Omicron Nanotechnology GmbH

Taunusstein, Germany

Omicron Nanotechnology GmbH

Taunusstein, Germany
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Wiessner M.,University of Würzburg | Wiessner M.,Karlsruhe Institute of Technology | Hauschild D.,University of Würzburg | Scholl A.,University of Würzburg | And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The properties of molecular films are determined by the geometric structure of the first layers near the interface. These are in contact with the substrate and feel the effect of the interfacial bonding, which particularly, for metal substrates, can be substantial. For the model system 3,4,9,10- perylenetetracarboxylic dianhydride on Ag(110), the geometric structure of the first monolayer can be modified by preparation parameters. This leads to significant differences in the electronic structure of the first layer. Here, we show that, by combining angle-resolved photoelectron spectroscopy with low-energy electron diffraction, we cannot only determine the electronic structure of the interfacial layer and the unit cell of the adsorbate superstructure, but also the arrangement of the molecules in the unit cell. Moreover, in bilayer films, we can distinguish the first from the second layer and, thus, study the formation of the second layer and its influence on the buried interface. © 2012 American Physical Society.


Escher M.,FOCUS GmbH | Winkler K.,Omicron Nanotechnology GmbH | Renault O.,CEA Grenoble | Barrett N.,French Atomic Energy Commission
Journal of Electron Spectroscopy and Related Phenomena | Year: 2010

The design and applications of an instrument for imaging X-ray photoelectron spectroscopy (XPS) are reviewed. The instrument is based on a photoelectron microscope and a double hemispherical analyser whose symmetric configuration avoids the spherical aberration (α2-term) inherent for standard analysers. The analyser allows high transmission imaging without sacrificing the lateral and energy resolution of the instrument. The importance of high transmission, especially for highest resolution imaging XPS with monochromated laboratory X-ray sources, is outlined and the close interrelation of energy resolution, lateral resolution and analyser transmission is illustrated. Chemical imaging applications using a monochromatic laboratory Al Kα-source are shown, with a lateral resolution of 610 nm. Examples of measurements made using synchrotron and laboratory ultra-violet light show the broad field of applications from imaging of core level electrons with chemical shift identification, high resolution threshold photoelectron emission microscopy (PEEM), work function imaging and band structure imaging. © 2009 Elsevier B.V. All rights reserved.


Lord A.M.,University of Swansea | Maffeis T.G.,University of Swansea | Kryvchenkova O.,University of Swansea | Cobley R.J.,University of Swansea | And 7 more authors.
Nano Letters | Year: 2015

The ability to control the properties of electrical contacts to nanostructures is essential to realize operational nanodevices. Here, we show that the electrical behavior of the nanocontacts between free-standing ZnO nanowires and the catalytic Au particle used for their growth can switch from Schottky to Ohmic depending on the size of the Au particles in relation to the cross-sectional width of the ZnO nanowires. We observe a distinct Schottky to Ohmic transition in transport behavior at an Au to nanowire diameter ratio of 0.6. The current-voltage electrical measurements performed with a multiprobe instrument are explained using 3-D self-consistent electrostatic and transport simulations revealing that tunneling at the contact edge is the dominant carrier transport mechanism for these nanoscale contacts. The results are applicable to other nanowire materials such as Si, GaAs, and InAs when the effects of surface charge and contact size are considered. © 2015 American Chemical Society.


Lord A.M.,University of Swansea | Maffeis T.G.,University of Swansea | Walton A.S.,University of Leeds | Kepaptsoglou D.M.,Daresbury Laboratory | And 4 more authors.
Nanotechnology | Year: 2013

Knowing and controlling the resistivity of an individual nanowire (NW) is crucial for the production of new sensors and devices. For ZnO NWs this is poorly understood; a 108 variation in resistivity has previously been reported, making the production of reproducible devices almost impossible. Here, we provide accurate resistivity measurements of individual NWs, using a four-probe scanning tunnelling microscope (STM), revealing a dependence on the NW dimensions. To correctly interpret this behaviour, an atomic level transmission electron microscopy technique was employed to study the structural properties of the NWs in relation to three growth techniques: hydrothermal, catalytic and non-catalytic vapour phase. All NWs were found to be defect free and structurally equivalent; those grown with a metallic catalyst were free from Au contamination. The resistivity measurements showed a distinct increase with decreasing NW diameter, independent of growth technique. The increasing resistivity at small NW diameters was attributed to the dominance of surface states removing electrons from the bulk. However, a fundamental variance in resistivity (102) was observed and attributed to changes in occupied surface state density, an effect which is not seen with other NW materials such as Si. This is examined by a model to predict the effect of surface state occupancy on the measured resistivity and is confirmed with measurements after passivating the ZnO surface. Our results provide an understanding of the primary influence of the reactive nature of the surface and its dramatic effect on the electrical properties of ZnO NWs. © 2013 IOP Publishing Ltd.


McDonnell S.,University of Texas at Dallas | Brennan B.,University of Texas at Dallas | Bursa E.,University of Texas at Dallas | Wallace R.M.,University of Texas at Dallas | And 2 more authors.
Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures | Year: 2014

The thermal decomposition of the native GaSb oxides is studied using time resolved x-ray photoelectron spectroscopy with a temperature resolution of better than 1 K. The expected transfer of oxygen from Sb-O to Ga-O before the eventual desorption of all oxides is observed. However, an initial reaction resulting in the reduction of Sb2O3 along with the concurrent increase in both Ga2O3 and Sb2O 4 is detected in the temperature range of 450-525 K. Using the relative changes in atomic concentrations of the chemical species observed; the initial reaction pathway is proposed. © 2014 American Vacuum Society.


Grant
Agency: European Commission | Branch: FP7 | Program: MC-ITN | Phase: FP7-PEOPLE-2012-ITN | Award Amount: 3.88M | Year: 2012

Scanning probe microscopy(SPM) has now evolved to the point where not only is imaging and manipulation with single atom resolution achievable but the state of the art in the field involves sub-molecular and sub-atomic resolution: individual chemical bonds can be resolved, their properties measured, and their spatial symmetry exploited. SPM is, however, increasingly a victim of its own success. The wide availability of commercial instruments means that the technique is now very commonly seen as a routine imaging and characterisation tool. This unfortunately engenders a mindset amongst young researchers where they see an SPM as a black box and typically have a superficial understanding of the operating principles, theoretical principles, and current (or ultimate) limits of the technique. In turn, this black box mentality has severe implications for the health and competitiveness of the SPM - and, by extension nanoscience and nanotechnology - sectors in the ERA which rely fundamentally on creative innovation. ACRITAS directly counters this decline in the skills base and creativity of young researchers by providing an exciting and challenging environment for SPM training, spanning the public and private sectors and redefining the state of the art. A defining aspect of the network is its integration of scanning probe groups whose research is carried out under what might be termed `extreme conditions (ultrahigh vacuum, cryogenic temperatures) with teams of scientists who focus on interactions and control in biologically relevant environments. Although both communities use the same types of experimental techniques, there has traditionally been rather little communication between the two, largely because of different disciplinary biases. ACRITAS will act as a new and important bridge between the physical- and life sciences in advanced SPM and will thus be unique in the training it provides in a field which underpins a vast amount of 21st century science


Majzik Z.,ASCR Institute of Physics Prague | Setvin M.,ASCR Institute of Physics Prague | Bettac A.,Omicron NanoTechnology GmbH | Feltz A.,Omicron NanoTechnology GmbH | And 2 more authors.
Beilstein Journal of Nanotechnology | Year: 2012

We present the results of simultaneous scanning-tunneling and frequency-modulated dynamic atomic force microscopy measurements with a qPlus setup. The qPlus sensor is a purely electrical sensor based on a quartz tuning fork. If both the tunneling current and the force signal are to be measured at the tip, a cross-talk of the tunneling current with the force signal can easily occur. The origin and general features of the capacitive cross-talk will be discussed in detail in this contribution. Furthermore, we describe an experimental setup that improves the level of decoupling between the tunneling-current and the deflection signal. The efficiency of this experimental setup is demonstrated through topography and site-specific force/tunneling-spectroscopy measurements on the Si(111) 7×7 surface. The results show an excellent agreement with previously reported data measured by optical interferometric deflection. © 2012 Majzik et al.


Barrett N.,French Atomic Energy Commission | Conrad E.,Georgia Institute of Technology | Winkler K.,Omicron Nanotechnology GmbH | Kromker B.,Omicron Nanotechnology GmbH
Review of Scientific Instruments | Year: 2012

We demonstrate dark field imaging in photoelectron emission microscopy (PEEM) of heterogeneous few layer graphene (FLG) furnace grown on SiC(000-1). Energy-filtered, threshold PEEM is used to locate distinct zones of FLG graphene. In each region, selected by a field aperture, the k-space information is imaged using appropriate transfer optics. By selecting the photoelectron intensity at a given wave vector and using the inverse transfer optics, dark field PEEM gives a spatial distribution of the angular photoelectron emission. In the results presented here, the wave vector coordinates of the Dirac cones characteristic of commensurate rotations of FLG on SiC(000-1) are selected providing a map of the commensurate rotations across the surface. This special type of contrast is therefore a method to map the spatial distribution of the local band structure and offers a new laboratory tool for the characterisation of technically relevant, microscopically structured matter. © 2012 American Institute of Physics.


Barrett N.,CEA Saclay Nuclear Research Center | Winkler K.,Omicron Nanotechnology GmbH | Kromker B.,Omicron Nanotechnology GmbH | Conrad E.H.,Georgia Institute of Technology
Ultramicroscopy | Year: 2013

We present real and reciprocal space photoelectron emission microscopy (PEEM) results on few layer graphene using laboratory based He I and II radiation. The combination of a focused high-intensity source and high transmission PEEM electron optics provides good signal to noise ratios for the different modes of acquisition. We demonstrate work function mapping and secondary electron analysis, related to the graphene layer thickness, band structure imaging from micron scale regions by wave vector resolved PEEM (k-PEEM) and local secondary electron spectroscopy, giving information on the valence and conduction band states and the dispersion relations of the bands. Dark field PEEM is done by selecting the Dirac cone corresponding to the specific rotation of each graphene layer and allows spatial mapping of the commensurate rotation angles. The use of He II radiation increases the volume of reciprocal space accessible to k-PEEM and improves signal to background. The preferential linear polarization of the light source is used to investigate aspects of the electronic chirality near the Dirac cone. Recent developments in sample manipulation and cooling are presented. © 2013 Elsevier B.V.

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