Facile Preparation of a Platinum Silicide Nanoparticle-Modified Tip Apex for Scanning Kelvin Probe Microscopy
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In this study, we propose an ultra-facile approach to prepare a platinum silicide nanoparticle-modified tip apex (PSM tip) used for scanning Kelvin probe microscopy (SKPM). We combined a localized fluoride-assisted galvanic replacement reaction (LFAGRR) and atmospheric microwave annealing (AMA) to deposit a single platinum silicide nanoparticle with a diameter of 32 nm on the apex of a bare silicon tip of atomic force microscopy (AFM). The total process was completed in an ambient environment in less than 3 min. The improved potential resolution in the SKPM measurement was verified. Moreover, the resolution of the topography is comparable to that of a bare silicon tip. In addition, the negative charges found on the PSM tips suggest the possibility of exploring the use of current PSM tips to sense electric fields more precisely. The ultra-fast and cost-effective preparation of the PSM tips provides a new direction for the preparation of functional tips for scanning probe microscopy.
KeywordsAnodic Aluminum Oxide Scanning Probe Microscopy Anodic Aluminum Oxide Template Electrostatic Force Microscopy Electron Beam Induce Deposition
With the prosperous development of nanotechnology, the demand on nondestructive analysis of the distribution of charge density , magnetic field , surface potential , etc. is surging in nanometrology. In the field of nondestructive analysis, scanning Kelvin probe microscopy (SKPM) has been widely used to analyze the surface potential distribution of materials [4, 5, 6]. Spatial resolutions of the geometry and surface potential are both crucial issues in SKPM. Traditionally, apexes of silicon (Si) tips coated with metallic thin film, e.g., platinum-iridium alloy (PtIr), are widely used for SKPM. However, the spatial resolution was seriously limited because of the stray-field generated by the metallic coating [7, 8, 9]. To reduce this stray-field phenomenon, many nanostructures have been proposed for tip modifications, including carbon nanotube [10, 11, 12], Pt nanowire , single metallic nanoparticle (NP) [14, 15], etc. Moreover, for many decades, electron beam induced deposition (EBID) has been a major approach for tip modification [16, 17, 18, 19]. However, the vacuum system required for the EBID process and the need to manipulate electron beams make the tip modification costly and inefficient. For these reasons, the development of nonvacuum technology for tip modifications has been presented. Electrodeposition  and electroless deposition  are both feasible approaches for tip modification under ambient conditions. Recently, we successfully prepared an apex of an Ag NP-modified silicon tip (Ag tip) by utilizing a localized fluoride-assisted galvanic replacement reaction (LFAGRR), which provides a facile and cost-effective process for tip modification . However, the instability of Ag under ambient conditions directly limits the commercialization of the Ag tips . In this paper, the LFAGRR was extended to prepare Pt NP-modified silicon tip apexes (Pt tips). Moreover, we introduced atmospheric microwave annealing (AMA) to further stabilize the tip apexes by transforming the Pt tips into platinum silicide NP-modified tip apexes (PSM tips). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), SKPM, and electrostatic force microscopy (EFM) were employed to study the PSM tips and the corresponding Si-based Pt silicide NPs. Our results demonstrate that the PSM tips benefit from both high spatial resolutions of topography and surface potential. Moreover, the facile and cost-effective approach combining the LFAGRR and AMA provides a new direction for preparing functional tips for scanning probe microscopy.
Preparation of Pt and PSM Tips
Surface Morphology and Material Characterization
SEM (Hitachi S-4000) and TEM (JEOL JEM2010F) were employed to investigate the surface profile of the prepared samples. Energy-dispersive X-ray spectroscopy (EDS) was used to analyze the elemental composition. The SKPM and EFM images were acquired by a scanning probe microscope (Bruker D3100). The SKPM measurement parameters were image size = 2 μm, scanning rate = 0.2 Hz, lift height = 30 nm, Vac = (1.1–1.5) V, and ω2 = (31–35) kHz. The EFM measurement parameters were: image size = 1 μm, scanning rate = 0.5 Hz, lift height = 30 nm, and substrate bias = (0, −0.5, −1.0, −1.5) V, respectively. All measurements were performed in constant environment conditions with temperature = (20 ± 0.3) °C and relative humidity = (40 ± 5) % RH. All of the chemicals used in the experiment were reagent grade.
Results and Discussion
In summary, we proposed an ultra-facile process combining LFAGRR and AMA to prepare PSM tips under ambient conditions. The improved potential resolution of Si-based Ag nanoislands in SKPM measurement was realized. Moreover, the resolution of the topography was comparable to that of a bare silicon tip. In addition, the negative charges found on the PSM tips suggests the possibility of exploring the use of current PSM tips to sense electric fields more precisely. The ultra-fast and cost-effective preparation of the PSM tips provides a new direction for preparing functional tips for scanning probe microscopy.
The authors would like to express appreciation to the Ministry of Science and Technology (MOST) of the Republic of China, Taiwan, for the financial supports under the following contract numbers: MOST104-2221-E-492-001, MOST104-2623-E-492-001-ET, and NSC101-2112-M-492-002-MY3.
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