| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS-MoA |
| Session: | Organics and Ionic Liquids: Surfaces, Layers, Interfaces and Chirality |
| Presenter: | Thomas Grehl, ION-TOF GmbH, Germany |
| Authors: | T. Grehl, ION-TOF GmbH, Germany P. Bruener, ION-TOF GmbH, Germany L. Calabria, Laboratory of Molecular Catalysis, UFRGS, Brazil P. Migrowski, Laboratory of Molecular Catalysis, UFRGS, Brazil D.L. Baptista, Laboratory of Molecular Catalysis, UFRGS, Brazil F. Bernardi, Laboratory of Molecular Catalysis, UFRGS, Brazil H. Brongersma, ION-TOF GmbH, Germany J. Dupont, Laboratory of Molecular Catalysis, UFRGS, Brazil |
| Correspondent: | Click to Email |
Metal nanoparticles (NPs) in ultrathin films have a variety of applications nano-optical and nano-electronic devices. Several methods have been developed in order to synthesize such films. However, those methods result in "capped" NPs, instead of free-standing NPs which would be a more versatile alternative precursor for ultrathin film growth.
Ionic liquids are known to facilitate well-defined formation of Au NPs from sputter deposition and self-organization of the particles close to the surface [1]. The size and potential shape of the NPs can be tailored by the properties of the ionic liquids. Applying this principle of NP formation to ultrathin films of ionic liquids is a promising route by which to easily form free-standing NPs in a well controlled manner.
In this study we analyze silicon wafer supported ultrathin films of both hydrophilic and hydrophobic imidazolium based ionic liquids forming an "ionic carpet like" structure. This structure is decorated with gold NPs having a size of 5 - 10 nm from the application of sputter deposition of gold onto the ionic liquid. A range of analytical techniques is applied to the samples, including XPS, XRD, AFM and electron microscopy. Here we present primarily the results from high resolution and high sensitivity Low Energy Ion Scattering (LEIS).
LEIS is the most surface sensitive technique for the elemental characterization of the outermost atomic layer. Noble gas ions having a kinetic energy of a few keV are scattered from the individual surface atoms. By measuring the energy loss in the scattering event, the mass of the respective surface atom can be determined, while the intensity of the scattering signal is proportional to the surface coverage. LEIS has been successfully applied to ionic liquids by several groups to elucidate the termination of the liquid. In addition the LEIS data contain information on the composition of the first few nm of the sample. The latter is used to determine the thickness of the self-organized layer of NPs and allows the thickness measurement of any film covering the gold.
The gold nanoparticles are deposited by sputtering into the hydrophobic (AMI.NTf2) and hydrophilic (AMI.BF4) ionic liquids on Si(111) for 5 and 10 s. The LEIS spectra show gold signal for the hydrophobic ionic liquid. Apparently the gold NPs are out of the probed range of the LEIS technique (10 nm). In contrast to that, the LEIS spectra of the hydrophilic ionic liquid after gold deposition show the presence of gold below the surface. The mean thickness of the organic layers covering the NPs is 6 nm (5 s deposition) and 4.3 nm (10 s deposition).
[1] Kauling et al., Langmuir 2013, 29 (46) 14301