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 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 is optimized for quantitative local measurements of nanomechanical phenomena. This is achieved by using a dynamic measurement method in which the cantilever is oscillated at ultra-small amplitudes of less than 1 Ångstrom and monitoring changes in this amplitude as the surface is approached or the lever is scanned across the surface. Such a small amplitude allows to perform linear and local measurements of force gradients and forces. To measure changes in such a tiny amplitude we use a highly sensitive, optical fiber interferometer mounted to a sub-micron resolution manipulator. The interferometer can achieve several 100 mV signal 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. We have recently build a new small-amplitude AFM operating in liquids. 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, structure and synamics in confined liquids, and forces associated with in biological macromolecules such as lipids and proteins.
Soft materials such as polymers, colloids, membranes, liquid crystals comprise almost all materials of our everyday life, including life itself. They are neither simple liquids, nor crystalline solids and many of the fascinating and useful properties of these materials result from thermal fluctuations in the local nanoenvironment. Within the last few years, this has become an exciting example of an emerging, interdisciplinary field of science drawing upon physicists, chemists, biologists, chemical engineers and materials scientists. The goal of our laboratory is to conduct fundamental research in the field of soft materials by developing spectroscopy techniques, which can offer structural and dynamical information with unprecedented spatial and temporal resolution, down to the atomic and molecular scale. The laboratory uses two main experimental approaches: (i) Infrared spectroscopic ellipsometry, which can describe the identity, composition, molecular interaction and orientation of the various parts of the molecules, as well as the thickness of the adsorbed film in the same measurement of the same sampling area. (ii) Fluorescence correlation spectroscopy using which the rate of dynamic processes such as diffusion, aggregation and chemical reactions can be inferred from the fluorescence-intensity autocorrelation function. The single-molecule sensitivity of this technique allows complementing, ensemble-averaged rate measurements of traditional methods of physical analysis with the distribution around the average. This is important to understand the issue of heterogeneities in soft matter systems. We are interested in a broad agenda of research problems including (i) micro- and nanofluidics with complex fluids (ii) single-molecule diffusion in confined fluids (iii) interfacial behavior of fluids at soft surfaces and (iv) direct visualization of molecules during spreading
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.
When dealing with large organic molecules one frequently finds that there are several stable phases between the solid and liquid. Our research uses a combined theoretical and experimental approach towards the elucidation of the structures of these liquid crystalline “mesophases” and their physical properties. We are particularly interested in investigating the critical phenomena associated with the phase transitions between these various phases. One main focus of our work is on the role that chirality (optical activity) plays in producing structures and phase transitions. Experimentally we use various optical probes such as polarization microscopy, interferometry, and laser light scattering, including photon correlation spectroscopy. Theoretically we work with the phenomenological Landau theory of phase transitions. In recent years we have studied: (1) chiral smectic phases, which display ferroelectric and antiferroelectric behavior; (2) lyotropic nematic phases formed by mixtures of water with detergents; (3) organometallic mesogens, a new class of liquid crystals having both magnetic and conducting properties; and (4) cholesteric blue phases, some of the most exotic structures found in condensed matter physics, whose complexity derives entirely from their strong chirality.
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.
Magnetic Nanoparticles (Lawes, Naik)
This research project focuses on synthesizing and characterizing the
properties of magnetic oxide nanoparticles, which typically range from
3 nm to 15 nm in diameter. In order to investigate how the magnetism
of materials changes on the nanoscale, extensive studies of the magnetic
properties of these systems are correlated with detailed measurements on
their structure. One particularly intriguing problem focuses on understanding
the role of interparticle interactions in determining the magnetic properties
of these materials. Magnetic nanoparticles may also be important
for biomedical applications. One system under extensive investigation
at Wayne State is gamma-Fe_2O_3 nanoparticles in an alginate matrix, which
is being studied for applications in targeted drug delivery, as an MRI
contrast agent, and for hyperthermic treatments of malignant tumors.
Multiferroics and Magnetodielectrics (Lawes)
Materials exhibiting simultaneous magnetic and ferroelectric order
(multiferroics) are particularly interesting systems in which to investigate
spin-charge coupling. Recently, in certain classes of multiferroic
materials, it has been established that ferroelectricity is induced by
the magnetic structure. These systems show very strong magnetoelectric
coupling, to the extent that in some cases the spontaneous polarization
can be switched by an external magnetic field. Understanding the
properties of these multiferroics is crucial for incorporating these materials
into novel magnetoelectric devices. Beyond single-phase multiferroics,
various nanocomposite materials can also show substantial magnetodielectric
effects. Magnetic nanoparticles embedded in an insulating matrix
have been observed to exhibit a magnetization dependent dielectric constant.
These composite materials may offer more versatility for device design
than the single-phase multiferroic materials.
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 investigates the properties of the important defects and defect complexes occurring in various semiconductors. In order to be able to identify the defects responsible for particular experimental properties (and suggest how to optimize these properties as desired for particular applications), 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, and compare these properties with the experimental observations. We also determine whether these energetically favorable defects have metastable higher energy configurations, and investigate their motion and interactions. Since these calculations are very demanding, they are supported by grants of supercomputing time from the Air Force Office of Scientific Research at ERDC, NAVO, and other national supercomputing centers.
There is currently a lot of interest in producing nanoscale devices and low-dimensional structures, such as quantum dots, in order to achieve faster response times, and the possibility of modifying the properties as desired by changing the geometrical dimensions. While changing the conditions during growth and processing can affect the quality of surfaces and interfaces and the concentrations of various defects remaining in important regions in larger devices as well, this can produce particularly dramatic changes in the properties of low-dimensional or very small structures. Therefore a better understanding of semiconductor growth at the atomic level is needed. Our research group is currently investigating how growth and processing under different conditions can lead to different concentrations of structural defects at the surface, and different concentrations of various defects remaining in the material after growth. In order to address these questions, we use first-principles calculations to study the dynamics and energetics of the microscopic processes occurring at the growing semiconductor surfaces, as well as the defects which can occur at the growing surface.
References and an overview of some of the first-principles methods we use, including codes written and maintained by our long-term collaborators at the Fritz-Haber-Institut der Max-Planck-Gesellschaft and a manual on how to do these calculations coauthored by us, is available at http://www.fhi-berlin.mpg.de/th/fhi98md/.
Some recent publications:
“First-Principles Study of As Interstitials in GaAs: Convergence, Relaxation,
and Formation Energy”,
J. T. Schick, C. G. Morgan, and P. Papoulias, Physical Review B66 195302
(2002).
“Optical and Electrical Properties of Low to Highly Degenerate InN Films”,
D. B. Haddad et al., Mat Res. Soc. Symp. Proc. 798 Y12.7.1-Y12.7.6 (2004).
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.