9 results found
lauri A, Velleman L, Xiao X, et al., 2017, 3D Confocal Raman Tomography to Probe Field Enhancements inside Supercluster Metamaterials, ACS Photonics, Vol: 4, Pages: 2070-2077, ISSN: 2330-4022
Spherical colloidal superclusters, composed from sub-100 nm plasmonic nanoparticles, have been proposed to possess collective plasmonic modes imbued with large field enhancements and tunable spectral response extending from the visible to infrared regions. Here, we report the experimental verification of collective near-IR plasmonic modes inside single superclusters, with dimensions ranging from 0.77 μm up to 2 μm. Raman reporters, coated onto the nanoparticle building blocks, were used as local probes of the electric field enhancement inside the metamaterial. By performing diffraction-limited 3D Raman tomography we were able to build up the electric field intensity distribution within the superclusters. We demonstrate that plasmonic responses of superclusters vary according to their size and excitation wavelength, in accordance with theoretical predictions of their tunable optical properties. The existence of three-dimensional internal collective modes in these superclusters enables the excitation of a large number of electromagnetic hot-spots, validating these self-assembled structures as promising candidates for molecular spectroscopy.
Velleman L, Scarabelli L, Sikdar D, et al., 2017, Monitoring plasmon coupling and SERS enhancement through in situ nanoparticle spacing modulation, Faraday Discussions, Vol: 205, Pages: 67-83, ISSN: 1364-5498
Self-assembled nanoparticle (NP) arrays at liquid interfaces provide a unique optical response which has opened the door to new tuneable metamaterials and for sensing and optical applications. NPs can spontaneously assemble at the liquid-liquid interface, forming an ordered, self-healing, low-defect 2D film. The close proximity of the NPs at the interface results in collective plasmonic modes with a spectral response dependent on the distance between the NPs and induces large field enhancements within the gaps. In this study, we assembled spherical and rod-shaped gold NPs with the aim of improving our understanding of NP assembly processes at liquid interfaces, working towards finely controlling their structure and producing tailored optical and enhanced Raman signals. We systematically tuned the assembly and spacing between NPs through increasing or decreasing the degree of electrostatic screening between NPs with the addition of electrolyte or pH adjustment. The in situ modulation of nanoparticle positioning on the same sample allowed us to monitor plasmon coupling and the resulting SERS enhancement processes in real time, with sub-nm precision.
Velleman L, Sikdar D, Turek V, et al., 2016, Tuneable 2D self-assembly of plasmonic nanoparticles at liquid | liquid interfaces, Nanoscale, Vol: 8, Pages: 19229-19241, ISSN: 2040-3372
Understanding the structure and assembly of nanoparticles at liquid | liquid interfaces is paramount to their integration into devices for sensing, catalysis, electronics and optics. However, many difficulties arise when attempting to resolve the structure of such interfacial assemblies. In this article we use a combination of X-ray diffraction and optical reflectance to determine the structural arrangement and plasmon coupling between 12.8 nm diameter gold nanoparticles assembled at a water | 1,2-dichloroethane interface. The liquid | liquid interface provides a molecularly flat and defect-correcting platform for nanoparticles to self-assemble. The amount of nanoparticles assembling at the interface can be controlled via the concentration of electrolyte within either the aqueous or organic phase. At higher electrolyte concentration more nanoparticles can settle at the liquid | liquid interface resulting in a decrease in nanoparticle spacing as observed from X-ray diffraction experiments. The coupling of plasmons between the nanoparticles as they come closer together is observed by a red-shift in the optical reflectance spectra. The optical reflectance and the X-ray diffraction data are combined to introduce a new ‘plasmon ruler’. This allows extraction of structural information from simple optical spectroscopy techniques, with important implications in understanding the structure of nanoparticle films at liquid interfaces and their self-assembly.
Turek VA, Francescato Y, Cadinu P, et al., 2015, Self-Assembled Spherical Supercluster Metamaterials from Nanoscale Building Blocks, ACS Photonics, Vol: 3, Pages: 35-42, ISSN: 2330-4022
We report on a simple, universal and large scale self-assembly method for generation of spherical superclusters from nanoscopic building blocks. The fundamentals of this approach relies on the ultra-high pre-concentration of nanoparticles (NP) followed by either using emulsification strategies or alternatively multiphase microfluidic microdroplets. In both cases drying of the NP droplets yield highly spherical self-assembled superclusters with unique optical properties. We demonstrate that the behaviour of these spheres can be controlled by surface functionalization before and after the self-assembly process. These structures show unique plasmonic collective response both on the surface and within the supercluster in the visible and infrared regions. Furthermore, we demonstrate that these strong, tunable optical modes can be used towards ultra-sensitive, reproducible, surface-enhanced spectroscopies.
She X, Chen L, Velleman L, et al., 2015, Fabrication of high specificity hollow mesoporous silica nanoparticles assisted by Eudragit for targeted drug delivery, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 445, Pages: 151-160, ISSN: 0021-9797
Favel BS, Jasieniak M, Velleman L, et al., 2013, Grafting of Poly(ethylene glycol) on Click Chemistry Modified Si(100) Surfaces, LANGMUIR, Vol: 29, Pages: 8355-8362, ISSN: 0743-7463
Velleman L, Bruneel J-L, Guillaume F, et al., 2011, Raman spectroscopy probing of self-assembled monolayers inside the pores of gold nanotube membranes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 13, Pages: 19587-19593, ISSN: 1463-9076
Dumee L, Velleman L, Sears K, et al., 2010, Control of porosity and pore size of metal reinforced carbon nanotube membranes., Membranes (Basel), Vol: 1, Pages: 25-36, ISSN: 2077-0375
Membranes are crucial in modern industry and both new technologies and materials need to be designed to achieve higher selectivity and performance. Exotic materials such as nanoparticles offer promising perspectives, and combining both their very high specific surface area and the possibility to incorporate them into macrostructures have already shown to substantially increase the membrane performance. In this paper we report on the fabrication and engineering of metal-reinforced carbon nanotube (CNT) Bucky-Paper (BP) composites with tuneable porosity and surface pore size. A BP is an entangled mesh non-woven like structure of nanotubes. Pure CNT BPs present both very high porosity (>90%) and specific surface area (>400 m2/g). Furthermore, their pore size is generally between 20-50 nm making them promising candidates for various membrane and separation applications. Both electro-plating and electroless plating techniques were used to plate different series of BPs and offered various degrees of success. Here we will report mainly on electroless plated gold/CNT composites. The benefit of this method resides in the versatility of the plating and the opportunity to tune both average pore size and porosity of the structure with a high degree of reproducibility. The CNT BPs were first oxidized by short UV/O3 treatment, followed by successive immersion in different plating solutions. The morphology and properties of these samples has been investigated and their performance in air permeation and gas adsorption will be reported.
Velleman L, Shearer CJ, Ellis AV, et al., 2010, Fabrication of self-supporting porous silicon membranes and tuning transport properties by surface functionalization, NANOSCALE, Vol: 2, Pages: 1756-1761, ISSN: 2040-3364
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