Hydrogen sensors from Pd‐functionalized multi‐layer graphene nanoribbon networks are fabricated. The fabrication method of these networks is simple, low cost, and scalable, and their high specific surface area facilitates efficient functionalization and gas adsorption. These networks show high sensitivity to hydrogen at parts‐per‐million concentration levels at room temperature with a fast response and recovery time.

Metal-semiconductor-metal (MSM) photodetectors based on graphene/p-type Si Schottky junctions are fabricated and characterized. Thermionic emission dominates the transport across the junctions above 260 K with a zero-bias barrier height of 0.48 eV. The reverse-bias dependence of the barrier height is found to result mostly from the Fermi level shift in graphene. MSM photodetectors exhibit a responsivity of 0.11 A/W and a normalized photocurrent-to-dark current ratio of 4.55 × 104 mW−1, which are larger than those previously obtained for similar detectors based on carbon nanotubes. These results are important for the integration of transparent, conductive graphene electrodes into existing silicon technologies.

We study the intrinsic transport properties of suspended graphene devices at high fields (≥1 V/μm) and high temperatures (≥1000 K). Across 15 samples, we find peak (average) saturation velocity of 3.6 × 10(7) cm/s (1.7 × 10(7) cm/s) and peak (average) thermal conductivity of 530 W m(-1) K(-1) (310 W m(-1) K(-1)) at 1000 K. The saturation velocity is 2-4 times and the thermal conductivity 10-17 times greater than in silicon at such elevated temperatures. However, the thermal conductivity shows a steeper decrease at high temperature than in graphite, consistent with stronger effects of second-order three-phonon scattering. Our analysis of sample-to-sample variation suggests the behavior of "cleaner" devices most closely approaches the intrinsic high-field properties of graphene. This study reveals key features of charge and heat flow in graphene up to device breakdown at ~2230 K in vacuum, highlighting remaining unknowns under extreme operating conditions.

We examine the transfer of graphene grown by chemical vapor deposition (CVD) with polymer scaffolds of poly(methyl methacrylate) (PMMA), poly(lactic acid) (PLA), poly(phthalaldehyde) (PPA), and poly(bisphenol A carbonate) (PC). We find that optimally reactive PC scaffolds provide the cleanest graphene transfers without any annealing, after extensive comparison with optical microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Comparatively, films transferred with PLA, PPA, and PMMA have a two-fold higher roughness and a five-fold higher chemical doping. Using PC scaffolds, we demonstrate the clean transfer of CVD multilayer graphene, fluorinated graphene, and hexagonal boron nitride. Our annealing free, PC transfers enable the use of atomically-clean nanomaterials in biomolecule encapsulation and flexible electronic applications. * Correspondence should be addressed to lyding@illinois.edu and epop@stanford.edu. Cu has proven the most fruitful platform for large-area graphene growth, as the low carbon solubility promotes monolayer growth. 8 Nevertheless, most applications using CVD-grown graphene require that the films be transferred to insulating substrates. The predominant graphene transfer approach is by using a poly(methyl methacrylate) (PMMA) scaffold. [12][13][14][15][16][17] In this method, the PMMA polymer coats the graphene, supporting it during Cu removal, underside contaminant cleaning, and placement on its destination substrate. 18, 19 However, PMMA removal from graphene after film transfer has proven challenging. 15 Approaches to remove it by high-temperature Ar/H2 forming gas annealing, 14, 20, 21 O2 based annealing, 15, 22, 23 and in situ annealing 16, 24, 25 have been marginally successful in removing PMMA without affecting the graphene. Furthermore, these processes are all at high-temperature, excluding graphene applications with low thermal budgets, including uses in flexible electronics and biomolecule encapsulation. Another process separated the graphene from the PMMA support by an Au interfacial layer, 26 but that process is subject to effective interfacial Au-graphene wetting. Recent transfer results using thermal release tape (TRT), [27][28][29] poly(bisphenol A carbonate) (PC), 30, 31 and sacrificial polymer release layers 26 required elevated temperature (over 100°C) during transfer and differed considerably in terms of surface contamination and graphene area coverage. To exploit the intrinsic properties of large-area graphene, a room temperature transfer process that comes off more cleanly than the established methods is needed. In print atIn this study, we compare the transfer of graphene with the conventional PMMA polymer scaffold with alternative poly(lactic acid) (PLA), poly(phthalaldehyde) (PPA), PC, and bilayer PMMA/PC scaffolds. We choose both PLA and PPA as scaffolds as they can supposedly be removed by modest heating or acid exposure. Further, we choose PC from its heightened reactivity as a condensation polymer and it...

The growth of high-density arrays of vertically oriented, single crystalline InAs NWs on graphene surfaces are realized through the van der Waals (vdW) epitaxy mechanism by metalorganic chemical vapor deposition (MOCVD). However, the growth of InGaAs NWs on graphene results in spontaneous phase separation starting from the beginning of growth, yielding a well-defined InAs-In(x)Ga(1-x)As (0.2 < x < 1) core-shell structure. The core-shell structure then terminates abruptly after about 2 μm in height, and axial growth of uniform composition In(x)Ga(1-x)As takes place without a change in the NW diameter. The In(x)Ga(1-x)As shell composition changes as a function of indium flow, but the core and shell thicknesses and the onset of nonsegregated In(x)Ga(1-x)As axial segment are independent of indium composition. In contrast, no InGaAs phase segregation has been observed when growing on MoS2, another two-dimensional (2D) layered material, or via the Au-assisted vapor-liquid-solid (VLS) mechanism on graphene. This spontaneous phase segregation phenomenon is elucidated as a special case of van der Waals epitaxy on 2D sheets. Considering the near lattice matched registry between InAs and graphene, InGaAs is forced to self-organize into InAs core and InGaAs shell segments since the lack of dangling bonds on graphene does not allow strain sharing through elastic deformation between InGaAs and graphene.