Search Results - (Author, Cooperation:D. U. Lee)

2011-02-05

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0028-0836

1476-4687

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Apoptosis ; Arabidopsis/*immunology/*microbiology/physiology ; Arabidopsis Proteins/*metabolism ; Circadian Clocks/*immunology ; Circadian Rhythm/genetics/immunology ; Gene Expression Regulation, Plant/genetics/immunology ; Genes, Plant/genetics/immunology ; Immunity, Innate/immunology ; Light ; Mutation ; Oomycetes/*immunology/pathogenicity ; Phenotype ; Plant Diseases/genetics/*immunology/microbiology ; Plant Immunity/*immunology ; Spores, Fungal/immunology/physiology ; Time Factors ; Transcription Factors/*metabolism

1089-7550

AIP Digital Archive

Physics

Electronic property variations of a two-dimensional electron gas (2DEG) in modulation-doped step quantum wells due to an embedded potential barrier were studied by performing Shubnikov–de Haas (SdH), Van der Pauw–Hall-effect, and cyclotron resonance measurements on two kinds of InxGa1−xAs/InyAl1−yAs step quantum wells which were one without and the other with an embedded barrier. The fast Fourier transformation results for the SdH data at 1.5 K indicated the electron occupation of two subbands in both step quantum wells. The total electron carrier density and the mobility of the 2DEG in the step quantum well with an embedded barrier were smaller than those in the quantum well without an embedded barrier. The electron effective masses were determined from the slopes of the main peak absorption energies as functions of the magnetic field, and satisfied qualitatively the nonparabolicity effects in both quantum wells. The electronic subband energies, the wave functions, and the Fermi energies were calculated by using a self-consistent method taking into account exchange-correlation effects together with strain and nonparabolicity effects. These present results indicate that the electronic parameters in modulation-doped InxGa1−xAs/InyAl1−yAs step quantum wells are significantly affected by an embedded barrier. © 2002 American Institute of Physics.

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1089-7550

AIP Digital Archive

Physics

Ion beam-assisted deposition of Ni on p-InP (100) at room temperature was performed in order to produce Ni thin films with high quality and Ni/p-InP (100) heterostructures with abrupt heterointerfaces. An atomic force microscopy image showed that the root mean square of the average surface roughness of the Ni film was 21.3 Å, and x-ray diffraction and transmission electron microscopy (TEM) measurements show that Ni film layers grown on InP (100) substrates were polycrystalline. Auger electron spectroscopy and TEM measurements showed that Ni films grown on p-InP (100) substrates at room temperature had no significant interdiffusion problems. The work function of the Ni thin film was determined from the secondary electron emission coefficients obtained with a focused ion beam. These results provide important information on the microstructural and electronic properties for Ni thin films grown on p-InP (100) substrates at room temperature. © 2002 American Institute of Physics.

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1089-7550

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Physics

SnO2 thin films were grown on p-InSb (111) substrates by radio-frequency magnetron sputtering at low temperature. Atomic force microscopy images showed that the root mean square of the average surface roughness of the SnO2 films grown on the InSb (111) substrates with an Ar/O2 flow rate of 0.667 and at a temperature of 200 °C had a minimum value of 2.71 nm, and x-ray diffraction and transmission electron microscopy (TEM) measurements showed that these SnO2 thin films were polycrystalline. Auger electron spectroscopy and bright-field TEM measurements showed that the SnO2/p-InSb(111) heterointerface was relatively abrupt. High-resolution TEM measurements revealed that the SnO2 films were nanocrystalline and that the grain sizes of the nanocystalline films were below 6.8 nm. The capacitance–voltage measurements at room temperature showed that the type and the carrier concentration of the nominally undoped SnO2 film were n type and approximately 1.67×1016 cm−3, respectively, and the current–voltage curve indicated that the Au/n-SnO2/p-InSb diode showed tunneling breakdown. Photoluminescence spectra showed that peaks corresponding to the donor acceptor pair transitions were dominant and that the peak positions did not change significantly as a function of the measured temperature. These results indicate that the SnO2 nanocrystalline thin films grown on p-InSb (111) substrates at low temperature hold promise for new kinds of potential optoelectronic devices based on InSb substrates, such as superior gas sensors and high-efficiency solar cells. © 2001 American Institute of Physics.

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1089-7550

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Physics

SnO2 thin films were grown on p-InP (100) substrates by using radio-frequency magnetron sputtering at low temperature. Transmission electron microscopy (TEM) and electron diffraction pattern measurements showed that these SnO2 thin films were nanocrystalline. The capacitance–voltage measurements at room temperature showed that the type and the carrier concentration of the nominally undoped SnO2 film were n type and approximately 1.62×1016 cm−3, respectively. Raman scattering measurements showed that the grain sizes of the nanocrystalline films were below 10 nm, which was in reasonable agreement with the result obtained from the high-resolution TEM measurements. Photoluminescence measurements showed a broad peak below the band-to-band emission. These results can help improve the understanding of SnO2 nanocrystalline films grown on p-InP (100) substrates for applications in high-sensitivity gas sensors. © 2000 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

Transmission electron microscopy (TEM) and Raman scattering spectroscopy measurements were performed to investigate strain effects in lattice-mismatched InxGa1−xAs/InyAl1−yAs modulation-doped coupled double quantum wells. The high-resolution TEM images showed that a 100-Å In0.8Ga0.2As deep quantum well and a 100-Å In0.53Ga0.47As shallow quantum well were separated by a 30-Å In0.25Ga0.75As embedded potential barrier. The selected-area electron-diffraction pattern obtained from TEM measurements on the InxGa1−xAs/InyAl1−yAs double quantum well showed that the InxGa1−xAs active layers were grown pseudomorphologically on the InP buffer layer. The values of the strain and the stress of the InxGa1−xAs layers were determined from the electron-diffraction pattern. Based on the TEM results, a possible crystal structure for the InxGa1−xAs/InyAl1−yAs coupled double quantum well is presented. © 1998 American Institute of Physics.

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1089-7550

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Physics

Magnetotransport and magneto-optical measurements on InxGa1−xAs/InyAl1−yAs modulation-doped strained double quantum wells with a 100 Å In0.8Ga0.2As well and a 100 Å In0.53Ga0.47As quantum wells separated by a 35 Å In0.25Ga0.75As potential barrier were carried out to investigate the electrical and the optical properties of the electron gas in the quantum wells. The Shubnikov-de Haas measurements at 1.5 K demonstrated clearly the occupation of three subbands in the quantum wells by a two-dimensional electron gas. The electron effective masses determined from the slopes of the cyclotron resonance peak energies as a function of the magnetic field were 0.06171 and 0.05228me. The electronic subband energies, the subband energy wavefunctions, and the Fermi energy in the quantum wells were self-consistently calculated a transfer matrix method taking into account the exchange-correlation effect, the strain effect, and the nonparabolicity effect, and the results of the cyclotron resonance measurements qualitatively show the nonparabolicity effect in the strained double quantum well. © 1997 American Institute of Physics.

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1089-7550

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Physics

Selected area electron diffraction pattern (SADP) and transmission electron microscopy (TEM) measurements were carried out to investigate the ordered structures in lattice-mismatched InxGa1−xAs/InyAl1−yAs 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 InxGa1−xAs/InyAl1−yAs heterointerfaces. This CuAu–I-type ordered structure had an antiphase boundary in the periodically regular InxGa1−xAs/InyAl1−yAs lattice-mismatched region. The existence of a CuAu–I-type ordered structure in InxGa1−xAs/InyAl1−yAs MQWs might originate from the lattice mismatch between the InxGa1−xAs and the InyAl1−yAs 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 InxGa1−xAs/InyAl1−yAs MQWs. © 2001 American Institute of Physics.

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1089-7550

AIP Digital Archive

Physics

The Shubnikov–de Haas (S–dH) measurements at 1.5 K clearly demonstrated the existence of a two-dimensional electron gas (2DEG) in the modulation-doped Al0.25Ga0.75As/InyGa1−yAs/GaAs single and step quantum wells, and the fast Fourier transformation results for the S–dH data clearly indicated the electron occupation of one subband in the asymmetric single and step quantum wells. While the electron carrier density of the 2DEG in the step quantum well was larger than that in the single quantum well due to the larger conduction-band discontinuities, the mobility of the 2DEG in the step quantum well was smaller than that in the single quantum well because of the interface scattering resulting from the embedded step well. The electron effective mass in the step quantum well was smaller than that in the single quantum well, which was consistent with a smaller mass of the embedded deep step layer. The electronic subband energy, the energy wave function, and the Fermi energy in the InyGa1−yAs step quantum wells were calculated by using a self-consistent method taking into account exchange-correlation effects together with strain and nonparabolicity effects. © 2001 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

Shubnikov–de Haas (SdH), Van der Pauw Hall-effect, and cyclotron resonance measurements on InxGa1−xAs/In0.52Al0.48As asymmetric step quantum wells were carried out to investigate the electrical properties of a free electron gas and to determine the effective mass of the electron gas, the subband energies, and the wave functions in the InxGa1−xAs quantum wells. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas in the InxGa1−xAs quantum wells, and the fast Fourier transformation results for the SdH data indicated clearly the occupation by that gas of two subbands in the quantum wells. The electronic effective masses determined from the slopes of the main peak absorption energies as a function of the magnetic field were 0.0477 and 0.053 me for the first excited and the ground subbands, respectively. The electronic subband energies and the wave functions in the InxGa1−xAs/In0.52Al0.48As step quantum wells were calculated by a self-consistent method taking into account exchange-correlation effects together with the strain and nonparabolicity effects. The results of the cyclotron resonance measurements qualitatively satisfied the nonparabolicity effects of the step quantum well. These results can help improve understanding for the application of InxGa1−xAs/In0.52Al0.48As step quantum wells in optoelectronic devices. © 1996 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the coalescence and electron activation energy in CdTe/ZnTe nanostructures. The results of the AFM images show that uniform CdTe quantum dots (QDs) are formed and that the transformation from CdTe QDs to CdTe quantum wires is caused by the coalescence. The excitonic peaks corresponding to the transition from the ground electronic subband to the ground heavy-hole band in the CdTe/ZnTe QDs shifted to higher energy in comparison with those of the CdTe/ZnTe quantum wires. The activation energy of the electrons confined in the CdTe QDs, as obtained from the temperature-dependent PL spectra, was higher than those in CdTe quantum wells and quantum wires. The present results can help to improve the understanding of coalescence and electron activation energy in CdTe/ZnTe nanostructures. © 2002 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

Selected area electron diffraction pattern (SADP) and transmission electron microscopy (TEM) measurements were carried out to investigate the ordered structure in CdxZn1−xTe epitaxial layers grown on (001) GaAs substrates. The SADP showed to sets of superstructure reflections with symmetrical intensities, and the corresponding high-resolution TEM image showed a doublet periodicity in the contrast of the {111} lattice planes. The results of the SADP and the TEM measurements showed the existence of a CuPt-type ordered structured in the CdxZn1−xTe epitaxial layers. This CuPt-type ordered structure had two different variants with an antiphase boundary existing between the two variants. The formation of a CuPt-type ordered structure in a CdxZn1−xTe epitaxial layer might originate from the minimization of the strain relaxation energy in the reconstructed GaAs (001) surface. A possible atomic arrangement of and a formation mechanism for the CuPt-type ordered structure in the CdxZn1−xTe epitaxial layer are presented based on the TEM results. These results provide important information on the microstructural properties for improving the efficiencies of optoelectronic devices operating in blue-green spectral regions. © 2001 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) measurements were carried out to characterize the composition of ZnTe films, and transmission electron microscopy (TEM) measurements were performed to investigate the lattice mismatch and the microstructural properties of the ZnTe/GaAs heterostructures. The AES and SIMS results showed that the ZnTe/GaAs heterointerfaces had relatively sharp interfaces. The TEM images and the selected-area electron-diffraction patterns showed a large lattice mismatch between the ZnTe epitaxial layer and the GaAs substrate, 60° and 90° dislocations together with stacking faults, near the ZnTe/GaAs heterointerface. The ZnTe epitaxial film grown on the GaAs substrate receives a compressive strain of −0.61%, and possible atomic arrangements of the 60° and the 90° dislocations are presented on the basis of the high-resolution TEM results. © 2001 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

The transmission electron microscopy image and selected area electron diffraction pattern showed that self-assembled InAs quantum-dot (QD) arrays embedded in GaAs barriers were periodically inserted in an Al0.25Ga0.75As/GaAs heterostructure. The temperature-dependent photoluminescence spectra of the InAs/GaAs quantum dots embedded in modulation-doped heterostructures showed interband transitions from the first-excited electronic subband to the first-excited heavy-hole subband together with those from the ground subband to the ground heavy-hole band (E1–HH1) while the spectra of the InAs/GaAs QDs alone showed only the peak related to the (E1–HH1) transitions. © 2001 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

Bright-field transmission electron microscopy (TEM) and high-resolution TEM images and an electron diffraction pattern showed that the SnO2 layers grown on heavily doped n-InP(100) substrates were nanoscale thin films. X-ray photoelectron spectroscopy showed that the positions of the peaks corresponding to the Sn 3d5/2, the Sn 3d3/2, and the O 1s levels for the SnO2 thin film were slightly shifted toward the lower energy side in comparison with those for bulk SnO2. The refractive indices obtained by spectroscopic ellipsometry were above 2.2 around the SnO2 energy gap of the SnO2 thin films. The maximum intensity of the optical transmittance for the SnO2 nanoscale thin film with 3939 Å thickness was above 90%. © 2001 American Institute of Physics.

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1573-4811

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