| 1. |
- Petersson, L.-G., et al.
(författare)
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A Pd-MOS structure as a hydrogen sensor in catalytic reactions
- 1984
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; A2, s. 1032-
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Tidskriftsartikel (refereegranskat)abstract
- By letting a catalytic reaction involving hydrogen occur on the Pd gate metal of a Pd–MOS structure the amount of hydrogen atoms on the surface can be monitored without any external probes by measuring the dipole induced by the hydrogen atoms that have diffused to the Pd–SiO2 interface. The ability to work over a wide pressure range (10-11 Torr to atm) makes the Pd–MOS structure an interesting device in the study of catalytic reactions. In this article, we will give a short review of some of the many applications of this component. We have combined this technique with other surface sensitive techniques such as UPS, XPS, work function measurements and mass spectrometry and, e.g., studied how the hydrogen adsorption–desorption processes are influenced by alloying the Pd surface with various amounts of Ag, thereby also changing the distribution of d states close to Fermi energy. We have also studied the H2+O→H2O reaction on Pd. It, e.g., turns out that the water reaction rate reaches a maximum when the oxygen coverage approaches zero and that the hydrogen atoms on the surface have a larger lateral mobility.
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| 2. |
- Ahlberg, Patrik, et al.
(författare)
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Toward synthesis of oxide films on graphene with sputtering based processes
- 2016
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 34:4
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Tidskriftsartikel (refereegranskat)abstract
- The impact of energetic particles associated with a sputter deposition process may introduce damage to single layer graphene films, making it challenging to apply this method when processing graphene. The challenge is even greater when oxygen is incorporated into the sputtering process as graphene can be readily oxidized. This work demonstrates a method of synthesizing ZnSn oxide on graphene without introducing an appreciable amount of defects into the underlying graphene. Moreover, the method is general and applicable to other oxides. The formation of ZnSn oxide is realized by sputter deposition of ZnSn followed by a postoxidation step. In order to prevent the underlying graphene from damage during the initial sputter deposition process, the substrate temperature is kept close to room temperature, and the processing pressure is kept high enough to effectively suppress energetic bombardment. Further, in the subsequent postannealing step, it is important not to exceed temperatures resulting in oxidation of the graphene. The authors conclude that postoxidation of ZnSn is satisfactorily performed at 300 degrees C in pure oxygen at reduced pressure. This process results in an oxidized ZnSn film while retaining the initial quality of the graphene film.
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| 3. |
- ANDERSEN, JN, et al.
(författare)
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SURFACE RELATED CORE LEVEL SHIFTS FOR THE SI(111)SQUARE-ROOT-3X SQUARE-ROOT-3 - AL SYSTEM
- 1991
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 9:4, s. 2384-2387
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Tidskriftsartikel (refereegranskat)abstract
- The Si(111) square-root 3 x square-root 3:Al reconstruction has been studied by surface sensitive high resolution core level spectroscopy. It is shown that three components are needed to fit the Si 2p spectra. The Al2p emission is found to consist of more than one component and it is argued that this is related to defects in the overlayer.
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| 4. |
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| 5. |
- Astromskas, Gvidas, et al.
(författare)
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Electrical characterization of thin InAs films grown on patterned W/GaAs substrates
- 2009
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 27:5, s. 2222-2226
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Tidskriftsartikel (refereegranskat)abstract
- InAs has been grown on W-GaAs patterned substrates using metal organic vapor phase epitaxy. It is shown that the W pattern guides the nucleation of the InAs on the GaAs substrate and that the islands formed may be used to embed metal features in a hybrid InAs/GaAs structure. A lower resistance (factor of 2) was measured for the hybrid structures as compared to reference structures. The reduction in the resistance is attributed to an increased carrier concentration as observed from Hall measurements on devices with different tungsten densities. Cross-sectional transmission electron microscopy investigations reveal a void-free overgrowth above the metal despite the large mismatch of the InAs/GaAs system. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3222859]
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| 6. |
- Astromskas, Gvidas, et al.
(författare)
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Thin InAs membranes and GaSb buffer layers on GaAs(001) substrates
- 2012
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 30:5
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Tidskriftsartikel (refereegranskat)abstract
- Thin InAs layers and membranes are fabricated on GaAs substrates using GaSb buffer layers grown by MOVPE. The quality of the GaSb buffer layers is optimized and epitaxial InAs layers are grown on GaSb layers of various thickness. The best GaSb buffer layers are obtained for a nucleation temperature of 450 degrees C and a subsequent growth temperature of 570 degrees C with a V/III ratio of 3, as confirmed by both the structural (high-resolution XRD, AFM) and electrical (Hall) measurements. Furthermore, a clear relationship between the structural quality of the GaSb and InAs layers is established. Finally, free-standing InAs structures are fabricated where Hall measurements reveal a mobility that depends on the film thickness.
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| 7. |
- Awan, Kashif Masud, et al.
(författare)
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Nanostructuring of GaAs with tailored topologies using colloidal lithography and dry etching
- 2014
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 32:2, s. 021801-
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on the fabrication of GaAs nanopillars with different profiles/topologies using colloidal lithography and dry etching. GaAs nanopillars with different shapes and dimensions were successfully fabricated using inductively coupled plasma reactive ion etching. Two different etch chemistries CH4/H-2/Cl-2 and Ar/Cl-2 were investigated. The fabricated nanopillar arrays had a typical period of similar to 500 nm, and the depths could be varied from a few nanometers to 4 mu m. The CH4/H-2/Cl-2 chemistry with optimized gas flows and plasma powers is shown to produce nanopillars with smooth sidewalls compared to those fabricated with the Ar/Cl-2 chemistry. The GaAs nanopillar arrays have appreciably lower reflectivities in the measured wavelength range from 400 to 850 nm and are typically one order of magnitude lower compared to planar GaAs, which shows their potential for photovoltaic applications.
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| 8. |
- Bell, David C., et al.
(författare)
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Precision material modification and patterning with He ions
- 2009
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 27:6, s. 2755-2758
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on the use of a helium ion microscope as a potential technique for precise nanopatterning. Combined with an automated pattern generation system, they demonstrate controlled etching and patterning of materials, giving precise command over the geometery of the modified nanostructure. After the determination of suitable doses, sharp edge profiles and clean etching of areas in materials were observed. In this article they present examples of patterning on SiO(2) and graphene, which is particularly relevant. This technique could be an avenue for precise material modification for future graphene based device fabrication. The technique has the potential to revolutionize the way that very thin, one-atomic layer materials are modified in a controlled and predictable way.
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| 9. |
- Berrier, Audrey, et al.
(författare)
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Accumulated sidewall damage in dry etched photonic crystals
- 2009
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 27:4, s. 1969-1975
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Tidskriftsartikel (refereegranskat)abstract
- Evidence for accumulated damage is provided by investigating the effect of etch duration on the carrier lifetime of an InGaAsP quantum well (QW) inside the InP-based photonic crystal (PhC) structures. It is found that once the quantum well is etched through, additional etching reduces the carrier lifetimes from 800 to 70 ps. The surface recombination velocity (SRV) at the exposed hole sidewalls is determined from the measured carrier lifetimes of the PhC fields with different lattice parameters. The observed variation in the SRV with etch duration also confirms the presence of accumulated sidewall damage. It increases from 6x10(3) to 1.2x10(5) cm s(-1) as the etching time increases from 3 to 50 min. A geometric model based on sputtering theory and on the evolution of the hole shape is developed to explain the accumulation of sidewall damage. The model is used to estimate the number of impact events from sputtered species reaching the QW sidewalls, and the variation in the accumulated impact events with etch duration is shown to be qualitatively consistent with the experimental observations. Finally, the results suggest a new method for tailoring the carrier lifetimes in PhC membrane structures.
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| 10. |
- Berrier, Audrey, et al.
(författare)
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Characterization of the feature-size dependence in Ar/Cl2 chemically assisted ion beam etching of InP-based photonic crystal devices
- 2007
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 25:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The authors address feature-size dependence in Ar/Cl-2, chemically assisted ion beam etching (CAIBE) in the context of the fabrication of photonic crystal (PhC) structures. They systematically investigate the influence of various parameters such as hole diameter (115-600 nm), etch duration (10-60 min), and ion beam energy (300-600 eV) on PhC etching in InP with Ar/Cl-2, CAIBE. For a 60 min etching at an Ar-ion energy of 400 eV, the authors report an etch depth of 5 mu m for hole diameters d larger than 300 nm; the etch depth is in excess of 3 mu m for d larger than 200 nm. The evolution of roughness at the bottom of the etched holes and its dependence on hole size and etching conditions,is discussed. The physical mechanism of the observed feature-size dependent etching (FSDE) is then discussed and the effect of the process parameters is qualitatively understood using a model combining the effect of ion sputtering and surface chemical reactions. Finally, the effect of FSDE on the PhC optical properties is assessed by measuring the quality factor of one-dimensional Fabry-Perot PhC cavities. The measured quality factors show a clear trend with the etch depth: the cavity Q increases as the etch depth increases.
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