Infrared Laser Catalyzed Chemical Reactions

The development of the laser some twelve years ago has resulted in the creation and/or the resuscitation of a number of experimental disciplines involving measurements of energy transfer, chemical reaction rates, high resolution spectroscopy as well as nonlinear effects. In the last three years more and more work involving the use of lasers has been reported on in the literature and a number of excellent review articles has been published dealing with many specific experimental and theoretical subfields⁽¹⁾ The audience tuned to laser and laser related research has steadily expanded to include widely varying disciplines ranging from Engineers to Chemists and from Artists to Meteorologists and is reflected in a variety of professional publications tailored for more or less specific audiences; but even a brief survey of the most widely read physical chemistry journals will convince anyone that one of the most extensive applications of the laser has been in the field of energy transfer studies. The study of energy transfer between the various internal modes and translation has been a topic of fundamental research for a number of decades, yet the detailed probing and “preparation” of well defined vibrational, rotational or electronically excited species have always been at best difficult. The availability of a monochromatic, high power, short pulse duration, and almost tunable sources was a boon to chemists, since the new research tool offered the intriguing possibility of measuring the rate constants for processes taking place between molecules “prepared” in well defined quantum states. As a field within a field, the specific application of vibrational excitation of molecules and the subsequent measurement of the various relaxation rates has received the most attention; partly due, no doubt, to the properties of the molecular lasers available in the infrared region and partly due to the significance of vibrational excitation on the rate and mechanism of chemical reactions.     

Near field properties of nanoparticle arrays fabricated by laser annealing of thin Au and Ag films

In this work we show the properties of the electromagnetic field in the vicinity of a monolayer nanoparticle array on SiO₂ substrate. The nanoparticle array is produced by a simple experimental procedure, where thin gold and silver films are deposited on a substrate by pulsed laser deposition technique and they are annealed by nanosecond laser pulses. At certain conditions the laser annealing leads to a homogeneous decomposition of the film into nanoparticles with diameters in the range of few tens of nanometers. Using FDTD simulations the near field distribution in array structures taken from SEM images are obtained. The distribution shows presence on “hot spots” where the near field intensity is enhanced more than two orders of magnitude compared to the incident one. The existence of enhanced field intensity is assumed to be the main reason on enhancement of the Raman scattering signal obtained experimentally using the produced structures as active substrates.     

Nanoparticle kinetic effects experimentally observed in a magnetic fluid under a quasi-homogeneous magnetic field

The effect of a quasi-homogeneous external magnetic field on a created and decaying space nanoparticle structure and its distribution in a sample of a magnetic fluid was studied. This space structure was created as a grating by applying an interference field of two crossed Ar laser beams. The magnetic field was formed using two electromagnets and was applied in three main directions of the created nanoparticle grating. The magnetic field oriented parallel to the strips of the grating or perpendicular to the grating plain does not significantly change the shape of it. The magnetic field oriented in the perpendicular direction to the grating plain causes redistribution of the nanoparticles and as a consequence a perpendicular nanoparticle “quasi-grating” arises.     

Collaboration range: Effects of geographical proximity on article impact

Spatial scientometrics studies how geography influences knowledge creation. In the recent years there has been a surge in this kind of studies, due to the increase of international collaborations. Most of the work in this field has been focused on the geographical distribution of researchers, whilst few have considered how proximity between coauthors influences research quality. In this work we leverage a dataset of geolocalized articles to assess the effect of geographical distance on article impact. More precisely, the dataset, provided by the Observatory of Science and Technology (O.S.T.), consists of roughly 10⁶ scientific articles, gathering all European articles written in 2000 and 2007, spanning 9 disciplines. We evaluate under which geographical extent coauthorships have higher probability of resulting in high impact articles (“high impact” is here approximated by “being in the top 10% most cited articles of its discipline”). We also describe spatial distribution of coauthorship, delineating geographical areas where the production is proportionally higher. The distribution is evaluated both in term of km (as the crow flies), and in terms of administrative partitions (authors’ cities, regions, countries).     

Probing the acoustic vibrations of single metal nanoparticles by ultrashort laser pulses

The strong interaction of metal nanoparticles with light makes it possible to detect individual particles by far‐field optical methods. In this article, the interaction of a metal nanoparticle with a short laser pulse is discussed, with the emphasis on the coherent excitation of mechanical (acoustic) modes and the optical detection of these vibrations. The literature on acoustic vibrations of single metal nanoparticles of different shapes (spheres, dumbbells, rods, cubes, wires, prisms) is reviewed, and the modes that have been excited and detected in these particles are discussed. Finally, the insights and potential applications enabled by these studies are summarized.     

Interferometry of a single nanoparticle using the Gouy phase of a focused laser beam

We provide a quantitative explanation of the mechanism of the far-field intensity modulation induced by a nanoparticle in a focused Gaussian laser beam, as was demonstrated in several recent direct detection studies. Most approaches take advantage of interference between the incident light and the scattered light from a nanoparticle to facilitate a linear dependence of the signal on the nanoparticle volume. The phase relation between the incoming field and the scattered field by the nanoparticle is elucidated by the concept of Gouy phase. This phase relation is used to analyze the far-field signal-to-noise ratio as a function of exact nanoparticle position with respect to the beam focus. The calculation suggests that a purely dispersive nanoparticle should be displaced from the Gaussian beam focus to generate a far-field intensity change.     

Sensor and microelectronic elements based on nanoscale granular systems

Specific effects observed in small metal particles due to their distinction from bulk material as well as phenomena inherent to an ensemble of these particles coupled by electron tunneling have attracted considerable attention to nanosized systems. Electron and photon emission was revealed as a power was fed into the metal nanoparticle films deposited on insulating substrates either by passage of an electrical current in the film plane or by laser irradiation in the infrared and visible range. The electrical conductivity of metal nanoparticle films close to the percolation threshold is sensitive to temperature, substrate bending and adsorption of various gases. Besides, the current–voltage characteristics of the conduction current of a system consisting of a metal nanoparticle film and an adsorbate exhibit a voltage-controlled negative resistance region. These peculiar properties enable nanosized particle systems to be used for various applications. The present review deals with a variety of sensors for physical properties and microelectronics elements based on nanoparticle films. The mechanisms underlying the special properties are discussed. Some technological methods ensuring better parameter definition and long-term stability of sensors are also described.     

The effect of spherical aberration on temperature distribution inside glass by irradiation of a high repetition rate femtosecond pulse laser

In this paper, we study the effect of spherical aberrations on the light intensity and the temperature distribution in the focal region in a 250-kHz femtosecond laser irradiated Ag⁺-doped borosilicate glass. When a focused beam goes through an interface between air and glass, spherical aberration will result in the separation of the focal point and then cause a clear change of the light intensity distribution along the incident direction. That phenomenon will further influence the longitudinal cross-section temperature distribution in glass. Here we use Ag nanoparticle formation as a marker for establishing temperature distribution and we find that the formation of nanoparticle shows a strong dependence on the temperature field and the detailed precipitation process is also discussed.     

Synthesis of nanoparticles and suspensions by pulsed laser ablation of microparticles in liquid

Recent studies demonstrated that the process to produce metal and oxide nanoparticles by laser ablation of consolidated microparticles is a convenient and energy-efficient way to prepare nanoparticles. In this work, the novel process is applied to nanoparticle synthesis in the liquid environment and the results are compared with those by the gas-phase process. Metal and oxide nanoparticles are synthesized by pulsed laser ablation of the compacted metal microparticles using a Q-switched Nd:YAG laser in water. It is shown that the process is effective for preparing nanoparticle suspensions having relatively uniform size distributions. While the laser fluence and the degree of compaction strongly influence the size of the produced nanoparticle in air, the sedimentation time is shown to be the most critical factor to determine the mean size of the suspended particles.     

Following the evolution of morphology, composition and crystallography of alumina based catalysts after laser ablation: Implications for analysis by LA-ICP-AES

Fundamental understanding of aerosol formation during laser ablation is important for the development of LA-ICP analysis of complex samples. Using a Lina Spark Atomizer™, the application of this technique to the field of heterogeneous catalysis gave an accuracy of 5–15% while extreme values of +100% could be obtained in some cases. To improve understanding of laser ablation processes, particles generated during ablation of alumina based catalysts were collected and analysed using different microscopy and surface analysis techniques. Morphological study by scanning electron microscopy showed that most of the particles leaving the ablation cell were nanoparticle aggregates generated from vapor condensation. An XRD study of these aerosols revealed that the condensation converge on the formation of a spinel structure with large coherence domains. Elemental composition of the aerosol was also followed and exhibited differences between a catalyst containing large Mo concentration or low Pt concentration.     

Large dielectrophoresis force and torque induced by localized surface plasmon resonance of Au nanoparticle array

A new approach is proposed for manipulating and rotating micro- or nano-objects by using polarized laser light with low intensity. The polarized light excites resonant dipoles on a cap-shaped Au nanoparticle array, which generates a highly nonuniform radiation field that induces large dielectrophoresis force on dielectric objects. The orientation control of the objects is realized by adjusting the polarization direction of the incident light. Theoretical modeling, fabrication, and characterization results for the cap-shaped Au nanoparticle array, as well as preliminary trapping results, are reported.     

用于飞秒激光纳米加工的TiO_2粒子阵列诱导多种基底表面近场增强

利用纳米粒子辅助对飞秒激光能量进行空间局域化,使其在基底表面诱导产生纳米尺度的近场增强,这对超衍射极限微结构加工具有重要意义.目前对于粒子阵列诱导飞秒激光纳米孔加工的研究仅限于金属Au粒子及低折射率聚苯乙烯介电粒子等,本文提出并开展了应用高折射率TiO_2介电粒子阵列作为辅助诱导激光近场增强从而进行飞秒激光超衍射纳米孔加工的研究.对TiO_2介电粒子阵列在Si,Pt及SiO_2表面的近场强度分布进行了数值模拟,研究其基底表面近场增强的规律及物理过程.研究结果发现,使用硅基底时,阵列与单一TiO_2球形粒子相比其近场增强仅下降约30%;相对于入射激光强度而言,在直径约为100nm的空间范围内获得140倍的近场增强,这一现象可用于百纳米孔的激光加工.同时在其他典型基底的理论计算结果中也表明,几乎在所有金属及介电材料表面均可以实现良好的百纳米空间范围内的近场增强,并且具有近场随着基底折射率变大而增强的规律.这些现象的产生归因于TiO_2粒子中磁四极振荡产生的激光前向场增强及粒子与基底的耦合作用.进一步引入镜像电荷模型对基底光学参数对其表面近场增强的影响规律进行了分析和解释.本文的模拟结果对飞秒激光近场超衍射极限纳米加工的应用有着重要的意义.     

Cerium oxide nanoparticles protect primary mouse bone marrow stromal cells from apoptosis induced by oxidative stress

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 10⁸ to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.     

Study of electrical field distribution of gold-capped nanoparticle for excitation of localized surface plasmon resonance

The specific optical characteristics which can be observed from noble metal nanostructured materials such as nanoparticles and nanoislands have wide variety of applications such as biosensors, solar cells, and optical circuit. Because, these noble metal nanostructures induce the increment of light absorption efficiency by the enhancing effect of electrical field from localized surface plasmon resonance (LSPR) excitation. However, the enhancing effects of electrical field from LSPR using simple structured noble metal nanostructures for several applications are not satisfactory. To realize the more effective light absorption efficiency by the enhancing effect of electrical field, quite different noble metal nanostructures have been desired for applying to several applications using LSPR. In this study, to obtain the more effective enhancing effect of electrical field, conditions for LSPR excitation using a gold-capped nanoparticle layer substrate are computationally analyzed using finite-difference time-domain (FDTD) method. From the previous research, LSPR excitation using such gold-capped nanoparticle layer substrates has a great potential for application to high-sensitive label-free monitoring of biomolecular interactions. For understanding of detailed LSPR excitation mechanism, LSPR excitation conditions were investigated by analyzing the electrical field distribution using simulation software and comparing the results obtained with experimental results. As a result of computational analysis, LSPR excitation was found to depend on the particle alignment, interparticle distance, and excitation wavelength. Furthermore, the LSPR optical characteristics obtained from the simulation analysis were consistent with experimentally approximated LSPR optical characteristics. Using this gold-capped nanoparticle layer substrate, LSPR can be excited easily more than conventional noble metal nanoparticle-based LSPR excitation without noble metal nanoparticle synthesis. Hence, this structure is detectable a small change of refractive index such as biomolecular interactions for biosensing applications.     

Dynamic changes of optical characteristics of resonant domains in metal nanoparticle aggregates under pulsed laser fields

A systematic analysis of the impact of laser radiation on disordered metal nanoparticle aggregates has been carried out using the simplest model of a resonance domain in the form of a bisphere. Such aggregates can be considered as a set of elementary domains with different eigen-resonant frequencies. The model is basically a pair of bound spherical nanoparticles having equal radii and covered with a polymer adsorption layer. A significant change in the resonance properties of the domain occurs due to the change of interparticle gaps under applied radiation. We investigated the temporal variation of parameters and hence optical characteristics of coupled Ag nanoparticles under pulsed laser radiation for different wavelengths, intensities and pulse durations and for different initial values of the interparticle gap.     

Transport of a spherical transparent nanoparticle by radiation forces in the field of a Gaussian laser beam

The motion of a spherical transparent nanoparticle under the influence of radiation forces in the field of a Gaussian laser beam is investigated based on solution of Langevin equation. Expressions governing transverse and longitudinal velocities of the nanoparticle under the action of gradient and scattering forces are derived and analyzed. The possibility of spatial separation of nanoparticles having different sizes and optical properties is discussed.     

Modeling photothermal and acoustical induced microbubble generation and growth

Previous experimental studies showed that powerful heating of nanoparticles by a laser pulse using energy density greater than 100 mJ/cm², could induce vaporization and generate microbubbles. When ultrasound is introduced at the same time as the laser pulse, much less laser power is required. For therapeutic applications, generation of microbubbles on demand at target locations, e.g. cells or bacteria can be used to induce hyperthermia or to facilitate drug delivery. The objective of this work is to develop a method capable of predicting photothermal and acoustic parameters in terms of laser power and acoustic pressure amplitude that are needed to produce stable microbubbles; and investigate the influence of bubble coalescence on the thresholds when the microbubbles are generated around nanoparticles that appear in clusters.

We develop and solve here a combined problem of momentum, heat and mass transfer which is associated with generation and growth of a microbubble, filled with a mixture of non-vaporized gas (air) and water vapor. The microbubble’s size and gas content vary as a result of three mechanisms: gas expansion or compression, evaporation or condensation on the bubble boundary, and diffusion of dissolved air in the surrounding water. The simulations predict that when ultrasound is applied relatively low threshold values of laser and ultrasound power are required to obtain a stable microbubble from a single nanoparticle. Even lower power is required when microbubbles are formed by coalescence around a cluster of 10 nanoparticles. Laser pulse energy density of 21 mJ/cm² is predicted for instance together with acoustic pressure of 0.1 MPa for a cluster of 10 or 62 mJ/cm² for a single nanoparticle. Those values are well within the safety limits, and as such are most appealing for targeted therapeutic purposes.     

Silver nanoparticles as matrix for laser desorption/ionization mass spectrometry of peptides

Silver nanoparticle synthesized from chemical reduction has been successfully utilized as a matrix in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) of peptides. Acting as a substrate to adsorb analytes, as well as a transmission medium for UV laser, silver nanoparticle was found to assist in the desorption/ionization of peptides with little or no induced fragmentation. The size of the nanoparticle was typically in the range of 160 ± 20 nm. One of the key advantages of silver nanoparticle for peptides analysis is its simple step for on-probe sample preparation. In addition, it also minimizes the interferences of sodium dodecyl sulfate (SDS) surfactant background signal, resulting in cleaner mass spectra and more sensitive signal, when compared to α–cyano-4-hydroxycinnamic acid (CCA) matrix.     

The impact of Solid State Communications in view of the ISI Citation data

Bibliometric techniques (i.e. citation analysis) are used to evaluate the impact and standing of Solid State Communications (SSC) among its competitor journals covering the field of condensed matter. In most cases, the analysis covers all issues dating back to the journal's inception in 1963. In some cases, however, the analysis only covers articles published after 1973 because of limited access to the previous data under the available search system. A listing of the most cited articles appeared in SSC since its inception is given. Several of them include Nobel laureates among their authors. An analysis of the articles which remained uncited is also presented. Bibliometric data from the Institute for Scientific Information (ISI) such as the Journal Impact Factor (JIF), the Citing Half-Life as well as the Cited Half-Life are compared with those for other journals covering condensed matter and related fields. Furthermore, an analysis of the impact according to the countries of origin of authors is presented. A discussion of the results exhibited in Tables and Figures is given.