Hierarchy in Au nanocrystal ordering in supracrystals: a potential approach to detect new physical properties.

Here we describe the morphologies of Au nanocrystals self-assembled in fcc 3D superlattices called supracrystals. The average size of the nanocrystals is either 5 or 7 nm with a very small size distribution (<7%). The coating agents used to stabilize the nanocrystals are dodecanethiol (C12H25-SH), tetradecanethiol (C14H29-SH), and hexadecanethiol (C16H33-SH). The influences of the evaporation time, the volume of the chamber used to evaporate the toluene solvent, and the substrate temperature are studied. For nanocrystals characterized by the same size and coating agent, the supracrystal morphologies markedly change on increasing the evaporation time from 8 to 9 to 25 h whereas a slight change takes place on increasing the chamber volume. The nanocrystals' ability to self-order in supracrystals decreases upon increasing the chain length of the coating agent from dodecanethiol (C12) to tetradecanethiol (C14) to hexadecanethiol (C16). Decreasing the evaporation rate (25 h) and/or increasing the substrate temperature (50 °C) improves the nanocrystal ordering in fcc supracrystals. A hierarchy in nanocrystal ordering has the following sequence disordered assemblies, supracrystal film sitting on a disordered nanocrystal film, supracrystal films grown layer-by-layer, and finally supracrystals grown in solution with various well-defined shapes.

Probing atomic ordering and multiple twinning in metal nanocrystals through their vibrations.

Control of nanocrystal (NC) crystallinity currently raises great interest because of its potential benefits in both physics modeling and technological applications. Advances in methods for synthesizing perfect single-crystalline NCs are recent, so that the effect of crystallinity on NC properties has received only limited study and still needs to be properly investigated. Here, we report that crystallinity of gold NCs dramatically modifies their vibrations. Using low-frequency Raman scattering, we clearly demonstrate that single-domain NCs vibrate differently than their multiply twinned counterparts, through the splitting of the quadrupolar vibrations, which is only observed for the former. Using the resonant ultrasound approach, we calculate the vibrational frequencies of a gold sphere and show that elastic anisotropy induces a lift of degeneracy of the quadrupolar mode in good agreement with our experimental measurements. These findings open up challenging perspectives on using Raman spectroscopy to characterize nanocrystallinity.

Shape-controlled platinum nanocubes and their assembly into two-dimensional and three-dimensional superlattices.

Liquid-liquid phase transfer has been used to synthesize platinum nanocrystals with a cubic morphology. By finely tuning the parameters controlling the nucleation and growth processes, nanometric truncated cubes or perfect cubes may be obtained. To our knowledge, this is the first time such shapes are obtained with this procedure. The importance of both the length of the capping agent to control the growth process and the bromide anions as poison for the (111) facet is shown. The low degree of size polydispersity allows these nanocrystals to self-assemble with a long-range ordering in two-dimensional and three-dimensional supracrystals. According to the nanocrystal shape, simple cubic or face-centered cubic supracrystals are observed. It is remarkable to notice that well-faceted supracrystals with sizes on the order of 10 microm may be obtained.

[Research, developmental care and NIDCAP: specific methodological issues]. / Recherche clinique, soins de développement et NIDCAP: aspects méthodologiques spécifiques.

Developmental care is the use of a range of medical and nursing interventions to decrease the stress of preterm neonates in neonatal intensive care units. Interventions may be integrated into an individualized approach known as the Neonatal Individualized Developmental Care and Assessment Programme (NIDCAP). In comparison with drug trials, it is more difficult to achieve a standard experimental design in this kind of study as the experiments may include several individual approaches. Randomized control trials must remain a predominant practice but use of other methodologies can help to evaluate the benefits of developmental care and offer a better understanding of the impact of this kind of care : qualitative research, benchmarking or animal studies.

Size and nanocrystallinity controlled gold nanocrystals: synthesis, electronic and mechanical properties.

The influence of nanocrystallinity on the electronic and mechanical properties of metal nanoparticles is still poorly understood, due to the difficulty in synthesizing nanoparticles with a controlled internal structure. Here, we report on a new method for the selective synthesis of Au nanoparticles in either a single-domain or a polycrystalline phase maintaining the same chemical environment. We obtain quasi-spherical nanoparticles whose diameter is tunable from 6 to 13 nm with a resolution down to ≈0.5 nm and narrow size distribution (4-5%). The availability of such high-quality samples allows the study of the impact of the particle size and nanocrystallinity on a number of parameters, such as plasmon dephasing time, electron-phonon coupling, period and damping time of the radial breathing modes.

Object and event representation in 6 1/2-month-old infants.

Two experiments were conducted in which infants had to use remembered knowledge of auditory-visual events to guide their reaching and grasping. The events involved a ball falling noisily through a tube and coming to rest at 1 of 2 locations, with either resting site specified by distinctive auditory information. The events were presented initially in the light and then in the dark to determine whether infants would remember and use the auditory cues when they could no longer see where the ball fell. In both experiments, infants' reaching behavior was initiated and carried out after the sound ended, which ensured that search for the ball took place without support from ongoing visual or auditory cues. Accurate searching for the ball depended on infants' experience in the light. The authors conclude that 6 1/2-month-olds can represent unseen objects and events and use this knowledge to guide their actions to achieve a goal. The success in this task was contrasted with the failures of infants this age in the Piagetian hidden object task.

Enhanced sucking engagement by preterm infants during intermittent gavage feedings.

Non-nutritive sucking (NNS) activities were recorded in preterm infants born at gestational age 32 weeks or less during nasogastric feedings. Six infants on intermittent nasogastric feeding schedules were tested with a pacifier in their mouth for three 5-minute periods (before, during, and after gavage feeding). Analysis of the recordings revealed that NNS activities increased markedly during the intermittent nasogastric feeding schedule. The overall proportions of sucking engagement, the mean duration of sucking burst, the mean number of sucks per burst, and the mean duration of individual sucks within a burst increased markedly during gavage feeding compared with both pre-test and post-test periods. NNS by a group of five infants on continuous nasogastric feedings was similar to the pre-test and post-test of the infants on the intermittent nasogastric feeding schedule. These results indicate that in the context of intermittent nasogastric feedings, NNS engagement in tube-fed infants depends on stomach cues and/or temperature changes associated with tube feedings.

Learning about pain in preterm newborns.

The first goal of the study was to explore whether preterm newborns can learn to predict painful stimulation. The second goal was to provide a description of physiological and behavioral responses to repeated heel-sticks over days. Preterm newborns, born between 28 and 32 weeks gestational age, were observed five times over a period of 2 weeks while undergoing heel-sticks. Infants' facial expressions, cardiac reactions, and movement durations were recorded before, during, and after the heel-stick procedure. On Tests 1, 3, and 5, the phlebotomist picked up the baby's leg and held it for 10 seconds before proceeding to the heel-stick. Infants showed significantly greater increase in heart rate during the leg pickup on Test 5 compared with Test 1. This increase in heart rate after 2 weeks of experience suggests that newborn infants learned to anticipate the painful stimulus. Infants also demonstrated reliable behavioral and cardiac reactions to the invasive part of the heel-stick, but no change was observed in reactivity over days. However, greater post-conceptional age (PCA) was associated with increased behavioral reactivity during heel-stick on Tests 4 and 5. The anticipatory heart rate increase during leg pickup highlights the preterm infant's early capacity to learn and react to experience in the neonatal intensive care unit. The lack of global change in reactivity to the invasive procedure over days illustrates the need to take into account specific factors such as PCA when investigating sensitivity to repeated pain experiences.

Electronic properties of supracrystals of Au nanocrystals: influence of thickness and nanocrystallinity.

Well-defined superlattices of colloidal nanocrystals, called supracrystals, are expected to have interesting physical properties. While the electronic properties of thin supracrystals have been extensively studied in the planar configuration, little is known about electron transport through micrometer-thick supracrystals. Here, we investigate the electronic properties of supracrystals made of Au nanocrystals with diameters of 5, 6, 7 and 8 nm using scanning tunneling microscopy/spectroscopy at low temperatures. The current-voltage characteristics show power-law dependences with exponents varying strongly with supracrystal thicknesses from 30 nm to a few microns. The crystallinity of these nanocrystals, called nanocrystallinity, is exclusively single domain for 5 nm nanocrystals and a mixture of single and polycrystalline phase for 6, 7 and 8 nm nanocrystals. We observed that supracrystals made of 5 nm nanocrystals have a different behavior than supracrystals made of 6, 7 and 8 nm nanocrystals and this might be related to the nanocrystallinity. These results help us to better understand the electron transport mechanism in such miniscule structures built from a bottom-up approach.

Large triangular single crystals formed by mild annealing of self-organized silver nanocrystals.

Nanocrystal organizations represent a new generation of materials with specific properties compared with those of isolated nanocrystals and of the bulk material. Here, we present the first intrinsic crystalline growth properties of highly ordered mono- and multilayers of 5 nm silver nanocrystals. Triangular single crystals with face-centred-cubic structures are obtained by annealing the ordered nanocrystals under atmospheric pressure at 50 degrees C. The triangles are mixed with well-crystallized coalesced particles of various shapes. Their size depends on the initial nanocrystal ordering range on the substrate, which is local on amorphous carbon and highly extended on highly oriented pyrolitic graphite (HOPG). Hence, the single-crystal size is larger on HOPG than on amorphous carbon. These observations show that the crystalline growth properties of silver nanocrystals can be tailored by controlling their organization. Furthermore, on HOPG an epitaxial orientation of the triangles is observed.

How infants use vision for grasping objects.

The role of vision was examined as infants prepared to grasp horizontally and vertically oriented rods. Hand orientation was measured prior to contact to determine if infants differentially oriented their hands relative to the object's orientation. Infants reached for rods under different lighting conditions. Three experiments are reported in which (1) sight of the hand was removed (N = 12), (2) sight of the object was removed near the end of the reach (N = 40, including 10 adults), and (3) sight of the object was removed prior to reach onset (N = 9). Infants differentially oriented their hand to a similar extent regardless of lighting condition and similar to control conditions in which they could see the rod and hand throughout the reach. In preparation for reaching, infants may use the current sight of the object's orientation, or the memory of it, to orient the hand for grasping; sight of the hand had no effect on hand orientation.