Single Charge Electronics with Gold Nanoparticles and Organic Monolayers
- PDF / 1,037,432 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 190 Views
passivated by hydrogen as shown on figure 1-a. These two surfaces were terminated with an ester and were modified following a two-step procedure. In the first step the ester was deprotected into a carboxylic moiety and in the second step a reaction with N-hydroxysuccinimyl (NHS) modified the exposed part of the surface into an amine group (figure 1-a) [20-22, 24]. The amine group serves for attaching gold nanoparticles through amine-gold bonding. The GOM is stable at air for ~2days, before a notable oxidation is observed [22] Gold nanoparticles (AuNPs) are prepared as colloidal solutions either from reduction of HAuCl4 by ascorbic acid[25] or following Natan method where HAuCl4 is reduced by NaBH4 and the surfactant is citrate [26, 27]. In the case of the ascorbic AuNPs, the amine terminated surfaces were dipped into the colloidal solution for about 10 min after the solution was acidified at pH~5. The samples were dipped directly in Natan nanoparticles since the pH of this colloidal solution is acidic [21, 22]. A surface Si-C11-NH2 decorated with Natan AuNPs was characterized with AFM (Multimode 8 from Bruker Corporation) and is shown in figure 1-b. The AFM operated in the socalled Peak-Force mode. The nanoparticles are well dispersed on the surface. Their sizes ranged from 4 to 10 nm as suggested by the profile drawn in figure 1-c (average and standard deviation: 6.6 ± 1.3 nm). Notice that the diameter is evaluated from the nanoparticle height (denoted h in figure 1-c) and that the planar width is slightly increased due to the convolution with the tip (very sharp in the present case). The ascorbic AuNPs are more dispersed and their diameter goes from 3 to 25 nm (8.5 ± 2.4 nm).
Figure 1. (a) scheme of the amine-terminated Grafted Organic Monolayers (GOMs) used in this study for attaching gold nanoparticles. These GOMs protect the silicon substrate from oxidation at air and establishes an electrically homogeneous tunnel barrier. (b) AFM image of 1x1µm of gold nanoparticles (AuNPs) bound to a Si-C11 layer. (c) Profiles running through AuNPs are used to evaluate the diameter of the nanoparticles, based on their height.
CHEMICAL AND ELECTRONIC CHARACTERIZATION OF THE GRAFTED ORGANIC MONOLAYERS Nature of the GOM for passivating a Si(111) substrate The chemical nature of the GOM’s discussed in the present study was characterized in previous publications with multiple techniques: XPS, FTIR, STM, ellipsometry and AFM [20-22, 24]. This molecular layer protects the silicon substrate from re-oxidation, and forms a highly ordered molecular layer. This is shown with FTIR in the case of the Si-C11 and Si-C7, when they are terminated with a carboxlylic acid (see figure 2). FTIR spectra were acquired in transmission at an angle of incidence of 74° with respect to the normal of the surface in a dry nitrogen-purged atmosphere. The spectrometer was a Nicolet 6700 FTIR equipped with a DTGS detector. We show transmission FTIR data for the SiC7 GOM referenced to the oxide-free H-terminated Si(111) surface. The negative peak at 2083 cm
Data Loading...
