The structure and bonding of molecular furan, C 4 H 4 O, on Pd(111) has been investigated using density functional theory (DFT) calculations and the results compared with those of a recent experimental investigation using scanned-energy mode photoelectron diffraction (PhD). The DFT results confirm the orientation of the molecular plane to be essentially parallel to the surface and show a clear energetic preference for one of the two possible structures identified in the PhD study, namely that with the molecule centred over the hollow sites of the surface. Two slightly different geometries at the hollow sites are found to be essentially energetically equivalent; in both cases, one Pd surface atom bonds to two C atoms, while two other Pd atoms each bond to one C atom. These structures differ in that in one case the pair of C atoms bonding to a single Pd atom are both β-C (C atoms not bonded to O in the furan molecule), whereas in the second case this pair of C atoms comprises one β-C and one α-C (adjacent to the O atom in furan). In both structures the C-Pd bonding is accompanied by displacements of the H and O atoms away from the surface and out of the molecular plane and local C-Pd coordination consistent with a rehybridisation of the C bonding to sp 3 character.

Epitaxial films including bulk-like cubic and wurtzite polymorphs of MnSb have been grown by molecular beam epitaxy on GaAs via careful control of the Sb4/Mn flux ratio. Nonzero-temperature density functional theory was used to predict ab initio the spin polarization as a function of reduced magnetization for the half-metals NiMnSb and cubic MnSb. In both cases, half-metallicity is lost at a threshold magnetization reduction, corresponding to a temperature T * < TC . This threshold is far higher for cubic MnSb compared to NiMnSb and corresponds to T * > 350K, making epitaxial cubic MnSb a promising candidate for room temperature spin injection into semiconductors.Efficient electrical spin injection is crucial for the development of semiconductor (SC) spintronics, in which spin-polarized charge carriers flow from a ferromagnetic (FM) material into a non-magnetic SC structure. An ideal FM material would provide a fully spin polarized current [1] and should possess "engineering compatibility" with its SC host, which includes controllable epitaxy and interfaces, and suitability for device processing. Certain half-metallic ferromagnetic (HMF) materials have a density-of-states (DOS) spin polarisation at the Fermi level of P DOS = 100% due to the presence of a band gap straddling the Fermi energy E F for one spin channel only [2]. Density functional theory (DFT) has predicted this property in several classes of materials [1], including Heusler alloys and transition metal pnictides (TMPs), at temperature T = 0K. On this basis, half-metallicity was first envisaged in NiMnSb, which has a minority spin gap E g ≈ 0.5 eV [3]. However, there is presently no HMF candidate with SC engineering compatibility which clearly maintains P DOS ≈ 100% at room temperature.Experimental verification of P DOS is not straightforward and after more than two decades' study, P DOS (T ) for NiMnSb is not known. Positron annihilation experiments on bulk NiMnSb at T = 27K support P DOS ≈ 100% [4]. Spin polarized photoemission spectroscopy (SPPES) can, in principle, measure P DOS more directly but it is strongly affected by the magnetic, chemical and structural conditions of the surface, which may differ from those of the bulk. Threshold SPPES measured [20]. It is crucial to address the intrinsic limitations on P DOS . It has been realised that HMF band structures change as T increases, even well below the Curie temperature T C [21][22][23][24]. The DOS in the minority spin gap becomes nonzero as the thermal fluctuations produce disorder in the local spin moment alignment. In fact, beyond a threshold temperature T * < T C , the value of P DOS collapses far more rapidly than the reduction of magnetisation M (T ) [22].We report here the successful stabilization of bulklike c-MnSb and w-MnSb crystallites within fully relaxed n-MnSb films grown by molecular beam epitaxy (MBE) on GaAs(111). We confirm by DFT that these are HMF materials at T = 0K. However, we also calculate P DOS as a function of magnetization M (T ) using nonzero-temperature DFT, and...

Density Functional Theory (DFT) calculations have been applied to investigate the known difference in behaviour of S adsorption on Cu(100) and Ni(100). Both surfaces form a 0.25 ML (2x2) adsorption phase, but while at higher coverage a 0.5 ML c(2x2) phase forms on Ni(100), on Cu(100) only a reconstructed 0.47 ML (17x17)R14°s tructure occurs. Calculations of the energy, structure, and surface stress of (2x2) and c(2x2) phases on both substrates show there is an energy advantage on both surfaces to form the higher coverage phase, but that both surfaces show local surface strain around the S atoms in the (2x2) phase, a phenomenon previously investigated only on Cu(100).More than forty different structural models of the Cu(100)(17x17)R14°-S phase have been investigated. The pseudo-(100)c(2x2) structure previously proposed, containing 16Cu adatoms per unit mesh in the reconstructed layer, is found to be less energetically favourable than many other possible structures, even after taking account of local structural relaxations. Significantly more favourable is a structure with 12 Cu adatoms per (17x17)R14°unit mesh, previously proposed on the basis of scanning tunnelling microscopy (STM), and found to yield simulated STM images in good agreement with experiment. This model has all S atoms in local 4-fold coordinated hollows relative to the Cu atoms below, half being located above Cu adatoms with the remainder lying above the underlying outermost substrate layer. However, an alternative model with only 4 Cu adatoms and with half the S atoms at 3-fold coordinated sites on the periphery of the Cu adatom cluster, has an even lower energy and gives simulated STM images in excellent agreement with experiment.