Remote Mesoscopic Signatures of Induced Magnetic Texture in Graphene.

Mesoscopic conductance fluctuations are a ubiquitous signature of phase-coherent transport in small conductors, exhibiting universal character independent of system details. In this Letter, however, we demonstrate a pronounced breakdown of this universality, due to the interplay of local and remote phenomena in transport. Our experiments are performed in a graphene-based interaction-detection geometry, in which an artificial magnetic texture is induced in the graphene layer by covering a portion of it with a micromagnet. When probing conduction at some distance from this region, the strong influence of remote factors is manifested through the appearance of giant conductance fluctuations, with amplitude much larger than e^{2}/h. This violation of one of the fundamental tenets of mesoscopic physics dramatically demonstrates how local considerations can be overwhelmed by remote signatures in phase-coherent conductors.

The emergence of the local moment molecular spin transistor.

Local moment molecular systems have now been used as the conduction channel in gated spintronics devices, and some of these three terminal devices might even be considered molecular spin transistors. In these systems, the gate voltage can be used to tune the molecular level alignment, while applied magnetic fields have an influence on the spin state, altering the magnetic properties, and providing insights to the magnetic anisotropy. More recently, the use of molecular spin crossover complexes, as the conduction channel, has led to devices that are both nonvolatile and have functionality at higher temperatures. Indeed, some devices have now been demonstrated to work at room temperature. Here, several molecular transistors, including those claiming to use single molecule magnets (SMM), are reviewed.

Manipulation of the molecular spin crossover transition of Fe(H2B(pz)2)2(bipy) by addition of polar molecules.

The addition of various dipolar molecules is shown to affect the temperature dependence of the spin state occupancy of the much studied spin crossover Fe(II) complex, [Fe{H2B(pz)2}2(bipy)] (pz = pyrazol-1-yl, bipy = 2,2'-bipyridine). Specifically, the addition of benzimidazole results in a re-entrant spin crossover transition, i.e. the spin state starts in the mostly low spin state, then high spin state occupancy increases, and finally the high spin state occupancy decreases with increasing temperature. This behavior contrasts with that observed when the highly polar p -benzoquinonemonoimine zwitterion C6H2(…NH2)2(…O)2 was mixed with [Fe{H2B(pz)2}2(bipy)], which resulted in locking [Fe{H2B(pz)2}2(bipy)] largely into a low spin state while addition of the ethyl derivative C6H2(…NHC2H5)2(…O)2 did not appear to perturb the spin crossover transition of [Fe{H2B(pz)2}2(bipy)].

Inkjet printable-photoactive all inorganic perovskite films with long effective photocarrier lifetimes.

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.

Comment on 'Electronic structure of Mo(1-x)Re x alloys studied through resonant photoemission spectroscopy'.

Further analysis of the resonant photoemission data, found within Sundar et al (2016 J. Phys.: Condens. Matter 28 315502), show the intensities do not follow the elemental composition in the Mo1-x Re x alloy. Similar trends are observed in the published data for Gd1-x Ni x alloy films. The analysis of the resonant photoemission intensities suggests that Mo in the Mo1-x Re x alloy and Gd in the Gd1-x Ni x alloy have nearest neighbor bonds to Re and Ni respectively. This means the A-B bond is favored over the average of the A-A bond and the B-B bond in these binary alloys, so that the short range order favors strong local ordering rather than clustering alloys.

Magnetization at the interface of Cr2O3 and paramagnets with large stoner susceptibility.

From the Cr 2p3/2 x-ray magnetic circular dichroism signal, there is clear evidence of interface polarization with overlayers of both Pd and Pt on chromia (Cr2O3). The residual boundary polarization of chomia is stronger for a Pt overlayer than in the case of a Pd overlayer. The reduction of chromia boundary magnetization with a paramagnetic metal overlayer, compared to the free surface, is interpreted as a response to the induced spin polarization in Pt and Pd. Magnetization induced in a Pt overlayer, via proximity to the chromia boundary magnetization, is evident in the polar magneto-optical Kerr measurements. These results are essential to explainations why Pt and Pd are excellent spacer layers for voltage controlled exchange bias, in the [Pd/Co] n /Pd/Cr2O3 and [Pt/Co] n /Pt/Cr2O3 perpendicular magneto-electric exchange bias systems. The findings pave the way to realize ultra-fast reversal of induced magnetization in a free moment paramagnetic layer, with possible application in voltage-controlled magnetic random access memory.

Surface-induced spin state locking of the [Fe(H2B(pz)2)2(bipy)] spin crossover complex.

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.

Low temperature growth of cobalt on Cr2O3(0 0 0 1).

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.

Symmetry-resolved surface-derived electronic structure of MoS2(0 0 0 1).

We find a wave vector dependence of the band symmetries for MoS(2)(0 0 0 1) in angle-resolved photoemission. The band structures are found to be significantly different for states of even and odd reflection parities, despite the absence of true mirror plane symmetry away from Γ, the Brillouin zone center, along the line to the K point, at the Brillouin zone edge. Our measurements agree with density functional theory (DFT) calculations for each band symmetry, with the notable exception of the Mo 4d(x(2)-y(2)) contributions to the valence band structure of MoS(2)(0 0 0 1). The band structure is indicative of strong S 3p and Mo 4d hybridization. In particular, the top of the valence band is predominantly composed of Mo 4d(3z(2)-r(2)) derived states near Γ, whereas near K Mo 4d(x(2)-y(2)) as well as Mo 4d(xy) dominate. In contrast, the bottom of the valence band is dominated by Mo 5s and S 3p(z) contributions.

Resonant photoemission and spin polarization of Co(1-x)Fe(x)S(2).

The valence band occupied state electronic structure of Co(1-x)Fe(x)S(2) in the region of the Fe/Co 3d bands has been investigated using photoemission and spin-polarized photoemission. As measured by using spin-polarized ultraviolet photoemission, the surface Fermi level spin polarization of Co(1-x)Fe(x)S(2) thin films at 50 K, specifically at x = 0, 0.05, 0.10 and 0.15, was found to be much reduced compared to that of the bulk. The spin polarization nonetheless increases with Fe concentration. The resonant photoemission spectroscopy provides evidence that S bands have a strong resonance at the photon energy corresponding to the Co 2p core level, indicating strong hybridization between Co and S bands in Co(1-x)Fe(x)S(2) (at small x). Similar evidence exists for Fe hybridization with the S bands.

The local metallicity of gadolinium doped compound semiconductors.

The local metallicities of Hf(0.97)Gd(0.03)O(2), Ga(0.97)Gd(0.03)N, Eu(0.97)Gd(0.04)O and EuO films were studied through a comparison of the findings from constant initial state spectroscopy using synchrotron light. Resonant enhancements, corresponding to the 4d → 4f transitions of Eu and Gd, were observed in some of the valence band photoemission features. The resonant photoemission intensity enhancements for the Gd 4f photoemission features are far stronger for the more insulating host systems than for the metallic system Eu(0.96)Gd(0.04)O. The evidence seems to suggest a correlation between the effective screening in the films and the resonant photoemission process.

A density functional theory study of the electron-phonon coupling at the Mo(112) surface.

The electron-phonon (e-p) coupling for the surface bands of Mo(112) has been studied by density functional theory (DFT). There are significant contributions from the surface phonon modes to the low frequency part of the phonon density of states and Eliashberg function, which results in enhanced e-p coupling at the surface and, consequently, an increase of the mass enhancement factor and the imaginary part of the self-energy. We suggest that the enhanced e-p coupling, together with anharmonic effects, scattering off impurities, as well as decay channels through adjacent bulk bands, leads to the increase of the linewidth of the electronic surface bands crossing the Fermi level observed in high resolution photoemission spectra of the Mo(112) surface.

When measured spin polarization is not spin polarization.

Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO(2) and Cr(2)O(3) illustrate some of the complications which hinders comparisons of spin polarization values.

The electron--phonon coupling at the Mo(112) surface.

We investigated the electron-phonon coupling (EPC), in the vicinity of the Fermi level, for the surface-weighted states of Mo(112) from high resolution angle-resolved photoemission data taken parallel to the surface corrugation (i.e. [Formula: see text]). The surface-weighted bandwidth may be discussed in terms of electron-electron interactions, electron impurity scattering and electron-phonon coupling and exhibits a mass enhancement factor λ = 0.42, within the Debye model, determined from the experimentally derived self-energy. Gold overlayers suppress the mass enhancement of the Mo(112) surface-weighted band crossing the Fermi level at 0.54 Å(-1).

Electronic structure of a graphene/hexagonal-BN heterostructure grown on Ru(0001) by chemical vapor deposition and atomic layer deposition: extrinsically doped graphene.

A significant BN-to-graphene charge donation is evident in the electronic structure of a graphene/h-BN(0001) heterojunction grown by chemical vapor deposition and atomic layer deposition directly on Ru(0001), consistent with density functional theory. This filling of the lowest unoccupied state near the Brillouin zone center has been characterized by combined photoemission/k vector resolved inverse photoemission spectroscopies, and Raman and scanning tunneling microscopy/spectroscopy. The unoccupied σ*(Γ(1) +) band dispersion yields an effective mass of 0.05 m(e) for graphene in the graphene/h-BN(0001) heterostructure, in spite of strong perturbations to the graphene conduction band edge placement.

The minority spin surface bands of CoS(2)(001).

Angle-resolved photoemission was used to study the surface electronic band structure of high quality single crystals of ferromagnetic CoS(2) (below 120 K). Strongly dispersing Co t(2g) bands are identified along the ⟨100⟩ [Formula: see text] direction, the [Formula: see text]-[Formula: see text] line of the surface Brillouin zone, in agreement with model calculations. The calculated surface band structure includes corrections for the previously determined surface structure of CoS(2)(001) and is in general agreement with the experimental photoemission spectra in the region of the Fermi level. There is evidence of the existence of several minority spin surface states, falling into a gap of the projected minority spin bulk CoS(2)(001) band structure.

The surface relaxation and band structure of Mo(112).

The experimental and theoretical surface band structures of Mo(112) are compared. This surface band structure mapping is presented with corrections included for the lattice relaxation of the Mo(112) surface. Quantitative low energy electron diffraction (LEED) has been used to determine the details of the Mo(112) surface structure. The first layer contraction is 14.9% by LEED intensity versus voltage analysis and is in general agreement with the 17.6% contraction found from total surface energy optimization. The electronic band structure is mapped out along [Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text] of the surface Brillouin zone (SBZ). There is strong evidence of electron-phonon coupling particularly in the region of the Fermi level band crossing at 0.54 Å(-1).

Comparison of n-type Gd(2)O(3) and Gd-doped HfO(2).

Gd(2)O(3) and Gd-doped HfO(2) films were deposited on p-type silicon substrates in a reducing atmosphere. Gd 4f photoexcitation peaks at roughly 7 and 5 eV below the valence band maximum have been identified using the resonant photoemission of Gd(2)O(3) and Gd-doped HfO(2) films, respectively. In the case of Gd(2)O(3), strong hybridization with the O 2p band is demonstrated, and there is evidence that the Gd 4f weighted band exhibits dispersion in the bulk band structure. The rectifying (diode-like) properties of Gd-doped HfO(2)-silicon and Gd(2)O(3)-silicon heterojunctions are demonstrated.

The influence of the molecular dipole on the electronic structure of isomeric icosahedral dicarbadodecaborane and phosphacarbadodecaborane molecular films.

We compare the molecular films of three different isomers of closo-dicarbadodecaborane (orthocarborane (1,2-C2B10H12), metacarborane (1,7-C2B10H12), paracarborane (1,12-C2B10H12)) and two related icosahedral cage molecules, 1-phospha-2-carbadodecaborane (1,2-PCB10H11) and 1-phospha-7-carbadodecaborane (1,7-PCB10H11) adsorbed on a variety of substrates. While the experimental electronic structure from combined photoemission and inverse photoemission studies of the molecular films are in good agreement with semiempirical calculations for the isolated molecule, there is a shift in the chemical potential for each molecule. The experimental position of the molecular chemical potential implicates an influence of both interface and adsorbate dipole.

Activated water desorption from poly(methylvinylidene cyanide).

We have investigated water desorption from the polymer poly(methylvinylidene cyanide). The angle resolved thermal desorption spectra show large deviations from the cosn theta distribution for water desorption from poly(methylvinylidene cyanide) indicative of an activated desorption process. The Arrhenius plots obtained from Polanyi-Wigner analysis of the thermal desorption data suggest that a two-state model of desorption applies, while theory suggests that lattice strain in the polymer plays a key role in the thermal desorption of water.