At the core of our research is the development and application of novel Atomic Force Microscopy (AFM) techniques. AFM is a powerful tool for measuring and imaging forces at surfaces down to the atomic scale. It can be used in any environment, including liquids, and has applications in surface physics, nanotechnology, materials science, chemistry, and biology. However, not all AFM's are created equal, and in our laboratory we focus on the application and further development of a novel AFM technique, which operates quite differently from common AFM. Our AFM measures force gradients by oscillating a high stiffness lever at an ultra-small amplitude of less than 1 Ångstrom and monitoring changes in this amplitude as the surface is approached or the lever is scanned across the surface. To measure changes in this already tiny amplitude we use an optical fiber interferometer mounted to a sub-micron resolution manipulator. The interferometer can achieve up to 600 mV per 1 Ångstrom deflection and can measure amplitude changes that correspond to a few hundredth of the diameter of a single hydrogen atom. Using such a small amplitude enables us to completely map any interaction point-by-point and achieve atomic resolution force gradient images at fixed separations. While we operate one instrument in ultra-high vacuum (UHV) for atomic resolution work, our technique also works well in liquids, where it allows for true non-contact imaging due to its unique operational principle (it operates below the lever resonance, and thus is not affected by damping). Interactions we have measured include bonding between single atoms (in UHV) and ordering of water molecules in a confined geometry (in liquid). We can also measure currents, charges and fields at the molecular/ atomic scale as well as atomic scale energy dissipation and molecular shear forces in liquids. Future and current research includes measuring forces during room temperature atomic manipulation, forces and currents associated with electronic/magnetic nanostructures, forces in liquids associated with functional groups in biomolecules and the development of packaged opto-mechanical sensors.
My research primarily involves an experimental investigation of the electrical and magnetic properties of metals. Studies have been conducted on pure metals, alloys, and different types of thin magnetic films such as single-layer, bilayer, sandwich, and multilayer samples. The investigation of magnetic films has been carried out in collaboration with Prof. R. Naik in the Department and colleagues at Nanjing University. My studies often make use of low temperatures (down to 1 Kelvin), strong magnetic fields (up to 20 Tesla), and microwaves (up to 80 GHz in frequency). A rather unique piece of equipment used in the lab is a Millimeter Microwave Transmission Spectrometer operating at the highest frequency and sensitivity to be found anywhere in the world. Our studies provide a wealth of information on conduction-electron characteristics and magnetic interactions, which are valuable both for the fundamental knowledge they provide as well as for potential applications for devices.
The modification in surface properties of solids due to interaction of energetic ions (charged particles) is investigated using sputtering (r.f. and d.c.) and ion implantation (100 kV Varian Extrion) facilities. Ion backscattering and channeling analysis is carried out using the department's 4.75 MV Van de Graaff accelerator. An ultra high vacuum facility for low energy ion beam analysis coupled to the existing ion channeling analysis facility is under development. Current experiments involve ion beam induced dynamic mixing and ion channeling studies of an electrode-electrolyte interface. Some of the experiments are carried out in collaboration with General Motors Research Laboratory and other local industries.
This research uses a combined theoretical and experimental approach towards the elucidation of the structures of new liquid crystalline phases and to understand their fluctuations properties, particularly in the vicinity of phase transitions. In recent years we have developed a new approach toward analyzing fluctuations of orientational order by including the fluctuations in the degree of orientational order as well as in the local biaxial states. Predictions of several new effects have been made in our light scattering experiments and other tests are ongoing. The role that chirality plays in the formation of liquid crystalline phases and its influence on their fluctuation properties is another subject being actively studied. Our studies of the least understood cholesteric blue phase, Blue Phase III, are of particular note because light scattering experiments have demonstrated that BPIII is not a liquid crystal at all, but rather a new type of amorphous liquid. Experimental and theoretical investigations of this new type of liquid state are continuing.
Our research program in magnetic materials focuses on the fabrication and property characterization of magnetic thin films and the development of these materials for device and sensor applications. Of particular interest are studies of domain structures in single-layered ferromagnetic thin films, multilayer structures exhibiting giant magnetoresistance, spin-polarized magnetic tunnel junctions, and hybrid semiconductor/ferromagnetic devices. Characterizations are primarily focused on transport (magnetoresistance and I-V characteristics) and magnetic (SQUID magnetometry, vibrating sample magnetometry, ac susceptometry, and ferromagnetic resonance) measurements between liquid helium and room temperature. Additionally magnetic force microscopy is utilized to determine the local magnetic structures of sub micron-size features and a point conductance technique based on the Andreev reflection of electrons has been developed for measuring the spin polarization of ferromagnetic materials. Magnetic films and devices are fabricated by molecular beam epitaxy (MBE), electron-beam, and sputter deposition systems.This program also makes extensive use of the facilities and research collaborations associated with the interdisciplinary Smart Sensor and Integrated Microsystems program.
Specific research projects include:
Spin Polarization Mapping (Nadgorny)
This research focuses on the implementation of nanoscale spin polarization measurements
utilizing Micro Electro Mechanical Systems (MEMS) positioning technology in combination
with electroforming of three-dimensional (3D) microstructures. A simple new technique of
electrodeposited (ED) photoresists makes possible conformal coatings of highly structured
surfaces and, when combined with electroplating, can form new types of advanced 3D metal
microstructures. By developing an array of micro-tips integrated with through-wafer
interconnects into a single testing chip, individually addressable m x n arrays of
microscopic superconducting tips on a testing chip can be fabricated. Then this testing
chip will be applied to thin films and planar magnetic nanostructures to map the spin
polarization over a larger cross-section and will allow non-destructive device evaluation
at any stage of the device fabrication. Furthermore, since both electrodeposition and
electroplating processes have the ability of forming complex topographies, this technique
has the potential to develop other 3D metallic microstructures for other potential
applications.
Synthesis and Characterization of Magnetic and Semiconducting Nanowires (Wenger)
This research project focuses on the synthesis of a self-assembled array of
ordered nanopores (10 -200 nm diameter) in an aluminum template using an anodization
technique developed at WSU. Metallic metals and alloys of varying composition and
length are then electrodeposited into the nanopores to study the relationship between
the physical properties and their structural geometry. SEM, XRD, electrical, and magnetic
measurement techniques are the primary tools used to characterize both structural and
physical properties of the nanowires assemblies as well as individual nanowires.
This interdisciplinary research program involves the study of various thin film materials for potential magnetic, pyroelectric, piezoelectric, and chemical sensor applications. Materials of prime interest are ferromagnetic multilayered structures, ferroelectric thin films, wide bandgap semiconducting (III-V) nitride films, and other oxide thin films. Plasma Source Molecular beam epitaxy (PSMBE), MBE, sputter deposition, and metallorganic decomposition (MOD) methods are used to fabricate these thin film materials and devices. Microstructural characterization is done using one or more of the following methods: in situ reflection high-energy electron diffraction (RHEED), X-ray diffraction, Raman spectroscopy, auger electron spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Our magnetic characterization laboratories include SQUID magnetometry, magnetoresistance (MR), ferromagnetic resonance (FMR), atomic force micrsoscopy (AFM), and magnetic force microscopy (MFM) measurement capabilities. Electrical property measurements include both temperature and frequency dependent C-V, I-V, and impedance capabilities. This program is part of the interdisciplinary Smart Sensor and Integrated Microsystems program for developing magnetoresistive and magnetostrictive materials for magnetic sensor applications, oxide thin films for gas sensors, graded ferroelectric thin films for IR sensors, and wide band gap semiconductors for high temperature applications.
This research focuses on experimental and theoretical studies of Josephson effects and properties of high-temperature cuprate oxide and conventional superconductors. Present experimental programs include (1) studies of various physical phenomena such as the paramagnetic Meissner effect and intrinsic Josephson coupling in layered superconducting materials through electrical, magnetic, and electrodynamic measurements, (2) the fabrication and development of high-temperature superconducting single crystals and thin films for potential applications, and (3) the exploration of novel materials and structures with enhanced superconducting transition temperatures.
Experimental studies are performed using a variety of techniques including SQUID magnetometry, vibrating sample magnetometry, ac susceptometry, heat capacity, resistance, and current-vs-voltage characteristics from dc to microwave frequencies in the temperature range between 0.3 K and 400 K. Materials are synthesized in ceramic, single crystal and thin film forms with structural characterization by DTA/TG, X-ray diffraction, scanning electron microscopy with EDS, and atomic force microscopy.
The nature of the atomic-scale defects in semiconductors often determines the optical, electronic, and structural properties of these materials, and how these properties change with time, heating, pressure, and application of fields. Our research group is collaborating with an experimental group at Berkeley to identify and study the properties of important defects and defect complexes occurring in semiconductors such as GaAs. We use first-principles quantum molecular dynamics calculations to search for low energy defect structures, characterize the electronic and optical properties of these low-energy defects, determine whether they have metastable higher energy configurations, and investigate their motion and interactions.
Because of the current interest in smaller devices and low-dimensional structures, such as quantum dots, a better understanding of growth processes on an atomic level is needed. We are using similar first-principles calculations to study the dynamics and energetics of the microscopic processes occurring at the growing GaAs surface - in particular, the adsorption, diffusion, and incorporation of arsenic at the surface. Other aspects of a large collaborative project covering growth processes in III-V semiconductors are being carried out predominantly by colleagues at the Fritz-Haber-Institut der Max-Planck-Gesellschaft.
Theoretical studies concentrate on understanding the microwave responses of layered superconductors and the physics of the dynamic states arising from the Josephson tunneling in these layered superconductors.