Temperature- and Light-Induced Spin Crossover Observed by X-ray Spectroscopy on Isolated Fe(II) Complexes on Gold

Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur

Spin crossover materials evaporated under clean high vacuum and ultra-high vacuum conditions: from thin films to single molecules

We report clean evaporation under ultra-high vacuum conditions of two spin crossover materials, yielding either microcrystallites or homogeneous thin films. Magnetic and photomagnetic studies show that thermal and light-induced spin crossover properties are preserved. Preliminary STM imaging of sub-monolayers indicates that the deposited molecules remain intact on the surface

Activation Energy Paths for Graphene Nucleation and Growth on Cu

The synthesis of wafer-scale single crystal graphene remains a challenge toward the utilization of its intrinsic properties in electronics. Until now, the large-area chemical vapor deposition of graphene has yielded a polycrystalline material, where grain boundaries are detrimental to its electrical properties. Here, we study the physicochemical mechanisms underlying the nucleation and growth kinetics of graphene on copper, providing new insights necessary for the engineering synthesis of wafer-scale single crystals. Graphene arises from the crystallization of a supersaturated fraction of carbon-adatom species, and its nucleation density is the result of competition between the mobility of the carbon-adatom species and their desorption rate. As the energetics of these phenomena varies with temperature, the nucleation activation energies can span over a wide range (1–3 eV) leading to a rational prediction of the individual nuclei size and density distribution. The growth-limiting step was found to be the attachment of carbon-adatom species to the graphene edges, which was independent of the Cu crystalline orientation

Control of single-spin magnetic anisotropy by exchange coupling

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation1, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons2 in water molecules in a host's tissue3. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices4, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices5 in which an individual magnetic atom or molecule is coupled to conducting leads.This work was supported by the Engineering and Physical Sciences Research Council, UK (EP/D063604/1 and EP/H002022/1), Ministry of Science and Education Spain (FIS2010-21883-C02-01, MAT2010-19236, CONSOLIDER CSD2007-0010 and Programa de Movilidad Postdoctoral), European Commission FP7 Programme (PER-GA-2009-251791) and GV grant Prometeo 2012-11

Assessment of hepatocyte growth factor in ovarian cancer mortality

BACKGROUND: Invasive ovarian cancer is a significant cause of gynecologic cancer mortality. METHODS: We examined whether this mortality was associated with inherited variation in ~170 candidate genes/regions (993 SNPs) in a multi-stage analysis based initially on 312 Mayo Clinic cases (172 deaths). Additional analyses used The Cancer Genome Atlas (TCGA; 127 cases, 62 deaths). For the most compelling gene, we immunostained Mayo Clinic tissue micro-arrays (TMAs, 326 cases) and conducted consortium-based SNP replication analysis (2,560 cases, 1,046 deaths). RESULTS: The strongest initial mortality association was in HGF (hepatocyte growth factor) at rs1800793 (HR 1.7, 95% CI 1.3–2.2, p=2.0×10(−5)) and with overall variation in HGF (gene-level test, p=3.7×10(−4)). Analysis of TCGA data revealed consistent associations (e.g., rs5745709 [r(2)=0.96 with rs1800793]: TCGA 2.4, 1.4–4.1, p=2.2×10(−3); Mayo Clinic+TCGA 1.6, 1.3–1.9, p=7.0×10(−5)) and suggested genotype correlation with reduced HGF mRNA levels (p=0.01). In Mayo Clinic TMAs, protein levels of HGF, its receptor MET, and phospho-MET were not associated with genotype and did not serve as an intermediate phenotype; however, phospho-MET was associated with reduced mortality (p=0.01) likely due to higher expression in early-stage disease. In eight additional ovarian cancer case series, HGF rs5745709 was not associated with mortality (1.0, 0.9–1.1, p=0.87). CONCLUSIONS: We conclude that although HGF signaling is critical to migration, invasion, and apoptosis, it is unlikely that genetic variation plays a major role in ovarian cancer mortality; any minor role is not related to genetically-determined expression. IMPACT: Our study demonstrates the utility of multiple data types and multiple datasets in observational studies