0.4Ga0.6N, the AlN, and the GaN layers were determined. Possible schematic diagrams of the two heterostructures, as well as diagrams of the [2110] projections of the GaN epilayer and the Al0.4Ga0.6N/AlN/GaN heterostructure, are presented based on the TEM and SADP results. These results can help improve the understanding of the microstructural properties of the strained AlxGa1-xN/AlN/GaN/sapphire heterostructures for applications in the high-speed and high-power electronic devices. [ABSTRACT FROM AUTHOR]

The relationship between the CuPt-type ordering and the surface undulation in CdxZn1-xTe epitaxial layers grown on ZnTe buffer layers was investigated. The results of selected area electron diffraction pattern and transmission electron microscopy measurements showed that CuPt-type ordered structures were formed in the CdxZn1-xTe epitaxial layers. The atomic force microscopy image showed that the surface undulations were created from lattice mismatch between the CdxZn1-xTe ZnTe thin films and the GaAs substrate. The surface undulations provided the [110] steps, which enhanced the formation of CuPt-type ordering in highly strained CdxZn1-xTe epilayers. These results provide important information on the relationship between the microstructural and surface properties in lattice mismatched heteroepilayers in the CdxZn1-xTe/ZnTe system. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of thermal annealing on multiple stacked InAs/GaAs quantum dots (QDs) embedded in an Al[sub 0.25]Ga[sub 0.75]As/GaAs heterostructure has been investigated by transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images show that the size of the InAs/GaAs QDs decreased slightly with an increase in growth temperature and that InAs/GaAs QDs annealed at 800 °C contained many dislocations due to annealing. Temperature-dependent PL spectra showed that peaks corresponding to the interband transitions of the InAs QDs shifted slightly towards the low-energy side and that the full width at half maximum of the peak decreased with an increase in annealing temperature. The integrated PL intensity decreased with an increase in temperature due to nonradiative defects resulting from the existence of dislocations. These results can help improve understanding of the thermal annealing effect on the microstructural and the optical properties of multiply stacked InAs/GaAs QDs embedded in modulation-doped heterostructures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Selected area electron diffraction pattern and high-resolution transmission electron microscopy measurements on a ZnTe/ZnSe heterointerface grown on a GaAs(001) substrate showed two structures of the CuPt[sub B]-type ordering structures, one for each direction of the doublet periodicity on the {111} lattice planes along the [110] axis, and superstructure spots related to CuAu-I-type ordering. Auger electron spectroscopy measurements showed that the Se atoms were interdiffused into the ZnTe thin film and that the diffused Se atoms formed a ZnSe[sub x]Te[sub 1-x] layer, which might be related to the coexistence of the two types of ordered structures. The coexisting behavior of the two ordered structures are discussed. The present results can help improve the understanding of the formation mechanism and the coexisting behaviors of the two ordered structure near the ZnTe/ZnSe heterointerface. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The microstructural and the optical properties of InAs/GaAs quantum-dot (QD) arrays inserted into undoped GaAs barriers embedded in an Al[sub x]Ga[sub 1-x]As/GaAs were investigated by using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images and the selected-area electron diffraction patterns showed that vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The temperature-dependent PL spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the InAs QDs shifted to lower energy with increasing temperature. The PL intensity of the InAs dots was significantly enhanced by the modulation-doped Al[sub x]Ga[sub 1-x]As/GaAs heterostructure, and the thermal activation energy of the InAs dots was decreased by the addition of the modulation-doped Al[sub x]Ga[sub 1-x]As/GaAs heterostructure. The present results can help to improve the understanding of the microstructural and the optical properties in InAs QD arrays inserted into GaAs barriers embedded in a modulation-doped Al[sub x]Ga[sub 1-x]As/GaAs heterostructure. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the effect of strain-induced indium clustering on the emission properties of InGaN/GaN multiple quantum wells grown with high indium composition by metalorganic chemical vapor deposition. Indium clustering confirmed by high-resolution transmission electron microscopy results in the redshift of the emission peak and the increase of the integrated photoluminescence (PL) intensity. We found that strong carrier localization in indium clustering induces the increases of the activation energy of PL integrated intensity, the temperature independence of PL decay profiles, and the intensity fluctuation of the cathodoluminescence images. All these observations suggest structurally and optically that the improved emission properties in the InGaN/GaN multiple quantum well with high indium composition are associated with the localized states in the strain-induced indium cluster. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Influence of strain relaxation on structural and optical properties of the InGaN/GaN multiple quantum wells (MQWs) with high indium composition grown by metalorganic chemical vapor deposition was investigated. From photoluminescence and transmission electron microscopy (TEM), we found that within the MQWs, the formation of misfit dislocation affects the degradation of optical properties more than the formation of stacking faults. For the MQWs with indium composition above the critical indium composition on the formation of misfit dislocation, the position of the main emission peak is significantly affected by the increase of quantum well numbers compared to samples with indium composition below the critical indium composition. The origins of redshift by the increase of quantum well numbers is believed to be caused by the increase of indium segregation in the MQWs using high-resolution TEM and energy dispersive x-ray spectroscopy. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A series of Permalloy films, of various shapes such as a square, a rectangle, a circle, and a rhombus, was made. The sample length to width ratio L/w varied from 1 (i.e., square) to 29 (i.e., rectangle). We studied how the planar Hall effect (PHE) signal was affected by adding a transverse field H[sub y] along the easy-axis direction of the sample. It was found that in a certain range of H[sub y], the PHE sensitivity S might become inoperative, i.e., S changed linearly as a function of H[sub y] from -S[sub max] to + S[sub max] (or vice versa), where S[sub max] was the maximum sensitivity. This phenomenon is explained by considering the Zeeman-energy and the single-domain-rotation effects. In particular, for the square sample, the following data exist: (1) S[sub max] is as high as 310 Ω/T at the film thickness t= 500 Å, and (2) the inoperative range for H[sub y] is the narrowest among all the samples. From this study, we conclude that the field of the Earth H[sub e]—as long as its horizontal component is larger than 0.25 Oe—can be employed to stabilize the magnetic structure of a Permalloy element and to achieve the best PHE performance with S[sub max]. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements were carried out to investigate the ordered structures near ZnTe/GaAs heterointerfaces, and Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) measurements were performed to determine the compositions of the ZnTe/GaAs interfacial layer. The SADP showed two sets of {[FRACTION SHAPE="CASE"][NUM]1[/NUM][DEN]2[/DEN][/FRACTION] [FRACTION SHAPE="CASE"][NUM]1[/NUM][DEN]2[/DEN][/FRACTION] [FRACTION SHAPE="CASE"][NUM]1[/NUM][DEN]2[/DEN][/FRACTION]} extra spots with symmetrical intensity, and the corresponding high-resolution TEM image showed doublet periodicity in contrast of the {111} lattice planes. The results of the SADP and the high-resolution TEM measurements showed that a CuPt-type ordered (Cd, Zn)Te structure was observed near the ZnTe/GaAs heterointerface, and the AES and SIMS results showed that the ordered structure was formed due to the diffusion of Cd atoms into the ZnTe layer. Two variants, one for each direction of the doublet periodicity on the {111} lattice, were observed in the ordering, and each variant had its own domain structure with a similar probability. The formation of the CuPt-type ordered structure near the ZnTe/GaAs heterointerface originated from both the existence of the Cd residual impurities during the initial growth stage of the ZnTe epilayer and the strain relaxation of the ZnTe epilayer. These results can help to improve the understanding of the microstructural properties of the ZnTe/GaAs heterointerface. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ferroelectric twin-domain structures in epitaxial Pb(Zr, Ti)O[sub 3] (PZT) thin films grown on various single-crystal substrates such as MgO(001), KTaO[sub 3](001), and SrTiO[sub 3](001) were investigated by two-dimensional reciprocal space mapping using synchrotron x-ray diffraction. Each system showed a characteristic domain structure. PbTiO[sub 3] thin films grown on MgO(001) showed highly c-axis oriented domain structures consisting of a periodic array of 90° twinlike domains. Perfectly c-axis oriented films were obtained on SrTiO[sub 3](001), while the films grown on KTaO[sub 3](001) showed a-domain dominant structures with a small amount of c domains embedded in matrix a domains. Contributions of net elastic strain stored in each heteroepitaxial layer and its relaxation to the final domain structures were evaluated considering thermodynamic equilibrium relief of coherency strain by misfit dislocation generation at the film growth temperature. A comparison between theoretical consideration and experimental results clearly demonstrates that the nature of effective misfit strain and its relaxation during film growth play a critical role in the formation of domain structures in epitaxial PZT thin films. Moreover, it was verified that the control of such critical strain factors by changing film composition could modify dominant domain structures in a drastic way. In addition, it was found that the crystalline quality of the films is closely correlated to the tilting nature of the domain structure in each system and coherency strain across the 90° domain boundary is accommodated mainly by the domain tilt of the minor domain. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report thermopower measurements for the nickel titanium shape memory alloy Ni[sub 0.507]Ti[sub 0.493]. Our measurements reveal abrupt changes in the temperature dependence of thermopower, which correlate well with the structural phase transition between the austenitic and martensitic phases. These transition effects in thermopower are more clearly defined than in the resistivity, which is also reported. In the martensitic phase, thermopower exhibits standard metallic diffusion behavior with a nonlinearity, which is consistent with either a small peak in the density of states just below the Fermi level, as calculated by Kulkova, Egorushkin, and Kalchikhin [Solid State Commun. 77, 667 (1991)], or else electron-phonon mass enhancement. For thermally or mechanically treated samples, the magnitude of the transition effects in thermopower are reduced. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the effect of hydrogenation on the electrical properties of InGaP epitaxy layers grown on gallium arsenide. Rectifying characteristics of InGaP diodes; Lamp-heating hydrogenation of molecular beam epitaxy; Experimental procedures; Results and discussion.

Focuses on a study which investigated the formation of amorphous layers and residual defects in SiF/BF[sub2] implanted and annealed silicon. Experimental details; Results and discussion; Conclusions.

Deals with a study which described the formation mechanism of crystallites in the as-deposited mixed-phase low pressure chemical vapor deposition silicon thin films. Background to the study; Experimental details; Results and discussion.

Presents a high-resolution transmission electron microscopy study of solid phase crystallized silicon thin films on silicon dioxide. Description of silicon crystallites formed at the initial stage of crystallization; Types of defects observed at the grain of the material; Explanation for the formation of defects.

Investigates the electrical and optical properties of electron gas in quantum wells. Magnetotransport and magneto-optical measurements on InxGa1-xAs/InyAl1-yAs modulation-doped strained double quantum wells; Determination of electron effective masses from the slopes of the cyclotron resonance peak energies; Nonparabolicity effect in the strained double quantum well.

Presents a study on the interface properties of Schottky contacts on nitrogen-hydrogen-sulfur-treated indium (In)-gallium (Ga)-phosphorus (P). Effects of sulfur treatment on Schottky barrier height; Use of capacitance-voltage and current-voltage measurements; Discussion on ternary compound semiconductor InGaP.

Examines defect formation in the solid phase epitaxial growth of gallium arsenide (GaAs) films on silicon (Si) (001) substrate. Factors that hamper GaAs growth on Si; Origin of stacking faults in GaAs films; Use of transmission electron microscopy for cross-sectional observation of the structural defects in the GaAs films on Si.

Carbonyl iron (CI) has been widely used as a suspended particle in magnetorheological (MR) fluids. However, pristine CI-based MR fluids have several drawbacks, including severe sedimentation of the CI particles due to the large density difference with the carrier liquid, difficulties in redispersion after caking, abrasion of device surfaces during long-term operation, and rust of iron by oxidation. To overcome these shortcomings, we coated the CI particles with a poly(vinyl butyral) (PVB) shell. CI and CI-PVB particles were suspended in mineral oil and their MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. Yield stress and flow response (shear stress and shear viscosity) were investigated at magnetic field strengths ranging from 0 to 343 kA/m. Although the MR properties, such as yield stress and shear viscosity of CI-PVB based MR fluids, changed slightly compared with those of the pristine CI based MR fluid, the dispersion qualities (e.g., sedimentation stability) were noticeably improve. [ABSTRACT FROM AUTHOR]

We have fabricated NiFe/Mn/FeMn/Mn/NiFe multilayers using ultrahigh vacuum ion-beam deposition system to study the diffusion effect of the inserted Mn on exchange biasing. As the thickness of the Mn layer was changed from 0 to 1.5 nm, the exchange biasing field H[SUBex](top) at the top interface of FeMn/Mn/NiFe was decreased from 258 Oe to 24 Oe. On the other hand, the H[SUBex](bottom) was slightly decreased 103 Oe to 78 Oe without a change in the coercive field H[SUBc]. Above 1.2 nm, a reverse phenomena of H[SUBex] was observed. After annealing at 200 °C, the H[SUBex](top) was increased by almost a factor of 2; however, the H[SUBex](bottom) did not change. The analyses of x-ray patterns and Auger spectroscopy showed that the abnormal tendency of H[SUBex](bottom) originated from the diffusion of Mn atoms at bottom interface into the FeMn layer during film growth, and that the Mn was concentrated at the interface by annealing. [ABSTRACT FROM AUTHOR]

Selected area electron diffraction pattern (SADP) and transmission electron microscopy (TEM) measurements were carried out to investigate the ordered structures in lattice-mismatched In[sub x]Ga[sub 1-x]As/In[sub y]Al[sub 1-y]As multiple quantum wells (MQWs). The SADP showed two sets of extra spots with asymmetrical intensity, and the high-resolution TEM image showed doublet periodicity in the contrast of the (001) lattice planes. The results of the SADP and the TEM measurements showed that a CuAu-I-type ordered structure was observed near the lattice-mismatched In[sub x]Ga[sub 1-x]As/In[sub y]Al[sub 1-y]As heterointerfaces. This CuAu-I-type ordered structure had an antiphase boundary in the periodically regular In[sub x]Ga[sub 1-x]As/In[sub y]Al[sub 1-y]As lattice-mismatched region. The existence of a CuAu-I-type ordered structure in In[sub x]Ga[sub 1-x]As/In[sub y]Al[sub 1-y]As MQWs might originate from the lattice mismatch between the In[sub x]Ga[sub 1-x]As and the In[sub y]Al[sub 1-y]As layers. These results provide important information on the microstructural properties for improving operating efficiencies in long-wavelength optoelectronic devices, such as strain compensated electroabsorption modulators utilizing lattice-mismatched In[sub x]Ga[sub 1-x]As/In[sub y]Al[sub 1-y]As MQWs. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on the synthesis of the barium-titanium-oxygen ferroelectric films of quality suitable for applying as dielectrics dynamic random access memory. Use of laser ablation technique; Crystal structure and microstructure of the films; Value of the leakage current density.

Studies the interfacial layer formation of the Al[sub2]O[sub3]/silicon structures grown by low-pressure metalorganic chemical vapor deposition. Interface state densities at the Al[sub2]O[sub3]/silicon interface; Significance of the growth of epitaxial insulator films on silicon; Auger depth profiles of the Al[sub2]O[sub3]/silicon structure.

We investigated influence of 4 wt. % BaSnO3 (BSO) addition on the thickness dependence of critical current density (Jc) of GdBa2Cu3O7-δ (GdBCO) thin films deposited by using the pulsed laser deposition technique. The results show that Jc measured at 77 K of the GdBCO films is significantly enhanced by the addition of BSO. Thickness dependence of self-field Jc in the BSO doped GdBCO films is reduced in comparison with that of pure GdBCO films. Improved field performance of Jc is also observed for the BSO-doped GdBCO films up to thickness of 1.5 μm. The enhancements are attributed to the growth of artificial pinning centers in the form of BSO nano precipitates confirmed by the cross-sectional transmission electron microscopy images. [ABSTRACT FROM AUTHOR]