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Precisely controllable and reversible p/n-type electronic doping of molybdenum ditelluride (MoTe2 ) transistors is achieved by electrothermal doping (E-doping) processes. E-doping includes electrothermal annealing induced by an electric field in a vacuum chamber, which results in electron (n-type) doping and exposure to air, which induces hole (p-type) doping. The doping arises from the interaction between oxygen molecules or water vapor and defects of tellurium at the MoTe2 surface, and allows the accurate manipulation of p/n-type electrical doping of MoTe2 transistors. Because no dopant or special gas is used in the E-doping processes of MoTe2 , E-doping is a simple and efficient method. Moreover, through exact manipulation of p/n-type doping of MoTe2 transistors, quasi-complementary metal oxide semiconductor adaptive logic circuits, such as an inverter, not or gate, and not and gate, are successfully fabricated. The simple method, E-doping, adopted in obtaining p/n-type doping of MoTe2 transistors undoubtedly has provided an approach to create the electronic devices with desired performance.

Growth of a uniform oxide film with a tunable thickness on two-dimensional transition metal dichalcogenides is of great importance for electronic and optoelectronic applications. Here we demonstrate homogeneous surface oxidation of atomically thin WSe2 with a self-limiting thickness from single- to trilayers. Exposure to ozone (O3) below 100 °C leads to the lateral growth of tungsten oxide selectively along selenium zigzag-edge orientations on WSe2. With further O3 exposure, the oxide regions coalesce and oxidation terminates leaving a uniform thickness oxide film on top of unoxidized WSe2. At higher temperatures, oxidation evolves in the layer-by-layer regime up to trilayers. The oxide films formed on WSe2 are nearly atomically flat. Using photoluminescence and Raman spectroscopy, we find that the underlying single-layer WSe2 is decoupled from the top oxide but hole-doped. Our findings offer a new strategy for creating atomically thin heterostructures of semiconductors and insulating oxides with potential for applications in electronic devices.

We study the second-order Raman process of mono- and few-layer MoTe$_2$, by combining {\em ab initio} density functional perturbation calculations with experimental Raman spectroscopy using 532, 633 and 785 nm excitation lasers. The calculated electronic band structure and the density of states show that the electron-photon resonance process occurs at the high-symmetry M point in the Brillouin zone, where a strong optical absorption occurs by a logarithmic Van-Hove singularity. Double resonance Raman scattering with inter-valley electron-phonon coupling connects two of the three inequivalent M points in the Brillouin zone, giving rise to second-order Raman peaks due to the M point phonons. The predicted frequencies of the second-order Raman peaks agree with the observed peak positions that cannot be assigned in terms of a first-order process. Our study attempts to supply a basic understanding of the second-order Raman process occurring in transition metal di-chalcogenides (TMDs) and may provide additional information both on the lattice dynamics and optical processes especially for TMDs with small energy band gaps such as MoTe$_2$ or at high laser excitation energy., Comment: 10 pages, 5 figures

Recently, there has been considerable interest in organic/c-Si heterojunction solar cells using organic conductive polymer such as poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) that blocks electrons but passes holes. This PEDOT:PSS/c-Si heterojunction works as a photovoltaic device without using p-n junction and TCO layer. η has reached at 10-13% without using textured c-Si, anti-reflection (AR) coating layer. These findings suggest that the PEDOT:PSS/c-Si heterojunctions is a promising for high-efficiency solution-processed solar cells. Thus, we termed this type of solar cell as c-Si heterojunction with organic thin-layers, “HOT” solar cell. In the present paper, we demonstrate the increased η with improved stability for air storage and light exposure of PEDOT:PSS/c-Si heterojunctuon solar cells by removal of PSS matrix from SC PEDOT:PSS thin film using a mixture of organosulfonic acid and organic solvent.

We investigate the micromechanical exfoliation and van der Waals (vdW) assembly of ferromagnetic layered dichalcogenide Fe0.25TaS2. The vdW interlayer coupling at the Fe-intercalated plane of Fe0.25TaS2 allows exfoliation of flakes. A vdW junction between the cleaved crystal surfaces is constructed by dry transfer method. We observe tunnel magnetoresistance in the resulting junction under an external magnetic field applied perpendicular to the plane, demonstrating spin-polarized tunneling between the ferromagnetic layered material through the vdW junction., Comment: 16 pages, 4 figures

As a stable and 'epitaxial' passivation of a Si surface, we propose the bilayer-GaSe termination of a Si(111) surface. This surface is fabricated by depositing one monolayer of Ga on a clean Si(111) surface and subsequent annealing in a Se flux at around 520 degreesC, which results in unreconstructed 1 x 1 termination of the Si(111) surface by bilayer-GaSe. We found by scanning tunneling microscopy observation that slow cooling of the clean Si(111) surface from 850 to 520 degreesC with simultaneous deposition of a Ga flux results in better termination of the Si(111) surface. It was also found that this surface is stable against heating around 400 degreesC in O-2 atmosphere of 3 x 10(-3) Pa. By utilizing these properties of the bilayer-GaSe terminated surface, we have succeeded in fabricating ZnO quantum dots on this substrate. (C) 2002 Elsevier Science B.V. All rights reserved.

The anionic ruthenium and iron complexes Li[(η5-C5Me5)M(CO)2] (M=Ru (1-Ru), Fe (1-Fe)) were generated by deprotonation of the transition metal hydride (η5-C5Me5)M(CO)2H with n-BuLi in tetrahydrofuran (THF). The reaction proceeded at −45 °C immediately. Reactions of 1 with various electrophiles (Me3SiCl, pTol2HSiCl, Me2SiCl2, MeSiCl3, SiCl4, Me3SiSiMe2Cl, and Ph2GeCl2) afforded the corresponding nucleophilic substitution products (η5-C5Me5)M(CO)2ER3 (E=Si, Ge) via salt-elimination.

Nano-scale oxide patterns were fabricated on a bilayer-GaSe terminated Si(1 1 1) surface using an atomic force microscope (AFM) in air. The Si(1 1 1) surface regularly terminated by bilayer-GaSe is very stable in air, although it can be oxidized through the electrochemical reaction when positive sample bias voltage is applied between the surface and a conductive cantilever tip of AFM. It has been revealed that higher sample bias voltage, slower tip velocity and/or higher ambient humidity produce wider and/or thicker oxide protrusions. Then, nano-scale oxide patterns as narrow as 50 nm have been successfully drawn on the terminated surface by adjusting these experimental conditions. These oxide lines can be etched away by dipping the sample into aqueous HF solution, and nano-scale grooves can be fabricated on the bilayer-GaSe terminated Si(1 1 1) surface. (C) 2002 Elsevier Science B.V. All rights reserved.

We have fabricated a vacancy-ordered Ga2Se3 epitaxial film by molecular beam epitaxy on a vicinal Si(001) surface tilted toward the [110] direction by 4degrees. It was found by reflection high-energy electron diffraction observations that Ga2Se3 films grown around 470degreesC with Se/Ga flux ratios higher than 100 show excellent ordering of Ga vacancies, The vacancy ordering was not observed when the substrate temperature was higher than 490degreesC. In addition, polycrystalline film growth was dominant when the substrate temperature was lower than 450degreesC, and no vacancy ordering was observed when the Se/Ga ratio was 10. Only a poor crystallinity Ga2Se3 film was obtained on a nominal Si(001) substrate, which suggests that the single-domain 2 x I reconstruction on the vicinal Si(001) surface is essential to the growth of the vacancy-ordered Ga2Se3 film. (C) 2002 Elsevier Science B.V. All rights reserved.

We demonstrate the potential of barium hydroxide, Ba(OH)2, as a hole blocking layer on the photovoltaic performance of front- and back-organic/n-type crystalline silicon (n-Si) heterojunction solar cells with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS). The power conversion efficiency (PCE) of the front-PEDOT:PSS/n-Si heterojunction solar cell was increased from 12.8% for pristine to 13.6% with a 2-nm-thick Ba(OH)2 interlayer at the rear n-Si and aluminum (Al) cathode interface due to the enhanced hole blocking as well as electron injection capability to the Al cathode in the infrared region. PCE was further increased to 14.3% with a short-circuit density JSC of 30.27 mA/cm2, an open-circuit voltage VOC of 0.632 V, and a fill factor FF of 0.75 using a 20-nm-thick 4,4′-Cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] as an antireflection layer. PCE of the back-PEDOT:PSS/n-Si heterojunction solar cells was also increased from 4.4% for pristine to 8.1% with a JSC of 33.40 mA/cm2, a VOC of 0.573 V, and an FF of 0.423 by inserting a 2-nm-thick Ba(OH)2 layer at the front-Al and isotropically textured n-Si interface. These findings imply that Ba(OH)2 has great potential as an efficient hole-blocking layer for both front- and back-PEDOT:PSS/n-Si heterojunction solar cells.

A high-efficiency bulk heterojunction organic photovoltaic cell (OPV) was achieved by the electrospray deposition method. The surface roughness of the P3HT:PCBM thin film can be reduced using the mixed solvent consisting of o-dichlorobenzene (o-DCB) and acetone. The effect of acetone concentration is related to its dielectric constant. Under an optimized concentration of acetone in o-DCB (20 vol%), the P3HT/PCBM active layer with a smooth surface can be formed, and the power conversion efficiency of the OPV was 1.9%. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Two-dimensional layered crystals could show phonon properties that are markedly distinct from those of their bulk counterparts, because of the loss of periodicities along the c-axis directions. Here we investigate the phonon properties of bulk and atomically thin α-MoTe2 using Raman spectroscopy. The Raman spectrum of α-MoTe2 shows a prominent peak of the in-plane E(1)2g mode, with its frequency upshifting with decreasing thickness down to the atomic scale, similar to other dichalcogenides. Furthermore, we find large enhancement of the Raman scattering from the out-of-plane B(1)2g mode in the atomically thin layers. The B(1)2g mode is Raman inactive in the bulk, but is observed to become active in the few-layer films. The intensity ratio of the B(1)2g to E(1)2g peaks evolves significantly with decreasing thickness, in contrast with other dichalcogenides. Our observations point to strong effects of dimensionality on the phonon properties of MoTe2.

Gallylene-bridged diiron complexes [Cp‘Fe(CO)2]2(μ-GaMes) (Cp‘ = η-C5Me5 (1a), η-C5H5 (1b); Mes = 2,4,6-trimethylphenyl) were synthesized by the reactions of M[Cp‘Fe(CO)2] (M = K, Na) with MesGaCl2 in THF. Photolysis of a toluene solution of complex 1a resulted in the formation of the trans isomer of the gallylene- and carbonyl-bridged diiron complex [Cp*Fe(CO)]2(μ-CO)(μ-GaMes) (2a: Cp* = η-C5Me5), in which the two Cp* rings are located on the opposite side with respect to the GaFe2C four-membered ring. In contrast to 1a, photolysis of a toluene solution of 1b afforded a mixture of the cis and trans isomers of [CpFe(CO)]2(μ-CO)(μ-GaMes) (2b: Cp = η-C5H5). Recrystallization of 2b from a toluene/hexane solution afforded pure trans-2b. Crystal structure analyses of 1a, 2a, and trans-2b revealed that the Fe−Ga distances of 2a (2.3147(9) A) and trans-2b (2.3438(5) A) are much shorter than those of 1a (2.4315(15) A). A kinetic investigation of the isomerization between cis-2b and trans-2b afforded the activat...

The characteristics of interaction between C 60 molecules and Si(1 1 1)-7×7, Ag/Si(1 1 1)-√3×√3 R 30° and layered material MoS 2 surfaces have been investigated using electron-energy-loss spectroscopy (EELS). The EEL spectrum of C 60 /Si(1 1 1)-7×7 shows a new peak at loss energy of 2.7 eV. This indicates the existence of charge transfer from the substrate to C 60 molecules. The EEL spectrum of a C 60 monolayer film grown on a cleaved surface of MoS 2 is almost the same as that of bulk C 60 . The EEL spectrum of a C 60 monolayer film on an Ag/Si(1 1 1) surface is quite different from that on a clean Si(1 1 1)-7×7 surface, although the films on those substrates have the same epitaxial arrangement. Furthermore, intensities of energy-loss peaks of C 60 /Ag/Si(1 1 1) are slightly smaller than those of C 60 /MoS 2 in spite of having the same loss-energy. This suggests that the interaction between C 60 molecules and the Ag/Si(1 1 1) surface is stronger than that between C 60 molecules and the MoS 2 surface.

We have investigated the electronic structure of K x C 60 ( x =0–6) using low-energy electron energy loss spectroscopy (LEELS), especially focusing on the K 3p core-electron excitation spectra. It is found that the structure of the K 3p -excitation spectrum of K x C 60 quite differs from that of KCl. Furthermore, the K 3p -excitation LEELS of K 3 C 60 has been revealed to be different from that of K 6 C 60 . K 3p electrons are excited into K 4s - and K 3d -derived empty states in both K x C 60 and KCl, but in the case of K x C 60 the K 3d -derived empty states have a rather complicated structure where several levels are not well separated. Consequently, K 3p -excitation LEEL spectra of K x C 60 show wide-spread plateau-like structures. The difference in the K 3p -excitation spectra of K 3 C 60 and K 6 C 60 is considered to originate from the different crystal field around K + cations in the C 60 molecular crystal.

Reaction of (silyl)(silylene)tungsten complex Cp*(OC)2W(SiMe3)(═SiMes2) (1) with sulfur reagents, S8 and ethylene sulfide 4, afforded cyclic carbene tungsten complex Cp*(S)W{═C(SiMe3)C(═O)OSi(Mes)2S} (3) via C═O bond fission of a carbonyl ligand and 1,2-migration of the SiMe3 group from W to the resulting carbene carbon. In contrast to the tungsten complex, reaction of (silyl)(silylene)molybdenum complex Cp*(OC)2Mo(SiMe3)(═SiMes2) (2) with 4 gave η2-thiocarbonyl complex Cp*(S)Mo[{η2-S═C(SiMe3)}C(═O)OSi(Mes)2S] (5), which would be formed by addition of a sulfur atom to the Mo═C bond of a molybdenum analogue of 3.

Addition of 2,2‘-bipyridine (bpy) to an acetonitrile solution of Fp2GaCl (1: Fp = CpFe(CO)2; Cp = η-C5H5) afforded quantitatively a salt consisting of a diiron cation bridged by a Ga·bpy fragment ...

Sub-monolayer films of layered semiconductor InSe were grown on MoS2 substrates by molecular beam epitaxy, and the change in their growth features with Se/In flux ratio was investigated using scanning tunneling microscope in vacuum. It was found that InSe domains grown at 340 degrees C have a hexagonal shape when the Se/In ratio is about 17. Detailed images of the hexagonal InSe domains have revealed that adjacent sides of the hexagon have different structures; one is a straight edge and the other is a disordered edge. When the Se/In ratio was decreased, the disordered edges became predominant, the straight edges disappeared, and the InSe domain became triangular. On the contrary, when the Se/In ratio was increased, InSe domains became triangular ones consisting of only straight edges. The growth mechanism of InSe domains is discussed by considering the crystal structure of InSe and the reactivity of each side with incoming atoms. It is suggested that the balance of incorporation rate of In and Se atoms determines the structure of InSe domains. (C) 2000 Elsevier Science B.V. All rights reserved.

Molecular arrangement and electronic structure of a La@C82 film epitaxially grown on an MoS2 surface have been studied using reflection high-energy electron diffraction and electron energy-loss spectroscopy ~EELS!. It was revealed that La@C82 molecules form a close-packed hexagonal lattice on a cleaved face of MoS2 with the intermolecular distance of 1.1360.03 nm. EELS of the La@C82 film in the valence excitation region indicated seven peaks coming from p→p* transitions together with the p-plasmon excitation. The absence of a distinct band gap means that the La@C82 epitaxial film is not semiconducting, but metallic or semimetallic. From the EELS result, we propose an electronic structure diagram of the La@C82 epitaxial film.

Layered materials, represented by graphite, mica, MoS2 or GaSe, have a lamellar structure consisting of two-dimensional unit layers. Each unit layer is formed via strong covalent or ionic type bonds, while there is no strong bond between two unit layers; they are bound together via van der Waals-type weak interaction. Then layered materials can be easily cleaved and the clean cleaved surface has a very wide and flat terrace without an active dangling bond. When the thin film growth is investigated on such an inactive surface of a layered material, only weak interaction works between the substrate and the grown material. This results in far small lattice-mismatch distortion in the grown film even if it has a different lattice constant or a crystal structure from the substrate. Consequently, single-crystalline heteroepitaxial growth of layered materials or organic molecular crystals can be achieved from the initial layer on the layered material substrate. In this paper we will explain structure, physical property and usage of some layered material substrates.

Single crystalline Ga 2 Se 3 thin films were grown on GaAs(1 0 0) by molecular beam epitaxial (MBE) under Se-rich atmosphere. Reflection high-energy electron diffraction (RHEED) analysis suggests that the Ga 2 Se 3 thin film is epitaxially grown on GaAs(1 0 0) with their 〈1 0 0〉 crystallographic directions aligned with each other. The electronic structure determined by the ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) revealed the forbidden band gap of 2.7 eV. Transmission electron microscopy has shown that vacancies are distributed on one set of {1 1 1} crystal planes of α-Ga 2 Se 3 structure by forming a 3 × 3 configuration, resulting in the three times larger modulation periodicity along one of the 〈1 1 0〉 crystal directions into vacancy ordered β-Ga 2 Se 3 structure. The crystal structure was consistent to a model proposed by Lubbers and Leute (J. Solid State Chem. 43 (1982) 339). There are two sets of planar defects, microtwin with {1 1 1} type twin planes and stacking faults. High population of planer defects observed in the thin film was regarded as a result of Ga vacancy ordering in the crystal structure of Ga 2 Se 3 .

Donor-bridged bis(silylene)molybdenum and -chromium complexes CpM(CO)2{(SiMe2)···Do···(SiMe2)} (Cp = η-C5H5; M = Mo, Do = OMe (1a); M = Mo, Do = NEt2 (1b); M = Cr, Do = OMe (2)) were synthesized by photolysis of a C6D6 solution containing CpM(CO)3Me and HSiMe2SiMe2Do. The X-ray crystal structures of 1a, 1b, and 2 revealed that the M−Si bonds (2.4795(9) and 2.4804(9) A for 1a, 2.4996(9) and 2.5008(9) A for 1b, and 2.355(2) A for 2) are significantly shorter than those of structurally similar silylmolybdenum and -chromium complexes, while the Si−O bonds in 1a (1.782(2) and 1.788(3) A) and 2 (1.788(3) A) and the Si−N bonds in 1b (1.933(2) and 1.923(3) A) are much longer than usual Si−O and Si−N single bonds. These structural data indicate that the M−Si bonds bear partial double-bond character, whereas the Si−O and Si−N bonds are regarded as a hybrid of covalent bonding and dative bonding. The unsaturated nature of the metal−silicon bonds is also shown by the significant downfield shift of the 29Si NMR signal...

Hydride abstraction from a hydrosilyliron complex FpSiH(p-Tol)2 (1: Fp = CpFe(CO)2, Cp =η-C5H5, p-Tol = 4-C6H4Me) with Ph3CPF6 in the presence of HMPA (HMPA = P(O)(NMe2)3) afforded a cationic silyleneiron complex stabilized by HMPA [Fp=Si(p-Tol)2·HMPA]PF6 (2) in 88% yield. The X-ray crystal structure analysis of 2 revealed the relatively long Fe-Si bond and the short Si-O dative bond compared to those of the known donor-stabilized silylene complexes.

The n-BuLi-initiated polymerization of (CH2CHMe2Si)2NR (R = Me, 1; R = SiMe3, 2) gave highly regular polymers 3 and 4 which consisted entirely of linked cyclic units with no detectable cross-links or linear segments. The substituent R profoundly affected the ring size found in the resulting cyclopolymer: monomer 2 gave only five-membered rings in the polymer backbone, while 1 formed both five- and six-membered rings. The stereochemistry of polymerization of 2 was found to be solvent-dependent: the ratio of cis to trans five-membered rings in 4 increased when the reaction was conducted in the presence of coordinating cosolvents (e.g., Et3N). Polymers 3 and 4 could be cleanly ring opened with HF(aq) to give poly(vinyldimethylfluorosilanes) 7 and 8. The synthetic utility of polymer 8 was demonstrated by its reaction with a variety of nucleophilic reagents to give highly regular, highly functionalized polymers of the type (CH2CHSi(CH3)2R‘)n.

C-60 molecules were deposited on a submonolayer InSe film which was grown on a MoS2 substrate. In the previous experiment on the growth of a C-60 thin film on a GaSe/MoS2 heterostructure, C-60 grew only on exposed MoS2 regions and never nucleated on GaSe domains at substrate temperature above 180 degrees C. In the present case, however, C-60 molecules grow only on InSe domains and do not nucleate on the exposed MoS2 when the substrate temperature is higher than 80 degrees C. Using this method, C-60 domains whose dimension is smaller than 100 nm could be fabricated on each InSe domain. The selectivity of the C-60 growth is supposed to originate not from the surface morphology of those heterostructures, but from the difference in adsorption energy and surface diffusion energy of C-60 molecules on the surfaces of three different layered materials and a C-60 film. (C) 1998 Elsevier Science B.V. All rights reserved.

The lattice mismatch at the heterostructure CdS/Si(111) is close to 8%. To relieve the structural stress at this interface, an InSe van der Waals-type buffer layer was grown between the Si substrate and the CdS film. After the Si(111) substrate surface was passivated by hydrogen, the InSe-buffer layer was grown on top by molecular beam epitaxy with high crystalline quality. The lattice orientations of the InSe film are in registry with the Si substrate, as shown by reflection high energy electron diffraction. As seen in the atomic force microscope, the InSe films have roughly the same terrace width of 50–70 nm as the Si substrate due to the wafer miscut. By contrast the step edges of the InSe film are more regular than those of the silicon. The CdS-film was grown on the InSe. The crystal axis of the film is in full registry with the InSe substrate as monitored by reflection high energy electron diffraction. The film morphology is determined as simultaneous growth of multilayers observed by atomic force microscope.

The 1:1 reaction of [Ru(bpy)2(solvent)2]2+ (bpy = 2,2'-bipyridine) with [Ni(aet)2] (aet = 2-aminoethanethiolate) gave a S-bridged Ru II 2 Ni II 2 tetranuclear complex with an eight-membered Ru 2 Ni 2 S 4 metallacycle, [{Ru(bpy) 2 } 2 -{Ni(aet) 2 } 2 ] 4+ , while a S-bridged Ru II Ni II dinuclear complex with a four-membered RuNiS2 metallacycle, [Ru(bpy) 2 -{Ni(aet) 2 }] 2+ , was obtained by the corresponding 1:2 reaction between [Ru(bpy)2(solvent)2]2+ and [Ni(aet)2].

Photolysis of Cp*Mo(CO)3Me (1; Cp* = η-C5Me5) in the presence of the hydrodisilane HSiMe2SiMeMes2 (Mes = 2,4,6-Me3C6H2) resulted in the formation of the donor-free (silyl)(silylene)molybdenum complex Cp*Mo(CO)2(SiMes2)(SiMe3) (2). The reaction of complex 2 with tBuCH2CMe2NC at 60 °C caused insertion of the isocyanide into the Si−C bond of the silylene ligand to give an intramolecular donor-stabilized silyl silylene complex, Cp*Mo(CO)2(Si(Mes)C(Mes)NCMe2CH2tBu)(SiMe3) (3).

We report two-dimensionality and effective thickness of the superconductivity of a SrTiO single-crystal surface induced by electric double-layer gating. The carrier density was tuned from 3 \ifmmode\times\else\texttimes\fi{} 10 to 1.1 \ifmmode\times\else\texttimes\fi{} 10 cm by gating, where superconductivity appears with ${T}_{c}$ of around 0.4 K. Typical two-dimensional behavior perfectly described by the Ginzburg--Landau equation was observed in the angular and temperature dependence of the upper critical magnetic field. The effective thickness of the superconducting layer remains nearly invariant, ranging from 11 to 13 nm, with increasing charge carrier density. This invariance contradicts the expected reduction in the thickness of the accumulation layer in a triangular quantum well model. This unexpected invariance of the superconducting layer thickness is probably a unique nature for a two-dimensional electron system in the incipient ferroelectric SrTiO.

Donor-stabilized bis(silylene)tungsten complexes CpW(CO)2{(SiMe2)···Do···(SiMe2)} (Cp = η-C5H5; Do = NEt2 (1), OMe (2)) were synthesized by photolysis of a C6D6 solution containing CpW(CO)3Me and HSiMe2SiMe2Do. The X-ray crystal structures of 1 and 2 revealed that the W−Si bonds (2.502(2) and 2.501(2) A for 1; 2.490(3) A for 2) are significantly shorter than those of structurally similar silyltungsten complexes, while the Si−N bonds (1.930(6) and 1.920(7) A) in 1 and the Si−O bonds (1.792(7) A) in 2 are much longer than usual Si−N and Si−O single bonds. These structural data indicate that the W−Si bonds bear partial double bond character, whereas the Si−N and Si−O bonds are regarded as a hybrid of covalent bonding and dative bonding. The unsaturated nature of the tungsten−silicon bonds is also indicated by the significant downfield shift of the 29Si NMR signals as well as large coupling constants between 29Si and 183W (1 δ = 62.1 ppm, 1JW-Si = 91.5 Hz; 2 δ = 99.3 ppm, 1JW-Si = 99.3 Hz) compared to those o...

We report ambipolar charge transport in α-molybdenum ditelluride (MoTe2 ) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed. The ambipolarity of the charge transport originated from the formation of Schottky barriers at the metal/MoTe2 contacts. The Schottky barrier heights as well as the current on/off ratio could be modified by modulating the electrostatic fields of the back-gate voltage (Vbg) and drain-source voltage (Vds). Using these ambipolar MoTe2 transistors we fabricated complementary inverters and amplifiers, demonstrating their feasibility for future digital and analog circuit applications.

The rhodium complex catalyzes both the initial hydrosilylation of α,β-unsaturated esters and the subsequent C-C bond formation of the resulting silyl enol ether with aroyl chlorides to yield β-keto esters (III).

The perpendicular magnetic anisotropy (PMA) of a Co (0.5 nm)/Pt (2.4 nm) bilayer film was electrostatically tuned using a high-κ dielectric, SrTiO3, with a back-gating configuration. The Co film was directly deposited onto a SrTiO3 (001) substrate and capped by a Pt layer. The coercivity was enhanced (reduced) by applying a positive (negative) gate bias. The efficiency of the PMA energy modulation by the electric field was determined to be 1300–23 100 fJ/V m, which is 1–3 orders of magnitude higher than the efficiencies obtained in previous studies. The superior efficiency of this system is most likely attributable to the large dielectric constant of the SrTiO3 gate insulator and could be evidence that the PMA energy modulation is induced by charge accumulation.

LiBr/Si(001) heterostructure has been investigated by scanning tunneling microscopy and spectroscopy (STM and STS). In the initial stage of LiBr growth, rectangular islands are observed consisting of accumulation of about 0.2 nm-thick unit layers. The STM results indicate that LiBr grows on Si(001) in a single layer fashion. The STS measurement shows a wide band gap region in I-V curve and the energy gap of the LiBr film shows no thickness dependence down to a nominal thickness of 1.2 monolayer (ML).

The emergence of exotic quantum phenomena is often triggered by a subtle change in the crystal phase. Transition metal dichalcogenides (TMDs) exhibit a wide variety of novel properties, depending on their crystal phases, which can be trigonal prismatic (2H) or octahedral (1T). Bulk NbSe2 crystallizes into the 2H phase, and the charge density wave and the superconductivity emerge simultaneously and interact with each other, thereby creating various anomalous properties. However, these properties and their interplay in another polymorph, 1T-NbSe2, have remained unclear because of the difficulty of synthesizing it. Here we report the first experimental realization of a monolayer 1T-NbSe2 crystal grown epitaxially on bilayer graphene. In contrast with 2H-NbSe2, monolayer 1T-NbSe2 was found to be a Mott insulator, with an energy gap of 0.4 eV. We also found that the insulating 1T and metallic 2H phases can be selectively fabricated by simply controlling the substrate temperature during epitaxy. The present results open a path to crystal-phase engineering based on TMDs. A thin film produced by a team in Japan could lead to field-effect transistors that combine superconductors and semiconductors. When thin monolayers of niobium selenide (NbSe2) are deposited on surfaces, quantum effects that are useful for electronic devices emerge. A team led by Takashi Takahashi from Tohoku University has discovered how to fabricate NbSe2 thin films with two crystal phases that have distinct properties. By growing monolayers of NbSe2 on a bilayer graphene surface and tweaking the reaction temperature, the researchers were able to generate crystalline nanoislands that behaved as either superconductors or Mott insulators — special materials whose conductivities can be tuned by varying parameters such as pressure and disorder. Atomic-resolution imaging confirmed the different island structures, which the team sees as a path towards ultrasmall transistors and switches. We have synthesized a monolayer 1T-NbSe2 on bilayer graphene by molecular-beam-epitaxy method and investigated its electronic states by angle-resolved photoemission spectroscopy. In contrast to metallic 2H-NbSe2, monolayer 1T-NbSe2 was found to show insulating characteristics with a finite energy gap and strong modulation of density of states with periodicity. This suggests the Mott-insulating ground state of monolayer 1T-NbSe2 with the formation of ‘star of David’ clusters. We also found that 1T and 2H phases are selectively fabricated by simply controlling the substrate temperature during epitaxy. The present result opens a pathway toward the crystal-phase engineering based with transition-metal dichalcogenides.

Isomerization between two geometrical isomers of the methoxy-bridged bis(silylene)iron complex, anti-and syn-Cp*(OC)Fe{(SiMe2)···OMe···(SiMeOMe)} (Cp* = η5-C5Me5), was investigated by means of a variable-temperature 1H NMR experiment. The equilibrium constant (K) for the isomerization and its thermodynamic parameters were determined to be K = [syn-isomer]/[anti-isomer] = 0.53 at 293 K in toluene-d8, ΔG°298 = 1.5 ± 0.5 kJ mol−1, ΔH° = 3.8 ± 0.2 kJ mol−1, and ΔS° = 7.7 ± 1.0 J mol−1 K−1. Computer simulation of the VT spectra and calculation using Eyring equation yielded activation parameters, ΔH‡ = 83.8 ± 3.2 kJ mol−1, ΔS‡ = 42.3 ± 9.6 J mol−1 K−1, and ΔG‡298 = 71.2 ± 6.0 kJ mol−1, for the isomerization from the anti-isomer, in which the terminal OMe group is located on the opposite side of the Cp* group with respect to the Fe–Si–O(bridged)–Si ring, to the syn-isomer. A mechanism in which the bridging OMe group is replaced by the terminal OMe group is proposed for the isomerization.

We investigated the relationship between the fine structure of spin-coated conductive polymer poly(3,4-ethylenedioxythiphene):poly(styrene sulfonate) (PEDOT:PSS) films and the photovoltaic performance of PEDOT:PSS crystalline-Si (PEDOT:PSS/c-Si) heterojunction solar cells. Real-time spectroscopic ellipsometry revealed that there were two different time constants for the formation of the PEDOT:PSS network. Upon removal of the polar solvent, the PEDOT:PSS film became optically anisotropic, indicating a conformational change in the PEDOT and PSS chain. Polarized Fourier transform infrared attenuated total reflection absorption spectroscopy and Raman spectroscopy measurements also indicated that thermal annealing promoted an in-plane π-conjugated Cα = Cβ configuration attributed to a thiophene ring in PEDOT and an out-of-plane configuration of -SO3 groups in the PSS chain with increasing composition ratio of oxidized (benzoid) to neutral (quinoid) PEDOT, Iqui/Iben. The highest power conversion efficiency for ...

NH 4 F treatment of a Si(111) substrate gives a very flat and chemically inactive surface because of the regular termination of each active dangling bond by a hydrogen atom. On this inactive surface, layered semiconductor GaSe and molecular crystal C 60 grow through weak Van der Waals interaction. As a result their epitaxial films can be grown with their own lattice structures in spite of the large difference in their lattice constants from the substrate. Atomic force microscope (AFM) analysis of the GaSe thin film revealed many triangular spiral structures, indicating screw dislocation growth mechanism. In contrast, AFM observation of the C 60 film showed that it grows in the island growth mode, and each island has a two-dimensional dendritic shape.

The first dinuclear complex bridged by a substituent-free gallium atom, Cp*Fe(dppe)(μ-Ga)Fe-(CO) 4 (1; Cp* = η-C 5 Me 5 , dppe = Ph 2 PCH 2 CH 2 PPh 2 ), was synthesized by the reaction of Cp*Fe(dppe)GaCl 2 with K 2 [Fe(CO) 4 ]. A crystal structure analysis of complex 1 revealed that the geometry around the gallium atom is essentially linear and the Fe-Ga bonds are significantly shorter than that of usual single bonds. These structural features indicate that the Fe-Ga bonds bear significantly unsaturated character.

The first gallane-coordinated metal complex, (OC) 5 W(η 1 -GaH 3 (quinuclidine)) (2), was synthesized by photolysis of a ca. 1:1 mixture of W(CO) 6 and quinuclidine-coordinated gallane, H 3 Ga(quinuclidine) (1), in toluene and by the reaction of (OC) 5 W(THF) with 1 equiv of gallane 1 in THF. X-ray crystal structure analysis of 2 revealed that gallane 1 is bound to the tungsten fragment via a W-H-Ga three-center-two-electron bond.

Photolysis of Cp‘W(CO)3Me (1a, Cp‘ = η-C5Me5; 1b, Cp‘ = η-C5Me4Et) in the presence of excess HSiMe2SiMe3 afforded a self-stabilized silyl(silylene)tungsten complex with a dimeric structure, [Cp‘W(CO)2(SiMe2)(SiMe3)]2 (2a, Cp‘ = η-C5Me5; 2b, Cp‘ = η-C5Me4Et), respectively. In contrast, photolysis of 1a in the presence of HSiMe2SiMeMes2 (Mes = 2,4,6-Me3C6H2) resulted in the formation of the first donor-free silyl(silylene) complex with only alkyl and aryl substituents on the silicon atoms, Cp‘W(CO)2(SiMes2)(SiMe3) (3).