2D materials beyond graphene (avsluttet)

• Polfus, Jonathan (2023). One-dimensional carbon chains encapsulated in hollandite. Communications chemistry. ISSN 2399-3669. 6(1). doi: 10.1038/s42004-023-01011-3. Fulltekst i vitenarkiv
• Barragan-Yani, Daniel; Polfus, Jonathan M. & Wirtz, Ludger (2022). Native defects in monolayer GaS and GaSe: Electrical properties and thermodynamic stability. PHYSICAL REVIEW MATERIALS. ISSN 2475-9953. 6(11). doi: 10.1103/PhysRevMaterials.6.114002. Fulltekst i vitenarkiv
• Polfus, Jonathan M.; Benthem, Marta; Ali, Ayaz; Barragan-Yani, Daniel; Vullum, Per Erik & Sunding, Martin Fleissner [Vis alle 9 forfattere av denne artikkelen] (2021). Temperature-Dependent Adhesion in van der Waals Heterostructures. Advanced Materials Interfaces. ISSN 2196-7350. 8(20). doi: 10.1002/admi.202100838. Fulltekst i vitenarkiv Vis sammendrag

  The interlayer coupling between 2D materials is immensely important for both the fundamental understanding of these systems, and for the development of transfer techniques for the fabrication of van der Waals (vdW) heterostructures. A number of uncertainties remain with respect to their adhesion characteristics due to the elusive nature of measured adhesion interactions. Moreover, it is theoretically predicted that the intrinsic ripples in 2D materials give rise to a temperature dependence in adhesion, although the vdW interactions themselves are principally independent of temperature. Here, direct measurements of the adhesion between reduced graphene oxide – coated by solution deposition on atomic force microscopy tips – and graphene, h-BN, and MoS2 supported on SiO2 substrates and as freestanding membranes are presented. The in situ nanomechanical characterization reveals a prominent reduction in the adhesion energies with increasing temperature which is ascribed to the thermally induced ripples in the 2D materials.

• Polfus, Jonathan M. & Jayasayee, Kaushik (2019). Robust nanocomposites of a-Fe2O3 and N-doped graphene oxide: Interfacial bonding and chemisorption of H2O. Carbon. ISSN 0008-6223. 152, s. 497–502. doi: 10.1016/j.carbon.2019.05.033. Fulltekst i vitenarkiv Vis sammendrag

  Nanocomposites of a-Fe2O3 (hematite) and (N-doped) graphene oxide (GO) were investigated using first- principles calculations with focus on structure, chemical bonding, electronic structure and H2O adsorption. The nanocomposites were modeled as the interface between the a-Fe2O3 (0 0 0 1) surface and the basal plane of reduced graphene oxide, comprising epoxy groups (C:O ratio of 8) as well as graphitic and pyridinic nitrogen doping. The composite structures exhibited strong chemical bonding by the formation of a bridging FeeOeC bond. The calculated binding energy between the materials was 0.56 eV per FeeOeC bond for GO and up to 1.14 eV for N-doped GO, and the binding energies were found to correlate with the charge of the bridging oxide ion. The composites exhibited partly occupied carbon states close to or above the a-Fe2O3 valence band maximum. Dissociative adsorption of H2O was found to be more exothermic for the composites compared to the individual materials, ranging from about 0.9 to 1.7 eV for the most stable configurations with hydroxide species adsorbed to GO and protons forming NH groups or adsorbed to the a-Fe2O3 surface.

• Sun, Xinwei; Xu, Kaiqi; Fleischer, Christian; Liu, Xin; Grandcolas, Mathieu & Strandbakke, Ragnar [Vis alle 9 forfattere av denne artikkelen] (2018). Earth-abundant electrocatalysts in proton exchange membrane electrolyzers. Catalysts. ISSN 2073-4344. 8:657(12), s. 1–41. doi: 10.3390/catal8120657. Fulltekst i vitenarkiv Vis sammendrag

  In order to adopt water electrolyzers as a main hydrogen production system, it is critical to develop inexpensive and earth-abundant catalysts. Currently, both half-reactions in water splitting depend heavily on noble metal catalysts. This review discusses the proton exchange membrane (PEM) water electrolysis (WE) and the progress in replacing the noble-metal catalysts with earth-abundant ones. The efforts within this field for the discovery of efficient and stable earth-abundant catalysts (EACs) have increased exponentially the last few years. The development of EACs for the oxygen evolution reaction (OER) in acidic media is particularly important, as the only stable and efficient catalysts until now are noble-metal oxides, such as IrOx and RuOx. On the hydrogen evolution reaction (HER) side, there is significant progress on EACs under acidic conditions, but there are very few reports of these EACs employed in full PEM WE cells. These two main issues are reviewed, and we conclude with prospects for innovation in EACs for the OER in acidic environments, as well as with a critical assessment of the few full PEM WE cells assembled with EACs.

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• Barragan-Yani, Daniel & Wirtz, Ludger (2021). Native defects in monolayer GaS and GaSe.
• Benthem Muñiz, Marta; Ali, Ayaz; Polfus, Jonathan & Belle, Branson (2019). 2D crystal temperature dependent adhesion in the development of Van der Waals heterostructures .
• Fleischer, Christian; Polfus, Jonathan M.; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2018). Defect Chemistry of Few- and Monolayer MoS2. Vis sammendrag

  Defect chemistry has given the possibility to control and tune properties to obtain better functional bulk materials. In comparison, and despite the recent interest and prospects of two-dimensional materials, their defect chemistry remains mainly unexplored. We believe that an understanding of the influence of the dielectric environment on the defect chemistry and properties is crucial for further developing new and superior 2D materials. Here, we present results for molybdenum disulphide (MoS2) films on Si/SiO2 substrates. Methods comprise magnetron sputtering of Mo with subsequent annealing in H2S atmosphere and the chemical vapour transport method. The films and defects are characterised by AFM, XPS, photoluminescence, optical microscopy and Raman spectroscopy in addition to electrical measurements in controlled atmospheres. Ab initio computations on a variety of point defects and defect clusters further elucidate the defect chemistry.

• Fleischer, Christian; Bjørheim, Tor Svendsen; Polfus, Jonathan M. & Norby, Truls Eivind (2018). Point Defects in Monolayer MoS2.
• Fleischer, Christian; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2018). Point Defects in Transition Metal Dichalcogenides. Vis sammendrag

  Defect chemistry has given the possibility to control and tune properties to obtain better functional bulk materials. In comparison, and despite the recent interest and prospects of twodimensional materials, their defect chemistry remains mainly unexplored. We believe that an understanding of the influence of the dielectric environment on the defect chemistry and properties is crucial for further developing new and superior 2D materials. Here, we present results from our computational work on selected point defects in monolayer MoS2. Investigated defects comprises molybdenum and sulphur vacancies in addition to hydrosulfide on sulphur site.

• Belle, Branson; Xing, Wen; Stange, Marit Synnøve Sæverud; S. Azar, Amin; Sunding, Martin Fleissner & Polfus, Jonathan M. (2018). Scalable MoS2 growth via Mo sputtering and post H2S treatment.
• Benthem, Marta (2020). Direct Measurement of Adhesion between 2D Materials using Atomic Force Microscopy. École Polytechnique Fédérale de Lausanne.

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