Pär Omling

Bio: Pär Omling is an academic researcher from Lund University. The author has contributed to research in topics: Electron paramagnetic resonance & Quantum dot. The author has an hindex of 33, co-authored 148 publications receiving 3664 citations.

Experimental tunneling ratchets

Abstract: Adiabatically rocked electron ratchets, defined by quantum confinement in semiconductor heterostructures, were experimentally studied in a regime where tunneling contributed to the particle flow. The rocking-induced electron flow reverses direction as a function of temperature. This result confirms a recent prediction of fundamentally different behavior of classical versus quantum ratchets. A wave-mechanical model reproduced the temperature-induced current reversal and provides an intuitive explanation.

Unidirectional electron flow in a nanometer-scale semiconductor channel: A self-switching device

Abstract: By tailoring the boundary of a narrow semiconductor channel to break its symmetry, we have realized a type of nanometer-scale nonlinear device, which we refer to as self-switching device (SSD). An applied voltage V not only changes the potential profile along the channel direction, but also either widens or narrows the effective channel depending on the sign of V. This results in a diode-like characteristic but without the use of any doping junction or barrier structure. The turn-on voltage can also be widely tuned from virtually zero to more than 10 V, by simply adjusting the channel width. The planar and two-terminal structure of the SSD also allows SSD-based circuits to be realized by only one step of lithography.

Deep level transient spectroscopy evaluation of nonexponential transients in semiconductor alloys

Abstract: Evaluation of data obtained from deep level transient spectroscopy (DLTS) is often based on the assumption that the transients are exponential. The applicability of DLTS to the study of deep energy levels in semiconductor alloys has therefore been questioned since thermal transients are often nonexponential in these materials. In this paper we present calculated DLTS spectra in a simple model for broadened defect levels. The calculated spectra are compared with experimental data for a deep electron trap in GaAs1−xPx . The main result is that, within the model, DLTS‐deduced activation energies and thermal emission rates are, indeed, relevant even when the transients are strongly nonexponential as a result of alloy broadening. A method of estimating the corrected concentration of deep levels and the distribution in binding energies is also presented.

Hole photoionization cross sections of EL2 in GaAs

Abstract: The spectral dependence of the hole photoionization cross section σ0p of EL2 in GaAs has been determined in absolute numbers at T=78 and 295 K. From simultaneous measurements of the electron photoionization cross section σ0n, accurate values of the photon energies and the cross sections at which σ0n=σ0p could be obtained. These data are of importance for rapid and accurate determination of concentration and charge states of EL2 in GaAs, e.g., in wafer mapping applications.

Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics

Abstract: Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have farreaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Quantum dot bioconjugates for imaging, labelling and sensing

Abstract: One of the fastest moving and most exciting interfaces of nanotechnology is the use of quantum dots (QDs) in biology. The unique optical properties of QDs make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations, in which traditional fluorescent labels based on organic molecules fall short of providing long-term stability and simultaneous detection of multiple signals. The ability to make QDs water soluble and target them to specific biomolecules has led to promising applications in cellular labelling, deep-tissue imaging, assay labelling and as efficient fluorescence resonance energy transfer donors. Despite recent progress, much work still needs to be done to achieve reproducible and robust surface functionalization and develop flexible bioconjugation techniques. In this review, we look at current methods for preparing QD bioconjugates as well as presenting an overview of applications. The potential of QDs in biology has just begun to be realized and new avenues will arise as our ability to manipulate these materials improves.

Synthetic molecular motors and mechanical machines.

Abstract: The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.