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"N-Heterocyclic Carbenes in Transition Metal Catalysis and Organocatalysis" features all catalytic reactions enabled by N-heterocyclic carbenes (NHCs), either directly as organocatalysts or as ligands for transition metal catalysts. An explosion in the use of NHCs has been reported in the literature during the past seven years making this comprehensive overview highly apropos. This book begins with an introductory overview of NHCs which could have been subtitled all you need to know about NHCs. The main body of the book is dedicated to applications of NHCs in catalysis. In addition t

Like graphite, transition metal dichalcogenide (TMDC) bulk crystals are formed of monolayers bound to each other by van-der-Waals attraction. TMDC monolayers have a direct band gap, and can be used in electronics as transistors and in optics as emitters and detectors. However, thickness-limited absorption poses a challenge for high efficiency. To overcome this issue, light-trapping techniques such as patterning is suggested. The possibility of direct writing structures with a laser on insulating substrates in a clean room-free process is attractive for its simplicity, cost effectiveness and wide choice of substrates allowed, including flexible plastic. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 840064

Like graphite, transition metal dichalcogenide (TMDC) bulk crystals are formed of monolayers bound to each other by van-der-Waals attraction. TMDC monolayers have a direct band gap, and can be used in electronics as transistors and in optics as emitters and detectors. However, thickness-limited absorption poses a challenge for high efficiency. To overcome this issue, light-trapping techniques such as patterning is suggested. The possibility of direct writing structures with a laser on insulating substrates in a clean room-free process is attractive for its simplicity, cost effectiveness and wide choice of substrates allowed, including flexible plastic. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 840064

This thesis is devoted towards physical vapor deposition (PVD) of thin films of transition-metal (TM) diborides, focused on the material system TiBx, Ti1-xAlxB2-y and CrBx. The metal diborides are a large family of compounds with both metallic and ceramic properties, due to its bonding nature being a mix of covalent and ionic bonds. Their characteristics include, e.g., good mechanical, electrical and thermal properties, while an improved oxidation and corrosion resistance are currently sought after. Furthermore, while the ideal composition of these diborides is TMB2, i.e. with a B to metal ratio of 2, the stoichiometry in the PVD deposited films typically diverges from this ratio. TiBx is often reported to be overstoichiometric, with x well above 2. One of the most known and commonly used member of the TM diboride family is TiBx, primarily used in hard-coating applications such as tools for machining Al. However, the material displays a fracture toughness and oxidation resistance that ideally needs to be improved. The films presented in this thesis were deposited by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Using both methods facilitates an improved control of both microstructure and composition, and hence the materials properties. With HiPIMS, understoichiometric TiBx films were grown and it was shown that these films can match and even exceed the overstoichiometric counterpart, deposited with DCMS, in terms of mechanical properties. The hardness and fracture toughness for TiB1.43 films were measured at 43.9±0.9 GPa and 4.2±0.1 MPa√m, compared to TiB2.70 films at 37.7±0.8 GPa and 3.1±0.1 MPa√m. Furthermore, the understoichiometric films significantly improve the oxidation resistance. Air annealing of TiB1.43, TiB2.20, and TiB2.70 films at 400 °C showed an average oxidation rate of 2.9±1.5, 7.1±1.0, and 20.0±5.0 nm/h, respectively, explained by the microstructural difference between over- and understoichiometric material. In TiBx films where x > 2, there is a B-rich tissue phase in the grain boundaries which is suggested to enhance oxidation. The hydroscopic nature of B2O3 causes more rapid oxidation and evaporation thus providing an easy oxidation pathway in B-rich regions. However, understoichiometric films where x 2), vilket i sin tur påverkar beständigheten mot oxidering negativt. Med hjälp av HiPIMS kan man kontrollera stökiometrin av filmen i större grad, och kan således generera understökiometrisk TiBx (x < 2) som jag visar på har bättre mekaniska egenskaper, bland annat högre hårdhet, bättre brottseghet och förbättrad beständighet mot oxidering, kontra den överstökiometriska motsvarigheten. Hur mikrostrukturen i överstökiometriska TiBx filmer ser ut är välkänt, där överflödigt B ansamlas i korngränserna och bilder en s.k. "B-rik vävnadsfas". Jag har påvisat hur motsvarande mikrostruktur ser ut för understökiometrisk TiBx filmer, något som fram tills nu varit okänt. I dessa faser saknas vävnadsfas i korngränserna, och istället hittas överskottet av Ti som plandefekter i de kolumnära TiB2-strukturerna i filmen. Jag visar på att avsaknaden av vävnadsfas i korngränserna tydligt förbättrar beständigheten mot oxidering, vilket troligtvis beror på att just korngränserna, och deras innehåll, agerar som en katalys for oxidering. På samma sätt undersöker jag hur materialsystemet Ti1-xAlxBy-2 beter sig med varierande Ti:Al förhållande och även B:M förhållande (bor till metall), i filmer skapade med både DCMS och HiPIMS. Målet med inkluderingen av Al är just att förbättra beständighet mot oxidering, och samtidigt bevara de åtråvärda mekaniska egenskaperna som filmer av TiBx har. Korngränserna i det här materialet består av en vävnadsfasblandning, rik på antingen Al eller B, beroende på förhållandet mellan x och y i Ti1- xAlxBy-2. Jag visar på att en reducering av denna vävnadsfas även här förbättrar beständigheten mot oxidering. Det påvisas genom att reducera Al- och B-innehållet i filmerna, vilket minskar vävnadsfasen i korngränserna, och således förbättras beständigheten mot oxidering. En systematisk undersökning av tunna filmer av CrBx, belagda med DCMS, har genomförts, då detta är ett materialsystem med potential för beständighet mot korrosion. Både lätt över- och understökiometriska filmer växtes, och fick sin mikrostruktur och lokala sammansättning undersökt. Alla filmer påvisade en (001) textur, med epitaxiell tillväxt när temperaturen ökade från 500 C° till 900 C°. Högre densitet (~5.2 g/cm3) och jämnare ytor sågs för filmer belagda vid lägre tryck, 5 mTorr (0.67 Pa), jämfört med högre tryck, 20 mTorr (2.67 Pa). Kompositionen för CrBx filmerna påvisade inte ett temperaturberoende, men visade ett marginellt beroende på beläggningstryck för prover växta vid 900 C°. Även observerat för understökiometriska CrB1.90 filmer är att underskottet av B presenteras som plandefekter med Cr-rika plan i de kolumnära CrB2- strukturerna i filmen, precis som i understökiometrisk TiBx. I överstökiometriska CrB2.08 filmer så visades stora inneslutningar av ansamlat B. ; Additional funding agencies: Swedish Government Strategic Research Area inMaterials Science, Advanced Functional Materials, at Linköping University

We review the thin film growth, chemistry, and physical properties of Group 4-6 transition-metal diboride (TMB2) thin films with AlB2-type crystal structure (Strukturbericht designation C32). Industrial applications are growing rapidly as TMB2 begin competing with conventional refractory ceramics like carbides and nitrides, including pseudo-binaries such as Ti1-xAlxN. The TMB2 crystal structure comprises graphite-like honeycombed atomic sheets of B interleaved by hexagonal close-packed TM layers. From the C32 crystal structure stems unique properties including high melting point, hardness, and corrosion resistance, yet limited oxidation resistance, combined with high electrical conductivity. We correlate the underlying chemical bonding, orbital overlap, and electronic structure to the mechanical properties, resistivity, and high-temperature properties unique to this class of materials. The review highlights the importance of avoiding contamination elements (like oxygen) and boron segregation on both the target and substrate sides during sputter deposition, for better-defined properties, regardless of the boride system investigated. This is a consequence of the strong tendency for B to segregate to TMB2 grain boundaries for boron-rich compositions of the growth flux. It is judged that sputter deposition of TMB2 films is at a tipping point towards a multitude of applications for TMB2 not solely as bulk materials, but also as protective coatings and electrically conducting high-temperature stable thin films. ; Funding: Swedish Energy Research [43606-1]; Carl Tryggers Foundation [CTS20:272, CTS16:303, CTS14:310]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Knut and Alice Wallenberg Foundation, Project Grant (The Boride Frontier) [KAW 2015.0043]; Swedish Research Council (VR)Swedish Research Council [621-2010-3921]; AForsk Foundation [16-430]

We analyze the properties of strongly coupled excitons and photons in systems made of semiconducting two-dimensional transition-metal dichalcogenides embedded in optical cavities. Through a detailed microscopic analysis of the coupling, we unveil novel, highly tunable features of the spectrum that result in polariton splitting and a breaking of light-matter selection rules. The dynamics of the composite polaritons is influenced by the Berry phase arising both from their constituents and from the confinement-enhanced coupling. We find that light-matter coupling emerges as a mechanism that enhances the Berry phase of polaritons well beyond that of its elementary constituents, paving the way to achieve a polariton anomalous Hall effect. ; A. G.-R., L. M.-M., and F. G. acknowledge the European Commission under the Graphene Flagship, Contract No. CNECTICT-604391. L. C. and F. G. acknowledge funding from the European Union's Seventh Framework Program (FP7/2007-2013) through the ERC Advanced Grant NOVGRAPHENE (Grant Award No. 290846), and L. C. acknowledges the Comunidad deMadrid through Grant No. MAD2D-CM, S2013/MIT-3007. L. M.-M. and F. J. G.-V. acknowledge financial support by the Spanish MINECO under Contract No. MAT2014-53432-C5. ; Peer reviewed

Magneto-ionics allows for tunable control of magnetism by voltage-driven transport of ions, traditionally oxygen or lithium and, more recently, hydrogen, fluorine, or nitrogen. Here, magneto-ionic effects in single-layer iron nitride films are demonstrated, and their performance is evaluated at room temperature and compared with previously studied cobalt nitrides. Iron nitrides require increased activation energy and, under high bias, exhibit more modest rates of magneto-ionic motion than cobalt nitrides. Ab initio calculations reveal that, based on the atomic bonding strength, the critical field required to induce nitrogen-ion motion is higher in iron nitrides (≈6.6 V nm-1) than in cobalt nitrides (≈5.3 V nm-1). Nonetheless, under large bias (i.e., well above the magneto-ionic onset and, thus, when magneto-ionics is fully activated), iron nitride films exhibit enhanced coercivity and larger generated saturation magnetization, surpassing many of the features of cobalt nitrides. The microstructural effects responsible for these enhanced magneto-ionic effects are discussed. These results open up the potential integration of magneto-ionics in existing nitride semiconductor materials in view of advanced memory system architectures. ; Financial support by the European Research Council (SPINPORICS 2014-Consolidator Grant, Agreement No. 648454, and the MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the Spanish Government (MAT2017-86357-C3-1-R), the Generalitat de Catalunya (2017-SGR-292 and 2018-LLAV-00032), the European Regional Development Fund (MAT2017-86357-C3-1-R and 2018-LLAV-00032), and the French ANR (ANR-18-CE24- 0017 "FEOrgSpin" and ELECSPIN ANR-16-CE24-0018 "ELECSPIN") is acknowledged. This work was partially supported by the Impulse- und Net-working fund of the Helmholtz Association (FKZ VH-VI-442 Memriox) and the Helmholtz Energy Materials Characterization Platform (03ET7015). The PALS measurements were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We thank the facility staff for assistance. L.A. thanks MINECO for a Ramón y Cajal Contract (RYC-2013-12640).

Due to their physical properties and potential applications in energy conversion and storage, transition-metal dichalcogenides (TMDs) have garnered substantial interest in recent years. Among this class of materials, TMDs based on molybdenum, tungsten, sulfur, and selenium are particularly attractive due to their semiconducting properties and the availability of bottom-up synthesis techniques. Here we report a method which yields high-quality crystals of transition-metal diselenide and ditelluride compounds (PtTe2, PdTe2, NiTe2, TaTe2, TiTe2, RuTe2, PtSe2, PdSe2, NbSe2, TiSe2, VSe2, ReSe2) from their solid solutions, via vapor deposition from a metal-saturated chalcogen melt. Additionally, we show the synthesis of rare-earth-metal polychalcogenides and NbS2 crystals using the aforementioned process. Most of the crystals obtained have a layered CdI2 structure. We have investigated the physical properties of selected crystals and compared them to state of the art findings reported in the literature. Remarkably, the charge density wave transition in 1T-TiSe2 and 2H-NbSe2 crystals is well-defined at TCDW ≈ 200 and 33 K, respectively. Angle-resolved photoelectron spectroscopy and electron diffraction are used to directly access the electronic and crystal structures of PtTe2 single crystals and yield state of the art measurements. © 2020 American Chemical Society. ; M.A.-H. acknowledges support from the VR starting grant 2018-05339 and KL1824/6. The crystal growth experiments were supported by the Russian Science Foundation, Project 19-12-00414. The work has been supported by the program 211 of the Russian Federation Government agreements 02.A03.21.0006 and 02.A03.21.0011, by the Russian Government Program of Competitive Growth of Kazan Federal University. We acknowledge MAX IV Laboratory for time on Beamline Bloch under Proposal 20190335. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152 the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. We acknowledge ARPES experiment support from Craig Polley (MAX IV), Maciej Dendzik (KTH) Antonija Grubisic-Cabo (KTH) and Oscar Tjernberg (KTH). H.R., D.P. and G.J.M. acknowledge the Swedish Research Council (2018-06465, 2018-04330) and the Swedish Energy Agency (P43549-1) for financial support.

We developed a nanostructure to enhance the photoluminescence intensity of two-dimensional monolayers of transition metal dichalcogenides based on plasmonic supercrystal arrays. These plasmonic supercrystal arrays are deposited on top the monolayers by means of a template-assisted assembly of gold nanospheres with patterned polydimethylsiloxane molds [1]. These supercrystals arrays consist on square arrays of hexagonally packed gold nanoparticles (50 nm of diameter) which exhibit well-defined surface lattice resonance modes that can be tuned from the visible through the near-infrared by simple variation of the lattice parameter. This tunability can be used to enhance the photoluminescence emission of different transition metal dichalcogenides monolayers. So, as proof of concept, the photoluminescence signal of the monolayer MoS2 and MoSe2 can be significantly enhanced up to 5-6-fold coupling the frequency of the surface lattice resonance of the plasmonic supercrystal to the frequency emission of the transition metal dichalcogenides monolayer. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 840064

We study the nature of spin excitations of individual transition metal atoms (Ti, V, Cr, Mn, Fe, Co, and Ni) deposited on a Cu2N/Cu(100) surface using both spin-polarized density functional theory (DFT) and exact diagonalization of an Anderson model derived from DFT. We use DFT to compare the structural, electronic, and magnetic properties of different transition metal adatoms on the surface. We find that the average occupation of the transition metal d shell, main contributor to the magnetic moment, is not quantized, in contrast with the quantized spin in the model Hamiltonians that successfully describe spin excitations in this system. In order to reconcile these two pictures, we build a zero bandwidth multi-orbital Anderson Hamiltonian for the d shell of the transition metal hybridized with the p orbitals of the adjacent nitrogen atoms, by means of maximally localized Wannier function representation of the DFT Hamiltonian. The exact solutions of this model have quantized total spin, without quantized charge at the d shell. We propose that the quantized spin of the models actually belongs to many-body states with two different charge configurations in the d shell, hybridized with the p orbital of the adjacent nitrogen atoms. This scenario implies that the measured spin excitations are not fully localized at the transition metal. ; J.F.R. acknowledges financial supported by MECSpain (FIS2013-47328-C2-2-P) and Generalitat Valenciana (ACOMP/2010/070), Prometeo. This work has been financially supported in part by FEDER funds. J.L.L. and J.F.R. acknowledge financial support by Marie-Curie-ITN 607904-SPINOGRAPH. A.F. acknowledges funding from the European Union's Seventh Framework Programme for research, technological development and demonstration, under the PEOPLE programme, Marie Curie COFUND Actions, Grant Agreement No. 600375, and CONICET.