| 1. |
- D'Acunto, Giulio, et al.
(författare)
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Atomic Layer Deposition of Hafnium Oxide on InAs : Insight from Time-Resolved in Situ Studies
- 2020
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Ingår i: ACS Applied Electronic Materials. - : American Chemical Society (ACS). - 2637-6113. ; 2:12, s. 3915-3922
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Tidskriftsartikel (refereegranskat)abstract
- III-V semiconductors, such as InAs, with an ultrathin high-κ oxide layer have attracted a lot of interests in recent years as potential next-generation metal-oxide-semiconductor field-effect transistors, with increased speed and reduced power consumption. The deposition of the high-κ oxides is nowadays based on atomic layer deposition (ALD), which guarantees atomic precision and control over the dimensions. However, the chemistry and the reaction mechanism involved are still partially unknown. This study reports a detailed time-resolved analysis of the ALD of high-κ hafnium oxide (HfOx) on InAs(100). We use ambient pressure X-ray photoemission spectroscopy and monitor the surface chemistry during the first ALD half-cycle, i.e., during the deposition of the metalorganic precursor. The removal of In and As native oxides, the adsorption of the Hf-containing precursor molecule, and the formation of HfOx are investigated simultaneously and quantitatively. In particular, we find that the generally used ligand exchange model has to be extended to a two-step model to properly describe the first half-cycle in ALD, which is crucial for the whole process. The observed reactions lead to a complete removal of the native oxide and the formation of a full monolayer of HfOx already during the first ALD half-cycle, with an interface consisting of In-O bonds. We demonstrate that a sufficiently long duration of the first half-cycle is essential for obtaining a high-quality InAs/HfO2 interface.
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| 2. |
- Ertürk Bergdahl, Gizem, et al.
(författare)
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In Vivo Detection and Absolute Quantification of a Secreted Bacterial Factor from Skin Using Molecularly Imprinted Polymers in a Surface Plasmon Resonance Biosensor for Improved Diagnostic Abilities
- 2019
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Ingår i: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 4:3, s. 717-725
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a surface plasmon resonance (SPR) biosensor was developed for the detection and quantification of a secreted bacterial factor (RoxP) from skin. A molecular imprinting method was used for the preparation of sensor chips and five different monomer-cross-linker compositions were evaluated for sensitivity, selectivity, affinity, and kinetic measurements. The most promising molecularly imprinted polymer (MIP) was characterized by using scanning electron microscopy, atomic force microscopy, and cyclic voltammetry. Limit of detection (LOD) value was calculated as 0.23 nM with an affinity constant of 3.3 × 10-9 M for the promising MIP. Besides being highly sensitive, the developed system was also very selective for the template protein RoxP, proven by the calculated selectivity coefficients. Finally, absolute concentrations of RoxP in several skin swabs were analyzed by using the developed MIP-SPR biosensor and compared to a competitive ELISA. Consequently, the developed system offers a very efficient tool for the detection and quantification of RoxP as an early indicator for some oxidative skin diseases especially when they are present in low-abundance levels (e.g., skin samples).
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| 3. |
- Heurlin, Magnus, et al.
(författare)
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Structural Properties of Wurtzite InP-InGaAs Nanowire Core-Shell Heterostructures
- 2015
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:4, s. 2462-2467
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Tidskriftsartikel (refereegranskat)abstract
- We report on growth and characterization of wurtzite InP-In1-xGaxAs core-shell nanowire heterostructures. A range of nanowire structures with different Ga concentration in the shell was characterized with transmission electron microscopy and X-ray diffraction. We found that the main part of the nanowires has a pure wurtzite crystal structure, with occasional stacking faults occurring only at the top and bottom. This allowed us to determine the structural properties of wurtzite In1-xGaxAs. The InP-In1-xGaxAs core-shell nanowires show a triangular and hexagonal facet structure of {1100} and {10 (10) over bar} planes. X-ray diffraction measurements showed that the core and the shell are pseudomorphic along the c-axis, and the strained axial lattice constant is closer to the relaxed In1-xGaxAs shell. Microphotoluminescence measurements of the nanowires show emission in the infrared regime, which makes them suitable for applications in optical communication.
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| 4. |
- Liu, Yen-Po, et al.
(författare)
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Hydrogen plasma enhanced oxide removal on GaSb planar and nanowire surfaces
- 2022
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332.
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Tidskriftsartikel (refereegranskat)abstract
- Due to its high hole-mobility, GaSb is a highly promising candidate for high-speed p-channels in electronic devices. However, GaSb exhibits a comparably thick native oxide causing detrimental interface defects, which has been proven difficult to remove. Here we present full oxide removal from GaSb surfaces using effective hydrogen plasma cleaning, studied in-situ by synchrotron-based X-ray photoelectron spectroscopy under ultrahigh vacuum (UHV). GaSb nanowires turn out to be cleaned faster and more efficiently than planar substrates. Since the UHV conditions are not scalable for industrial sample processing, H-plasma cleaning is furthermore used as pre-treatment prior to atomic layer deposition (ALD) of a protective high-k layer to demonstrate the use of the cleaning step in a more realistic fabrication situation. We observe a cleaning effect of the H-plasma even in the ALD environment, but we also find residual Ga- and Sb-oxides at the GaSb-high-k interface, which we attribute to re-oxidation of the cleaned surface. Our results indicate that an improved control of the ALD reactor vacuum environment could realize oxide- and defect-free interfaces in GaSb-based electronics.
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| 5. |
- McKibbin, Sarah R., et al.
(författare)
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In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering
- 2019
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Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 12:1, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N2 gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 105 particles/cm3) corresponding to a volume fraction below 3 × 10–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions. [Figure not available: see fulltext.].
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| 6. |
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| 7. |
- 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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| 8. |
- Troian, Andrea, et al.
(författare)
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InAs-oxide interface composition and stability upon thermal oxidation and high-k atomic layer deposition
- 2018
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 8:12
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Tidskriftsartikel (refereegranskat)abstract
- Defects at the interface between InAs and a native or high permittivity oxide layer are one of the main challenges for realizing III-V semiconductor based metal oxide semiconductor structures with superior device performance. Here we passivate the InAs(100) substrate by removing the native oxide via annealing in ultra-high vacuum (UHV) under a flux of atomic hydrogen and growing a stoichiometry controlled oxide (thermal oxide) in UHV, prior to atomic layer deposition (ALD) of an Al2O3 high-k layer. The semiconductor-oxide interfacial stoichiometry and surface morphology are investigated by synchrotron based X-ray photoemission spectroscopy, scanning tunneling microscopy, and low energy electron diffraction. After thermal oxide growth, we find a thin non-crystalline layer with a flat surface structure. Importantly, the InAs-oxide interface shows a significantly decreased amount of In3+, As5+, and As0 components, which can be correlated to electrically detrimental defects. Capacitance-voltage measurements confirm a decrease of the interface trap density in gate stacks including the thermal oxide as compared to reference samples. This makes the concept of a thermal oxide layer prior to ALD promising for improving device performance if this thermal oxide layer can be stabilized upon exposure to ambient air.
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| 9. |
- Wu, Jun, et al.
(författare)
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Low Trap Density in InAs/High-k Nanowire Gate Stacks with Optimized Growth and Doping Conditions
- 2016
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:4, s. 2418-2425
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we correlate the growth of InAs nanowires with the detailed interface trap density (Dit) profile of the vertical wrap-gated InAs/high-k nanowire semiconductor-dielectric gate stack. We also perform the first detailed characterization and optimization of the influence of the in situ doping supplied during the nanowire epitaxial growth on the sequential transistor gate stack quality. Results show that the intrinsic nanowire channels have a significant reduction in Dit as compared to planar references. It is also found that introducing tetraethyltin (TESn) doping during nanowire growth severely degrades the Dit profile. By adopting a high temperature, low V/III ratio tailored growth scheme, the influence of doping is minimized. Finally, characterization using a unique frequency behavior of the nanowire capacitance-voltage (C-V) characteristics reveals a change of the dopant incorporation mechanism as the growth condition is changed.
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| 10. |
- Yngman, Sofie, et al.
(författare)
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GaN nanowires as probes for high resolution atomic force and scanning tunneling microscopy
- 2019
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 90
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Tidskriftsartikel (refereegranskat)abstract
- GaN nanowires are potential candidates for use in scanning probe microscopy due to their well-defined, reproducible, geometric shapes, their hardness, and their light guiding properties. We have developed and investigated probes for high resolution atomic force microscopy and scanning tunneling microscopy utilizing GaN nanowires as probes. The nanowires are n-doped and the morphology of the nanowires has been tailored for scanning probe microscopy by growing them with a sharp tip for measurements and high thickness for robustness. The individual GaN nanowires were removed from their growth substrate and attached onto commercial atomic force microscopy cantilevers or etched tungsten wires for scanning tunneling microscopy. A standard scanning electron microscope equipped with a nanoprobe, a focused ion beam column and a gas injection system was used to locate, transfer, and attach the nanowires. We evaluated the properties of the GaN probes on different substrates including HOPG, Au, SiO2, InAs, and GaAs. We demonstrate both atomic force microscopy and scanning tunneling microscopy measurements with single atomic layer resolution and evaluate the robustness of the tips by monitoring them before and after scanning. Finally, we explore the use of the tips for scanning tunneling spectroscopy demonstrating that reliable results, which can reveal information on the electronic properties of the surface-tip system, are obtainable. The fundamental properties of these probes, which are demonstrated in this work, show promise for future use of the probes in exploring semiconductor-semiconductor tunneling junctions at the nanoscale as well as for other scanning probe techniques where high resolution is required.
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