| 1. |
- Deppert, Knut, et al.
(författare)
-
Feasibility study of nanoparticle synthesis from powders of compounds with incongruent sublimation behavior by the evaporation/condensation method
- 1998
-
Ingår i: Nanostructured Materials. - 0965-9773. ; 10:4, s. 565-573
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate the feasibility of a fabrication route to produce nanocrystals of compound material with incongruent sublimation behavior via the simple evaporation of the powder of the compound. The generation of stoichiometric particles would only be possible if the particle formation occurs at temperatures below the incongruent sublimation point. Our experiments, done on three different III-V compounds, show that the simple evaporation of the powder of those materials to obtain stoichiometric particles is not possible. Particle formation does not start at temperatures below the incongruent sublimation point. Particles synthesized consisted not of the compound but almost entirely of the more volatile group-Velement, leading to a change in the composition of the source material and thus to irreproducible behavior.
|
|
| 2. |
- Gooth, Johannes, et al.
(författare)
-
Local Magnetic Suppression of Topological Surface States in Bi2Te3 Nanowires
- 2016
-
Ingår i: ACS Nano. - Washington : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 10:7, s. 7180-7188
-
Tidskriftsartikel (refereegranskat)abstract
- Locally induced, magnetic order on the surface of a topological insulator nanowire could enable room-temperature topological quantum devices. Here we report on the realization of selective magnetic control over topological surface states on a single facet of a rectangular Bi2Te3 nanowire via a magnetic insulating Fe3O4 substrate. Low-temperature magnetotransport studies provide evidence for local time-reversal symmetry breaking and for enhanced gapping of the interfacial 1D energy spectrum by perpendicular magnetic-field components, leaving the remaining nanowire facets unaffected. Our results open up great opportunities for development of dissipation-less electronics and spintronics.
|
|
| 3. |
- Gooth, Johannes, et al.
(författare)
-
Thermoelectric performance of classical topological insulator nanowires
- 2015
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 30:1
-
Tidskriftsartikel (refereegranskat)abstract
- There is currently substantial effort being invested into creating efficient thermoelectric (TE) nanowires based on topological insulator (TI) chalcogenide-type materials. A key premise of these efforts is the assumption that the generally good TE properties that these materials exhibit in bulk form will translate into similarly good or even better TE performance of the same materials in nanowire form. Here, we calculate TE performance of TI nanowires based on Bi2Te3, Sb2Te3 and Bi2Se3 as a function of diameter and Fermi level. We show that the TE performance of TI nanowires does not derive from the properties of the bulk material in a straightforward way. For all investigated systems the competition between surface states and bulk channel causes a significant modification of the TE transport coefficients if the diameter is reduced into the sub 10 mu m range. Key aspects are that the surface and bulk states are optimized at different Fermi levels or have different polarity as well as the high surface to volume ratio of the nanowires. This limits the maximum TE performance of TI nanowires and thus their application in efficient TE devices.
|
|
| 4. |
- Gooth, Johannes, et al.
(författare)
-
Transition to the quantum hall regime in InAs nanowire cross-junctions
- 2019
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 34
-
Tidskriftsartikel (refereegranskat)abstract
- We present a low-temperature electrical transport study on four-terminal ballistic InAs nanowire cross-junctions in magnetic fields aligned perpendicular to the cross-plane. Two-terminal longitudinal conductance measurements between opposing contact terminals reveal typical 1D conductance quantization at zero magnetic field. As the magnetic field is applied, the 1D bands evolve into hybrid magneto-electric sub-levels that eventually transform into Landau levels for the widest nanowire devices investigated (width = 100 nm). Hall measurements in a four-terminal configuration on these devices show plateaus in the transverse Hall resistance at high magnetic fields that scale with (ve 2/h)−1. e is the elementary charge, h denotes Planck's constant and v is an integer that coincides with the Landau level index determined from the longitudinal conductance measurements. While the 1D conductance quantization in zero magnetic field is fragile against disorder at the NW surface, the plateaus in the Hall resistance at high fields remain robust as expected for a topologically protected Quantum Hall phase.
|
|
| 5. |
|
|
| 6. |
- Johansson, Anders, 1976-
(författare)
-
Template-Based fabrication of Nanostructured Materials
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Materials prepared on the nanoscale often exhibit many different properties compared to the same materials in their bulk-state. Interest in nanostructured materials has increased because of these properties in fields such as microelectronics, catalysis, optics and sensors. This increased interest in nanostructured materials calls for new and more precise fabrication techniques.This thesis describes how to use the porous anodic aluminium oxide as a template for the fabrication of a variety of nanostructured materials. Palladium and copper nanoparticles were deposited along the pore walls in anodic aluminum oxide using electroless deposition and atomic layer deposition. In both cases, it was possible to control the size of the nanoparticles by carefully monitoring the deposition parameters. The thesis also describes how Prussian blue nanoparticles and nanotubes can be fabricated using the anodic aluminium oxide as a template. The deposition of Prussian blue was performed by a sequential wet-chemical method. By using atomic layer deposition, it was also possible to deposit thin films of amorphous Nb2O5 on the pore walls. When the template was removed by etching, freestanding nanotubes were obtained. The anodic aluminium oxide membrane was also used as a mask for high energy (MeV) ion irradiation of an underlying substrate. The tracks produced were etched away with hydrogen fluoride. In this way, it was possible to transfer the highly ordered porous pattern from the mask onto other oxides such as SiO2 and TiO2.All fabricated structures were characterized using a variety of analysis techniques: scanning electron microscopy for evaluating sample morphology; transmission electron microscopy for better resolved investigations of the morphology; X-ray diffraction to assess crystallinity; energy dispersive spectroscopy and X-ray fluorescence spectroscopy to determine the elemental composition and identify possible contaminants.The general aim of the work described in this thesis has been to create a set of tools for use in the fabrication of a variety of nanostructured materials, whose dimensions composition can be tailored by selecting appropriate fabrication methods and parameters.
|
|
| 7. |
- Pohl, Darius, et al.
(författare)
-
Atom size electron vortex beams with selectable orbital angular momentum
- 2017
-
Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- The decreasing size of modern functional magnetic materials and devices cause a steadily increasing demand for high resolution quantitative magnetic characterization. Transmission electron microscopy (TEM) based measurements of the electron energy-loss magnetic chiral dichroism (EMCD) may serve as the needed experimental tool. To this end, we present a reliable and robust electron-optical setup that generates and controls user-selectable single state electron vortex beams with defined orbital angular momenta. Our set-up is based on a standard high-resolution scanning TEM with probe aberration corrector, to which we added a vortex generating fork aperture and a miniaturized aperture for vortex selection. We demonstrate that atom size probes can be formed from these electron vortices and that they can be used for atomic resolution structural and spectroscopic imaging - both of which are prerequisites for future atomic EMCD investigations.
|
|
| 8. |
- Schneider, Sebastian, et al.
(författare)
-
Simple method for optimization of classical electron magnetic circular dichroism measurements : The role of structure factor and extinction distances
- 2018
-
Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
-
Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic circular dichroism (EMCD), the electron wave analog of x-ray magnetic circular dichroism (XMCD), allows for the element specific measurement of the spin and orbital magnetic moments with up to nanometer resolution. However, due to dynamical diffraction effects, the signal-to-noise ratios of EMCD spectra are often very low. We describe a simple set of rules, how to set up a geometry for a classical EMCD experiment on an arbitrary crystal structure to get a maximum dichroic signal. The procedure is based on an evaluation of the structure factor and extinction distances. Proof-of-concept simulations and experiments on a FeGe crystal present a successful test of these guidelines.
|
|
| 9. |
- Wu, Phillip, et al.
(författare)
-
Large Thermoelectric Power Factor Enhancement Observed in InAs Nanowires.
- 2013
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:9, s. 4080-4086
-
Tidskriftsartikel (refereegranskat)abstract
- We report the observation of a thermoelectric power factor in InAs nanowires that exceeds that predicted by a single-band bulk model by up to an order of magnitude at temperatures below about 20 K. We attribute this enhancement effect not to the long-predicted 1D subband effects but to quantum-dot-like states that form in electrostatically nonuniform nanowires as a result of interference between propagating states and 0D resonances.
|
|
