| 1. |
|
|
| 2. |
- Hilner, Emelie, et al.
(författare)
-
Au wetting and nanoparticle stability on GaAs(111)B
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89
-
Tidskriftsartikel (refereegranskat)abstract
- Au nanoparticles and Au films for growth of nanowires on the GaAs(111)B surface have been studied by a combination of experimental and theoretical techniques. If Au is present in either form, annealing to temperatures relevant for nanowire growth results in the formation of a thin Au wetting layer. Based on density functional theory calculations and experimental data, a structural model is proposed with an Au atom on every third threefold hollow hcp site of the Ga lattice. The authors observe that the stability of Au nanoparticles is governed by the presence of the wetting layer and outdiffusion of Au from the nanoparticles.
|
|
| 3. |
- Hilner, Emelie
(författare)
-
Characterization of Surfaces Relevant to Nanotechnology
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis investigations of the structure and dynamics of semiconductor surfaces relevant for the synthesis of nanostructures are presented. The studies were performed using Scanning Tunneling Microscopy (STM), Low Energy Electron Diffraction (LEED), and Spectroscopic PhotoEmission and Low Energy Electron Microcopy (SPELEEM). Nanostructures are defined as objects with one or more dimensions on the nanometer scale. Examples are the rod shaped nanowires synthesized by epitaxial crystal growth methods or the many different structures that can be fabricated by the Focused Ion Beam (FIB) technique. Nanostructures have many applications in devices for electronics, optoelectronics and life sciences. One part of the thesis is dedicated to studies of substrates used in nanowire growth. Diffusion of growth materials on the substrate and nanowire surfaces has a strong effect on the morphology of the resulting wires. Studies of the atomic scale structure of these surfaces are therefore important. The presence of gold particles used as seeds for nanowire growth may also in some cases alter the surface structure. In this thesis studies of the structures of GaAs(111)B, InAs(111)B, and GaP(111)B with and without gold particles and films are presented. A gold free growth method for III-V nanowires on Si have also been investigated. In this case an organic film is used to create an oxide template with patches on which the nanowires can nucleate and grow. Another part of the thesis is dedicated to the characterization of nanostructures. A method for studying the surfaces of III-V nanowires with STM was developed. Atomic scale images and Scanning Tunneling Spectroscopy (STS) measurements on surfaces of InAs/InP heterostructure nanowires are presented. Nanogrooves fabricated by FIB milling with Ga+ ions on Si were characterized with respect to their surface chemistry. It was found that a Ga layer forms in the grooves during milling. At temperatures as low as 150C Ga diffuses out of the grooves and spreads several micrometers on the substrate surface. Finally the thermal decomposition of the GaP(111)B surface has been investigated. Ga droplets form after annealing at a temperature above the maximum temperature for congruent evaporation. The droplets move across the surface, perpendicular to and uphill the steps introduced by the wafer miscut. When gold nanoparticles are deposited on the surface, the droplet movement become random instead of unidirectional.
|
|
| 4. |
- Hilner, Emelie, et al.
(författare)
-
Direct Atomic Scale Imaging of III-V Nanowire Surfaces.
- 2008
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:11, s. 3978-3982
-
Tidskriftsartikel (refereegranskat)abstract
- We have succeeded in direct atomic scale imaging of the exterior surfaces of III-V nanowires by scanning tunneling microscopy (STM). By using atomic hydrogen, we expose the crystalline surfaces of InAs nanowires with regular InP segments in vacuum while retaining the wire morphology. We show images with atomic resolution of the two major types of InAs wurtzite nanowire surface facets and scanning tunneling spectroscopy (STS) data. Ab initio calculations of the lowest energy surface structures and simulated STM images, agree very well with experiments.
|
|
| 5. |
- Hilner, Emelie, et al.
(författare)
-
Faceting and surface reconstruction of the GaP(111)B surface
- 2010
-
Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421. ; 42:10-11, s. 1524-1527
-
Konferensbidrag (refereegranskat)abstract
- Using Low Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM) we have investigated the structure of the GaP(111)B surface. We have previously studied the formation of Ga droplets on GaP(111)B above the maximum temperature for congruent evaporation. In the present work, we investigate the nanometer-sized pyramid-shaped crystallites that are found on the GaP(111)B surface and that were only briefly mentioned in our previous paper. We suggest that the pyramids have {-1-10} side facets. We also find that the size of the pyramids decrease upon annealing. Finally, we present a model for the atomic scale structure of the flat GaP(111)B surface found between the pyramids. Copyright (C) 2010 John Wiley & Sons, Ltd.
|
|
| 6. |
|
|
| 7. |
- Hilner, Emelie, et al.
(författare)
-
Ordering of the Nanoscale Step Morphology As a Mechanism for Droplet Self-Propulsion.
- 2009
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9, s. 2710-2714
-
Tidskriftsartikel (refereegranskat)abstract
- We establish a new mechanism for self-propelled motion of droplets, in which ordering of the nanoscale step morphology by sublimation beneath the droplets themselves acts to drive them perpendicular and up the surface steps. The mechanism is demonstrated and explored for Ga droplets on GaP(111)B, using several experimental techniques allowing studies of the structure and dynamics from micrometers to the atomic scale. We argue that the simple assumptions underlying the propulsion mechanism make it relevant for a wide variety of materials systems.
|
|
| 8. |
- Hilner, Emelie, et al.
(författare)
-
Surface structure and morphology of InAs(111)B with/without gold nanoparticles annealed under arsenic or atomic hydrogen flux
- 2010
-
Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 604:3-4, s. 354-360
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the structure and morphology of the InAs(1 1 1)B surface using Low Energy Electron Diffraction (LEED), Scanning Tunneling Microscopy (STM) and Scanning Electron Microscopy (SEM). The surface was prepared by annealing in the presence of an arsenic or atomic hydrogen pressure. A (2 x 2) reconstruction that changes into a (1 x 1) unreconstructed surface after prolonged annealing was observed irrespective of preparation method, while the surface morphology was distinctly different in the two cases. Detailed atomic scale models are proposed to explain the behavior. Deposition of An aerosol nanoparticles on the sample prior to annealing was found to have no effect on the surface reconstruction. The Au particles were found to sink into the surface. (C) 2009 Elsevier B.V. All rights reserved.
|
|
| 9. |
|
|
| 10. |
- Mandl, Bernhard, et al.
(författare)
-
Growth Mechanism of Self-Catalyzed Group III-V Nanowires.
- 2010
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:Online October 7, 2010, s. 4443-4449
-
Tidskriftsartikel (refereegranskat)abstract
- Group III-V nanowires offer the exciting possibility of epitaxial growth on a wide variety of substrates, most importantly silicon. To ensure compatibility with Si technology, catalyst-free growth schemes are of particular relevance, to avoid impurities from the catalysts. While this type of growth is well-documented and some aspects are described, no detailed understanding of the nucleation and the growth mechanism has been developed. By combining a series of growth experiments using metal-organic vapor phase epitaxy, as well as detailed in situ surface imaging and spectroscopy, we gain deeper insight into nucleation and growth of self-seeded III-V nanowires. By this mechanism most work available in literature concerning this field can be described.
|
|
