One-dimensional minigaps in inversion layer subbands on high index surfaces of InSb

In metal-oxide-semiconductor structures prepared on high index surfaces ofp-InSb onedimensional minigaps are observed in the quasi-two-dimensional subband structure of the inversion layer electrons at low temperatures. From anisotropic structure in the inversion channel conductance energetical position and size of the minigap are deduced and studied in dependence on surface orientation. The measured energetical position of the minigap is well described by two models, the valley projection model by Sham et al. and the staircase interface model by Volkov et al. In the magnetoconductance the Shubnikov-de Haas oscillations are found to contain several periods, reflecting the possible electron orbits of a two-dimensional electron gas with a one-dimensional minigap in a magnetic field applied normal to the two-dimensional plane. The size of the minigap determined from magnetic breakdown is found to be comparable to the one deduced from the anisotropic structure in the zero-field conductance.Dedicated to K. Dransfeld on the occasion of his 60th birthday     

Two-dimensional magnetoplasmon in the silicon inversion layer

The influence of a magnetic field on the behavior of the two-dimensional plasmon is studied in the n-inversion layer of p-type silicon at fixed wavevector as a function of electron density and magnetic field. Most of the behavior is well described by a dispersion relation and lineshape based on a classical theory of the electron gas. However, deviations from the theory are observed which may indicate an interaction with other modes of the system.     

Electronic excitations in microstructured MOS - systems

We have investigated the DC- and dynamic electronic properties of MOS-systems with spatially modulated charge density. The charge density modulation is induced via oxide modulation in lateral and cross-grating structures with typical periodicities of 500 nm. Magneto-conductance measurements are performed to characterize the charge density modulation. In spectroscopic investigations we find, that the charge density modulation strongly affects the collective excitation spectrum of the 2D-electron gas and induces minigaps in the 2D-plasmon dispersion.     

Rectification in mesoscopic systems with broken symmetry: quasiclassical ballistic versus classical transport

In suitably designed mesoscopic semiconductor structures, the phenomenon of ballistic rectification can be observed. A currently discussed microscopic model relates the observations to the interplay between fully quantized and quasiclassical current paths. We present measurements that contribute substantially to the clarification of the fascinating topic. In particular, we observe the opposite sign of the output voltage as compared to the prediction. Demonstrating the basic principle upon which the rectification is based--the asymmetry of the voltage drop in a quasiclassical wire--and extending the model to the classical transport regime, we can well explain our experiments as being caused by the interplay of quasiclassical ballistic and classical transport. Tunable ballistic rectifiers generating very large output signals and operating at room temperature raise the hope for future applications.     

Lateral tunneling through the controlled barrier between edge channels in a two-dimensional electron system

A study is made of the lateral tunneling between edge channels at the depletion-induced edges of a gated two-dimensional electron system, through a gate-voltage-controlled barrier arising when the donor layer of the heterostructure is partly removed along a fine strip by means of an atomic force microscope. For a sufficiently high barrier the typical current-voltage characteristic is found to be strongly asymmetric, having, in addition to the positive tunneling branch, a negative branch that corresponds to the current overflowing the barrier. It is established that the barrier height depends linearly on both the gate voltage and the magnetic field, and the data are described in terms of electron tunneling between the outermost edge channels. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 8, 561–566 (25 April 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Single-electron tunneling in silicon nanostructures

We present a brief overview on different realizations of single-electron devices fabricated in silicon-on-insulator films. Lateral structuring of highly doped silicon films allows us to observe quasi-metallic Coulomb blockade oscillations in shrunken wires where no quantum dot structure is geometrically defined. Embedding quantum dot structures into the inversion channel of a silicon-on-insulator field-effect transistor Coulomb blockade up to 300 K is observed. In contrast to the quasi-metallic structures, in these devices the influence of the quantum mechanical level spacing inside the dot becomes visible. Suspending highly doped silicon nanostructures leads to a novel kind of Coulomb blockade devices allowing both high-power application as well as the study of electron–phonon interaction. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000     

Spectroscopy of one-dimensional subbands on InSb

By means of high resolution optical lithography two-dimensional (2D) electron inversion layers in metal-oxide-semiconductor (MOS) structures on InSb are laterally confined to narrow channels. The widths of the channels (w≈100nm) are comparable to the de-Broglie wavelength of the electrons and formation of one-dimensional (1D) subbands results. This is verified by direct spectroscopy of intersubband transitions between the 1D subbands at far-infrared frequencies. Cyclotron resonance experiments also show the importance of the lateral confining potential. In particular, the transition from 1D to 2D electronic behavior is observed when the magnetic field strength is increased and the cyclotron radius ℓ becomes much less than the channel width w.     

Gels of shape-persistent macrocycles: the role of the interior

The aggregation of shape-persistent macrocycles with an empty cavity, an undecyldiether strand and a tetraethylene glycol strand leads in all cases to a macroscopic gelation of the solvent. However, the gelation temperatures are fine-tuned by the intraannular substituents.     

Structure and Mechanism Leading to Formation of the Cysteine Sulfinate Product Complex of a Biomimetic Cysteine Dioxygenase Model

Cysteine dioxygenase is a unique nonheme iron enzyme that is involved in the metabolism of cysteine in the body. It contains an iron active site with an unusual 3‐His ligation to the protein, which contrasts with the structural features of common nonheme iron dioxygenases. Recently, some of us reported a truly biomimetic model for this enzyme, namely a trispyrazolylborato iron(II) cysteinato complex, which not only has a structure very similar to the enzyme–substrate complex but also represents a functional model: Treatment of the model with dioxygen leads to cysteine dioxygenation, as shown by isolating the cysteine part of the product in the course of the work‐up. However, little is known on the conversion mechanism and, so far, not even the structure of the actual product complex had been characterised, which is also unknown in case of the enzyme. In a multidisciplinary approach including density functional theory calculations and X‐ray absorption spectroscopy, we have now determined the structure of the actual sulfinato complex for the first time. The Cys‐SO₂^? functional group was found to be bound in an η²‐O,O‐coordination mode, which, based on the excellent resemblance between model and enzyme, also provides the first support for a corresponding binding mode within the enzymatic product complex. Indeed, this is again confirmed by theory, which had predicted a η²‐O,O‐binding mode for synthetic as well as the natural enzyme.