Effect of argon implantation on solid-state dewetting: control of size and surface density of silicon nanocrystals.

Thermally induced solid-state dewetting of ultra-thin films on insulators is a process of prime interest, since it is capable of easily forming nanocrystals. If no particular treatment is performed to the film prior to the solid-state dewetting, it is already known that the size, the shape and the density of nanocrystals is governed by the initial film thickness. In this paper, we report a novel approach to control the size and the surface density of silicon nanocrystals based on an argon-implantation preliminary surface treatment. Using 7.5 nm thin layers of silicon, we show that increasing the implantation dose tends to form smaller silicon nanocrystals with diameter and height lower than 50 nm and 30 nm, respectively. Concomitantly, the surface density is increased by a factor greater than 20, going from 5 µm-2 to values over 100 µm-2.

Identification of ethyl 2-hydroxy-4-methylpentanoate in red wines, a compound involved in blackberry aroma.

The aroma profile of Bordeaux red wines is known to be marked by blackberry and blackcurrant flavours; this study focused on the fresh blackberry aroma in Bordeaux red wines, using sensory gas chromatography-olfactometry (GC-O) and two-dimensional gas chromatography analysis (GC-GC-MS). A previous HPLC fractionation of red wine extracts on a C18 column produced four fractions with blackberry aromas that were then analysed by GC-O, GC-GC-MS and GC-MS. From these fractions, 10 esters, corresponding to red- or black-berry fruit descriptors, were characterised by GC-MS. Ethyl 2-hydroxy-4-methylpentanoate (ethyl leucate, EL) was identified for the first time in red and white table wines as a compound directly associated with a "fresh blackberry" aroma. Its perception thresholds were 900 and 300µg/l, respectively, in dearomatized red wine and model wine solution (alcohol 12%, pH 3.5), and the average concentration in the various wines was ∼400µg/l. Sensory omission tests highlighted the importance of this compound and identified a perceptive interaction with ethyl butanoate.

Role of botrytized grape micro-organisms in SO2 binding phenomena.

AIMS: The purpose of this work was to study the involvement of micro-organisms, which develop together with Botrytis cinerea on grapes, in the SO2 binding power of musts. METHODS AND RESULTS: Yeasts and bacteria were involved. Most bacteria were acetic acid bacteria, mainly of the Gluconobacter genus. Unlike oxidative yeasts, Gluconobacter produce gluconic acid (in balance with delta-gluconolactone) from glucose, 5-oxofructose from fructose and dihydroxyacetone from glycerol. Production of carbonyl compounds from other sugars and polyols was not detected or was very weak. CONCLUSION: Acetic acid bacteria are responsible for the increases in SO2 binding power of musts from botrytized grapes by oxidizing the three main sugars of these grapes. SIGNIFICANCE AND IMPACT OF THE STUDY: Up to 80% of the SO2 binds with products of Gluconobacter which easily grow on 'botrytized' grapes. Depending on climatic conditions, some vintages are particularly difficult to stabilize.

Role of carbonyl compounds in SO(2) binding phenomena in musts and wines from botrytized grapes.

Carbonyl compounds play an important role in musts from botrytized grapes. Some of them, such as glyoxal and methylglyoxal, may explain a considerable part of bindable SO(2). Others, such as 2- and 5-oxogluconic acids, produced by gluconic acid oxidation in proportions respectively from 2.5 per 1 play an interesting role as SO(2) binding indicator. Finally, the levels of some compounds such as dihydroxyacetone, 5-oxofructose, and delta-gluconolactone in balance with gluconic acid are well correlated with SO(2) binding powers and also explain a large part of the bindable SO(2) in musts. During alcoholic fermentation, only dihydroxyacetone among these three compounds is metabolized by yeast. Thus, two compounds present in grapes, delta-gluconolactone and 5-oxofructose, with three yeast SO(2)-binding byproducts, ethanal, pyruvic, and 2-oxoglutaric acids, explain much of the SO(2) binding power in wines from botrytized grapes.