ORCID Profile
0000-0002-5828-4312
Current Organisation
Northwestern Polytechnical University
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Photonics and Electro-Optical Engineering (excl. Communications) | Photonics, Optoelectronics and Optical Communications | Nanophotonics | Nanotechnology
Expanding Knowledge in the Physical Sciences | Emerging Defence Technologies | Expanding Knowledge in Engineering |
Publisher: AIP Publishing
Date: 08-2012
DOI: 10.1063/1.4740455
Abstract: We demonstrate that the interfacial hole injection barrier Δh between p-type organic materials (i.e., CuPc and pentacene) and Co substrate can be tuned by the insertion of a MoO3 buffer layer. Using ultraviolet photoemission spectroscopy, it was found that the introduction of MoO3 buffer layer effectively reduces the hole injection barrier from 0.8 eV to 0.4 eV for the CuPc/Co interface, and from 1.0 eV to 0.4 eV for the pentacene/Co interface, respectively. In addition, by varying the thickness of the buffer, the tuning effect of Δh is shown to be independent of the thickness of MoO3 interlayer at both CuPc/Co and pentacene/Co interfaces. This Fermi level pinning effect can be explained by the integer charge-transfer model. Therefore, the MoO3 buffer layer has the potential to be applied in p-type organic spin valve devices to improve the device performance via reducing the interfacial hole injection barrier.
Publisher: AIP Publishing
Date: 26-03-2007
DOI: 10.1063/1.2719033
Abstract: Energy level alignment of rubrene adsorbed on Au(111) was studied by photoemission spectroscopy. After rubrene adsorption, the work function is reduced from 5.24eV for clean Au to 4.31eV, suggesting the invalidity of vacuum level alignment and the presence of a strong interfacial dipole. The frontier molecular orbital energies of rubrene are modified by electrode surface polarization in the submonolayer regime. As a consequence, the hole injection barrier is thickness dependent and varies from about 0.4eV for a monolayer of rubrene to 0.9eV for a thick layer.
Publisher: AIP Publishing
Date: 03-2010
DOI: 10.1063/1.3310367
Abstract: Photocurrent generation and photodetection are usually based on semiconductor crystals including Si, CdS, and PbS. This work reports the enhanced photoabsorption and photodetection of close-packed metallic Au nanoparticles (NPs) in the UV-VIS (visible)-NIR (near infrared) region. Photoabsorption in the UV-VIS regions is associated with the interband transition and surface plasmon resonance of AuNPs, while the enhanced NIR absorption is due to the collective effect of interacting AuNPs in the close-packed network. Consequently, the AuNPs exhibits photodetection behavior in the wavelength range of 300–1500 nm. It is proposed that the inter-AuNP photoejection and delocalization of electron-hole pairs changes the carrier lifetime and transit dynamics in favor of photocarrier conduction, thus significantly facilitating photocurrent generation in the metallic AuNP close-pack. Moreover, due to the power-law conduction mechanism in AuNP networks, the quantum yield of AuNPs can be tuned from 10−6 to 10−1 photoelectron hoton by increasing the bias voltage from 0 to 5 V. The AuNP quantum yield of 10−1 at 5 V is as high as that of commercial Si photodetectors at 0 V, and this demonstrates the immediate applicability of AuNPs in photodetection. In view of the compatibility of AuNPs with wet-chemistry and inkjet printing processes at low temperatures, metallic AuNPs may provide a convenient alternative to semiconductor crystals in photodetection and perhaps photovoltaic applications.
Publisher: AIP Publishing
Date: 25-01-2016
DOI: 10.1063/1.4940749
Abstract: Surface transfer doping of hydrogen-terminated diamond has been achieved utilising V2O5 as a surface electron accepting material. Contact between the oxide and diamond surface promotes the transfer of electrons from the diamond into the V2O5 as revealed by the synchrotron-based high resolution photoemission spectroscopy. Electrical characterization by Hall measurement performed before and after V2O5 deposition shows an increase in hole carrier concentration in the diamond from 3.0 × 1012 to 1.8 × 1013 cm−2 at room temperature. High temperature Hall measurements performed up to 300 °C in atmosphere reveal greatly enhanced thermal stability of the hole channel produced using V2O5 in comparison with an air-induced surface conduction channel. Transfer doping of hydrogen-terminated diamond using high electron affinity oxides such as V2O5 is a promising approach for achieving thermally stable, high performance diamond based devices in comparison with air-induced surface transfer doping.
Publisher: American Chemical Society (ACS)
Date: 28-02-2006
DOI: 10.1021/JP056785I
Abstract: The adsorption of allyl alcohol, acrylic acid, and allyl chloride, as well as unsaturated organic molecules such as acetylene and 1,3 butadiene, on reconstructed diamond (100) 2 x 1 have been investigated using high-resolution electron energy loss (HREELS) spectroscopy and synchrotron radiation spectroscopy. The cycloadditions of these organic molecules produce chemically adsorbed adlayers with varying degree of coverages on the clean diamond. The organic adsorbed surface has a lowered electron affinity and shows a secondary electron yield that varies between 12 and 40% of the yield obtained from a fully hydrogenated diamond surface. The diamond surface can be functionalized with hydroxyl, carboxylic, and chlorine functionalities by the adsorption of these allyl organics. The [2 + 2] adduct of acetylene on the diamond (100) 2 x 1 surface can be observed. 1,3-butadiene attains a higher coverage as well as forms a thermally more stable adlayer on the diamond surface compared to the other organic molecules, due to its ability to undergo [4 + 2] cycloaddition.
Publisher: American Chemical Society (ACS)
Date: 12-06-2007
DOI: 10.1021/JA072133R
Publisher: Elsevier BV
Date: 07-2007
Publisher: Springer Science and Business Media LLC
Date: 22-11-2019
DOI: 10.1038/S41427-019-0170-6
Abstract: Inorganic perovskites have recently attracted much attention as promising new nanocrystalline materials that have interesting fundamental phenomena and great potential in several applications. Herein, we reveal unusual structural and electronic changes in nanocrystalline cesium lead bromide (CsPbBr 3 ) as a function of temperature using high-resolution spectroscopic ellipsometry, high-resolution transmission electron microscopy and terahertz spectroscopy measurements supported by first-principles calculations. New dual phases of crystalline and electronic structures are observed due to the nanocrystalline nature of the material. Interestingly, a change in the electronic structure occurs below 150 K, and the rate at which the nanocrystal transitions from the tetragonal to orthorhombic phase is found to be nonlinear with temperature. Our results show the importance of the charge and lattice interplay in determining the dual phases and fundamental properties of nanocrystalline materials.
Publisher: MDPI AG
Date: 09-06-2010
DOI: 10.3390/MA3063642
Publisher: American Physical Society (APS)
Date: 10-08-2011
Publisher: American Chemical Society (ACS)
Date: 03-02-2007
DOI: 10.1021/JP066600N
Publisher: IEEE
Date: 10-2010
Publisher: Wiley
Date: 24-05-2005
Publisher: Wiley
Date: 04-2014
Abstract: Organic semiconductor materials have important applications in organic electronics and other novel hybrid devices. In these devices, the transport of charge carriers across the interfaces between organic molecules and electrodes plays an important role in determining the device performance. Charge transfer dynamics at the organic/electrode interface usually occurs at the several femtoseconds timescale, and quantitative charge transfer dynamics data can been inferred using synchrotron-based core-hole clock (CHC) spectroscopy. In this research news, we have reviewed recent progress in the applications of CHC spectroscopy on the quantitative characterization of charge transfer dynamics at organic/electrode interfaces. By examining charge transfer dynamics at different types of interface, from weakly interacting van der Waals-type interfaces to interfaces with strong covalent bonds, we discuss a few factors that have been found to affect the charge transfer dynamics. We also review the application of CHC spectroscopy to quantify through-bonds and through-space charge transport in organic molecules.
Publisher: American Chemical Society (ACS)
Date: 05-08-2009
DOI: 10.1021/NN9005335
Abstract: Size and ligand effects are the basis for the novel properties and applications of metallic nanoparticles (NPs) in nanoelectronics, optoelectronics, and biotechnology. This work reports the first observation of enhanced photoelectron emission from metallic Au NPs ligated by alkanethiols. The enhancement is based on a conceptually new mechanism: the AuNP provides electrons while the alkane ligand emits electrons due to its low or negative electron affinity. Moreover, the AuNP-ligand chemical bonding is found to significantly facilitate the transmission of photoexcited electrons from the AuNP to the ligand emitter. Consequently the smooth NP film, which is a typical low-aspect-ratio two-dimensional structure, exhibits strong and stable field emission behavior under photoillumination conditions. The photoenhanced field emission is related to the interband and surface plasmon transitions in AuNPs, and a photoenhancement factor of up to approximately 300 is observed for the AuNP-based field emission. This is highly remarkable because field emission is often based on one-dimensional, high-aspect-ratio nanostructures (e.g., nanotubes and nanowires) with geometrical field enhancement effect. The chemical linkage of electron-supplying AuNP and electron-emitting alkane ligand represents a fundamentally new mechanism for efficient photoexcitation and emission. Being low-temperature/solution processable, and inkjet printable, AuNPs may be a flexible material system for optoelectronic applications such as photodetection and photoenhanced field emission.
Publisher: Wiley
Date: 09-2017
Publisher: American Chemical Society (ACS)
Date: 24-05-2013
DOI: 10.1021/JP311092S
Publisher: American Chemical Society (ACS)
Date: 22-10-2019
Publisher: American Chemical Society (ACS)
Date: 23-11-2006
DOI: 10.1021/JP065821Q
Abstract: Self-assembled functionalized aromatic thiols (oligophenylenes composed of building blocks of dimethoxy-substituted phenylenes, perfluoro-substituted phenylenes, and a terminal thiol group) were used to tune the hole injection barrier (Delta(h)) of copper(II) phthalocyanine (CuPc) on Au(111). Synchrotron-based high-resolution photoemission spectroscopy study reveals a significant reduction of Delta(h) by as much as 0.75 eV from Delta(h) = 0.9 eV for CuPc/Au(111) to Delta(h) = 0.15 eV for CuPc/BOF/Au(111), where BOF represents 4-pentafluorophenyl-1-(p-thiophenyl)-2,5-dimethoxybenzene. The delocalized pi orbitals of these functionalized aromatic thiols greatly facilitate effective charge transfer (hole or electron) across the SAM interface as compared to alkanethiols, hence making this novel interface modification scheme a simple and effective way to tune the hole injection barrier. This method has potential applications in molecular electronics, organic light-emitting diodes (OLED), organic field-effect transistors (OFETs), and organic solar cells.
Publisher: AIP Publishing
Date: 17-08-2009
DOI: 10.1063/1.3206654
Abstract: In this work, we demonstrate room temperature ferromagnetism of ZnO nanocrystals (NCs) embedded in alumina-based amorphous matrix. Our study has shown that solid solution occurred for lower Al concentration [≤x=0.09 for (Zn1−x,Alx)O]. No ferromagnetism appears in Al-doped ZnO with x≤0.09. With higher Al concentration, alumina-based amorphous structure appeared and fully amorphous was found in the composition of (Zn0.30,Al0.70)O. Ferromagnetism was found in (Zn1−x,Alx)O with a threshold of 16 mol % of Al. The room temperature ferromagnetism was found to be attributed to ZnO NCs in an alumina-based amorphous ZnO–Al2O3 matrix. Ferromagnetism reached a maximum with a volume percentage of ZnO NCs to be ∼27 vol %. The detailed investigations (transmission electron microscopy, x-ray photoelectron spectroscopy, and superconducting quantum interference device) show that the optimized size of these NCs is in the range of 4–5 nm. No ferromagnetism appears if the s le contains a fully amorphous structure.
Publisher: American Chemical Society (ACS)
Date: 02-02-2006
DOI: 10.1021/JA0577241
Abstract: We report the creation of polymeric micro/nanostructures which exhibit distinct chemical and physical characteristics from the matrix poly(N-vinyl carbazole) (PVK). The structure formation is based on atomic force microscopy (AFM) facilitated cross-linking and oxygenation. The reaction of PVK with AFM lithographically induced nanoscale discharge produces raised structures in which bridge oxygen links neighboring carbazole groups. The cross-linking by bridge oxygen converts the initially insulating PVK matrix to chemically modified conducting patterns through the formation of extended pi-conjugations. A comprehensive AFM, PES (photoelectron spectroscopy), FTIR (Fourier transform infrared spectroscopy), and DFT (density functional theory) analysis is presented to address the chemophysical identity of the patterned structures. Our results demonstrate new capabilities of AFM nanolithography in generating heterogeneous functional structures in a polymer matrix.
Publisher: Springer Science and Business Media LLC
Date: 15-10-2012
DOI: 10.1038/SREP00737
Publisher: American Chemical Society (ACS)
Date: 30-11-2011
DOI: 10.1021/JP2083924
Publisher: American Chemical Society (ACS)
Date: 11-02-2014
DOI: 10.1021/JP4103542
Publisher: Wiley
Date: 09-09-2015
Abstract: Graphene-gold metasurface architectures that can provide significant gains in plasmonic detection sensitivity for trace-amount target analytes are reported. Benefiting from extreme phase singularities of reflected light induced by strong plasmon-mediated energy confinements, the metasurface demonstrates a much-improved sensitivity to molecular bindings nearby and achieves an ultralow detection limit of 1 × 10(-18) m for 7.3 kDa 24-mer single-stranded DNA.
Publisher: American Physical Society (APS)
Date: 03-06-2013
Publisher: AIP Publishing
Date: 09-05-2011
DOI: 10.1063/1.3589970
Abstract: We report room temperature ferromagnetism in partially hydrogenated epitaxial graphene grown on 4HSiC(0001). The presence of ferromagnetism was confirmed by superconducting quantum interference devices measurements. Synchrotron-based near-edge x-ray absorption fine structure and high resolution electron energy loss spectroscopy measurements have been used to investigate the hydrogenation mechanism on the epitaxial graphene and the origin of room temperature ferromagnetism. The partial hydrogenation induces the formation of unpaired electrons in graphene, which together with the remnant delocalized π bonding network, can explain the observed ferromagnetism in partially hydrogenated epitaxial graphene.
Publisher: Elsevier BV
Date: 09-2009
Publisher: American Chemical Society (ACS)
Date: 28-10-2019
Abstract: Being a metallic transition-metal dichalcogenide, monolayer vanadium diselenide (VSe
Publisher: American Chemical Society (ACS)
Date: 24-06-2009
DOI: 10.1021/JP903139Q
Publisher: American Chemical Society (ACS)
Date: 06-11-2019
Abstract: We present a combined experimental and theoretical study of monolayer vanadium ditelluride, VTe
Publisher: Proceedings of the National Academy of Sciences
Date: 12-01-2023
Abstract: Liquid methanol has the potential to be the hydrogen energy carrier and storage medium for the future green economy. However, there are still many challenges before zero-emission, affordable molecular H 2 can be extracted from methanol with high performance. Here, we present noble-metal-free Cu–WC/W plasmonic nanohybrids which exhibit unsurpassed solar H 2 extraction efficiency from pure methanol of 2,176.7 µmol g −1 h −1 at room temperature and normal pressure. Macro-to-micro experiments and simulations unveil that local reaction microenvironments are generated by the coperturbation of WC/W’s lattice strain and infrared-plasmonic electric field. It enables spontaneous but selective zero-emission reaction pathways. Such microenvironments are found to be highly cooperative with solar-broadband-plasmon-excited charge carriers flowing from Cu to WC surfaces for efficient stable CH 3 OH plasmonic reforming with C 3 -dominated liquid products and 100% selective gaseous H 2 . Such high efficiency, without any CO x emission, can be sustained for over a thousand-hour operation without obvious degradation.
Publisher: American Chemical Society (ACS)
Date: 07-08-2014
DOI: 10.1021/NN503287M
Abstract: Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.
Publisher: American Physical Society (APS)
Date: 22-09-2008
Publisher: Springer Science and Business Media LLC
Date: 21-01-2021
Publisher: American Physical Society (APS)
Date: 08-11-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8NH00306H
Abstract: Phonon depletion in the indirect recombination process of bilayer WS 2 has been proposed to unveil exceptionally robust valley polarization.
Publisher: AIP Publishing
Date: 15-11-2010
DOI: 10.1063/1.3514553
Abstract: We demonstrate that the electron injection barrier (Δe) between Co and C60 can be tuned by inserting a thin Alq3 interlayer. Using ultraviolet photoemission spectroscopy, Δe of C60 on Alq3-predecorated Co (Δe=0.3 eV) was found to be reduced by 0.3 eV compared with that of C60 deposited directly on the bare Co metal surface (Δe=0.6 eV). Due to Fermi level pining at the Alq3/Co interface, this tuning effect is independent of the thickness of Alq3 interlayer from multilayer to monolayer. Based on the experimental results, band level alignment diagrams are proposed for C60/Co and C60/Alq3/Co interfaces with two different Alq3 thicknesses. Our findings could have potential applications for the reduction in the carrier injection barrier in organic spin valves.
Publisher: AIP Publishing
Date: 19-07-2010
DOI: 10.1063/1.3466914
Abstract: The electronic properties of rubrene films exposed to oxygen have been studied by photoemission and x-ray absorption spectroscopies. Oxygen incorporation causes the highest occupied molecular orbital of rubrene to shift to a ∼1.0 eV deep level due to chemical bonds formed by the oxygen atoms with the carbon atoms within the tetracene backbone of rubrene molecules. Deformation of the molecular backbone induced by the C–O bonds destroys the delocalized nature of the molecular orbitals. The oxidized rubrene molecules in a single crystal are proposed to act as point defects that disturb the long-range periodicity and produce localized acceptor states.
Publisher: Elsevier
Date: 2020
Publisher: AIP Publishing
Date: 07-2021
DOI: 10.1063/5.0052458
Abstract: Two-dimensional (2D) layered lead halide perovskites with large exciton binding energies, efficient radiative recombination, and outstanding environmental stability are regarded as supreme candidates for realizing highly compact and ultralow threshold lasers. However, continuous-wave (CW) pumped lasing of 2D lead halide perovskites, as the precondition for the electrically pumped lasing, is still challenging. Here, we tackled this challenge by demonstrating lasing emission in phenylethylammonium lead iodide [(PEA)2PbI4] embedded in a vertical microcavity under continuous pumping at room temperature. The millimeter-sized (PEA)2PbI4 single crystal was obtained from a two-step seed-growth method, showing high crystallization, excellent thermal stability, and outstanding optical properties. We used the exfoliated (PEA)2PbI4 thin flake as the gain medium to construct a vertical-cavity surface-emitting laser (VCSEL), showing robust single-mode CW lasing operation with an ultra-low threshold of 5.7 W cm−2 at room temperature, attributed to strong optical confinement in the high-Q cavity. Our findings provide a strategy to design and fabricate solution-based 2D perovskite VCSELs and mark a significant step toward the next-generation of coherent light sources.
Publisher: American Chemical Society (ACS)
Date: 13-02-2012
DOI: 10.1021/NN204907T
Abstract: With a thin insulator sandwiched between two electrodes, the negative differential resistance (NDR) behavior has been frequently reported for its potential device applications. Here we report the experimental observation of a symmetric NDR characteristic in a resistive switching device based on TiO(2). We propose a charge storage mechanism for the NDR effect, with oxygen molecular ions working as the active source, in a thin insulating layer. Current-voltage measurements demonstrated a highly reproducible state at about 0.65 eV, and the photoelectron spectroscopy measurements showed that it complies well with the Ti3d band gap state. Our first-principle calculations confirm that charge storage and release arise from trapping and detrapping of oxygen molecular ions at the defect sites. The results and mechanism demonstrated here in a thin layer could be extended to other systems approaching molecular dimensions for device applications.
Publisher: Wiley
Date: 24-06-2008
Publisher: American Chemical Society (ACS)
Date: 04-06-2012
DOI: 10.1021/AM300887J
Abstract: We demonstrate the use of chemical-vapor-deposited (CVD) graphene as an effective indium-tin-oxide (ITO) electrode surface modifier to engineer the organic donor-acceptor heterojunction interface properties in an inverted organic solar cell device configuration. As revealed by in situ near-edge X-ray adsorption fine structure measurement, the organic donor-acceptor heterojunction, comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) and copper phthalocyanine (CuPc), undergoes an obvious orientation transition from a standing configuration (molecular π-plane nearly perpendicular to the substrate surface) on the bare ITO electrode to a less standing configuration with the molecular π-plane stacking adopting a large projection along the direction perpendicular to the electrode surface on the CVD graphene-modified ITO electrode. Such templated less-standing configuration of the organic heterojunction could significantly enhance the efficiency of charge transport along the direction perpendicular to the electrode surface in the planar heterojunction-based devices. Compared with the typical standing organic-organic heterojunction on the bare ITO electrode, our in situ ultraviolet photoelectron spectroscopy experiments reveal that the heterojunction on the CVD graphene modified ITO electrode possesses better aligned energy levels with respective electrodes, hence facilitating effective charge collection.
Publisher: Wiley
Date: 13-06-2008
Abstract: We investigate the interface between a C(60) fullerite film, C(60)F(36), and diamond (100) by using core-level photoemission spectroscopy, cyclic voltammetry (CV), and high-resolution electron energy loss spectroscopy (HREELS). We show that C(60) can be covalently bonded to reconstructed C(100)-2x1 and that the bonded interface is sufficiently robust to exhibit characteristic C(60) redox peaks in solution. The bare diamond surface can be passivated against oxidation and hydrogenation by covalently bound C(60). However, C(60)F(36) is not as stable as C(60) and desorbs below 300 degrees C (the latter species being stable up to 500 degrees C on the diamond surface). Neither C(60) fullerite nor C(60)F(36) form reactive interfaces on the hydrogenated surface-they both desorb below 300 degrees C. The surface transfer doping process of hydrogenated diamond by C(60)F(36) is the most evident one among all the adsorbate systems studied (with a coverage-dependent band bending induced by C(60)F(36)).
Publisher: American Chemical Society (ACS)
Date: 23-08-2006
DOI: 10.1021/LA060974Q
Abstract: The information depth of near-edge X-ray absorption fine structure spectroscopy in the total electron yield mode (TEY-NEXAFS) is given by the escape depth of the TEY electrons z(TEY). This is determined by the effective ranges both of the inelastically scattered secondary electrons and of the primary excited electron before they thermalize below the vacuum level. For regioregular poly(3-hexylthiophene) (rreg-P3HT) thin films, we have measured the total electron emission efficiency to be 0.028 +/- 0.005 e h at an incident photon energy of 320 eV. The range of the primary electron was computed using optical dielectric-loss theory to be 7.5 nm. The range of the secondary electrons was then found by modeling to be 3.0 nm. This gives z(TEY) to be 2.5 nm, which is considerably less than the often-assumed value of 10 nm in the literature. It is also considerably smaller than the computed electron-electron scattering inelastic mean free path in the material, which suggests the predominance of electron-phonon scattering. Thus, TEY-NEXAFS has sufficient surface sensitivity to probe the frontier molecular layers of these organic conjugated polymers. In a second aspect of this report, the rreg-P3HT films have been characterized by in-situ core and valence photoemission spectroscopies and by ex-situ microattenuated total-reflection vibrational spectroscopy as a function of irradiation dose. No damage was observed in composition, bonding, orientation, and surface morphology under typical TEY-NEXAFS spectral acquisition conditions. For an integrated TEY that exceeds 2 x 10(-3) C cm(-2), however, the material degrades via alkyl side-chain dehydrogenation to unsaturated units, cross linking, ring opening of the backbone, and sulfur extrusion. Given that secondary electrons are the dominant cause of radiation damage, this exposure threshold measured by integrated TEY should also be valid at other X-ray energies.
Publisher: Elsevier BV
Date: 02-0005
Publisher: Wiley
Date: 27-11-2019
DOI: 10.1002/INF2.12050
Publisher: Elsevier BV
Date: 06-2004
Publisher: AIP Publishing
Date: 15-09-2007
DOI: 10.1063/1.2778636
Abstract: The conformation degree and molecular orientation during the growth of rubrene films on Si(111) and Au(111) have been studied by in situ x-ray absorption spectroscopy. The backbones of rubrene molecules on Au(111) are twisted at the first few layers in contrast, no appreciable twisting is observed on Si(111) even at a thickness of approximately 1.5 nm. The planarization of the backbone in the first few layers is due to strong molecule–substrate interactions between rubrene and Si(111). The rubrene molecules on Au(111) have a backbone tilt angle of 41° and a phenyl side group tilt of 64° with respect to the substrate surface, suggesting the crystalline nature of the films. Ex situ atomic force microscopy measurements confirm that the rubrene film grown on Au(111) is crystalline and the growth direction is along its crystallographic c axis.
Publisher: American Chemical Society (ACS)
Date: 22-11-2013
DOI: 10.1021/JP4099733
Publisher: Elsevier BV
Date: 12-2004
Publisher: Springer Science and Business Media LLC
Date: 23-06-2015
DOI: 10.1038/SREP11430
Abstract: Magnetic materials have found wide application ranging from electronics and memories to medicine. Essential to these advances is the control of the magnetic order. To date, most room-temperature applications have a fixed magnetic moment whose orientation is manipulated for functionality. Here we demonstrate an iron-oxide and graphene oxide nanocomposite based device that acts as a tunable ferromagnet at room temperature. Not only can we tune its transition temperature in a wide range of temperatures around room temperature, but the magnetization can also be tuned from zero to 0.011 A m 2 /kg through an initialization process with two readily accessible knobs (magnetic field and electric current), after which the system retains its magnetic properties semi-permanently until the next initialization process. We construct a theoretical model to illustrate that this tunability originates from an indirect exchange interaction mediated by spin-imbalanced electrons inside the nanocomposite.
Publisher: Springer Science and Business Media LLC
Date: 08-2015
Publisher: American Chemical Society (ACS)
Date: 20-02-2017
Abstract: As an iron oxyhydroxide, nanosized ferrihydrite (Fh) is important in Earth science, biology, and industrial applications. However, its basic structure and origin of its magnetism have long been debated. We integrate synchrotron-based techniques to explore the chemical structures of 2-line ferrihydrite and to determine the origin of its magnetism during hydrothermal aging in air. Our results demonstrate that both the magnetism and X-ray magnetic circular dichroism (XMCD) signal of 2-line ferrihydrite are enhanced with aging time, and that XMCD spectral patterns resemble that of maghemite (γ-Fe
Publisher: Wiley
Date: 08-12-2010
Abstract: Organic–organic heterojunctions (OOHs) are critical features in organic light‐emitting diodes, ambipolar organic field‐effect transistors and organic solar cells, which are fundamental building blocks in low‐cost, large‐scale, and flexible electronics. Due to the highly anisotropic nature of π‐conjugated molecules, the molecular orientation of organic thin films can significantly affect the device performance, such as light absorption and charge‐carrier transport, as well as the energy level alignment at OOH interfaces. This Feature Article highlights recent progress in the understanding of interface energetics at small molecule OOH interfaces, focusing on the characterization and fabrication of OOH with well‐defined molecular orientations using a combination of in situ low‐temperature scanning tunneling microscopy, synchrotron‐based high‐resolution ultraviolet photoelectron spectroscopy and near‐edge X‐ray absorption fine structure measurements. The orientation dependent energy level alignments at the OOH interfaces will be discussed in detail.
Publisher: The Royal Society
Date: 28-10-2012
Abstract: We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti 1− x Ta x O 2 ( x ∼0.05) thin films grown by pulsed laser deposition on LaAlO 3 substrates. Rutherford backscattering spectrometry (RBS), X-ray diffraction, proton-induced X-ray emission, X-ray absorption spectroscopy (XAS) and time-of-flight secondary-ion mass spectrometry indicated negligible magnetic contaminants in the films. The presence of FM with concomitant large carrier densities was determined by a combination of superconducting quantum interference device magnetometry, electrical transport measurements, soft X-ray magnetic circular dichroism (SXMCD), XAS and optical magnetic circular dichroism, and was supported by first-principles calculations. SXMCD and XAS measurements revealed a 90 per cent contribution to FM from the Ti ions, and a 10 per cent contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites, though carrier activation was only 50 per cent at 5 per cent Ta concentration, implying compensation by cationic defects. The role of the Ti vacancy ( V Ti ) and Ti 3+ was studied via XAS and X-ray photoemission spectroscopy, respectively. It was found that, in films with strong FM, the V Ti signal was strong while the Ti 3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localized magnetic moments, V Ti sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to FM in wide-band-gap semiconducting oxides without any magnetic elements.
Publisher: American Chemical Society (ACS)
Date: 18-11-2009
DOI: 10.1021/LA901204X
Abstract: The molecular orientations of copper phthalocyanine (CuPc) organic semiconductor molecules on hydrogenated and bare diamond (001)-2 x 1 surfaces are studied using synchrotron-based photoemission spectroscopy (PES) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Angular-dependent NEXAFS reveals that the CuPc molecular assemblies are orientationally ordered and lying down on hydrogenated diamond, whereas they undergo a molecular reorientation on bare diamond from lying down at submonolayer coverage to standing up in multilayers. The molecular film on bare diamond also exhibits an order-disorder-order transition in the molecular orientations. The distinct molecular orientation within the CuPc films on both diamond (001) surfaces is explained in terms of the interplay between intermolecular interactions and molecule-substrate interactions.
Publisher: Springer Science and Business Media LLC
Date: 06-05-2016
DOI: 10.1038/NCOMMS11283
Abstract: Impressive properties arise from the atomically thin nature of transition metal dichalcogenide two-dimensional materials. However, being atomically thin limits their optical absorption or emission. Hence, enhancing their photoluminescence by plasmonic nanostructures is critical for integrating these materials in optoelectronic and photonic devices. Typical photoluminescence enhancement from transition metal dichalcogenides is 100-fold, with recent enhancement of 1,000-fold achieved by simultaneously enhancing absorption, emission and directionality of the system. By suspending WSe 2 flakes onto sub-20-nm-wide trenches in gold substrate, we report a giant photoluminescence enhancement of ∼20,000-fold. It is attributed to an enhanced absorption of the pump laser due to the lateral gap plasmons confined in the trenches and the enhanced Purcell factor by the plasmonic nanostructure. This work demonstrates the feasibility of giant photoluminescence enhancement in WSe 2 with judiciously designed plasmonic nanostructures and paves a way towards the implementation of plasmon-enhanced transition metal dichalcogenide photodetectors, sensors and emitters.
Publisher: American Chemical Society (ACS)
Date: 09-2009
DOI: 10.1021/CM901127R
Publisher: Wiley
Date: 10-2020
Publisher: American Chemical Society (ACS)
Date: 06-2007
DOI: 10.1021/JA071658G
Abstract: Epitaxial graphene thermally grown on 6H-SiC(0001) can be p-type doped via a novel surface transfer doping scheme by modifying the surface with the electron acceptor, tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Synchrotron-based high-resolution photoemission spectroscopy reveals that electron transfer from graphene to adsorbed F4-TCNQ is responsible for the p-type doping of graphene. This novel surface transfer doping scheme by surface modification with appropriate molecular acceptors represents a simple and effective method to nondestructively dope epitaxial graphene for future nanoelectronics applications.
Publisher: American Chemical Society (ACS)
Date: 21-04-2021
Publisher: IOP Publishing
Date: 20-01-2010
Publisher: Elsevier BV
Date: 09-2007
Publisher: American Chemical Society (ACS)
Date: 11-06-2021
Publisher: Wiley
Date: 03-05-2021
Abstract: Lead halide perovskites are intriguing semiconductors for lasers due to high quantum yield, tunable bandgaps, and facile solution‐process ability. However, limited by the weak optical confinement, continuous‐wave (CW) pumped lasing, as one prerequisite for the electrically pumped lasing, is still challenging in bare lead halide perovskites without high‐quality factor ( Q ) artificial optical cavity. Herein, the lasing emission in methylammonium lead tribromide (MAPbBr 3 ) incorporated with a vertical microcavity under continuous pumping at 80 K is reported. The single‐crystalline MAPbBr 3 perovskite nanoplates are fabricated by the two‐step solution method. The MAPbBr 3 ‐based vertical cavity surface‐emitting laser (VCSEL) presents a low threshold of 55.2 W cm −2 and a high Q ‐factor of 1140 at low temperature. The low threshold lasing emission can be attributed to strong optical confinement in the high‐ Q cavity and great photoluminescence enhancement at 80 K, which is induced by a transition from tetragonal to orthorhombic phase, demonstrated by in situ temperature Raman spectroscopy. These findings envisage the prospective applications of single‐crystalline metal halide perovskites in practicable laser devices.
Publisher: Wiley
Date: 21-02-2019
Abstract: The emerging field of valleytronics has boosted intensive interests in investigating and controlling valley polarized light emission of monolayer transition metal dichalcogenides (1L TMDs). However, so far, the effective control of valley polarization degree in monolayer TMDs semiconductors is mostly achieved at liquid helium cryogenic temperature (4.2 K), with the requirements of high magnetic field and on-resonance laser, which are of high cost and unwelcome for applications. To overcome this obstacle, it is depicted that by electrostatic and optical doping, even at temperatures far above liquid helium cryogenic temperature (80 K) and under off-resonance laser excitation, a competitive valley polarization degree of monolayer WS
Publisher: IOP Publishing
Date: 07-04-2008
Publisher: American Chemical Society (ACS)
Date: 30-06-2007
DOI: 10.1021/LA063165F
Abstract: Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates have been studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-film structures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurements revealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which is attributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74+/-5 degrees and 46+/-5 degrees molecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene molecules stand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domains with molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to an average tilt angle of 46 degrees for the whole film and the change in valence band structures. STM and distance-voltage (z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties. z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase".
Publisher: Wiley
Date: 28-03-2013
Publisher: Springer Science and Business Media LLC
Date: 02-02-2018
Publisher: AIP Publishing
Date: 29-04-2002
DOI: 10.1063/1.1476398
Abstract: Scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS) were used to observe the formation of metastable (6×6)-Si nanoclusters (diameter ∼16.5±0.1 A) on 6H–SiC(0001)-(3×3) surface. STM and XPS data suggest that these clusters are derived from the ejection of the Si-tetracluster unit of the initial (3×3) reconstruction at elevated temperatures and occur in a less Si-rich environment than the initial surface. The observed surface restructuring is related to the reconfiguration of coplanar Si bonds within the (3×3) unit cell. The occurrence of these regularly sized “magic” clusters demonstrates the potential of nanostructure formation of Si on SiC.
Publisher: American Physical Society (APS)
Date: 12-11-2020
Publisher: IOP Publishing
Date: 12-02-2016
DOI: 10.1088/0953-8984/28/9/094006
Abstract: Understanding the charge transport properties in general of different molecular components in a self-assembled monolayer (SAM) is of importance for the rational design of SAM molecular structures for molecular electronics. In this study, we study an important aspect of the charge transport properties, i.e. the charge transfer (CT) dynamics between the active molecular component (in this case, the ferrocenyl moieties of a ferrocenyl-n-alkanethiol SAM) and the electrode using synchrotron-based core-hole clock (CHC) spectroscopy. The characteristic CT times are found to depend strongly on the character of the ferrocenyl-derived molecular orbitals (MOs) which mediate the CT process. Furthermore, by systemically shifting the position of the ferrocenyl moiety in the SAM, it is found that the CT characteristics of the ferrocenyl MOs display distinct dependence on its distance to the electrode. These results demonstrate experimentally that the efficiency and rate of charge transport through the molecular backbone can be modulated by resonant injection of charge carriers into specific MOs.
Publisher: American Physical Society (APS)
Date: 29-03-2010
Publisher: AIP Publishing
Date: 14-05-2007
DOI: 10.1063/1.2737908
Abstract: MnSb nanoparticles with average lateral diameters ⟨d⟩ from 5to30nm are synthesized on ultra thin silicon nitride covered Si(111) by codeposition of Mn and Sb. These MnSb particles possess sharp interfaces and a NiAs-type lattice. The Mn 2p x-ray absorption spectroscopy analysis shows broad line shapes due to the itinerant Mn 3d states. The particles with ⟨d⟩=5 and 8.5nm are superparamagnetic at room temperature, while those of ⟨d⟩=15 and 30nm exhibit ferromagnetic behavior.
Publisher: American Scientific Publishers
Date: 10-2007
DOI: 10.1166/JNN.2007.807
Abstract: Ni-doped ZnO flower-like nanocones with wurzite structures were produced by oxidative evaporation of Zn and Ni powders. The Ni doping did not change the ZnO wurtzite structure. Raman scattering indicated that the normal lattice vibration modes are related to the hexagonal ZnO. Ni clusters and Ni oxides phases did not existed in the s le as characterized by XRD, XPS, and TEM. Upon excitations the nanocones could emit strong green light at 525 nm, which can be directly observed with a digital camera. The magnetic measurement indicated that the Ni-doped ZnO nanocone was high-Curie-temperature magnetic semiconductor.
Publisher: AIP Publishing
Date: 11-02-2008
DOI: 10.1063/1.2857460
Abstract: In situ synchrotron-based near-edge x-ray absorption fine structure measurements and photoemission spectroscopy have been used to investigate the effect of molecular orientation on the interfacial dipole and the energy level alignment at the interfaces of organic heterojunctions comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) on both standing-up and lying-down copper(II) phthalocyanine (CuPc) thin films. It is found that F16CuPc thin films adopt the same molecular orientation of the underlying CuPc thin films. An interfacial dipole of 0.45eV forms at the interface of lying-down F16CuPc∕CuPc on highly ordered pyrolytic graphite. In contrast, a much larger interfacial dipole of 1.35eV appears at the interface of standing-up F16CuPc∕CuPc on octane-1-thiol terminated Au(111).
Publisher: Wiley
Date: 03-04-2007
Publisher: American Chemical Society (ACS)
Date: 29-01-2008
DOI: 10.1021/JP0726337
Publisher: AIP Publishing
Date: 15-07-2013
DOI: 10.1063/1.4815998
Abstract: We demonstrate a polyaniline-iron oxide nanoparticle (PANI-NP) organic hybrid composite device with room temperature positive magnetoresistance of 85.7%. Temperature dependent resistivity measurements attribute this observation to the decrease in localization length of the charge carriers in the presence of an external magnetic field which result in them being trapped within the device between the insulating PANI layer, hence allowing the device to maintain its resistive state even when the power is switched off, thus exhibiting a memory effect.
Publisher: AIP Publishing
Date: 29-08-2011
DOI: 10.1063/1.3629812
Abstract: Chemical vapor deposition (CVD) graphene has been used as an effective structural template to manipulate molecular orientation of organic thin film of chloroaluminium phthalocyanine (ClAlPc) on indium tin oxide (ITO) electrode. As revealed by in-situ near-edge x-ray adsorption fine structure measurement, ClAlPc molecules on the CVD graphene modified ITO electrode adopt a well-aligned lying-down configuration with their molecular π-plane nearly parallel to the electrode surface, in contrast to the random orientation of ClAlPc molecules on the bare ITO electrode. This lying-down configuration results in an optimized stacking of the molecular π-plane perpendicular to the electrode surface and hence facilitates efficient charge transport along this direction.
Publisher: American Chemical Society (ACS)
Date: 17-08-2007
DOI: 10.1021/LA701285H
Abstract: The tuning of electron affinity and secondary electron emission on diamond (100) surfaces due to cycloaddition with 1,3-butadiene is investigated by photoemission experiments and density functional theory (DFT) calculations. A significant reduction in electron affinity up to 0.7 eV and enhancement of secondary electron emission were observed after 1,3-butadiene adsorption. The lowering of vacuum level via 1,3-butadiene adsorption is supported by DFT calculations. The C-H bonds in the covalently bonded organics on diamond contribute to the enhanced secondary electron emission and reduced electron affinity in a mechanism similar to that of C-H bonds on hydrogenated diamond surfaces. This combination of strong secondary emission and low electron affinity by the organic functionalization of diamond has potential applications in diamond-based molecular electronic devices.
Publisher: American Physical Society (APS)
Date: 08-07-2010
Publisher: Elsevier BV
Date: 04-2006
Publisher: American Chemical Society (ACS)
Date: 15-02-2016
DOI: 10.1021/ACS.NANOLETT.5B04066
Abstract: Owing to direct band gap and strong spin-orbit coupling, monolayer transition-metal dichalcogenides (TMDs) exhibit rich new physics and great applicable potentials. The remarkable valley contrast and light emission promise such two-dimensional (2D) semiconductors a bright future of valleytronics and light-emitting diodes (LEDs). Though the electroluminescence (EL) has been observed in mechanically exfoliated small flakes of TMDs, considering real applications, a strategy that could offer mass-product and high compatibility is greatly demanded. Large-area and high-quality s les prepared by chemical vapor deposition (CVD) are perfect candidates toward such goal. Here, we report the first demonstration of electrically tunable chiral EL from CVD-grown monolayer WS2 by constructing a p-i-n heterojunction. The chirality contrast of the overall EL reaches as high as 81% and can be effectively modulated by forward current. The success of fabricating valley LEDs based on CVD WS2 opens up many opportunities for developing large-scale production of unconventional 2D optoelectronic devices.
Publisher: American Chemical Society (ACS)
Date: 04-05-2009
DOI: 10.1021/JP810804T
Publisher: AIP Publishing
Date: 09-09-2013
DOI: 10.1063/1.4811758
Abstract: We report on the emerging and admixture of Frenkel and charge transfer (CT) excitons near the absorption onset in pentacene single crystals. Using high energy-resolution spectroscopic generalized ellipsometry with in-plane polarization dependence, the excitonic nature of three lowest lying excitations is discussed. Their distinct polarization dependence strongly indicates the presence of both Frenkel and CT types of excitons near the excitation onset. In particular, the peculiar polarization behavior of the second excitation can only be rationalized by taking into account the inherent CT transition dipole moment. This observation has important implications for the pentacene-based optoelectronic devices.
Publisher: AIP Publishing
Date: 21-01-2011
DOI: 10.1063/1.3546034
Abstract: The electronic structures at the MoO3/Co interface were investigated using synchrotron-based ultraviolet and x-ray photoelectron spectroscopy. It was found that interfacial chemical reactions lead to the reduction of Mo oxidation states and the formation of Co-O bonds. These interfacial chemical reactions also induce a large interface dipole, which significantly increases the work function of the cobalt substrate. In addition, two interface states located at 1.0 and 2.0 eV below the Fermi level are identified. These two states overlap at film thickness of between 2–4 nm, which suggests the MoO3 intermediate layer may facilitate ohmic charge transport.
Publisher: Elsevier BV
Date: 03-2011
Publisher: Wiley
Date: 27-12-2018
Abstract: 2D Td-WTe
Publisher: AIP Publishing
Date: 15-09-2009
DOI: 10.1063/1.3225918
Abstract: Molecular orientation-controlled charge transfer has been observed at the organic-organic heterojunction interfaces of copper-hexadecafluoro-phthalocyanine (F16CuPc) or copper(II) phthalocyanine (CuPc) on both standing-up and lying-down CuPc or F16CuPc thin films. In situ synchrotron-based photoemission spectroscopy reveals that the charge transfer at the standing F16CuPc/CuPc or CuPc/F16CuPc interface is much larger than that at the lying F16CuPc/CuPc or CuPc/F16CuPc interface. This can be explained by the orientation-dependent ionization potentials of well-ordered organic thin films, which place the highest-occupied molecular orbital of the standing CuPc film much closer to the lowest-unoccupied molecular orbital of the standing F16CuPc film, facilitating stronger charge transfer as compared to that at the lying OOH interfaces. Our results suggest the possibility of manipulating interfacial electronic structures of organic heterojunctions by controlling the molecular orientation, in particular for applications in ambipolar organic field transistors and organic photovoltaics.
Publisher: American Chemical Society (ACS)
Date: 20-12-2019
Publisher: AIP Publishing
Date: 09-01-2006
DOI: 10.1063/1.2162800
Abstract: We report the creation of polymeric structures by atomic force microscopy (AFM) probe induced electrohydrodynamic (EHD) instability and nanofluidic flow. By biasing the AFM probe in a high field regime, single conical structure was produced on poly(methylmethacrylate) due to the initiation of strong EHD instability in the locally heated polymer melts. The pattern formation is dominated by the interplay of polymer EHD motion, polymer ablation, and AFM tip repulsion. The dependence of cone formation probability on the bending of AFM cantilevers with different stiffness was also discussed.
Publisher: The Electrochemical Society
Date: 2008
DOI: 10.1149/1.2806801
Publisher: Wiley
Date: 20-01-2007
Publisher: IOP Publishing
Date: 23-05-2016
DOI: 10.1088/0957-4484/27/27/275201
Abstract: A combination of synchrotron-based x-ray spectroscopy and contact potential difference measurements have been used to examine the electronic structure of the (3 × 1) silicon terminated (100) diamond surface under ultra high vacuum conditions. An occupied surface state which sits 1.75 eV below the valence band maximum has been identified, and indications of mid-gap unoccupied surface states have been found. Additionally, the pristine silicon terminated surface is shown to possess a negative electron affinity of -0.86 ± 0.1 eV.
Publisher: American Chemical Society (ACS)
Date: 15-02-2021
Publisher: American Chemical Society (ACS)
Date: 31-08-2011
DOI: 10.1021/NN202910T
Abstract: We demonstrated a novel method to obtain charge neutral quasi-free-standing graphene on SiC (0001) from the buffer layer using fluorine from a molecular source, fluorinated fullerene (C(60)F(48)). The intercalated product is stable under ambient conditions and resistant to elevated temperatures of up to 1200 °C. Scanning tunneling microscopy and spectroscopy measurements are performed for the first time on such quasi-free-standing graphene to elucidate changes in the electronic and structural properties of both the graphene and interfacial layer. Novel structures due to a highly localized perturbation caused by the presence of adsorbed fluorine were produced in the intercalation process and investigated. Photoemission spectroscopy is used to confirm these electronic and structural changes.
Publisher: AIP Publishing
Date: 05-2006
DOI: 10.1063/1.2201615
Abstract: Core-hole clock spectroscopy and near-edge x-ray-absorption fine structure measurements have been used to investigate the ultrafast electron transfer dynamics at the Copper(II) phthalocyanine (CuPc)∕Au(111) interface. It was found that the strong electronic coupling between the first layer of CuPc molecules and Au(111) substrate favors ultrafast electron transfer from the lowest unoccupied molecular orbital of the CuPc molecules to the conduction band of Au(111) in the time scale of ∼6fs. In contrast, the intermolecular electron transfer within multilayers of CuPc molecules via the weak van der Waals interaction was much slower.
Publisher: Wiley
Date: 09-2021
Abstract: 2D platinum diselenide (PtSe 2 ) has received significant attention for 2D transistor applications due to its high carrier mobility. Here, using molecular beam epitaxy, the growth of 2D PtSe 2 is investigated on highly oriented pyrolytic graphite (HOPG) and their electronic properties are unveiled via X‐ray photoelectron spectroscopy, Raman spectra, and scanning tunnelling microscopy/spectroscopy as well as density functional theory (DFT) calculations. PtSe 2 adopts a layer‐by‐layer growth mode on HOPG and shows a decreasing bandgap with increasing layer number. For the layer numbers from one to four, PtSe 2 has bandgaps of 2.0 ± 0.1, 1.1 ± 0.1, 0.6 ± 0.1, and 0.20 ± 0.1 eV, respectively, and becomes semimetal from the fifth layer. DFT calculations reproduce the layer‐dependent evolution of both the bandgap and band edges, suggest an indirect bandgap structure, and elucidate the underlying physics at the atomic level.
Publisher: AIP Publishing
Date: 20-04-2009
DOI: 10.1063/1.3122940
Abstract: The molecular orientation of copper(II) phthalocyanine (CuPc) thin films on monolayer C60 on Ag(111) was studied by in situ near-edge x-ray absorption fine structure measurements and low-temperature scanning tunneling microscopy. It is found that in densely packed thin films, CuPc molecules adopt a standing-up configuration with the molecular π-plane tilting slightly from the surface normal on monolayer C60.
Publisher: Wiley
Date: 28-02-2014
Publisher: Elsevier BV
Date: 12-2005
Publisher: Springer Science and Business Media LLC
Date: 27-07-2018
Publisher: Springer Science and Business Media LLC
Date: 08-02-2006
Publisher: American Chemical Society (ACS)
Date: 05-01-2010
DOI: 10.1021/NN901476M
Abstract: The template-directed assembly of two planar molecules (copper phthalocyanine (CuPc) and pentacene) on SiC nanomesh has been studied by scanning tunneling microscopy and photoelectron spectroscopy, respectively. Both molecules are trapped as single molecules in the cells of SiC nanomesh at low coverage. At high coverage, CuPc forms a highly ordered single-molecular array with identical symmetry and periodicity as the substrate, whereas pentacene forms a quasi-amorphous layer due to the random mixture of three different adsorption configurations. This difference in adsorption behavior is attributed to differences in molecular geometries. The measured changes of work functions reveal weak charge transfer between the molecules and substrate. Both molecules are preferentially adsorbed on the SiC nanomesh rather than on graphene. The CuPc single-molecular array possesses good long-range order, large area coverage, and a molecular density of over 3.0 x 10(13) molecules/cm(2).
Publisher: AIP Publishing
Date: 11-2011
DOI: 10.1063/1.3656834
Abstract: Charge transfer dynamics across the lying-down 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) organic semiconductor molecules on Au(111) interface has been investigated using the core-hole clock implementation of resonant photoemission spectroscopy. It is found that the charge transfer time scale at the PTCDA/Au(111) interface is much larger than the C 1s core-hole lifetime of 6 fs, indicating weak electronic coupling between PTCDA and the gold substrate due to the absence of chemical reaction and/or bonding.
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2021
End Date: 12-2027
Amount: $34,935,112.00
Funder: Australian Research Council
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