Search

The effective Debye temperatures ([Formula: see text]) of the surface region of UO

The inherent advantages of ME-MTJ devices are extremely low power consumption and the device level memory capability. We demonstrate the complex circuit design required for Magneto-Electric Magnetic Tunnel Junction (ME-MTJ) based logic. The clocking required is readily achievable, permitting large-scale designs to be considered. Compact models for the ME-MTJ based devices have been previously proposed. Using the models and circuits, we present simulation results of a 5-bit adder along with a complex clocking scheme.

The structural transition at about 1000 {\deg}C, from the hexagonal to the orthorhombic phase of LuFeO3, has been investigated in thin films of LuFeO3. Separation of the two structural phases of LuFeO3 occurs on a length scale of micrometer, as visualized in real space using X-ray photoemission electron microscopy (X-PEEM). The results are consistent with X-ray diffraction and atomic force microscopy obtained from LuFeO3 thin films undergoing the irreversible structural transition from the hexagonal to the orthorhombic phase of LuFeO3, at elevated temperatures. The sharp phase boundaries between the structural phases are observed to align with the crystal planes of the hexagonal LuFeO3 phase. The coexistence of different structural domains indicates that the irreversible structural transition, from the hexagonal to the orthorhombic phase in LuFeO3, is a first order transition, for epitaxial hexagonal LuFeO3 films grown on Al2O3.

The electronic structure for the conduction bands of both hexagonal and orthorhombic LuFeO3 thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectral features and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states have not changed, the spectra are sensitive to the changes in the local environments of the Fe(3+) and Lu(3+) sites in the hexagonal and orthorhombic structures. Using the crystal-field splitting and the hybridizations that are extracted from the measured electronic structures and the structural distortion information, we derived the occupancies of the spin minority states in Fe(3+), which are non-zero and uneven. The single ion anisotropy on Fe(3+) sites is found to originate from these uneven occupancies of the spin minority states via spin-orbit coupling in LuFeO3.

The overall goal of this basic research has been to develop novel, boron carbide-based polymers with novel chemical and electronic structures to enhance sensitivity to neutron detection. Films containing orthocarboranes with benzene, 1,4- diaminobenzene, or pyridine have been developed and characterized by photoemission and neutron voltaics studies at zero bias. Orthocarborane/pyridine films with pyridine:orthocarborane ratios1 deposited on n-type Si show greatly enhanced sensitivity to thermal neutrons, even with lower total B content, than pure boron carbide films, while remaining gamma-blind. The enhanced sensitivity indicates greatly enhanced charger collection efficiency in the carborane/pyridine films.

The adsorption of molecular films made of small molecules with a large intrinsic electrical dipole has been explored. The data indicate that such dipolar molecules may be used for altering the interface dipole screening at the metal electrode interface in organic electronics. More specifically, we have investigated the surface electronic spectroscopic properties of zwitterionic molecules containing 12π electrons of the p-benzoquinonemonoimine type, C(6)H(2)(···NHR)(2)(···O)(2)(R = H (1), n-C(4)H(9) (2), C(3)H(6)-S-CH(3) (3), C(3)H(6)-O-CH(3) (4), CH(2)-C(6)H(5) (5)), adsorbed on Au. These molecules are stable zwitterions by virtue of the meta positions occupied by the nitrogen and oxygen substituents on the central ring, respectively. The structures of 2-4 have been determined by single crystal X-ray diffraction and indicate that in these molecules, two chemically connected but electronically not conjugated 6π electron subunits are present, which explains their strong dipolar character. We systematically observed that homogeneous molecular films with thickness as small as 1 nm were formed on Au, which fully cover the surface, even for a variety of R substituents. Preferential adsorption toward the patterned gold areas on SiO(2) substrates was found with 4. Optimum self-assembling of 2 and 5 results in ordered close packed films, which exhibit n-type character, based on the position of the Fermi level close to the conduction band minimum, suggesting high conductivity properties. This new type of self-assembled molecular films offers interesting possibilities for engineering metal-organic interfaces, of critical importance for organic electronics.

Direct graphene growth on oxides, without a metal catalyst, is a critical step towards the industrial-scale development of graphene devices. Such growth has been accomplished on MgO(111) by physical and chemical vapor deposition, and on Co3O4(111) by molecular beam epitaxy. For MgO(111), there is evidence of significant oxide reconstruction and reaction with the first carbon layer, and a ~ 0.5-1 eV band gap, suggesting a commensurate graphene/oxide interface. For Co3O4(111), growth occurs in a layer-by-layer fashion, with an incommensurate interface. In both cases, there is significant graphene-to-oxide charge transfer. The different results for the two different oxides appear to be due to the relative instability of the O-terminated (111) MgO surface. These results suggest a broad variety of potential electronic/spintronic applications, and indicate feasible routes towards fabrication of graphene devices by industrially practical and scalable methods.

We compare the electronic structure of a quinonoid zwitterionic type molecule adsorbed on both gold and graphene on copper substrates. This (6Z)-4-(butylamino)-6-(butyliminio)-3-oxocyclohexa-1,4-dien-1-olate, C6H2( ⋯ NHR)2( ⋯ O)2 where R = n-C4H9, film is made of small molecules with a large intrinsic dipole of 10 Debyes. We find that the photoemission and inverse photoemission final states are well screened for these dipolar molecules on gold. This is not observed when they are adsorbed on graphene on copper. This weaker screening results in a larger highest occupied molecular orbital to lowest unoccupied molecular orbital gap for the molecules on graphene.

Structural, electronic, and magnetic properties of the Fe-, Co-, Ni-, and V-intercalated graphene bilayer sandwich (denoted by C2|M|C2, M = Fe, Co, Ni, and V) and graphene on hexagonal boron nitride (h-BN) bilayer sandwich (denoted by C2|M|BN, M = Fe, Co, Ni, and V) are studied by using density functional theory method. We find that both the graphene bilayer and graphene-h-BN bilayer in all the C2|M|C2 and C2|M|BN sandwiches favor AB stacking over AA stacking mode. The Fe, Co, and Ni atoms prefer to be located over the center of C–C bonds whereas V atoms prefer to be located above the C atoms on graphene, and they all prefer to be located above the N atoms on h-BN sheet, regardless of the stacking mode. The C2|Fe|C2, C2|Co|C2, C2|Fe|BN, and C2|Co|BN sandwiches of AB stacking are all ferromagnetic metals with the spin polarization of 86%, 67%, 65%, and 46% at the Fermi level, respectively. By contrast, both C2|Ni|C2 and C2|Ni|BN sandwiches of AB stacking are nonmagnetic semiconductors with bandgaps of 0.64...

The electronic structure of several arene-based monomolecular films on Au(111), with and without an alkyl linker between the aromatic unit and thiol headgroup, has been investigated by photoemission and inverse photoemission. While the HOMO–LUMO gap in these films was found to depend on the aromatic backbone, the molecular band offset of the electronic states was strongly affected by the interfacial dipole. The smallest HOMO–LUMO gap was found for the strongly conjugated anthracene moiety, intermediate for terphenyl, and widest for the perfluorinated terphenyl. The perfluorinated terphenyl-based films appear to be more n-type as a semiconductor than the terphenyl or anthracene-based monolayers, as indicated by the placement of the Fermi level (chemical potential) relative to the conduction or lowest molecular orbital band edge. Accordingly, the occupied electronic states related to the aromatic rings sink to greater binding energies, well below those for the alkyl linker, and thus for the perfluorinated t...

We have investigated the chemisorption of two isomers of diiodobenzene on the molecular ferroelectric copolymer poly(vinylidene fluoride) with trifluoroethylene (70:30) as a function of the polymeric ferroelectric domain orientation. We find that the 1,4-p-diiodobenzene adsorption at 150 K strongly favors a positive ferroelectric domain orientation while the 1,2-o-diiodobenzene adsorption at 150 K strongly favors a negative ferroelectric domain orientation. Both polar and nonpolar adsorbates are influenced by the substrate dipole direction. Because a nonpolar isomer is also affected by the surface dipole direction, and hence the surface chemical termination, it is clear that surface chemistry and not simply surface dipoles matter in the chemisorption process.

We investigated the electron–phonon coupling (EPC), in the vicinity of the Fermi level, for the surface states of the Au-covered Mo(1 1 2) surface from high-resolution angle resolved photoemission data taken parallel to the surface corrugation (i.e. 〈 1 _ 1 _ 1 〉 ). The changes of the widths of the surface weighted bands, induced by Au layers, are discussed in terms of electron–electron interactions, electron impurity scattering and electron–phonon coupling. Gold overlayers suppress the mass enhancement of the Mo(1 1 2) surface band crossing the Fermi level at 0.54 A−1. The data indicate that significant contributions from impurity and defect scattering must be considered in any serious analysis of the imaginary part of the self energy and that there are interface effects that can have a profound influence on the imaginary part of the self energy.

We have compared the photovoltaic charging of the (1 0 0) surface termination for Cu doped and undoped Li 2 B 4 O 7 . While the surface charging at the (1 0 0) surface of Li 2 B 4 O 7 is significantly greater than observed at (1 1 0) surface, the Cu doping plays a role in reducing the surface photovoltage effects. With Cu doping of Li 2 B 4 O 7 , the surface photovoltaic charging is much diminished at the (1 0 0) surface. The density of states observed with combined photoemission and inverse photoemission remains similar to that observed for the undoped material, except in the vicinity of the conduction band edge.

We have investigated the absorption and adsorption of three isomers of di-iodobenzene on molecular films of a zwitterionic p-benzoquinonemonoimine-type molecule which is characterized by a large in...

Wave vector-resolved inverse photoelectron spectroscopy (IPES) measurements demonstrate that there is a large variation of interfacial charge transfer for graphene grown by chemical vapor depositio...

Gd/Ni compounds with different Gd concentration have been investigated with constant initial state spectroscopy (CIS) of photoemission utilizing the light of synchrotron radiation. The photoemission cross-sections of Gd 5d and 4f states show a strong resonance in CIS spectra at the Gd 5p absorption edge. The screenings of Gd ions by Ni 3d conduction electrons results in a dramatic suppression of the 5p 6 4f 7 5d 1 6s 2 to 5p 5 4f 7 5d 2 6s 2 resonant enhancement of photoemission valence band intensities. This decrease in the super-Coster―Kronig photoemission resonant enhancement of the valence band can be related to the hybridized Gd 5d and Ni 3d bands near the Fermi level, consistent with performed first-principles calculations of local densities of states.

Based on the experimentally determined pairwise site locations of transition metal atoms in doped semiconducting boron carbides, model spin-polarized electronic structure calculations indicate that some transition metal doped semiconducting boron carbides may act as excellent spin filters when used as the dielectric barrier in a magnetic tunnel junction structure. The local spin configuration of all the 3d transition metals, Ti to Cu, doped boron carbides are compared using first-principle total energy calculations on cluster and infinite icosahedral chain models. In the case of Ti and Fe doping, there may be considerable enhancements in the magneto-resistance of the heterostructure. The models also confirm that the favorable sites 3d transition metal atoms occupied are within the icosahedral cage, in a pairwise fashion on adjacent icosahedra.

We review the pyroelectric properties and electronic structure of Li2B4O7(110) and Li2B4O7(100) surfaces. There is evidence for a pyroelectric current along the [110] direction of stoichiometric Li2B4O7 so that the pyroelectric coefficient is nonzero but roughly 103 smaller than along the [001] direction of spontaneous polarization. Abrupt decreases in the pyroelectric coefficient along the [110] direction can be correlated with anomalies in the elastic stiffness C33D contributing to the concept that the pyroelectric coefficient is not simply a vector but has qualities of a tensor, as expected. The time dependent surface photovoltaic charging suggests that surface charging is dependent on crystal orientation and doping, as well as temperature.

The electronic structure of methylammonium lead bromide (CH3NH3PbBr3) single crystals has been investigated through a combination of resonant photoemission and theoretical modeling. There are Pb spectral contributions throughout the valence band. Importantly, the electronic structure at the top of the valence band is found to be dominated by the hybridized Pb-Br bands, not methylammonium bromide. The results line up with the partial density of states obtained from density functional theory and confirm that much of the valence band has some Pb spectral weight.

The dehydrogenation of semiconducting boron carbide (B(10)C(2)H(x)) films as well as the three closo-carborane isomers of dicarbadodecaborane (C(2)B(10)H(12)) and two isomers of the corresponding closo-phosphacarborane (PCB(10)H(11)) all appear to be very similar. Photoionization mass spectrometry studies at near-threshold gas phase photoionization indicate that the preferred pathway for dissociation of the parent cation species (C(2)B(10)H(10)(+) or PCB(10)H(9)(+)) is, in all cases, the loss of H(2). Ab initio density functional theory (DFT) calculations indicate that energetically preferred sites for exopolyhedral hydrogen (B-H) bond dissociation are in all cases at B atoms opposite the C atoms in the parent cage molecule. The site of photodissociation of hydrogen from semiconducting boron carbide (B(10)C(2)H(x)) films, fabricated by plasma-enhanced chemical vapor deposition, is a cage boron atom that can bond to nitrogen upon exposure to VUV light in the presence of NH(3). Shifts in core level binding energies due to nitrogen bond formation indicate that B-N bond formation occurs only at B atoms bound to other boron atoms (B-B sites) and not at B-C sites or at C sites, in agreement with gas phase results.

We have successfully prepared EuO films on Si(100) wafers via pulsed laser deposition (PLD). It is well recognized that EuO grows with texture growth along (100) but the addition of 4% Gd changes the lattice constant and the texture growth to (111) as well as having a profound influence on the magnetic properties. The differences in the effects between Gd doping and oxygen vacancies, both expected to be n-type (donor state) dopants in EuO, are discussed.

The structure−electronic structure relationship of nonmetalated meso-tetraphenyl porphyrin (2H-TPP) on the (111) surfaces of Ag, Cu, and Au was studied with a combination of scanning tunneling microscopy, photoelectron spectroscopy, and density functional theory. We observe that the molecules form a 2D network on Ag(111), driven by attractive intermolecular interactions, while the surface migration barriers are comparatively small and the charge transfer to the adsorbed molecules is minimal. This is in contrast to a significant charge transfer observed in 2H-TPP/Cu(111), resulting in repulsive forces between the molecules that prevent molecular adlayer network formation. It is shown that the limiting factor in formation of self-organized networks is the nature of the frontier orbital overlap and the adsorbate−interface electron transfer. Further, the electronic structure, most notably the HOMO−LUMO splitting, are found to be dependent on the substrate as well. The comparison of the results in this article...

Atomic-scale structure of the growth of a gold film on (1 1 2) plane of Mo single crystal was investigated by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) up to two monolayers (ML) of gold coverage. Both LEED and STM results establish that Au grows on Mo(1 1 2) in a layer-by-layer mode, for at least the first two monolayers. A number of ordered structures are formed and both the first and second layers adopt the Mo(1 1 2) 1 × 1 surface structure upon completion. For some gold layers on Mo(1 1 2), notably the 1.66 monolayer 3 × 1 and 1.75 monolayer 4 × 1 gold overlayers, we find evidence of a phase transition associated with increasing disorder in gold layers with structural corrugation and anisotropic band structure. The signature of this phase transition, at temperatures in the range of 400–500 K, is a sharp decrease in the overlayer effective Debye temperature.

Photoactive perovskite quantum dot films, deposited via an inkjet printer, have been characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The crystal structure and bonding environment are consistent with CsPbBr3 perovskite quantum dots. The current-voltage (I-V) and capacitance-voltage (C-V) transport measurements indicate that the photo-carrier drift lifetime can exceed 1 ms for some printed perovskite films. This far exceeds the dark drift carrier lifetime, which is below 50 ns. The printed films show a photocarrier density 109 greater than the dark carrier density, making these printed films ideal candidates for application in photodetectors. The successful printing of photoactive-perovskite quantum dot films of CsPbBr3, indicates that the rapid prototyping of various perovskite inks and multilayers is realizable.

We find a pyroelectric current along the 〈110〉 direction of stoichiometric Li2B4O7 so that the pyroelectric coefficient is nonzero but roughly 10−3 smaller than along the 〈001〉 direction of spontaneous polarization. Abrupt decreases in the pyroelectric coefficient along the 〈110〉 direction can be correlated with anomalies in the elastic stiffness C33D contributing to concept that the pyroelectric coefficient is not simply a vector but has qualities of a tensor, as expected. The time dependent surface photovoltaic charging suggests that an inverse piezoelectric effect occurs at the (110) surface but not the (100) surface. Both effects along the 〈110〉 direction or at the (110) surface are distinct the conventional as a bulk pyroelectric effect.

The shallow Li 1s core level exhibits a surface-to-bulk core level shift for the stoichiometric Li 2 B 4 O 7 (1 1 0) surface. Angle-resolved photoemission spectroscopy was used to indentify Li 1s bulk and surface core level components at binding energies −56.5±0.4 and −53.7±0.5 eV, respectively. We find photoemission evidence for surface states of Li 2 B 4 O 7 (1 1 0) that exist in the gap of the projected bulk density of states. The existence of surface states is consistent with the large surface-to-bulk core level shift for the Li 1s core.

Differences are seen in the adsorption of 1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene on graphite, as a function of exposure, using core level photoemission. The isomer 1,3-di-iodobenzene exhibits significant differences from 1,2-di-iodobenzene, and 1,4-di-iodobenzene in apparent sticking coefficients and core level binding energies. 1,3-Di-iodobenzene adsorb on graphite at 110 K in a strongly Stranski–Krastanov or Volmer–Weber (island) growth mode. The implication is that, even for small molecules adsorption, the adsorbate dipole in the plane of surface and the choice of isomer may matter.

We discuss the interactions of adsorbates with the organic ferroelectric copolymer poly(vinylidene fluoride (PVDF)–trifluoroethylene (TrFE)). Range of molecular adsorbates is discussed from the smaller polar molecules like water, which is small enough to both adsorb and absorb, to the larger macrocyclic metal–organic metal phthalocyanines. The changes in local dipole orientation may affect the strength of the coupling between adsorbate or absorbate and the copolymer poly(vinylidene fluoride–trifluoroethylene). The interface dipole interactions may also affect device properties. The dipole interactions are implicated at the interface between copper phthalocyanine and poly(vinylidene fluoride with trifluoroethylene) affecting the band offsets and the diode properties.

Time-of-flight mass analysis with multi-stop coincidence detection was used to study the multi-cation ionic fragmentation of the closo carborane cage molecule closo -1,2-orthocarborane (C2B10H12) following inner-shell excitation in or above the B 1s regime. Electron ion coincidence spectra reveal the cationic products which are formed after core level excitation. Distinct changes in fragmentation pattern are observed as a function of excitation energy. Photoelectron–photoion–photoion coincidence (PEPIPICO) spectroscopy was used to study the dominant fission routes in the core level excitation regime. Series of ion pairs are identified, where asymmetric fission dominates, leading to ion pairs of different mass. Suitable fission and fragmentation mechanisms are discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Single molecular layers of 2-(4-pyridylethyl)triethoxysilane have been deposited on native oxide surfaces of silicon, with the triethoxysilylethyl groups towards the silicon oxide interface and pyridine at the surface. It is possible to “shave” or mechanically break the molecular bonds at the alkoxy-silane (Si–C) bond using scanning atomic force microscope, leaving large swaths of surface area cut to a depth of 0.64 ± 0.06 nm, exposing the silicon of the alkoxy-silane ligand. Mechanical cleavage of the pyridine ligand alone is also possible, but more difficult to control selectively.

There is interplay between intra-atomic orbital hybridization and extra-atomic hybridization in various gadolinium systems, which affects magnetic coupling and electron itinerancy (localization). The results do not always follow expectation. The experimental band structure of thin Gd(0001) films, grown on the Mo(112) surface, along the Γ-M does not agree with expectations even qualitatively. In particular, the dispersion of the gadolinium band, with strong 5d weight near 2 eV binding energy provides considerable evidence to support the case for 4f-5d hybridization, with increasing 5d localization. On the other hand, there is also evidence of extra-atomic Gd 4f hybridization leading band dispersion in the occupied 4f levels in Gd 2 O 3 .

Reversible bromoform adsorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF–TrFE 70:30) was examined by photoemission and inverse photoemission spectroscopies. The adsorption of bromoform on this polymer surface is associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state, whose intensity scales with the unscreened photoemission final state.

Thin films of the metal organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)), deposited on ferromagnetic Co(111) at 40 K, exhibit a finite electron spin polarization. The spin polarization magnitude and sign for Cu(CNdpm)2 deposited on Co(111) is coverage dependent, but deviates from the mean field expectations for a simple paramagnet on a ferromagnetic substrate. The spin asymmetry is seen to favor select molecular orbitals, consistent with the predicted single molecule density of states. The overlayer polarization observed indicates a strong influence of the ferromagnetic Co(111) substrate and some extra-molecular magnetic coupling.

The effects of vacuum ultraviolet radiation on the adsorbed copper center molecule bis(4-cyano-2,2,6,6tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)) was studied by photoemission spectroscopy. Changes in the ultraviolet photoemission spectra (UPS) of Cu(CNdpm)2, adsorbed on Co(1 1 1), indicate that the ultraviolet radiation leads to decomposition of Cu(CNdpm)2 and this decomposition is initially dominated by loss of peripheral hydrogen.

Using light-polarization-dependent angle-resolved photoemission, the metal−organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2, i.e., C24H36N2O4Cu, Cu(II))...

An increase in the density of states between the oxygen 2p bands and the Fermi level is seen with increasing Gd concentrations. In addition, for the Gd-doped HfO 2 films, the Gd 4f photoexcitation peak at 5.5 eV below the valence band maximum was identified using resonant photoemission. Electrical measurements show pronounced rectification properties for lightly-doped Gd:HfO 2 films on p -Si and for heavily-doped Gd:HfO 2 films on n -Si, suggesting a crossover from n -type to p -type behavior with increasing doping level. In addition, there is an increase in the reverse bias current with neutron irradiation.

The layered In4Se3 system does have a bulk band structure (i.e. discernable and significant band dispersion) perpendicular to the cleavage plane. Band widths (the extent of dispersion) of 300 meV or more are observed, for In-p and Se-p weighted bands within the valence region, and is indicative of a bulk band structure. Two-dimensionality of state is clearly not conserved, and there must exist interactions between layers sufficient to support a bulk band structure. Fil: Liu, J.. University Of Nebraska; Estados Unidos Fil: Losovyj, Y. B.. University Of Nebraska; Estados Unidos Fil: Komesu, T.. University Of Nebraska; Estados Unidos Fil: Dowben, P.A.. University Of Nebraska; Estados Unidos Fil: Makinistian, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Albanesi, Eduardo Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Petukhov, A.G.. South Dakota School of Mines; Estados Unidos Fil: Galiy, P.. Lviv National University; Ucrania Fil: Fiyala, Y.. Lviv National University; Ucrania

We show that at the hetero-molecular interface, the molecular band offsets can be modified by either adjusting the dopant or dopant concentration of one or both molecular layers or by changing the dipole orientation at the intermolecular interface. Photoemission studies reveal the changes in electronic structure and diode devices exhibit conduction properties that are altered in response to changes to the molecular band offsets. As a demonstration, thin film copper phthalocyanine to crystalline ferroelectric copolymer poly(vinylidene fluoride with trifluoroethylene) heterojunction diodes, without additional dopants, are compared with doped polyaniline layers on the crystalline ferroelectric copolymer poly(vinylidene fluoride with trifluoroethylene).

The adsorption of two very different adsorbates, gold and oxygen, induce the formation of a (3 × 1) surface structure on both W(1 1 2) and Mo(1 1 2). In spite of similar adsorbate unit cells, the surface electronic structure, derived from photoemission, exhibits pronounced differences for the two adsorbates. Indeed, both experiment and simulations indicate substantial changes in electronic structures of (1 × 1) and (3 × 1) gold overlayers supported by highly anisotropic (1 1 2) plane. We speculate that (3 × 1) is a favored periodicity in the atomic rearrangement of the (1 1 2) surfaces of molybdenum and tungsten due in part as a result of the initial state band structure of these surfaces.

The effective Debye temperatures of the highly spin-polarized material CoS 2 were measured using temperature dependent low energy electron diffraction and shown to be dependent upon electron kinetic energy. The normal dynamic motion of the (100) surface results in the effective surface Debye temperature of 326 ± 9 K compared to a bulk Debye temperature of 612 ± 24 K . Similar values for the bulk Debye temperature have been obtained through LEED I(V) analysis and core level photoemission with a lower value for the bulk Debye temperature found from heat capacity measurements.

International audience; Driven by the huge potential of engineering the molecular band offset with highly dipolar molecules for improving charge injection into organic electrics, the anchoring of various N-alkyl substituted quinonoid zwitterions of formula image file: c5nj03251b-t1.tif (R = iPr, Cy, CH2CH(Et)CH2CH2CH2CH3,…) on gold surfaces is studied. The N–Au interactions result in an orthogonal arrangement of the zwitterions cores with respect to the surface, and stabilize adsorbed compact rows of molecules. IR spectroscopy is used as a straightforward diagnostic tool to validate the presence of ultra-thin molecular films. When combined with computational studies, IR measurements indicate that the presence of a CH2 group in α position to the nitrogen atom is important for a successful anchoring through N–Au interactions. The presence of such a flexible CH2 spacer, or of aryl groups, enables π-interactions with the surface, making possible the anchoring of enantiopure or sterically-hindered zwitterions. X-ray diffraction analyses indicate that the intermolecular spacing within a row of molecules can be modulated by the nature of the alkyl substituent R. This modulation is directly relevant to the electronic properties of the corresponding molecular films since these zwitterions are expected to form rows on gold surfaces similar to those observed in the bulk crystalline state.

The thickness and temperature dependence of in situ grown cobalt thin films on Cr2O3(0 0 0 1) single crystalline substrate has been studied by low energy electron microscopy (LEEM). The LEEM images indicate that growth of thin Co films (⩽5 monolayers) on chromia at 100 K tends to be continuous and flat with suppressed island growth compared to films grown on chromia at room temperature and above (to ~440 K). Low energy electron diffraction indicates that disorder builds and crystallinity of the cobalt thin film decreases with increased film thickness. Compared with cobalt thin films on Al2O3(0 0 0 1) single crystalline substrate, cobalt thin films on Cr2O3(0 0 0 1) show larger magnetic contrast in magnetic force microscopy indicating enhancement of perpendicular anisotropy induced by Cr2O3.

International audience; Temperature- and coverage-dependent studies of the Au(1 1 1)-supported spin crossover Fe(II) complex (SCO) of the type [Fe(H2B(pz)2)2(bipy)] with a suite of surface-sensitive spectroscopy and microscopy tools show that the substrate inhibits thermally induced transitions of the molecular spin state, so that both high-spin and low-spin states are preserved far beyond the spin transition temperature of free molecules. Scanning tunneling microscopy confirms that [Fe(H2B(pz)2)2(bipy)] grows as ordered, molecular bilayer islands at sub-monolayer coverage and as disordered film at higher coverage. The temperature dependence of the electronic structure suggest that the SCO films exhibit a mixture of spin states at room temperature, but upon cooling below the spin crossover transition the film spin state is best described as a mix of high-spin and low-spin state molecules of a ratio that is constant. This locking of the spin state is most likely the result of a substrate-induced conformational change of the interfacial molecules, but it is estimated that also the intra-atomic electron–electron Coulomb correlation energy, or Hubbard correlation energy U, could be an additional contributing factor.

Growth by chemical vapor deposition (CVD) leads to multilayer WS2 of very high quality, based on high-resolution angle-resolved photoemission spectroscopy. The experimental valence band electronic structure is considered to be in good agreement with that obtained from density functional theory calculations. We find the spin-orbit splitting at the K¯ point to be 420 ± 20 meV with a hole effective mass of −0.35 ± 0.02 me for the upper spin-orbit component (the branch closer to the Fermi level) and −0.43 ± 0.07 me for the lower spin-orbit component. As predicted by theory, a thickness-dependent increase of bandwidth is observed at the top of the valence band, in the region of the Brillouin zone center. The top of the valence band of the CVD-prepared films exhibits a substantial binding energy, consistent with n-type behavior, and in agreement with transistor characteristics acquired using devices incorporating the same WS2 material.

Lanthana (La2O3) thin films were grown by atomic layer deposition using the homoleptic amino precursor La[N(TMS)2]3. This volatile metal-organic was synthesized on a large scale using commercially available lanthanum triflate (La(OTf)3) and the amino was recovered in excellent yields and high analytical purity. La2O3 thin films (∼25 nm) were grown on p-type (1 0 0) silicon substrates using a hot-wall ALD reactor at 300 °C and exhibit smooth, featureless surfaces with rms roughnesses of 2.5 nm. PXRD indicates that the existing lanthana crystallites can be indexed in the hexagonal system.

Gd-doped HfO2 films were deposited on p-type silicon substrates in a reducing atmosphere. Photoemission measurements indicate the n-type character of Gd-doped HfO2 due to overcompensation with oxygen vacancies. The Gd 4f photoexcitation peak at 5.5 eV below the valence band maximum is identified using both resonant photoemission and first-principles calculations of the f hole. The rectifying (diode-like) properties of Gd-doped HfO2 to silicon heterojunctions are demonstrated.

The decomposition of cobaltocene under low energy electron irradiation appears facile, and evidence suggests that the decomposition products lead to an increase in the carrier concentration in semiconducting boron carbides. Using cobaltocene to introduce dopants, we fabricated a semiconducting boron carbide homojunction

In calculating band structure, the local density approximation and density functional theory are widely popular and do reproduce a lot of the basic physics. Regrettably, without some fine tuning, the local density approximation and density functional theory do not generally get the details of the experimental band structure correct, in particular the band gap in semiconductors and insulators is generally found to be too small when compared with experiment. For experimentalists using commercial packages to calculate the electronic structure of materials, some caution is indicated, as some long-standing problems exist with the local density approximation and density functional theory.

The absorption of water in Langmuir–Blodgett films of ferroelectric copolymers of polyvinylidene fluoride with trifluoroethylene is shown to depend upon the film thickness. This water absorption can have a profound effect on the dielectric properties of the copolymer films.

The possible origins of a low density of defect states within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap are suggested for regioregular poly(3-hexylthiophene). A number of “chemical” defects, impurities, and structural defects could contribute to features in photoemission for regioregular poly(3-hexylthiophene), observed within the highest occupied molecular orbital to lowest unoccupied molecular orbital gap of regioregular poly(3-hexylthiophene). POLYM. ENG. SCI., 47:1359–1364, 2007. © 2007 Society of Plastics Engineers