2023 |
Wang, J., Ouvrard, A., Zheng, W., Carrez, S., Ghalgaoui, A., & Bourguignon, B. (2023). In situ study of catalytic CO oxidation on ultrathin MgO film supported Pd nanoparticles by sum frequency generation: size and site effects. Phys. Chem. Chem. Phys., 25(15), 10845–10852.
Résumé: Controlling the reactive sites of nanoparticles (NPs) is crucial to improve catalyst efficiency. In this work, sum-frequency generation is used to probe CO vibrational spectra on MgO(100) ultrathin film/Ag(100) supported Pd nanoparticles ranging from 3 to 6 nm in diameter and compared to those of coalesced Pd NPs and Pd(100) single crystals. We aim to demonstrate in situ the role played by active adsorption sites in the catalytic CO oxidation reactivity trends varying with the NP size. From ultrahigh vacuum to the mbar range and temperatures from 293 K to 340 K, our observations suggest that bridge sites are the main active sites for CO adsorption and catalytic oxidation. On Pd(100) single crystals at 293 K, CO oxidation predominates over CO poisoning at a pressure ratio of O2/CO greater than 300; on Pd NPs, both the site coordination due to NP geometry and MgO-induced Pd–Pd interatomic distance change impact the reactivity trend varying with size in different ways. Edge sites with low coordination are more reactive than facet sites, while facet sites with a smaller Pd–Pd atomic length are more reactive than that with a larger length. The interplay of both site and size effects gives rise to a non-monotonic reactivity trend of CO on the MgO(100) ultrathin film supported Pd NPs: the reactivity of Pd NPs increases for the smaller NP size side due to a higher edge/facet ratio and meanwhile increases for the larger NP size side due to the terrace facet with a smaller Pd–Pd atomic length at the NP surface and a lower diffusion barrier.
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2022 |
Thébault, P., Ammoun, M., Boudjemaa, R., Ouvrard, A., Steenkeste, K., Bourguignon, B., & Fontaine-Aupart, M. - P. (2022). Surface functionalization strategy to enhance the antibacterial effect of nisin Z peptide. Surf. Interfaces, 30, 101822.
Résumé: One of the main challenges when building antibacterial surfaces with antimicrobial peptides (AMPs) is to preserve their antimicrobial activity after stable immobilization of the peptides. Among all parameters, order/conformation of self-assembled monolayers, used as spacer, is one the most important. Herein we report the covalent immobilization of the nisin Z peptide on a gold surface functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) alone or mixed with 6-mercaptohexanol, used as a spacer. The MUA acid is activated by treatment with carbodiimide/N-hydroxysuccinimidine and then reacts with nisin Z to form amide bonds via the N terminal part of the peptide. We have characterized each step of the surface modification using X-ray photoelectron spectroscopy, FTIR-ATR spectroscopy and contact angle measurements. The combined results show the success of each functionalization step. Additionally, SFG brings information on the orientation and conformational ordering of the self-assembled monolayers. Indeed, a better order of MUA25 layers compared to MUA was observed due to the spacing of carboxylic acid groups. The antibacterial activity of the immobilized AMPs against Staphylococcus aureus is evaluated using confocal microscopy and bacterial counting: it increases with a better order of the SAMs rather than a greater peptide concentration. This study provides fundamental insights on how to engineer AMPs and substrate to produce efficient biocidal surfaces.
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2020 |
Alyabyeva, N., Ouvrard, A., Bavencoffe, M., Lindfors-Vrejoiu, I., Kolomiytsev, A., Solodovnik, M., Ageev, O., & McGrouther, D. (2020). Control of binary states of ferroic orders in bi-domain BiFeO3 nanoislands. Appl. Phys. Lett., 116(19), 192904.
Résumé: Understanding switching mechanisms in multiferroics such as BiFeO3 (BFO) is an important challenge to control ferroic orders (ferroelectric or ferroelastic) as it could lead to the design of non-volatile memories based on magnetoelectric coupling. Here, we demonstrate an alternative way to control the binary states of ferroic orders by locally applying pressure and electric field in ferroelectric bi-domains confined in single BFO nanoislands. The study of the electronic transport properties and domain orientations using atomic force microscopy (AFM) based techniques enabled us to determine the electric and mechanical parameters at which ferroelectric and ferroelastic resistive switching can be observed. Nanoislands exhibited binary high and low resistance states without scaling effect, with high performance switching characteristics. Positive-forward rectifying behavior at high tip force was interpreted by the formation of a subsurface non-conductive interface due to the strain gradient. Ferroelastic switching at the surface was associated with a symmetry-breaking induced by electromechanical coupling between the AFM tip and the BFO thin film. It led to out-of-plane polarization pinning that allows performing only in-plane switching accompanied by nucleation and propagation of a conductive domain wall. The control of ferroic binary states by the electric field and pressure may pave the way for multilevel data storage devices.
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2019 |
Alyabyeva, N., Ouvrard, A., Lazzari, R., & Bourguignon B. (2019). Ordered Hybrid Assembly of Palladium Nanoparticles and Perylene Molecules on an Alumina Template. J. Phys. Chem. C, 123(31), 19175–19182.
Résumé: Combining in a synergic way inorganic and organic matter at a nanometer level has become a key research pathway for nanoelectronics, light harvesting, energy storage, or sensing. Herein, we demonstrate the nanoscale ordering at room temperature of a two-dimensional hybrid assembly combining a long-range ordered array of Pd nanoparticles (NPs) with perylene molecules. The ordering, driven by the periodic superstructure of the Al2O3 ultrathin layer support, has been achieved for 0.9 nm diameter NPs and flat-lying molecules with a 2:1 perylene/NP relative ratio. At a larger NP size and perylene coverage, molecules tilt up on alumina and adsorb on NPs. Combined near-field microscopy and optical spectroscopies provide a detailed understanding of the structural properties as a function of NP size and molecular coverage. This hybrid assembly opens the way to study at the molecular level the optical and electronic properties resulting from the coupling of organic molecules and nanoparticles using multiscale surface sensitive techniques.
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Alyabyeva, N., Ouvrard, A., Zakaria, A. M., & Bourguignon, B. (2019). Probing nanoparticle geometry down to subnanometer size: The benefits of vibrational spectroscopy. J. Phys. Chem. Lett., 10(3), 624–629.
Résumé: Understanding the role of nanoparticle size and shape in the binding of molecules is very relevant for heterogeneous catalysis and molecular electronics. The geometry of Pd nanoparticles (NPs) has been studied from very small clusters containing 4 atoms up to large (>500 atoms), well-faceted NPs. Their geometry was retrieved by combining scanning tunneling microscopy and vibrational sum frequency generation (SFG) spectroscopy of adsorbed CO. SFG has been revealed to be highly sensitive to the geometry of NPs smaller than 100 atoms by identifying the nature of CO adsorption sites. NP growth could be followed layer by layer in the critical size range corresponding to the transition from a nonmetallic to a metallic state and to oscillations of CO adsorption energy. NP height remained at two Pd planes up to 30 atoms, and adsorption energy minima correspond to the completion of successive layers.
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2018 |
Alyabyeva, N., Ouvrard, A., Lindfors-Vrejoiu, I., Kolomiytsev, A., Solodovnik, M., Ageev, O., & McGrouther, D. (2018). Modified cantilevers to probe unambiguously out-of-plane piezoresponse. Phys. Rev. Mater., 2(6), 064402.
Résumé: We demonstrate and investigate the coupling of contributions from both in-plane (IP) polarization and out-of-plane (OP) components in BiFeO3 (BFO) thin-film polarization probed by piezoresponse force microscopy (PFM). Such coupling leads to image artifacts which prevent the correct determination of OP polarization vector directions and the corresponding piezoelectric coefficient d33. Using material strength theory with a one-dimensional modeling of the cantilever oscillation amplitude under electrostatic and elastic forces as a function of the tip length, we have evidenced the impact of IP piezoresponse to the OP signal for tip length longer than 4 μm. The IP polarization vector induces a significant longitudinal bending of the cantilever, due to the small spring constant of long tips, which provokes a normal deviation superimposed to the OP piezoresponse. These artifacts can be reduced by increasing the longitudinal spring constant of the cantilever by shortening the tip length. Standard cantilevers with 15-μm-long tips were modified to reach the desired tip length, using focused ion-beam techniques and tested using PFM on the same BFO thin film. Tip length shortening has strongly reduced IP artifacts as expected, while the impact of nonlocal electrostatic forces, becoming predominant for tips shorter than 1 μm, has led to a non-negligible deflection offset. For shorter tips, a strong electric field from a cantilever beam can induce polarization switching as observed for a 0.5-μm-long tip. Tip length ranging from 1 to 4 μm allowed minimizing both artifacts to probe unambiguously OP piezoresponse and quantify the d33 piezoelectric coefficient.
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Alyabyeva, N., Ouvrard, A., Zakaria, A. - M., Charra, F., & Bourguignon, B. (2018). Transition from disordered to long-range ordered nanoparticles on Al 2 O 3 /Ni 3 Al(111). Appl. Surf. Sci., 444, 423–429.
Résumé: Application of preparation recipes of the literature failed to produce an ordered array of NPs on our particular Ni3Al sample. This has motivated a systematic survey of Pd NP nucleation as a function of experimental parameters. We have shown that the increase of oxidation temperature during the preparation of Al2O3 ultra-thin film on Ni3Al(111) leads to a transition from disordered to long-range ordered Pd nanoparticle (NP) nucleation. Alumina films were prepared at different temperatures ranging from 990 to 1140 K. Crystallinity, electronic structure of the alumina film and Pd nucleation and growth have been investigated using Low Energy Electron Diffraction and Scanning Tunnelling Microscopy. NP density and long-range order nucleation along the so-called “dot structure” of 4.2 nm periodicity, strongly increase for temperatures higher than a threshold value of 1070 ± 20 K. This transition relies on the alumina film improvement and suggests that the modulation of Pd adsorption energy at nucleation centres which is necessary to nucleate NPs at ordered sites, requires higher preparation temperature. Long-range ordered NPs with a high density were obtained 140 K above reported recipes in the literature. This optimized temperature has been tested on a fresh sample (issued from the same supplier) for which just a few cleanings were enough to obtain long-range ordered NPs. Presumably the variability of the optimal oxidation temperature for our samples with respect to the literature is related to fluctuations of the stoichiometry from sample to sample.
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Bourguignon B. (2018). Pulse Shaping in Surface Science. Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, , 604–610.
Résumé: Pulse shaping consists in adjusting the spectral and temporal shapes of a laser pulse to enhance the efficiency of specific laser-induced processes. Only ultrafast lasers have a suitable (broad enough) spectrum. Spatial pulse shaping is another type of shaping which consists in controlling the wave front profile to keep the beam spatially uniform and allow precise control of the energy distribution around the focus point. Pulse shaping has been developed to optimize the intrinsic quality of lasers, in particular to make ultrahigh intensity lasers, and to optimize specific light–matter interactions. In surface science, pulse shaping is mainly used for optimization of laser ablation and for Broad Band Sum Frequency Generation vibrational spectroscopy.
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Ghalgaoui, A., Horchani, R., Wang, J., Ouvrard, A., Carrez, S., & Bourguignon, B. (2018). Identification of active sites in oxidation reaction from real-time probing of adsorbate motion over Pd nanoparticles. J. Phys. Chem. Lett., 9(18), 5202–5206.
Résumé: Obtaining insight into the type of surface sites involved in a reaction is essential to understand catalytic mechanisms at the atomic level and a key for understanding selectivity in surface-catalyzed reactions. Here we use ultrafast broad-band vibrational spectroscopy to follow in real-time diffusion of CO molecules over a palladium nanoparticle surface toward an active site. Site-to-site hopping is triggered by laser excitation of electrons and followed in real-time from subpicosecond changes in the vibrational spectra. CO photoexcitation occurs in 400 fs and hopping from NP facets to edges follows within ∼1 ps. Kinetic modeling allows to quantify the contribution of different facet sites to the catalytic reaction. These results provide useful insights for understanding the mechanism of chemical reactions catalyzed by metal NPs.
Supporting Information
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2017 |
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Alyabyeva, N., Ouvrard, A., Lindfors-Vrejoiu, I., Ageev, O., & McGrouther, D. (2017). Back-scattered electron visualization of ferroelectric domains in a BiFeO3epitaxial film. Appl. Phys. Lett., 111(22), 222901.
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Ghalgaoui, A., Ouvrard, A., Wang, J., Carrez, S., Zheng, W., & Bourguignon, B. (2017). Electron to Adsorbate Energy Transfer in Nanoparticles: Adsorption Site, Size, and Support Matter. J. Phys. Chem. Lett., 8(12), 2666–2671.
Résumé: Confinement of hot electrons in metal nanoparticles (NPs) is expected to lead to increased reactivity in heterogeneous catalysis. NP size as well as support may influence molecule-NP coupling. Here, we use ultrafast nonlinear vibrational spectroscopy to follow energy transfer from hot electrons generated in Pd NP/MgO/Ag(100) to chemisorbed CO. Photoexcitation and photodesorption occur on an ultrashort time scale and are selective according to adsorption site. When the MgO layer is thick enough, it becomes NP size-dependent. Hot electron confinement within NPs is unfavorable for photodesorption, presumably because its dominant effect is to increase relaxation to phonons. An avenue of research is open where NP size and support thickness, photon energy, and molecular electronic structure will be tuned to obtain either molecular stability or reactivity in response to photon excitation.
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Lu, W., Zhang, G., Wei, F., Li, W., Cheng, K., Ding, F., Zhang, J., & Zheng, W. (2017). Shape-controlled synthesis of Pd nanocrystals in an aqueous solution by using amphiphilic triblock copolymers as both the stabilizer and the reductant. Colloid Polym Sci, 295(4), 703–707.
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Ouvrard, A., Ghalgaoui, A., Michel, C., Barth, C., Wang, J., Carrez, S., Zheng, W., Henry, C. R., & Bourguignon, B. (2017). CO Chemisorption on Ultrathin MgO-Supported Palladium Nanoparticles. J. Phys. Chem. C, 121(10), 5551–5564.
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Wang, L., Shen, Y., Yang, Y., Lu, W., Li, W., Wei, F., Zheng, G., Zhou, Y., Zheng, W., & Cao, Y. (2017). Stern-Layer Adsorption of Oligonucleotides on Lamellar Cationic Lipid Bilayer Investigated by Polarization-Resolved SFG-VS. ACS Omega, 2(12), 9241–9249.
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2016 |
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Poumellec, B., Lancry, M., Desmarchelier, R., Hervé, E., & Bourguignon, B. (2016). Parity violation in chiral structure creation under femtosecond laser irradiation in silica glass? Light. Sci. Appl., 5(11), e16178.
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Wei, F., Xia, W. -xiu, Hu, Z. -jin, Li, W. -hui, Zhang, J. -ying, & Zheng, W. -quan. (2016). Laser Linewidth and Spectral Resolution in Infrared Scanning Sum Frequency Generation Vibrational Spectroscopy System. Chinese Journal of Chemical Physics, 29(2), 171–178.
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Xian, Z., Liu, R., Li, H., Zhang, S., Yang, Z., Zheng, W., Chen, C., Cao, H., & Zhang, G. (2016). Photocatalytic Reduction Synthesis of Ternary Ag Nanoparticles/Polyoxometalate/Graphene Nanohybrids and Its Activity in the Electrocatalysis of Oxygen Reduction. J Clust Sci, 27(1), 241–256.
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Xiao, X., Wenjun, W., Shuhong, L., Wanquan, Z., Dong, Z., Qianqian, D., Xuexi, G., & Bingyuan, Z. (2016). Investigation of defect modes with Al2O3 and TiO2 in one-dimensional photonic crystals. Optik – International Journal for Light and Electron Optics, 127(1), 135–138.
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2015 |
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He, X., Wang, W., Li, S., Liu, Y., Zheng, W., Shi, Q., & Luo, X. (2015). Experimental and theoretical analysis of ZnO/Au/ZnO transparent conducting thin films. Vacuum, 120, 17–21.
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He, X., Wang, W., Li, S., Wang, Q., Zheng, W., Shi, Q., & Liu, Y. (2015). High Efficiency Electron Transfer Layer based on Ag-Al Co-Doped ZnS in Organic Lighting Emission Devices. ECS SOLID STATE LETTERS, 4(2), R10–R12.
Résumé: Electron transmission improvement in organic light-emitting devices with Ag-Al co-doped ZnS has been demonstrated. The electroluminescence (EL) of device with co-doped ZnS electron transfer layer (ETL) is more than that of devices without ETL and the co-doped ZnS ETL device performs higher EL compared to pure ZnS ETL device. The using of co-doped ZnS can reduce the thickness of ETL from 40 nm to 8 nm and performs comparable efficiency and higher EL. According to the PL spectra studies and current density-voltage characters, the improved electron transmission is attributed to the introduction of impurity energy level and the increased concentration of electron. (C) 2014 The Electrochemical Society. All rights reserved.
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He, X., Wang, W., Li, S., Wang, Q., Zheng, W., Shi, Q., & Liu, Y. (2015). Localized Surface Plasmon-Enhanced Electroluminescence in OLEDs by Self-Assembly Ag Nanoparticle Film. Nanoscale Res Lett, 10(1), 468.
Résumé: We fabricated Ag nanoparticle (NP) film in organic light emission diodes (OLEDs), and a 23 times increase in electroluminescence (EL) at 518 nm was probed by time-resolved EL measurement. The luminance and relative external quantum efficiency (REQE) were increased by 5.4 and 3.7 times, respectively. There comes a new energy transport way that localized surface plasmons (LSPs) would absorb energy that corresponds to the electron-hole pair before recombination, promoting the formation of electron-hole pair and exciting local surface plasmon resonance (LSPR). The extended lifetime of Alq3 indicates the existence of strong interaction between LSPR and exciton, which decreases the nonradiative decay rate of OLEDs.
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Liu, R., Xian, Z., Zhang, S., Chen, C., Yang, Z., Li, H., Zheng, W., Zhang, G., & Cao, H. (2015). Electrochemical-reduction-assisted assembly of ternary Ag nanoparticles/polyoxometalate/graphene nanohybrids and their activity in the electrocatalysis of oxygen reduction. RSC ADVANCES, 5(91), 74447–74456.
Résumé: The green, facile, electrochemical-reduction-assisted assembly of ternary Ag nanoparticles (NPs)@polyoxometalate (POM)/reduced graphene oxide (rGO) is reported. The POM served as an electrocatalyst and bridging molecule. Characterization using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman and FT-IR spectroscopy analysis, etc., was performed and verified the structure of the prepared nanohybrids of Ag NPs@POM/rGO. The density and size of the Ag NPs on the rGO can be simply tuned by changing the concentration of Ag+. Most importantly, it is interesting to find that the ternary Ag NPs@POM/rGO nanohybrids showed much better electrocatalytic activities towards the oxygen reduction reaction than binary Ag NPs@POM and POM/rGO nanohybrids, and a direct four-electron transfer pathway was observed because of the synergistic effect of the Ag NPs and rGO. The electrocatalytic performance of Ag NPs@POM/rGO depended on the loading amount of Ag NPs, and 30% Ag NPs@POM/rGO showed the best electrocatalytic performance.
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Wei, F., Tian, K., & Zheng, W. (2015). Interfacial Structure and Transformation of Guanine-Rich Oligonucleotides on Solid Supported Lipid Bilayer Investigated by Sum Frequency Generation Vibrational Spectroscopy. J. Phys. Chem. C, 119(48), 27038–27044.
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Wei, F., Xiong, W., Li, W., Lu, W., Allen, H. C., & Zheng, W. (2015). Assembly and relaxation behaviours of phosphatidylethanolamine monolayers investigated by polarization and frequency resolved SFG-VS. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17(38), 25114–22.
Résumé: The assembly conformation and kinetics of phosphatidylethanolamine (PE) lipids are the key to their membrane curvatures and activities, such as exocytosis, endocytosis and Golgi membrane fusion. In the current study, a polarization and frequency resolved (bandwidth 1 cm(-1)) picosecond sum frequency generation (SFG) system was developed to characterize phosphatidylethanolamine monolayers. In addition to obtaining pi-A isotherms and Brewster angle microscopy (BAM) images, the conformational changes and assembly behaviors of phosphatidylethanolamine molecules are investigated by analyzing the SFG spectra collected at various surface pressures (SPs). The compression kinetics and relaxation kinetics of phosphatidylethanolamine monolayers are also reported. The conformational changes of PE molecules during the monolayer compression are separated into several stages: reorientation of the head group PO2(-) in the beginning of the liquid-expanded (LE) phase, conformational changes of head group alkyl chains in the LE phase, and conformational changes of tail group alkyl chains in the LE-liquid condensed (LE-LC) phase. Such an understanding may help researchers to effectively control the lipid molecular conformation and membrane curvatures during the exocytosis/endocytosis processes.
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2014 |
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Fan, C., Poumellec, B., Desmarchelier, R., Zeng, H., Bourguignon, B., Chen, G., & Lancry, M. (2014). Asymmetric orientational writing dependence on polarization and direction in Li2O–Nb2O5–SiO2 glass with femtosecond laser irradiation. Appl. Phys. B, 117(2), 737–747.
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Liu, J., Yu, X., Liu, Q., Liu, R., Shang, X., Zhang, S., Li, W., Zheng, W., Zhang, G., Cao, H., & Gu, Z. (2014). Surface-phase junctions of branched TiO2 nanorod arrays for efficient photoelectrochemical water splitting. APPLIED CATALYSIS B-ENVIRONMENTAL, 158, 296–300.
Résumé: Flower-like branched TiO2 nanorod arrays (NRs) owning the surface anatase/rutile junctions on FTO substrates with operational diameter were successfully fabricated by a modified hydrothermal method. Transmission electron microscopy, Raman spectroscopy, field emission scanning electron microscopy, and X-ray diffraction revealed a unique flower-like ranched morphology, surface features, a crystal phase, and lattice constant of TiO2. Photoelectrochemical (PEC) measurements showed excellent photocatalytic properties of the flower-like branched TiO2 NRs. The surface phase formed between anatase and rutile TiO2 NRs which efficiently enhances the separation of photo-generated electron-hole pairs and accelerates the transport of charges is the key influence factor. The results suggest that the branched TiO2 NRs owning the surface anatase/rutile junctions are very promising platform to make highly efficient photoanodes for energy devices. (C) 2014 Elsevier B.V. All rights reserved.
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Ouvrard, A., Wang, J., Ghalgaoui, A., Nave, S., Carrez, S., Zheng, W., Dubost, H., & Bourguignon, B. (2014). CO Adsorption on Pd(100) Revisited by Sum Frequency Generation: Evidence for Two Adsorption Sites in the Compression Stage. J. Phys. Chem. C, 118(34), 19688–19700.
Résumé: Sum frequency generation (SFG) and low-energy electron diffraction (LEED) have been used to revisit CO adsorption on Pd(100) from very low coverages up to saturation at 300 K Below 0.5 ML, variations of SFG frequency and intensity with coverage are consistent with IRAS results from the literature. Novel observations are done above 0.5 ML, where the CO adlayer compression takes place. The existing compression model postulates the coexistence of compressed and uncompressed CO. We observe two bands in the spectral region of bridge sites and assign them to compressed and uncompressed CO. Both types of CO behave very differently: the molecular hyperpolarizability at compressed sites is smaller by a factor of 2 than at uncompressed sites. The frequency of uncompressed CO red-shifts during compression as the partial coverage decreases, while that of compressed CO continues to blue-shift as coverage increases. In the time domain, the coexistence of compressed and uncompressed sites results in oscillations in the decay of SFG intensity. A strong decrease from 690 to 222 fs of the phase relaxation time of uncompressed CO is observed during compression, indicating a stronger coupling to the substrate. These results are complemented by calculations of dipole-dipole interactions and DFT VASP calculations. While continuing blue-shift of compressed sites reflects a combination of increasing dipolar coupling and chemisorption change with coverage like below 0.5 ML, the very large red-shift amplitude of uncompressed CO indicates a large chemical contribution opposite to compressed CO. DFT VASP calculations allow us to follow the surface structure evolution from 0.5 to 0.67 ML and CO frequency changes with coverage. Pd atoms below compressed CO rows are pushed up, and compressed CO is tilted by 8-90 with respect to the surface normal. A frequency split between compressed and uncompressed CO is found in agreement with experimental data. These results suggest that while compressed CO is less strongly bonded as compression proceeds the remaining uncompressed CO is more strongly bonded.
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Wang, J., Dubost, H., Ghalgaoui, A., Zheng, W., Carrez, S., Ouvrard, A., & Bourguignon, B. (2014). Effect of visible pulse shaping on the accuracy of relative intensity measurements in BBSFG vibrational spectroscopy. Surf. Sci., 626, 26–39.
Résumé: Quantitative analysis of BroadBand Sum Frequency Generation (BBSFG) vibrational spectra by deconvolution into Lorentzian components has been shown recently to suffer from complications that depend on the spectrotemporal properties and delay of the visible pulse which has to be shaped in order to achieve spectral resolution and possibly temporal discrimination. We present a comprehensive spectro-temporal analysis of BBSFG in order to evaluate quantitatively the consequences of delay dependent spectral changes on the accuracy of BBSFG spectra. We compare purely spectral deconvolution of single spectra and spectro-temporal analysis of multiple spectra obtained with a picosecond visible pulse produced by either a Fabry-Perot (FP) etalon or a 4f pulse shaper (PS). The case of OctaDecaneThiol Self Assembled Monolayer is used for comparison of theory and experiment. Accurate relative intensities can only be obtained from the analysis of multiple spectra generated by the FP-produced visible pulse. Although the spectra obtained with the PS are not delay dependent contrarily to those of the FP, the purely spectral deconvolution does not provide accurate values of the relative intensities. The need for a spectro-temporal analysis is explained by the fact that the first-order IR polarization is distorted both in the time domain by the ps visible pulse shape and in the frequency domain by interferences between the bands that are complicated by a frequency and delay dependent phase shift (C) 2014 Elsevier B.V. All rights reserved.
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2013 |
Thon, R., Chin, W., Galaup, J. - P., Ouvrard, A., Bourguignon, B., & Crepin, C. (2013). Vibrational Perturbations of W(CO)(6) Trapped in a Molecular Lattice Probed by Linear and Nonlinear Spectroscopy. J. Phys. Chem. A, 117(34), 8145–8156.
Résumé: Vibrational dynamics of the T-1u CO stretching mode of tungsten hexacarbonyl is explored when the molecule is embedded in a nitrogen matrix at low temperature. Experiments combined infrared (IR) absorption spectroscopy and IR stimulated photon echoes at the femtosecond time scale. W(CO)(6) is found to be trapped in two main families of sites differing by their symmetry (called hereafter O-h and D-2h sites). In O-h sites, the vibrational coherence is strongly temperature dependent, exhibiting a coupling with librational phonons of the nitrogen lattice. Perturbation in D-2h sites results in the splitting of the T-1u band in three components. Each component is inhomogeneously broadened, with dephasing times in the tens of picoseconds, and is weakly coupled to the lattice phonons. Experiments in solid krypton are performed to compare the effect of atomic and diatomic host lattices. Dephasing time in Kr does not depend on temperature and remains in the hundreds of picoseconds, highlighting the molecular origin of the dephasing process in N-2. Additionally, nonlinear signals show oscillations due to quantum beats and polarization interferences between different frequency components of the induced third order polarization, giving information, in particular, on the overtone vibrational transition.
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2012 |
Bulard, E., Fontaine-Aupart, M. - P., Dubost, H., Zheng, W., Bellon-Fontaine, M. - N., Herry, J. - M., & Bourguignon, B. (2012). Competition of Bovine Serum Albumin Adsorption and Bacterial Adhesion onto Surface-Grafted ODT: In Situ Study by Vibrational SFG and Fluorescence Confocal Microscopy. Langmuir, 28(49), 17001–17010.
Résumé: The interaction of hydrophilic and hydrophobic ovococcoid bacteria and bovine serum albumin (BSA) proteins with a well ordered surface of octadecanethiol (ODT) self assembled monolayer (SAM) has been studied in different situations where proteins were either preadsorbed on ODT or adsorbed simultaneously with bacterial adhesion as in life conditions. The two situations lead to very different antimicrobial behavior. Bacterial adhesion on preadsorbed BSA is very limited, while the simultaneous exposure of ODT SAM to proteins and bacteria lead to a markedly weaker antimicrobial effect. The combination of sum frequency generation spectroscopy and fluorescence confocal microscopy experiments allow one to draw conclusions on the factors that govern the ODT SAM or BSA film interaction with bacteria at the molecular level. On the hydrophobic ODT surface, interaction with hydrophobic or hydrophilic biomolecules results in opposite effects on the SAM, namely, a flattening or a raise of the terminal methyl groups of ODT. On an amphiphilic BSA layer, the bacterial adhesion strength is weakened by the negative charges carried by both BSA and bacteria. Surprisingly, preadsorbed BSA that cover part of the bacteria cell walls increase the adhesion strength to the BSA film and reduce hydrophobic interactions with the ODT SAM. Finally, bacterial adhesion on a BSA film is shown to modify the BSA proteins in some way that change their interaction with the ODT SAM. The antimicrobial effect is much stronger in the case of a preadsorbed BSA layer than when BSA and bacteria are in competition to colonize the ODT SAM surface.
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Bulard, E., Fontaine-Aupart, M. - P., Dubost, H., Zheng, W., Herry, J. - M., Bellon-Fontaine, M. - N., Briandet, R., & Bourguignon, B. (2012). The Effect of Bacterial Adhesion on Grafted Chains Revealed by the Non-Invasive Sum Frequency Generation Spectroscopy. Spectrosc.-Int. J., 27(5-6), 571–579.
Résumé: In biomedical and food industry, surface colonization by bacteria is harmful: it leads to biofilm formation, a microbial consortia more resistant to antibiotics than planktonic bacteria. In order to design materials able to limit the biofilm formation, the effect of bacteria on materials has to be well characterized. In this work, a well-defined surface composed of a self-assembled monolayer (SAM) of octadecanethiol (ODT) onto a gold surface is probed in situ. The SAM conformation is obtained using the femtosecond vibrational sum frequency generation (SFG) spectroscopy. This technique provides selectively the molecular vibrational signature of the interface. The behaviour of the ODT SAM is studied in different environments: in air, in water, and upon exposure to hydrophilic or hydrophobic Lactococcus lactis bacteria. Modelling the experimental SFG spectra reveals a measurable change of the SAM conformation which depends on the environment, especially on the hydrophilic-hydrophobic character.
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Fan, C., Poumellec, B., Zeng, H., Desmarchelier, R., Bourguignon, B., Chen, G., & Lancry, M. (2012). Gold Nanoparticles Reshaped by Ultrafast Laser Irradiation Inside a Silica-Based Glass, Studied Through Optical Properties. J. Phys. Chem. C, 116(4), 2647–2655.
Résumé: Quasi-spherical or quasi-rod gold nanoparticles with an average diameter of 3.8 nm are randomly precipitated in a silica-based glass by a heat-treatment method. After ultrafast laser irradiation at 400 and 620 nm, optical absorption, birefringence, and dichroism measurements are performed to investigate the modification of gold nanoparticles shape. Theoretical simulations have been carried out to interpret the experimental results. We suggest that a small fraction of gold nanospheres are transformed mainly into nanodisks but also into nanorods oriented along the laser polarization for both fs laser wavelength. Absorption simulation suggests that they have an aspect ratio of 1.8 and 0.5, respectively, for fs laser irradiation at 400 nm. For 620 nm, the aspect ratio of the nanorods increases and the one of the nanodisks decreases. In such a way, we demonstrate that reshaping of gold nanoparticles, i.e. a property that was previously found for silver nanoparticles in multicomponent glass is also possible. By imaging the distribution of the birefringence according to the probe wavelength, we show that nanopartides are aligned into nanorods mainly out of irradiated volume and into nanopellets mainly in the irradiated volume.
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Lancry, M., Poumellec, B., Desmarchelier, R., & Bourguignon, B. (2012). Oriented creation of anisotropic defects by IR femtosecond laser scanning in silica. Opt. Mater. Express, 2(12), 1809–1821.
Résumé: Irradiation of non-luminescent silica with polarized IR femtosecond laser light produced a significant amount of luminescent defects. We have investigated the properties of luminescence produced by the defects using UV-VUV excitation experiment depending on the relative orientation of the laser polarization and its scanning direction. Silicon Oxygen Deficient Center (SiODC) is identified. SiODC related luminescence is much stronger when the excitation polarization is parallel to the sample scanning direction and moved at low velocity, regardless of the writing polarization direction. This indicates that the creation of this anisotropic defect is oriented by the movement of the femtosecond laser beam. (C)2012 Optical Society of America
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2011 |
Bulard, E., Dubost, H., Fontaine-Aupart, M. - P., Zheng, W., Herry, J. - M., Bellon-Fontaine, M. - N., Briandet, R., & Bourguignon, B. (2011). Non invasive SFG spectroscopy: a tool to reveal the conformational change of grafted chains due to bacterial adhesion. In CLINICAL AND BIOMEDICAL SPECTROSCOPY AND IMAGING II (Vol. 8087).
Résumé: In many fields such as biomedical or food industry, surface colonization by micro-organisms leads to biofilms formation that are tridimentional biostructures highly resistant to the action of antimicrobials, by mechanisms still unclear. In order to deepen our understanding of the initial interaction of bacteria cells with a solid surface, we analyze by in situ vibrational Sum Frequency Generation (SFG) spectroscopy the effect of the adhesion of hydrophilic Lactoccocus lactis bacteria and its hydrophobic mutants in distilled water on a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film. When a homogeneous bacterial monolayer is deposited on this ordered surface, SFG spectrum of the ODT SAM shows significant intensity changes from that in air or in water. Its modelling as a function of conformation allows to distinguish optical effects due to the water solution surrounding bacteria from conformational changes of the ODT SAM due to the presence of the bacteria cells. Futhermore, bacterial adhesion induces different measurable effects on the ODT SAM conformation, depending on the hydrophobic / hydrophilic character of the bacterial surface. Such a result deserves to be taken into account for the design of new materials with improved properties or to control biofilm formation.
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Bulard, E., Guo, Z., Zheng, W., Dubost, H., Fontaine-Aupart, M. - P., Bellon-Fontaine, M. - N., Herry, J. - M., Briandet, R., & Bourguignon, B. (2011). Non-Invasive Vibrational SFG Spectroscopy Reveals That Bacterial Adhesion Can Alter the Conformation of Grafted “Brush” Chains on SAM. Langmuir, 27(8), 4928–4935.
Résumé: Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials.
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Fan, C., Poumellec, B., Zeng, H., Lancry, M., Yang, W., Bourguignon, B., & Chen, G. (2011). Directional Writing Dependence of Birefringence in Multicomponent Silica-based Glasses with Ultrashort Laser Irradiation. JOURNAL OF LASER MICRO NANOENGINEERING, 6(2), 158–163.
Résumé: We reveal laser-induced high birefringence in multicomponent silica-based glass by means of ultrashort laser irradiation. It is attributed to the residual stress. A systematic study of birefringence variation is carried out according to laser parameters such as pulse energy, writing speed and direction, and laser polarization. Strong writing directional dependence is clearly observed when the writing direction is perpendicular to the laser polarization at the writing speeds of 20 μm/s – 120 μm/s, which was likely due to an asymmetry of the laser beam or an asymmetry of interaction mechanism. DOI: 10.2961/jlmn.2011.02.0011
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Ouvrard, A., Niebauer, J., Ghalgaoui, A., Barth, C., Henry, C. R., & Bourguignon, B. (2011). Characterization of Thin MgO Films on Ag(001) by Low-Energy Electron Diffraction and Scanning Tunneling Microscopy. J. Phys. Chem. C, 115(16), 8034–8041.
Résumé: The evolution of the MgO(001) film morphology on Ag(001) was studied in dependence on the growth temperature (373-673 K) and grown MgO quantity (0.2-2 ML) by low-energy electron diffraction and scanning tunneling microscopy. We evidence an island growth mode of MgO for all temperatures. At 373 K, the MgO film exhibits a high island density, which is due to a too small surface mobility of the film compounds during the film growth. At a growth temperature of 673 K, silver hampers a perfect growth of MgO islands due to its high mobility, which leads to dendrites of MgO. The flattest and. largest MgO islands are obtained at a growth temperature of around 573 K, which is a compromise guaranteeing a sufficiently high Mg or MgO mobility but also an enough low diffusion of silver.
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2009 |
Bourguignon, B., Zheng, W., Carrez, S., Ouvrard, A., Fournier, F., & Dubost, H. (2009). Deriving the complete molecular conformation of self-assembled alkanethiol molecules from sum-frequency generation vibrational spectra. Phys. Rev. B, 79(12), 125433.
Résumé: The sum frequency generation (SFG) spectrum of CH(2) and CH(3) modes in the self-assembled monolayer of octadecanethiol is modeled in order to understand the reasons of the very low SFG intensity of CH(2) modes and to investigate quantitatively the two types of L-shaped conformations qualitatively suggested in the literature. CH(2) modes are assumed local in order to calculate easily the spectrum of any conformation, and ab initio molecular hyperpolarizabilities are used. It is found that the absence of CH(2) bands does not imply an all-trans conformation and vice versa. Several conformations are compatible with SFG, but only one of them can be arranged on Au(111) and completely agrees with x-ray diffraction. All conformational details of the L-shape molecules are obtained.
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2008 |
Guo, Z., Zheng, W., Hamoudi, H., Dablemont, C., Esaulov, V. A., & Bourguignon, B. (2008). On the chain length dependence of CH3 vibrational mode relative intensities in sum frequency generation spectra of self assembled alkanethiols. SURFACE SCIENCE, 602(23), 3551–3559.
Résumé: A global modelling of Sum Frequency Generation (SFG) spectra of the self assembly of alkanethiols is presented. All CH modes are modelled together. CH2 modes are assumed local to allow easy calculation of the spectrum as a function of molecular conformation. Ab initio molecular hyperpolarizabilities are used. A phenomenological approach is used to include the Fermi resonance in the model: the calculated intensity of the CH3 symmetric stretch is redistributed according to intensity borrowing by the Fermi resonance. The model is applied to octadecanethiol (ODT) and pentadecanethiol (PDT). The even/odd intensity alternation of SFG CH3 vibrational bands as a function of chainlength is used to test the model. It is found that the relative magnitudes of the hyperpolarizability tensors of the CH3 asymmetric and symmetric modes need to be adjusted. The model provides tilt and twist angles of the alkyl chain in agreement with the literature. It shows that the all trans conformation does not imply the absence of CH2 bands in SFG spectra. In addition, new information is obtained. In particular, if two types of molecular conformations are assumed, the C planes of the two molecules must be perpendicular to each other. (C) 2008 Elsevier B.V. All rights reserved.
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Hamoudi, H., Guo, Z., Prato, M., Dablemont, C., Zheng, W. Q., Bourguignon, B., Canepa, M., & Esaulov, V. A. (2008). On the self assembly of short chain alkanedithiols. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10(45), 6836–6841.
Résumé: A study of the self-assembly of nonane-alkanedithiol monolayers on gold in n-hexane and ethanol solvents is presented. Self-assembled monolayers (SAMs) are characterised by reflection-absorption infrared spectroscopy (RAIRS), sum frequency generation (SFG) and spectroscopic ellipsometry (SE) measurements. Data obtained for alkanethiols SAMs are also shown for comparison. The measurements show that nicely organized HSC(9)SH SAMs can be obtained in n-hexane provided that N(2)-degassed solutions are used and all preparation steps are performed in the absence of ambient light. SFG measurements show that these SAMs have free standing SH groups. Use of an un-degassed and/or light-exposed n-hexane solutions leads to a worse layer organization. Preparation in ethanol, even in degassed solutions with processing in the dark, leads to poorly organized layers and no sign of free-SH groups was observed.
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