M. F. Crommie

University of California, Berkeley, Berkeley, CA, United States

Are you M. F. Crommie?

Claim your profile

Publications (187)1323.27 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The optical transparency and high electron mobility of graphene make it an attractive material for photovoltaics. We present a field-effect solar cell using graphene to form a tunable junction barrier with an Earth-abundant and low cost zinc phosphide (Zn3P2) thin-film light absorber. Adding a semi-transparent top electrostatic gate allows for tuning of the graphene Fermi level, and hence the energy barrier at the graphene-Zn3P2 junction, going from an ohmic contact at negative gate voltages to a rectifying barrier at positive gate voltages. We perform current and capacitance measurements at different gate voltages in order to demonstrate the control of the energy barrier and depletion width in the zinc phosphide. Our photovoltaic measurements show that the efficiency conversion is increased two-fold when we increase the gate voltage and the junction barrier to maximize the photovoltaic response. At an optimal gate voltage of +2 V, we obtain an open-circuit voltage of Voc=0.53 V and an efficiency of 1.9% under AM 1.5 1-sun solar illumination. This work demonstrates that the field effect can be used to modulate and optimize the response of photovoltaic devices incorporating graphene.
    Nano letters. 07/2014;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gate-controlled tuning of the charge carrier density in graphene devices provides new opportunities to control the behavior of molecular adsorbates. We have used scanning tunneling microscopy (STM) and spectroscopy (STS) to show how the vibronic electronic levels of 1,3,5-tris(2,2-dicyanovinyl)benzene molecules adsorbed onto a graphene/BN/SiO2 device can be tuned via application of a backgate voltage. The molecules are observed to electronically decouple from the graphene layer, giving rise to well-resolved vibronic states in dI/dV spectroscopy at the single-molecule level. Density functional theory (DFT) and many-body spectral function calculations show that these states arise from molecular orbitals coupled strongly to carbon-hydrogen rocking modes. Application of a back-gate voltage allows switching between different electronic states of the molecules for fixed sample bias.
    ACS Nano 04/2014; · 12.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The design of stacks of layered materials in which adjacent layers interact by van der Waals forces has enabled the combination of various two-dimensional crystals with different electrical, optical and mechanical properties as well as the emergence of novel physical phenomena and device functionality. Here, we report photoinduced doping in van der Waals heterostructures consisting of graphene and boron nitride layers. It enables flexible and repeatable writing and erasing of charge doping in graphene with visible light. We demonstrate that this photoinduced doping maintains the high carrier mobility of the graphene/boron nitride heterostructure, thus resembling the modulation doping technique used in semiconductor heterojunctions, and can be used to generate spatially varying doping profiles such as p-n junctions. We show that this photoinduced doping arises from microscopically coupled optical and electrical responses of graphene/boron nitride heterostructures, including optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene.
    Nature Nanotechnology 04/2014; · 31.17 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit novel electrical and optical properties and are emerging as a new platform for exploring 2D semiconductor physics. Reduced screening in 2D results in dramatically enhanced electron-electron interactions, which have been predicted to generate giant bandgap renormalization and excitonic effects. Currently, however, there is little direct experimental confirmation of such many-body effects in these materials. Here we present an experimental observation of extraordinarily large exciton binding energy in a 2D semiconducting TMD. We accomplished this by determining the single-particle electronic bandgap of single-layer MoSe2 via scanning tunneling spectroscopy (STS), as well as the two-particle exciton transition energy via photoluminescence spectroscopy (PL). These quantities yield an exciton binding energy of 0.55 eV for monolayer MoSe2, a value that is orders of magnitude larger than what is seen in conventional 3D semiconductors. This finding is corroborated by our ab initio GW and Bethe Salpeter equation calculations, which include electron correlation effects. The renormalized bandgap and large exciton binding observed here will have a profound impact on electronic and optoelectronic device technologies based on single-layer semiconducting TMDs.
    Nature materials. 04/2014;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The design of stacks of layered materials in which adjacent layers interact by van der Waals forces[1] has enabled the combination of various two-dimensional crystals with different electrical, optical and mechanical properties, and the emergence of novel physical phenomena and device functionality[2-8]. Here we report photo-induced doping in van der Waals heterostructures (VDHs) consisting of graphene and boron nitride layers. It enables flexible and repeatable writing and erasing of charge doping in graphene with visible light. We demonstrate that this photo-induced doping maintains the high carrier mobility of the graphene-boron nitride (G/BN) heterostructure, which resembles the modulation doping technique used in semiconductor heterojunctions, and can be used to generate spatially-varying doping profiles such as p-n junctions. We show that this photo-induced doping arises from microscopically coupled optical and electrical responses of G/BN heterostructures, which includes optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene.
    02/2014;
  • Source
    Dataset: jp408539x
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Semiconducting π-conjugated polymers have attracted significant interest for applications in light-emitting diodes, field-effect transistors, photovoltaics, and nonlinear optoelectronic devices. Central to the success of these functional organic materials is the facile tunability of their electrical, optical, and magnetic properties along with easy processability and the outstanding mechanical properties associated with polymeric structures. In this work we characterize the chemical and electronic structure of individual chains of oligo-(E)-1,1'-bi(indenylidene), a poly-acetylene derivative that we have obtained through cooperative C1-C5 thermal enediyne cyclizations on Au(111) surfaces followed by a step-growth polymerization of the (E)-1,1'-bi(indenylidene) diradical intermediates. We have determined the combined structural and electronic properties of this class of oligomers by characterizing the atomically precise chemical structure of individual monomer building blocks and oligomer chains (via non-contact atomic force microscopy (nc-AFM)), as well as by imaging their localized and extended molecular orbitals (via scanning tunneling microscopy and spectroscopy (STM/STS)). Our combined structural and electronic measurements reveal that the energy associated with extended π-conjugated states in these oligomers is significantly lower than the energy of the corresponding localized monomer orbitals, consistent with theoretical predictions.
    Nano Letters 01/2014; · 13.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Recently developed processes have enabled bottom-up chemical synthesis of graphene nanoribbons (GNRs) with precise atomic structure. These GNRs are ideal candidates for electronic devices because of their uniformity, extremely narrow width below 1 nm, atomically perfect edge structure, and desirable electronic properties. Here, we demonstrate nano-scale chemically synthesized GNR field-effect transistors, made possible by development of a reliable layer transfer process. We observe strong environmental sensitivity and unique transport behavior characteristic of sub-1 nm width GNRs.
    Applied Physics Letters 12/2013; 103:253114. · 3.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Graphene resonators are fabricated using a polymer-free, direct transfer method onto metal reinforced holey carbon grids. The resonators are distinguished by the absence of organic residues and excellent crystallinity. The normal mode frequencies are measured using a Fabry–Perot technique; resonance curves indicate highly linear behaviour but very little built-in strain, which is consistent with device geometry examined by atomic force microscopy. We conclude that the oscillators' restoring force is due instead to graphene's intrinsic bending rigidity; our measurements indicate a value of approximately 1.0 eV, consistent with previous theoretical and experimental work. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (RRL) - Rapid Research Letters 12/2013; 7(12). · 2.39 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The atomic structure of graphene edges is critical in determining the electrical, magnetic and chemical properties of truncated graphene structures, notably nanoribbons. Unfortunately, graphene edges are typically far from ideal and suffer from atomic-scale defects, structural distortion and unintended chemical functionalization, leading to unpredictable properties. Here we report that graphene edges fabricated by electron beam-initiated mechanical rupture or tearing in high vacuum are clean and largely atomically perfect, oriented in either the armchair or zigzag direction. We demonstrate, via aberration-corrected transmission electron microscopy, reversible and extended pentagon-heptagon (5-7) reconstruction at zigzag edges, and explore experimentally and theoretically the dynamics of the transitions between configuration states. Good theoretical-experimental agreement is found for the flipping rates between 5-7 and 6-6 zigzag edge states. Our study demonstrates that simple ripping is remarkably effective in producing atomically clean, ideal terminations, thus providing a valuable tool for realizing atomically tailored graphene and facilitating meaningful experimental study.
    Nature Communications 11/2013; 4:2723. · 10.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the structural and electronic properties of individual ethylene molecules on the GaP(110) surface by combining low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) with density functional theory (DFT) calculations. Isolated molecules were adsorbed on in-situ cleaved GaP(110) surfaces through ethylene exposures at 300K and 15 K. DFT calculations suggest two possible stable adsorption geometries for a single ethylene molecule on GaP(110) at low tem- perature. High-resolution STM images, however, reveal only one adsorption geometry for this system, consistent with the site having the largest computed binding energy. Unlike adsorption of ethylene on other metallic and semiconducting surfaces, ethylene physisorbs to GaP(110) through a weak hybridization of molecular π-states with Differential conductivity spectra acquired on single molecules are consistent with self energy corrected DFT calculations.
    The Journal of Physical Chemistry C 10/2013; · 4.84 Impact Factor
  • Source
    The Journal of Physical Chemistry C 10/2013; · 4.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions.
    Physical Review Letters 09/2013; 111(12):126101. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study theoretically and experimentally the infrared (IR) spectrum of an adamantane monolayer on a Au(111) surface. Using a new STM-based IR spectroscopy technique (IRSTM) we are able to measure both the nanoscale structure of an adamantane monolayer on Au(111) as well as its infrared spectrum, while DFT-based ab initio calculations allow us to interpret the microscopic vibrational dynamics revealed by our measurements. We find that the IR spectrum of an adamantane monolayer on Au(111) is substantially modified with respect to the gas-phase IR spectrum. The first modification is caused by the adamantane--adamantane interaction due to monolayer packing and it reduces the IR intensity of the 2912 cm$^{-1}$ peak (gas phase) by a factor of 3.5. The second modification originates from the adamantane--gold interaction and it increases the IR intensity of the 2938 cm$^{-1}$ peak (gas phase) by a factor of 2.6, and reduces its frequency by 276 cm$^{-1}$. We expect that the techniques described here can be used for an independent estimate of substrate effects and intermolecular interactions in other diamondoid molecules, and for other metallic substrates.
    Physical Review B 09/2013; · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Anticorrosion and antioxidation surface treatments such as paint or anodization are a foundational component in nearly all industries. Graphene, a single-atom-thick sheet of carbon with impressive impermeability to gases, seems to hold promise as an effective anticorrosion barrier, and recent work supports this hope. We perform a complete study of the short- and long-term performance of graphene coatings for Cu and Si substrates. Our work reveals that although graphene indeed offers effective short-term oxidation protection, over long time scales it promotes more extensive wet corrosion than that seen for an initially bare, unprotected Cu surface. This surprising result has important implications for future scientific studies and industrial applications. In addition to informing any future work on graphene as a protective coating, the results presented here have implications for graphene's performance in a wide range of applications.
    ACS Nano 06/2013; · 12.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A prerequisite for future graphene nanoribbon (GNR) applications is the ability to fine-tune the electronic bandgap of GNRs. Such control requires the development of fabrication tools capable of precisely controlling width and edge geometry of GNRs at the atomic scale. Here we report a technique for modifying GNR bandgaps via covalent self-assembly of a new species of molecular precursors that yields n = 13 armchair GNRs, a wider GNR than those previously synthesized using bottom-up molecular techniques. Scanning tunneling microscopy and spectroscopy reveal that these n = 13 armchair GNRs have a bandgap of 1.4 eV, 1.2 eV smaller than the gap determined previously for n = 7 armchair GNRs. Furthermore, we observe a localized electronic state near the end of n = 13 armchair GNRs that is associated with hydrogen terminated sp2-hybridized carbon atoms at the zigzag termini.
    ACS Nano 06/2013; · 12.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Observing the intricate chemical transformation of an individual molecule as it undergoes a complex reaction is a longstanding challenge in molecular imaging. Advances in scanning probe microscopy now provide the tools to visualize not only the frontier orbitals of chemical reaction partners and products, but their internal covalent bond configurations as well. Here, we demonstrate the use of noncontact atomic force microscopy to investigate reaction-induced changes in the detailed internal bond structure of individual oligo-(phenylene-1,2-ethynylenes) on Ag(100) as they undergo a series of cyclization processes. Our images reveal the complex surface reaction mechanisms underlying thermally induced cyclization cascades of enediynes. Additional evidence for the proposed reaction pathways is obtained using ab initio density functional theory.
    Science 05/2013; · 31.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have combined scanning tunneling microscopy with inelastic electron tunneling spectroscopy (IETS) and density functional theory (DFT) to study a tetracyanoethylene monolayer on Ag(100). Images show that the molecules arrange in locally ordered patterns with three non-equivalent, but undeterminable, adsorption sites. While scanning tunneling spectroscopy only shows subtle variations of the local electronic structure at the three different positions, we find that vibrational modes are very sensitive to the local atomic environment. IETS detects sizeable mode frequency shifts of the molecules located at the three topographically detected sites, which permits us to determine the molecular adsorption sites through identification with DFT calculations.
    Nano Letters 05/2013; · 13.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Relativistic quantum mechanics predicts that when the charge of a super-heavy atomic nucleus surpasses a certain threshold, the resulting strong Coulomb field causes an unusual "atomic collapse" state which exhibits an electron wave function component that falls toward the nucleus as well as a positron component that escapes to infinity. In graphene, where charge carriers behave as massless relativistic particles, it has been predicted that highly charged impurities should exhibit resonances corresponding to these atomic collapse states. We have observed the formation of such resonances around artificial nuclei (clusters of charged calcium dimers) fabricated on gated graphene devices via atomic manipulation with a scanning tunneling microscope (STM). The energy and spatial dependence of the atomic collapse state measured using STM revealed unexpected behavior when it is occupied by electrons.
    Science 03/2013; · 31.20 Impact Factor

Publication Stats

5k Citations
1,323.27 Total Impact Points

Institutions

  • 1987–2013
    • University of California, Berkeley
      • Department of Physics
      Berkeley, CA, United States
  • 1995–2012
    • Boston University
      • Department of Physics
      Boston, Massachusetts, United States
  • 2010
    • Fudan University
      Shanghai, Shanghai Shi, China
  • 2003–2009
    • CSU Mentor
      Long Beach, California, United States
  • 2008
    • Lawrence Berkeley National Laboratory
      • Physics Division
      Berkeley, CA, United States
  • 1995–1996
    • Harvard University
      • Department of Physics
      Cambridge, Massachusetts, United States