Hrvoje Petek | |
---|---|
Born | Zagreb, Croatia | January 13, 1958
Nationality | American, Croatian |
Alma mater | Massachusetts Institute of Technology (1980, B.S., Chemistry) University of California, Berkeley (1985, Ph.D., Chemistry) |
Known for | Ultrafast laser spectroscopy, Ultrafast microscopy, Plasmonics, Two-photon photoelectron spectroscopy |
Scientific career | |
Fields | Experimental physics |
Institutions | Institute for Molecular Science Hitachi University of Pittsburgh |
Hrvoje Petek (born January 13, 1958) is a Croatian-born American physicist and the Richard King Mellon Professor of Physics and Astronomy, [1] at the University of Pittsburgh, where he is also a professor of chemistry. [2]
Petek received his B.S. degree in chemistry from Massachusetts Institute of Technology in 1980. [3] Subsequently, he obtained his Ph.D. degree in chemistry from the University of California, Berkeley in 1985. [4]
Petek has developed coherent photoelectron spectroscopy [5] [6] and microscopy [7] as methods for studying the dephasing and spatial propagation of polarization fields in solid state materials and nanostructure. He is developing methods for multidimensional multiphoton-photoemission spectroscopy. [8] Together with Taketoshi Minato, Yousoo Kim, Maki Kawai, Jin Zhao Archived 2019-07-16 at the Wayback Machine , Jinlong Yang and Jianguo Hou, Petek discovered a delocalized electronic structure created by oxygen vacancy on titanium dioxide surface. [9] Together with Jin Zhao Archived 2019-07-16 at the Wayback Machine , Ken Jordan and Ken Onda, Petek also discovered wet electron states, where electrons are partially solvated by water and other protic solvents at molecule vacuum interfaces. [10] Together with Min Feng and Jin Zhao Archived 2019-07-16 at the Wayback Machine , Petek discovered atom-like superatom states of C60, and similar hollow molecules. [11] Petek's research of metal plasmon excitations with semiconductor substrates, unrevealed the charge injection from optically active plasmonic modes into semiconductor substrates. [12]
Petek is editor-in-chief of Progress in Surface Science [13] and has organized conferences such as the 11th International Symposium of Ultrafast Surface Dynamics, held in Qiandao Lake, China. [14] Petek has been (2015-2019) a member of the National Research and Development Agency Committee for the National Institute for Materials Science and is currently a senior scientific advisor to the Institute for Molecular Science in Japan. [15]
The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, solid state, and quantum chemistry to draw inferences about the properties of atoms, molecules and solids. The effect has found use in electronic devices specialized for light detection and precisely timed electron emission.
Photoluminescence is light emission from any form of matter after the absorption of photons. It is one of many forms of luminescence and is initiated by photoexcitation, hence the prefix photo-. Following excitation, various relaxation processes typically occur in which other photons are re-radiated. Time periods between absorption and emission may vary: ranging from short femtosecond-regime for emission involving free-carrier plasma in inorganic semiconductors up to milliseconds for phosphoresence processes in molecular systems; and under special circumstances delay of emission may even span to minutes or hours.
Molecular engineering is an emerging field of study concerned with the design and testing of molecular properties, behavior and interactions in order to assemble better materials, systems, and processes for specific functions. This approach, in which observable properties of a macroscopic system are influenced by direct alteration of a molecular structure, falls into the broader category of “bottom-up” design.
Photoemission spectroscopy (PES), also known as photoelectron spectroscopy, refers to energy measurement of electrons emitted from solids, gases or liquids by the photoelectric effect, in order to determine the binding energies of electrons in the substance. The term refers to various techniques, depending on whether the ionization energy is provided by X-ray, XUV or UV photons. Regardless of the incident photon beam, however, all photoelectron spectroscopy revolves around the general theme of surface analysis by measuring the ejected electrons.
Photoemission electron microscopy is a type of electron microscopy that utilizes local variations in electron emission to generate image contrast. The excitation is usually produced by ultraviolet light, synchrotron radiation or X-ray sources. PEEM measures the coefficient indirectly by collecting the emitted secondary electrons generated in the electron cascade that follows the creation of the primary core hole in the absorption process. PEEM is a surface sensitive technique because the emitted electrons originate from a shallow layer. In physics, this technique is referred to as PEEM, which goes together naturally with low-energy electron diffraction (LEED), and low-energy electron microscopy (LEEM). In biology, it is called photoelectron microscopy (PEM), which fits with photoelectron spectroscopy (PES), transmission electron microscopy (TEM), and scanning electron microscopy (SEM).
Organic semiconductors are solids whose building blocks are pi-bonded molecules or polymers made up by carbon and hydrogen atoms and – at times – heteroatoms such as nitrogen, sulfur and oxygen. They exist in the form of molecular crystals or amorphous thin films. In general, they are electrical insulators, but become semiconducting when charges are injected from appropriate electrodes or are introduced by doping or photoexcitation.
Tungsten ditelluride (WTe2) is an inorganic semimetallic chemical compound. In October 2014, tungsten ditelluride was discovered to exhibit an extremely large magnetoresistance: 13 million percent resistance increase in a magnetic field of 60 tesla at 0.5 kelvin. The resistance is proportional to the square of the magnetic field and shows no saturation. This may be due to the material being the first example of a compensated semimetal, in which the number of mobile holes is the same as the number of electrons. Tungsten ditelluride has layered structure, similar to many other transition metal dichalcogenides, but its layers are so distorted that the honeycomb lattice many of them have in common is in WTe2 hard to recognize. The tungsten atoms instead form zigzag chains, which are thought to behave as one-dimensional conductors. Unlike electrons in other two-dimensional semiconductors, the electrons in WTe2 can easily move between the layers.
Laser-based angle-resolved photoemission spectroscopy is a form of angle-resolved photoemission spectroscopy that uses a laser as the light source. Photoemission spectroscopy is a powerful and sensitive experimental technique to study surface physics. It is based on the photoelectric effect originally observed by Heinrich Hertz in 1887 and later explained by Albert Einstein in 1905 that when a material is shone by light, the electrons can absorb photons and escape from the material with the kinetic energy: , where is the incident photon energy, the work function of the material. Since the kinetic energy of ejected electrons are highly associated with the internal electronic structure, by analyzing the photoelectron spectroscopy one can realize the fundamental physical and chemical properties of the material, such as the type and arrangement of local bonding, electronic structure and chemical composition.
LeRoy W. Apker was an American experimental physicist. Along with his colleagues E. A. Taft and Jean Dickey, he studied the photoelectric emission of electrons from semiconductors and discovered the phenomenon of exciton-induced photoemission in potassium iodide. In 1955, he received the Oliver E. Buckley Condensed Matter Prize of the American Physical Society for his work.
A localized surface plasmon (LSP) is the result of the confinement of a surface plasmon in a nanoparticle of size comparable to or smaller than the wavelength of light used to excite the plasmon. When a small spherical metallic nanoparticle is irradiated by light, the oscillating electric field causes the conduction electrons to oscillate coherently. When the electron cloud is displaced relative to its original position, a restoring force arises from Coulombic attraction between electrons and nuclei. This force causes the electron cloud to oscillate. The oscillation frequency is determined by the density of electrons, the effective electron mass, and the size and shape of the charge distribution. The LSP has two important effects: electric fields near the particle's surface are greatly enhanced and the particle's optical absorption has a maximum at the plasmon resonant frequency. Surface plasmon resonance can also be tuned based on the shape of the nanoparticle. The plasmon frequency can be related to the metal dielectric constant. The enhancement falls off quickly with distance from the surface and, for noble metal nanoparticles, the resonance occurs at visible wavelengths. Localized surface plasmon resonance creates brilliant colors in metal colloidal solutions.
Ortwin Hess is a German-born theoretical physicist at Trinity College Dublin (Ireland) and Imperial College London (UK), working in condensed matter optics. Bridging condensed matter theory and quantum optics he specialises in quantum nanophotonics, plasmonics, metamaterials and semiconductor laser dynamics. Since the late 1980s he has been an author and coauthor of over 300 peer-reviewed articles, the most popular of which, called "'Trapped rainbow' storage of light in metamaterials", was cited more than 400 times. He pioneered active nanoplasmonics and metamaterials with quantum gain and in 2014 he introduced the "stopped-light lasing" principle as a novel route to cavity-free (nano-) lasing and localisation of amplified surface plasmon polaritons, giving him an h-index of 33.
Time-resolved two-photon photoelectron (2PPE) spectroscopy is a time-resolved spectroscopy technique which is used to study electronic structure and electronic excitations at surfaces. The technique utilizes femtosecond to picosecond laser pulses in order to first photoexcite an electron. After a time delay, the excited electron is photoemitted into a free electron state by a second pulse. The kinetic energy and the emission angle of the photoelectron are measured in an electron energy analyzer. To facilitate investigations on the population and relaxation pathways of the excitation, this measurement is performed at different time delays.
Oleg V. Prezhdo is a Ukrainian–American physical chemist whose research focuses on non-adiabatic molecular dynamics and time-dependent density functional theory (TDDFT). His research interests range from fundamental aspects of semi-classical and quantum-classical physics to excitation dynamics in condensed matter and biological systems. His research group focuses on the development of new theoretical models and computational tools aimed at understanding chemical reactivity and energy transfer at a molecular level in complex condensed phase environment. Since 2014, he is a professor of chemistry and of physics & astronomy at the University of Southern California.
Helen H. Fielding is a Professor of physical chemistry at University College London (UCL). She focuses on ultrafast transient spectroscopy of protein chromophores and molecules. She was the first woman to win the Royal Society of Chemistry (RSC) Harrison-Meldola Memorial Prize (1996) and Marlow Award (2001).
Tamar Seideman is the Dow Chemical Company Professor of Chemistry and Professor of Physics at Northwestern University. She specialises in coherence spectroscopies and coherent control in isolated molecules and dissipative media as well as in ultrafast nanoplasmonics, current-driven phenomena in nanoelectronics and mathematical models.
Ultrafast scanning electron microscopy (UFSEM) combines two microscopic modalities, Pump-probe microscopy and Scanning electron microscope, to gather temporal and spatial resolution phenomena. The technique uses ultrashort laser pulses for pump excitation of the material and the sample response will be detected by an Everhart-Thornley detector. Acquiring data depends mainly on formation of images by raster scan mode after pumping with short laser pulse at different delay times. The characterization of the output image will be done through the temporal resolution aspect. Thus, the idea is to exploit the shorter DeBroglie wavelength in respect to the photons which has great impact to increase the resolution about 1 nm. That technique is an up-to-date approach to study the dynamic of charge on material surfaces.
Olga Smirnova is a German physicist who is Head of the Strong Field Theory Group at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy and Professor at Technische Universität Berlin. Her research considers the interaction of strong fields with atoms and molecules.
In physics and chemistry, photoemission orbital tomography is a combined experimental / theoretical approach which was initially developed to reveal information about the spatial distribution of individual one-electron surface-state wave functions and later exteded to study molecular orbitals. Experimentally, it uses angle-resolved photoemission spectroscopy (ARPES) to obtain constant binding energy photoemission angular distribution maps. In their pioneering work, Mugarza et al. in 2003 used a phase-retrieval method to obtain the wave function of electron surface states based on ARPES data acquired from stepped gold crystalline surfaces; they obtained the respective wave functions and, upon insertion into the Schrödinger equation, also the binding potential. More recently, photoemission maps, also known as tomograms, have been shown to reveal information about the electron probability distribution in molecular orbitals. Theoretically, one rationalizes these tomograms as hemispherical cuts through the molecular orbital in momentum space. This interpretation relies on the assumption of a plane wave final state, i.e., the idea that the outgoing electron can be treated as a free electron, which can be further exploited to reconstruct real-space images of molecular orbitals on a sub-Ångström length scale in two or three dimensions. Presently, POT has been applied to various organic molecules forming well-oriented monolayers on single crystal surfaces or to two-dimensional materials.
Nano Angle-Resolved Photoemission Spectroscopy (Nano-ARPES), is a variant of the experimental technique ARPES. It has the ability to precisely determine the electronic band structure of materials in momentum space with submicron lateral resolution. Due to its demanding experimental setup, this technique is much less extended than ARPES, widely used in condensed matter physics to experimentally determine the electronic properties of a broad range of crystalline materials. Nano-ARPES can access the electronic structure of well-ordered monocrystalline solids with high energy, momentum, and lateral resolution, even if they are nanometric or heterogeneous mesoscopic samples. Nano-ARPES technique is also based on Einstein's photoelectric effect, being photon-in electron-out spectroscopy, which has converted into an essential tool in studying the electronic structure of nanomaterials, like quantum and low dimensional materials.
Professor Günther Rupprechter is a distinguished Austrian scientist, full professor and currently Head of the Institute of Materials Chemistry, Technische Universität Wien. He is renowned for his contributions to the fields of physical chemistry, surface science, nanoscience and nanotechnology, particularly in the area of catalytic surface reactions on heterogeneous catalysts, identifying fundamental reaction steps at the atomic level by in situ and operando spectroscopy and microscopy.