Winter 2004-2005 Schedule
NANO-CHARACTERIZATION OF MATERIALS
January 14, 2005; 3:30pm
Presented by:
Prof. Robert Sinclair
Dept. of Materials Science and Engineering
Stanford University
As research in nano-technology gathers momentum, the necessity for characterizing materials at the nano-scale becomes increasingly important. The tools to do this are becoming more powerful and sophisticated themselves. This presentation gives an overview of this rapidly developing field. In terms of microscopy, SEM's now have a resolution of 1-2nm, and it is when this is combined with the superior depth of field that their great power is realized. Focused ion-beam machines allow ion or electron imaging, local deposition or etching, material fashioning and extraction. They far extend the capabilities of conventional microscopes. And TEM has now combined atomic resolution with chemical mapping on the sub-nanometer level. Surface science analyses cannot yet be carried out at the same scale, but they provide important complementary information on surface chemistry using XPS, SIMS or AES. Finally these developments will be illustrated with a case study of highly localized property measurements in a high-k dielectric oxide using a combination of SEM, FIB and TEM.
ACTIVE INTERFACES AND LOCAL PROBING OF PROPERTIES AND STRUCTURE
January 21, 2005; 3:30pm
Presented by:
Prof. Eva Olsson
Physics, Microscopy and Microanalysis
Chalmers University of Technology, Sweden
The scanning tunneling microscope (STM) allows us to image and measure properties on the nanoscale and also subnanaoscale. However, it is not possible to perform both imaging and measurements simultaneously. In addition, the images contain information about the surface while processes below the surface are not directly accessible. The combination of STM and transmissions electron microscopy (TEM) enables us to simultaneously image and measure as well as to obtain direct information about the surface and the structure beneath the surface. This talk will address experiments on carbon nanotubes including electromigration and a nanopipette function using a TEM-STM. Local probing of properties and structure of active interfaces in oxides and photoactive nanostructures will also be discussed.
X-ray Spectroscopy and Microscopy Studies of Chemical and Biological Processes at Environmental Interfaces
January 28, 2005; 3:30pm
Presented by:
Prof. Gordon E. Brown, Jr.
School of Earth Sciences and Stanford Synchrotron Radiation
Laboratory
Stanford University
Interfaces between solids and water are the locations of most chemical and many biological reactions in the environment. Interfacial reactions can be studied at the molecular level under in situ conditions using a variety of synchrotron radiation methods involving both hard and soft x-rays. Information derived from these studies is essential for defining the processes by which pollutants are transformed into more (or less) toxic forms by microbial organisms, plants, and mineral surfaces in polluted soils and aquatic systems. This seminar will focus on recent applications of various synchrotron radiation methods to complex environmental materials and processes, including photoemission studies of the interaction of water with metal oxide surfaces, XAFS studies of the structure of water, grazing incidence XAFS studies of metal ion adsorption at metal oxide-aqueous solution interfaces, crystal truncation rod diffraction studies of the hydrated surfaces of metal oxides, x-ray standing wave studies of the effect of microbial biofilms on the chemical reactivity of common metal oxide surfaces, and scanning transmission x-ray microscopy studies of biocolloids, microbe-mineral interactions, and biomineral formation.
Fall 2004-2005 Schedule
Resonant X-Ray Scattering Studies of Nanoscale Magnetism
October 8, 2004; 3:30pm
Presented by: Dr. Jeff Kortright Materials Sciences Division Lawrence Berkeley National Laboratory
Materials with magnetic and chemical heterogeneity at very small (1 - 100 nm) length scales underlie current magnetic recording technology, and as such continue to be the subject of intense research. One challenge in studying these materials has been the difficultly in resolving magnetic structure and interactions at these very small length scales. We have been developing and applying techniques to study magnetic materials at these length scales using resonant soft x-ray scattering. The large resonances in charge and magnetic scattering factors at the 3d transition metal L edges underlie these techniques, which otherwise use relatively standard small-angle scattering approaches in applied magnetic fields. This talk will review relevant basics of scattering theory. It will then summarize several studies utilizing resonant scattering to resolve magnetic and charge scattering in a variety of magnetic systems of current interest, including domains in Co/Pt films with perpendicular anisotropy, magnetic correlation lengths in recording media, and dipolar interactions between superparamagnetic nanoparticle assemblies.
The Whys and Hows of Ultrafast X-ray Science
October 15, 2004; 3:30pm
Presented by: Dr. Jerome Hastings Assistant Director Stanford Linear Accelerator Center
The invention of ultrafast optical lasers with pulse durations comparable to vibrational periods in solids and motions of molecules undergoing structural changes has provided a look at the dynamics that govern important processes in nature. X-rays, on the other hand, with wavelengths comparable to the distances between atoms, have been the key tool to study the average structure of liquids and solids at atomic resolution. With recent developments of ultrafast X-ray sources, the combination of appropriate temporal resolution and spatial resolution is opening new scientific opportunities to directly observe atomic scale dynamics. The Sub-Picosecond Pulse Source at SLAC is just such a source. The science and technology of ultrafast X-ray studies will be discussed in this context and the extension of these studies to opportunities afforded by the LCLS X-ray free electron laser will be presented.
Multifunctional Complex Oxide Heterostructures
October 22, 2004; 3:30pm
Presented by: Prof. R. Ramesh Dept. of Materials Science & Engineering and Dept. of Physics University of California, Berkeley
Comple perovskite oxides exhibit a rich spectrum of functional responses, including magnetism, ferroelectricity, highly correlated electron behavior, superconductivity, etc. There exists a small set of materials which exhibit multiple order parameters; these are known as multiferroics. Using our work in the field of ferroelectrics and ferromagnetics as the background, we are now exploring such materials, as epitaxial thin films as well as nanocomposites. Specifically, we are studying the role of thin film growth, heteroepitaxy and processing on the magnitude of the coupling between the order parameters. In single phase multiferroic perovskites, such as BiFeO3, we have found significant enhancements in magnetism and ferroelectricity compared to bulk. Detailed measurements indicate that the enhancement in magnetism is due to a mixed Fe+2/Fe+3 state in the films. A very exciting new development has been the discovery of the formation of spontaneously assembled nanostructures consisting of a ferromagnetic phase embedded in a ferroelectric matrix that exhibit very strong coupling between the two order parameters. This involves 3-dimensional heteroepitaxy between the substrate, the matrix perovskite phase and spinel phase that is embedded as single crystalline pillars in this matrix. This epitaxial coupling is critical and is responsible for the significantly higher magnetoelectric coupling and magnetic anisotropy in such vertical heterostructures compared to a conventional heterostructure. This work is supported by the UMD-MRSEC and by the ONR under a MURI program.
Application of Atomic Layer Deposition in the Semiconductor Industry
October 29, 2004; 3:30pm
Presented by: Dr. Glen Wilk Executive Scientist ASM America, Inc.
The use of high-k dielectric materials in integrated circuit applications has gained considerable attention recently. Technology roadmaps predict the need to replace SiO2 and SiN dielectrics for transistors, capacitors and other devices in the next few years. The dimensions of these devices are scaling rapidly, and they therefore require very low leakage currents as well as excellent reliability. Efforts are being focused on Al-based, Hf-based and Ta-based dielectrics, depending on the particular needs of each application. These materials are tailored according to the specific device requirements imposed by industry, such as minimizing scattering phenomena for gate dielectrics, or excellent capacitance linearity response to voltage and temperature for RF linear capacitors. The particular merits of the materials under consideration will be discussed, including applications to non-Si technologies.
Fundamental Material Interactions in Nanotechnology
November 5, 2004; 3:30pm
Presented by: Dr. Sadasivan Shankar Intel Corp.
Over the past 3 decades the semiconductor industry has doubled the number of transistors on integrated circuits every 2 years, following an empirical law widely known as Moore?s law. The ability of the semiconductor industry to stay on Moore?s law has enabled the digital revolution and now the convergence of communications and computing. However, as the size of the smallest structures decrease, this has required the introduction of many new materials and the interactions of these heterogeneous materials and processing is increasing in complexity. Due to the presence of multiple thin films and metal alloys in the process, grains, and interfaces assume more significance than before. This paper reviews some of the challenges in materials and the opportunities for using fundamental modeling and characterization techniques to enable successful management of these heterogeneous interactions. The three specific topics expected to be covered are 1) Electromigration, 2) Mechanical integrity, and 3) Interface adhesion.
Ferroelectric Thin Films for RF Devices
November 12, 2004; 3:30pm
Presented by: Dr. Stephen R. Gilbert Agilent Laboratories, Palo Alto, CA
Ferroelectric thin films have attracted considerable attention for use in a wide range of wireless communications products. For advanced digital baseband circuits, high-density, embedded ferroelectric memory (FeRAM) based upon Pb(Zr,Ti)O3 (PZT) has the potential to be a low-power, high-performance substitute for embedded DRAM, SRAM, and Flash technologies. In the RF front end of wireless devices, the large and voltage-variable permittivity of (Ba,Sr)TiO3 (BST) is being exploited for thin film varactor and high-density capacitor applications, and shows considerable promise for use within compact, frequency agile front end modules. Moreover, the piezoelectric properties of PZT may be exploited for a variety of filter and sensor components. In this presentation, we will review several of these applications, and describe the primary materials requirements and integration issues that must be considered when fabricating parallel plate capacitors for advanced memory and RF passive devices.
Designing Organic Semiconductors for Thin Film Electronics
November 19, 2004; 3:30pm
Presented by:
Prof. Zhenan Bao Department of Chemical Engineering Stanford
University
Organic semiconducting materials are now being considered as the active materials in displays, electronic circuits, solar cells, chemical and biological sensors, actuators, lasers, memory elements, and fuel cells. The flexibility of their molecular design and synthesis makes it possible to fine-tune the physical properties and material structure of organic solids to meet the requirements of technologically significant applications. In contrast to inorganic materials, active organic thin films can be deposited at much lower substrate temperatures (less than 120 ?C) in low vacuum or atmospheric pressure environments. It has been demonstrated that low-cost deposition techniques such as solution spin-coating, casting, and even printing can be used for deposition of solution soluble organic materials. These processing advantages, together with the natural abundance of organic solids, make semiconducting organics attractive for large-area and low cost applications. In this talk, the materials requirements and designs for high performance organic thin film field effect transistors will be discussed. An overview of the current status of organic transistors and their potential applications in low-cost flexible displays and circuits will be presented.