| 1. |
- Schwenke, Jörg, et al.
(författare)
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Digital in-line holography on amplitude and phase objects prepared with electron beam lithography.
- 2012
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720. ; 247:2, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and characterization of amplitude and phase samples consisting of well defined Au or Al features formed on ultrathin silicon nitride membranes. The samples were manufactured using electron beam lithography, metallization and a lift-off technique, which allow precise lateral control and thickness of the metal features. The fabricated specimens were evaluated by conventional microscopy, atomic force microscopy and with the digital in-line holography set-up at the Lund Laser Centre. The latter uses high-order harmonic generation as a light source, and is capable of recovering both the shape and phase shifting properties of the samples. We report on the details of the sample production and on the imaging tests with the holography set-up.
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| 2. |
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| 3. |
- Schwenke, Jörg, et al.
(författare)
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Single-shot holography using high-order harmonics
- 2008
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Ingår i: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 55:16, s. 2723-2730
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Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates single-shot holography with ultrashort XUV pulses. The pulses are generated by high-harmonic generation in an Ar gas cell and focused to produce a strongly divergent reference beam suitable for in-line holography of micrometer size objects. The achieved intensity of the high-order harmonics in the XUV regime is sufficient for single-shot holography with good signal-to-noise ratio. A numerical algorithm is applied to reconstruct real images from the recorded holograms, which also includes an iterative process to reduce the twin-image blurring. Holograms and reconstructed images of microscope tips are presented and a description of the algorithm is given.
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| 4. |
- Persson, Olof, et al.
(författare)
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Interface characterization of metal-HfO2-InAs gate stacks using hard x-ray photoemission spectroscopy
- 2013
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 3:7
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Tidskriftsartikel (refereegranskat)abstract
- MOS devices based on III-V semiconductors and thin high-k dielectric layers offer possibilities for improved transport properties. Here, we have studied the interface structure and chemical composition of realistic MOS gate stacks, consisting of a W or Pd metal film and a 6- or 12-nm-thick HfO2 layer deposited on InAs, with Hard X-ray Photoemission Spectroscopy. In and As signals from InAs buried more than 18 nm below the surface are clearly detected. The HfO2 layers are found to be homogeneous, and no influence of the top metal on the sharp InAs-HfO2 interface is observed. These results bridge the gap between conventional photoemission spectroscopy studies on various metal-free model samples with very thin dielectric layers and realistic MOS gate stacks. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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| 5. |
- Persson, Olof, et al.
(författare)
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Scanning Tunneling Spectroscopy on InAs-GaSb Esaki Diode Nanowire Devices during Operation.
- 2015
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:6, s. 3684-3691
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Tidskriftsartikel (refereegranskat)abstract
- Using a scanning tunneling and atomic force microscope combined with in-vacuum atomic hydrogen cleaning we demonstrate stable scanning tunneling spectroscopy (STS) with nanoscale resolution on electrically active nanowire devices in the common lateral configuration. We use this method to map out the surface density of states on both the GaSb and InAs segments of GaSb-InAs Esaki diodes as well as the transition region between the two segments. Generally the surface shows small bandgaps centered around the Fermi level, which is attributed to a thin multielement surface layer, except in the diode transition region where we observe a sudden broadening of the bandgap. By applying a bias to the nanowire we find that the STS spectra shift according to the local nanoscale potential drop inside the wire. Importantly, this shows that we have a nanoscale probe with which we can infer both surface electronic structure and the local potential inside the nanowire and we can connect this information directly to the performance of the imaged device.
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| 6. |
- Suyatin, Dmitry, et al.
(författare)
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Strong Schottky barrier reduction at Au-catalyst/GaAs-nanowire interfaces by electric dipole formation and Fermi-level unpinning
- 2014
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Ingår i: Nature Communications. - London : Springer Science and Business Media LLC. - 2041-1723. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Nanoscale contacts between metals and semiconductors are critical for further downscaling of electronic and optoelectronic devices. However, realizing nanocontacts poses significant challenges since conventional approaches to achieve ohmic contacts through Schottky barrier suppression are often inadequate. Here we report the realization and characterization of low n-type Schottky barriers (~0.35 eV) formed at epitaxial contacts between Au-In alloy catalytic particles and GaAs-nanowires. In comparison to previous studies, our detailed characterization, employing selective electrical contacts defined by high-precision electron beam lithography, reveals the barrier to occur directly and solely at the abrupt interface between the catalyst and nanowire. We attribute this lowest-to-date-reported Schottky barrier to a reduced density of pinning states (~1017 m−2) and the formation of an electric dipole layer at the epitaxial contacts. The insight into the physical mechanisms behind the observed low-energy Schottky barrier may guide future efforts to engineer abrupt nanoscale electrical contacts with tailored electrical properties.
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| 7. |
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| 8. |
- Timm, Rainer, et al.
(författare)
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Current−Voltage Characterization of Individual As-Grown Nanowires Using a Scanning Tunneling Microscope
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:11, s. 5182-5189
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing semiconductor nanowires for (opto)- electronics requires exact knowledge of their current−voltage properties. We report accurate on-top imaging and I−V characterization of individual as-grown nanowires, using a subnanometer resolution scanning tunneling microscope with no need for additional microscopy tools, thus allowing versatile application. We form Ohmic contacts to InP and InAs nanowires without any sample processing, followed by quantitative measurements of diameter dependent I−V properties with a very small spread in measured values compared to standard techniques.
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| 9. |
- Timm, Rainer, et al.
(författare)
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Self-cleaning and surface chemical reactions during hafnium dioxide atomic layer deposition on indium arsenide
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) enables the ultrathin high-quality oxide layers that are central to all modern metal-oxide-semiconductor circuits. Crucial to achieving superior device performance are the chemical reactions during the first deposition cycle, which could ultimately result in atomic-scale perfection of the semiconductor-oxide interface. Here, we directly observe the chemical reactions at the surface during the first cycle of hafnium dioxide deposition on indium arsenide under realistic synthesis conditions using photoelectron spectroscopy. We find that the widely used ligand exchange model of the ALD process for the removal of native oxide on the semiconductor and the simultaneous formation of the first hafnium dioxide layer must be significantly revised. Our study provides substantial evidence that the efficiency of the self-cleaning process and the quality of the resulting semiconductor-oxide interface can be controlled by the molecular adsorption process of the ALD precursors, rather than the subsequent oxide formation.
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| 10. |
- Webb, James, et al.
(författare)
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High resolution scanning gate microscopy measurements on InAs/GaSb nanowire Esaki diode devices
- 2014
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 7:6, s. 877-887
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Tidskriftsartikel (refereegranskat)abstract
- Gated transport measurements are the backbone of electrical characterization of nanoscale electronic devices. Scanning gate microscopy (SGM) is one such gating technique that adds crucial spatial information, accessing the localized properties of semiconductor devices. Nanowires represent a central device concept due to the potential to combine very different materials. However, SGM on semiconductor nanowires has been limited to a resolution in the 50-100 nm range. Here, we present a study by SGM of newly developed III-V semiconductor nanowire InAs/GaSb heterojunction Esaki tunnel diode devices under ultra-high vacuum. Sub-5 nm resolution is demonstrated at room temperature via use of quartz resonator atomic force microscopy sensors, with the capability to resolve InAs nanowire facets, the InAs/GaSb tunnel diode transition and nanoscale defects on the device. We demonstrate that such measurements can rapidly give important insight into the device properties via use of a simplified physical model, without the requirement for extensive calculation of the electrostatics of the system. Interestingly, by precise spatial correlation of the device electrical transport properties and surface structure we show the position and existence of a very abrupt (<10 nm) electrical transition across the InAs/GaSb junction despite the change in material composition occurring only over 30-50 nm. The direct and simultaneous link between nanostructure composition and electrical properties helps set important limits for the precision in structural control needed to achieve desired device performance.
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