Experimental research on condensed matter physics at
Laboratory for Surface Modification
The Laboratory for Surface Modification is an interdisciplinary laboratory with state-of-the art equipment, involving over twenty faculty members from different departments (Physics & Astronomy, Chemistry and Chemical Biology, Materials Science and Engineering, Electrical and Computer Engineering, Chemical and Biochemical Engineering, and Biomedical Engineering). The focus of LSM is on the physics, chemistry and engineering of surfaces and interfaces, often at the atomic scale. The facility is centered in the Nanophysics Laboratory (NPL) adjacent to Serin Physics Laboratory, and is directed by Professor Robert Bartynski. Aside from the considerable conceptual interest in this area, progress in surface and interface science is having an impact on such diverse fields as electronic materials, petrochemistry, computer science, biomedical science, and nanotechnology.
Professor Eva Andrei
Our research program focuses on the diverse phases of matter and associated dynamic and thermodynamic properties arising from the competition between particle-particle interactions and fluctuations. The former are inherent to the particles while the latter are external, stemming from a random potential, temperature or quantum effects. By varying the relative strength of these ingredients new phases and physical properties can be engineered. We use two model systems which are exceptionally versatile and easy to manipulate under standard laboratory conditions: a) magnetic vortices in type II superconductors and b) two-dimensional (2D) electron systems. a) Vortices. This work is currently centered on the dynamics of moving vortex phases and order-disorder transitions. We have developed novel transport techniques including swept radio frequency spectroscopy, current pulsing and ultra-fast current ramps which have enabled us to follow the vortex state as its motion unfolds in response to an applied current. Our experiments lead to the discovery of a new vortex state which exhibits a number of striking properties including frequency memory and unusual training effects. b) 2D electron systems. 2D electron layers are created by depositing electrons on the surface of a weakly polarizable substrate such as liquid helium or by trapping them at a semiconductor junction. The in-plane physics is governed by competing energy scales which give rise to a variety of phases such as electron crystal, dipole crystal, glass, a quantum liquid, quantum Hall states, etc. We use broad band radio frequency spectroscopy and transport measurements to study the dynamics, thermodynamics and the mechanisms driving the various phase transitions.
Professor Robert Bartynski
Our group is engaged in experimental studies of the electronic properties of surfaces and interfaces. The research focuses primarily on three areas: The influence that quantum size effects in ultrathin metal films have on their interaction with adsorbed atoms and molecules; the growth and morphology of metal overlayers on ferroelectric oxides; and the electronic properties of solids and their surfaces as probed by Auger-photoelectron coincidence spectroscopy. Our research employs a number of electron based spectroscopies, including angle resolved inverse and direct photoemission, both in-house and at synchrotron radiation facilities, as well as scanning tunneling microscopy and spectroscopy.
Professor Sang-W. Cheong
New physics on new materials, particularly correlated materials. The primary focus has been the experimental study of the charge and spin states in correlated electron systems including high Tc superconductors and colossal magnetoresistance (CMR) compounds. The recent success includes the understanding of the quantum magnetism in 2D S=1/2 antiferromagnets, the discovery of the charge/spin stripe states, and the understanding of the strong coupling of spin, charge and the lattice in the CMR manganites. This type of exploration requires wide-range interdisciplinary researches and extensive collaboration, allowing students accustomed to various fields such as condensed matter physics, chemistry, and materials science and also helping students to develop a scientific network. Our research employs magneto-transport and thermodynamic measurements, neutron and x-ray elastic/inelastic scattering experiments, and spectroscopic experiments such as optics and photoemission experiments as well as new phase synthesis and crystal growth.
Professor Mark Croft
The current central thrust of Prof. Croft's research involves the use of synchrotron radiation x-ray spectroscopy measurements to probe the structure and electronic states of new, novel, and technologically important materials. Both x-ray absorption spectroscopy and x-ray diffraction experiments are carried out in runs at the Brookhaven National Synchrotron Light Source. A wide range of materials and solid state problems are encompassed in this effort, a representative selection of examples of which are noted. One area of concentration addresses the electronic structure of High Tc related compounds that underlies the collapse of magnetism, the insulator- metal transition, and the superconductivity that occur in these materials. [Both bulk and pulsed laser deposited thin films are used in this work.] Another area of effort deals with the transition metal d-orbital role in the electronic structure of compounds. Recent work has also involved the question of face versus body centered cubic structure in metallic/magnetic multilayered materials. Prof. Croft also has an on going involvement in mixed valent, heavy Fermion problem. In these studies the evolution from local-magnetic- moment to delocalized-band electronic behavior is studied by low temperature magnetic, transport, and thermal measurements in conjunction with spectroscopic measurements. All of the work in this program emphasize broadly based materials synthesis techniques.
Professor Leonard Feldman
Feldmanís research interests center on thin film and surface-interface science, mostly involving semiconductors. Much of the program focuses on the use of ion beams for surface and interface analysis and materials modification.† Most recently he has been active in applying these concepts to the critical problem of the silicon carbide/dielectric interfaces. Current interests also include the study of nano-clusters and cluster fabrication, phase transitions in nano-scale materials, nano-scale fluidics and the organic/inorganic interface. The semiconductor thrust also includes investigation of the dynamical properties of defects, specifically measurements of the pico-second vibrational lifetimes of localized defects such as hydrogen in silicon and radiation damage in emerging silicon-based materials. A particular focus concerns the IR resonant desorption of hydrogen covered surfaces.
Professor Eric Garfunkel (Chemistry)
The broad goal of our research program is to learn how to design surfaces, interfaces and thin films for microelectronics and other advanced materials applications. We employ electron spectroscopy, ion scattering, scanning probe microscopy, vibrational spectroscopy, and other surface science and thin film methods. Recent work has included studies of oxidation, molecular and metal adsorption and reaction, and thin film growth. One major project involves studies of ultrathin dielectrics (silicon oxynitrides and metaloxides) for nanoelectronic devices. We examine problems of composition, reaction mechanism, structure and electrical properties. Other projects include structural and thermochemical aspects of metallization, studies of the polymer-metal interface, and basic studies for molecular electronics.
Professor Michael Gershenson
Our research focuses on the electronic transport in nanoscale systems at
ultra-low temperatures. For the sample fabrication and characterization, we
employ nanolithography, various thin-film deposition methods, and ultra-low-noise
measurements at milliKelvin temperatures. †Our recent projects included the study of
quantum transport in mesoscopic conductors (decoherence, localization in
low-dimensional conductors, etc.), the electron-electron interactions in
two-dimensional high-mobility systems, and the development of ultra-sensitive
hot-electron detectors of far-infra-red electromagnetic radiation for the
deep-space NASA missions. Currently, we are involved in the work on the
realization of topologically protected superconducting bits for quantum
computing. This effort on quantum computing is aimed at the experimental
verification of the ideas developed by
Professor Torgny Gustafsson
Our research is mainly in the area of properties of ultrathin films, especially films for potential utility in the microelectronics industry. We develop new experimental techniques for determining the structure and composition of such films, primarily based on methods using energetic ions, and utilizing our experience from surface science. Using these, we are studying the basic mechanisms for formation of oxides on metal and semiconductor substrates. We are also trying to understand thermal and electrical properties of novel amorphous oxides on silicon and germanium and to develop and characterize new epitaxial materials on silicon surfaces.
Professor Jane Hinch (Chemistry)
We are investigating atomic and molecular beam scattering from surfaces prepared under ultrahigh vacuum conditions. We investigate the nature of the molecular surface interactions and quantify processes such as phonon creation/annihilation, electron-hole pair excitation, electron transfer or trapping, and adsorption. The major focus of our research efforts involves thermal-energy atomic helium scattering as a technique in the study of clean and adsorbate covered surfaces. Helium is an extremely inert, surface-sensitive, diffractive probe of surface topographies and long range ordering phenomena. We investigate also the dynamics of surfaces and low energy excitations and surface diffusion processes. Each of these features are of utmost importance in thin film growth at surfaces. In addition we use both diffraction and real-space scanning tunneling microscopy in in-situ studies of the growth of thin films by both thermal evaporation and chemical vapor deposition.
Professor Valery Kiryukhin
Our research is focused on electronic, structural, and magnetic properties of novel materials. Strongly-correlated systems are of primary interest.† Colossal magnetoresistance, high-temperature superconductivity, and materials with self-organized nanostructure are examples of current problems under investigation. We address questions of fundamental importance in condensed matter physics, such as low-dimensional and frustrated magnetism, charge/orbital order, and electronic phase separation. The investigated materials also hold potential for practical applications, e.g. in magnetic recording. Our main experimental techniques are x-ray and neutron scattering. Experiments are performed on campus, and at leading national facilities, such as Brookhaven National Laboratory, and National Institute of Standards and Technology. We work in close collaboration with Prof. Cheong's group. Students get a broad exposure to worlds-best experimental scattering facilities, as well as to state-of-the-art laboratory techniques for crystal growth and characterization. Our group provides great opportunities for establishment of scientific contacts and collaborations.
Professor Haruo Kojima
In my laboratory, experiments are carried out on materials from ~ 10-3 to ~ 104 K under variety of conditions: (1) Superfluid He-3, which occurs below 2.6 mK, has a rich variety of phenomena whose analogs can be found in superfluid He-4, nematic liquid crystals, antiferromagnets, and ferromagnets. Our most recent research has been with the superfluid He-3 A-1 phase in magnetic fields as high as 15 tesla. A unique hybrid form of second sound, a spin-entropy wave, exists in A-1 phase. The velocity and attenuation of the spin-entropy are being measured to extract the superfluid fraction, the spin diffusivity, and the thermal conductivity. Under suitable conditions, the spin-entropy wave can be used to study liquid crystal-like anisotropy effects. Textural transitions induced by superfluid flows are being studied using the spin-entropy wave. Another experiment currently underway is the unique magnetic fountain effect in A-1 phase. When a magnetic field gradient is applied, a pressure gradient is induced. The effect is used to study the important spin relaxation at very low temperature. (2) It has been predicted that solid He-4 should exhibit superfluid properties below a critical temperature. That is, solid He-4 should become a ‚Äúsupersolid"! Recent experiments using torsion pendulum showed an evidence for such behavior below 250 mK. We are searching for other manifestation of supersolidity by looking for new propagating modes unique to excitations in supersolid. The research is aimed at discovering wave modes analogous to second and fourth sounds in other superfluid systems. (3) When a solid material in equilibrium with its melt is uni-axially stressed, the initially flat surface of the solid material is predicted to deform into a undulating surface. This effect is analogous to the formation quantum dots of Si-Ge alloy in Si substrate surface. The stress-driven instability is being studied using solid He-4 as the working material. Cryogenic optics system has been developed for observing bi-axially applied stressed solid He-4 surface below 4.2 K and in pressure up to 25 bars. (4) Single bubble sonoluminescence is the phenomenon in which a trapped gas bubble in water is driven by intense ultrasonic fields such that the trapped noble gas in the bubble undergoes temperature swings to more that 10^4 K such that light visible to naked eyes is emitted. Mixtures of noble gases are introduced into the bubbles to search for spatial segregations of different species of the gasses. The spatial segregation is expected to increase the bubble interior temperature. The radiation emission spectra from the sonoluminescing bubble between 0 and 30 C temperature of water.
Professor Theodore E. Madey
My research is in experimental surface physics. Particular emphasis is on the use of ultrahigh vacuum methods to characterize the physics and chemistry of surface processes. My present research activities are focused mainly in three areas: (1) we are studying the relation between surface structure, electronic properties, and reactivity of unstable metal surfaces, i.e., surfaces that undergo nanoscale faceting when they are covered by adsorbed monolayers, and heated. Methods are used in this program include atomic-resolution scanning tunneling microscopy, electron diffraction, and synchrotron radiation. (2) we are determining the mechanisms of electron- and photon-stimulated desorption of atoms and ions from surfaces and of radiation-stimulated surface reactions. The radiation-induced origin of tenuous planetary atmospheres and the physics of radiation damage in extreme UV lithography are topics of special interest. (3) We probe the fascinating properties of water and ice on surfaces, from contact angle measurements of superhydrophobicity in air, to the physics of ultrathin ice films grown on single crystal surfaces.
Professor Seongshik (Sean) Oh
The main thread of our research is search for new physics and applications by means of atomic-scale material engineering. A typical project of our group will be composed of four stages of research activities: design and growth of artificial thin-film materials, material characterization, device fabrication using micro/nano-lithography, and their quantum transport studies over a range of temperatures and magnetic fields. We are building a unique atomic-layer-controllable molecular-beam-epitaxy (MBE) system for the growth of artificial materials. We will also make use of other thin-film growth techniques such as pulsed-laser-deposition (PLD) and sputtering in order to complement the MBE technique. With such a unique thin-film growth capability, we can design new materials that do not normally exist in nature. One example is the incorporation of multiple functionalities such as superconductivity, magnetism, and ferroelectricity into a single material platform in search of multifunctionality. We can also create novel multiferroic, superconducting or ferroelectric materials by means of atomic-scale crystal-symmetry engineering. At times, micro/nano-lithography needs to follow. For instance, many strongly-correlated materials undergo nanoscale phase-separation at low temperatures, and nano-patterned wires help uncover what is happening at the nanoscale. Electric-field effect devices, tunnel junctions and Hall-bars are some of the common micro/nano-fabricated structures. By combining these bottom-up and top-down approaches together, we will investigate a variety of oxide heterostructures for multifunctionality and strongly- correlated physics, and also study decoherence mechanism for superconducting quantum computation.
Professor Vitaly Podzorov
My research is mainly focused on intrinsic electronic proceses that determine operation of organic semiconductor devices, such as transistors and solar cells. In my lab, we perform organic semiconductor growth, device fabrication and characterization. Fundamentals of charge carrier mobility and exiton dynamics in organic lattices are studied by means of electrical transport and optical measurements.† In addition, we work on field-effect transistors based on other novel (inorganic) semiconductors, such as WSe2 and STO, and on molecular self assembly at various surfaces that results in modifications of material's electronic properties.† Some particular projects in our lab include:
1. High-performance single-crystal organic transistors:
fundamentals of charge transport.
2. Conjugated polymers: physics of charge transport.†
3. Memory devices based on organic semiconductors.
4. Excitons in highly crystalline organic semiconductors.
5. Physics of photovoltaic effect in highly crystalline organic (and hybrid) solar cells.
6. Molecular self-assembly at the surface of organic and inorganic semiconductors.
Professor Weida Wu
The current focus of my research is to study the nanoscale magnetic structure of emergent materials, like multiferroic systems, colossal magnetoresistive (CMR) manganites and magnetic nano-particles, and the evolution of the structure as experimental parameters (temperature, magnetic field and stress) vary. I am also interested in vortex glasses, its dynamics and related order-disorder transition in type II superconductors. Magnetic structure (e.g. domains in ferromagnets) originates from competitions and the delicate balance of many interactions/couplings between various degrees of freedom (spin, orbit, lattice, etc.). We try to understand these competitions and the effect of dimensionality by imaging the magnetic texture with low temperature scanning probe microscopes, both magnetic force microscope (MFM) and spin-polarized scanning tunneling microscope (SP-STM).
Professor Frank Zimmerman
Our research in experimental surface physics is directed at obtaining a detailed understanding of the fundamental mechanisms involved in dynamical surface processes, in particular laser-induced thermal and photochemical surface processes. We seek to understand the excitation mechanisms and the dynamics of laser-induced desorption, dissociation, and reaction of adsorbed molecules. A powerful way to gain insight into the dynamics uses quantum state resolved, laser spectroscopic detection of desorbed products to determine their final state distributions in the translational, rotational, vibrational, and electronic degrees of freedom. In addition, we intend to use ultra-short ("femtosecond") laser pulses to probe surface dynamics in real time.
Revised May, 2008