Showing papers by "Hang Zhang published in 2010"
TL;DR: It is demonstrated that the application of covalent bond-forming chemistry modifies the periodicity of the graphene network thereby introducing a band gap (∼0.4 eV), which is observable in the angle-resolved photoelectron spectroscopy of aryl-functionalized graphene.
Abstract: In order to engineer a band gap into graphene, covalent bond-forming reactions can be used to change the hybridization of the graphitic atoms from sp2 to sp3, thereby modifying the conjugation length of the delocalized carbon lattice; similar side-wall chemistry has been shown to introduce a band gap into metallic single-walled carbon nanotubes. Here we demonstrate that the application of such covalent bond-forming chemistry modifies the periodicity of the graphene network thereby introducing a band gap (∼0.4 eV), which is observable in the angle-resolved photoelectron spectroscopy of aryl-functionalized graphene. We further show that the chemically-induced changes can be detected by Raman spectroscopy; the in-plane vibrations of the conjugated π-bonds exhibit characteristic Raman spectra and we find that the changes in D, G, and 2D-bands as a result of chemical functionalization of the graphene basal plane are quite distinct from that due to localized, physical defects in sp2-conjugated carbon.
504 citations
TL;DR: In this article, the authors presented a lithography-free technique for fabrication of clean, high quality graphene devices, which is based on evaporation through hard Si shadow masks, and eliminates contaminants introduced by lithographical processes.
Abstract: We present a lithography-free technique for fabrication of clean, high quality graphene devices. This technique is based on evaporation through hard Si shadow masks, and eliminates contaminants introduced by lithographical processes. We demonstrate that devices fabricated by this technique have significantly higher mobility values than those obtained by standard electron beam lithography. To obtain ultra-high mobility devices, we extend this technique to fabricate suspended graphene samples with mobilities as high as 120 000 cm 2 /(V·s).
95 citations
TL;DR: In this paper, the authors report pronounced magnetoconductance oscillations observed on suspended bilayer and trilayer graphene devices with mobilities up to $270\text{ }000,000, 000, 000/€ 1/3/€ 2/€ 3/€ 4.
Abstract: We report pronounced magnetoconductance oscillations observed on suspended bilayer and trilayer graphene devices with mobilities up to $270\text{ }000\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{V}\text{ }\mathrm{s}$. For bilayer devices, we observe conductance minima at all integer filling factors $\ensuremath{
u}$ between 0 and $\ensuremath{-}8$, as well as a small plateau at $\ensuremath{
u}=1/3$. For trilayer devices, we observe features at $\ensuremath{
u}=\ensuremath{-}1$, $\ensuremath{-}2$, $\ensuremath{-}3$, and $\ensuremath{-}4$, and at $\ensuremath{
u}\ensuremath{\sim}0.5$ that persist to 4.5 K at $B=8\text{ }\text{ }\mathrm{T}$. All of these features persist for all accessible values of ${V}_{g}$ and $B$, and could suggest the onset of symmetry breaking of the first few Landau levels and fractional quantum Hall states.
73 citations
TL;DR: In this paper, the conductance fluctuations on transitions between quantum Hall (QH) plateaus as the top gate voltage is varied are observed in high-quality graphene $pnp$ junctions, with Coulomb-induced charging of electron- or hole-doped localized states.
Abstract: Using high-quality graphene $pnp$ junctions, we observe prominent conductance fluctuations on transitions between quantum Hall (QH) plateaus as the top gate voltage ${V}_{tg}$ is varied. In the ${V}_{tg}\text{\ensuremath{-}}B$ plane, the fluctuations form crisscrossing lines that are parallel to those of the adjacent plateaus, with different temperature dependences for the conductance peaks and valleys. These fluctuations arise from Coulomb-induced charging of electron- or hole-doped localized states when the device bulk is delocalized, underscoring the importance of electronic interactions in graphene in the QH regime.
29 citations
TL;DR: In this paper, a multi-level lithographical technique was used to suspend atomic membranes, which can be applied to the vast majority of substrate, membrane and electrode materials, and fabricated suspended graphene devices with Al electrodes and mobility of 5500 cm^2/Vs.
Abstract: Coupling high quality, suspended atomic membranes to specialized electrodes enables investigation of many novel phenomena, such as spin or Cooper pair transport in these two dimensional systems. However, many electrode materials are not stable in acids that are used to dissolve underlying substrates. Here we present a versatile and powerful multi-level lithographical technique to suspend atomic membranes, which can be applied to the vast majority of substrate, membrane and electrode materials. Using this technique, we fabricated suspended graphene devices with Al electrodes and mobility of 5500 cm^2/Vs. We also demonstrate, for the first time, fabrication and measurement of a free-standing thin Bi2Se3 membrane, which has low contact resistance to electrodes and a mobility of >~500 cm^2/Vs.
6 citations
TL;DR: In this article, the authors present a lithography-free technique for fabrication of clean, high quality graphene devices, based on evaporation through hard Si shadow masks, and eliminate contaminants introduced by lithographical processes.
Abstract: We present a lithography-free technique for fabrication of clean, high quality graphene devices. This technique is based on evaporation through hard Si shadow masks, and eliminates contaminants introduced by lithographical processes. We demonstrate that devices fabricated by this technique have significantly higher mobility values than those by standard electron beam lithography. To obtain ultra-high mobility devices, we extend this technique to fabricate suspended graphene samples with mobility as high as 120,000 cm^2/Vs.
4 citations