Nanotechnology Seminar Series: 2009 - 2013

THURSDAY April 25, 2013, 10:30 AM - Bldg 215, Rm C103-106

Of Light, Electrons, and Metamaterials

Nader Engheta
University of Pennsylvania

Metamaterials and plasmonic optics provide mechanisms for controlling and taming photons and electrons in unprecedented ways. In my group we are exploring various features and characteristics of these concepts and investigate new classes of applications such paradigms may provide. We have been developing several concepts such as "metamaterials that do mathematical operations", "digital metamaterials", "extreme-parameter metamaterials", "nonreciprocal plasmonics", "meta-electronics" in which one can tailor the effective mass of electrons for ultrafast response, and "optical metatronics", i.e. metamaterial-inspired optical nanocircuitry and nanostrcutures, in which the three fields of "nanoelectronics", "nanophotonics" and "magnetics" can be merged together. In such a unifying platform, the concept of metamaterials and plasmonics optics can be exploited to bridge the gaps among these fields, to modularize, standardize, and parameterize some of the optical and electronic phenomena, and to transplant concepts from one field into another. We have now extended some of these concepts to other platforms such as graphene as one-atom-thick metamaterials and one-atom-thick optical devices and circuitry. I will present an overview of our most recent results from a sample of these topics and discuss future directions and potentials.

THURSDAY March 14, 2013, 10:30 AM - Bldg 215, Rm C103-106

Modulated Interface Lithography {MIL}:
The Nanoworld Beyond Bénard Instability

Sandra M. Troian
California Institute of Technology

During the past decade, several groups have demonstrated spontaneous formation of nanopillar arrays using molten nanofilms whose surface is exposed to a thermal gradient. These arrays adopt various symmetries and shapes depending on conditions, and once the thermal gradient is removed, the structures rapidly solidify resulting in nanostructures with extraordinarily smooth surfaces, particularly advantageous for optical and photonic applications. Control over structure formation requires identification of the dominant physical mechanism which establishes the minimum lateral feature size as well the material and geometric properties affecting growth rate. In this talk, we discuss structure formation in the context of extremely large thermocapillary forces ("nano-Bénard flow") which rapidly outweigh stabilization by capillary forces. Analysis of the governing equations indicates no critical number for instability and no steady state, and if not mass-limited the nanopillars may grow continuously until contact with a cooler target occurs. The results suggest a novel patterning technique for 3D lithography and film sculpting based on interface modulation.

THURSDAY February 14, 2013, 10:30 AM - Bldg 215, Rm C103-106

Photonic Materials for Solar Energy Conversion at the Thermodynamic Limit

Harry Atwater
California Institute of Technology

Ever since serious scientific thinking went into improving the efficiency of photovoltaic energy conversion more than 50 years ago, thermodynamics has been used to assess the limits to performance, guiding advances in materials science and photovoltaic technology. Photovoltaics have advanced considerably, resulting in single-junction solar cells with a record efficiency of 28.8% and multi-junction cells with an efficiency of 44%. As impressive as these advances are, these record efficiencies and also today's manufactured cell efficiencies in the 10–18% range fall far short of the thermodynamic limits. Why such a large gap? There is no fundamental reason, and in this lecture, I will discuss methods for systematically addressing the efficiency losses in current photovoltaics that can enable a next phase of photovoltaic science and engineering – ultrahigh efficiency photovoltaics. This development takes advantage of recent advances in the control of light trapping and emission at the nanometer and micron length scales, coupled with emerging spectrum splitting optical design and materials fabrication approaches that will allow the development of photovoltaics with efficiencies in the 50–70% range.

THURSDAY November 1, 2012, 10:30 AM - Bldg 215, Rm C103-106

Precision Materials Engineering: Nanomanufacturing Technology for Electronics, Energy and Display

Omkaram Nalamasu
Applied Materials

Nanomanufacturing technology, the cost-effective and practical manufacturing solutions based on equipment and process solution platforms have been translating the promise of nanotechnology to reality in advancing the electronics and display technology and product roadmaps. Advances in nanomanufacturing technology are also fundamental to solving the energy and environment challenges. In this presentation, I will detail the challenges and opportunities facing the electronics, display, energy and other industries and how advances in nanomanufacturing are fundamental to resolving these challenges.

 

THURSDAY October 11, 2012, 10:30 AM - Bldg 215, Rm C103-106

Graphene at the Boundaries

Paul McEuen
Goldwin Smith Professor of Physics
Cornell University Director
Kavli Institute at Cornell for Nanoscale Science

Many thousands of papers have investigated graphene's remarkable structural, mechanical, optical, and electronic properties. Most of these studies, however, have focused on only one of graphene's attributes at a time, neglecting its unique combination of properties. In this talk we will look at these interdisciplinary boundaries, examining cases when a combination of graphene's properties, e.g. electrical and mechanical, are simultaneously important. For example, we will discuss experiments on graphene atomic membranes where electronic and optical signals can control the frequency, amplitude, and damping of a graphene drumhead resonance. We also present ultrafast measurements of photocurrent in graphene p-n junctions. At the boundary of graphene electronics and optics, these measurements probe the fundamental relaxation processes that are key to applications ranging from photodetectors to optical saturable absorbers. Finally, we explore the properties of a literal boundary that occurs in bilayer graphene. We present the first atomic resolution images of the soliton-like boundaries between bilayer graphene's different broken-symmetry structural ground states. True to form, these boundaries are predicted to dramatically influence both the mechanical and electronic properties of bilayer graphene.

THURSDAY May 31, 2012, 10:30 AM - Bldg 215, Rm C103-106

Nanomaterials in 1-d: Exploring Mesoscopic Phenomena in Template-Grown Nanowires

Thomas Mallouk
Penn State University

Mesoscopic properties are those that emerge when the size of an object matches a characteristic physical length scale, such as the exciton radius in a semiconductor or the coherence length of Cooper pairs in a superconductor. Nanowires are particularly interesting in this context as quasi-1D materials. By using anodic alumina and track-etched polymer membranes act as hard templates, we have made "striped" and core-shell nanowires with precise control over dimensions and composition. These structural features allow one to explore unusual electronic transport properties of single-crystal nanowires and their possible applications in molecular and nanoscale electronics. The motion of nano- and microwires in fluids is also a mesoscopic phenomenon at low Reynolds number. In this application, bi- and trimetallic nanorods are catalytically self-propelled in fuel-containing solutions at speeds that are comparable to those of flagellar bacteria. Despite the difference in propulsion mechanisms, catalytic nano- and micromotors are subject to the same external forces as natural motors such as bacteria. Therefore they follow the same scaling laws and exhibit similar emergent behavior (e.g., magnetotaxis, chemotaxis, schooling, and predator-prey behavior). Recently we have found that bimetallic nanowires also undergo autonomous motion and a range of collective behavior in fluids when excited by low power ultrasound. The acoustophoretic propulsion mechanism may be particularly useful for biomedical applications because it is salt-tolerant and does not involve chemical fuels.

THURSDAY May 31, 2012, 10:30 AM - Bldg 215, Rm C103-106

In Quest of a Fast, Low-Voltage Digital Switch

Thomas N. Theis
IBM T.J. Watson Research Center

Because the performance of today's computational systems is severely constrained by economic limits on allowable power dissipation, reduced dissipation in device switching may be the most critical attribute for the success of any new switch which can replace the field effect transistor for digital logic. There are two broad and very distinct physical approaches to reduced power dissipation. The first approach is to store less energy in the device to distinguish digital logic states. The second approach is to conserve the stored energy from switching event to switching event by implementing near-adiabatic switching protocols and energy-conserving logic circuits. In this talk, I focus on the first approach, and further limit the discussion to three-terminal, voltage-controlled current switches – devices which should be broadly compatible with silicon interconnection technology and with well-established FET circuit families. I discuss several classes of proposed low-voltage devices, and identify the underlying operating principles which enable those devices to overcome the voltage-scaling limit of the conventional field effect transistor. I argue that the operating principles exemplified by these devices are quite general, and can be applied in ways that have not yet been explored. It is therefore likely that we are still in the early stages of the quest for a fast, low-voltage digital switch.

THURSDAY April 19, 2012, 10:30 AM - Bldg 215, Rm C103-106

Semiconductor Nanomaterials for Bio-Integrated Electronics

John Rogers
University of Illinois, Urbana-Champaign

Biology is curved, soft and elastic; silicon wafers are not. Semiconductor technologies that can bridge this gap in form and mechanics will create new opportunities in devices that adopt biologically inspired designs or require intimate integration with the human body. This talk describes the development of ideas for electronics that offer the performance of state-of-the-art, wafer-based systems but with the mechanical properties of a rubber band. We explain the underlying materials science and mechanics of these approaches, and illustrate their use in bio-integrated, "tissue-like" electronics with unique capabilities for mapping cardiac electrophysiology, in both endocardial and epicardial modes, and for performing electrocorticography. Demonstrations in live animal models illustrate the functionality offered by these technologies, and suggest several clinically relevant applications.

THURSDAY March 29, 2012, 10:30 AM - Bldg 215, Rm C103-106

Finding the Missing Memristor

Stan Williams
VP Hewlett Packard Laboratories

The existence of a fourth passive circuit element was proposed by Prof. Leon Chua of UC Berkeley in 1971 from fundamental symmetry arguments and mathematical analyses to augment the familiar resistance, inductance and capacitance circuit equations. Although he showed that such a 'memristor' had many interesting and useful circuit properties, he did not know of a material example of such an element. We now understand that the memristor is a model of the circuit properties of a wide range of devices that display a "pinched hysteresis loop" in their current-voltage characteristics, including both unipolar and bipolar resistance switching devices (ReRAM or RRAM), spin-transfer torque (STT) RAM, and phase change devices. We have built nanoscale titanium dioxide and tantalum pentoxide switching devices in our laboratory and have demonstrated both their fundamental electrical properties and several potential uses, including new forms of memory and logic circuits. Memristors can rather easily be integrated into electronic circuits using conventional fabrication techniques and materials available in standard CMOS fabrication facilities. In this talk, I will present some recent results on understanding device mechanisms as well as switching speed and energy measurements.

THURSDAY November 17, 2011, 10:30 AM - Bldg 215, Rm C103-106

Bioimaging on the Nanoscale: Single-Molecule and Super-Resolution Fluorescence Microscopy

Xiaowei Zhuang
Howard Hughes Medical Institute, Harvard University

Light microscopy is an essential tool in biological research. However, the spatial resolution of Light microscopy, classically limited by diffraction to several hundred nanometers, is substantially larger than typical molecular length scales in cells. Hence many subcellular structures cannot be resolved by light microscopy. We recently developed a new form of super-resolution light microscopy, stochastic optical reconstruction microscopy (STORM), that surpasses the diffraction limit. STORM uses single-molecule imaging and photo-switchable fluorescent probes to temporally separate the spatially overlapping images of individual molecules. This approach allows the localization of fluorescent probes with nanometer precision and the construction of sub-diffraction-limit images. Using this method, we have achieved multicolor and three-dimensional (3D) imaging of living cells with nanometer-scale resolution. We applied this method to investigate bacterial cells and neurons, in particular the organization of bacterial chromosome and the molecular architecture of synapses. In this talk, I will discuss the general concept, recent technological advances and biological applications of STORM.

THURSDAY May 19, 2011, 10:30 AM - Bldg 215, Rm C103-106

Functional Imaging of Nanowires

Lincoln J. Lauhon
Northwestern University, Evanston, IL

Nanowires are nanoscale in two dimensions and microscale in a third dimension, providing a wealth of opportunities to exploit novel nanoscale electronic, optical, magnetic, and thermal properties in devices with well-defined microscale electrical contacts. An attendant challenge is the establishment of quantitative structure-property relationships that enable rational engineering of new and/or superior function. In semiconductors, the dopant concentration determines the carrier concentration, so correlated studies of dopant distribution and local conductivity are important when intentional or unintentional inhomogeneities are present. In materials that undergo phase-changes near room temperature, such as vanadium oxide (VO2), the crystal structure influences the conductivity, so local mapping of phase domains is important to understanding and controlling switching behaviors. Doping in VO2 can also be used to control the phase transition temperature. The talk will describe the functional imaging of nanowires, that is, the correlation of local structure and electronic properties with the characteristics of devices by integrating scanning probe techniques with electrical transport measurements. We have used atom probe tomography to map the distribution of dopant atoms in Si and Ge nanowires [1,2], and we have used scanning photocurrent microscopy to correlate non-uniform dopant distributions with device characteristics [2]. Single nanowire Raman spectroscopy, combined with finite-difference time domain modeling, provides additional insights into the distribution of carriers within nanowires and nanowire heterostructures [3]. In VO2 nanowires, we have used temperature-dependent Raman spectroscopy to map structural domains in devices under test, revealing the key role of the Mott insulator M2 phase in the metal-insulator transition of clamped devices [4]. We find that charge injection can induce an electronic phase transition even in the absence of a structural phase transformation, i.e., we observe metallic monoclinic phases. While external strain has been used to modify the phase formation sequence and stabilize the metastable M2 phase in nanowires, we have determined that stoichiometry may also play a crucial role. Specifically, we find that the M2 phase is favored under oxygen rich conditions, whereas an oxygen deficiency can stabilize the rutile metallic phase to unexpectedly low temperatures.[5] These findings are potentially relevant to the development of a Mott field-effect transistor.

THURSDAY April 21, 2011, 10:30 AM - Bldg 215, Rm C103-106

Assembly of Hierarchically Scaled Semiconductor Nanostructures

Robert Hull
Rensselaer Polytechnic Institute

I will discuss how we have combined the short range processes of strain-induced self assembly with longer range lithographic forcing functions to create semiconductor nanostructures arrays that can be controlled over many orders of magnitude of length scales. Our work uses the input of positional maps from focused ion beam pulses that locally modify Si substrate surfaces to template the subsequent assembly of (Si)Ge nanostructure arrays through epitaxial growth. We examine the transfer functions that translate the original template maps into the observed distributions of nanostructures in the assembled array, and show that it is possible to accurately template nanostructure arrays over length scales ranging from nanometers to macroscopic dimensions. I will also discuss novel focused ion beam methods to deliver pulses of electronic or magnetic doping species with doses as small as a few ions per pulse and positional accuracy of order ten nm. With such methods we hope to functionalize ordered nanostructure arrays to develop prototype nanoelectronic devices based on motion of just a few units of electronic charge or spin.
Work in collaboration with J. Floro (UVa), J. Gray (U. Pittsburgh), Frances Ross (IBM), M. Gherasimova (S. Connecticut State), A. Portavoce (CNRS), P. Balasubramanian, S. W. Chee and J. Murphy (RPI).

THURSDAY March 17, 2011, 10:30 AM - Bldg 215, Rm C103-106

Towards Reliable Quantitative Observations by In-situ (Scanning) Transmission Electron Microscopy

Nigel D. Browning
Professor, University of California-Davis

The last few years have seen a paradigm change in instrumentation for (scanning) transmission electron microscopy with spatial resolution now extending to the sub-angstrom level, spectroscopic resolution into the sub-100meV regime and temporal resolution to the nanosecond scale. In addition, in-situ stages have been developed that allow the dynamic response of nanoscale systems to be observed under a wide array of environmental conditions. However, while these developments have brought successes, they have also challenged the established experimental protocols and our fundamental understanding of electron beam interactions with the sample. Here, examples of the use of this new instrumentation will be described and the challenges associated with moving towards reliable quantitative measurements will be discussed. Finally, a personal perspective on the technology that will shape (S)TEM capabilities in the next few years will be presented.

TUESDAY February 1, 2011, 2:00 pM - Bldg 215, Rm C103-106

Negative refraction, light pressure and attraction, equation E=mc² and wave-particle dualism

Victor Veselago
A.M. Prokhorov Institute of General Physics, Moscow, Russia

The process of mass transfer from the emitter to the receiver is considered for different connection between energy and momentum. Shown, in particular, that in the case when the energy is transferred by radiation, this relationship has the form E = mv_phv_gr, where v_ph-phase velocity, and v_gr-group velocity. From this equation immediately shows that in media with negative refraction radiation transfers the mass not from the transmitter to receiver, but rather from the receiver to the transmitter. In addition, from the above conclusion follows, that the mass transferred from the transmitter to the receiver is determined not only by transferred energy, but also by transferred linear momentum, which may be associated with energy in different ways. Thus, the well-known relation E=mc² is a special case of E = mv_phv_gr .

THURSDAY anuary 13, 2011, 10:30 AM - Bldg 215, Rm C103-106

Optical Fluorescent Super-Resolution Microscopy for Biological Applications

Gleb Shtengel
Senior Scientist, HHMI Janelia Farm

In 1873, Ernst Abbe discovered that the optical resolution of the lens-based microscope is limited by the effect of optical diffraction. This resolution limit is approximately half of the wavelength of light, and fundamental as it may seem, it is true only under certain assumptions. In last 20 years a number of techniques had been developed that allow for optical imaging with resolution far beyond the diffraction limit.

I will first describe the concepts of some of these optical "super-resolution" techniques and then focus on Interferometric Photo-Activation Localization Microscope (iPALM). iPALM can measure the 3D positions of individual molecules with accuracy of 10-20 nm even for relatively dim fluorescent proteins. This facilitates high resolution optical imaging with endogenous fluorescent markers providing high specificity, short linker length, and high labeling density. 

I will describe some of the biological applications of this technique.

Wednesday November 17, 2010, 11:00 AM - Bldg 215, Rm C103-106

The Diamond Age of Magnetometry

Amir Yacoby
Harvard University

Detection of weak magnetic fields with nanoscale spatial resolution is an outstanding problem in the biological and physical sciences. For example, at a distance of 10 nm, the spin of a single electron produces a magnetic field of about 1 micro Tesla, and the corresponding field from a single proton is a few nano Tesla. A sensor able to detect such magnetic fields with nanometer spatial resolution would enable powerful applications, ranging from the detection of magnetic resonance signals from individual electrons or nuclear spins in complex biological molecules to readout of classical or quantum bits of information encoded in an electron or nuclear spin memory.

In this talk I will review our recent experimental approach to such nanoscale magnetic field sensing using coherent manipulation of an individual electronic spin qubit associated with a nitrogen-vacancy impurity in diamond at room temperature. I will discuss how ideas from quantum information theory are aiding in reaching higher levels of sensitivity as well as some of the recent advances in the development of a scanning based diamond magnetometer.

Wednesday October 13, 2010, 11:00 AM - Bldg 215, Rm C103-106

IMPROVED CHARGE COLLECTION IN CONFINED ORGANIC SEMICONDUCTOR BULK HETEROJUNCTION SOLAR CELLS

C. T. Black
Center for Functional Nanomaterials / Brookhaven National Laboratory

High-performing organic bulk heterojunction active layers form via a self-assembly process of phase separation of blended donor and acceptor materials. Optimizing the device performance is a delicate balance of trapping the blended material in a non-equilibrium configuration. I will describe our experimental efforts to confine both organic semiconductors and semiconductor blends within nanometer-scale volumes to better control material phase separation and understand the effect of geometry on material structure, electronic properties, and photovoltaic performance.  

For example, confining blended poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester organic solar cell active layers within nanometer-scale cylindrical volumes nearly more than doubles the supported photocurrent density compared to equivalent unconfined volumes of the same blend, and increases the poly(3-hexylthiophene) hole mobility in the blend by 1000 times. Grazing incidence x-ray diffraction measurements show that the confining volume disrupts polymer ordering by reducing crystallinity and grain size, as well as changing crystal orientation. Similar confined volumes of single-component poly(3-hexylthiophene) show a 400 times enhancement in hole mobility, while the conductivity of confined [6,6]-phenyl-C61-butyric acid methyl ester decreases by 50 times upon confinement.

THURSDAY January 29, 2009, 10:30 AM - Bldg 215, Rm C103-106

UNDERSTANDING NANOSTRUCTURE NUCLEATION, GROWTH AND GROWTH TERMINATION THROUGH REAL TIME TEM OBSERVATIONS

Eric A. Stach
Purdue Electron Microscopy Consortium

In order for nanostructure materials to find application in real technologies, we must have a thorough understanding of how to create reproducible materials. I will detail our work using environmental and ultra-high vacuum transmission electron microscopy methods to image nanostructure nucleation and growth as it happens, thereby allowing unique insights into both growth mechanisms and kinetics. In particular, I will describe in detail the kinetics of the vapor-liquid-solid growth of silicon nanowires, with a focus on the kinetics of both Au dissolution in the AuSi eutectic liquid, and on the nucleation of Si from this same liquid at higher saturations. Careful quantification of the images and correlation with a simple model of the process indicates that the nucleation process is highly repeatable down to very small scales (of order 10 nm), and that we can extract information regarding the critical supersaturations required for nucleation. I will also discuss our latest results concerning growth termination during the creation of carbon nanotube 'carpets', wherein we correlate the end of growth with an Ostwald ripening of the catalysts require to mediate the conversion of hydrocarbon source gases to carbon nanotubes. Throughout, I will try to demonstrate the power of the in-situ TEM technique to visualize how things happen during nanostructure creation.