Evolution of Graphene Growth on Pt(111): From Carbon Clusters to Nanoislands

We study the growth of graphene on a Pt(111) surface in stages by varying the annealing temperature of the precursor hydrocarbon decomposition through an atomic-scale analysis using scanning tunneling microscopy (STM) and studying the geometry-affected electronic properties of graphene nanoislands (GNs) through scanning tunneling spectroscopy. STM reveals that graphene grows on a Pt(111) surface from dome-shaped carbon clusters to flat GNs with the intermediate stages of dome-shaped and basin-shaped hexagonal GN structures. Density functional theory calculations confirm the changes in direction of the concavity upon increase in the size of the GNs. The structural changes are also found to have a significant effect on the electronic properties. Landau levels arise from strain-induced pseudomagnetic fields because of the large curvature, and the nanoscale-size effect promotes electron confinement

Quenching of the Resonant States of Single Carbon Vacancies in Graphene/Pt(111)

For more than a decade, investigations of single carbon vacancies in graphene have sought to increase the fundamental understanding of the local electronic, magnetic, and mechanical properties of such vacancies. The single C vacancy in graphene has been known to generate a resonant state through the integration of π orbitals near the missing C atom. Here, we examine single C vacancies in graphene/Pt(111) to explore the effects of graphene–substrate interactions on the local electronic properties of imperfect graphene. Our scanning tunneling microscopy, scanning tunneling spectroscopy, and related density functional theory calculations show the resulting modifications, including the complete disappearance of the resonant state attributable to strong graphene–substrate coupling near the vacancy. The different relative positions of single C vacancies corresponding to the Pt atoms lead both to varying C–Pt bonding structures and strengths and to corresponding changes in the local density of states

Oxygen Concentration Control of Dopamine-Induced High Uniformity Surface Coating Chemistry

Material surface engineering has attracted great interest in important applications, including electronics, biomedicine, and membranes. More recently, dopamine has been widely exploited in solution-based chemistry to direct facile surface modification. However, unsolved questions remain about the chemical identity of the final products, their deposition kinetics and their binding mechanism. In particular, the dopamine oxidation reaction kinetics is a key to improving surface modification efficiency. Here, we demonstrate that high O₂ concentrations in the dopamine solution lead to highly homogeneous, thin layer deposition on any material surfaces via accelerated reaction kinetics, elucidated by Le Chatelier’s principle toward dopamine oxidation steps in a Michael-addition reaction. As a result, highly uniform, ultra-smooth modified surfaces are achieved in much shorter deposition times. This finding provides new insights into the effect of reaction kinetics and molecular geometry on the uniformity of modifications for surface engineering techniques

Confinement of the Pt(111) Surface State in Graphene Nanoislands

We present a combined experimental and theoretical study of electron confinement in graphene nanoislands (GNs) grown on a Pt(111) substrate using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. We observed standing wave patterns in the STM images of GNs, and the bias dependency of the standing wave pattern was reproduced by considering free electrons with an effective mass of <i>m</i>* ≈ (0.27 ± 0.03)<i>m</i>_e. Because the effective mass of Pt is <i>m</i>* = 0.28<i>m</i>_e, our results reveal that the electron confinement is due to the effect of the Pt substrate rather than the massless Dirac electrons of graphene. Our calculated maps of the local density of states (LDOS) for the GNs confirm that the electronic properties of the confinement may be described in terms of electrons with an effective mass. The DFT-calculated charge distribution for graphene on the Pt system also shows a clear hybridization between the p_<i>z</i> orbitals of both the first layer of the Pt substrate and the carbon atoms

<i>A</i>, MR images from a 63-year-old female patient with glioblastoma taken 2 weeks after concurrent chemo-radiation.

<p>The contrast-enhanced MRI (left) and ASL (right) showed negative perfusion in the surgical cavity wall enhancement (SCWE). <i>B</i>, Follow-up images taken 2 months later show evident tumour progression. Note that enhancing lesions increased mostly at the regions of previously negative perfusion, the posterior portion of SCWE.</p

Clinical characteristics and outcome of the study patients.

<p>Clinical characteristics and outcome of the study patients.</p

Accrual process for determining the perfusion status of surgical cavity wall enhancements.

<p>The perfusion fraction was calculated by dividing the area of the high perfusion on ASL MR imaging by the area of contrast-enhancement on postcontrast T1-weighted imaging. The perfusion fraction was 58.8% for reader 1 and 69% for reader 2.</p

Cox proportional model analysis of time-to-progression.

<p>Cox proportional model analysis of time-to-progression.</p

Results of linear regression between the perfusion fraction and TTP.

<p>Results of linear regression between the perfusion fraction and TTP.</p

Comparison of SCWE imaging characteristics.

<p>Comparison of SCWE imaging characteristics.</p