CNST Nanotechnology Seminar Series

Upcoming Talks

We discuss techniques for making gated nanoelectronics based on carbon nanotubes and graphene, and some of the new physics and possible applications that is available in these systems. Here we will focus on few-electron quantum dots in nanotubes –ndash; possibly for application to quantum information –ndash; and p-n junctions in graphene.

Nanophotonics in which light is manipulated at subwavelength scales is emerging as one the most exciting and potentially useful areas of physical optics. I will highlight recent research in my group aimed at a new class of light-sources in which the near field and the far-field properties are fundamentally altered by means of plasmonic nanostructures and metamaterials monolithically integrated on the laser facets. As a platform to demonstrate these new beam shaping concepts, such as reduction of beam divergence, nanospot light concentration, super-focusing and polarization control, we have used mid-infrared and near-IR lasers but these techniques are broadly applicable to all solid-state lasers.
I will also discuss a novel technique called nanoskiving that combines photolithography, thin-film metal deposition, and thin-film sectioning, and demonstrate its capabilities in the realization of metallic nanowires with engineered plasmon resonances and frequency selective surfaces.

Miniaturization of electronic devices with atomic-scale active components is a great technological undertaking and presents a major challenge in metrology. To understand the underlying physics and behavior at the molecular level, which by the very definition is not a static but essentially dynamic process, our group is developing an ultrafast electron microscope (UEM). This methodology combines extreme spatial and temporal resolutions, which allows for the simultaneous characterization of spatiotemporal properties at relevant scales. The versatility of the UEM technology and its applications in electronics, photonics and biotechnology will be illustrated with two distinct examples. The first is the "conventional" pump-probe imaging of ultrafast dynamics during a phase transition in vanadium dioxide, and the second is the direct visualization of a laser controlled reversible transformation in molecular crystals.

The adaptive pressures displayed across the flora and fauna result in a variety of sophisticated nanostructured materials that are perfected to perform multiple biological functions. Our understanding of the underlying principles of their formation provides ample opportunities in the synthesis of next generation, bio-inspired, nanostructured materials. To date, there has been demonstrable progress in materials fabrication harnessing the functional power of biological systems. There is, however, a number of challenges related to the characterization of both biological and synthetic bio-related structures. I will exemplify this point by describing new synthetic strategies and devices that have been inspired by the study of two organisms – echinoderms and sponges. The topics will include self-assembly, control of crystallization, adaptive optical structures, fiber-optics, biomechanics, hybrid materials and novel actuation systems.

The growing amount of exiting demonstration of photovoltaic, (photo-) catalytic and sensor devices based on quasi 1D and 2D metal oxide nanostructures requires the fundamental understanding of their surfaces affecting the transport and the optical properties. In conjunction with transport measurements, we have applied a range of spectroscopic and imaging techniques to individual metal oxide nanostructure to address the chemical and photochemical processes taking place on its surface. In particular, we use an array of scanning probe, electron, and synchrotron radiation based photoelectron emission spectro-microscopies to investigate in situ the evolution of structural, electronic and chemical particularities in an operating nanodevice under wide range of the experimental conditions such as temperature, chemical environments (including liquids) electrostatic field, sensitization with catalyst particles, radiation etc,. Benefiting from the gained knowledge, we develop the real world prototypes for nanowire based (photo-) catalytic and chemical sensor platforms.

In this talk I will give examples of the rapid development in the areas of growth, processing and applications of semiconductor nanowires. The approach is based on the combination of top-down patterning and self-organized growth, as guided self-assembly. Axial and radial heterostructures, also of non lattice-matched combinations, can be formed with abruptness on the atomic level, thus allowing great freedom in design of electronic and opto-electronic devices. I will describe the state-of-the-art in materials properties, in control of dimensions and positions as well as give examples of the use of semiconductor nanowires in different quantum device applications.

Semiconductor photocatalysis using nanoparticlate TiO₂ has proven to be a promising technology for use in photocatalytic reactions, in the cleanup of water, or as a photoactive material in nanocrystalline solar cells. We have found that reconstructed surface of metal oxide nanoparticles differs form the bulk by the presence of highly reactive under-coordinated surface. This can be viewed as a curse or as an opportunity. The under-coordinated surface metal atoms trap light-induced charges, but also exhibit high affinity for oxygen-containing ligands. As a result of this strong interaction, delocalized bands of metal oxide nanoparticles are electronically coupled to organic linkers, improving their optical properties in the visible region and photovoltaic response due to enhanced charge separation across nanoparticle interface. In the same manner we use photoinduced charge separation in order to control and manipulate processes within living cells.

The miniaturization of mechanical devices opens new opportunities for investigating and exploiting novel phenomena that occur for components in close proximity. The Casimir force, for example, originates from the zero-point quantum fluctuations of the electromagnetic fields. I will describe experiments that demonstrated the Casimir effect in micromechanical devices.
In another effort, subwavelength structures are fabricated on the surface of metal films to strongly modify their interaction with light. The evanescent fields channel the optical energy to specific locations, resulting in strong and localized field enhancement. Coupling of the enhanced evanescent field to the nanomechanical motion of the metallic elements opens new opportunities for tunable optical elements and high sensitivity displacement detection.

The generation of high-frequency current oscillations when a constant voltage is applied across an insulating tunnel gap separating two superconductors was one of the celebrated predictions made by B. Josephson in 1962. I will present evidence that Josephson current oscillations interact with atomic-scale mechanical motion. We generated weak links that contain a single niobium dimer (Nb2) suspended between two bulk niobium electrodes. We found spectral features in the electronic transport curves through the dimer, which correspond to excitations of its vibrational eigenmodes by Josephson current oscillations. This phenomenon persists up to the frequency of about 10 terahertz. This is applications-rich but largely unexplored frequency range ("terahertz gap"), which interrogates the lowest frequency vibrational modes of complex organic and biological molecules. I will describe possible applications in the fields of chemical and biological material sensing and characterization.

We are currently developing a system for using biological macromolecules as scaffolding for the construction of nanostructures comprising multiple inorganic nanoparticles. The system utilizes the geometry of the macromolecules to define the three-dimensional arrangement of inorganic particles in the structure. A massively parallel assembly process will be used to provide for the mass production of identical nanostructures. We envision applications to include, for example, (i) construction of small assemblies of metallic nanoparticles to form nanolenses capable of focusing surface plasmons and (ii) the construction of magnetic cellular automata.

Modeling, design, and control of micro-scale devices for bio-chemical and medical applications. The focus is on applications where control can dramatically improve or allow new system capabilities. We consider all aspects of the design pathway from initial application choice, to system modeling, device fabrication, phrasing of design tasks as tractable mathematical problems, control algorithm development, and experimental demonstration and validation. Projects include steering of cells by micro flow control, precision control of electrowetting flows, modeling and control of bio-compatible conducting plastic micro-actuators, monitoring cells on chip, and magnetically targeted deep-tissue drug delivery.

In typical magnetic devices and measurements, the magnetization states of the elements are controlled with applied magnetic fields. However, over the last several years it has been shown that the magnetization state of ferromagnetic devices can be similarly controlled by a dc spin-polarized current passing through the device, via the so-called "spin-transfer interaction". This represents a fundamentally new way to manipulate ferromagnetic materials and is particularly important at device dimensions below about 100 nm. In this talk I will give an introduction to the spin transfer effect, and a general overview of our work using the spin transfer interaction to induce high-speed (< 500 ps) switching and coherent high-frequency (> 40 GHz) large-amplitude precession in magnetic nanostructures.

Understanding and controlling the magnetic properties of nanoscale systems is crucial for the implementation of future data storage and computation paradigms. Here we show how the magnetic properties of individual atoms can be probed with a low-temperature, high-field scanning tunneling microscope when the atom is placed on a thin insulator. In extended one-dimensional spin chains, which we build one atom at a time, we find strong spin-coupling into collective quantum-spins, even for the longest chains of length 3.5nm. The spectroscopic results can be understood with the model of spin-excitations in a system with antiferromagnetic coupling, controlled on the atomic scale.

Although it is generally accepted that nanoparticles and nano-structured materials are mostly surfaces or interfaces, the impacts of the nature of that surface are often ignored or minimized. Surface and interface contamination is present on many nanoparticles and may be, in the words of one colleague "the dirty secret" of nanotechnology. It has been demonstrated that the nature of the environment around nanoparticles can alter the structure of the particles. The properties of individual nanoparticles or isolated nanoparticles can also be altered when they are assembled or packed into aggregate systems, even if there is no significant binding or chemical interactions. The effective media of the aggregate will have properties that differ from the individual particles. Some of these effects will be described based on our studies of iron oxide and ceria oxide nanoparticles and other work in the literature.

Transparent oxide semiconductors have been extensively studied due to the direct commercial applications including displays, solar cells, sensors, and energy-efficient windows. There has been an increased interest in transparent electronics due to the possibility of forming active transparent components, which can enable new optoelectronic applications. The synthesis, characterization, and integration of these materials will be presented. We are focusing on several ternary oxides, including Zn₂In₂O₅ and ZnSnO₃. These materials have been determined to be amorphous as deposited and have excellent electrical properties when used as channel materials for thin film transistors on flexible substrates. Initial results will also be presented for ternary oxide nano-materials.

In this talk, I will discuss the obstacles that have to be overcome to achieve high-resolution images using AFM. As we will see, the techniques that we have to apply vary depending on the specific kind of samples we are interested in. While soft biological samples require liquid environment and extremely low tip-sample interaction forces, other samples are best imaged in ultrahigh vacuum, possibly even at low temperatures. Whatever the sample, however, AFM is in principle able to deliver high-resolution images on all material classes, no matter how delicate. An example is given in the illustration, featuring a 3D atomic-scale image of crystalline xenon, which cannot be obtained with any other technique. We will further elaborate where the limitations of current state-of-the-art high-resolution AFM imaging are, and where possibilities for progress exists.

The purpose of my work is to generate new concepts and the corresponding knowledge that enables the design/fabrication/implementation of small-scale, six-axis nanopositioning systems. In this talk, we will discuss the utility of smaller-scale nanopositioners and their performance limits. We will examine several new machine elements (silicon-based elements and nascent designs for carbon nanotube-based elements) and the nanopositioners that have been created using these elements. We will also discuss the high-level aspects of case studies where these devices are being created for probe-based nanofabrication processes. The case studies are the result of collaborations wherein we have partnered with process researchers in order to co-develop process-equipment pairs for future nanofabrication processes.

Organic materials can offer new electronic functionality not available in the inorganic devices. However, the integration of organics within nanoscale electronic circuitry poses new challenges for material physics, chemistry and nanofabrication.

I will discuss different approaches to engineer useful electronic properties in small molecular devices. In the first case, the electronic functionality is to be provided by the backbones of short molecules. We have developed a set of fabrication and characterization techniques allowing us to build devices with self-assembled monolayers from nearly single-molecule size up to ~300 nm on a side. In the second approach, we build devices with monolayers of macromolecules. The electronic properties are determined by the composition, the chemical conversions and electric-field-induced chemical reactions of the side groups.

In 2006, the Semiconductor Research Corporation’s research community, with colleagues from several other industries and government laboratories, identified a joint set of critical research needs1 in the area of nanomaterials modeling and verification. The goal was to develop an enhanced predictive capability of nanomaterials structure-property correlations and enable robust high performance application specific nanomaterials by design. Predictive models are needed for the integrated optimization of: the synthesis of nanoparticles, surface chemical reactivity, electronic and transport properties, nanomechanical properties, properties of self-assembled materials, and other application properties. Some nanomaterials families possess unique properties that make them candidates to enhance or replace conventional materials and approaches, but the need for optimization of multiple properties requires models that correlate atomic and nanostructure and local environments to desired properties. This presentation will summarize a joint set of strategic modeling and characterization needs, which are shared by multiple industries, and propose a framework for collaboratively engaging industrial, academic, and government research communities. Additionally, it will provide a summary of strategic research opportunities in several enabling material systems and emerging high potential impact application areas.

Intel believes that silicon based CMOS technology will remain the workhorse of information processing technology for approximately the next 15 years and beyond that, silicon will form the platform upon which alternative information processing technologies will be built and integrated. This presentation will survey the long range research relating to the search for beyond CMOS logic alternatives. It will focus on measurement and characterization challenges associated with using alternative state variables such as magnetization, polarization and spin and the interaction of these variables with applied and induced fields. The measurement and characterization challenges are magnified by the likely introduction of new material systems and the need to ultra high spatial and temporal resolution. This presentation will draw heavily on ideas developed within the ITRS ERD and implemented in the Nanotechnology Research Initiative and Focused Center Research Programs.

(Image courtesy of Y. Acermman, Stanford University)

Magnetic Force Microscopy is an ideal tool to image magnetic stray fields emanating from surfaces but also from hidden interfaces of magnetic or superconducting samples. A lateral resolution of 10nm is routinely obtained on flat samples. Tip calibration techniques were developed for a quantitative evaluation of the magnetic surface charge or surface dipole density from the measured MFM signal.
The latter was performed to map the spatial density of pinned uncompensated spins (UCS) in exchange-biased ferromagnet/antiferromagnet multilayers. In order to further characterize these samples, different magnetization histories in magnetometry and magnetic force microscopy measurements were used advantageously to demonstrate the co-existence of pinned UCS that are parallel and antiparallel to the cooling field in metallic (IrMn) and oxidic (CoO) EB systems. We found that the exchange-bias-effect (EB-effect) is a result of pinned interfacial UCS, which are antiparallel to the spins of the ferromagnet. The often observed positive vertical shift of the magnetization loop after field cooling is due to pinned UCS that align parallel to the cooling field, but are of little importance for the EB-effect.
Whereas magnetic force microscopy seems to reach its final state of development, considerable instrumental progress remains to be achieved in scanning force microscopy with true atomic resolution. A scanning force microscope optimized for surface science would allow the simultaneous measurement of vertical and lateral forces, energy loss and tunneling current. Our recent developments will be discussed.

Fueled by the ever increasing data density in magnetic storage technology and the need for a better understanding of the physical properties of magnetic nanostructures, there exists a strong demand for high resolution, magnetically sensitive microscopy techniques. The technique with the highest available resolution is spin-polarized scanning tunneling microscopy (SP STM) which combines the atomic resolution capability of conventional STMs with spin sensitivity by making use of the tunneling magnetoresistance effect between a magnetic tip and a magnetic sample surface. Beyond the investigation of ferromagnetic surfaces, thin films, and epitaxial nanostructures with unforeseen precision, it also allows the achievement of a long-standing dream: the real space imaging of atomic spins in antiferromagnetic surfaces.

The lecture addresses a wide variety of phenomena in surface magnetism which in most cases could not be imaged directly before the advent of SP-STM. After starting with a brief introduction of the basics of the contrast mechanism, recent major achievements will be presented, like the direct observation of the atomic spin structure of domain walls in antiferromagnets and the visualization of thermally driven switching events in superparamagnetic particles consisting of a few hundreds atoms only. To conclude the lecture, recently observed complex spin structures containing 15 or more atoms will be presented.

Progress in optical lithography has paced the enormous progress in integrated circuits. Thus, the question of the ultimate capabilities of optical lithography is of great importance as we proceed into the deep sub-wavelength regime. The spatial frequency transmission bandwidth of free-space is 2/λ, leading to a dense (equal line/space) pattern at a half-pitch of λ/4 (or 48 nm for a 193-nm λ). Immersion provides another factor of ∼ 1.44 (H₂O) or greater down to a ½ pitch CD < 33 nm. Nonlinear processes, based on photoresist chemistry and pattern transfer, allow further extension of optics beyond the single-exposure linear-systems limits, much as frequency multiplication processes allow extension of fundamental laser frequencies. The conclusion is that there is no fundamental limit to the resolution of optical lithography; there remain process latitude and manufacturing (e.g. cost) issues.

For many nanotechnology applications, large numbers of nanostructures covering a large sample area with a well-defined long-range order are required. One such example is a metamaterial with a structure- (as opposed to material-) dependent resonance. The figure shows an infrared metamaterial (an assemblage of LC tank circuits). Negative-index materials (NIMs) are another emerging area. Photonic crystals – periodic arrays of nanoscale structures (with or without aperiodic defects) – providing another example of the exciting physics accessible with current interferometric lithography capabilities. Nanostructuring for semiconductor materials development and nanofluidics for biological applications are other emerging research directions. The overall message is that a nanoscale lithography capability enables many exciting nanotechnology research directions.

Nanoelectromechanical systems (NEMS) have been at the center of recent applied and fundamental research. Most NEMS are resonant devices —much like simple tuning forks— with submicron dimensions. In this size regime, NEMS come with extremely high fundamental resonance frequencies, diminished active masses and tolerable force constants; the quality (Q) factors of resonance are in the range Q∼103-105. These attributes collectively make NEMS suitable for a multitude of technological applications— such as ultrasensitive force and mass sensing, narrow band filtering, and time keeping. From a fundamental physics point of view, NEMS are expected to enable the observation of quantum behavior in mesoscopic mechanical systems.
This presentation will start with a brief description of our recent work on nanomechanical mass sensing. It will then outline some of the challenges involved in realizing a practical NEMS mass sensor and focus on our efforts in addressing these challenges. One of the challenges, namely the operation of a nanomechanical resonator in a rarefied gas atmosphere, has led us to re-investigate a well-known fluid dynamics problem: Stokes’ second problem of an oscillating plate in a fluid. At the frequencies of NEMS motion, Stokes’ second problem needs to be reformulated in order to accurately describe NEMS motion. On the other hand, our efforts to develop tunneling displacement transducers have resulted in progress towards a functional radio-frequency scanning tunneling microscope (STM).