| 1. |
- Abbott, Michele, et al.
(författare)
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Examining the food-energy-water and conflict nexus
- 2017
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Ingår i: Current Opinion in Chemical Engineering. - : Elsevier BV. - 2211-3398. ; 18, s. 55-60
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Forskningsöversikt (refereegranskat)abstract
- There is growing evidence of a strong linkage or 'nexus' between conflict - both domestic and international - and food, energy, and water (FEW) resources and services. This article demonstrates a positive, significant correlation between two measures, FEW security and political stability, and reviews the evidence for how each of these three types of resource insecurities affects political and social stability. We describe what is known about the FEW-conflict nexus itself, note that remaining knowledge gaps include evidence on developing governance structures and preparing for climate change, and examine the types of policies that countries and international donors might take to help mitigate the role that FEW can play in affecting stability.
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| 2. |
- Asad, Shno, et al.
(författare)
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Inorganic nanoparticles for oral drug delivery : opportunities, barriers, and future perspectives
- 2022
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Ingår i: Current Opinion in Chemical Engineering. - : Elsevier. - 2211-3398. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- Oral delivery is the preferred route of drug administration due to patient compliance and convenience. Despite this, nanomedicines have so far primarily been developed for the parenteral route. Inorganic nanoparticles hold great promise as theranostics for oral drug delivery. This is gaining importance especially for the local treatment of gastrointestinal (GI) diseases. However, successful oral delivery of inorganic nanoparticles is challenged by complex physiological conditions in the GI tract. We discuss the main GI barriers and their impact on nanoparticle biotransformation and toxicity. An improved understanding of the complex interplay of inorganic nanoparticles with the dynamic GI environment can facilitate the development of efficient oral nanomedicines.
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| 3. |
- Backes, Claudia, et al.
(författare)
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Production and processing of graphene and related materials
- 2020
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a 'hands-on' approach, providing practical details and procedures as derived from literature as well as from the authors' experience, in order to enable the reader to reproduce the results. Section I is devoted to 'bottom up' approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section II covers 'top down' techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers' and modified Hummers' methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by employing a theoretical data-mining approach. The exfoliation of LMs usually results in a heterogeneous dispersion of flakes with different lateral size and thickness. This is a critical bottleneck for applications, and hinders the full exploitation of GRMs produced by solution processing. The establishment of procedures to control the morphological properties of exfoliated GRMs, which also need to be industrially scalable, is one of the key needs. Section III deals with the processing of flakes. (Ultra)centrifugation techniques have thus far been the most investigated to sort GRMs following ultrasonication, shear mixing, ball milling, microfluidization, and wet-jet milling. It allows sorting by size and thickness. Inks formulated from GRM dispersions can be printed using a number of processes, from inkjet to screen printing. Each technique has specific rheological requirements, as well as geometrical constraints. The solvent choice is critical, not only for the GRM stability, but also in terms of optimizing printing on different substrates, such as glass, Si, plastic, paper, etc, all with different surface energies. Chemical modifications of such substrates is also a key step. Sections IV-VII are devoted to the growth of GRMs on various substrates and their processing after growth to place them on the surface of choice for specific applications. The substrate for graphene growth is a key determinant of the nature and quality of the resultant film. The lattice mismatch between graphene and substrate influences the resulting crystallinity. Growth on insulators, such as SiO2, typically results in films with small crystallites, whereas growth on the close-packed surfaces of metals yields highly crystalline films. Section IV outlines the growth of graphene on SiC substrates. This satisfies the requirements for electronic applications, with well-defined graphene-substrate interface, low trapped impurities and no need for transfer. It also allows graphene structures and devices to be measured directly on the growth substrate. The flatness of the substrate results in graphene with minimal strain and ripples on large areas, allowing spectroscopies and surface science to be performed. We also discuss the surface engineering by intercalation of the resulting graphene, its integration with Si-wafers and the production of nanostructures with the desired shape, with no need for patterning. Section V deals with chemical vapour deposition (CVD) onto various transition metals and on insulators. Growth on Ni results in graphitized polycrystalline films. While the thickness of these films can be optimized by controlling the deposition parameters, such as the type of hydrocarbon precursor and temperature, it is difficult to attain single layer graphene (SLG) across large areas, owing to the simultaneous nucleation/growth and solution/precipitation mechanisms. The differing characteristics of polycrystalline Ni films facilitate the growth of graphitic layers at different rates, resulting in regions with differing numbers of graphitic layers. High-quality films can be grown on Cu. Cu is available in a variety of shapes and forms, such as foils, bulks, foams, thin films on other materials and powders, making it attractive for industrial production of large area graphene films. The push to use CVD graphene in applications has also triggered a research line for the direct growth on insulators. The quality of the resulting films is lower than possible to date on metals, but enough, in terms of transmittance and resistivity, for many applications as described in section V. Transfer technologies are the focus of section VI. CVD synthesis of graphene on metals and bottom up molecular approaches require SLG to be transferred to the final target substrates. To have technological impact, the advances in production of high-quality large-area CVD graphene must be commensurate with those on transfer and placement on the final substrates. This is a prerequisite for most applications, such as touch panels, anticorrosion coatings, transparent electrodes and gas sensors etc. New strategies have improved the transferred graphene quality, making CVD graphene a feasible option for CMOS foundries. Methods based on complete etching of the metal substrate in suitable etchants, typically iron chloride, ammonium persulfate, or hydrogen chloride although reliable, are time- and resource-consuming, with damage to graphene and production of metal and etchant residues. Electrochemical delamination in a low-concentration aqueous solution is an alternative. In this case metallic substrates can be reused. Dry transfer is less detrimental for the SLG quality, enabling a deterministic transfer. There is a large range of layered materials (LMs) beyond graphite. Only few of them have been already exfoliated and fully characterized. Section VII deals with the growth of some of these materials. Amongst them, h-BN, transition metal tri- and di-chalcogenides are of paramount importance. The growth of h-BN is at present considered essential for the development of graphene in (opto) electronic applications, as h-BN is ideal as capping layer or substrate. The interesting optical and electronic properties of TMDs also require the development of scalable methods for their production. Large scale growth using chemical/physical vapour deposition or thermal assisted conversion has been thus far limited to a small set, such as h-BN or some TMDs. Heterostructures could also be directly grown. Section VIII discusses advances in GRM functionalization. A broad range of organic molecules can be anchored to the sp(2) basal plane by reductive functionalization. Negatively charged graphene can be prepared in liquid phase (e.g. via intercalation chemistry or electrochemically) and can react with electrophiles. This can be achieved both in dispersion or on substrate. The functional groups of GO can be further derivatized. Graphene can also be noncovalently functionalized, in particular with polycyclic aromatic hydrocarbons that assemble on the sp(2) carbon network by pi-pi stacking. In the liquid phase, this can enhance the colloidal stability of SLG/FLG. Approaches to achieve noncovalent on-substrate functionalization are also discussed, which can chemically dope graphene. Research efforts to derivatize CNMs are also summarized, as well as novel routes to selectively address defect sites. In dispersion, edges are the most dominant defects and can be covalently modified. This enhances colloidal stability without modifying the graphene basal plane. Basal plane point defects can also be modified, passivated and healed in ultra-high vacuum. The decoration of graphene with metal nanoparticles (NPs) has also received considerable attention, as it allows to exploit synergistic effects between NPs and graphene. Decoration can be either achieved chemically or in the gas phase. All LMs,
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| 4. |
- Bauer, Fredric, et al.
(författare)
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Mapping GHG emissions and prospects for renewable energy in the chemical industry
- 2023
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Ingår i: Current Opinion in Chemical Engineering. - : Elsevier BV. - 2211-3398. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- Chemicals is the industrial sector with the highest energy demand, using a substantial share of global fossil energy and emitting increasing amounts of greenhouse gasses following rapid growth over the past 25 years. Emissions associated with energy use have increased with growth in coal-dependent regions but are also commonly underestimated in regions with higher shares of renewable energy. Renewable energy is key to reducing greenhouse gas emissions but remains a niche area when considering corporate targets and initiatives aiming at emission reductions, which instead favour incremental energy efficiency improvements. These findings point to a risk for continued lock-in to fossil energy in the industry.
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| 5. |
- Del, Sepideh Khandan, et al.
(författare)
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Optimizing the optical and electrical properties of graphene ink thin films by laser-annealing
- 2015
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Ingår i: Current Opinion in Chemical Engineering. - : Institute of Physics (IOP). - 2211-3398. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a facile fabrication technique for graphene-based transparent conductive films. Highly flat and uniform graphene films are obtained through the incorporation of an efficient laser annealing technique with one-time drop casting of high-concentration graphene ink. The resulting thin films are uniform and exhibit a transparency of more than 85% at 550 nm and a sheet resistance of about 30 kΩ/sq. These values constitute an increase of 45% in transparency, a reduction of surface roughness by a factor of four and a decrease of 70% in sheet resistance compared to un-annealed films.
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| 6. |
- Holt, Ann Julie U., et al.
(författare)
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Electronic properties of single-layer CoO2/Au(111)
- 2021
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Ingår i: Current Opinion in Chemical Engineering. - : IOP Publishing. - 2211-3398. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- We report direct measurements via angle-resolved photoemission spectroscopy (ARPES) of the electronic dispersion of single-layer (SL) CoO2. The Fermi contour consists of a large hole pocket centered at the (Gamma) over bar point. To interpret the ARPES results, we use density functional theory (DFT) in combination with the multi-orbital Gutzwiller Approximation (DFT+GA), basing our calculations on crystalline structure parameters derived from x-ray photoelectron diffraction and low-energy electron diffraction. Our calculations are in good agreement with the measured dispersion. We conclude that the material is a moderately correlated metal. We also discuss substrate effects, and the influence of hydroxylation on the CoO2 SL electronic structure.
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| 7. |
- Jain, Sandeep K., et al.
(författare)
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Structure of twisted and buckled bilayer graphene
- 2017
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Ingår i: Current Opinion in Chemical Engineering. - : Institute of Physics Publishing (IOPP). - 2211-3398. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- We study the atomic structure of twisted bilayer graphene, with very small mismatch angles (theta similar to 0.28(0)), a topic of intense recent interest. We use simulations, in which we combine a recently presented semi-empirical potential for single-layer graphene, with a new term for out-of-plane deformations, (Jain et al. 2015 J. Phys. Chem. C119 9646) and an often-used interlayer potential (Kolmogorov et al 2005 Phys. Rev. B 71 235415). This combination of potentials is computationally cheap but accurate and precise at the same time, allowing us to study very large samples, which is necessary to reach very small mismatch angles in periodic samples. By performing large scale atomistic simulations, we show that the vortices appearing in the Moire pattern in the twisted bilayer graphene samples converge to a constant size in the thermodynamic limit. Furthermore, the well known sinusoidal behavior of energy no longer persists once the misorientation angle becomes very small (theta < 1(0)). We also show that there is a significant buckling after the relaxation in the samples, with the buckling height proportional to the system size. These structural properties have direct consequences on the electronic and optical properties of bilayer graphene.
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| 8. |
- Janssen, Tjbm, et al.
(författare)
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Operation of graphene quantum Hall resistance standard in a cryogen-free table-top system
- 2015
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 2:3, s. 035015-
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Tidskriftsartikel (refereegranskat)abstract
- Wedemonstrate quantum Hall resistance measurements with metrological accuracy in a small cryogen-free system operating at a temperature of around 3.8Kand magnetic fields below 5 T. Operating this system requires little experimental knowledge or laboratory infrastructure, thereby greatly advancing the proliferation of primary quantum standards for precision electrical metrology. This significant advance in technology has come about as a result of the unique properties of epitaxial graphene on SiC.
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| 9. |
- Jia, Tao, et al.
(författare)
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Epitaxial growth of TiSe2/TiO2 heterostructure
- 2019
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Ingår i: Current Opinion in Chemical Engineering. - : Institute of Physics (IOP). - 2211-3398. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Here we report that TiSe2 thin films can be epitaxially grown on TiO2 substrates despite different lattice symmetry between the two materials. The TiSe2 thin films can be prepared on TiO2 via molecular beam epitaxy (MBE) in two ways: by conventional co-deposition using selenium and titanium sources, and by evaporating just selenium on reconstructed surfaces of TiO2. Both growth methods yield crystalline thin films with similar electronic band structures. TiSe2 films on TiO2 substrates exhibit large electron doping and a lack of charge density wave (CDW) order, which is different from both bulk single crystal TiSe2 and TiSe2 thin films on graphene. These phenomena can be explained by selenium vacancies in the TiSe2 films, which naturally occur when these films are grown on TiO2 substrates. Our successful growth of transition metal dichalcogenide (TMDC) films on a transition metal oxide (TMO) substrate provides a platform to further tune the electrical and optical properties of TMDC thin films.
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| 10. |
- Jones, Alfred J. H., et al.
(författare)
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Visualizing band structure hybridization and superlattice effects in twisted MoS2/WS2 heterobilayers
- 2022
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Ingår i: Current Opinion in Chemical Engineering. - : IOP Publishing Ltd. - 2211-3398. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- A mismatch of atomic registries between single-layer transition metal dichalcogenides (TMDs) in a two-dimensional (2D) van der Waals heterostructure produces a moire superlattice with a periodic potential, which can be fine-tuned by introducing a twist angle between the materials. This approach is promising both for controlling the interactions between the TMDs and for engineering their electronic band structures, yet direct observation of the changes to the electronic structure introduced with varying twist angle has so far been missing. Here, we probe heterobilayers comprised of single-layer MoS2 and WS2 with twist angles ranging from 2 degrees to 20 degrees and determine the twist angle-dependent evolution of the electronic band structure using micro-focused angle-resolved photoemission spectroscopy. We find strong interlayer hybridization between MoS2 and WS2 electronic states at the (Gamma) over bar -point of the Brillouin zone, leading to a shift of the valence band maximum in the heterostructure. Replicas of the hybridized states are observed at the center of twist angle-dependent moire mini Brillouin zones. We confirm that these replica features arise from the inherent moire potential by comparing our experimental observations with density functional theory calculations of the superlattice dispersion. Our direct visualization of these features underscores the potential of using twisted heterobilayer semiconductors to engineer hybrid electronic states and superlattices that alter the electronic and optical properties of 2D heterostructures for a wide range of twist angles.
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