We have carried out a femtosecond two-photon photoemission study of layered semiconductor $2H\ensuremath{-}{\mathrm{MoS}}_{2}(0001)$ surface. From the detailed time-resolved two-photon photoemission measurements as a function of electron excitation energy, it is found that the relaxation lifetime of hot-electron is extremely short (\ensuremath{\leqslant}60 fs) and the inverse lifetime depends linearly on the excess energy above the conduction-band minimum. Deviation from the Fermi liquid behavior in layered semiconductor $2H\ensuremath{-}{\mathrm{MoS}}_{2}$ is discussed.
We have investigated the initial stages of vacuum-deposited sexithiophene (alpha-6T) adlayer formation on Au(111) vicinal surfaces at room temperature. The in situ scanning tunneling microscopy (STM) and photoemission spectroscopy (PES) reveal a step edge-driven growth of alpha-6T on the Au(111) vicinal surfaces that first leads to the formation of an ordered monolayer, comprising two phases with the molecular major axes aligned along the step edges. The monolayer formation is then followed by the appearance of a single-phase 2D superstructure at a two-monolayer coverage. The results highlight the potential of using vicinal metal surfaces as templates for generating organized organic nanostructures over macroscopic areas for applications in organic electronics and moletronics.
We report a compact light collection scheme suitable for retrofitting a scanning tunneling microscope (STM) for STM-induced light emission experiments. The approach uses a pair of optical fibers with large core diameters and high numerical apertures to maximize light collection efficiency and to moderate the mechanical precision required for alignment. Bench tests indicate that efficiency reduction is almost entirely due to reflective losses at the fiber ends, while losses due to fiber misalignment have virtually been eliminated. Photon-map imaging with nanometer features is demonstrated on a stepped Au(111) surface with signal rates exceeding 104counts∕s.
Malignant Rhabdoid Tumor (MRT) is a rare pediatric cancer predominantly occurring in the kidney and CNS that is highly resistant to current treatment protocols. MRT is almost exclusively characterized by homozygous inactivation of SMARCB1, a critical subunit of the SWI/SNF chromatin-remodeling complex, implicating epigenetic deregulation in the pathogenesis of the disease. Recently, we showed that sustained treatment of human MRT cell lines with the Histone deacetylase inhibitor, Panobinostat, at low-dose, inhibited tumor growth by driving multi-lineage differentiation in vitro and in vivo. Furthermore, re-expression of SMARCB1 in MRT cells phenocopied low-dose Panobinostat treatment and led to growth inhibition, senescence and terminal differentiation in vitro and in vivo, suggesting similar mechanistic functionality. Enhancer of Zeste homolog 2 (EZH2), a core subunit of the Polycomb Repressive Complex 2, confers transcriptional silencing via the addition of methyl groups to Lysine 27 of Histone 3 (H3K27me3), and is a transcriptional target of SMARCB1. EZH2 expression and H3K27me3 were drastically reduced following sustained low-dose Panobinostat treatment and re-expression of SMARCB1 in MRT cells. Sustained siRNA knockdown of EZH2 in G401 cells resulted in reduced cell growth and changes in mRNA expression, mimicking low-dose Panobinostat treatment and SMARCB1 re-expression. Treatment of MRT cells with the EZH2-catalytic domain inhibitors, GSK126, GSK343 and UNC1999, had no effect on EZH2 expression and only partially reduced cell growth despite dose-dependent reductions in H3K27me3 implying important non-catalytic EZH2 function. Remarkably, co-treatment of MRT with low-dose Panobinostat and GSK126 resulted in reduced EZH2 and H3K27me3 expression, significantly reduced cell growth and increased differentiation in vitro and in vivo compared to single agent controls, demonstrating a synergistic relationship. This data suggests EZH2 is an important mediator of MRT proliferation and differentiation and provides evidence for improved efficacy of dual therapeutic targeting of EZH2 with low-dose Panobinostat.
The electronic structure of metal-organic interfaces incorporated in organic electro-optic and optoelectronic devices, e.g., organic light emitting diodes and photovoltaics, is important in determining some of the critical device operating parameters such as power efficiencies, and threshold and operating voltages. The interfacial electronic structure depends on the nature of the interactions between the organic material and the metal, which can be roughly divided into two groups: electrostatic and chemical interactions. The electrostatic interactions result in the rearrangement of the electronic charge within the near-interface layer of the organic, which may, in some cases, depend on the organic film crystal structure. The chemical interaction, on the other hand, depends on the chemical reactivity of the metal and the organic material, and may involve the formation of metal–organic charge transfer complexes, or bond breaking and making giving rise to new species. By carefully selecting the components of metal – organic interfaces we have been able to study the interfacial electronic structure both in the presence and in the absence of chemical interactions.
The electronic structures of interfaces between metals and Copper phthalocyanine (CuPc) organic films are investigated using the combination of ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES). The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) can be directly observed by IPES and UPS simultaneously. We found that the Fermi level, EF, in the organic film can be modified by metals through charge transfer or doping. The FERMI level at the Cs/CuPc interface is observed to shift to less than 0.2 eV below the CuPc LUMO. The IPES observation is the first direct confirmation of Fermi level pinning near the LUMO in organic films. The pinning of the Fermi level close to the LUMO can be explained by electron transfer from Cs to CuPc, which is supported by the presence of a gap state in CuPc as observed with UPS. On the other hand, the Au/CuPc interface is characterized by electron transfer from CuPc to Au, resulting in a reduced HOMO intensity shown in the UPS spectra and a new feature below the LUMO shown in the IPES spectra. These observations shed new light onto the understanding of interface formation in organic semiconductor devices.
The electronic structures of 2,5-bis(6′-(2′,2″-bipyridyl))-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy) and 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PPSPP) at their interfaces with Mg were investigated using ultraviolet, inverse, and x-ray photoemission spectroscopies. PyPySPyPy and PPSPP have been used as both electron injection/transport layers and emitters in high-efficiency organic light-emitting diodes (OLEDs). Deposition of either PyPySPyPy or PPSPP onto Mg results in the appearance of two energy levels within the energy gap of the organic. Upon deposition of Mg onto PyPySPyPy there is a shift of the occupied energy level structure to higher binding energy, away from the Fermi level, and appearance of two energy levels within the energy gap of PyPySPyPy. The lowest unoccupied molecular orbital is also shifted to higher binding energy. Upon deposition of Mg onto PPSPP there is also a rigid shift of the occupied energy level structure to higher binding energy, away from the Fermi level, but there are no apparent energy levels created within the energy gap of PPSPP. The different chemical reactivity of the two silole derivatives with magnesium is shown to have pronounced effects on the formation of cathode contacts in OLED structures.
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