Scattering mechanisms in graphene are critical to understanding the limits of signal-to-noise ratios of unsuspended graphene devices. Here we present the four-probe low-frequency noise (1/f) characteristics in back-gated single layer graphene (SLG) and bilayer graphene (BLG) samples. Contrary to the expected noise increase with the resistance, the noise for SLG decreases near the Dirac point, possibly due to the effects of the spatial charge inhomogeneity. For BLG, a similar noise reduction near the Dirac point is observed, but with a different gate dependence of its noise behavior. Some possible reasons for the different noise behavior between SLG and BLG are discussed.

With the motivation of realizing an all graphene-based circuit for low power, we present a reliable nonvolatile graphene memory device, single-layer graphene (SLG) ferroelectric field-effect transistor (FFET). We demonstrate that exfoliated single-layer graphene can be optically visible on a ferroelectric lead-zirconate-titanate (PZT) substrate and observe a large memory window that is nearly equivalent to the hysteresis of the PZT at low operating voltages in a graphene FFET. In comparison to exfoliated graphene, FFETs fabricated with chemical vapor deposited (CVD) graphene exhibit enhanced stability through a bi-stable current state operation with long retention time. In addition, we suggest that the trapping/de-trapping of charge carriers in the interface states is responsible for the anti-hysteresis behavior in graphene FFET on PZT.

We demonstrate vertical graphene-base hot-electron transistors (GB-HETs) with a variety of structures and material parameters. Our GB-HETs exhibit a current saturation with a high current on-off ratio (>10(5)), which results from both the vertical transport of hot electrons across the ultrathin graphene base and the filtering of hot electrons through a built-in energy barrier. The influences of the materials and their thicknesses used for the tunneling and filtering barriers on the common-base current gain α are studied. The optimization of the SiO2 thickness and using HfO2 as the filtering barrier significantly improves the common-base current gain α by more than 2 orders of magnitude. The results demonstrate that GB-HETs have a great potential for high-frequency, high-speed, and high-density integrated circuits.

ABSTRACT:We report the direct measurement of the Dirac point, the Fermi level, and the work function of graphene by performing internal photoemission measurements on a graphene/SiO 2 /Si structure with a unique optical-cavity enhanced test structure. A complete electronic band alignment at the graphene/SiO 2 /Si interfaces is accurately established. The observation of enhanced photoemission from a one-atom thick graphene layer was possible by taking advantage of the constructive optical interference in the SiO 2 cavity. The photoemission yield was found to follow the well-known linear density-of-states dispersion in the vicinity of the Dirac point. At the flat band condition, the Fermi level was extracted and found to reside 3.3 eV ± 0.05 eV below the bottom of the SiO 2 conduction band. When combined with the shift of the Fermi level from the Dirac point, we are able to ascertain the position of the Dirac point at 3.6 eV ± 0.05 eV with respect to the bottom of the SiO 2 conduction band edge, yielding a work function of 4.5 eV ± 0.05 eV which is in an excellent agreement with theory. The accurate determination of the work function of graphene is of significant importance to the engineering of graphene-based devices, and the measurement technique we have advanced in this Letter will have significant impact on numerous applications for emerging graphene-like 2-dimensional material systems. KEYWORDS: Graphene, work function, internal photoemission, band alignment, graphene−insulator−semiconductor S ince the pioneering work of Novoselov et al. in 2004, 1 graphene has attracted an immense amount of interest from many related disciplines.2,3 Fundamental knowledge of the physical properties of graphene and the physical mechanisms governing the electrical operation of graphenebased devices has grown dramatically. 4 With the recent success of large area chemical vapor deposition (CVD) growth of graphene, 5 industrial applications such as transparent electrodes, 6 field-effect transistors (FETs), 7 and quantum well devices 8 are becoming more promising. Many studies have been conducted to characterize the various physical properties of graphene, including the work function, which is one of the most important electronic parameters. Among the numerous investigations by techniques such as Kelvin probe measurements, 9−11 ab initio calculations, 9,12 and recently by capacitance−voltage measurements, 13 the values of work function scatter in a rather wide range from 4.2 to 5.0 eV. Experimentally, the work function may be found to vary depending on the type of metal contact due to interactions between the graphene and the metal, which may result in pinning of the work function.9−13 Surprisingly, there is little information on the intrinsic electronic band alignment of the graphene/oxide interface to date, despite its important role in the design, fabrication, and characterization of graphene-based devices. For example, the accurate band alignment between graphene and another material determines how effectively to turn on an...

In this study, we report on the formation of a single-crystalline Ni(2)Ge/Ge/Ni(2)Ge nanowire heterostructure and its field effect characteristics by controlled reaction between a supercritical fluid-liquid-solid (SFLS) synthesized Ge nanowire and Ni metal contacts. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal a wide temperature range to convert the Ge nanowire to single-crystalline Ni(2)Ge by a thermal diffusion process. The maximum current density of the fully germanide Ni(2)Ge nanowires exceeds 3.5 × 10(7) A cm(-2), and the resistivity is about 88 μΩ cm. The in situ reaction examined by TEM shows atomically sharp interfaces for the Ni(2)Ge/Ge/Ni(2)Ge heterostructure. The interface epitaxial relationships are determined to be [Formula: see text] and [Formula: see text]. Back-gate field effect transistors (FETs) were also fabricated using this low resistivity Ni(2)Ge as source/drain contacts. Electrical measurements show a good p-type FET behavior with an on/off ratio over 10(3) and a one order of magnitude improvement in hole mobility from that of SFLS-synthesized Ge nanowire.