| 1. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Adsorption of Cs on InAs(111) surfaces
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:15, s. 5267-5270
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Tidskriftsartikel (refereegranskat)abstract
- Caesiated InAs(111)B (1 x 1) and InAs(111)A (2 x 2) surfaces have been studied by photoelectron spectroscopy. On the InAs(111)B a new (root 3 x root 3)R30 degrees reconstruction was observed. During Cs evaporation remarkably small changes are observed in the lone pair states, and no sign of an accumulation layer at the surface can be observed. Instead, the additional charge provided by Cs is rapidly transported towards the bulk. On the InAs(111)A cesium behaves as a typical electropositive alkali metal donator that enhances the already existing accumulation layer.
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| 2. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Correlated development of a (2x2) reconstruction and acharge accumulation layer on the InAs(111)-Bi surface
- 2011
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 605:1-2, s. 12-17
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the formation of a Bi induced (2x2) reconstruction on the InAs(111)Bsurface. In connection to the development of the (2x2) reconstruction, a two dimensionalcharge accumulation layer located in the bottom of the InAs conduction band appears as seenthrough a photoemission structure at the Fermi level. Not well ordered Bi layers do not inducea charge accumulation. The Bi induced reconstruction reduces the polarisation of the pristinesurface and changes the initial charge distribution. InAsBi alloying occurs below the surfacewhere Bi act as charge donor leading to the charge accumulation layer.
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| 3. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Electronic structure of bismuth terminated InAs(100)
- 2009
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 603:1, s. 190-196
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Tidskriftsartikel (refereegranskat)abstract
- Deposition of Bi onto (4 x 2)/c(8 x 2)-InAs(1 0 0) and subsequent annealing results in a (2 x 6) surface reconstruction as seen by low electron energy diffraction. The Bi condensation eliminates the original (4 x 2) Surface reconstruction and creates a new Structure including Bi-dimers. This Surface is metallic and hosts a charge accumulation layer seen through photoemission intensity near the Fermi level. The accumulation layer is located in the bulk region below the surface, but the intensity of the Fermi level structure is strongly dependent oil the Surface order.
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| 4. |
- Agnarsson, Björn, et al.
(författare)
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Investigation on the role of indium in the removal of metallic gallium from soft and hard sputtered GaN (0001) surfaces
- 2009
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:21, s. 6023-6026
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Tidskriftsartikel (refereegranskat)abstract
- Cleaning of GaN by argon sputtering and subsequent annealing introduces metallic gallium on the GaN surface. Once formed, this metallic gallium can be difficult to remove. it has a strong influence on the Fermi level position in the band gap and poses a problem for subsequent epitaxial growth on the surface. We present a method of removing metallic gallium from moderately damaged GaN surfaces by deposition of indium, and formation of an In-Ga alloy that can be desorbed by annealing at similar to 550 degrees C. After the In-Ga alloy has desorbed, photoemission spectra show that the Ga3d bulk component becomes narrower indicating a smoother and more homogeneous surface. This is also reflected in a sharper low energy electron diffraction pattern. On heavily damaged GaN surfaces, caused by hard sputtering, larger amount of metallic gallium forms after annealing at 600 degrees C. This gallium readily alloys with deposited indium, but the alloy does not desorb until a temperature of 840 degrees C is reached and even then, traces of both indium and metallic gallium could be found on the surface.
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| 5. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Creation of a metallic channel at the Sn/InAs(111)B surface studied using synchrotron-radiation photoelectron spectroscopy
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:205406
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Tidskriftsartikel (refereegranskat)abstract
- The properties of a Sn-induced two-dimensional electron gas at the As-terminated InAs(111)B(1x1) surface was studied by synchrotron radiation photoelectron spectroscopy. The two-dimensional electron gas reveals itself via a narrow structure at the Fermi level, visible close to normal emission for tin coverage in the range 0.5 to 2 monolayers. Although this electron gas exhibits properties that in several respects resemble those of intrinsic charge accumulation layers on free InAs surfaces, our observations suggest that the present electron gas is much more linked to the Sn adlayer.
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| 6. |
- Szamota-Leandersson, Karolina, 1968-
(författare)
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Electronic structure of clean and adsorbate-covered InAs surfaces
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is the result of investigations regarding the processes in InAs III-V semiconductor surfaces induced by additional charge incorporated by adsorbates. The aim of the project is to study the development of the accumulation layer on the metal/InAs(111)A/B surfaces and its electronic structure. InAs(111)A is indium-terminated and InAs(111)B is arsenic-terminated. In addition, InAs(100) is also studied. These three substrates are different; InAs(111)A has a (2x2)-termination, explained by an indium vacancy model, and the clean surface exhibits a two-dimensional electron gas (2DEG). InAs(111)B(1x1) is bulk-truncated and unreconstructed and does not host a 2DEG. InAs(100)(4x2)/c(8x2) exhibits a more covalent character of the surface bonds compared to InAs(111)A/B, and the surface is terminated by a complex reconstruction. Photoelectron spectroscopy and LEED (low energy electron diffraction) have been used as the main tools to study surfaces with sub-monolayer to monolayer amounts of adsorbates. A photoemission peak related to a two-dimensional electron gas appears close to the Fermi level. This 2DEG has in most cases InAs bulk properties, since it is located in the InAs conduction band. A systematic study of core levels and valence bands reveals that the appearance of the 2DEGs is a complex process connected to the surface order. Adsorption of lead, tin or bismuth on InAs(111)B(1x1) induces emission from a 2DEG, but only at monolayer coverage and when the surface is ordered. Cobalt reacts strongly with InAs forming InCo islands and no accumulation is observed. Examination of Cs/InAs(111)B does not reveal any 2DEG and the surface reaction is strongly related to the clean surface stabilization process. Examination of the In-terminated InAs(111)A(2x2) surface shows that In reacts strongly with cobalt and tin adatoms and with oxygen in cases of large exposure, which decreases the 2DEG intensity, while adatoms of cesium and small doses of oxygen enhance the emission from the 2DEG. InAs(100) is terminated with one kind of atom - the InAs(100)(4x2)/c(8x2) is indium terminated. Bismuth creates dimers on the surface and a 2DEG is observed. More generally, this thesis describes some of the general physical background applied to surface science and 2DEG. The first part is a general overview of the processes on the surface. The second part concentrates on the methods related to preparation of samples, and the third part on the measurement methods. The photoelectron spectroscopy part concerns the theory used in mapping electronic structure. The inserted figures are taken from different experiments, including results for InAs(111)A not previously published.
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| 7. |
- Szamota Leandersson, Karolina, et al.
(författare)
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Interaction between oxygen and InAs(111) surfaces, influence of the electron accumulation layer
- 2003
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 212, s. 589-594
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of InAs(1 1 1) surfaces has been studied by photoelectron spectroscopy. Both the InAs(1 1 1)A and the InAs(1 1 1)B surfaces are studied and it. is found that the initial oxidation follows different paths for the two surfaces. At low oxygen exposures of the A face the Fermi level structure, which is due to the electron accumulation layer, increases in intensity. On the B-side the intensity of the lone pair surface state decreases with increasing oxygen exposure. For larger exposures significant changes can be observed in the line shape of the In 4d and the As 3d core levels.
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| 8. |
- Szamota-Leandersson, Karolina, et al.
(författare)
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Pb induced charge accumulation on InAs(111)B
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:15, s. 3246-3252
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Tidskriftsartikel (refereegranskat)abstract
- The Pb/InAs(111)B interface has been studied by synchrotron radiation photoelectron spectroscopy (SR-PES) of valence band and ln4d, As3d and Pb5d core levels. Room temperature deposition of similar to 1 ML of Pb on InAs(I I I)B leads to an ordered overlayer that induces a metallic channel at the surface, as seen through a weak emission in the vicinity of the Fermi level. Its narrow localization in reciprocal space supports the formation of a two-dimensional free electron gas (2DEG) in the surface region. It is proposed that the adsorbed metal layer swaps the initial polarisation of the surface and thus pulls electrons back to the surface. This charge re-arrangement increases the charge density in the accumulation layer and reduces the screening length and thus the depth of the potential well at the surface.
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