Controlled Second Harmonic Generation with Optically Trapped Lithium Niobate Nanoparticles.

We report the second harmonic generation (SHG) response from a single 34 nm diameter lithium niobate nanoparticle. The experimental setup involves a first beam devoted to the optical trapping of single nanoparticles, whereas a second arm involves a femtosecond laser source leading to the SHG emission from the trapped nanoparticles. SHG operation where one to three nanoparticles are present in the optical trap is first demonstrated, highlighting the transition between coherent and incoherent SHG, the latter known as hyper-Rayleigh scattering (HRS). With a spatial light modulator moving the optical trap in and out of the focus of the femtosecond beam, the SHG intensity is switched back and forth between a low and a high level. This controlled operation opens new avenues for nanoparticle characterization and applications in sensing or communication and information technologies and constitutes the first step in the design of active substrateless metasurfaces.

Nonclassical Nucleation and Crystallization of LiNbO3 Nanoparticles from the Aqueous Solvothermal Alkoxide Route.

The exact molecular reaction pathway and crystallization mechanisms of LiNbO3 nanoparticles under solvothermal conditions are derived through extensive time- and temperature-resolved experiments allowing to track all the transient molecular and solid species. Starting with a simple mixing of Li/Nb ethoxides, water addition is used to promote condensation after ligand exchange with different co-solvents including alcohols and glycols of variable carbon-chain length. A nonclassical nucleation scheme is first demonstrated after the identification of new octanuclear complexes with a {Li4Nb4O10} core whose solvophobic interactions mediate their aggregation, thus, resulting in a colloidal gel at room-temperature. Upon heating, a more or less frustrated aggregation-mediated crystallization process is then evidenced leading to LiNbO3 nanocrystals of adjustable mean size between 20 and 100 nm. Such a fine control can be attributed to the variable Nb-OR (R = alkoxy/glycoxy ligand) binding interactions at the surface of crystalline intermediates. Demonstration of such a nonclassical nucleation process and crystallization mechanism for LiNbO3 not only sheds light on the entire growth process of multifunctional nanomaterials with non-perovskite crystalline structures, but also opens new avenues for the identification of novel bimetallic oxoclusters involved in the formation of several mixed oxides from the aqueous alkoxide route.

Solution-Based Synthesis Routes for the Preparation of Noncentrosymmetric 0-D Oxide Nanocrystals with Perovskite and Nonperovskite Structures.

With the miniaturization of electronic-based devices, the foreseen potential of new optical nanoprobes and the assessment of eventual size and shape effects, elaboration of multifunctional noncentrosymmetric nanocrystals with ferroelectric, pyroelectric, piezoelectric, and nonlinear optical properties are the subject of an increasing research interest. Here, the recent achievements from the solution-based methods (coprecipitation in homogeneous and nanostructured media, sol-gel processes including various chemistries and hydro/solvothermal techniques) to prepare 0-D perovskite and nonperovskite oxides in the 5-500 nm size range are critically reviewed. To cover a representative list of covalent- and ionic-type materials, BaTiO3 and its derivatives, niobate compounds (i.e., K/Na/LiNbO3 ), multiferroic BiFeO3, and crystals of lower symmetry including KTiOPO4 and some iodate compounds such as Fe(IO3 )3 and La(IO3 )3 are systematically in focus. The resulting size, morphology, and aggregation state are discussed in light of the proposed formation mechanisms. Because of a higher complexity related to their chemical composition and crystalline structures, improving the rational design of these multifunctional oxides in terms of finely-tuned compositions, crystalline hosts and structure-property relationships still need in the future a special attention of the research community to the detailed understanding of the reaction pathways and crystallization mechanisms.

Orthogonal chemical functionalization of patterned Au/TiW substrate for selective immobilization of nanoparticles.

The evolution of nanobiosensors stresses the need for multi-material nanopatterned surfaces to enhance sensing performances. Titanium tungsten (TiW) has been mastered and routinely implemented in nanoelectronic devices, in a reproducible way and at industrial production scales. Such a material may be envisioned for use in (bio)chemical nanoelectronic sensors, but the surface functionalization of such material has yet to be studied. In the present article, the orthogonal chemical functionalization of patterned Au on TiW substrates has been explored for the first time. Surface functionalizations were assessed by x-ray photoelectron spectroscopy, polarization modulation infrared reflection-absorption spectroscopy and time-of-flight secondary ion mass spectrometry imaging. Au/TiW patterned substrates were functionalized with mercapto-undecamine. Thanks to the orthogonality of thiol/Au versus phosphonic acid/TiW reactions, only the Au features were modified leading to the amine derivatized surface. This allowed for the localizing of carboxy-functionalized nanoparticles by electrostatic interaction on Au with a selectivity above 10 when compared to TiW.

Cedar Wood-Based Biochar: Properties, Characterization, and Applications as Anodes in Microbial Fuel Cell.

In this study, the relationship between pyrolysis temperature of woody biomass and physicochemical properties of derived biochar was investigated for microbial fuel cell (MFC) application. Physical and chemical properties of biochar were characterized for different pyrolysis temperatures. Results showed that biochar obtained at 400 °C was not conductor, while biochars prepared at 600 °C, 700 °C, and 900 °C exhibited decreased electrical resistivity of (7 ± 6) × 103 Ω.m, (1.8 ± 0.2) Ω.m, and (16 ± 3) × 10-3 Ω.m, respectively. Rising pyrolysis temperature from 400 to 700 °C exhibited honeycomb-like macroporous structures of biochar with an increase in the specific surface area from 310 to 484 m2.g-1. However, the production of biochar at 900 °C reduced its specific surface area to 136 m2.g-1 and caused the loss of the ordered honeycomb structure. MFCs using anodes based on biochar prepared at 900 °C produced maximum power densities ((9.9 ± 0.6) mW.m-2) higher than that obtained with biochar pyrolyzed at 700 °C ((5.8 ± 0.1) mW.m-2) and with conventional carbon felt anodes ((1.9 ± 0.2) mW.m-2). SEM images of biochar-based anodes indicated the clogging of macropores in honeycomb structure of biochar prepared at 700 °C by growth of electroactive biofilms, which might impede the supply of substrate and the removal of metabolites from the inside of the electrode. These findings highlight that electrical conductivity of biochar is the major parameter for ensuring efficient anodes in microbial fuel cell application. Schematic representation of cedar wood-based biochar and its application as anode in MFC.

On the Reaction Pathways and Growth Mechanisms of LiNbO3 Nanocrystals from the Non-Aqueous Solvothermal Alkoxide Route.

Phase-pure, highly crystalline sub-50 nm LiNbO3 nanocrystals were prepared from a non-aqueous solvothermal process for 72 h at 230 °C and a commercial precursor solution of mixed lithium niobium ethoxide in its parent alcohol. A systematic variation of the reaction medium composition with the addition of different amounts of co-solvent including butanol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol resulted in the formation of nanocrystals of adjustable mean size and shape anisotropy, as demonstrated from XRD measurements and TEM imaging. Colloidal stability of ethanol- and water-based suspensions was evaluated from dynamic light scattering (DLS)/zeta potential studies and correlated with FTIR data. Thanks to the evolution in the nanocrystal size and shape distribution we observed, as well as to the available literature on the alkoxide chemistry, the reaction pathways and growth mechanisms were finally discussed with a special attention on the monomer formation rate, leading to the nucleation step. The polar, non-perovskite crystalline structure of LiNbO3 was also evidenced to play a major role in the nanocrystal shape anisotropy.

Gold-seeded Lithium Niobate Nanoparticles: Influence of Gold Surface Coverage on Second Harmonic Properties.

Hybrid nanoparticles composed of an efficient nonlinear optical core and a gold shell can enhance and tune the nonlinear optical emission thanks to the plasmonic effect. However the influence of an incomplete gold shell, i.e., isolated gold nano-islands, is still not well studied. Here LiNbO3 (LN) core nanoparticles of 45 nm were coated with various densities of gold nano-seeds (AuSeeds). As both LN and AuSeeds bear negative surface charge, a positively-charged polymer was first coated onto LN. The number of polymer chains per LN was evaluated at 1210 by XPS and confirmed by fluorescence titration. Then, the surface coverage percentage of AuSeeds onto LN was estimated to a maximum of 30% using ICP-AES. The addition of AuSeeds was also accompanied with surface charge reversal, the negative charge increasing with the higher amount of AuSeeds. Finally, the first hyperpolarizability decreased with the increase of AuSeeds density while depolarization values for Au-seeded LN were close to the one of bare LN, showing a predominance of the second harmonic volumic contribution.

Luminescence nanothermometry with alkyl-capped silicon nanoparticles dispersed in nonpolar liquids.

Silicon nanoparticles (Si NPs) with a diameter size ranging from 4 to 8 nm were successfully fabricated. They exhibit a visible photoluminescence (PL) due to the quantum confinement effect. Chemical functionalization of these Si NPs with alkyl groups allowed to homogeneously disperse them in nonpolar liquids (NPLs). In comparison to most of literature results for Si NPs, an important PL peak position variation with temperature (almost 1 meV/K) was obtained from 303 to 390 K. The influence of the liquid viscosity on the peak positions is also presented. These variations are discussed considering energy transfer between nanoparticles. The high PL thermal sensitivity of the alkyl-capped Si NPs paves the way for their future application as nanothermometers.

DNA directed immobilization glycocluster array: applications and perspectives.

The present review concerns the recent advances in DNA directed immobilization (DDI) based glycocluster array. The impact of glycan immobilization on subsequent interactions with protein is discussed and the consequent pros and cons of DDI-based glycocluster array are reviewed. Finally, application in the discovery of anti-pathogen molecules is illustrated by screening for galactose or fucose glycoclusters targeting two Pseudomonas aeruginosa virulence factors (PA-IL and PA-IIL).