Onset Of Breakdown Research Articles

Effect of ionic strength on shear-thinning nanoclay-polymer composite hydrogels.

Nanoclay-polymer shear-thinning composites are designed for a broad range of biomedical applications, including tissue engineering, drug delivery, and additive biomanufacturing. Despite the advances in clay-polymer injectable nanocomposites, colloidal properties of layered silicates are not fully considered in evaluating the in vitro performance of shear-thinning biomaterials (STBs). Here, as a model system, we investigate the effect of ions on the rheological properties and injectability of nanoclay-gelatin hydrogels to understand their behavior when prepared in physiological media. In particular, we study the effect of sodium chloride (NaCl) and calcium chloride (CaCl2), common salts in phosphate buffered saline (PBS) and cell culture media (e.g., Dulbecco's Modified Eagle's Medium, DMEM), on the structural organization of nanoclay (LAPONITE® XLG-XR, a hydrous lithium magnesium sodium silicate)-polymer composites, responsible for the shear-thinning properties and injectability of STBs. We show that the formation of nanoclay-polymer aggregates due to the ion-induced shrinkage of the diffuse double layer and eventually the liquid-solid phase separation decrease the resistance of STB against elastic deformation, decreasing the yield stress. Accordingly, the stress corresponding to the onset of structural breakdown (yield zone) is regulated by the ion type and concentration. These results are independent of the STB composition and can directly be translated into the physiological conditions. The exfoliated nanoclay undergoes visually undetectable aggregation upon mixing with gelatin in physiological media, resulting in heterogeneous hydrogels that phase separate under stress. This work provides fundamental insights into nanoclay-polymer interactions in physiological environments, paving the way for designing clay-based injectable biomaterials.

Spatial Heterogeneities and Onset of Passivation Breakdown at Lithium Anode Interfaces

Effective passivation of lithium metal surfaces, and prevention of battery-shorting lithium dendrite growth, are critical for implementing lithium-metal-anodes for batteries with increased power densities. Nanoscale surface heterogeneities can be "hot spots" where anode passivation breaks down. Motivated by the observation of lithium dendrites in pores and grain boundaries in all-solid batteries, we examine lithium metal surfaces covered with Li(2)O and/or LiF thin films with grain boundaries in them. Electronic structure calculations show that, at >0.25 V computed equilibrium overpotential, L(2)O grain boundaries with sufficiently large pores can accommodate Li(0) atoms which aid electron leakage and passivation breakdown. Strain often accompanies Li-insertion, applying a ~1.7% strain already lowers the computed overpotential to 0.1 V. Lithium metal nanostructures as thin as 12 Angstroms are thermodynamically favored inside cracks in Li(2)O films, becoming "incipient lithium filaments." LiF films are more resistant to lithium metal growth. The models used herein should in turn inform passivating strategies in all-solid-state batteries.

Spectral and temporal characteristics of Ba I emission in femtosecond laser-induced breakdown on the surfaces of aqueous solutions

Temporal behavior of the intensity of Ba I emission lines (413.24 and 553.55 nm) in plasma of optical breakdown induced by femtosecond laser pulses (800 nm, 45 fs, 0.82 mJ) on the surface of BaCl2 aqueous solution was experimentally studied as dependent on delay time t d relative to the breakdown onset. The maximum intensity of the Ba I (413.24 nm) line was observed at t d = 20 ns, while the intensity of the Ba I (553.55 nm) line reached a maximum at t d = 40 ns. At t d = 10 ns, the intensity of the Ba I (413.24 nm) line was almost three times as large as that of Ba I (553.55 nm) line (despite the about two orders of magnitude lower probability of spontaneous transition for the former line), which is explained by the recombination cascade. It is established that, in the subsystem of 5d6p 3 D 0 and 6s6p 1 P 0 levels, the Boltzmann distribution is not valid and the local thermodynamic equilibrium is absent.

Uniform lifetime prolongation of a high density plasma channel left in the wake of femtosecond filament

We demonstrate uniform lifetime prolongation of an entire plasma filament generated by a high-power femtosecond laser pulse. The entire filament is irradiated by a secondary nano-second laser pulse that co-propagates with the femtosecond laser. The plasma filament partially absorbs the nanosecond laser radiation, and plasma lifetime is extended along the entire channel resulting in a smooth and continuous high-density plasma column with lifetime longer than 30 ns. We present an experimental and theoretical study of the intensity range of the secondary laser required for effective lifetime prolongation and the behavior of the plasma density at the onset of breakdown triggered by the secondary laser. Our study shows that an efficient prolongation of the lifetime of plasma filament occurs in the intensity range of 0.03–0.3 TW/cm2.

Effect of the volume fraction of the icosahedral phase on the microstructures, hot compressive behaviors and processing maps of Mg-Zn-Y alloys

The effect of the volume fraction (0.6–8.4 vol %) of the icosahedral phase (I-phase, Mg3Zn6Y1) on the microstructure, hot deformation mechanism and hot workability of cast Mg-Y-Zn alloys was studied. As the volume fraction of I-phase increased, the fraction of dynamically recrystallized (DRXed) grains increased, indicating that I-phase promoted dynamic recrystallization (DRX) by providing the preferred nucleation sites for DRXed grains through particle stimulated nucleation mechanism. There was, however, a critical amount of I-phase (about 5 vol %) beyond which the fraction of DRXed grains decreased. This was attributed to the formation of relatively coarse divorced eutectic I-phase and lamellar I-phase structures at the volume fraction of I-phase ≥5%. This result indicates that besides the amount of I-phase, the size of I-phase structure is another important factor affecting DRX. Processing maps were constructured to evaluate the hot workability of the alloys with different volume fraction of I-phase. The hot workability increased as the volume fraction of I-phase increased up to about 5 vol % but decreased afterward, confirming that DRX and hot workability are correlated with each other. The hot workability increases with increasing I-phase amount because the occurrence of extensive DRX delays the onset of power-law breakdown and flow instability to higher strain rates and lower temperatures.

Infrared Optical Measurements of Thermal Breakdown in Battery Electrolytes

Electrolyte thermal stability is critical for both battery safety and extending battery life. Battery fires are often the result of thermal breakdown of the liquid electrolyte leading to a flammable mixture of volatile products. Even in the absence of fire, electrolyte decomposition leads to battery swelling, harmful precipitates, reduced ion conductivities, and undesirable battery chemistry. Current methods of determining electrolyte stability using ex-situ techniques, such as thermal gravimetric analysis or differential scanning calorimetry, can over predict thermal stability, do not address materials compatibility within batteries, and cannot identify chemical decomposition mechanisms. Infrared optical detection of thermal stability offers an in-situ approach providing: speciation, identification of chemical bonds involved in decomposition, real-time detection, and chemical kinetics. In this work, the thermal stability of the room temperature ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO4]) is investigated using infrared (IR) spectroscopy. Quantitative IR absorption spectral data are measured for the heated ionic liquid. Spectra have been collected between 25°C and 100°C using a heated optical cell. Multiple samples and cell path lengths were used to determine quantitative values of the absorption coefficient. These results were compared to previous computational models of the ion pair to identify each absorption band with corresponding chemical bonds. The quantitative spectra were then used to measure the rate of thermal decomposition at elevated temperatures revealing the onset of breakdown above 75°C.

Accelerated onset of cellular breakdown at increased solidification speed after laser melting of indium in silicon

We report on the incidence of cellular breakdown in silicon wafers implanted with indium and pulsed laser melted at varying laser fluence. We predict from heat flow calculations that as laser fluence is decreased, (a) the melt depth decreases, (b) the solidification velocity increases, and (c) the solidification front should be more stable with respect to cellular breakdown (based on the binary alloy solidification theory), which should result in observed incidence of cellular breakdown at a relatively shallower depth below the surface. However, secondary ion mass spectrometry (SIMS) data show that cellular breakdown at lower fluence is observed deeper, indicating that the interface became unstable earlier in its solidification. The SIMS data show significant In evaporation, with greater evaporation occurring as fluence increases. Calculations show that surface evaporation can reduce the bulk liquid concentration during solidification, reducing the degree of instability. The longer melt durations after irradiation at higher fluence give more time for evaporation, which may result in a relatively larger delay in the onset of breakdown compared to lower fluence by suppressing the bulk liquid concentration and suppressing the growth of unstable perturbation. Under certain conditions, this effect could dominate over the role of reducing the interface speed, which would tend to accelerate amplification of a perturbation, which leads to breakdown. Calculations qualitatively support this interpretation.

An Improved Analytical Model for Carrier Multiplication Near Breakdown in Diodes

The charge carrier contributions to impact ionization and avalanche multiplication are analyzed in detail. A closed-form analytical model is derived for the ionization current before the onset of breakdown induced by both injection current components. This model shows that the ratio of both injection current components affects the multiplication factor at relatively low fields before breakdown, but does not affect the reverse breakdown voltage. Furthermore, the model indicates that in case the ionization coefficients of electrons and holes are quite different in value, which depends upon the semiconductor material, the ionization coefficient of the charge carrier with the highest value can be extracted at those low fields. The one with the lowest value can be obtained by fitting the current close to breakdown. The model is compared and verified with TCAD simulations, and to some extent with experimental data, for silicon p-i-n diodes.

Continuous Strip Reduction Test Simulating Tribological Conditions in Ironing

Abstract Laboratory testing of tribo-systems for sheet metal forming applications must ensure similar conditions with the tribo-parameters that are commonly utilized in real production in order to generate data that is meaningful for industry. The main parameters to consider are the tool and workpiece materials, surface roughnesses, normal pressure, sliding length, sliding speed, interface temperature and lubrication. This paper proposes a new Strip Reduction Test (SRT) for industrial ironing processes that is capable of replicating the highly severe tribological conditions that are experienced during both the forward stroke and the backward retraction of the punch. The new SRT tool design is implemented in a new Universal Sheet Tribo-Tester (UST), which can run multiple tests continuously from a coil. The test is capable of simulating various process parameters such as reduction, drawing speed, tool temperature, sliding length and quantifying the onset of breakdown of the lubricant film and subsequent galling after several strokes not only when emulating the forward strokes but also the backward strokes. Preliminary tests disclose promising results as regards the identification of lubricant film breakdown by detecting changes in measured force, surface roughness and/or torque values.

Algaenan structure in the microalga Nannochloropsis oculata characterized from stepwise pyrolysis

Dried biomass of the eustigmatophyte Nannochloropsis oculata was subjected to stepwise pyrolysis at 50°C intervals from 310 to 610°C to test the potential of the technique for investigating the algaenan structure of N. oculata and for determining a broad suite of biochemical constituents. Pyrolysis at 310°C yielded mainly free lipids such as phytol, cholesterol, C32 alkyl diols, hexadecanamide and large amounts of phytol-derived alkenes from thermal desorption. Indole generated from protein degradation first appeared at 360°C, indicating the onset of biopolymer breakdown. The pyrolyzate of 410°C showed a simpler composition, dominated by 2-methyl-1H-indole and indole, and accompanied by low amounts of phenol and hexadecanamide. At 460°C, algaenan breakdown was evident from the detection of C15–C19n-alkan-2-ones with a strong predominance of C17, and of C29–C33 mid-chain ketones composed of a remarkable predominance of the symmetrical ketone C31n-alkan-16-one. Small amounts of the mono-unsaturated C31:1 mid-chain ketone and n-alkene/n-alkane doublets were also present. The chromatograms suggest that the algaenan structure of N. oculata is composed of repeating, interlinked C32n-alkan-1,17-diols, whereas the free plus bound lipids were dominated by the C32n-alkan-1,15-diol. The pyrolyzate at 510°C was dominated by a bimodal distribution of C8–C32n-alkene/n-alkane doublets showing a maximum at n-C14:1 and n-C26, with lesser amounts of ketones. Such a wide chain length distribution implies that other aliphatic lipids, perhaps derived from the long chain n-alkenols, might also be involved in the algaenan structure. Major constituents of the 560°C pyrolyzate were aromatic compounds, including toluene, phenol and indole, but absolute abundances were low. It is notable that high molecular weight compounds such as the n-alkene/n-alkane doublets were no longer detected at 560°C. The results show that stepwise pyrolysis provides simpler chromatograms than a single pyrolysis of a whole sample at 610°C and so can be a useful tool for identifying algaenan structures and/or related compounds in ancient sediments and modern microalgae.

Longitudinal stability in multiharmonic standing wave linacs

Accelerating cavities that excite multiple modes at integer harmonics of the fundamental frequency have the potential to be used to suppress the onset of rf breakdown and reduce the pulsed surface heating at high accelerating gradients. Understanding the effect of an additional harmonic cavity mode on the longitudinal beam dynamics is important to their development and use. A Hamiltonian that describes the longitudinal motion of a particle as it traverses a chain of multiharmonic cavities has been derived and is applied to the case of a second harmonic cavity. The Hamiltonian is based upon formalisms found in literature for the fundamental harmonic and is extended to include different longitudinal field distributions and harmonic frequencies. The study initially explores the longitudinal motion for moderate accelerating gradients with high-$\ensuremath{\beta}$ protons, as this will allow fundamental properties of the stable region (acceptance and shape of the rf bucket) to be determined. High accelerating gradients are also investigated but the focus will be on phase stability throughout. This work concludes by considering the longitudinal dynamics of a modified European Spallation Source accelerator, comprised of multiharmonic cavities that has specifications broadly consistent with the accelerator.

Insights from Studying the Origins of Reversible and Irreversible Capacities on Silicon Electrodes

Coulombic efficiency (CE) of a lithium-ion battery (LIB) anode is a measure of the charge capacity over discharge capacity for a given cycle. A low CE is not a major issue for half cell tests, where there is plenty of lithium in the counter electrode. However, full cell battery performance can be significantly affected by CE, especially the first cycle efficiency. Most battery research attributes the first cycle irreversible capacity to processes such as solid electrolyte interphase (SEI) formation and electrolyte decomposition [1,2]. This, however, does not adequately give a full picture of what is going on in the electrode. A better understanding of the different contributions leading to the reversible and irreversible capacities is necessary in order to suggest strategies for improvements. In this study, we use a systematic approach to separate the charge-discharge capacities of silicon electrodes into different contributions, in particularly SEI formation, lithium accommodation in carbon and binder, and lithiation and delithiation of the active material. This is possible because the three different contributions have different characteristics. Firstly, we note that SEI is typically formed during the first discharge above 0.1V before the lithiation of silicon [3]. So by comparing the CE of electrodes discharged to different capacities, SEI contribution can be identified. Secondly, the lithium accommodation in carbon and binder depends on their amount. So by comparing electrodes with different compositions, this contribution can also be distinguished. The remaining capacity is attributed to the lithiation and delithiation of silicon. The experimental is as follows. Silicon electrodes using commercial silicon particles (Sigma Aldrich), conductive carbon (acetylene black (AB)) and carboxymethyl cellulose (CMC) binder were made with a ratio of 4:3:3, 6:2:2 and 8:1:1. We kept the same ratio between AB and CMC so that the two components can be considered as one. Multiple cells were made, and each of them is initially discharged to different cutoff capacity (250, 500, 1000, 1500, 2000, 2500, 3000 and 3500mAh g-1), and the corresponding charge capacity is recorded. Figure 1a shows a summary of the initial discharge-charge curves of different cells with a composition of 4:3:3. The respective first charge capacity vs. first discharge capacity is summarized in Figure 1b, which shows a linear behavior that is shifted from the origin. The slope of the line corresponds to the intrinsic first cycle efficiency of Si, which is about 90% and is relatively constant regardless of the degree of lithiation. This suggests that no matter how much lithium is initially inserted into the material, 10% of them remains in the lattice and cannot be removed. On the other hand, the x-intercept corresponds to the irreversible capacity of the electrode. About 16 mAh (g Si)-1 can be attributed to SEI formation and electrolyte decomposition in our electrodes. It is interesting to note that despites the use of the same materials, the behavior of the 8:1:1 electrode deviates from those of the other two electrodes at high discharge capacity. Since the only difference is the electrode composition, the behavior is attributed to insufficient mechanical strength of the electrode, which significantly reduces the reversibility of lithium accommodation. So, our method also enables us to identify the onset of mechanical breakdown in the electrode. We have developed a method here to distinguish the different contributions to the overall capacity of silicon. The obtained information is valuable for designing electrode to increase its stability. Further works on the analysis of subsequent cycles, effect of particle surface area and binder type are underway and will be presented at the meeting. Reference: 1) Chen, X., Li, X., Mei, D., Feng, J., Hu, M. Y., Engelhard, M., Zheng, J., Xu, W., Xiao, J., Liu, Jun. & Zhang, J. G. ChemPubSoc. 7, 549-554 (2014). 2) Lin, Y. M., Klavetter, K. C., Abel, P. R., Davy, N. C., Sinder, J. L., Heller, A. & Mullins, B. ChemComm. 48, 7268-7270 (2012). 3) Wang,Z. C., Xu, J., Yao, W. H., Yao, Y. & Yang, W. Y. ECS Trans. 41, 29– 40 (2012). Figure 1

TCAD analysis of the leakage current and breakdown versus temperature of GaN-on-Silicon vertical structures

A TCAD-based approach has been used to investigate the leakage current and breakdown regime of vertical GaN/AlGaN/Si structures at different ambient temperatures. TCAD modeling has been used to assess possible mechanisms of the forward-bias leakage current. A good agreement with experimental data has been obtained by implementing both trap-assisted and Poole–Frenkel conduction mechanisms into the deeper buffer layers, indicating that conduction is dominated by electron injection from silicon into a continuum of states at a given energy offset in the transition layer, which might be associated with conductive dislocation defects. The latter mechanisms have been proven to anticipate the onset of breakdown at high temperatures.

Multipactor threshold calculation of coaxial transmission lines in microwave applications with nonstationary statistical theory

This paper presents a statistical theory for the initial onset of multipactor breakdown in coaxial transmission lines, taking both the nonuniform electric field and random electron emission velocity into account. A general numerical method is first developed to construct the joint probability density function based on the approximate equation of the electron trajectory. The nonstationary dynamics of the multipactor process on both surfaces of coaxial lines are modelled based on the probability of various impacts and their corresponding secondary emission. The resonant assumption of the classical theory on the independent double-sided and single-sided impacts is replaced by the consideration of their interaction. As a result, the time evolutions of the electron population for exponential growth and absorption on both inner and outer conductor, in response to the applied voltage above and below the multipactor breakdown level, are obtained to investigate the exact mechanism of multipactor discharge in coaxial lines. Furthermore, the multipactor threshold predictions of the presented model are compared with experimental results using measured secondary emission yield of the tested samples which shows reasonable agreement. Finally, the detailed impact scenario reveals that single-surface multipactor is more likely to occur with a higher outer to inner conductor radius ratio.

Electrochemical Reduction of Triclocarban at a Silver Cathode

Triclocarban (TCC) is an environmentally persistent antimicrobial agent commonly used in personal care products such as hand soaps, lotions, and toothpastes. Although the use of TCC and similar compounds (such as triclosan) is intended to minimize human exposure to harmful bacteria, recent research has indicated that these substances may themselves cause health problems. TCC, in addition to being a likely endocrine disruptor, also probably contributes to the development of drug-resistant bacteria as it builds up in municipal wastewaters.1 As of 2013, TCC accounted for more than 50% of pharmaceuticals in municipal sludge, making the possible dangers of its accumulation a primary concern.2 A need for removal and remediation of TCC has inspired research into many methods of degradation, including the use of ozone, photolysis, and electro-Fenton processes.3–5 Other promising methods, however, have attracted less attention. For example, earlier literature shows that other organohalogen pollutants can be electrochemically dehalogenated, particularly at silver cathodes, leading to less harmful products.6 In this study, we have explored the electrochemical reduction of TCC at a silver cathode as a possible method of remediation. Cyclic voltammograms for the reduction of TCC show three cathodic peaks at both glassy carbon and silver cathodes in dimethylformamide (DMF) containing 0.050 M tetramethylammonium tetrafluoroborate (TMABF4). In comparison with a glassy carbon electrode, each peak is shifted approximately 30 mV toward more positive values at silver, the respective peak potentials being –1.27, –1.37, and –1.80 V vs. a cadmium amalgam reference electrode (with a potential of –0.76 V vs. the saturated calomel electrode). Whereas the two most positive cathodic peaks for reduction of TCC are nearly merged at a typical scan rate of 100 mV s–1, lower scan rates can be employed to increase the separation of these peaks. Three comparable cathodic peaks for TCC are seen for a silver cathode in dimethyl sulfoxide, but only two cathodic peaks are observed in acetonitrile. In a solvent consisting of 10% water–90% DMF, only one cathodic peak, corresponding to the most positive peak in the other solvents, is seen before the onset of electrolytic breakdown of the solvent–electrolyte. Diphenylurea, the product anticipated from complete dechlorination of TCC, exhibits a single cathodic peak at –1.80 V in DMF, with a significantly smaller current than the corresponding peak for reduction of TCC. Preliminary results obtained from controlled–potential (bulk) electrolyses in DMF with a silver gauze cathode indicate that partial dechlorination of TCC does occur over a range of initial concentrations. Analyses of catholytes by means of HPLC–MS strongly suggest that the major products of electrolyses at a potential corresponding to the second reduction peak are the expected di- and monochlorinated species; under these conditions, no completely dechlorinated product has been identified, and unreduced starting material is present. In future work, bulk electrolyses of TCC will be conducted at potentials corresponding to the most negative cathodic peak in DMF and DMF–water mixtures, and products will be identified and quantitated with the aid of HPLC–MS. References Halden, R. Environ. Sci. Technol. 2014, 48, 3603–3611.Deo, R.; Halden, R. Water 2013, 5, 1346–1365.Tizaoi, C.; Grima, N.; Hilal, N. Chem. Eng. Process. 2011, 50, 637–643.Ding, S.; Wang, X.; Jiang, W.; Meng, X.; Zhao, R.; Wang, C.; Wang, X. Environ. Sci. Pollut. Res. 2013, 20, 3195–3201.Sirés, I.; Oturan, N.; Oturan, M. A.; Rodríguez, R. M.; Garrido, J.A. Brillas, E. Electrochim. Acta 2007, 52, 5493–5503.Peverly, A.A.; Karty, J.A.; Peters, D.G. J. Electroanal. Chem. 2013, 692, 66–71. Figure 1

Perception of Arabidopsis AtPep peptides, but not bacterial elicitors, accelerates starvation-induced senescence.

Members of the AtPep group of Arabidopsis endogenous peptides have frequently been reported to induce pattern-triggered immunity (PTI) and to increase resistance to diverse pathogens by amplifying the innate immune response. Here, we made the surprising observation that dark-induced leaf senescence was accelerated by the presence of Peps. Adult leaves as well as leaf discs of Col-0 wild type plants showed a Pep-triggered early onset of chlorophyll breakdown and leaf yellowing whereas pepr1 pepr2 double mutant plants were insensitive. In addition, this response was dependent on ethylene signaling and inhibited by the addition of cytokinins. Notably, addition of the bacterial elicitors flg22 or elf18, both potent inducers of PTI, did not provoke an early onset of leaf senescence. Continuous darkness leads to energy deprivation and starvation and therewith promotes leaf senescence. We found that continuous darkness also strongly induced PROPEP3 transcription. Moreover, Pep-perception led to a rapid induction of PAO, APG7, and APG8a, genes indispensable for chlorophyll degradation as well as autophagy, respectively, and all three hallmarks of starvation and senescence. Notably, addition of sucrose as a source of energy inhibited the Pep-triggered early onset of senescence. In conclusion, we report that Pep-perception accelerates dark/starvation-induced senescence via an early induction of chlorophyll degradation and autophagy. This represents a novel and unique characteristic of PEPR signaling, unrelated to PTI.

Interaction of C60 with Tungsten: Modulation of Morphology and Electronic Structure on the Molecular Length Scale

The evolution of morphology and electronic structure in sequential depositions of W and C60 on graphite has been studied by scanning tunneling microscopy/spectroscopy. The deposition sequence decisively controls morphology expression. W deposited on a graphite surface forms small clusters whose morphology is consistent with the predictions of a liquid droplet model in the size regime below 5 nm in diameter; these small clusters then agglomerate without sintering. These agglomerates are immobilized by the subsequent C60 deposition. C60 shows very little interaction with the W-cluster agglomerates, and the formation of typical close packed fullerene islands is observed. The inverse deposition sequence, W deposition on the surface of C60 multilayer islands, leads simultaneously to the formation of ultrasmall W clusters (d < 2 nm) due to limited mobility on the highly corrugated surface, and the intercalation of W in the C60 matrix. The signature of intercalation is cessation of molecule rotation, which is recognized by imaging of molecular orbitals. The electronic structure of C60 is not significantly modified by the presence of W agglomerates, clusters, and intercalation of W. However, if W is deposited on a single layer of C60 its impact on the electronic structure is considerable and expressed in a compression of the band gap, which might be attributable to charge screening due to image charges, or the onset of molecule breakdown. The morphology as well as the electronic structure of this layer is highly inhomogeneous and can be described as a composite of W and C60 due to accumulation of W at the graphite substrate–C60 interface.

On two optomechanical effects of laser-induced electrostriction in dielectric liquids

This paper presents electrostriction from the phenomenological perspective, and gives details on two mechanical effects arising from laser-matter interaction. Electrostriction is the tendency of materials to compress in the presence of a varying electric field. In this paper, the investigated materials are polar and nonpolar dielectric liquids. It is stressed that the dominant factor is the time evolution of the laser pulse, which causes tensile stresses and acoustic waves. The study is supported by experimental realization of electrostriction, which can be detected only at favorable conditions (observed in water, but not in castor oil). This study will shed light in developing measurement techniques (e.g., laser-induced grating spectroscopy) and in explaining the onset of cavities and laser-induced liquid breakdown.

The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation

In past studies, we have observed copious emissions of ionic and atomic Zn from single-crystal ZnO accompanying irradiation of single-crystal ZnO with 193-nm excimer laser irradiation at fluences below the onset of optical breakdown. The Zn+ and ground state Zn° are studied using time-of-flight techniques and are mass selected using a quadrupole mass spectrometer. Simultaneously, we have observed emitted particles that are detectable with a Channeltron electron multiplier but cannot be mass selected. It is a reasonable hypothesis that these particles correspond to a neutral atom or molecule in highly excited long lived states. We provide strong evidence that they correspond to high lying Rydberg states of atomic Zn. We propose a production mechanism involving laser excitation via a two photon resonance excitation of Zn°.

The role of electronic defects and brittle microstructure in laser-driven material failure

The microstructural thermal response of fused silica subjected to laser-induced breakdown was investigated. Rapid thermal annealing of laser modified material at the surface was achieved using a CO2 laser and the relaxation response of photoluminescence, infrared (IR) reflectance, electron and white light microscope images were recorded. Subsequent nanosecond-pulsed laser damage threshold measurements revealed thermally driven kinetics which were dominated by absorbing defect annealing at heat-treatment temperatures (THT) below ∼1200 K and material toughening at higher THT. A decrease in the peak photoluminescence lifetime with THT revealed two types of defects which were correlated with non-bridging IR vibrational modes. Near the glass transition temperature, a weakening of the laser modified material was observed and explained in terms of a residual compressive stress relaxation. A nonlinear absorption model was used to predict optical breakdown threshold and compared with critical fracture predictions based on crack tip annealing. Combined with a qualitative stress relaxation analysis, our model agrees well with the experimental data and yields insight to the rate-limiting contributions driving the onset of laser-induced breakdown in defective silica.