| 1. |
- Bericat Vadell, Robert, et al.
(författare)
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Single-electron transfer reactions on surface-modified gold plasmons
- 2023
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Ingår i: Materials Today Chemistry. - : Elsevier. - 2468-5194. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- Photoredox catalysis's relevance in organic synthesis research and innovation will increase in the coming decades. However, the processes rely almost exclusively on expensive noble metal complexes, most notably iridium complexes, to absorb light and transfer a single charge to a substrate or a catalyst to initiate cascade transformations. Light-triggered plasmon resonances generate a non-Fermi-Dirac energy distribution with many hot carriers that decay in similar to 1 ps. Their ultrafast relaxation makes performing single electron transfer (SET) transformations challenging. Herein, a novel photosystem is proposed based on surface-modified gold nanoparticles (aka plasmon "molecularization"), which improved charge separation and, more importantly, enabled SET reactions, expanding the portfolio of photocatalysts available for photoredox catalysis. The photosystem was made into an electrode, permitting its use in photoelectrochemical arrangements that leverage electro- and photo-chemical approaches' benefits and chemical engineering solutions, helping the synthetic chemistry efforts towards greener synthesis and synthesis of more complex structures on a scale.
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| 2. |
- Dey, Ananta, et al.
(författare)
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Exploiting hot electrons from a plasmon nanohybrid system for the photoelectroreduction of CO2
- 2024
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Ingår i: Communications Chemistry. - : Springer Nature. - 2399-3669. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic materials convert light into hot carriers and heat to mediate catalytic transformation. The participation of hot carriers (photocatalysis) remains a subject of vigorous debate, often argued on the basis that carriers have ultrashort lifetime incompatible with drive photochemical processes. This study utilises plasmon hot electrons directly in the photoelectrocatalytic reduction of CO2 to CO via a Ppasmonic nanohybrid. Through the deliberate construction of a plasmonic nanohybrid system comprising NiO/Au/ReI(phen-NH2)(CO)3Cl (phen-NH2 = 1,10-Phenanthrolin-5-amine) that is unstable above 580 K; it was possible to demonstrate hot electrons are the main culprit in CO2 reduction. The engagement of hot electrons in the catalytic process is derived from many approaches that cover the processes in real-time, from ultrafast charge generation and separation to catalysis occurring on the minute scale. Unbiased in situ FTIR spectroscopy confirmed the stepwise reduction of the catalytic system. This, coupled with the low thermal stability of the ReI(phen-NH2)(CO)3Cl complex, explicitly establishes plasmonic hot carriers as the primary contributors to the process. Therefore, mediating catalytic reactions by plasmon hot carriers is feasible and holds promise for further exploration. Plasmonic nanohybrid systems can leverage plasmon’s unique photophysics and capabilities because they expedite the carrier’s lifetime.
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| 3. |
- Fritze, Stefan, et al.
(författare)
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Elemental distribution and fracture properties of magnetron sputtered carbon supersaturated tungsten films
- 2024
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 477
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Tidskriftsartikel (refereegranskat)abstract
- The combination of strength and toughness is a major driving force for alloy design of protective coatings, and nanocrystalline tungsten (W)-alloys have shown to be promising candidates for combining strength and toughness. Here we investigate the elemental distribution and the fracture toughness of carbon (C) alloyed W thin films prepared by non-reactive magnetron sputtering. W:C films with up to ~4 at.% C crystallize in a body-centered-cubic structure with a strong 〈hh0〉texture, and no additional carbide phases are observed in the diffraction pattern. Atom probe tomography and X-ray photoelectron spectroscopy confirmed the formation of such a supersaturated solid solution. The pure W film has a hardness ~13 GPa and the W:C films exhibit a peak hardness of ~24 GPa. In-situ micromechanical cantilever bending tests show that the fracture toughness decreases from ~4.5 MPa·m1/2 for the W film to ~3.1 MPa·m1/2 for W:C films. The results show that C can significantly enhance the hardness of W thin films while retaining a high fracture toughness.
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| 4. |
- Gopakumar, Geethanjali, 1992-, et al.
(författare)
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X-ray Induced Fragmentation of Protonated Cystine
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Protein structure determination using high-intensity X-ray sources induces damage in the protein. Disulfide bridges, formed between two cysteine amino acid residues stabilize the protein structure. Owing to the higher absorption cross-section of sulfur for X-ray photons, and a large number of electrons released from sulfur atoms, these disulfide bridges are hot spots for a higher level of noise in structural studies. But it is yet to be understood how exactly the damage occurs through the interaction of the disulfide bridges with photons. Here we study the fragmentation of protonated cystine in the gas phase, which is the dimer of cysteine, by irradiation with X-rays across the sulfur L-edge using an electrospray ionization source (ESI) in combination with an ion trap. This is complemented with the calculation of the sulfur NEXAFS spectrum on the level of Restricted Open-Shell Configuration Interaction (ROCIS) and Density Functional Theory (DFT) calculations for molecular orbital visualization as well as Molecular Dynamics (MD) simulations for the fragmentation of triply charged cystine ions. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons by combining the experiments and simulations. The disulfide bridge breaks for resonant excitation at lower energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments formed subsequently break into smaller fragments.
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| 5. |
- Gopakumar, Geethanjali, 1992-, et al.
(författare)
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X-ray Induced Fragmentation of Protonated Cystine
- 2022
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 126:9, s. 1496-1503
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate site-specific X-ray induced fragmentation across the sulfur L-edge of protonated cystine, the dimer of the amino acid cysteine. Ion yield NEXAFS were performed in the gas phase using electrospray ionization (ESI) in combination with an ion trap. The interpretation of the sulfur L-edge NEXAFS spectrum is supported by Restricted Open-Shell Configuration Interaction (ROCIS) calculations. The fragmentation pathway of triply charged cystine ions was modeled by Molecular Dynamics (MD) simulations. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons. The disulfide bridge breaks for resonant excitation at lower photon energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments initially formed subsequently break into smaller fragments.
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| 6. |
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| 7. |
- Kalha, Curran, et al.
(författare)
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Hard x-ray photoelectron spectroscopy : a snapshot of the state-of-the-art in 2020
- 2021
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:23
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Forskningsöversikt (refereegranskat)abstract
- Hard x-ray photoelectron spectroscopy (HAXPES) is establishing itself as an essential technique for the characterisation of materials. The number of specialised photoelectron spectroscopy techniques making use of hard x-rays is steadily increasing and ever more complex experimental designs enable truly transformative insights into the chemical, electronic, magnetic, and structural nature of materials. This paper begins with a short historic perspective of HAXPES and spans from developments in the early days of photoelectron spectroscopy to provide an understanding of the origin and initial development of the technique to state-of-the-art instrumentation and experimental capabilities. The main motivation for and focus of this paper is to provide a picture of the technique in 2020, including a detailed overview of available experimental systems worldwide and insights into a range of specific measurement modi and approaches. We also aim to provide a glimpse into the future of the technique including possible developments and opportunities.
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| 8. |
- Lindblad, Rebecka, et al.
(författare)
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Electronic Structure of CH3NH3PbX3 Perovskites : Dependence on the Halide Moiety
- 2015
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Ingår i: The Journal of Physical Chemistry C. - American Chemical Society : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:4, s. 1818-1825
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Tidskriftsartikel (refereegranskat)abstract
- A combination of measurements using photoelectron spectroscopy and calculations using density functional theory (DFT) was applied to compare the detailed electronic structure of the organolead halide perovskites CH3NH3PbI3 and CH3NH3PbBr3. These perovskite materials are used to absorb light in mesoscopic and planar heterojunction solar cells. The Pb 4f core level is investigated to get insight into the chemistry of the two materials. Valence level measurments are also included showing a shift of the valence band edges where there is a higher binding energy of the edge for the CH3NH3PbBr3 perovskite. These changes are supported by the theoretical calculations which indicate that the differences in electronic structure are mainly caused by the nature of the halide ion rather than structural differences. The combination of photoelectron spectroscopy measurements and electronic structure calculations is essential to disentangle how the valence band edge in organolead halide perovskites is governed by the intrinsic difference in energy levels of the halide ions from the influence of chemical bonding.
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| 9. |
- Sundberg, Jill, et al.
(författare)
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Understanding the effects of sputter damage in W–S thin films by HAXPES
- 2014
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 305, s. 203-213
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Tidskriftsartikel (refereegranskat)abstract
- WS2 is an excellent solid lubricant in dry conditions, and can be applied as thin films. The analysis of WS2 and WS2-based films by x-ray photoelectron spectroscopy (XPS) can be challenging, due to contaminationand oxidized material on the surface. The investigations have traditionally therefore included sputter etching by ion bombardment, which however leads to changes of the remaining material. In this study, hard x-ray photoelectron spectroscopy (HAXPES) has been used to study W–S films deposited bymagnetron sputtering. High-resolution reference measurements for crystalline WS2 and metallic W are also presented. The W–S films were analyzed before and after sputter cleaning by Ar+ ion bombardment, using photon energies of 3 and 6 keV. The as-deposited films were found to consist mainly of a WSx phase,similar to WS2 but with a broader range of chemical states. It is shown that ion bombardment of the surface not only removes the outermost oxidized material, but also leads to preferential sputtering of sulfur and the formation of metallic tungsten. The results are of strong interest for the analysis of WS2-based materials, as they demonstrate that spectra from sputter-cleaned films include effects of sputter damage,and may not be representative of the original sample.
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| 10. |
- Villamayor, Michelle Marie S., et al.
(författare)
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Wafer-sized WS2 monolayer deposition by sputtering
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 14:17, s. 6331-6338
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that tungsten disulphide (WS2) with thicknesses ranging from monolayer (ML) to several monolayers can be grown on SiO2/Si, Si, and Al2O3 by pulsed direct current-sputtering. The presence of high quality monolayer and multilayered WS2 on the substrates is confirmed by Raman spectroscopy since the peak separations between the A(1g)-E-2g and A(1g)-2LA vibration modes exhibit a gradual increase depending on the number of layers. X-ray diffraction confirms a textured (001) growth of WS2 films. The surface roughness measured with atomic force microscopy is between 1.5 and 3 angstrom for the ML films. The chemical composition WSx (x = 2.03 +/- 0.05) was determined from X-ray Photoelectron Spectroscopy. Transmission electron microscopy was performed on a multilayer film to show the 2D layered structure. A unique method for growing 2D layers directly by sputtering opens up the way for designing 2D materials and batch production of high-uniformity and high-quality (stochiometric, large grain sizes, flatness) WS2 films, which will advance their practical applications in various fields.
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| 11. |
- von Fieant, Kristina, et al.
(författare)
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In Situ Formation of Ge Nanoparticles by Annealing of Al-Ge‑N ThinFilms Followed by HAXPES and XRD
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:16, s. 11100-11109
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Tidskriftsartikel (refereegranskat)abstract
- Ge nanoparticles embedded in thin films have attracted a lot of attention due to their promising optical and electronic properties that can be tuned by varying the particle size and choice of matrix material. In this study, Ge nanoparticle formation was investigated for Al-Ge-N based thin films by simultaneous measurements of HAXPES and grazing incidence XRD during in situ annealing in vacuum conditions. As-deposited Al-Ge-N thin films, synthesized by reactive dc magnetron sputtering, consisted of a nanocrystalline (Al1–xGex)Ny solid solution and an amorphous tissue phase of Ge3Ny. Upon annealing to 750 °C, elemental Ge was formed shown by both HAXPES and XRD measurements, and N2 gas was released as measured by a mass spectrometer. Postannealed ex situ analysis by SEM and TEM showed that the elemental Ge phase formed spherical nanoparticles on the surface of the film, with an average size of 210 nm. As the annealing temperature increased further to 850 °C, the Ge particles on the film surface evaporated, while the phase segregation of Ge still could be observed within the film. Thus, these results show the possibility for a controlled synthesis of Ge nanoparticles through annealing of Al-Ge-N thin films to produce materials suitable for use in electronic or optoelectronic devices.
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| 12. |
- Ahlberg, Patrik, et al.
(författare)
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Defect formation in graphene during low-energy ion bombardment
- 2016
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- This letter reports on a systematic investigation of sputter induced damage in graphene caused by low energy Ar+ ion bombardment. The integral numbers of ions per area (dose) as well as their energies are varied in the range of a few eV's up to 200 eV. The defects in the graphene are correlated to the dose/energy and different mechanisms for the defect formation are presented. The energetic bombardment associated with the conventional sputter deposition process is typically in the investigated energy range. However, during sputter deposition on graphene, the energetic particle bombardment potentially disrupts the crystallinity and consequently deteriorates its properties. One purpose with the present study is therefore to demonstrate the limits and possibilities with sputter deposition of thin films on graphene and to identify energy levels necessary to obtain defect free graphene during the sputter deposition process. Another purpose is to disclose the fundamental mechanisms responsible for defect formation in graphene for the studied energy range.
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| 13. |
- Alfoeldi, Jessica, et al.
(författare)
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The genome of the green anole lizard and a comparative analysis with birds and mammals
- 2011
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 477:7366, s. 587-591
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the amniotic egg was one of the great evolutionary innovations in the history of life, freeing vertebrates from an obligatory connection to water and thus permitting the conquest of terrestrial environments(1). Among amniotes, genome sequences are available for mammals and birds(2-4), but not for non-avian reptiles. Here we report the genome sequence of the North American green anole lizard, Anolis carolinensis. We find that A. carolinensis microchromosomes are highly syntenic with chicken microchromosomes, yet do not exhibit the high GC and low repeat content that are characteristic of avian microchromosomes(2). Also, A. carolinensis mobile elements are very young and diverse-more so than in any other sequenced amniote genome. The GC content of this lizard genome is also unusual in its homogeneity, unlike the regionally variable GC content found in mammals and birds(5). We describe and assign sequence to the previously unknown A. carolinensis X chromosome. Comparative gene analysis shows that amniote egg proteins have evolved significantly more rapidly than other proteins. An anole phylogeny resolves basal branches to illuminate the history of their repeated adaptive radiations.
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| 14. |
- Almdalal, Tarik, et al.
(författare)
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Predictive characteristics for disease recurrence and overall survival in non-metastatic clinical T1 renal cell carcinoma : results from the National Swedish Kidney Cancer Register
- 2023
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Ingår i: Scandinavian journal of urology. - : Taylor & Francis. - 2168-1805 .- 2168-1813. ; 57:1-6, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- ObjectivePatients with clinical T1 renal cell carcinoma (cT1RCC) have risks for recurrence and reduced overall survival despite being in the best prognostic group. This study aimed to evaluate the association of different treatments on disease recurrence and overall survival using clinical and pathological characteristics in a nation-wide cT1RCC cohort.Materials and methodsA total of 4,965 patients, registered in the National Swedish Kidney Cancer Register (NSKCR) between 2005 and 2014, with ≥ 5-years follow-up were identified: 3,040 males and 1,925 females, mean age 65 years. Times to recurrence and overall survival were analyzed with Kaplan-Meier curves, log-rank test, and Cox regression models.ResultsAge, TNM-stage, tumor size, RCC-type, and performed treatment were all associated with disease recurrence. Patients selected for ablative treatments had increased risk for recurrent disease: hazard ratio (HR) = 3.79 [95% confidence interval (CI) = 2.69–5.32]. In multivariate analyses, age, gender, tumor size, RCC-type, N-stage, recurrence and performed treatment were all independently associated with overall survival. Patients with chRCC had a 41% better overall survival (HR = 0.59, 95% CI = 0.44–0.78; p < 0.001) than ccRCC. Patients treated with partial nephrectomy (PN) had an 18% better overall survival (HR = 0.83, 95% CI = 0.71–0.95, p < 0.001) than patients treated with radical nephrectomy.ConclusionsAge, gender, T-stage, tumor size, RCC type and treatment modality are all associated with risk of recurrence. Furthermore, age, male gender, tumor size, N-stage and recurrence are associated with reduced overall survival. Patients with chRCC, compared with ccRCC and pRCC patients, and PN compared with RN treated patients, had an advantageous overall survival, indicating a possible survival advantage of nephron sparing treatment.
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| 15. |
- Amemiya, Chris T., et al.
(författare)
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The African coelacanth genome provides insights into tetrapod evolution
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 496:7445, s. 311-316
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of a living coelacanth specimen in 1938 was remarkable, as this lineage of lobe-finned fish was thought to have become extinct 70 million years ago. The modern coelacanth looks remarkably similar to many of its ancient relatives, and its evolutionary proximity to our own fish ancestors provides a glimpse of the fish that first walked on land. Here we report the genome sequence of the African coelacanth, Latimeria chalumnae. Through a phylogenomic analysis, we conclude that the lungfish, and not the coelacanth, is the closest living relative of tetrapods. Coelacanth protein-coding genes are significantly more slowly evolving than those of tetrapods, unlike other genomic features. Analyses of changes in genes and regulatory elements during the vertebrate adaptation to land highlight genes involved in immunity, nitrogen excretion and the development of fins, tail, ear, eye, brain and olfaction. Functional assays of enhancers involved in the fin-to-limb transition and in the emergence of extra-embryonic tissues show the importance of the coelacanth genome as a blueprint for understanding tetrapod evolution.
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| 16. |
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| 17. |
- Angermayr, S. Andreas, et al.
(författare)
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Energy biotechnology with cyanobacteria
- 2009
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Ingår i: Current Opinion in Biotechnology. - : Elsevier BV. - 0958-1669 .- 1879-0429. ; 20:3, s. 257-263
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Forskningsöversikt (refereegranskat)abstract
- The world's future energy demand calls for a sustainable alternative for the use of fossil fuels, to restrict further global warming. Harvesting solar energy via photosynthesis is one of Nature's remarkable achievements. Existing technologies exploit this process for energy 'production' via processing of, for example, part of plant biomass into ethanol, and of algal biomass into biodiesel. Fortifying photosynthetic organisms with the ability to produce biofuels directly would bypass the need to synthesize all the complex chemicals of 'biomass'. A promising way to achieve this is to redirect cyanobacterial intermediary metabolism by channeling (Calvin cycle) intermediates into fermentative metabolic pathways. This review describes this approach via the biosynthesis of fermentation end products, like alcohols and hydrogen, driven by solar energy, from water (and CO2).
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| 18. |
- Arion, Tiberiu, et al.
(författare)
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New insight into the Auger decay process in O-2: The coincidence perspective
- 2012
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 234-243
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron-Auger electron coincidence spectroscopy is a powerful tool for the investigation of Auger decay processes with different core-ionized intermediate states. In this paper we describe an investigation into the Auger decay of the O-2 molecule, with the purpose of bringing new insight into the dynamics of the core hole decay mechanism. Using a novel experimental approach to measuring such coincidence spectra we report the highest resolution Auger spectrum of O-2 recorded hitherto. In our approach, we have combined the advantages of these coincidence spectra with the high resolution and excellent signal-to-noise ratios of non-coincident Auger spectra and a state-of-the-art fit analysis. In this way we have derived information about the potential energy curves of the final states W-3 Delta(u), B-3 Pi(g), and B' (3)Sigma(-)(u) and concluded that the corresponding Auger transitions are formed to a large part by strongly overlapping vibrational progressions. The present findings are compared to earlier results reported in the literature confirming some theoretical predictions. (C) 2012 Elsevier B.V. All rights reserved.
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| 19. |
- Ashraf, Shakeel, 1984-, et al.
(författare)
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Surface modification of SU-8 for metal/SU-8 adhesion using RF plasma treatment for application in thermopile detectors
- 2015
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Ingår i: Materials Research Express. - : Institute of Physics (IOP). - 2053-1591. ; 2:8
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Tidskriftsartikel (refereegranskat)abstract
- This article reports on plasma treatment of SU-8 epoxy in order to enhance adhesive strength for metals. Its samples were fabricated on standard silicon wafers and treated with (O2 & Ar) RF plasma at a power of 25W at a low pressure of (3×10-3 torr) for different time spans (10 sec – 70 sec). The sample surfaces were characterized in terms of contact angle, surface (roughness and chemistry) and using a tape test. During the contact angle measurement, it was observed that the contact angle was reduced from 73° to 5° (almost wet) and 23° for (O2 & Ar) treated samples, respectively. The RMS surface roughness was significantly increased by 21.5% and 37.2% for (O2 & Ar) treatment, respectively. A pattern of metal squares was formed on the samples using photolithography for a tape test. An adhesive tape was applied to the samples and peeled off at 180o. The maximum adhesion results, more than 90%, were achieved for the O2-treated samples, whereas the Ar-treated samples showed no change. The XPS study shows the formation of new species in the O2-treated sample compared to the Ar-treated samples. The high adhesive results were due to the formation of hydrophilic groups and new O2 species in the O2-treated samples, which were absent in Ar-treated samples.
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| 20. |
- Barone, Giovanni D., et al.
(författare)
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Recent developments in the production and utilization of photosynthetic microorganisms for food applications
- 2023
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Ingår i: Heliyon. - : Elsevier. - 2405-8440. ; 9:4
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Forskningsöversikt (refereegranskat)abstract
- The growing use of photosynthetic microorganisms for food and food-related applications is driving related biotechnology research forward. Increasing consumer acceptance, high sustain-ability, demand of eco-friendly sources for food, and considerable global economic concern are among the main factors to enhance the focus on the novel foods. In the cases of not toxic strains, photosynthetic microorganisms not only provide a source of sustainable nutrients but are also potentially healthy. Several published studies showed that microalgae are sources of accessible protein and fatty acids. More than 400 manuscripts were published per year in the last 4 years. Furthermore, industrial approaches utilizing these microorganisms are resulting in new jobs and services. This is in line with the global strategy for bioeconomy that aims to support sustainable development of bio-based sectors. Despite the recognized potential of the microalgal biomass value chain, significant knowledge gaps still exist especially regarding their optimized production and utilization. This review highlights the potential of microalgae and cyanobacteria for food and food-related applications as well as their market size. The chosen topics also include advanced production as mixed microbial communities, production of high-value biomolecules, photopro-duction of terpenoid flavoring compounds, their utilization for sustainable agriculture, applica-tion as source of nutrients in space, and a comparison with heterotrophic microorganisms like yeast to better evaluate their advantages over existing nutrient sources. This comprehensive assessment should stimulate further interest in this highly relevant research topic.
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| 21. |
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| 22. |
- Belotcerkovtceva, Daria, et al.
(författare)
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Insights and Implications of Intricate Surface Charge Transfer and sp3-Defects in Graphene/Metal Oxide Interfaces
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:31, s. 36209-36216
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Tidskriftsartikel (refereegranskat)abstract
- Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced p-type doping in graphene, in sharp contrast to TiOx, the AlOx/graphene interface shows the presence of appreciable sp3 defects. Electronic structure calculations disclose that significant p-type doping occurs due to a combination of sp3 bonds formed between C and O atoms at the interface and possible slightly off-stoichiometric defects of the aluminum oxide layer. Furthermore, the sp3 hybridization at the AlOx/graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spin-lifetimes in AlOx barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.
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| 23. |
- Berg, Andreas, et al.
(författare)
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Cyanobacteria as a source of hydrogen for methane formation
- 2014
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Ingår i: World Journal of Microbiology & Biotechnology. - : Springer Verlag (Germany). - 0959-3993 .- 1573-0972. ; 30:2, s. 539-545
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Tidskriftsartikel (refereegranskat)abstract
- In a study during the 1970s co-variation of nitrogenase activity and methane formation associated with Sphagnum riparium was observed. This was suggested as evidence for a possible mechanism of hydrogen transfer from cyanobacteria to methanogens. We show experimentally that such a pathway is feasible. In a series of laboratory experiments, using a hydrogenase deficient strain of the heterocystous cyanobacterium Nostoc punctiforme and the hydrogenotrophic methanogen Methanospirillum hungateii in co-cultures, increasing light intensities resulted in elevated nitrogenase activity and methane production. The increase in methane production can be directly deduced from the nitrogenase activity of the N. punctiforme based on hydrogen balance calculations. These experimental results clearly suggest the possible existence of a novel photosynthetically regulated pathway for methane formation.
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| 24. |
- Bergersen, Henrik, et al.
(författare)
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A photoelectron spectroscopic study of aqueous tetrabutylammonium iodide
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:32, s. 326101-
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra of tetrabutylammonium iodide (TBAI) dissolved in water have been recorded using a novel experimental set-up, which enables photoelectron spectroscopy of volatile liquids. The set-up is described in detail. Ionization energies are reported for I− 5p, I− 4d, C 1s and N 1s. The C 1s spectrum shows evidence of inelastic scattering of the photoelectrons, that differs from the case of TBAI in formamide.
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| 25. |
- Bergersen, Henrik, et al.
(författare)
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First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.
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