Three-level stencil alignment fabrication of a high-k gate stack organic thin film transistor

In this work a high-k double-gate pentacene field-effect transistor architecture is presented. The devices are fabricated on a flexible polyimide substrate by three aligned levels of stencil lithography combined with standard photolithography. ALD-deposited high-k HfO2 and parylene D device passivation, together with Pt top-gate deposition provide very good electrostatic control of the channel, showing low leakage current and improved subthreshold. The ION/IOFF ratio is of the order of 106 and the IOFF lower than 0.1 pA/μm. We also report a comparison of the normal, FET-like (VD 0) modes of the p-OFET. We find a higher current drive in the reverse diode-like mode compared to normal FET-like mode. The reverse mode has clearly defined OFF and ON states versus the drain voltage and non-saturated output characteristics, which makes it suitable for the use in RF and analog applications of OFETs

Valley Zeeman effect in elementary optical excitations of monolayer WSe2

A monolayer of a transition metal dichalcogenide such as WSe2 is a two-dimensional direct-bandgap valley-semiconductor(1,2) having an effective honeycomb lattice structure with broken inversion symmetry. The inequivalent valleys in the Brillouin zone could be selectively addressed using circularly polarized light fields', suggesting the possibility for magneto-optical measurement and manipulation of the valley pseudospin degree of freedom(6-8). Here we report such experiments that demonstrate the valley Zeeman effect-strongly anisotropic lifting of the degeneracy of the valley pseudospin degree of freedom using an external magnetic field. The valley-splitting measured using the exciton transition deviates appreciably from values calculated using a three-band tight-binding model(9) for an independent electron-hole pair at +/- K valleys. We show, on the other hand, that a theoretical model taking into account the strongly bound nature of the exciton yields an excellent agreement with the experimentally observed splitting. In contrast to the exciton, the trion transition exhibits an unexpectedly large valley Zeeman effect that cannot be understood within the same framework, hinting at a different contribution to the trion magnetic moment. Our results raise the possibility of controlling the valley degree of freedom using magnetic fields in monolayer transition metal dichalcogenides or observing topological states of photons strongly coupled to elementary optical excitations in a microcavity(10)

Optically active quantum dots in monolayer WSe2

Semiconductor quantum dots have emerged as promising candidates for the implementation of quantum information processing, because they allow for a quantum interface between stationary spin qubits and propagating single photons(1-3). In the meantime, transition-metal dichalcogenide monolayers have moved to the forefront of solid-state research due to their unique band structure featuring a large bandgap with degenerate valleys and non-zero Berry curvature(4). Here, we report the observation of zero-dimensional anharmonic quantum emitters, which we refer to as quantum dots, in monolayer tungsten diselenide, with an energy that is 20-100 meV lower than that of two-dimensional excitons. Photon antibunching in second-order photon correlations unequivocally demonstrates the zero-dimensional anharmonic nature of these quantum emitters. The strong anisotropic magnetic response of the spatially localized emission peaks strongly indicates that radiative recombination stems from localized excitons that inherit their electronic properties from the host transition-metal dichalcogenide. The large similar to 1 meV zero-field splitting shows that the quantum dots have singlet ground states and an anisotropic confinement that is most probably induced by impurities or defects. The possibility of achieving electrical control in van der Waals heterostructures(5) and to exploit the spin-valley degree of freedom(6) renders transition-metal-dichalcogenide quantum dots interesting for quantum information processing

Double-gate pentacene thin-film transistor with improved control in sub-threshold region

In this work double-gate pentacene TFT architecture is proposed and experimentally investigated. The devices are fabricated on a polyimide substrate based on a process that combines three levels of stencil lithography with standard photolithography. Similarly to the operation of a conventional double-gate silicon FET, the top-gate bias modulates the threshold voltage of the bottom-gate transistor and significantly improves the transistor sub-threshold swing and leakage current. Moreover, the double gate TFT shows good promise for the enhancement of I-ON/I-OFF, especially by the control of I-OFF in devices with poor top interfaces. (C) 2010 Elsevier Ltd. All rights reserved

Sub-100 nm-scale Aluminum Nanowires by Stencil Lithography: Fabrication and Characterization

We present the fabrication process and electrical characterization of sub-100 nm scale Al nanowires (NWs) fabricated by stencil lithography (SL). We use a stencil with sub- 100 nm wide nanoslits patterned by focused ion beam (FIB) milling. The stencil is aligned and clamped onto a substrate containing predefined electrical contacts. Then a 60 nm-thick layer of Aluminum (Al) is deposited through the stencil producing NWs with lengths of ~1, 2 and 5 μm and widths down to 65 nm. The NWs show an ohmic behavior with values varying from 30 Ω up to 300 Ω, depending on the dimensions of the structures. We have extracted a resistivity for the Al NWs of ~10 x 10-8 Ωm. We also show that stencils can be cleaned and reused, proving that SL is a cost-efficient and scalable manufacturing method for the direct fabrication of metallic NWs on a full wafer scale

Organometallic iridium(III) anticancer complexes with new mechanisms of action: NCI-60 screening, mitochondrial targeting, and apoptosis

Platinum complexes related to cisplatin, cis-[PtCl2(NH3)2], are successful anticancer drugs; however, other transition metal complexes offer potential for combating cisplatin resistance, decreasing side effects, and widening the spectrum of activity. Organometallic half-sandwich iridium (IrIII) complexes [Ir(Cpx)(XY)Cl]+/0 (Cpx = biphenyltetramethylcyclopentadienyl and XY = phenanthroline (1), bipyridine (2), or phenylpyridine (3)) all hydrolyze rapidly, forming monofunctional G adducts on DNA with additional intercalation of the phenyl substituents on the Cpx ring. In comparison, highly potent complex 4 (Cpx = phenyltetramethylcyclopentadienyl and XY = N,N-dimethylphenylazopyridine) does not hydrolyze. All show higher potency toward A2780 human ovarian cancer cells compared to cisplatin, with 1, 3, and 4 also demonstrating higher potency in the National Cancer Institute (NCI) NCI-60 cell-line screen. Use of the NCI COMPARE algorithm (which predicts mechanisms of action (MoAs) for emerging anticancer compounds by correlating NCI-60 patterns of sensitivity) shows that the MoA of these IrIII complexes has no correlation to cisplatin (or oxaliplatin), with 3 and 4 emerging as particularly novel compounds. Those findings by COMPARE were experimentally probed by transmission electron microscopy (TEM) of A2780 cells exposed to 1, showing mitochondrial swelling and activation of apoptosis after 24 h. Significant changes in mitochondrial membrane polarization were detected by flow cytometry, and the potency of the complexes was enhanced ca. 5× by co-administration with a low concentration (5 μM) of the γ-glutamyl cysteine synthetase inhibitor L-buthionine sulfoximine (L-BSO). These studies reveal potential polypharmacology of organometallic IrIII complexes, with MoA and cell selectivity governed by structural changes in the chelating ligands