Early stages of ZnS growth studied by stopped-flow UV absorption spectroscopy: effects of educt concentrations on the nanoparticle formation

The growth of ZnS nanoparticles by precipitation from supersaturated aqueous solution is studied by stopped-flow UV absorption spectroscopy. The average size, size distribution, and concentration of the particles are monitored within the sub-second time regime with a resolution of 1.28 ms. Particle growth at these early stages is governed by pronounced ripening. The UV absorption data strongly suggest that growth occurs by preferential adsorption of HS- anions relative to Zn(2+) or ZnOH(+) cations. Correspondingly, the initial sulfide concentration has a much more pronounced influence on the growth kinetics than the initial zinc concentration. These findings are verified by zeta-potential measurements which confirm that the particle surfaces are negatively charged under near-neutral pH conditions.     

Interactions of salicylic acid derivatives with calcite crystals

Investigation of basic interactions between the active pharmaceutical compounds and calcium carbonates is of great importance because of the possibility to use the carbonates as a mineral carrier in drug delivery systems. In this study the mode and extent of interactions of salicylic acid and its amino acid derivates, chosen as pharmaceutically relevant model compounds, with calcite crystals are described. Therefore, the crystal growth kinetics of well defined rhombohedral calcite seed crystals in the systems containing salicylic acid (SA), 5-amino salicylic acid (5-ASA), N-salicyloil-l-aspartic acid (N-Sal-Asp) or N-salicyloil-l-glutamic acid (N-Sal-Glu), were investigated. The precipitation systems were of relatively low initial supersaturation and of apparently neutral pH. The data on the crystal growth rate reductions in the presence of the applied salicylate molecules were analyzed by means of Cabrera & Vermileya's, and Kubota & Mullin's models of interactions of the dissolved additives and crystal surfaces. The crystal growth kinetic experiments were additionally supported with the appropriate electrokinetic, spectroscopic and adsorption measurements. The Langmuir adsorption constants were determined and they were found to be in a good correlation with values obtained from crystal growth kinetic analyses. The results indicated that salicylate molecules preferentially adsorb along the steps on the growing calcite surfaces. The values of average spacing between the adjacent salicylate adsorption active sites and the average distance between the neighboring adsorbed salicylate molecules were also estimated.     

Direct observation of surface ethyl to ethane interconversion upon C2H4 hydrogenation over Pt/Al2O3 catalyst by time-resolved FT-IR spectroscopy

Time-resolved FT-IR spectra of ethylene hydrogenation over alumina-supported Pt catalyst were recorded at 25 ms resolution in the temperature range of 323-473 K using various H2 concentrations (1 atm total gas pressure). Surface ethyl species (2870 and 1200 cm(-1)) were detected at all temperatures along with the gas-phase ethane product (2954 and 2893 cm(-1)). The CH3CH2Pt growth was instantaneous on the time scale of 25 ms under all experimental conditions. At 323 K, the decay time of surface ethyl (122 +/- 10 ms) coincides with the rise time of ethane (144 +/- 14 ms). This establishes direct kinetic evidence for surface ethyl as the relevant reaction intermediate. Such a direct link between the temporal behavior of an unstable surface intermediate and the final product in a heterogeneous catalytic system has not been demonstrated before. A fraction (25%) of the asymptotic ethane growth at 323 K is prompt, indicating that there are surface ethyl species that react much faster than the majority of the CH3CH2Pt intermediates. The dispersive kinetics is attributed to the varying strength of interaction of the ethyl species with the Pt surface caused by heterogeneity of the surface environment. At 473 K, the majority of ethyl intermediates are hydrogenated prior to the recording of the first time slice (24 ms), and a correspondingly large prompt growth of ethane is observed. The yield and kinetics of the surface ethylidyne are in agreement with the known spectator nature of this species.     

Analysis of tear protein patterns of dry-eye patients using fluorescent staining dyes and two-dimensional quantification algorithms.

Tear proteins of nonstimulated tears of 29 patients (healthy subjects, n = 8; dry-eye syndrome patients, n = 12; diabetic dry-eye patients, n = 9) were electrophoretically separated and stained by SYPRO Orange, followed by Coomassie blue staining. Both, the fluorescent and the Coomassie stains were subsequently analyzed by an automated two-dimensional algorithm for finding and quantification of peaks and by a discriminant analysis. Using SYPRO Orange, an average number of peaks/sample between three (at 200 ms) and 15 (at 3000 ms) could be found. In comparison, Coomassie staining resulted only in an average number of six peaks/sample. This corresponds to a sensitivity obtained at approx. 400-600 ms exposure time of SYPRO Orange stained gels. For all exposure times, the protein patterns of the three clinical groups were statistically significantly different from each other (P < 0.05). Only at 200 ms the distances between the groups decreased slightly. The Coomassie-stained gels revealed only a mid range discrimination power similar to that of 200-400 ms exposure in the fluorescing gels. The use of SYPRO Orange provides faster results than those obtained by Coomassie staining. In addition, the sensitivity of staining can be varied even in the same gel by changing the exposure time. The use of the two-dimensional algorithm allows to distinguish between the three clinical groups in accordance to earlier studies using one-dimensional densitographic raw data. Thus, the high speed of evaluation and the more sensitive results as compared to earlier studies could be a step further in the use of tear protein patterns in the diagnosis of DRY.     

不同粒径尿微晶的ζ电位、自相关曲线和聚集状态

采用纳米粒度仪和透射电子显微镜(TEM)比较研究了10例尿石症患者和10例健康对照者的尿液经不同孔径滤膜(0.22、0.45、1.2、3.0、10μm)过滤后,尿微晶平均粒径(d)、粒度分布、自相关曲线、ζ电位和聚集状态的变化。随着滤膜孔径由0.22μm增至10μm,患者尿微晶的d值由162 nm增至3 227 nm,自相关曲线平滑性变差,自相关时间(Ta)由1.92 ms增至2100 ms,ζ由-2.65 mV减小至-9.21 mV,TEM显示尿微晶尺寸差异大,部分尿微晶处于聚集状态。而对照者尿微晶的d值仅由187 nm增加至1 010 nm,自相关曲线平滑,Ta由1.40 ms增加至6.67 ms,ζ平均值由-5.22 mV减小至-6.89 mV,TEM显示尿微晶均匀分散,尺寸较小。上述结果表明:尿石患者的尿液体系不稳定,其尿微晶聚集程度高,导致尿石症形成的危险性增加。     

Effectiveness of tumor electrochemotherapy as a function of electric pulse strength and duration

The aim of this study was to evaluate the effectiveness of electrochemotherapy (ECT) as a function of various combinations of pulse strength and duration. C57Bl mice bearing LLC tumors were injected i.p. with bleomycin (BLM) at doses 5 mg/kg in 0.2 ml of physiological saline. Thirty minutes later, tumors were positioned between plate electrodes and were pulsed with eight-square wave electric pulses with an individual pulse strength of 900, 1100, 1300 or 1500 V/cm and duration of 0.1, 0.25, 0.5 or 1 ms. Effectiveness of ECT was estimated by measuring inhibition of tumor growth and by estimating extent of necrosis in histological slices of the treated tumors. At pulse strength of 900 V/cm and duration of 0.1 ms, electrochemotherapy was ineffective. Noticeable inhibition of tumor growth (threshold of ECT) was obtained when pulse duration at this field strength was increased up to 0.25 ms. Further increase of pulse strength and/or duration resulted in progressive enhancement of antitumor effects. Using tumor doubling time (DT) as a criteria, we showed that the same efficacy of ECT could be achieved using various pairs of values for pulse strength and duration. Largest antitumor efficacy of ECT was obtained at pulse strength of 1500 V/cm and duration of 1 ms. These pulse conditions applied alone neither significantly suppressed tumor growth nor induced noticeable side effects of the surrounding tissues. The results of this study thus suggest that the effectiveness of electrochemotherapy can be enhanced (in comparison to widely accepted conditions of electrochemotherapy--8 pulses of 1300 V/cm, 0.1 ms) if 1500-V/cm, 1-ms electric pulses are used. Our study also implicates that other pulse conditions could be found for this enhanced ECT.     

Molecular exchange through the vesicle membrane of siloxane surfactant in water/glycerol mixed solvents

The effect of glycerol on the permeability of vesicle membranes of a siloxane surfactant, the block copolymer polyethyleneoxide-b-polydimethylsiloxane-polyethyleneoxide, (EO)15-(DMS)15-(EO)15, was studied with freeze-fracture transmission electron microscopy (FF-TEM) and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy. The FF-TEM results show that, in pure water, the surfactant can form small vesicles with diameters of less than 25 nm, as well as a few multilamellar vesicles with diameters larger than 250 nm. Gradual substitution of water with glycerol to a glycerol content of 40% leads to significant structural transformations: small vesicles are gradually swollen, and large multilamellar vesicles disappear. A glycerol content of 60% results in the complete disintegration of the vesicles into membrane fragments. PFG-NMR measurements indicate that the vesicle membrane does not represent an effective barrier for water molecules on the NMR time scale; hence, the average residence time of water in the encapsulated state is below tau b = 2 ms. In contrast, the average residence time of glycerol molecules in the encapsulated state can be as large as tau b = 910 ms. The permeability of the vesicle membrane increases with increasing glycerol concentration in the solvent: At a concentration of 40%, the residence time tau b is lowered to approximately 290 ms. After vesicle destruction at higher glycerol concentrations, a small glycerol fraction is still bound by membrane fragments that are formed after the disintegration of the vesicles.     

FLASH PHOTOLYSIS OF BOVINE SERUM ALBUMIN: IDENTIFICATION AND DECAY KINETICS OF TRANSIENT INTERMEDIATES

Abstract. Using the method of flash photolysis, the triplet of the single indole side chain of human serum albumin was detected at room temperature. In a nitrogen saturated solution, this species was found to decay exponentially for over a factor of ten with a lifetime τ 0.5 ms. Analogous experiments, reported here, with bovine serum albumin yield a non-exponential decay which may be decomposed into two components. The yield of the longer lived triplet, with an average τ of ∼6 ms, is significantly enhanced by addition of a 20 fold excess of sodium dodecyl sulfate or 1 M Br^-. The yield of the shorter lived triplet, τ 0.4 ms, is unaffected by these treatments as was previously observed for the single indole in HSA. Thus, the short lived triplet may be assigned to the indole in BSA which is homologous to the one in HSA. The longer lived triplet may be assigned to the remaining indole of BSA. On the bases of wavelength dependence studies, two additional transients may be identified; the electron adduct of the disulfide bond, λ; 420 with a τ 30 ms, and the neutral indole radical,λ; 520 nm with τ ls. These results suggest that the triplet, because of its long τ, will be a valuable intrinsic reporter group for the study of the structure and dynamics of proteins in solution at room temperature.     

Mapping the cytochrome C folding landscape

The solution to the riddle of how a protein folds is encoded in the conformational energy landscape for the constituent polypeptide. Employing fluorescence energy transfer kinetics, we have mapped the S.cerevisiae iso-1 cytochrome c landscape by monitoring the distance between a C-terminal fluorophore and the heme during folding. Within 1 ms after denaturant dilution to native conditions, unfolded protein molecules have evolved into two distinct and rapidly equilibrating populations: a collection of collapsed structures with an average fluorophore-heme distance (r) of 27 A and a roughly equal population of extended polypeptides with r > 50 A. Molecules with the native fold appear on a time scale regulated by heme ligation events ( approximately 300 ms, pH 7). The experimentally derived landscape for folding has a narrow central funnel with a flat upper rim on which collapsed and extended polypeptides interchange rapidly in a search for the native structure.     

Room Temperature Phosphorescence from Tryptophan and Halogenated Tryptophan Analogs in Amorphous Sucrose

Abstract. Tryptophan phosphorescence lifetime and quantum yield are sensitive to the local environment. The phosphorescence from tryptophan analogs, however, has not been studied. We report here data on the room temperature phosphorescence of tryptophan, 4-, 5- and 6-fluoro-DL-tryptophan (4-F-trp, 5-F-trp and 6-F-trp) and 5-bromo-DL-tryptophan (5-Br-trp) embedded in glassy powders of freeze-dried sucrose. In aqueous solution, the absorption of the analogs was either blue-shifted (4-F-trp), red-shifted (5-F-trp and 5-Br-trp) or not shifted (6-F-trp) with respect to tryptophan. The phosphorescence emission spectra of all analogs were red-shifted compared to trp (442 nm) with maxima at 446 nm (5-F-trp), 451 mn (6-F-trp), 452 nm (5-Br-trp) and 469 nm (4-F-trp). The 5-F-trp and 6-F-trp analogs had emission intensities similar to tryptophan (relative quantum yields of 0.68 and 0.91, respectively, compared to tryptophan), while the intensities of the 4-F and 5-Br analogs were lower (relative quantum yields of 0.039 and 0.022, respectively). All analogs exhibited complex decay behavior requiring several exponentials for an adequate fit; the average lifetimes were all lower than that of trp (1039 ms). The average lifetimes of the fluorinated analogs (5-F, 721 ms; 6-F, 482 ms and 4-F, 35 ms) scaled approximately with the relative quantum yields while that of 5-Br (0.53 ms) was significantly lower. Analysis of the individual lifetimes suggested that the fluorinated analogs differ in their sensitivity to environmental interactions, with 5-F- and 6-F-trp quenched 1.5-2-fold and 4-F-trp about 23-fold more efficiently than tryptophan. The red-shifted 5-F-trypto-phan analog, which has been incorporated into proteins, may provide an alternative phosphorescence probe for selective phosphorescence detection of a specific protein in a complex mixture.     

Size of elementary clusters and process period in silver nanoparticle formation

The time dependence of small-angle X-ray scattering (SAXS) curves for silver nanoparticle formation was followed in situ at a time resolution of 0.18 ms, which is 3 orders of magnitude higher than that used in previous reports (ca. 100 ms). The starting materials were silver nitrate solutions that were reacted with reducing solutions containing trisodium citrate. The SAXS analyses showed that silver nanoparticles were formed in three distinct periods from a peak diameter of ca. 0.7 nm (corresponding to the size of a Ag(13) cluster) during the nucleation and the early growth period. The Ag(13) clusters are most likely elementary clusters that agglomerate to form silver nanoparticles.     

Watching nanoparticles form: an in situ (small-/wide-angle X-ray scattering/total scattering) study of the growth of yttria-stabilised zirconia in supercritical fluids

Understanding nanoparticle-formation reactions requires multi-technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS)/total-scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria-stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y(2)O(3) equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub-nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit-cell dimensions. At yttria-doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time-resolved nanoparticle size distributions are calculated based on whole-powder-pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle-size distributions occur. In situ total scattering provides structural insight into the sub-nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six-coordinated zirconium atoms in the initial amorphous clusters to eight-coordinated zirconia atoms in stable crystallites. Representative samples prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.     

Temporal evolution of an electron-free afterglow in the pulsed plasma polymerisation of acrylic acid

By use of time and energy-resolved mass spectrometry, negative ions with masses ranging from m/z = 1-287 amu have been observed in the afterglow of a low-pressure (10 mTorr) pulsed acrylic acid polymerizing plasma. The most intense peaks, seen at m/z = 71, 143, 215, and 287, are assigned to the dehydrogenated oligomer of the form [nM-H](-) for n = 1, 2, 3, and 4, respectively. The results strongly suggest that both m/z = 71 and 143 ions are produced in the on period of the pulse cycle (0.1 ms duration), with higher masses m/z = 215 and 287 being produced by neutral ion chemistry in the off period (up to 40 ms in duration). The increase in the intensity of the [3M-H](-) and [4M-H](-) peaks in the off period is accompanied by a rapid fall in the concentration of [M-H]- ions and electrons, the latter decreasing from approximately 10(15) m(-3) to zero within 150 micros. Deep into the afterglow, Langmuir probe measurements show that the charge species only consist of positive and negative ions, present at equal concentrations in excess of approximately 10(14) m(-3) even after 10 ms that is, the plasma is wholly electron free. To describe the growth of large negative ions a number of possible ion-neutral chemical pathways have been postulated, and a calculation of the ambipolar diffusion rates to the walls suggests that, in the off period, the positive and negative ion contribution to the deposition rate is small ( approximately 1%) compared to the net total deposition rate. However, the observations do indicate that it may be necessary to update models of film growth in the pulsed plasma polymerization of acrylic acid to account for negative ions.     

Preparation and photoluminescence properties of Y2SiO5:Eu3+ nanocrystals

The sol-emulsion-gel method is used for the preparation of about 5-7 nm size Eu2O3 doped and coated Y2SiO5 nanoparticles at 1300 degrees C. Here, we report the role of surface coating, dopant concentration and temperature of heating on the modification of crystal structure and the photoluminescence properties of Y2SiO5:Eu3+ nanocrystals. It is found that photoluminescence properties are sensitive to the crystal structure which is again controlled by surface coating, concentration and heating temperature. The decay times are 0.76, 1.14, 1.23 and 1.40 ms for 0.25, 0.5, 1.0 and 2.5 mol% Eu2O3 doped Y2SiO5 nanocrystals prepared at 1100 degrees C (X1-Y2SiO5). However, in X2-Y2SiO5 crystal phase (at 1300 degrees C) the average decay times are 1.05, 1.35, 1.55 and 1.60 ms for 0.25, 0.5, 1.0 and 2.5 mol% Eu2O3 doped Y2SiO5 nanocrystals, indicating the photoluminescence properties depend on both the crystal structure and the concentration of ions. The emission intensity of the peak at 612 nm (5D0-->7F2) of the Eu3+-ions is found to be sensitive to the doping and surface coating of Y2SiO5 nanocrystals. The decay times are 1.55 and 1.70 ms for 1300 degrees C heated 1.0 mol% Eu2O3 doped and coated Y2SiO5 nanocrystals, respectively. Our analysis suggests that the site symmetry of ions plays a most important role in the modification of radiative relaxation mechanisms and as a result on the overall photoluminescence properties.     

A study of the formation, purification and application as a SWNT growth catalyst of the nanocluster [HxPMo12O40[subset]H4Mo72Fe30(O2CMe)15O254(H2O)98

The synthetic conditions for the isolation of the iron-molybdenum nanocluster FeMoC [HxPMo12O40 [subset]H4Mo72Fe30(O2CMe)15O254(H2O)98], along with its application as a catalyst precursor for VLS growth of SWNTs have been studied. As-prepared FeMoC is contaminated with the Keplerate cage [H4Mo72Fe30(O2CMe)15O254(H2O)98] without the Keggin [HxPMo12O40]n- template, however, isolation of pure FeMoC may be accomplished by Soxhlet extraction with EtOH. The resulting EtOH solvate is consistent with the replacement of the water ligands coordinated to Fe being substituted by EtOH. FeMoC-EtOH has been characterized by IR, UV-vis spectroscopy, MS, XPS and 31P NMR. The solid-state 31P NMR spectrum for FeMoC-EtOH (delta-5.3 ppm) suggests little effect of the paramagnetic Fe3+ centers in the Keplerate cage on the Keggin ion's phosphorous. The high chemical shift anisotropy, and calculated T1 (35 ms) and T2 (8 ms) values are consistent with a weak magnetic interaction between the Keggin ion's phosphorus symmetrically located within the Keplerate cage. Increasing the FeCl2 concentration and decreasing the pH of the reaction mixture optimizes the yield of FeMoC. The solubility and stability of FeMoC in H2O and MeOH-H2O is investigated. The TGA of FeMoC-EtOH under air, Ar and H2 (in combination with XPS) shows that upon thermolysis the resulting Fe : Mo ratio is highly dependent on the reaction atmosphere: thermolysis in air results in significant loss of volatile molybdenum components. Pure FeMoC-EtOH is found to be essentially inactive as a pre-catalyst for the VLS growth of single-walled carbon nanotubes (SWNTs) irrespective of the substrate or reaction conditions. However, reaction of FeMoC with pyrazine (pyz) results in the formation of aggregates that are found to be active catalysts for the growth of SWNTs. Activation of FeMoC may also be accomplished by the addition of excess iron. The observation of prior work's reported growth of SWNTs from FeMoC is discussed with respect to these results.     

ZnO/ZnS大面积单晶异质结及其光电性能研究

ZnO和ZnS是重要的Ⅱ-Ⅵ族宽禁带半导体材料,二者之间形成的异质结具有Ⅱ型能带结构,可以促使受激载流子实现空间分离,延长受激载流子的寿命,从而提高材料的光催化和光电探测性能。本文利用物理气相沉积方法,首次在ZnO块状单晶衬底上生长了一层ZnS单晶薄膜,薄膜由厚约4nm、边长几百纳米,取向一致的等边三角形纳米片组成。X射线衍射和透射电子显微镜的表征结果显示,ZnS薄膜与ZnO衬底具有单一外延取向关系。阴极射线荧光光谱表明ZnS薄膜的制备显著提高了ZnO单晶片可见光荧光发光峰的强度。此外,对ZnO/ZnS异质结的紫外光电探测性能的研究结果显示,异质结对不同波长的紫外光均有响应,光响应的上升弛豫时间和下降弛豫时间分别为200ms和1050ms,展示了较好的光电应用潜力。     

Investigation of high-speed gas chromatography using synchronized dual-valve injection and resistively heated temperature programming

High-speed temperature programming is implemented via the direct resistive heating of the separation column (2.3m MXT-5 Silicosteel column with a 180 microm I.D. and a 0.4 microm 5% phenyl/95% dimethyl polysiloxane film). Resistive temperature programming was coupled with synchronized dual-valve injection (with an injection pulse width of 2 ms), producing a complete high-speed gas chromatography (GC) system. A comparison of isothermal and temperature programmed separations of seven n-alkanes (C(6) and C(8)-C(13)) shows a substantial improvement of peak width and peak capacity with temperature programming. The system was further implemented in separations of a mixture of analytes from various chemical classes. Separations of the n-alkane mixture using three different temperature programming rates are reported. A temperature programming rate as high as 240 degrees C/s is demonstrated. The method for determination of temperature programming rate, based on isothermal data, is discussed. The high-speed resistive column heating temperature programming resulted in highly reproducible separations. The highest rate of temperature programming (240 degrees C/s) resulted in retention time and peak width RSD, on average, of 0.5 and 1.4%, respectively, for the n-alkane mixture. This high level of precision was achieved with peak widths-at-half-height ranging from 13 to 36 ms, and retention times ranging from 147 to 444 ms (for n-hexane to n-tridecane).     

Subsecond luminescence intensity fluctuations of single CdSe quantum dots

Photoluminescence (PL) intermittency characteristics are examined for single quantum dots (QDs) in a CdSe QD sample synthesized at a slow rate at 75 degrees C. Although the PL quantum efficiency was relatively low ( approximately 0.25), we noticed that the PL intensity of single CdSe QDs fluctuated on a subsecond time scale with short-lived "on" and "off" states. The subsecond PL intensity fluctuations of CdSe QDs are different from "on" and "off" PL blinking generally observed for QDs fluctuating on a millisecond to minute time scale. We characterized single QDs by identifying polarized excitations, topographic imaging using atomic force microscopy (AFM), and transmission electron microscopy (TEM). From analysis of the PL intensity trajectories from >100 single CdSe QDs, the average intermittency time was 213 ms. From the PL quantum efficiency, slow growth of QDs, intensity trajectory analyses, and previous reports relating surface trap states and PL properties of QDs, we attribute the subsecond PL intensity fluctuations of single CdSe QDs and short-lived "on" and "off" states to a high-density distribution of homogeneous surface trap states.     

Electron and photon emission accompanying deformation and fracture of polycarbonate

Electron and photon emission accompanying tensile loading and failure of polycarbonate show weak emissions during the onset of neck formation and intense emissions during the fracture event itself. These results are interpreted in terms of formation of active species by bond breaking followed by emission driven by energy released by recombination. Fast time scale measurements during fracture show that intense electron and photon emission typically begins about 50 μs prior to the completion of fracture and is most intense at the completion of fracture. The gradual onset reflects the final stages of growth of the failure-initiating defect. Defect growth was monitored by measuring the intensity of a light beam transmitted through the gauge length of the sample; the transmission is sensitive to scattering by surface and bulk defects. A marked decrease in transmission begins some tens of ms prior to fracture due to scattering from the fracture-initiating defect. These measurements allow accurate correlations of defect growth with the onset of the electron and photon signals. © 1993 John Wiley & Sons, Inc.     

Vapour-growth of Sn on stearic acid molecular layers

Tin metal was vacuum deposited at room temperature on to Langmuir–Blodgett (LB) films with surfaces of either hydrophilic head groups or hydrophobic tail groups. Different growth modes on different surfaces of the LB films were observed with an atomic force microscope. Fine Sn particles deposited on the hydrophobic surface were uniform in size and similar in shape, but on the hydrophilic surface large Sn particles were observed. Chemical interactions between organic functional groups and deposited metal seems critical for the manner of crystal growth. The possibility of control over the crystallization of metals using two-dimensionally assembled organic molecules is demonstrated.