The manipulation of optical energy in structures smaller than the wavelength of light is key to the development of integrated photonic devices for computing, communications and sensing. Wide band gap semiconductor nanostructures with near-cylindrical geometry and large dielectric constants exhibit two-dimensional ultraviolet and visible photonic confinement (i.e. waveguiding). Combined with optical gain, the waveguiding behavior facilitates highly directional lasing at room temperature in controlled-growth nanowires with suitable resonant feedback. This concept of using well-cleaved nanowires as natural optical cavities may be extendable to many other different semiconductor systems. We have further explored the properties and functions of individual ultralong crystalline oxide nanoribbons that act as subwavelength optical waveguides and assess their applicability as nanoscale photonic elements. The length, flexibility and strength of these structures enable their manipulation on surfaces, including the optical linking of nanoribbon waveguides and other nanowire elements to form networks and device components. We have demonstrated the assembly of ribbon waveguides with nanowire light sources and detectors as a first step toward building nanowire photonic circuitry.
- 2001 – First Nanowire Laser. “Room-temperature ultraviolet nanowire nanolasers”, M. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, P. Yang, Science
- 2002 – First GaN Nanowire Laser. “Single gallium nitride nanowire lasers”, J. Johnson, H. J. Choi, K. P. Knutsen, R. D. Schaller, P. Yang, R. J. Saykally, Nature Materials
- 2003 – First Quantum Wire Laser. “Self-organized GaN quantum wire UV lasers”, H. Choi, J. Johnson, R. He, S. Lee, F. Kim, P. Pauzauskie, J. Goldberger, R. Saykally, P. Yang, J. Phys. Chem. B
- 2004 – Epitaxial growth of high-density GaN nanowire arrays. “Crystallographic Alignment of High Density Gallium Nitride Nanowire Arrays”, T. Kuykendall*, P. J. Pauzauskie*, Y. Zhang, J. Goldberger, D. Sirbuly, J. Denlinger, P. Yang, Nature Materials
- 2004 – Nanoribbons used for nanoscale photonic elements. “Nanoribbon Waveguides for Subwavelength Photonics Integration”, M. Law*, D. Sirbuly*, J. Johnson, J. Goldberger, R. Saykally, P. Yang, Science
- 2005 – Assembling optical networks with nanowires. “Optical routing and sensing with nanowire assemblies”, D. J. Sirbuly*, M. Law*, P. Pauzauskie, H. Yan, A. V. Maslov, K. Knudsen, R. J. Saykally, P. Yang, Proc. Nat. Acad. Sci., 102, 7800, 2005.
- 2006 – Using light to assemble nanowires in water. “Optical Trapping and Integration of Semiconductor Nanowire Assemblies in Water”, P. Pauzauskie, A. Radenovic, E. Trepagnier , H. Shroff, P. Yang, J. Liphardt, Nature. Materials.
- 2006 – New geometry to modify the optical modes in nanowire lasers. “Semiconductor Nanowire Ring Resonator Laser”, P. Pauzauskie, D. Sirbuly, P. Yang, Phys. Rev. Lett.
- 2007 – Demonstration of a nanowire made from a nonlinear material and used as a nanoscale optical probe with tunable emission. “Tunable nanowire nonlinear optical probe”, Y. Nakayama*, P. J. Pauzauskie*, A. Radenovic*, R. M. Onorato*, R. J. Saykally, J. Liphardt, P. Yang, Nature
- 2007 – Demonstration of utilizing the nanowire geometry to alloy InGaN across the complete compositional range to obtain band gaps across the visible spectrum. “Complete Composition Tunability of InGaN Nanowires using a Combinatorial Approach”, T. Kuykendall, P. Ulrich, S. Aloni, P. Yang, Nature Materials
- 2008 – Demonstration of assembling and manipulating metallic nanowires with light. “Dynamic manipulation and separation of individual semiconducting and metallic nanowires using optoelectronic tweezers”, A. Jamshidi*, P. J. Pauzauskie*, P. J. Schuck, A. T. Ohta, P. Chiou, J. Chou, P. Yang, M. C. Wu, Nature Photonics
- 2009 – Imaging emission along a single vertical ZnO nanowire laser. “Imaging Single ZnO Vertical Nanowire Laser Cavities Using UV-laser Scanning Confocal Microscopy”, D. Gargas, M.E. Toimil-Molares, P. Yang, J. Am. Chem. Soc.
- 2009 – “Nanowire Photonics”, R. Yan, D. Gargas, P. Yang, Nature Photonics (Invited Review)
- 2009 – Demonstration of coupling a plasmon excitation into a photonic waveguide in nanowires. “Direct Photonic-Plasmonic Coupling and Routing in Single Nanowires”, R. Yan, P. Pausauskie, J. Huang, P. Yang, Proc. Natl. Acad. Sci. USA
- 2013 – Demonstration of precise control of lasing modes in nanowires by coupling cavities. “Cleaved-Coupled Nanowire Lasers”, H. Gao*, A. Fu*, S. C. Andrews, P. Yang, Proc. Natl. Acad. Sci. USA
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Excitonic solar cells – including organic, hybrid organic-inorganic and dye-sensitised cells (DSCs) – are promising devices for inexpensive, large-scale solar energy conversion. The DSC is currently the most efficient and stable excitonic photocell. Central to this device is a thick nanoparticle film that provides a large surface area for the adsorption of light-harvesting molecules. However, nanoparticle DSCs rely on trap-limited diffusion for electron transport, a slow mechanism that can limit device efficiency, especially at longer wavelengths. We have introduced a new version of the dye-sensitised cell in which the traditional nanoparticle film is replaced by a dense array of oriented, crystalline ZnO nanowires. The direct electrical pathways provided by the nanowires ensure the rapid collection of carriers generated throughout the device, and a full Sun efficiency of 3.5% has been demonstrated, limited primarily by the surface area of the nanowire array. We are now extending our synthetic strategy to design nanowire electrodes with much larger areas available for dye adsorption. It is worth noting that the advantages of the nanowire geometry are even more compelling for other types of excitonic photocells, such as inorganic-polymer, inorganic composite hybrid devices, in which an oriented, continuous and crystalline inorganic phase could greatly improve charge collection.
- 2005 – Improvement of the injection and transport of electrons in a dye-sensitized solar cell using ZnO nanowires. “Nanowire dye-sensitized solar cells”, M. Law*, L. E. Greene*, J. C. Johnson, R. Saykally, P. Yang, Nature Materials
- 2008 – Fabrication of silicon nanowire array solar cells with radial p-n junctions using wafer-scale electroless etching. “Silicon Nanowire Radial p-n Junction Solar Cells”, E. C. Garnett, P. Yang, J. Am. Chem. Soc.
- 2010 – Enhanced solar cell performance from light trapping in silicon nanowire array solar cells. “Light Trapping in Silicon Nanowire Solar Cells”, E. Garnett, P. Yang, Nano Lett.
- 2011 – An efficient heterojunction single-nanowire solar cell produced using solution-processed cation-exchange chemistry. “Solution processed core-shell nanowires for efficient photovoltaic cells”, J. Tang*, Z. Huo*, S. Brittman, H. Gao, P. Yang, Nature Nanotech.
- 2011 – Demonstration that a plasmonic nanocrystal modifies the photocurrent of a single-nanowire silicon solar cell. “Absorption of Light in a Single-nanowire Silicon Solar Cell Decorated with an Octahedral Silver Nanocrystal”, S. Brittman*, H. Gao*, E. C. Garnett, P. Yang, Nano Lett.
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Direct solar energy conversion to storable fuels such as hydrogen offers a promising route toward less reliance on fossil fuels. For example, photoelectrolysis of water to generate H2 on a semiconductor/electrolyte interface has the attractive advantages of clean processing and energy savings over steam reforming of natural gas. One of the most critical issues in solar water splitting is the development of a photoanode with high efficiency and long-term durability in an aqueous environment. TiO2 has been extensively studied as a photoanode due to its high resistance to photocorrosion. However, its conversion efficiency of solar energy to hydrogen is still low due to its large bandgap. Semiconductor heterojunctions can absorb a different region of the solar spectrum. The advantage of composite structures is that each semiconductor needs to satisfy one energetic requirement: matching the conduction band minimum (CBM) or VBM with either the H2 reduction or O2 oxidation potential. Single semiconductor materials typically cannot satisfy the requirements of suitable bandgap energies for efficient solar absorption and meantime with band-edges aligned with both the H2 and O2 redox potential of water. We are currently exploring semiconductor nanowire heterojunctions for the direct solar-to-fuel conversion.
- 2002 – “Semiconductor nanowire array: potential substrates for photocatalysis and photovoltaics”, Y. Wu, H. Yan, P. Yang, Topics in Catalysis
- 2009 – Demonstration of the first solar-to-fuel application of semiconductor nanowires. “High density n-Si/n-TiO2 core/shell nanowire arrays with enhanced photoactivity”, Y. J. Hwang, A. Bukai, P. Yang, Nano Lett.
- 2011 – First demonstration of light-induced charge transport within an asymmetric nanowire heterojunction. “Light Induced Charge Transport within a Single Asymmetric Nanowire”, C. Liu*, Y. J. Hwang*, H. E. Jeong, P. Yang, Nano Lett.
- 2011 – Introduction to the use of semiconductor nanowires from large-scale solution synthesis for photoelectrochemistry. “Surfactant-Free, Large-Scale, Solution-Liquid-Solid (SLS) Growth of Gallium Phosphide Nanowires and Their Use for Visible-Light-Driven Hydrogen Production from Water Reduction”, J. Sun, C. Liu, P. Yang, J. Am. Chem. Soc.
- 2012 – System-level planning of theoretical and experimental efforts is increasingly important for the development of modern materials science. “Towards Systems Materials Engineering”, P. Yang, J. Tarascon, Nature Materials.
- 2013 – “A Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting”, C. Liu*, J. Tang*, H. Chen, B. Liu, P. Yang, Nano Lett
- 2013 – “Atomic Layer Deposition of Platinum Catalysts on Nanowire Surfaces for Photoelectrochemical Water Reduction”, N. P. Dasgupta*, C. Liu*, S. Andrews, F. B. Prinz, P. Yang, JACS
- 2014 – “Semiconductor nanowires for artificial photosynthesis”, C. Liu, N. Dasgupta, P. Yang, Chem. Mater.
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Phonon transport is expected to be greatly impeded in thin (i.e., d<Λ, where d is the diameter and Λ is the phonon mean free path) 1D nanostructures as a result of increased boundary scattering and reduced phonon group velocities stemming from phonon confinement. Detailed models of phonon heat conduction in cylindrical semiconducting nanowires that consider modified dispersion relations and all important scattering processes predict a large decrease in the lattice thermal conductivity of wires tens of nanometers in diameter. Size-dependent thermal conductivity in nanostructures presents a major hurdle in the drive toward miniaturization in the semiconductor industry. Yet poor heat transport is advantageous for thermoelectric materials, which are characterized by a figure of merit (ZT = α2T/[ρ(κp + κe)], with α, T, ρ, κp and κe the Seebeck coefficient, absolute temperature, electronic resistivity, lattice thermal conductivity and electronic thermal conductivity, respectively) that improves as phonon transport worsens. A decade ago, the Dresselhaus group predicted that ZT can be increased above bulk values in thin nanowires by carefully tailoring their diameters, compositions and carrier concentrations. Recent work in our laboratories has focused on understanding the thermal transport properties of pure silicon and Si/SiGe superlattice nanowires as the first step in the experimental verification of enhanced ZT values in these complex nanostructures.
- 2002 – Growth of Si/SiGe Supperlattice Nanowires for potential thermoelectrics applications. “Block-by-Block Growth of Single-Crystalline Si/SiGe Superlattice Nanowires”, Y. Wu, R. Fan, P. Yang, Nano Lett.
- 2003 – First measurement of thermal conductivity of silicon nanowires. “Thermal conductivity of individual silicon nanowires” D. Li, Y. Wu, P. Kim, L. Shi, N. Mingo, Y. Liu, P. Yang, A. Majumdar, Appl. Phys. Lett.
- 2003 – First measurement of thermal conductivity of superlattice nanowires. “Thermal conductivity of individual Si/SiGe superlattice nanowires” D. Li, Y. Wu, P. Kim, L. Shi, N. Mingo, Y. Liu, P. Yang, A. Majumdar, Appl. Phys. Lett.
- 2008 – First demonstration of using rough nanowires for enhanced thermoelectric performance. “Enhanced thermoelectric performance of rough silicon nanowires”, A. I. Hochbaum*, R. Chen*, R. D. Delgado, W. Liang, E. C. Garnett, M. Najarian, A. Majumdar, P. Yang, Nature.
- 2008 – Examination of heat transport in a quasi-1D structure. “Thermal Conductance of Thin Silicon Nanowires”, R. Chen, A. I. Hochbaum, P. Murphy, J. Moore, P. Yang, A. Majumdar, Phys. Rev. Lett.
- 2010 – Demonstration of an efficient thermoelectric from a 2D structure of silicon. “Holey Silicon as an Efficient Thermoelectric Material”, J. Tang*, H. Wang*, D. H. Lee, M. Fardy, Z. Huo, T. P. Russell, P. Yang, Nano Lett.
- 2011 – Using facile conversion chemistry leading to enhanced thermoelectric performance. “Atomic-Level Control of the Thermoelectric Properties in Polytypoid Nanowires”, S. C. Andrews*, M. A. Fardy*, M. C. Moore*, S. Aloni, M. Zhang, V. Radmilovic, P. Yang, Chem. Sci.
- 2012 – Development of a methodology to quantify the effect of surface roughness on heat transport in Si nanowires. “Quantifying Surface Roughness Effects on Phonon Transport in Silicon Nanowires”, J. Lim*, K. Hippalgaonkar*, S. Andrews, A. Majumdar, P. Yang, Nano Lett.
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We are in the process of developing a fully-integrated and highly-sensitive nanowire probe platform for single cell endoscopy. Developing of such flexible nanowire probes would enable us to monitor in-vivo biological processes within single living cells and will greatly improve our fundamental understanding of cell functions, intracellular physiological processes, and cellular signal pathway. There are several key features associated with these cell endoscopy nanowire probes: Minimal invasiveness; high flexibility; high refractive index; evanescent wave optical sensing principle with highly localized excitation and detection scheme; and nonlinear optical conversion capability. Such novel nanowire probes promise intracellular imaging with greatly enhanced 3-dimensional spatial resolution as well as temporal resolution. In addition, these nanowire probes could also be used to spot-delivery or extraction of chemicals (proteins/DNAs) from single living cells with much improved spatial resolution as compared to conventional delivery/extraction methods.
- 2007 – “Interfacing silicon nanowires with mammalian cells”, W. Kim, J. K. Ng, M. E. Kunitake, B. R. Conklin, P. Yang, J. Am. Chem. Soc.
- 2012 – “Nanowire-based Single Cell Endoscopy”, R. Yan*, J. Park*, Y. Choi, C. Heo, S. Yang, L. P. Lee, P. Yang, Nature Nanotech.
- 2015 – “Nanowire-Bacteria Hybrids for Unassisted Solar Carbon Dioxide Fixation to Value-Added Chemicals”, C. Liu, J. J. Gallagher, K. K. Sakimoto, E. M. Nichols, C. J. Chang, M. C. Y. Chang, P. Yang, Nano Lett.
- 2015 – “Nanowire-bacteria hybrids for unassisted solar carbon dioxide fixation to value-added chemicals”, C. Liu, et al. Nano lett.
- 2016 – “Self-photosensitization of Nonphotosynthetic Bacteria for Solar-to-chemical Production”, K. K. Sakimoto, A. B. Wong, P. Yang, Science
- 2016 – “Single nanowire photoelectrochemistry”,Y. Su, C. Liu, S. Brittman, J. Tang, A. Fu, N. Kornienko, Q. Kong, P. Yang, Nature Nanotech.
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Ionic transport through nanoscale channels is receiving increasing attention due to recent experiments that report modulation of ion currents during the passage of single molecules of DNA or protein through the protein ion channel ?-hemolysin. The possibility of rapid DNA sequencing by monitoring the ionic conductance signatures of passing nucleotide oligomers has prompted the synthesis of artificial nanopores and the study of biomolecular transport through them. Nanotubes provide a unique high aspect ratio channel in which to study ion transport and fluid flow. A theoretical treatment of ion behavior in gated silica nanotubes suggests that when the tube diameter is smaller than the Debye length, an applied gate bias can completely expel ions of like charge and produce a unipolar solution of counter-ions within the channel. Modifying the surface charge on the nanotube with the gate electrode modulates the ionic current through the tube – the basis for a unipolar ionic field-effect transistor. Also, the 5-20 ?m length of the nanotube channels now being fabricated in this lab opens up the possibility of imaging and manipulating single molecules as they pass through a tube.
- 2003 – “Single crystal gallium nitride nanotubes”, J. Goldberger, R. He, S. Lee, Y. Zhang, H. Yan, H. Choi, P. Yang, Nature
- 2004 – “Ion transport in nanofluidic channels”, H. Daiguji, P. Yang, A. Majumdar, Nano Lett.
- 2005 – “Electrostatic Control of Ions and Molecules in Nanofluidic Transistors”, R. Karnik*, R. Fan*, M. Yue, D. Li, P. Yang, A. Majumdar, Nano Lett.
- 2005 – “DNA translocation in inorganic nanotubes”, R. Fan, R. Karnik, M. Yue, D. Li, A. Majumdar, P. Yang, Nano Lett.
- 2005 – “Polarity switching and transient responses in single nanotube nanofluidic transistors”, R. Fan, R. Karnik, M. Yue, A. Majumdar, P. Yang, Phys. Rev. Lett.
- 2006 – “Inorganic Nanotubes: A Novel Platform for Nanofluidics”, J. Goldberger, R. Fan, P. Yang, Acct. Chem. Res.
- 2008 – “Gated proton transport in aligned mesoporous silica films”, R. Fan, S. Huh, R. Yan, J. Arnold, P. Yang, Nature Materials
- 2009 – “Nanofluidic diodes based on heterojunction nanotubes”, R. Yan, W. Liang, R. Fan, P. Yang, Nano Lett.
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Known to the ancient Greeks, there are five Platonic solids that can be constructed by selecting a regular convex polygon and having the same number of them meet at each corner: tetrahedron, octahedron, hexahedron (cube), icosahedron, dodecahedron. The beauty in their symmetry and their apparent simplicity continue to inspire generations of mathematicians and scientists. In nature, certain viruses and radiolaria also routinely take the form of these polyhedral shapes. Recently, the concept of shape control has started to revitalize the centuries-old metal colloidal synthesis. Nanoparticles of various shapes, rods, wires, prisms, cubes, particularly those of silver and platinum, have been prepared using a variety of different methodologies. We recently demonstrated a systematic shape-evolution of metal nanocrystals with sizes of 5-300 nm in a modified polyol process. By adding surface-regulating polymer and foreign ions, we can readily access the distinct shapes of tetrahedron, cube, octahedron, and icosahedron with high yield and good uniformity. These nanocrystals have the perfect symmetry for 2- and 3-dimensional packing and therefore could enable the rational tuning of their optical (surface plasmon) and catalytic properties.
- 2004 – “Platonic Gold Nanocrystals”, F. Kim, S. Connor, H. Song, T. Kuykendall, P. Yang, Angew. Chem. Int. Ed.
- 2005 – “Spontaneous formation of nanoparticlestripe patterns through dewetting”, J. Huang*, F. Kim*, A. Tao*, S. Conner, P. Yang, Nature Mater
- 2007 – “Tunable plasmonic lattices of silver nanocrystals”, A. R. Tao, P. Sinsermsuksakul, P. Yang, Nature Nanotech.
- 2012 – “Self-assembly of uniform polyhedral silver nanocrystals into densely packed supercrystals”, J. Henzie, M. Grünwald, A. Widmer-Cooper, P. L. Geissler, P. Yang, Nature Mater.
- 2012 – “Membrane-Protein Binding Measured with Solution-Phase Plasmonic Nanocube Sensors”, H. Wu, J. Henzie, W. Lin, C. Rhodes, Z. Li, E. Sartorel, J. Thorner, P. Yang, J. T. Groves, Nature Methods
- 2013 – “Oriented Assembly of Polyhedral Plasmonic Nanoparticle Clusters”, J. Henzie, S. Andrews, X. Ling, Z. Li, P. Yang, Proc. Natl. Acad. Sci. USA
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The ultimate goal of catalysis research is to achieve 100% selectivity for the desired products at maximum turnover rate (activity) without generating undesired byproducts. Methods for optimizing activity and selectivity have been investigated on the atomic and nanoscopic levels using shape, size, and composition control in nanocrystal synthesis. Incorporating two or more elements in a given material can provide multifunctional surface sites or materials properties not possible with a single element. Compositional gradients and specific elemental positioning can further tune the surface properties, as can shape and size control to expose desired surface facets. On a macroscopic level, nanocrystals are precisely arranged on supporting substrates to achieve desired functionality. One-dimensional supports can provide directionality for catalyst deposition. Two-dimensional supports can provide a platform for highly oriented arrays of nanoparticles, while three-dimensional supports provide the capability to obtain extremely high loading density and activity. Atomically-sensitive characterization techniques both ex situ and in situ allow the underlying mechanisms of selectivity and activity enhancement to be elucidated for a given nanocrystal design.
- 2007 – “Shaping binary metal nanocrystals through epitaxial seeded growth”, S. Habas, H. Lee, V. Radmilovic, G. Somorjai, P. Yang, Nature Mater.
- 2009 – “Thermally Stable Nanocatalyst for High Temperature Reactions: Pt-Mesoporous Silica Core-Shell Nanoparticles”, S. Joo, J. Park, C. Tsung, Y. Yamada, P. Yang, G. A. Somorjai, Nature Mater.
- 2011 – “Nanocrystal Bilayer for Tandem Catalysis”, Y. Yamada, C. Tsung, W. Huang, Z. Huo, S. E. Habas, T. Soejima, C. E. Aliaga, G. A. Somorjai, P. Yang, Nature Chem.
- 2014 – “Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces”, C. Chen*, Y. Kang*, Z. Huo, Z. Zhu, W. Huang, H. Xin, J. D. Snyder, D. Li, J. A. Herron, M. Mavrikakis, M. Chi, K. L. More, Y. Li, N. M. Markovic, G. A. Somorjai, P. Yang, V. R. Stamenkovic, Science.
- 2014 – “Synergistic Geometric and Electronic Effects for Electrochemical Reduction of Carbon Dioxide Using Gold–copper Bimetallic Nanoparticles”, D. Kim, J. Resasco, Y. Yu, A.M. Asiri, P. Yang. Nature Comm.
- 2016 – “Anisotropic phase segregation and migration of Pt in nanocrystals en route to nanoframe catalysts”, Zhiqiang Niu*, Nigel Becknell*, Yi Yu, Dohyung Kim, Chen Chen, Nikolay Kornienko, Gabor A Somorjai, and Peidong Yang. Nature Mater.
- 2017 – “Room-Temperature Dynamics of Vanishing Copper Nanoparticles Supported on Silica”, Dohyung Kim, Nigel Becknell, Yi Yu, and Peidong Yang. Nano Letters
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