Controlling the reproducibility of Coulomb blockade phenomena for gold nanoparticles on an organic monolayer/silicon system

Abstract

Two types of highly ordered organic layers were prepared on silicon modified with an amine termination for binding gold nanoparticles (AuNPs). These two grafted organic monolayers (GOMs), consisting of alkyl chains with seven or 11 carbon atoms, were grafted on oxide-free Si(111) surfaces as tunnel barriers between the silicon electrode and the AuNPs. Three kinds of colloidal AuNPs were prepared by reducing HAuCl4 with three different reactants: citrate (Turkevich synthesis, diameter ∼16 nm), ascorbic acid (diameter ∼9 nm), or NaBH4 (Natan synthesis, diameter ∼7 nm). Scanning tunnel spectroscopy (STS) was performed in a UHV STM at 40 K, and Coulomb blockade behaviour was observed. The reproducibility of the Coulomb behavior was analysed as a function of several chemical and physical parameters: size, crystallinity of the AuNPs, influence of surrounding surfactant molecules, and quality of the GOM/Si interface (degree of oxidation after the full processing). Samples were characterized with scanning tunneling microscope, STS, atomic force microscope, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy (XPS), and high resolution transmission electronic microscope. We show that the reproducibility in observing Coulomb behavior can be as high as ∼80% with the Natan synthesis of AuNPs and GOMs with short alkyl chains.

Static and dynamic electronic characterization of organic monolayers grafted on a silicon surface

“…The fully reacted surfaces, with Au nanoparticles, remain stable enough in an Ar-filled plastic container for shipping from Texas to France (for XPS, STM and AFM characterization) and to California (for conductive AFM measurements). Gold nanoparticles (AuNPs) are prepared as a colloidal solution from reduction of HAuCl 4 by ascorbic acid 27,36,39,40 (details in the ESI). The amine terminated surfaces are dipped into the colloidal solution for about 10 min after the solution was acidified at pH~5.…”

“…The XPS chemical analysis of C 7 -NH 2 and C 11 -NH 2 surfaces was essential for confirming the bonding of the organic layer as depicted in Figure 1 and published earlier. 27,36 We focus now on analyzing the traces of oxide at the interface since they are responsible of most of the electronic surface defects. The Si 2p core-levels spectra for three C 11 GOMs are presented in Figure 3.…”

Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides

“…The band corresponding to water molecules of crystallization is also present in both samples, at 1675 (Figure 9). On the spectrum of the K W Sn[COOH] monolayer, the C=O stretching band decreases drastically relatively to two bands at 1548 and 1390 cm -1 that can be attributed to the asymmetric and symmetric stretching mode of the carboxylate function; on the spectrum of the 55 showing that the layer of SiO2 slightly increased during the K W Si[COOH] deposition, probably due to the more disordered aspect of the K W Si[COOH] monolayer, which let place to the formation of random SiO2 islands. The characteristic bands of the POMs below 1000 cm -1 , typically around 960 and 870 cm -1 are yet detectable.…”

Ammonia modification of oxide-free Si(111) surfaces

“…Surface amination has become more important for applications in microelectronics, [1][2][3][4] biotechnology, [5][6][7][8] and nanotechnology. [1,6,9,10] Ammonia has been widely used to achieve surface nitridation and amination, particularly on silicon surfaces.…”

“…Surface amination has become more important for applications in microelectronics, [1][2][3][4] biotechnology, [5][6][7][8] and nanotechnology. [1,6,9,10] Ammonia has been widely used to achieve surface nitridation and amination, particularly on silicon surfaces. Early work examined adsorption and dissociation of gas phase ammonia on clean, reconstructed Si(100) 2x1 [11][12][13][14][15][16][17] or Si(111) 7x7 [14,[18][19][20] surfaces; only recently has the attention been placed on ammonia reactions with passivated surfaces, such as H-terminated silicon surfaces.…”