Fernando Stavale

Quantifying Defects in Graphene via Raman Spectroscopy at Different Excitation Energies

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.

Raman study of ion-induced defects in N-layer graphene

Raman scattering is used to study the effect of low energy (90 eV) Ar(+) ion bombardment in graphene samples as a function of the number of layers N. The evolution of the intensity ratio between the G band (1585 cm(-1)) and the disorder-induced D band (1345 cm(-1)) with ion fluence is determined for mono-, bi-, tri- and ∼50-layer graphene samples, providing a spectroscopy-based method to study the penetration of these low energy Ar(+) ions in AB Bernal stacked graphite, and how they affect the graphene sheets. The results clearly depend on the number of layers. We also analyze the evolution of the overall integrated Raman intensity and the integrated intensity for disorder-induced versus Raman-allowed peaks.

Direct immobilization of avidin protein on AFM tip functionalized by acrylic acid vapor at RF plasma

The atomic force microscopy (AFM) has been used as a force sensor to measure unbinding forces of single bound complexes in the nanonewton and piconewton range. Force spectroscopy measurements can be applied to study both intermolecular and intramolecular interactions of complex biological and synthetic macromolecules. Although the AFM has been extensively used as a nano force sensor, the commercially available cantilever is limited to silicon and silicon nitride. Those materials reduce the adhesion sensitivity with specific surface and/or molecule. Here, we functionalized the AFM tip with carboxylic groups by applying acrylic acid (AA) vapor at radio frequency plasma treatment at 100 W for 5 min. This method provides a remarkable sensitivity enhancement on the functional group interaction specificity. The functionalized tip was characterized by scanning electron microscopy. The electron beam high resolution images have not shown significant tip sharpness modification. Silicon wafers (1 0 0)—no treated and functionalized by AA plasma treatment—were characterized by Auger electron spectroscopy to elucidate the silicon surface sputtering and demonstrate functionalization. The Fourier transform‐infrared spectroscopy spectrum shows a high absorbance of avidin protein over the silicon surface functionalized by AA plasma treatment.We carried out force spectroscopy assay to measure the unbinding force between the well‐established pair biotin–avidin. At pulling speed of 2 µm/s, we measured the unbinding force of 106 ± 23 pN, which is in good agreement with the literature, demonstrating the effectiveness of the tip functionalization by AA plasma treatment in biological studies. Copyright

Quantitative Characterization of the Interface Between a V 2 O 3 Layer and Cu 3 Au (001) by Cs Corrected HREM

Vanadium oxides are materials of interest due to their electronic, magnetic and catalytic properties. In the case of V 2 O 3 and Cu 3 Au, the interfacial bonding is rather difficult to describe since the two component materials have strongly different electronic structures. Thus a local investigation of the interface becomes important. In this investigation, the incoherent interface between a V 2 O 3 (0001, corundum structure) layer and a Cu 3 Au (001, L1 2 structure) substrate is characterized with the help of image corrected high resolution electron microscopy (HRTEM) and focal series reconstruction in order to investigated both the true position of atoms and the nature of the atomic species. Semi-quantitative results can be shown for the chemical composition of columns and strains at one side of the interface.