Photoemission Spectroscopy

Contains reports on two research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020

Decoupling Graphene from SiC(0001) via Oxidation

When epitaxial graphene layers are formed on SiC(0001), the first carbon layer (known as the "buffer layer"), while relatively easy to synthesize, does not have the desirable electrical properties of graphene. The conductivity is poor due to a disruption of the graphene pi-bands by covalent bonding to the SiC substrate. Here we show that it is possible to restore the graphene pi-bands by inserting a thin oxide layer between the buffer layer and SiC substrate using a low temperature, CMOS-compatible process that does not damage the graphene layer

The role of second-neighbor effects in photoemission: Are silicon surfaces and interfaces special?

A widely used assignment scheme for Si 2p2p core-level photoemission studies of silicon oxidation relies solely on the formal oxidation state of the silicon. The tacit assumption of this assignment methodology is that second-neighbor effects have no measurable effect on observed Si 2p2p binding energies. In this letter, new experiments are combined with literature precedents to make the case that the second-neighbor effects play an important role in determining binding energy shifts. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70944/2/APPLAB-72-1-46-1.pd

Photoemission Spectroscopy

Contains report on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104

Photoemission Spectroscopy

Contains reports on two research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020

Large-scale and rapid synthesis of disk-shaped and nano-sized graphene

We synthesized disk-shaped and nano-sized graphene (DSNG) though a novel ion-exchange methodology. This new methodology is achieved by constructing metal ion/ion-exchange resin framework. The morphology and size of the graphene can be modulated by changing the mass ratio of the carbon-containing resin to the cobalt-containing precursor. This is the first time to show that the DSNG formed on the granular transition metal substrate. The DSNG gives a high intensity of photoluminescence at near-UV wavelength of 311 nm which may provide a new type of fluorescence for applications in laser devices, ultraviolet detector UV-shielding agent and energy technology. The emission intensity of the DSNG is thirty times higher than that of the commercial large graphene. Our approach for graphene growth is conveniently controllable, easy to scale-up and the DSNG shows superior luminescent properties as compared to conventional large graphene

Probing the Thermal Deoxygenation of Graphene Oxide using High Resolution In Situ X-Ray based Spectroscopies

Despite the recent developments in Graphene Oxide due to its importance as a host precursor of Graphene, the detailed electronic structure and its evolution during the thermal reduction remain largely unknown, hindering its potential applications. We show that a combination of high resolution in situ X-ray photoemission and X-ray absorption spectroscopies offer a powerful approach to monitor the deoxygenation process and comprehensively evaluate the electronic structure of Graphene Oxide thin films at different stages of the thermal reduction process. It is established that the edge plane carboxyl groups are highly unstable, whereas carbonyl groups are more difficult to remove. The results consistently support the formation of phenol groups through reaction of basal plane epoxide groups with adjacent hydroxyl groups at moderate degrees of thermal activation (~400 {\deg}C). The phenol groups are predominant over carbonyl groups and survive even at a temperature of 1000 {\deg}C. For the first time a drastic increase in the density of states (DOS) near the Fermi level at 600 {\deg}C is observed, suggesting a progressive restoration of aromatic structure in the thermally reduced graphene oxideComment: Pagona Papakonstantinou as Corresponding author, E-mail: [email protected]

Spectroscopic investigations of small-molecule interactions on metal oxide surfaces. Final report, September 1, 1978-December 31, 1981

Angle integrated and angle resolved ultraviolet photoelectron spectroscopy (UPS and ARPES) and high resolution electron energy loss spectroscopy (HREELS) have been performed on the low index single crystal surfaces of zinc oxide. Study of CO/ZnO shows that the mode of binding is dominated by 5sigma donation from the carbon end of the molecule to the unsaturated surface zinc ion with little ..pi.. backbonding to the CO2..pi..* orbital. This electronic structure is verified by a HREELS study. The geometry of CO binding is consistent with LEED studies where no symmetry changing reconstructions are observed to occur, and where the CO molecule forms an approximately linear Zn-C-O surface complex along the coordinatively unsaturated directions of the surface zinc ions. Implications of these studies to the mechanism of methanol synthesis is described. These UPS studies have also provided insight into the bonding interaction between small molecules such as NH/sub 3/ and CO/sub 2/ (as well as H/sub 2/O, C/sub 2/H/sub 4/, CH/sub 3/OH, H/sub 2/S and CH/sub 3/SH) and the ZnO single crystal surfaces