HREELS study of alkanethiol passivated gold clusters on graphite

Passivated metal (e.g. gold) nanoclusters consist of a metal particle core surrounded by a ligand coat. We have investigated films of gold particles passivated with alkanethiol (C8H17S) ligands deposited from solution onto a graphite surface using high-resolution electron energy loss spectroscopy (HREELS). Vibrational modes of the CH, groups of the ligands are observed, together with their overtones. Incident energy dependent measurements show an enhancement in intensity of these vibrational modes at a specific energy, similar to 10 eV, consistent with a negative ion resonance state. This observation is compared with previous studies of self-assembled monolayers of thiols on the Au (111) surface

Sintering of passivated gold nanoparticles under the electron beam

Time-lapse studies of a film of passivated gold nanoparticles under electron beam irradiation have been performed using a transmission electron microscope, revealing the microscopic dynamics of the sintering process at the single nanoparticle level. It is found that the sintering of individual passivated gold nanoparticles under electron irradiation is local and mainly depends on the sensitivity of the passivating ligands to the electron beam. A multilayer film is less stable than monolayer film, consistent with the enhanced generation of secondary electrons. The observations also reveal a significant difference between the sintering of passivated nanoparticles and bare metal particles, especially regarding the size effect on the sintering rate. The formation of a neck between adjacent nanoparticles further indicates a mechanism driven by surface diffusion rather than Ostwald ripening at the initial sintering stage

Local Three-Dimensional Visualization of Nanoparticle Assemblies

High-angle annular dark-field (HAADF) imaging technique in the scanning transmission electron microscope has been exploited to study self-assembled multilayer structures of Au/Ag nanoparticles. The HAADF image intensity depends monotonically on the mass and thickness of the sample. Various film thickness between one to four monolayers can be easily distinguished by evaluating the contrast

Direct imaging of core-shell structure in silver-gold bimetallic nanoparticles

High-angle annular dark field imaging in the electron microscope has been exploited to reveal the internal structure of monodispersed, bimetallic gold (Au) - silver (Ag) nanoparticles of similar to 4 nm diameter, prepared using a seed-growth wet chemical method and passivated with an organic layer. Starting with a 3 nm Ag seed particle, deposition of Au atoms to a final overall atomic ratio of Ag:Au=1:2 leads to nanoparticles with an Ag-rich core and an Au-rich shell, as expected. If the overall atomic ratio is 2:1, the core/shell structure is not observed. The physical significance of these observations is discussed in terms of the stability of particles of nanoscale dimensions

Assessment of the Socio-Economic Impact of Late Blight and State-of-the-Art Management in European Organic Potato Production Systems

In Europe, late blight, caused by Phytophthora infestans, is the most devastating disease affecting organic (and conventional) potato production. Under suitable environmental conditions the disease can spread rapidly and it can cause complete crop loss. The extent of damage due to late blight depends on several factors: in organic production systems these factors include climate, choice of variety, soil management and use of crop protection agents such as copper. Therefore, the extent of economic damage varies between European regions. Council Regulation (EEC) No 2092/91, amended by Commission Regulation (EC) No 473/2002 of 15 March 2002 regulates the use of copper in organic agriculture. Copper has been the single most important control agent in organic late blight control. Therefore, the reduction or an eventual phasing out of copper use will have varying impacts in different regions. This report presents the results of a detailed survey that has been conducted in 7 European countries in the year 2001. It is a subproject of the EU-funded project Blight-MOP (QLRT 31065). The survey investigates legislative, socio-economic and production parameters. The aim of this study was: (i) to obtain an inventory of the current organic potato production techniques, (ii) to assess the impact of a potential ban of copper on yields and viability of organic potato production and (iii) to identify alternative plant protection strategies that are used by organic farmers. This report includes: (i) statistics on yields, farm gate prices, and production techniques, (ii) an analysis offarmer observations and experiences on the extent and impact of late blight epidemics, (iii) an analysis of the farmer¿s motivations, expectations and their assessment of the potential impact of a copper ban. Using multiple linear regression we identified production factors which appear to consistently contribute to production succes

Assessment of the Socio-Economic Impact of Late Blight and State-of-the-Art Management in European Organic Potato Production Systems

In Europe, late blight, caused by Phytophthora infestans, is the most devastating disease affecting organic (and conventional) potato production. Under suitable environmental conditions the disease can spread rapidly and it can cause complete crop loss. The extent of damage due to late blight depends on several factors: in organic production systems these factors include climate, choice of variety, soil management and use of crop protection agents such as copper. Therefore, the extent of economic damage varies between European regions. Council Regulation (EEC) No 2092/91, amended by Commission Regulation (EC) No 473/2002 of 15 March 2002 regulates the use of copper in organic agriculture. Copper has been the single most important control agent in organic late blight control. Therefore, the reduction or an eventual phasing out of copper use will have varying impacts in different regions. This report presents the results of a detailed survey that has been conducted in 7 European countries in the year 2001. It is a subproject of the EU-funded project Blight-MOP (QLRT 31065). The survey investigates legislative, socio-economic and production parameters. The aim of this study was: (i) to obtain an inventory of the current organic potato production techniques, (ii) to assess the impact of a potential ban of copper on yields and viability of organic potato production and (iii) to identify alternative plant protection strategies that are used by organic farmers. This report includes: (i) statistics on yields, farm gate prices, and production techniques, (ii) an analysis offarmer observations and experiences on the extent and impact of late blight epidemics, (iii) an analysis of the farmer¿s motivations, expectations and their assessment of the potential impact of a copper ban. Using multiple linear regression we identified production factors which appear to consistently contribute to production succes