ToF-SIMS Depth Profiling of PS-b-PMMA Block Copolymers Using Arn+, C60++, and Cs+ Sputtering Ions.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a high performance tool for molecular depth profiling of polymer films, in particular when they are structured in microphases. However, a major issue is the degradation of polymer materials under ion irradiation in reactions such as cross-linking, chain breaking, or reorganization processes of polymers which have been demonstrated for materials such as polystyrene (PS) and poly(methyl methacrylate) (PMMA). This work aims at comparing ToF-SIMS molecular depth profiling of structured polymers (polystyrene (PS)-b-polymethyl methacrylate (PMMA) block copolymers (BCP)) using either ultralow energy cesium or the more recently introduced C60++ (under NO dosing and with sample cooling) and argon cluster ion beams (using Ar1500+ ions at 5 keV). The latter improved the quality of the depth profiles, especially the argon cluster ion beam, as it is characterized by a greater homogeneity for the sputter yields of PS and PMMA. No significant artifacts were observed, and this was confirmed by the comparison of depth profiles obtained from films with variable thickness, annealing time, and morphology (cylindrical blocks vs spherical blocks). Comparison to a theoretical model (hexagonal centered pattern) ensured that the ToF-SIMS depth profiles described the real morphology and may thus be a relevant characterization tool to verify the morphology of the films as a function of the deposition parameters.

3D correlative morphological and elemental characterization of materials at the deep submicrometre scale.

This paper shows how X-ray computed nanotomography (CNT) can be correlated with focused ion beam time-of-flight secondary ion mass spectrometry (FIB-TOF-SIMS) tomography on the same sample to investigate both the morphological and elemental structure. This methodology is applicable to relatively large specimens with dimensions of several tens of microns whilst maintaining a high spatial resolution of the order of 100 nm. However, combining X-ray CNT and FIB-TOF-SIMS tomography requires innovative sample preparation protocols to allow both experiments to be conducted on exactly the same sample without chemically or structurally modifying the sample between measurements. Moreover, dedicated algorithms have been developed for effective data fusion that is biased with nine degrees of freedom. This methodology has been tested using a porous and heterogeneous solid oxide fuel cell (SOFC) that has features varying in size by three orders of magnitude - from hundreds of nanometre large pores and grains to tens of micron wide functional layers.

3D analysis of advanced nano-devices using electron and atom probe tomography.

The structural and chemical properties of advanced nano-devices with a three-dimensional (3D) architecture have been studied at the nanometre scale. An original method has been used to characterize gate-all-around and tri-gate silicon nanowire transistor by combining electron tomography and atom probe tomography (APT). Results show that electron tomography is a well suited method to determine the morphological structure and the dimension variations of devices provided that the atomic number contrast is sufficient but without an absolute chemical identification. APT can map the 3D chemical distribution of the atoms in devices but suffers from strong distortions in the dimensions of the reconstructed volume. These may be corrected using a simple method based on atomic density correction and electron tomography data. Moreover, this combination is particularly useful in helping to understand the evaporation mechanisms and improve APT reconstructions. This paper demonstrated that a full 3D characterization of nano-devices requires the combination of both tomography techniques.

Strain measurement at the nanoscale: Comparison between convergent beam electron diffraction, nano-beam electron diffraction, high resolution imaging and dark field electron holography.

Convergent beam electron diffraction (CBED), nano-beam electron diffraction (NBED or NBD), high resolution imaging (HRTEM and HRSTEM) and dark field electron holography (DFEH or HoloDark) are five TEM based techniques able to quantitatively measure strain at the nanometer scale. In order to demonstrate the advantages and disadvantages of each technique, two samples composed of epitaxial silicon-germanium layers embedded in a silicon matrix have been investigated. The five techniques are then compared in terms of strain precision and accuracy, spatial resolution, field of view, mapping abilities and ease of performance and analysis.

Specifications for hard condensed matter specimens for three-dimensional high-resolution tomographies.

Tomography is a standard and invaluable technique that covers a large range of length scales. It gives access to the inner morphology of specimens and to the three-dimensional (3D) distribution of physical quantities such as elemental composition, crystalline phases, oxidation state, or strain. These data are necessary to determine the effective properties of investigated heterogeneous media. However, each tomographic technique relies on severe sampling conditions and physical principles that require the sample to be adequately shaped. For that purpose, a wide range of sample preparation techniques is used, including mechanical machining, polishing, sawing, ion milling, or chemical techniques. Here, we focus on the basics of tomography that justify such advanced sample preparation, before reviewing and illustrating the main techniques. Performances and limits are highlighted, and we identify the best preparation technique for a particular tomographic scale and application. The targeted tomography techniques include hard X-ray micro- and nanotomography, electron nanotomography, and atom probe tomography. The article mainly focuses on hard condensed matter, including porous materials, alloys, and microelectronics applications, but also includes, to a lesser extent, biological considerations.

How ischaemic region shape affects ST potentials in models of cardiac tissue.

This numerical study uses a simple bidomain model of cardiac tissue to compare the effect of three different ischaemic region geometries (rectangular, cylindrical and semi-ellipsoidal) on the extracellular epicardial potentials during the ST segment. Results are obtained using anisotropic conductivities based on experimentally derived data. The model is then altered, to include heterogeneous conductivities in the ischaemic region and larger border zone widths, in order to better reproduce realistic scenarios. Initial results for the rectangular and cylindrical ischaemic shapes show a central depression over the ischaemic region, for low ischaemic thicknesses, which separates into three depressions as the ischaemic thickness increases. For ischaemic thicknesses above 70% an elevation appears over the ischaemic region and this increases in magnitude as the ischaemia becomes transmural. Results for the semi-ellipsoidal shape, however, differ, with the central depression separating into only two depressions as the thickness increases. Changing the conductivity inside the ischaemic region significantly affects results for each geometry, with depression staying over the ischaemic region for much higher levels of ischaemia (up to 90% thickness). Increasing the intramural border zone thickness did not significantly affect the epicardial potential distributions.

Quantitative profiling of SiGe/Si superlattices by time-of-flight secondary ion mass spectrometry: the advantages of the extended Full Spectrum protocol.

The abundance of work on SiGe-based devices demonstrates the importance of the compositional characterization of such materials. However, Secondary Ion Mass Spectrometry (SIMS) characterization of SiGe layers often suffers from matrix effects due to the non-linear variation of ionization yields with Ge content. Several solutions have been proposed in order to overcome this problem, each having its own limitations such as a restricted germanium concentration range, or a weak sensitivity to dopants or impurities. Here, we studied the improvements brought by an alternative protocol: the extended Full Spectrum protocol, which states proportionality between the composition of the secondary ion beam and that of the actual material. Previous studies on this protocol showed that it was extremely precise and reproducible for Ge quantification in a permanent regime, because of minimized matrix effects. In this study we thus investigated its accuracy for the simultaneous quantitative depth profiling of both matrix elements (Si, Ge) and impurities (B, C or P) in strained SiGe/Si superlattices by comparing results with those from more classic protocols. The profiles provided by the extended Full Spectrum protocol were found to be accurate, and to exhibit better properties than classic protocols in terms of signal/noise ratio and signal stability, along with a slight enhancement in depth resolution.

Dark field electron holography for strain measurement.

Dark field electron holography is a new TEM-based technique for measuring strain with nanometer scale resolution. Here we present the procedure to align a transmission electron microscope and obtain dark field holograms as well as the theoretical background necessary to reconstruct strain maps from holograms. A series of experimental parameters such as biprism voltage, sample thickness, exposure time, tilt angle and choice of diffracted beam are then investigated on a silicon-germanium layer epitaxially embedded in a silicon matrix in order to obtain optimal dark field holograms over a large field of view with good spatial resolution and strain sensitivity.

Structural studies of pulsed-laser deposited nanocomposite metal-oxide films.

Pulsed laser deposition in vacuum has been used to develop metal-oxide nanocomposite films with well controlled structural quality. Results for the copper-aluminium oxide (Cu:Al2O3) system are used to illustrate the main morphological and structural features of these films. High resolution transmission electron microscopy (TEM) analysis shows that the films consist of Cu nanocrystals with average dimensions that can be controlled between 2 nm and 10 nm embedded in an amorphous Al2O3 matrix. It is observed that the in-plane shape of the nanocrystals evolves from circular to elongated, and the number of nanocrystals per unit area decreases as their size increases. This evolution is explained in terms of nucleation at the substrate surface and coalescence during the later stages of growth. The thermal stability of the films has been studied by in situ TEM annealing and no transformation could be observed up to about 800 degrees C when partial crystallization of the Al2O3 starts.

A multifrequency electron spin resonance study of T4 lysozyme dynamics.

Electron spin resonance (ESR) spectroscopy at 250 GHz and 9 GHz is utilized to study the dynamics and local structural ordering of a nitroxide-labeled enzyme, T4 lysozyme (EC 3.2.1.17), in aqueous solution from 10 degrees C to 35 degrees C. Two separate derivatives, labeled at sites 44 and 69, were analyzed. The 250-GHz ESR spectra are well described by a microscopic ordering with macroscopic disordering (MOMD) model, which includes the influence of the tether connecting the probe to the protein. In the faster "time scale" of the 250-GHz ESR experiment, the overall rotational diffusion rate of the enzyme is too slow to significantly affect the spectrum, whereas for the 9-GHz ESR spectra, the overall rotational diffusion must be accounted for in the analysis. This is accomplished by using a slowly relaxing local structure model (SRLS) for the dynamics, wherein the tether motion and the overall motion are both included. In this way a simultaneous fit is successfully obtained for both the 250-GHz and 9-GHz ESR spectra. Two distinct motional/ordering modes of the probe are found for both lysozyme derivatives, indicating that the tether exists in two distinct conformations on the ESR time scale. The probe diffuses more rapidly about an axis perpendicular to its tether, which may result from fluctuations of the peptide backbone at the point of attachment of the spin probe.

Dynamics and ordering in mixed model membranes of dimyristoylphosphatidylcholine and dimyristoylphosphatidylserine: a 250-GHz electron spin resonance study using cholestane.

We report here on a 250-GHz electron spin resonance (ESR) study of macroscopically aligned model membranes composed of mixtures of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylserine (DMPS), utilizing the nixtroxide-labeled cholesterol analog cholestane (CSL). Two clearly resolved spectral components, distinct in both their ordering and dynamics, are resolved. The major component in membranes composed mostly of DMPC shows typical characteristics, with the long axis of CSL parallel to the bilayer normal with slow (10(6)

The distribution of electron trapping in DNA: one-electron-reduced oligodeoxynucleotides of adenine and thymine.

A series of single- and double-stranded oligodeoxynucleotides of adenine and thymine, 8 to 12 nucleotides in length, were one-electron-reduced at 10 K in a > 8 M LiCl/H2O glass. The Q-band electron paramagnetic resonance (EPR) spectra of these radicals show that thymine is the dominant trapping site for mobile electrons in these oligomers. The spectra of the reduced oligomers in the series pd(AnT10-n).pd(A10-nTn) with n = 5-->10 showed a trend which is interpreted as either an increase in the probability of trapping at an adenine base in tracks of adenine > 7 base pairs in length, or the presence of different protonated states of the one-electron-reduced bases due to the adoption of a different conformational state for longer tracks of adenine, or a combination of these two possibilities. Analysis of the trends in the EPR spectra of the radicals as a function of sequence using multicomponent analysis is presented.

Metabolism of cycloate in radish leaf: metabolite identification by packed capillary flow fast atom bombardment tandem mass spectrometry.

The metabolism of cycloate, a thiocarbamate herbicide, was investigated in mature radish leaf. Twelve new metabolites were identified by liquid chromatographic/mass spectrometric analysis using fast atom bombardment and packed capillary liquid chromatography columns. Full-scan and tandem mass spectrometric methods were employed. Application of the on-column focusing technique resulted in identifications with injections of as little as 15 ng of metabolite (20 ppb in radish). This injection technique allows the practical use of packed capillary liquid chromatography/mass spectrometry in sample-limited applications. Cycloate is oxidized to several ring-hydroxylated isomers that are subsequently glucosylated and esterified with malonic acid. Cycloate is also conjugated with glutathione. Metabolic hydrolysis of the glutathione conjugate formed a cysteine conjugate that is further metabolized by amidation with either malonic or acetic acid. Transamination of the cysteine conjugate gave a thiolactic acid derivative. Metabolites were also identified that were the result of both ring-hydroxylation and conjugation with glutathione. One of these, an N-acetylcysteine conjugate, is the first report of a mercapturic acid in plants. The structures of two of the new metabolites were confirmed by chemical synthesis.

Distribution of targets for avian retrovirus DNA integration in vivo.

The targeting of DNA integration in retrovirus-infected cells is a central yet very poorly understood aspect of the biology of the virus. To investigate this problem, we have assessed the use of specific sites for integration targets of avian leukosis virus (ALV) DNA within defined regions of turkey embryo fibroblast (TEF) cellular DNA. For this purpose, we developed an assay of sufficient sensitivity and specificity to allow detection and location of single integration events in a population of 5 million cells. Targets selected for study were either regions cloned by virtue of a previous integration event or clones chosen at random from cellular DNA. By use of this approach, we found that all genomic regions tested contained integration targets, with a frequency that varied from approximately 0.2 to 4 times that expected for random integration. Within regions, the frequency of use of specific sites varied considerably, with some sites used up to 280 times random frequency. When one region was introduced into cells at moderately high copy number by transfection, it provided integration targets in a pattern very much like that seen with the same sequence in vitro. On the basis of our sampling, we conclude that most or all regions of the TEF genome are accessible to ALV retroviral integration. As with integration in vitro, integration specificity seems to be determined largely by local structural features rather than accessibility of specific regions.

Leukocyte common antigen-related receptor-linked tyrosine phosphatase. Regulation of mRNA expression.

Receptor-linked tyrosine phosphatases regulate cell growth by dephosphorylating proteins involved in tyrosine kinase signal transduction. Within this gene family, the leukocyte common antigen-related (LAR) gene is of particular interest with respect to the nervous system because it has sequence similarity to the neural cell adhesion molecule N-CAM and is located in a chromosomal region (1p32-33) frequently deleted in neuroectodermal tumors. However, immunostaining has detected LAR in non-neural tissues, but not in the central nervous system, peripheral neurons, or adrenal medulla. In this study, rat brain cDNA library LAR clones corresponding to cytoplasmic and 3'-untranslated regions of human LAR were identified. Using probes derived from these clones, high stringency Northern blots revealed approximately 8 kilobase and variable length tissue- and cell-specific LAR transcripts in cortex, brainstem, cerebellum, spinal cord, peripheral tissues, and cultured neural, glial, and pheochromocytoma cells. In situ hybridization showed expression by brain and dorsal root ganglion neurons. LAR expression was developmentally regulated in a region-dependent manner. Changes in LAR expression were also found during nerve growth factor-induced PC12 pheochromocytoma cell differentiation and with contact-mediated inhibition of fibroblast growth. These observations and studies demonstrating neurotrophins functioning via tyrosine kinase receptors suggest that LAR represents an additional mechanism regulating neural development.

Current techniques in laparoscopic appendectomy.

An improved technique for laparoscopic appendectomy based on an experience of > 120 cases is presented. This method includes numerous additions to and modifications of previously described techniques and is effective for gangrenous and perforated appendicitis as well as for less severe cases. The most important elements are that (a) it is a safer procedure for attaining insertion of the Veress needle and the primary trocar; (b) it employs electrocautery to separate the appendix from the mesoappendix; (c) an Endosac can be used for removal of the appendix from the abdomen without contamination of the abdominal wall; (d) no laser is necessary; and (e) staples are rarely necessary.

Laparoscopic appendectomy: treatment of choice for suspected appendicitis.

Results and complications in 100 patients treated over a 3-year period with the laparoscopic approach for clinically diagnosed acute appendicitis are evaluated. They are compared with results and complications in 100 patients with the same diagnosis who had been treated with the open technique performed by the same surgeon during the same 3 years. The results suggest that laparoscopy provides excellent exposure of the appendix regardless of its position. In the absence of pathology of the appendix, laparoscopy allows for a thorough examination of the entire abdomen and pelvis and good exposure and definitive treatment of most surgical conditions encountered. In the event of appendicitis, regardless of its severity, laparoscopic appendectomy results in less postoperative pain, shorter hospital stays, faster return to normal activities, fewer postoperative complications, and superior cosmetic results. Our experience suggests that the laparoscopic approach is the best approach to diagnosis and treatment of the conditions encountered in patients with suspected appendicitis.

Recurrent inguinal hernia in relation to ideal body weight.

The records of 686 patients who underwent herniorrhaphy for primary or initially recurrent inguinal hernia during the years 1975 through 1985 were reviewed. Patients were divided into groups according to percentage of ideal body weight. Analysis showed that, compared with the patients with primary hernia, a larger proportion of patients with recurrent hernia were near or below ideal body weight. A follow-up survey of 64 patients who underwent primary repair of hernia indicated that the percentage of ideal body weight of a patient had no apparent effect on the recurrence rate of inguinal hernia.

Inguinal hernia repair with routine use of Marlex mesh.

An analysis of an 11 year experience with the routine use of Marlex (polypropylene) mesh reinforcement of the canal floor in both indirect and direct inguinal herniorraphy is presented. All patients in good general health were accepted regardless of their age or weight. Survey responses were obtained from a large and representative sample of this experience. The results of this series demonstrate that Marlex mesh is well tolerated in the inguinal canal and that the recurrence rates are low for both direct and indirect inguinal hernias. In particular, there were no recurrences in patients less than 60 years of age and no recurrence in patients weighing less than 185 kilograms. The average weight of patients with a recurrence was 92 kilograms and the average age was 72 years old. Several possible ways to improve the technique are discussed.

Role of benzoxazinones in allelopathy by rye (Secale cereale L.).

Two phytotoxic compounds [2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) and 2(3H)-benzoxazolinone (BOA)] were previously isolated and identified in 35-day-old greenhouse-grown rye shoot tissue. Both compounds were also detected by TLC in greenhouse-grown root and fieldgrown shoot tissue. The concentration of DIBOA varied in the tissues, with the greatest quantity detected in greenhouse-grown shoots. DIBOA and BOA were compared with ß-phenyllactic acid (PLA) and ß-hydroxybutyric acid (HBA) for activity on seed germination and seedling growth and were consistently more toxic than either compound. Dicot species tested, including lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), and redroot pigweed (Amaranthus retroflexus L.), were 30% more sensitive than the monocots tested. Of the two benzoxazinone compounds, DIBOA was most toxic to seedling growth. DIBOA and BOA reduced chlorophyll production inChlamydomonas rheinhardtii Dangeard, by 50% at 7.5 × 10(-5) M and 1.0 × 10(-3) M, respectively. Both DIBOA and BOA inhibited emergence of barnyardgrass (Echinochloa crusgalli L. Beauv.), cress (Lepidium sativum L.), and lettuce when applied to soil, indicating their potential for allelopathic activity.