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We have studied the effect of the trimethylgallium (TMGa) flow rate in the GaN buffer layer on the optical and structural quality. From low temperature photoluminescence measurements, a GaN overlayer grown on a buffer layer with the TMGa flow rate of 80 μmol/min shows the intense donor-acceptor pair transition peak at 3.27 eV and the weak yellow band emission at 2.2 eV, which are related with stacking faults and threading dislocations from transmission electron microscopy images, respectively. As the TMGa flow rate of the GaN buffer increases, the threading dislocation density rapidly decreased and stacking faults increased in the GaN overlayers. Also, a total threading dislocation density at the optimum condition of the buffer layer is the very low 1×108 cm−2, which is due to the interaction of stacking faults with the vertical threading dislocations and the bending of threading dislocations near the stacking faults. High-resolution x-ray diffraction results show that a high density of stacking faults is...

The defect formation in (100) Si at low temperatures during electron cyclotron resonance hydrogen plasma treatment has been studied. The temperature effect on crystalline defect morphology is studied by transmission electron microscopy and high resolution transmission electron microscopy. A high density of hydrogen-stabilized {111} platelets is observed at 240 °C, whereas a large number of amorphous {100} platelets is observed at 385 °C. The formation of amorphous {100} platelets without {111} platelets at 385 °C is reported. The amorphous {100} platelet at 385 °C results from the precipitation of oxygen promoted by hydrogen-enhanced oxygen diffusion. The low-temperature photoluminescence study and the spreading resistance profiles for the hydrogenated Si support the proposed mechanism of the amorphous {100} platelet.

InAs self-assembled quantum dots were grown on InGaAs lattice-matched on InP by metalorganic chemical vapor deposition. The facet formation on the dot was investigated by atomic force microscopy and transmission electron microscopy. The {136}-faceted InAs dots were elongated along either [13¯0] or [3¯10] to form parallelogram-shaped islands analogous to hut cluster formation in SiGe∕Si quantum dots. Some parallelogram dots also exhibited {110} faceting, presumably on undergoing a shape transition toward dots with facets of higher symmetry.

The origin of hydrogen-induced structural deformation of ferroelectric SrBi2Nb2O9 (SBN) thin films is investigated by annealing in forming gas (3%H2–97%N2). High resolution transmission electron microscopy and fast Fourier transformation analysis reveal that the {115} planes are shifted upward and downward by 0.92A along {115} plane after forming gas annealing, resulting in (00l) planes inclined by 9.54°. This shifted distance of 0.92A means that the perovskite structure is distorted by 29.98% compared to the normal interatomic distance of 3.077A. This distorted perovskite structure results in degradation of ferroelectric properties. However, this lattice deformation and ferroelectric property of SBN films are recovered after annealing in oxygen ambient.

Nanostructured silicon was formed by means of the ionized N2 gas reaction on SiO2/Si, and the electronic structure, surface morphology, and optical properties were investigated. The physicochemically modified thin layers were resolved to SiNy and SiOxNy through the observation of Si 2p, O 1s, and N 1s core-level spectra in x-ray photoelectron spectroscopy. The formations of SiOxNy and SiO2 nanostructures (3–4 nm in size), performed by the etching process followed by adsorption of ionized nitrogen, were confirmed by atomic force microscopy. The nanocrystalline Si (6 nm in size) distributed within the modified layer (approximately 10 nm thick) was observed after the in situ rapid thermal annealing processes, using high-resolution transmission electron microscopy. Photoluminescence with a wavelength peaking at around 400 nm was emitted from the nanocrystalline Si formed from the SiOxNy/SiO2/Si structures. This work suggests that the nanocrystalline-Si formation and the nanostructured surface modification met...

Transmission electron microscopy (TEM) measurements were carried out to investigate the spontaneously ordered structure in InxAl1−xAs epitaxial layers grown on (001) InP substrates. The selected area diffraction pattern showed two sets of superstructure reflections with symmetrical intensity at (100) and (010) positions, indicating that CuAu-I-type ordered structures with two different variants were formed in the InxAl1−xAs epitaxial layers. The dark-field TEM image showed that the size of the CuAu-I-type ordered domains with a needle-like shape was approximately 3∼4 nm thick, with lengths ranging from 10 to 20 nm. Based on the TEM results, explanations are given to describe the formation of only two variants of CuAu-I-type ordering.

The strain relaxation mechanism via the homogeneous nucleation of misfit dislocations from the heterointerface in coherently strained layers has been investigated with transmission electron microscopy. It is identified that the dislocations nucleated from the interface are displayed in the form of 90° partial, 30° partial, and 60° perfect dislocations, depending on stress sign and thickness of the strained layer. The tendency is interpreted in terms of the strain relaxation efficiency which is given by the ratio of relieved strain energy to dislocation line energy.

The structural and electrical characteristics of 300 keV Si+ or 380 keV Ar+ ion‐implanted epitaxial ReSi2 films grown on an n‐Si(100) substrate have been studied by using 2 MeV 4He+ ion backscattering spectrometry, x‐ray diffraction, high‐resolution transmission electron microscopy, and electrical measurement. Ion implantation causes static disorder in the film, which overlap and grow to become an amorphous layer. The threshold dose for amorphizing the ReSi2 film is ∼5×1014/cm2 for 28Si+ and ∼1×1014/cm2 for 40Ar+. Although the resistivity of the implanted ReSi2 film decreases when the degree of disorder (or the implantation dose) is increased, the resistivity reaches a minimum value at a dose of ∼1×1015/cm2 for Si+ or ∼5×1014/cm2 for Ar+. The 28Si+‐implanted amorphous ReSi2 films recovered original epitaxy after thermal annealing at 700 °C for 30 min in vacuum, as do the partly amorphized ReSi2 films by 40Ar+ implantation. On the other hand, those films fully amorphized by 40Ar+ implantation (dose≥1×1014/...

Influence of Mg doping on structural defects in Al0.13Ga0.87N layers grown on sapphire substrates by metalorganic chemical vapor deposition were studied using transmission electron microscopy. By increasing the Mg source flow rate, the reduction of dislocation density occurred up to the Mg source flow rate of 0.103 μmol/min. While the vertical type inversion domain boundaries (IDBs) were observed in the Al0.13Ga0.87N layers grown with the low Mg source flow rate, the IDBs in the Al0.13Ga0.87N layers grown with the high Mg source flow rate have horizontally multifaceted shapes. The change of polarity by the IDBs of horizontal type also resulted in the 180° rotation of pyramidal defects within the same AlGaN layer.

Amorphous silicon films are deposited by ion-beam-assisted electron beam deposition and subsequently oxidized by a rapid thermal oxidation process. The oxidized film contains a large density of nanocrystals specifically localized at a certain depth from the Si/SiOx interface, whereas no evidence of nanocrystals is found for oxidized films deposited without ion beam assistance. Such a marked contrast resulted from the enhancement of nucleation rate by ion beam irradiation. The metal-oxide-semiconductor structure utilizing the film shows an ultralarge capacitance‐voltage hysteresis whose width is over 20 V. In addition capacitance‐time measurement shows a characteristic capacitance transient indicating nondispersive carrier relaxation. The retention time shows a dependence on applied bias and the maximum time of ;70 s is obtained near midgap voltage. The retention time dependence on applied bias and large capacitance‐voltage hysteresis are attributed to direct tunneling of trapped charges in the deep traps of nanocrystals to the interface states. © 2001 American Institute of Physics. @DOI: 10.1063/1.1337618#

The microstructural degradation of a lattice‐matched Ga0.28In0.72As0.61P0.39/InP heterointerface during Zn diffusion has been investigated using high resolution transmission electron microscopy and Auger electron spectroscopy. The diffusion‐induced intermixing of In and Ga across the GaInAsP/InP interface causes tensile stress in the Ga‐mixed InP side and compressive stress in the In‐mixed GaInAsP side. The effect of the localized interfacial stress on the nucleation of misfit dislocations and on the strain accommodation behaviors thereof are clearly revealed throughout the intermixed region, reaching several thousand angstroms on each side of the interface. The interfacial strain is relaxed by generation of paired dislocations with antiparallel Burgers vectors initiating from the intermixed GaInAsP/GaInP interface. The dislocation morphologies reveal striking contrasts across the intermixed interface: stacking faults in the tensile layer and perfect dislocation tangles in the compressive layer. The dislo...

The growth of Ti and the formation of epitaxial Ti silicide on Si(111)‐7×7 were investigated by using reflection high‐energy electron diffraction (RHEED) and high‐resolution transmission electron microscopy (HRTEM). The growth mode of Ti is Stransky–Krastanov type when the substrate temperature is room temperature (RT). On the other hand, it is Volmer–Weber type when the substrate temperature is ∼550 °C. The HRTEM lattice image and transmission electron diffraction pattern show that C54 TiSi2 is grown epitaxially on a Si substrate when 160 ML of Ti is deposited on a Si(111)‐7×7 surface at RT followed by in situ annealing at 750 °C for 10 min in ultrahigh vacuum (UHV). The TiSi2/Si interface is somewhat incoherent, but the developed TiSi2 crystallites are single crystal with matching face relationships of TiSi2(111)∥Si(111), TiSi2(311)∥Si(111), and TiSi2(022)∥Si(111). A thin single‐crystal Si overlayer with [111] direction is grown on the TiSi2 surface when TiSi2/Si(111) is annealed at ∼900 °C in UHV, whic...

During the crystallization of amorphous YMnO3 thin film on Si (100) at 870 °C in a dry O2 ambient, a nanoprecipitate layer was found between the YMnO3 and the Si substrate. Lattice image processing as well as high-resolution transmission electron microscopy showed that the nanoprecipitate layer was a cubic Y2O3 phase. Also, it showed that a native oxide was consumed by the reaction with the Y atoms. This [111] Y2O3 layer exhibited a local epitaxial relationship to the c-axis oriented (0001) YMnO3. The formation of Y2O3 phase and the consumption of native oxide at the YMnO3/Si interface are due to the Y atom which is better than Mn in its ability to oxidize during heat treatment in O2 ambient.

Lattice damages induced by BF+2 ion implantation in single‐crystalline silicon have been analyzed using secondary‐ion mass spectrometry, ion channeling technique in Rutherford backscattering spectroscopy, and transmission electron microscopy. Concentration depth profiles of boron and fluorine showed the same values of projection range 400 A at all doses for 50‐keV energy. A considerable amount of damage was formed in the silicon lattice and the surface region of the substrate was amorphized when the dosage exceeded a critical value, which was determined to be 8.0 × 1014/cm2 experimental dose. The amorphized layer showed a clear boundary to the crystalline silicon, which contains severely damaged regions identified to be microamorphous clusters. He2+ ion channeling data revealed that the integrated damage in implanted layers increases linearly with dosage up to the critical dose and increases with a much smaller rate with further increase in the dosage. It is suggested that the integrated damage shows a smaller damage rate once the surface was amorphized because there can be no further increase of lattice damage in the amorphous layer. The calculated values of the integrated damage based on a model for damage formation agree well with the measured ones.

We observed violet/blue light emitted from cerium silicates which may be useful for silicon-based optoelectronics. The cerium silicate was produced during a rapid thermal annealing at high temperature (>1100 °C) from the interface between silicon substrate and cerium oxide film. Detailed experiments including x-ray diffraction, high-resolution transmission electron microscope, and Auger depth profiling showed that the cerium silicate consists of Ce4.667(SiO4)3O and Ce2Si2O7 phases. The photoluminescence of the cerium silicate is very strong at room temperature. Specifically, the 358 nm luminescence line is attributed to the Ce2Si2O7 phase.

The depth distributions of vacancy‐type defects in Si+ ‐implanted and thermally activated GaAs were studied by a slow positron beam technique and were compared with the results observed with a transmission electron microscope. In as‐implanted GaAs, the concentration of vacancy‐type defects decreased monotonically with increasing depth below the surface and the generation of point defects was demonstrated by the lattice image of transmission electron microscopy. The vacancy concentration is not dependent upon activation conditions; however, the electrical activation coefficiency obtained from Hall measurements is enhanced with increasing activation annealing time. This indicates that the electrical activation of Si+ ‐implanted GaAs is proceeding by the exchange of interstitial Si with substitutional Ga rather than the recombination of interstitial Si into Ga‐related vacancies. The maximum number of extrinsic‐type stacking faults was observed at 70–80 nm below the surface after the activation annealing, which is compared with that of vacancy‐type defects, at 25–35 nm, obtained by the slow positron beam technique. This discrepancy in both of the damage distributions could originate in different types of defects existing along the depth below the surface, which was discussed with the high‐energy recoil theory.

Microstructural evidence on direct contact of Au/Ge/Ni/Au ohmic metals to a InGaAs channel in AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped GaAs/AlGaAs cap layer was found using transmission electron microscopy, and the results were used to interpret the electrical properties of the contact. The lowest contact resistivity of 3.8×10−6 Ω cm2, obtained at 420 °C annealing, is due to the penetration of the interfacial compounds, Au2Ga and Au2Al, into the buried InGaAs channel. The direct contact of the compounds to the channel causes the reduction of series resistances between the ohmic compounds and the channel, resulting in the low contact resistivity.

Aluminum nitride (AlN) and hydrogenated aluminum nitride (AlN:H) films on Si substrate have been deposited by the radio frequency reactive magnetron sputtering. The microstructures of the two films have been examined and compared by transmission electron microscopy (TEM) and high-resolution TEM. In the growth of the AlN:H film, it has been observed that the amorphous phase is formed at the initial stage of deposition, and c-axis oriented crystallite nucleates at the amorphous layer. The lattice mismatch between the film and substrate and the stress in the film are reduced, and the film surface is smooth due to this amorphous phase. A schematic model explaining the growth of AlN and AlN:H films is proposed, and the reason for the easy formation of the amorphous phase in AlN:H film is discussed.

We introduce visible photoluminescences (PL) of violet (432 nm) and yellow (561 nm) at room temperature from thermally treated silicon dioxide thin films. These luminescences were very strong with a near infinite degradation time. At an oxide layer thickness less than 200 nm, these luminescences were not seen, even with high temperature annealing at about 1000 °C. As a result of photoluminescence, x‐ray photoelectron spectroscopy, Fourier transform infrared, and high‐resolution transmission electron microscopy measurements, we conclude that the violet PL originates from the nanocrystalline silicon formed in the silicon oxide film by the thermal strain effect between the silicon substrate and the silicon dioxide film, while the yellow PL originates from the radiative decay of self‐trapped excitons that are confined to oxygen sufficient structures.

The evolution of the cross‐hatch pattern (CHP) in InxGa1−xAs/GaAs heterostructures has been studied. It is found that stress is concentrated at the valleys of the CHP from the results of crack formation at the CHP valleys in the thick GaAs cap layer grown on an InGaAs layer. Residual strain in the InGaAs/GaAs epitaxial layer showing a CHP is confined along the valleys of the CHP with a nonuniform distribution throughout the epitaxial layer. The skeleton of the CHP is formed at the beginning of the rapid strain relaxation period and the depth of the CHP valleys increases after most of the strain has been released. We propose that the development of the CHP in the later stage of the growth takes place by the growth suppression at the CHP valleys due to the high level of stress concentration.

Ferroelectric PbTiO3 thin films were grown on Si(100) substrates by metalorganic chemical vapor deposition via thermal pyrolysis at relatively low temperature (∼500 °C) using Pb(tmhd)2, Ti(OC3H7)4, and N2O. Transmission electron microscopy results suggested that the grown PbTiO3 films were polycrystalline layers. Auger depth profiles indicated that the compositions of the as‐grown films consisted of lead, titanium, and oxygen uniformly distributed throughout the films and that the films exhibited smooth interfaces. These results indicate that the growth of polycrystalline PbTiO3 layers instead of epitaxial films originated from the formation of an interfacial amorphous layer prior to the creation of the films. Further, a mechanism for the formation of an interfacial layer between the PbTiO3 thin films and the p‐Si substrates is presented.

Thermally stable tungsten nitride/tungsten bilayer has been proposed for the application of metallization. This bilayer is sequentially formed by plasma enhanced chemical vapor deposition without breaking vacuum. The Rutherford backscattering spectrometry and cross‐sectional transmission electron microscopy reveal that the interaction between the W and Si substrate can be prevented by interposing a 800‐A‐thick W67N33 layer. The W67N33/W bilayer maintains the integrity of the interface during annealing at 850 °C for 30 min without the formation of Si2W and interdiffusion phenomena. Sheet resistivity of the W67N33/W bilayer is gradually decreased from 17 to 12 μΩ cm at annealing temperatures up to 850 °C.

C49‐TiSi2 film was grown epitaxially on Si(111) substrate by depositing Ti film on Si(111)‐ 7×7 surface followed by in situ annealing in ultrahigh vacuum. The deposition was monitored by means of reflection high energy electron diffraction as a function of the thickness of Ti film. The best result for the growth of epitaxial C49‐TiSi2 was obtained from the Ti(30 ML)/Si(111)‐7×7 sample which was annealed at 650 °C for 20 min. Images of cross‐sectional high resolution transmission electron microscopy shows that the silicide/silicon interface is shown to be clear and flat. The orientation relationships are TiSi2[211]∥Si[011], TiSi2 (120)∥Si(111) without misorientation angle. Almost the whole area of the TiSi2 layer is revealed as an epitaxial C49 structure.

The microstructural degradation of a lattice‐matched Ga0.28In0.72As0.61P0.39/InP heterointerface induced by Zn diffusion has been investigated using transmission electron microscopy. The localized interfacial stress caused by intermixing appears to create stacking faults in the Ga‐mixed InP substrate, and dislocation tangles in the In‐mixed GaInAsP layer. The observed results are attributed to the contrasted effect of tensile and compressive stresses upon the nucleation of dislocations from both sides of the GaInAsP/GaInP interface. As an evidence of the interface nucleation, we find a stacking fault at the tensile interface, which is bounded by a pair of partials having opposite Burgers vectors. A model is proposed to explain the strain relaxation in the intermixed region in terms of nucleation and splitting mechanisms of the paired dislocations.

A low‐energy ion‐beam‐assisted deposition (IBAD) technique has been developed to fabricate W‐Si‐N Schottky contacts of enhanced thermal stabilities on n‐GaAs. By implementing remote sputtering and glancing angle low‐energy N+ ion irradiation, the thermal stabilities of the W‐Si‐N/n‐GaAs Schottky contacts were enhanced to be stable up to 850 °C, while keeping the Schottky barrier heights to the best values obtained with conventional sputtering. Thermal stabilities of the IBAD refractory metals/n‐GaAs interfaces were investigated also for various W‐Si‐N compositions by examining the microstructure and Schottky diode characteristics. WSi0.3N0.4 showed the most stable Schottky contacts on n‐GaAs of which the barrier height changed only 20 meV after thermal annealing between 700 and 850 °C, and that is proposed to be due to the stable metallurgical microstructure compared to the element tungsten and tungsten nitride.

The atomic structure of In3Sb1Te2 was investigated by high-resolution transmission electron microscopy (HRTEM) and the National Center for Electron Microscopy Simulation System. In3Sb1Te2 has a disordered NaCl structure; In atoms are positioned in a face-centered cubic lattice, and Sb and Te atoms are located at randomly occupied octahedral sites. However, the observed HRTEM images of the ordered In3Sb1Te2 phase show that Sb and Te atoms are located in specific positions, that is, at the center and edge of the unit cell, respectively. The atomic model of the ordered In3Sb1Te2 is confirmed by simulated images, which match the experimental HRTEM images.

The origin of multilevel resistances of In3Sb1Te2 (IST) phase-change random access memory cell has been investigated with high-resolution transmission electron microscopy (HR-TEM). The HR-TEM indicates that the microstructure of IST in the programming volume changes from amorphous to InSb and amorphous at the first state, and InSb and InTe at the second state, and IST at the third state, which are fairly consistent with four different levels of resistance. The resistance difference between the amorphous and the IST is about four orders of magnitude.

To clarify the resistive switching and failure mechanisms in Al/amorphous TiO2/Al devices we investigate the microscopic change in amorphous titanium oxide films and interface layers after the set process according to film deposition temperatures. For low temperature (

We present a flexible room temperature NO2 gas sensor consisting of vertical carbon nanotubes (CNTs)/reduced graphene hybrid film supported by a polyimide substrate. The reduced graphene film alone showed a negligible sensor response, exhibiting abnormal N–P transitions during the initial NO2 injection. A hybrid film, formed by the growth of a vertically aligned CNT array (with CNTs 20 μm in length) on the reduced graphene film surface, exhibited remarkably enhanced sensitivities with weak N–P transitions. The increase in sensitivity was mainly attributed to the high sensitivity of the CNT arrays. The outstanding flexibility of the reduced graphene films ensured stable sensing performances in devices submitted to extreme bending stress.

Pd nanoparticle-doped vanadium pentoxide nanowires (Pd-VONs) were synthesized. Electrical current suppression was observed when the Pd-VON was exposed to hydrogen gas, which cannot be explained by the work function changes mentioned in previous report such as Pd-doped carbon nanotubes and SnO2 nanowires. Using the x-ray photoelectron spectroscopy, we found that the reduction in PdO due to hydrogen exposure plays an important role in the current suppression of the Pd-VON.

20 nm SiO2 elliptical membrane nanopores with various thicknesses were directly formed in situ by using a focused electron beam with transmission electron microscopy (TEM). The shrinkage and the expansion behaviors of the SiO2 ellipse nanopores with different thicknesses were attributed to variations in their geometries, in particular their curvatures. The geometric mechanisms of elliptical nanopores with various thicknesses fabricated utilizing a SiO2 membrane with a thickness gradient by using an electron beam irradiation are described on the basis of TEM images, which depend on the electron beam irradiation time.

We measure the resistivity of platinum-silicide nanowires (Pt2Si NWs) epitaxially formed on a Si(100) surface using double-scanning-probe tunneling microscope. Despite the large Schottky barrier height reported on a macroscopic Pt2Si∕n-Si interface, leakage current through the substrate is observed in the resistance measurement, and is quantitatively estimated to be separated from the current through the nanowire. The measured resistivity of Pt2Si NWs is about half the reported resistivity of thick Pt2Si films, which could be due to additional conduction paths through surface or interface states on NWs.

Microstructural properties of GeTe thin films were investigated by an in situ heating method within a high voltage electron microscope (HVEM). The results confirm that the transformation from an amorphous state to a fcc crystalline state yields a GeTe binary alloy with a ring-shaped amorphous structure. The fcc structured GeTe transforms into a GeTe orthorhombic structure during the experiment. The crystallization behavior of the GeTe orthorhombic structure in the HVEM is quite different from thermal crystallization. Our observation of real-time structural change confirms that the relaxed amorphous structure participates in the crystallization process in the electron beam irradiation condition.

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.

We report significant reduction of threading dislocations in GaN films grown by hydride vapor phase epitaxy on AlN/sapphire templates by employing CrN nanoislands on the AlN. High quality GaN films with very small twist mosaic as well as small tilt mosaic have been grown on the AlN/sapphire templates, which had small tilt but very large twist mosaic. The CrN nanoislands were formed by nitridation of a thin Cr film deposited by sputtering on the AlN/sapphire template, where the AlN/sapphire template was prepared by metal organic vapor phase epitaxy. The full width at half maximum values of x-ray rocking curves from the GaN film with the CrN were 114, 209, and 243arcsec for (0002), (10−12), and (11−20) reflections, respectively, while those of the GaN film without the CrN were 129, 1130, and 1364arcsec, respectively. Evaluation of total dislocation density of the GaN films by plan view transmission electron microscopy revealed that the dislocation density was reduced to 2.7×108 from 6.4×109cm−2 by employing...

A grazing incidence x-ray diffraction with a synchrotron radiation and a cross-sectional high-resolution transmission electron microscopy were performed on the sapphire surface nitrided at 1080°C for 30min. The thickness of the nitrided layer was about 2nm. It was found out that the wurtzite, zinc-blende, and 30° rotated zinc-blende aluminum nitrides were formed on the sapphire surface. The 30° rotated zb-AlN formed the incoherent interface and has higher activation energy of formation, while the nonrotated zb-AlN formed the coherent interface.

We report the evolution of ZnO nanorods by metalorganic chemical vapor deposition on sapphire substrates and an investigation of their microstructure. Well-aligned ZnO nanorods with a high aspect ratio were grown on an interfacial layer with several types of defects at a lower reactor pressure. Planar defects such as stacking mismatch boundaries and inversion domain boundaries were formed in the interfacial layer during the coalescence of the islands, and finally constituted the side facets of the nanorods. Based on the microstructural changes and origin of the defects in the interfacial layers, we propose a model to explain the growth evolution of ZnO nanorods on sapphire substrates.

Structural transformation of the Ge2Sb2Te5 was investigated by a high resolution transmission electron microscopy (HRTEM). It was found that Ge atoms undergo umbrella-flip motion from a tetrahedral site into an octahedral site in transforming from the amorphous to the metastable phase of Ge2Sb2Te5. The presence of a twin boundary between fcc and hexagonal structured Ge2Sb2Te5 was also confirmed through the HRTEM observations. These results support the umbrella-flip model proposed by Kolobov et al. [Nat. Mater. 3, 703 (2004)] and the epitaxial growth model proposed by Park et al. [Appl. Surf. Sci. 256, 8102 (2006)].

Electron-beam-induced Zn nanocrystal islands were formed in a dielectric SiO2 layer. When a ZnO thin film on a p-type Si with amorphous SiOx interface layer is subjected to a 900°C annealing followed by electron irradiation in a transmission electron microscope environment, an amorphous Zn2xSi1−xO2 layer is formed. Upon irradiation with a 300keV electrons, metallic and single crystal nanoislands of Zn with ∼7–10nm diameter were formed and embedded within the SiO2 interface layer. Possible mechanisms for the formation of Zn nanocrystals are presented.

Superlattice films have been proposed to get dilute magnetic semiconductor (DMS) with an intrinsic room-temperature ferromagnetism. For a TiO2-based DMS superlattice structure, each layer was alternately doped by two different transition metals (Fe and Mn) and deposited to a thickness of approximately 2.7A on r-Al2O3(1102) substrates by pulsed laser deposition. Samples of Ti0.94Fe0.06O2 (TiFeO), Ti0.94Mn0.06O2 (TiMnO), and Ti0.94(Fe0.03Mn0.03)O2 show a low remanent magnetization and coercive field, as well as superparamagnetic features at room temperature. On the other hand, superlattice films (TiFeO∕TiMnO) show a high remanent magnetization and coercive field, resulting in intrinsic ferromagnetic properties. The superlattice films composed of alternating layers of Ti0.94Fe0.06O2 and Ti0.94Mn0.06O2 exhibit intrinsic ferromagnetic properties for dilute magnetic semiconductor applications.

High-quality Au-catalyzed GaAs nanowires were grown on Si substrates by vapor-liquid-solid growth in a solid source molecular beam epitaxy system. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy reveal that the GaAs nanowires were epitaxially grown on Si substrates with uniform diameters along the nanowires. While GaAs nanowires on Si(111) and (001) substrates were mainly grown along the ⟨111⟩ direction with zinc-blende and wurtzite structures, unusual GaAs nanowires grown along ⟨001⟩ with a pure zinc-blende structure were also observed. Strong photoluminescence was observed from GaAs nanowires grown on a Si(001) substrate at room temperature.

Surface energy and the equilibrium shape of hexagonal structured grain in Ge2Sb2Te5 were investigated by a transmission electron microscopy (TEM) study. As a result, we have found that the equilibrium shape of hexagonal structured Ge2Sb2Te5 is a lengthened shape with (0001) plane at the major axis, which was experimentally revealed by TEM images. The hexagonal structured Ge2Sb2Te5 grain has low surface energy in {0001}, {11¯03}, and {1¯106} planes which have no additional broken bonds from the atoms on the steps. Therefore, it is strongly facetted by the plane having low surface energy, thus, becoming an equilibrium shape.

Zinc-blende structured MnAs epiaxial films with half metallic characteristics were grown on GaAs (100) substrates. The formation of the zinc-blende structured MnAs on GaAs was made possible via introduction of a strained yet epirelated InAs intermediate layer, the thickness of which was found critical for enabling the half metallic structure. The magnetization curves as functions of the magnetic fields showed magnetic hysteresis and isotropic ferromagnetic properties. The magnetoresistance behavior at various temperatures indicates that the MnAs thin film is half-metallic in nature.

We have studied the atomic structure of YMnO3 deposited on Si and Y2O3 with high-resolution transmission electron microscopy and fast Fourier transforms-filtered lattice image analysis during furnace and rapid thermal annealing (RTA) processes. For the YMnO3/Si, it is found that the YMnO3 layer is c-axis oriented with an amorphous bottom region after furnace annealing at 850 °C for 1 h. In contrast, after RTA at 850 °C for 3 min the bottom region forms YMnO3 polycrystalline layer with the {1212} plane parallel to the surface. When an Y2O3 layer is interposed between YMnO3 and Si, a c-axis oriented YMnO3 layer grows on a [111]-oriented Y2O3 layer. Memory window and leakage current density of the c-axis YMnO3/[111] Y2O3 bilayers are strongly improved due to an aligned [0001] unipolar axis.

Alternately hydrogen diluted a-Si:H multilayers are shown to be a promising concept for the fabrication of stable a-Si:H solar cells or other a-Si:H based devices. The alternately hydrogen diluted amorphous silicon multilayers were obtained by toggling both the H2/SiH4 dilution ratio and the total flow rate of the gases under continuous UV light irradiation into the reaction chamber of a photochemical vapor deposition system. The films were characterized by Fourier transformed infrared spectroscopy, spectroscopic ellipsometry, cross-sectional transmission electron microscopy, and atomic force microscopy. We applied these multilayers as the active layer of p–i–n type thin film solar cells. The multilayer solar cells are compared to solar cells incorporating a-Si:H made from pure SiH4 gas and to solar cells incorporating a-Si:H made at a constant hydrogen dilution ratio containing nearly the same hydrogen amount as the multilayer. We report on the light-soaking and annealing behavior of the solar cells. The...

Two types of twins with different atomic structure may exist in GaAs: rotation type and reflection type. A selective chemical etching technique was employed to clarify which of these two twin types occurs in practical GaAs crystals. Twins in an As‐rich horizontal Bridgman (HB) GaAs, a Ga‐rich HB GaAs, and a liquid‐encapsulated Czochralski GaAs were studied, and the results showed that all of the studied twins were rotation type. This suggests that the bonding configuration at the twin plane is a more important factor than stoichiometry of the crystal, in determining the type of twins in GaAs.