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Education |
- 1987-1993 Ph.D in Physics, The University of Texas at Austin, U.S.A.
- 1981-1985 B.E. in Electronic Engineering, National Chiao Tung University, R.O.C.
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Professional Experience |
Current position:
- 2002-present, Professor of Physics, National Tsing Hua Univ.,
Experience:
- 1997-2002, Associate Professor of Physics, National Tsing Hua Univ., R.O.C.
- 1996-1997, Research Fellow of Atom Technology Group, National Instiitute for advanted Interdisciplinary Research
- 1994-1996, Postdoc of Tokumoto Group, Joint Research Center for Atom Technology
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Honors and Awards |
- Outstanding Research Award, National Science Council (2000)
- Outstanding Research Award, National Science Council (2004)
- Ten Outstanding Youths in Taiwan (2001年)
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Research Fields |
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- Scanning Probe Microscopy/Spectroscopy
- Nanostructure Physics
- Surface Physics
- Molecular beam epitaxy of nitride semiconductors
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Research Interests and achievement |
Updated on September 3, 2006
The research interests in my group are focused on low-dimensional, atomic-scale to nanometer-scale condensed matter systems, mainly based on semiconductor epitaxial materials. Our recent studies include plasma-assisted molecular-beam epitaxy of group-III nitride (InN, GaN, AlN, and their alloys) epitaxial films and nanostructures, optical spectroscopy of light emitting nanomaterials inside optical microcavities, scanning probe microscopy (STM, AFM, EFM, and related novel nanolithographic methods), nanomanipulation and controlled self-assembly of low-dimensional nanomaterials, and scanning tunneling and synchrotron-radiation photoelectron spectroscopies of III-nitride surface and interface electronic structures.
Some highlighted research topics are listed as follows:
- Epitaxial studies of commensurately matched indium nitride (InN), gallium nitride (GaN), aluminum nitride (AlN) epitaxial systems, including heterojunctions, quantum wells, quantum dots, self-aligned nanorods, and quantum disks in nanorods
By using plasma-assisted molecular-beam epitaxy, we have recently demonstrated that high-quality III-nitride heterojunctions can be realized via the concept of commensurate lattice match. In particular, we showed that atomically abrupt InN/AlN heterojunction can be formed despite of a tremendous mismatch in lattice constants (>10%). This finding can open up new pathways for III-nitride-related fundamental studies and device applications. In addition, we have developed epitaxial growth techniques for forming III-nitride quantum dots, self-aligned nanorods, and quantum disks in nanorods. These nanomaterials would be very useful for future device applications in the fields of light-emitting devices, solar cells, and high-speed transistors.
- Optical spectroscopy
We are using the techniques of spatially- and time-resolved photoluminescence spectroscopy for studying the interactions of light-emitting nanomaterials within optical microcavities (such as III-nitride nanorods or whispering-gallery-mode silica microspheres/rings). We are interested in both weak- and strong-coupling regimes. Theses studies can lead to novel light-emitting devices and can be used develop the necessary means for quantum manipulation of matter states, which is important in solid-state quantum information processing.
- Electronic structures of III-nitride surfaces and interfaces
Band structure line-ups of III-nitride heterojunctions are important electronic properties to realize both electronic and photonic device applications. Also, surface and interface electronic structures of III-nitride are crucial for understanding the characteristics of III-nitride materials (especially for InN, a focused material for recent III-nitride research activities). For these largely unexplored research areas, we will utilize the techniques of scanning tunneling microscopy/spectroscopy and synchrotron-radiation photoelectron spectroscopy for a comprehensive understanding of related electronic properties.
- Nanofabrication
Using various scanning probe lithography and pattern transfer techniques, we have succeeded in developing new methods for fabricating nanostructures which can be used in micooptics and optoelectronics as well as devices based on artificial photonic/plasmonic bandgap structures. Recently, we have also built a specialized scanning electron microscope (SEM) system, which allows in-situ manipulation, assembly, and measurement of individual one-dimensional nanomaterials via a four-probe nanomanipulator. At present, we are working on nanosensing and nanophotonic applications based on these assembled one-dimensional nanomaterials.
- Soft condensed matter systems Colloidal nanoparticles are important building blocks for the emerging applications in nanosensing and nanophotonics. We have developed and are continually working on novel approaches for multiple-length-scale (nm to mm) controlled self-assembly of functionalized colloidal nanoparticles onto patterned molecular layers or electrostatic charge patterns.
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Selected Publications |
- [2006] C.-F. Chen, S.-D. Tzeng, M.-H. Lin, and S. Gwo,* “Electrostatic assembly of gold colloidal nanoparticles on organosilane monolayers patterned by microcontact electrochemical conversion,” Langmuir 22, 7819 (2006).
- [2006] C.-H. Shen, H.-Y. Chen, H.-W. Lin, S. Gwo,* A. A. Klochikhin, and V. Yu. Davydov, “Near-infrared photoluminescence from vertical InN nanorod arrays grown on silicon: Effects of surface electron accumulation layer,” Appl. Phys. Lett. 88, 253104 (2006).
- [2006] S.-D Tzeng, K.-J. Lin, J.-C. Hu, L.-J. Chen, and S. Gwo,* “Templated self-assembly of colloidal nanoparticles controlled by electrostatic nanopatterning on Si3N4/SiO2/Si electret,” Adv. Mater. 18, 1147 (2006)
- [2006] C.-L. Wu, C.-H. Shen, and S. Gwo,* “Valence band offset of wurtzite InN/AlN commensurate heterojunction determined by photoelectron spectroscopy,” Appl. Phys. Lett. 88, 032105 (2006).
- [2005] C.-L. Wu, C.-H. Shen, H.-W. Lee, H.-M. Lee, and S. Gwo,* “Direct evidence of 8:9 commensurate heterojunction formed between InN and AlN on c-plane,” Appl. Phys. Lett. 87, 241916 (2005).
- [2005]Ahn,* C.-H. Shen, C.-L. Wu, and S. Gwo, “Spectroscopic ellipsometry study of wurtzite InN epitaxial films on Si(111) with varying carrier concentrations,” Appl. Phys. Lett. 86, 201905 (2005).
- [2005] C.-F. Chen, S.-D Tzeng, H.-Y. Chen, and S. Gwo,* “Silicon microlens structures fabricated by scanning-probe gray-scale oxidation,” Optics Lett. 30, 652 (2005).
- [2004] C.-L. Wu, L-J. Chou, and S. Gwo,* “Size- and shape-controlled GaN nanocrystals grown on Si(111) substrate by reactive epitaxy,” Appl. Phys. Lett. 85, 2071 (2004).
- [2004] S. Gwo,* C.-L. Wu, C.-H. Shen, W.-H. Chang, T. M. Hsu, J.-S. Wang, and J.-T. Hsu, “Heteroepitaxial growth of wurtzite InN films on Si(111) exhibiting strong near-infrared photoluminescence at room temperature,” Appl. Phys. Lett. 84, 3765 (2004)
- [2003] S. Gwo,* C.-P. Chou, C.-L. Wu, Y.-J. Yeh, S.-J. Tsai, W.-C. Lin, and M.-T. Lin, “Self-limiting size distribution of supported cobalt nanoclusters at room temperature,” Phys. Rev. Lett. 90, 185506 (2003).
- [2002] S.-D. Tzeng, C.-L. Wu, Y.-C. You, T. T. Chen, S. Gwo,* and H. Tokumoto, “Charge imaging and manipulation using carbon nanotube probes,” Appl. Phys. Lett. 81, 5042 (2002).
- [2001]H. Ahn, C.-L. Wu, S. Gwo, C. M. Wei, and Y. C. Chou,* “Structure determination of the Si3N4/Si(111)-(8�e8) surface: A combined study of Kikuchi electron holography, scanning tunneling microscopy, and ab initio calculations,” Phys. Rev. Lett. 86, 2818 (2001).
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A. Refereed Papers:
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- S. Gwo, A. R. Smith, C. K. Shih, K. Sadra, B. G. Streetman, "Scanning tunneling microscopy of GaAs multiple pn-junctions," Appl. Phys. Lett. Vol. 61, 1104-1106 (1992).
- S. Gwo, K. J. Chao, C. K. Shih, K. Sadra, and B. G. Streetman, "Direct Mapping of Electronic Structure Across Al0.3Ga0.7As/GaAs Heterojunctions: Band offsets, Asymmetrical Transition Widths, and Multiple-Valley Band Structures," Phys. Rev. Lett. Vol. 71, 1883-1886 (Sep. 20, 1993).
- S. Gwo and C. K. Shih, "Site-selective imaging in scanning tunneling microscopy of graphite: The nature of site asymmetry", Phys. Rev. B Rapid Communication Vol. 47, 13059-13062 (May 15,1993).
- S. Gwo, A. R. Smith, and C. K. Shih, "Vacancy migration, adatom motion, and atomic bistability on the GaAs(110) surface studied by scanning tunneling microscopy," J. Vac. Sci. Technol. A Vol. 11, 1644-1648 (Jul/Aug, 1993).
- S. Gwo, K. J. Chao, A. R. Smith, C. K. Shih, K. Sadra, and B. G. Streetman, "Scanning tunneling microscopy of doping and compositional III-V homo- and heterostructures," J. Vac. Sci. and Technol. B Vol. 11, 1509-1513 (Jul/Aug, 1993).
- S. Gwo, K. J. Chao, C. K. Shih, "Cross-sectional scanning tunneling microscopy of doped and undoped AlGaAs/GaAs heterostructures," Appl. Phys. Lett. Vol. 64, 493-495 (Jan.24, 1994).
- S. Gwo, A. R. Smith, K.J. Chao, C. K. Shih, K. Sadra, and B. G. Streetman, "Cross-sectional scanning tunneling microscopy and spectroscopy of passivated III-V heterostructures," J. Vac. Sci. and Technol. A Vol. 12, 2005-2008 (Jul/Aug, 1994).
- A. R. Smith, S. Gwo, K. Sadra, T. C. Shih, B. G. Streetman, and C. K. Shih, "Comparative study of cross-sectional scanning tunneling microscopy/spectroscopy on III-V hetero- and homostructures: ultrahigh vacuum-cleaved versus sulfide passivated," J. Vac. Sci. and Technol. B Vol. 12, 2610-2615 (Jul/Aug, 1994).
- A. R. Smith, S. Gwo, and C. K. Shih, "A new high-resolution two-dimensional micropositioning device for scanning probe microscopy applications," Rev. Sci. Instrum. Vol. 65, 3216-3219 (Oct., 1994).
- S. Gwo, H. Ohno, S. Miwa, J. F. Fan, and H. Tokumoto, "Atomic-scale studies of point defects in compound semiconductors by scanning tunneling microscopy," in Proceedings of the 18th International Conference on Defects in Semiconductors, Sendai, Japan, July 23-28,1995, Material Science Forum (Trans Tech Publications, Switzerland), Vol. 196-201, 1949-1954 (1995).
- S. Gwo, S. Miwa, H. Ohno, J. F. Fan, H. Tokumoto, "Direct observation of precipitates and self-organized nanostructures in molecuar-beam eipitaxy grown heavily doped GaAs:Si," Appl. Phys. Lett. Vol. 67, 3123-3125 (Nov.20, 1995).
- S. Gwo, and H. Tokumoto, "Cross-sectional scanning tunneling microscopy and spectroscopy of semiconductor heterostructures," Journal of the Vacuum Society of Japan Vol.38, 1009-1019 (Dec. 1995).
- H. Ohno, L. A. Nagahara, S. Gwo, and H. Tokumoto, "Nanometer-Scale Wires of Monolayer Height Alkanethiols on AlGaAS/GaAs Heterostructures by Selective Chemisorption," Jpn. J. Appl. Phys, Vol. 35, L512-L515 (Apr. 15,1996).
- S. Gwo, H. Ohno, S. Miwa, J. F. Fan, and H. Tokumoto, "Structural and doping properties of molecular-beam epitaxy grown Si-doped GaAs(001) surfaces," Surf. Sci. Vol. 358, 446-450 (1996).
- T. Komeda, S. Gwo, and H.Tokumoto, "Cross-Sectional Scanning -Tunneling-Microscopy on Cleaved Si(111)-Observation of Novel Reconstruction and Structural and Electrical Properties of MOS Interface," Jpn. J. Appl. Phys. Part 1 Vol. 35, 3724-3729 (1996).
- T. Komeda, S. Gwo, and H.Tokumoto, "MOS interface characterization by cross-sectional STM," Surf. Sci. Vol. 358, 38-41 (1996).
- S. Gwo, H. Ohno, and H. Tokumoto, "Surface Reconstruction and Ultrasmooth Morphology of High-Temperature Grown AlAs(001)-3x2," in Proceedings of the 23rd International Conference on the Physics of Semiconductors, Berlin, Germany, July 21-26,1996 (World Scientific, Singapore), Vol.2, 875-878 (1996).
- S. Gwo, H. Ohno, and H. Tokumoto, "In Situ Tunneling Microscopic Study of GaAs/AlAs Wire Superlattices on Vicinal Substrates," in Proceedings of the 23rd International Conference on the Physics of Semiconductors, Berlin, Germany, July 21-26,1996 (World Scientific, Singapore), Vol. 2, 1145-1148 (1996).
- S. Gwo, H. Ohno, and H. Tokumoto, "Atomic-scale Surface Structure and Ultrasmooth Morphology of Molecular-Beam Epitaxy Grown AlAs(001)-(3x2)," Phys. Rev. B Rapid Communication Vol. 55,R1962-R1965 (Jan 15,1997).
- H. Ohno, L. A. Nagahara, S. Gwo, W. Mizutani, H. Tokumoto, "Formation of Self-Assembled Monolayer on Cleaved Compound Semiconductor Surfaces and Its Nano-structure on AlGaAs/GaAs Heterostructure," Journal of the Surface Society of Japan, Vol. 18, No. 6, 373-379 (June 1997).
- H. Ohno, L. A. Nagahara, S. Gwo, W. Mizutani, H. Tokumoto, "Nanostructural Formation of Self-Assembled Monolayer Films on Cleaved AlGaAs/GaAs Heterojunctions," Mol. Cryst. Liq. Cryst., Vol. 295, 189-192 (1997).
- S. Gwo, H. Tokumoto, S. Miwa, "Atomic-scale nature of the (3x3)-ordered GaAs(001):N surface prepared by plasma-enhanced molecular-beam epitaxy," Appl. Phys. Lett. Vol. 71, 362-364 (July 21, 1997).
- S. Gwo, C.-L. Yeh, P.-F. Chen, Y.-C. Chou, T. T. Chen, T. S. Chao, S.-F. Hu, and T.-Y. Huang, "Local electric-field-induced oxidation of titanium nitride films," Appl. Phys. Lett. Vol. 74, 1090-1092 (February 22, 1999). (NSC88-2112-M-007-002)
- S. Gwo, T.-T. Lian, Y.-C. Chou, and T. T. Chen, "Nano-Oxidation Kinetics of Titanium Nitride Films," in Proceedings of The Croucher Advanced Study Institute: Physics and Chemistry of Nano-structured Materials, Hong Kong University of Science and Technology, Hong Kong, January 10-15, 1999, edited by S. Yang and P. Sheng, p. 60-63 (Taylor and Francis, London, U. K., 2000). (NSC88-2112-M-007-002)
- Y. H. Wu, W. J. Chen, S. L. Chang, A. Chin, S. Gwo, and C. Tsai, "Improved Electrical Characteristics of CoSi2 Using HF-Vapor Treatment," IEEE Electron Device Letters, Vol. 20, 200-202 (May, 1999).
- F. S.-S. Chien, C.-L. Wu, Y.-C. Chou, T. T. Chen, S. Gwo, and W.-F. Hsieh, "Nanomachining of (110)-oriented silicon by scanning probe lithography and anisotropic wet etching," Appl. Phys. Lett. 75, 2429 (October 18, 1999). (NSC88-2112-M-007-002)
- F. S.-S. Chien, J.-W. Chang, S.-W. Lin, Y.-C. Chou, T. T. Chen, S. Gwo, T.-S. Chao, and W.-F. Hsieh, "Nanometer-scale conversion of Si3N4 to SiOx," Appl. Phys. Lett. Vol. 76, 360-362 (January 17, 2000). (NSC88-2112-M-007-002)
- T. Yasuda, S. Yamasaki, and S. Gwo, "Nanoscale selective-area epitaxial growth of Si using an ultrathin SiO2/Si3N4 mask patterned by an atomic force microscope," Appl. Phys. Lett. Vol. 77, 3917-3919 (Dec. 11, 2000). (the Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- F. S.-S. Chien, Y. C. Chou, T. T. Chen, W.-F. Hsieh, T.-S. Chao, and S. Gwo, "Nano-oxidation of silicon nitride films with an atomic force microscope: chemical mapping, kinetics, and applications," J. Appl. Phys. Vol. 89, 2465-2472 (Feb. 15, 2001). (NSC-89-2112-M-007-077 and Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- H. Ahn, C.-L. Wu, S. Gwo, C. M. Wei, and Y. C. Chou, "Structure determination of the Si3N4/Si(111)-(8x8) surface: a combined study of Kikuchi electron holography, scanning tunneling microscopy, and ab initio calculations," Phys. Rev. Lett. Vol. 86, 2818-2821 (March 26, 2001). (NSC-89-2112-M-007-093 and Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- S. Gwo, F. S.-S. Chien, C.-L. Wu, T. Yasuda, and S. Yamasaki "Scanning probe microscopy and lithography of ultrathin Si3N4 films grown on Si(111) and Si(001)," Jpn. J. Appl. Phys. Vol. 40, 4368-4372 (June, 2001). (NSC-89-2112-M-007-093 and Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- S. Gwo, T. Yasuda, and S. Yamasaki, "Selective-area chemical vapor deposition of Si using a bilayer dielectric mask patterned by proximal probe oxidation," J. Vac. Sci. Technol. A Vol. 19, 1806-1811 (Jul./Aug., 2001). (NSC-89-2112-M-007-077 and Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- M. Berg, C. DeWitt-Morette, S. Gwo, E. Kramer, "The pin groups in physics: C, P, and T," Reviews in Mathematical Physics Vol. 13, 953-1034 (August, 2001).
- S. Gwo, S.-Y. Huang, and T.-R. Yang, "Enhancement of direct optical transition in nano-crystallized GaAsN alloy," Phys. Rev. B Vol. 64, 113312 (4 pages) (September 15, 2001). (NSC-89-2112-M-007-093 and Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- J. A. Dagata, F. S.-S. Chien, S. Gwo, K. Morimoto, T. Inoue, J. Itoh, and H. Yokoyama, "Electric force microscopy with a single carbon nanotube tip," submitted (2001).
- Ruth Klauser, I.-H. Hong, T.-H. Lee, G.-C. Yin, D.-H. Wei, and K.-L. Tsang, T. J. Chuang, S.-C. Wang, S. Gwo, M. Zharnikov, J.-D. Liao, "Zone-plate-based scanning photoelectron microscopy at SRRC: performance and applications," accepted for publication in Surface Review and Letters (2001).
- (Review Article) S. Gwo, "Scanning probe oxidation of silicon nitride masks for nanoscale lithography, micromachining, and selective epitaxial growth on silicon," Journal of Physics and Chemistry of Solids Vol. 62, 1673-1687 (Sep./Oct., 2001). (Program for Promoting Academic Excellence of Universities No. 89-FA04-AA)
- R. Klauser, I.-H. Hong, H.-J. Su, T. T. Chen, S. Gwo, S.-C. Wang, T. J. Chuang, and V. A. Gritsenko, "The oxidation states in scanning-probe-induced Si3N4 to SiOx conversion studied by scanning photoemission microscopy," Appl. Phys. Lett. Vol. 79, 3143-3145 (Nov. 5, 2001). (NSC-90-2112-M-007-061)
- S. Gwo, T. T. Chen, T. Yasuda, and S. Yamasaki, "Nanometer-scale conversion of Si3N4 to SiOx for applications in lithography, micromachining, and selective-area CVD," Phys. Stat. Sol. (a) Vol. 188, 383-387 (2001). (NSC-89-2112-M-007-077)
- C.-L. Wu, J.-L. Hsieh, H.-D. Hsueh, and S. Gwo, "Thermal nitridation of the Si(111)-(7x7) surface studied by scanning tunneling microscopy and spectroscopy," Phys. Rev. B Vol. 65, 045309 (6 pages) (Jan. 15, 2002). (NSC-90-2112-M-007-059)
- F. S.-S. Chien, W. F. Hsieh, S. Gwo, A. E. Vladar, and J. A. Dagata, "Silicon nanostructures fabricated by scanning probe oxidation and tetra-methyl ammonium hydroxide etching," J. Appl. Phys. Vol. 91, 10044-10050 (June 15, 2002).
- S.-D. Tzeng, C.-L. Wu, Y.-C. You, T. T. Chen, S. Gwo, and H. Tokumoto, "Charge imaging and manipulation with carbon nanotube probes," submitted (2002).
- T. M. Hong, C.-H. Wu, S. D. Tzeng, and S. Gwo, "Utilizing the Coulomb force on a carbon nanotube to enhance the resolution of electrostatic force microscope," International Journal of Nanoscience Vol. 2, 219-224 (2003).
- S. Gwo, C.-P. Chou, C.-L. Wu, Y.-J. Yeh, S.-J. Tsai, W.-C. Lin, and M.-T. Lin, "Self-limiting size distribution of supported cobalt nanoclusters at room temperature," Phys. Rev. Lett. Vol. 90, 185506 (2003).
- C.-S. Chen, J.-T. Lue, C.-L. Wu, S. Gwo, and K.-Y. Lo, "A study of surface and interlayer structures of epitaxially growth group-III nitride compound films on Si(111) substrates by second-harmonic generation," J. Phys.-Condens. Mat. Vol. 15, 6537-6548 (2003).
- C.-L. Wu, J.-C. Wang, M.-H. Chan, T. T. Chen, and S. Gwo, "Heteroepitaxy of GaN on Si(111) realized with a coincident-interface AlN/β-Si3N4(0001) double-buffer structure," Appl. Phys. Lett. Vol. 83, 4530-4532 (2003).
- S. Gwo, C.-L. Wu, C.-H. Shen, W.-H. Chang, T. M. Hsu, J.-S. Wang, and J.-T. Hsu, "Heteroepitaxial growth of wurtzite InN films on Si(111) exhibiting strong near-infrared photoluminescence at room temperature," Appl. Phys. Lett. Vol. 84, 3765-3767 (2004).
- T. Yasuda, T. Tada, S. Yamasaki, S. Gwo, and. L.-S. Hong, "Position-specific formation of epitaxial Si grains on thermally oxidized Si(001) surface via isolated nanodots," Chem. of Mater. Vol. 16, 3518-3523 (2004).
- C.-L. Wu, L-J. Chou, and S. Gwo, "Size- and shape-controlled GaN nanocrystals grown on Si(111) substrate by reactive epitaxy," Appl. Phys. Lett. Vol. 85, 2071-2073 (2004).
- H. Ahn, C.-H. Shen, C. -L. Wu, and S. Gwo, "Spectroscopic ellipsometry study of wurtzite InN epitaxial films on Si(111) with varying carrier concentrations," submitted to Appl. Phys. Lett. (2004).
- C.-F. Chen, S.-D Tzeng and S. Gwo, "Silicon microlens fabricated by scanning probe gray-scale nanolithography," submitted to Optics Lett. (2004).
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