Multiscale deposition of noble metal nanoparticles
Building nanoscale devices is a crucial step towards the success of nanotechnologies. The assembly of colloidal nanoparticles is a technology in development that may outperform standard lithography techniques in the future. Three-dimensional materials with possibly sub-nanometric inter-distances would be easily manufactured this way. Many groups work towards this goal, but some challenges still need to be addressed, such as the propagation of the order to large length scales. In this work, we demonstrate the organization of anisotropic nanoparticles with controlled local order, which spans the whole sample area.
Two complementary techniques (SAXS and TEM) are used to characterize assemblies of Au/Ag heterostructures. In SAXS, the spot size is macroscopic, about 500×200 µm², while in TEM the characterization is made locally, over hundreds of nanometers. The nanoparticles are pointing toward us in the TEM image, organized here in a square in-plane arrangement that can be modulated according to their cross-section.
In this work we used hybrid Au/Ag particles due to their fascinating optical properties. These nanoobjects consist of gold nanorods encased in silver shells with a thickness that can be controlled from a few atomic layers to tens of nanometers. The section of the nanoparticle, initially octagonal, becomes square for a sufficiently thick silver shell. We aimed at studying the impact of the morphological changes of the building blocks on their assembly into superlattices. Usually, nanoparticle assemblies are characterized locally by transmission electronic microscopy (TEM) and give only a limited picture of the assembly on a larger scale. In addition, we used Small Angle X-Ray Scattering (SAXS) to scan the sample area with a probe having much larger dimensions than the nanoparticles. This structural study shows that the nanorods are oriented in the same direction over the whole sample area, thanks to a well-chosen surface chemistry. Furthermore, hexagonal or square phases were formed depending on the octagonal or square cross section of the nanoparticles respectively, demonstrating a control of the multi-scale organization in the system.
Reference: C. Hamon, C. Goldmann and D. Constantin, Nanoscale, 2018, DOI: 10.1039/C8NR06376A.
1 PhD position (ANR)
Spontaneous organization of mineral nanoparticles
The recent expansion of the field of “chimie douce” (soft chemistry) has led to a wide variety of anisotropic nanoparticles of all kinds of nature and shape (nanotubes, nanosheets, nanorods, etc.). These nanoparticles can often be dispersed in water or in organic solvents as colloidal suspensions. Quite often, these suspensions spontaneously organize in liquid-crystalline phases of different types (nematic, lamellar, columnar …).1,2 Moreover, these suspensions can also be destabilized to produce aggregates with well-defined structures.3-5 These two kinds of phenomena are very useful to manipulate and organize nanoparticles in order to obtain original physical properties. For example, by applying electric or magnetic fields, we can align anisotropic nanoparticles and even sometimes order them on a lattice.
At this moment, we have suspensions of various nanoparticles (clay and H3Sb3P2O14 nanosheets, imogolite nanotubes, CdSe and CeF3 nanoplatelets …) whose phase diagrams and original physical properties still need to be fully explored. This thesis will take place at the LPS which is a joint research unit of CNRS and University Paris-Saclay, specialized in condensed-matter physics. This PhD topic belongs to a more general project, funded by ANR, which aims at using the properties of these nanoparticles to elaborate sensors to monitor water quality.
 E.Paineau et al, Liquid Crystals Reviews, 1, 110 (2013).
 E.Paineau et al, Nature Communications, 7, 10271 (2016).
 B.Abécassis et al, Nanoletters, 14, 710 (2014).
 S.Jana et al, Angewandte Chemie, 55, 9371 (2016).
 S.Jana et al, Science Advances, 3, e1701483 (2017).
Techniques: X-ray scattering in-house and at large synchrotron radiation facilities (SOLEIL, ESRF), optical and electron microscopies, UV-vis spectroscopies, classical laboratories techniques of sample elaboration.
Required profile: Good level physicist or physical chemist. This thesis in experimental physics / physical chemistry will nevertheless involve a strong collaboration with chemists and theorists.
Funding: Project funded by ANR
Thesis advisors: Patrick Davidson, Jean-Christophe Gabriel
2 PhDs positions opening
The 2018 doctoral award campaign of the Ministry of Higher Education, Research and Innovation (MESRI in french) is open for ED 2MIB.
It takes place in 4 phases:
2/ Selection of only one candidate for each project before April 30th
3/ Audition of the candidates by the CIM Pole Jury of the ED (May 18th)
4/ Validation and publication of the results by the ED (June 15th).
click here for details and application:
The surprising self-organization of nanotubes in a very dilute columnar liquid-crystal phase
Liquid crystals have found wide applications in many fields ranging from detergents to information displays. They are an important class of “soft matter” and they are increasingly being used in the “bottom-up” self-assembly approach of the nano-structuration of materials. Moreover, liquid-crystalline organizations are frequently observed by biologists. A research team of the LPS, in collaboration with researchers from CEA-Saclay (NIMBE-LIONS), has recently discovered that one of the four major lyotropic liquid-crystal phases, the columnar one, is actually much more stable (by a factor 100 in concentration!) than considered up to now.
Nanotubes (or nanorods) in colloidal suspensions form a columnar liquid-crystal when they spontaneously organize parallel to each other, on a two-dimensional lattice perpendicular to their axes, like a bunch of pencils (Figure a). This organization was so far only expected in concentrated suspensions where the nanorods are close to contact. Here, researchers at LPS and LIONS have shown that very dilute suspensions of clay imogolite nanotubes form a columnar liquid-crystal. Imogolites are aluminosilicates (or aluminogermanates) that have raised increasing interest in the last decade. In contrast with carbon nanotubes, they are easily obtained by sol-gel processes at low temperature. Moreover, the presence of hydroxyl groups on their surface makes these nanotubes quite hydrophilic, which allows producing aqueous suspensions.
Figure: a) Schematic representation of the organisation of the nanotubes in the columnar hexagonal liquid-crystalline phase (a et b are the unit vectors of the hexagonal lattice) ; b) Small angle X-ray scattering pattern of the columnar phase aligned in an electric field; c) Structure factor showing the reflections (indicated by the red lines) of the hexagonal lattice.
Texture observations of very dilute suspensions (volume fraction ~ 0.3%) by polarized-light microscopy revealed the existence of an unexpected liquid-crystalline phase. Small-angle X-ray scattering measurements, performed at the SOLEIL synchrotron (Swing beamline) showed that this new phase is a columnar hexagonal liquid crystal (Figure b, c).
Despite the high dilution, the nanotubes are perfectly organized on a hexagonal lattice with a spacing (~ 80 nm) fifteen times larger than the nanotube diameter. This dilute liquid-crystal is so fluid that the nanotubes are easily aligned in an electric field, which is a prerequisite for future applications. This work has important implications for the statistical physics of colloidal suspensions of charged rod-like particles, like biopolymers, and their fundamental understanding. It also opens new perspectives, for instance, in the field of nanocomposite materials where the organization of anisotropic particles is required to improve physical properties.
Paineau E., Krapf, M.E.M., Amara M.S., Matskova, N.V., Dozov, I., Rouzière S., Thill, A., Launois, P. et Davidson, P.. A liquid-crystalline hexagonal columnar phase in highly-dilute suspensions of imogolite nanotubes. Nat. Commun., 7, 10271 (2016)
Erwan Paineau (email@example.com)
Patrick Davidson (firstname.lastname@example.org)
Laboratoire de Physique des Solides, CNRS, Univ. Paris Sud, Université Paris Saclay, 91405 Orsay cedex, France
Review article free to download
We are pleased to share our review article "Colloidal Design of Plasmonic Sensors Based on Surface Enhanced Raman Scattering", published in Journal of Colloid and Interface Science, is now available online and free to download until December 26, 2017. This is a joint work with Luis Liz Marzan (CIC Biomagune, Spain). You can access the article by cliking on the following link: https://authors.elsevier.com/a/1W0BD4-sDFY5b.
Abstract: This feature article focuses on the use of colloid chemistry to engineer metallic nanostructures toward application in surface enhanced Raman scattering (SERS) sensing, in particular for ‘real-life’ applications, where the analyte may be present in complex mixtures. We present a broad summary of the field, including recent advances that have been developed during the past 10â€¯years. Real-life applications require a rational design and we aimed at identifying the key elements involved in it. The discussion is centered around colloidal plasmonic nanoparticles and therefore we start from the library of morphologies that have been reported in the literature. To complete the picture, colloidal self-assembly, surface chemistry and the combination with materials science techniques are highlighted. Considering the progress in the field, SERS may ultimately realize its full potential as an ultrasensitive tool for routine analytical applications.