We present a robust method for forming high quality ohmic contacts to graphene, which improves the contact resistance by nearly 6000 times compared to untreated metal/graphene interfaces. The optimal specific contact resistance for treated Ti/Au contacts is found to average <10−7 Ω cm2. Additionally, we examine Al/Au, Ti/Au, Ni/Au, Cu/Au, Pt/Au, and Pd/Au contact metallizations and find that most metallizations result in similar specific contact resistances in this work regardless of the work function difference between graphene and the metal overlayer. The results presented in this work serve as a foundation for achieving ultralow resistance ohmic contacts to graphene for high speed electronic and optoelectronic applications.

Electrically-induced electron spin polarization is imaged in n-type ZnSe epilayers using Kerr rotation spectroscopy. Despite no evidence for an electrically-induced internal magnetic field, currentinduced in-plane spin polarization is observed with characteristic spin lifetimes that decrease with doping density. The spin Hall effect is also observed, indicated by an electrically-induced out-ofplane spin polarization with opposite sign for spins accumulating on opposite edges of the sample. The spin Hall conductivity is estimated as 3 ± 1.5 Ω −1 m −1 /|e| at 20 K, which is consistent with the extrinsic mechanism. Both the current-induced spin polarization and the spin Hall effect are observed at temperatures from 10 K to 295 K. PACS numbers: 75.25.Pn, 75.25.Dc, 71.70.Ej, 78.47.+p The ability to manipulate carrier spins in semiconductors through the spin-orbit (SO) interaction is one of the primary motivations behind the field of spintronics. SO coupling provides a mechanism for the generation and manipulation of spins solely through electric fields [1,2,3], obviating the need for applied magnetic fields. Much of the recent interest in the consequences of SO coupling in semiconductors surrounds the production of a transverse spin current from an electric current, known as the spin Hall effect. Though predicted three decades ago [4], the first experimental observations of the spin Hall effect have appeared only recently [5,6,7]. Subsequent work into the spin Hall effect has addressed the importance of extrinsic or intrinsic mechanisms of the spin Hall conductivity [7,8,9,10], the nature of spin currents [11,12], and the potential ability both to produce and to detect spin Hall currents using only electric fields [13,14].Previous experiments showing electrical generation of spin polarization in semiconductors through SO coupling have been performed at cryogenic temperatures in GaAs, the archetypical III-V zincblende semiconductor. In contrast, the wide band gap and long spin coherence times of II-VI semiconductors allow many spin-related effects to persist to higher temperatures than typically observed in the GaAs system [15]. Many of the effects of SO coupling on the electrical manipulation of spin polarization have not been studied in detail in these compounds. In ZnSe, the extrinsic SO parameter λ ZnSe = 1.06 eÅ 2 , as calculated from an extended Kane model, is five times less than that in GaAs, with λ GaAs = 5.21 eÅ 2 [10, 16]. Despite weaker SO coupling, large extrinsic SO skewscattering has been observed in the anomalous Hall effect in magnetically doped ZnSe [17]. In this Letter we optically measure electrically-induced spin polarization in ZnSe epilayers that persists to room temperature. We observe in-plane current-induced spin polarization (CISP) in ZnSe with n-doping ranging over two orders of magnitude and out-of-plane electrically-induced spin accumulation at the edges of an etched channel, providing evidence for the extrinsic spin Hall effect. Unlike in previous studies of CISP and the spin Hall eff...

We explore the effect of high-κ dielectric seed layer and overlayer on carrier transport in epitaxial graphene. We introduce a novel seeding technique for depositing dielectrics by atomic layer deposition that utilizes direct deposition of high-κ seed layers and can lead to an increase in Hall mobility up to 70% from as-grown. Additionally, high-κ seeded dielectrics are shown to produce superior transistor performance relative to low-κ seeded dielectrics and the presence of heterogeneous seed/overlayer structures is found to be detrimental to transistor performance, reducing effective mobility by 30-40%. The direct deposition of high-purity oxide seed represents the first robust method for the deposition of uniform atomic layer deposited dielectrics on epitaxial graphene that improves carrier transport.

The structures of self-assembled monolayers formed by chemisorption of octadecanethiol onto the surfaces of GaAs(001), (110), (111-A)-Ga, and (111-B)-As have been characterized in detail by a combination of X-ray photoelectron, near-edge X-ray absorption fine structure, and infrared spectroscopies and grazing incidence X-ray diffraction. In all cases, the molecular lattices are ordered with hexagonal symmetry, even for the square and rectangular intrinsic substrate (001) and (110) lattices, and the adsorbate lattice spacings are all incommensurate with their respective intrinsic substrate lattices. These results definitively show that the monolayer organization is driven by intermolecular packing forces to assemble in a hexagonal motif, such as would occur in the approach to a limit for an energetically featureless surface. The accompanying introduction of strain into the soft substrate surface lattice via strong S substrate bonds forces the soft substrate lattice to compliantly respond, introducing quasi-2D strain. A notably poorer organization for the (111-A)-Ga case compared to the (111-B)-As and other faces indicates that that the Ga-terminated surface lattice is more resistant to adsorbate packing-induced stress. Overall, the results show that surface molecular self-assembly must be considered as a strongly cooperative process between the substrate surface and the adsorbate and that inorganic substrate surfaces should not be considered as necessarily rigid when strong intermolecular adsorbate packing forces are operative.