Monatomic layers of graphite are emerging as building blocks for novel optoelectronic devices. Experimental studies on a single graphite layer (graphene) are today possible since very thin graphite can be identified on a dielectric substrate using a normal optical microscope. We investigate the mechanism behind the strong visibility of graphite, and we discuss the importance of substrates and of the microscope objective used for the imaging.

We report the Au-assisted chemical beam epitaxy growth of defect-free zincblende InSb nanowires. The grown InSb segments are the upper sections of InAs/InSb heterostructures on InAs(111)B substrates. We show, through HRTEM analysis, that zincblende InSb can be grown without any crystal defects such as stacking faults or twinning planes. Strain-map analysis demonstrates that the InSb segment is nearly relaxed within a few nanometers from the interface. By post-growth studies we have found that the catalyst particle composition is AuIn(2), and it can be varied to a AuIn alloy by cooling down the samples under TDMASb flux.

We investigate tunable hole quantum dots defined by surface gating Ge/Si core-shell nanowire heterostructures. In single level Coulomb-blockade transport measurements at low temperatures spin doublets are found, which become sequentially filled by holes. Magnetotransport measurements allow us to extract a g factor g approximately 2 close to the value of a free spin-1/2 particle in the case of the smallest dot. In less confined quantum dots smaller g factor values are observed. This indicates a lifting of the expected strong spin-orbit interaction effects in the valence band for holes confined in small enough quantum dots. By comparing the excitation spectrum with the addition spectrum we tentatively identify a hole exchange interaction strength chi approximately 130 microeV.

We report current transmission data through a split-gate constriction fabricated onto a twodimensional electron system in the integer quantum Hall (QH) regime. Split-gate biasing drives inter-edge backscattering and is shown to lead to suppressed or enhanced transmission, in marked contrast with the expected linear Fermi-liquid behavior. This evolution is described in terms of particle-hole symmetry and allows us to conclude that an unexpected class of gate-controlled particlehole-symmetric chiral Luttinger Liquids (CLLs) can exist at the edges of our QH circuit. These results highlight the role of particle-hole symmetry on the properties of CLL edge states.PACS numbers: 73.43. Jn, 71.10.Pm, 73.21.Hb Quantum Hall (QH) states [1] are created at integer and peculiar fractional values of the filling factor ν, defined as the ratio between the electron density n and the magnetic flux density n φ measured in units of φ 0 = h/e. Charge excitations confined at the edge are the only charged modes that can propagate in the QH phase along the direction set by the external magnetic field. These edge excitations at the fractional filling factor ν = 1/m, with m odd integer, form a onedimensional liquid that was predicted to be equivalent to a CLL [2] with interaction parameter g = ν [3, 4, 5]. These predictions were tested by a large number of experiments [6,7,8,9,10,11,12] even if many open issues remain, in particular for the case of the edge states at ν = 1/m.A split-gate (SG) technique [13] can be exploited to define a nanofabricated constriction in order to induce a controllable scattering between counter-propagating edge channels that are locally brought in close proximity (see Fig.1a). The constriction thus realizes an artificial impurity and can be used to test one of the most significant manifestations of CLL behavior: the complete suppression of the (low-temperature, low-bias) transmission through the impurity and its related power-law behavior [3,4,5]. Backscattering at the constriction is controlled by the split-gate voltage V g : by increasing |V g | the inter-edge distance is decreased; at larger |V g | values, in addition, the density of the two-dimensional electron system in proximity to the SG is appreciably reduced. In the presence of a uniform external magnetic field, this leads to a reduced filling factor ν * within the constriction region (see Fig. 1a).Here we show that the SG voltage V g not only modifies the backscattering strength but also defines unexpected robust CLLs that are related by particle-hole symmetry. In order to demonstrate this we study the constriction transmission in the QH regime at bulk integer filling factor ν = 1. The measured low-energy conductance displays a non-linear behavior determined by the SG voltage. Both suppression and enhancement of the transmis- The constriction is obtained by a metallic splitgate deposited on the surface of the semiconductor. After application of a perpendicular magnetic field, a QH state with filling factor ν = 1 is formed. Chiral edge states that ...

wafer-scale, with good crystallinity and with contamination levels compatible with large-scale back-end-of-line (BEOL) integration. At present, chemical vapor deposition (CVD) on catalytic copper (Cu) substrates is widely recognized as the most promising route to obtain scalable monolayer graphene for electronic and optoelectronic applications. [1][2][3][4] However, significant hurdles are limiting the actual integration of CVD graphene grown on Cu for most applications. In the first instance, the unavoidable transfer process over wafer-scale is rather cumbersome and introduces contamination, unintentional doping, and mechanical stress, [5][6][7] which adversely impact the physical integrity and electrical performance [8] of the graphene layer. The significant challenge involved in carrying out this seemingly straightforward task is reflected by the vast literature on large-scale transfer processes. Second, metallic contamination levels in transferred CVD graphene grown on Cu are typically well-above the specifications requested for BEOL integration. [6] Clearly, asThe adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high-quality material on technologically relevant substrates, over wafer-scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al-rich reconstruction9° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm 2 V −1 s −1 . The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back-end-ofline integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.