Size contrast of Pt nanoparticles formed on neighboring domains within suspended and supported graphene.

Graphene (Gr) is one of the most explored 2D materials with unique combination of exotic properties, which have allowed for impressive wide spectrum of applications ranging from electronics and sensors to bio and electrochemical devices. However, it is still a challenge to produce high-quality Gr on a large scale.
One of the appealing applications is the use of Gr as a catalyst support for Pt in fuel cells, which requires to shed light on the Pt-Gr interactions at local scale that should lead to modification of Pt and Gr properties. Due to the small size of the low thickness (one or few layers) and high quality Gr films that can be obtained nowadays, it is, indeed, extremely difficult to study the behavior of suspended Gr flakes by characterization techniques other than the electron microscopies. That is why for most of the studies Gr flakes have been grown or transferred on a substrate, which undoubtable will exert certain effect on the Gr-Pt interactions. In this work we used a perforated Si3N4 membrane which allowed us to have on the same sample suspended and supported thin Gr layers and to demonstrate the capabilities of spatially resolved photoemission to explore simultaneously the properties of suspended and Si3N4-supported Gr and its interaction with deposited Pt atoms.
Photoemission measurements were carried out using the scanning photoemission microscope (SPEM) hosted at the Escamicroscopy beamline at the Elettra synchrotron laboratory while high-resolution transmission electron microscopy maps were obtained at the Electron Microscopy Facility of the Istituto Italiano di Tecnologia.
The contrast levels of the C1s image of the perforated Si3N4 membrane show clearly the holes with suspended Gr surrounded by Gr on the Si3N4 support membrane where the holes are covered by thin Gr layers (Fig.1-a)).As evidenced by scanning transmission electron microscopy (TEM) room temperature Pt deposition resulted in nm-sized islands and agglomerated clusters but there are distinct difference in the morphology of the Pt deposits on the suspended and supported Gr. Detailed images reveal the distribution of particles in two regions: the suspended Gr images (Figs. 1(d) and 1(e)) acquired at two different magnification factors show the presence of two distinct areas, one covered with nanometer-sized Pt particles well-separated from each other with larger particles at the boundary line, and another where larger particles agglomerate to form clusters dispersed with a lower density. Fig. 1-b) and c) are the corresponding maps acquired on the supported Gr flakes. They show a surface almost entirely covered by the nanometer-sized Pt particles without a significant presence of the larger Pt agglomerates, in comparison with the suspended portion.

Figure 1. (a) C 1s SPEM image of the perforated Si3N4 membrane used for the experiments where the holes are covered by thin Gr layers. (b) and (c) high angle annular dark field-scanning TEM (HAADF-STEM) images of the supported Gr after the Pt deposition. (d) and (e) same images for suspended Gr.
 

Comparing the C 1s spectra of pristine and Pt covered suspended and supported Gr surface shown in Fig. 2 one can clearly see that in both regions the deposition of Pt results in an increase in the intensity of the low BE component at 283.7 eV generated by C vacancies in the graphene sheet; moreover, to achieve a good deconvolution of the much lower BE region of the C 1s, it was necessary to add an additional component, located at 283.0 eV BE. This component is generated by the C atoms neighboring a C vacancy in the perfect Gr sheet.
As presented in this work, the structural and/or electronic changes of the ideal atomic chain can completely modify the behavior of purposely deposited atoms interacting with the graphene-based surface.
 

Figure 2C 1s photoemission core level spectra acquired on the suspended and supported Gr. Spectra (a) and (b) are the pristine Gr. Spectra (c) and (d) were acquired after the Pt evaporation. See text for details.

 

This research was conducted by the following research team:

Dario Roccella1, Matteo Amati2, Hikmet Sezen2,*, Rosaria Brescia3, and Luca Gregoratti2

 

1Università degli Studi di Genova - Facoltà di Scienze Matematiche, Fisiche e Naturali, Italy
2 Elettra – Sincrotrone Trieste S.C.p.A, Trieste, Italy
3 Electron Microscopy Facility, Istituto Italiano di Tecnologia (IIT), Genova, Italy
*Present address: Helmholtz-Zentrum Berlin GmbH, Berlin, Germany



Contact person:

Luca Gregoratti, email: luca.gregoratti@elettra.eu

 

Reference

D. Roccella, M. Amati, H. Sezen, R. Brescia and L. Gregoratti “Size contrast of Pt nanoparticles formed on neighboring domains within suspended and supported graphene” Nano Research (2017) doi.org/10.1007/s12274-017-1774-1
 
Last Updated on Friday, 13 October 2017 11:35