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Omar Lozano,
Q. Y. Chen,
B. P. Tilakaratne, H. W. Seo,
X. M. Wang,
P. V. Wadekar,
P. V. Chinta,
L. W. Tu,
N. J. Ho,
D. Wijesundera,
W. K. Chu
[show abstract]
[hide abstract]
ABSTRACT: Si wafers of (100), (110) and (111) orientations were bombarded by gas cluster ion beam (GCIB) of 3000 Ar-atoms/cluster on average at a series of angles. Similar surface morphology ripples developed in different nanoscales. A simple scaling functional satisfactorily describe the roughness and wavelength of the ripple patterns as a function of dosage and angle of incidence. The ripples are formed orthogonal to the incident cluster-ions at large off-normal angles. An ellipsoidal pattern was created by two consecutive irradiations incident in mutually orthogonal directions with unequal exposure times between each irradiation, from 7:1 to 10:1, beyond which the original ripple imprints would be over-written. This work was inspired by use of the ripples to seed growth of controlled nanostructures without patterning by lithography or predeposition of catalysts.
AIP Advances 3, 062107 (2013); http://dx.doi.org/10.1063/1.4811171. 06/2013;
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Omar Lozano,
Q. Y. Chen,
B. P. Tilakaratne, H. W. Seo,
X. M. Wang,
P. V. Wadekar,
P. V. Chinta,
L. W. Tu,
N. J. Ho,
D. Wijesundera,
Wei-Kan Chu
[show abstract]
[hide abstract]
ABSTRACT: Si wafers of (100), (110) and (111) orientations were bombarded by gas cluster ion
beam (GCIB) of 3000 Ar-atoms/cluster on average at a series of angles. Similar
surface morphology ripples developed in different nanoscales. A simple scaling
functional satisfactorily describe the roughness and wavelength of the ripple patterns
as a function of dosage and angle of incidence. The ripples are formed orthogonal
to the incident cluster-ions at large off-normal angles. An ellipsoidal pattern was
created by two consecutive irradiations incident in mutually orthogonal directions
with unequal exposure times between each irradiation, from 7:1 to 10:1, beyond
which the original ripple imprints would be over-written. This work was inspired
by use of the ripples to seed growth of controlled nanostructures without patterning
by lithography or predeposition of catalysts.
AIP Advances in Physics. 06/2013; 3:062107.
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O Lozano,
QY Chen,
PV Wadekar, HW Seo,
PV Chinta,
LH Chu,
LW Tu,
Ikai Lo,
SW Yeh,
NJ Ho,
others
Solar Energy Materials and Solar Cells 01/2013; 113:171-178. · 4.54 Impact Factor
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PV Wadekar,
QY Chen,
HC Huang,
YT Lin,
CW Chang, HW Seo,
TW Dung,
MC Chou,
SW Feng,
NJ Ho,
others
Journal of Electronic Materials 01/2013; · 1.47 Impact Factor
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HW Seo,
QY Chen,
IA Rusakova,
ZH Zhang,
D Wijesundera,
SW Yeh,
XM Wang,
LW Tu,
NJ Ho,
YG Wu,
others
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2012; · 1.21 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The growth of Indium nitride (InN) was studied in the nucleation stage by metal-organic chemical vapor deposition technique using atomic nitrogen from an RF microwave plasma source. Deposition was carried out through a range of substrate temperatures from 375 to 550 °C and at varying V/III ratios from 950 to 3150. We found that the diffusion lifetime of In atoms on the substrate becomes maximized at the growth temperature 475 °C, in which low temperature photoluminescence exhibits the excellent optical properties of the materials with a bandgap of 0.69 eV and a width of 34 meV. In addition, we observed that nitrogen cracking efficiency is significantly improved by using plasma so that high quality InN crystallites were grown with a very low V/III ratio around 950.
Journal of Applied Physics 03/2011; 109(6):063517-063517-6. · 2.17 Impact Factor
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[show abstract]
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ABSTRACT: We have successfully grown non-tapered InN nanorods on Si substrate using an RF plasma assisted metalorganic chemical vapor deposition technique. Employment of 50 W nitrogen plasma reduces the optimal growth temperature to 500 degrees C. In order to study the temperature dependent bandgap and thermal quenching mechanism in relation to the localized states, photoluminescence measurement over a temperature range from 7 to 160 K are conducted. The photoluminescence at 7 K shows a strong near-band-emission energy of 0.682 eV with a narrow band width of 0.027 eV, which reveals excellent optical and structural qualities of the InN nanorods.
Journal of Nanoscience and Nanotechnology 10/2010; 10(10):6783-6. · 1.56 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: A III-nitride-based photogated transistor using photons to control the channel width of an otherwise gateless field effect transistor (FET) is investigated. This is accomplished by stacking sequential layers of p-GaN/InGaN/n-GaN on a Si substrate in an array of nanorods. The nitride p-i-n diode can be activated by light, whereupon the nanorod device shows phototransistor characteristics in forward bias but behaves like a photoconductor when in reverse bias. An optically pumped FET model, as justified by the low-dimensional nanogeometry, is used in analysis of the device. The resulting photogate efficiency and photocarrier mobilities are estimated to be ∼ 0.04 V/(W/cm2) and, ∼ 2000–3000 cm2/V s, respectively.
Applied Physics Letters 03/2010; 96(10):101114-101114-3. · 3.84 Impact Factor
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Applied Physics Letters. 05/2009; 94:201907--3.
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LH Chu,
D Wijesundera,
Wei-Kan Chu, HW Seo,
LW Tu,
YS Chang,
WY Pang,
IK Lo,
SW Yeh,
NJ Ho,
others
Bulletin of the American Physical Society. 01/2009; 54.
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O Lozano,
QY Chen,
PV Chinta,
PV Wadekar,
LH Chu,
D Wijesundera,
Wei-Kan Chu, HW Seo,
LW Tu,
YS Chang,
others
APS Meeting Abstracts. 01/2009; 1:21012.
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K. R. Wang,
S. J. Lin,
L. W. Tu,
M. Chen,
Q. Y. Chen,
T. H. Chen,
M. L. Chen, H. W. Seo,
N. H. Tai,
S. C. Chang,
I. Lo,
D. P. Wang,
W. K. Chu
[show abstract]
[hide abstract]
ABSTRACT: Unidirectional single crystalline InN nanoemitters were fabricated on the silicon (111) substrate via ion etching. These InN nanoemitters showed excellent field emission properties with the threshold field as low as 0.9 V/μm based on the criterion of 1 μA/cm2 field emission current density. This superior property is ascribed to the double enhancement of (1) the geometrical factor of the InN nanostructures and (2) the inherently high carrier concentration of the degenerate InN semiconductor with surface electron accumulation layer induced downward band bending effect that significantly reduced the effective electron tunneling barrier even under very low external field.
Applied Physics Letters 03/2008; 92(12):123105-123105-3. · 3.84 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have investigated the interfacial reaction between platinum and InGaP in a Schottky diode structure. There was a 7.5-nm-thick amorphous layer formed at the interface between Pt and InGaP after metal deposition. After annealing at 325 °C for 1 min, this amorphous layer increased to 12.8 nm and the reverse leakage current also decreased. The diffusion of Pt atoms and the crystallization of amorphous layer took place after annealing at 325 °C for 10 min. Prolonging the annealing to 3 h led to formation of Ga2Pt and GaPt3 phases in InGaP and Schottky diodes degraded after these new phases were observed.
Applied Physics Letters 02/2008; 92(8):082108-082108-3. · 3.84 Impact Factor
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O Lozano,
PV Chinta,
PV Wadekar,
LH Chu, HW Seo,
QY Chen,
XM Wang,
D Wijesundera,
LW Tu,
NJ Ho,
others
Bulletin of the American Physical Society. 01/2008; 53.
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[show abstract]
[hide abstract]
ABSTRACT: X-ray photoemission spectroscopy has been used to investigate the depth dependent crystal structures and chemical compositions of sequentially chemical-etched YBa2Cu3O7-d (YBCO) ultrathin film superconductors. In the near-interface region the crystal structure is severely oxygen deficient and of tetragonal symmetry. We consider this a revelation of retarded oxygen diffusion into the O(1) sites during the post-deposition annealing in the presence of interface mismatch strain. Near the free surface, the oxygen-deficiency was much alleviated because of the partial strain relaxation and the crystal symmetry becomes orthorhombic. Compared with as-deposited films of equivalent thickness, which is less oxygen deficient and shows superconducting transition, the stripped-down near-interface layer exhibits no sign of superconductivity.
04/2006;
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[show abstract]
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ABSTRACT: We have examined the effects of 20-keV electron irradiation on the [-Cu(1)-O(1)-]n chain-oxygen arrangements in oxygen-deficient but otherwise twin-free YBa2Cu3O7−δ single crystals. Comparison of polarized Raman spectra of nonirradiated and irradiated areas provides evidence that electron bombardments instigate the collective hopping of oxygen atoms either from an interstitial at O(5) site to a vacant O(1) chain site or by reshuffling the chain segments to extend the average length of chains without changing the overall oxygen content. This oxygen ordering effect, while counterintuitive, is analogous to that found in photoexcitation-induced ordering in which temporal charge imbalance from electron-hole pair creation by inelastic scattering of incident electrons causes a local lattice distortion which brings on the atomic rearrangements.
Phys. Rev. B. 08/2005; 72(5).
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[show abstract]
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ABSTRACT: Intrinsic catalytic process by capillary condensation of Ga atoms into nanotrenches, formed among impinging islands during the wurzite-GaN thin film deposition, is shown to be an effective path to growing GaN nanorods without metal catalysts. The nanocapillary brings within it a huge imbalance in equilibrium partial pressure of Ga relative to the growth ambient. GaN nanorods thus always grow out of a holding nanotrench and conform to the boundaries of surrounding islands. The nanorods are epitaxially orientated with ⟨0001⟩GaN‖⟨111⟩Si and ⟨211̱0⟩GaN‖⟨110⟩Si similar to the matrix. Concaved geometry is essential and is a condition that limits the axial dimension of the nanorods protruding above the base (matrix) material region. Revelation of the growth mechanism in the current context suggests that fabrication of nanoquantum structures with controlled patterns is enabling for any attainable dimensions.
Phys. Rev. B. 06/2005; 71(23).
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[show abstract]
[hide abstract]
ABSTRACT: Intrinsic catalytic process by capillary condensation of Ga-atoms into nanotrenches, formed among impinging islands during the wurzite-GaN thin film deposition, is shown to be an effective path to growing GaN nanorods without metal catalysts. The nano-capillary brings within it a huge imbalance in equilibrium partial pressure of Ga relative to the growth ambient. GaN nanorods thus always grow out of a holding nanotrench and conform to the boundaries of surrounding islands. The nanorods are epitaxially orientated with <0001>GaN // <111>Si and <2110>GaN // <110>Si similar to the matrix. Concaved geometry is essential and is a condition that limits the axial dimension of the nanorods protruding above the base (matrix) material region. Revelation of the growth mechanism in the current context suggests that fabrication of nano quantum structures with controlled patterns is enabling for any attainable dimensions
04/2005;
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[show abstract]
[hide abstract]
ABSTRACT: GaN-nanorods grown on Si(111) substrates are found strain- and defect-free as characterized by micro Raman spectroscopy, secondary electron (SE) and cathode-luminescence (CL) imaging. The matrix supporting the nanorods bears the brunt of all strains, strain-relaxations, and defect generations, giving the nanorods an ideal environment to grow to perfection. Photo-excitations by the Raman laser source and electron irradiation during CL imaging lead to an increase of non-equilibrium electrons, suggesting an effective approach to photo-emitting or field emitting device applications. The nanorods, largely isolated from but perfectly aligned with the sustaining matrix, are grown in excellent epitaxy with the Si substrates.
04/2005;
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[show abstract]
[hide abstract]
ABSTRACT: We have examined the effects of 20 keV electron irradiation on [-Cu(1)-O(1)-]n chain oxygen arrangements in oxygen deficient but otherwise twin-free YBa2Cu3O6+x single crystals. Comparison of polarized Raman spectra of non-irradiated and irradiated areas provides evidence that electron bombardments instigate the collective hopping of oxygen atoms either from an interstitial at O(5) site to a vacant O(1) chain site or by reshuffling the chain segments to extend the average length of chains without changing the overall oxygen content. This oxygen ordering effect, while counter-intuitive, is analogous to that found in the photoexcitation induced ordering in which temporal charge imbalance from electron-hole pair creation by inelastic scattering of incident electrons causes a local lattice distortion which brings on the atomic rearrangements.
03/2005;
