Non‐Covalent Functionalization of Graphene Using Self‐Assembly of Alkane‐Amines

A simple, versatile method for non‐covalent functionalization of graphene based on solution‐phase assembly of alkane‐amine layers is presented. Second‐order Møller–Plesset (MP2) perturbation theory on a cluster model (methylamine on pyrene) yields a binding energy of ≈220 meV for the amine–graphene interaction, which is strong enough to enable formation of a stable aminodecane layer at room temperature. Atomistic molecular dynamics simulations on an assembly of 1‐aminodecane molecules indicate that a self‐assembled monolayer can form, with the alkane chains oriented perpendicular to the graphene basal plane. The calculated monolayer height (≈1.7 nm) is in good agreement with atomic force microscopy data acquired for graphene functionalized with 1‐aminodecane, which yield a continuous layer with mean thickness ≈1.7 nm, albeit with some island defects. Raman data also confirm that self‐assembly of alkane‐amines is a non‐covalent process, i.e., it does not perturb the sp² hybridization of the graphene. Passivation and adsorbate n‐doping of graphene field‐effect devices using 1‐aminodecane, as well as high‐density binding of plasmonic metal nanoparticles and seeded atomic layer deposition of inorganic dielectrics using 1,10‐diaminodecane are also reported.     

Analysis of exoskeleton triglycerides ofLeptinotarsa decemlineata say

The exoskeleton triglyceride fraction isolated from the Colorado beetle,Leptinotarsa decemlineata Say, was studied. Analysis of the hydrolysis products and direct capillary column gas chromatography showed that, apart from triglycerides, the fraction contained no diol lipids. The composition of the natural triacylglccerol mixture was assessed by gas chromatography and by field desorption and electron impact mass spectrometry. Triglycerides isolated from the Colorado beetle are typical glycerol triesters, with long chain (mainly oleic or palmitic) fatty acids. The structures of two major components (91%), i.e., trioleoyl glycerol and 1,2-dioleoyl-3-palmitoyl glycerol, were determined.     

Effect of fluorination on preparation of Bi(Pb)SCCO 2 2 2 3 by the citrate precursor process

Citrate precursor technology was used to prepare fluorine substituted Bi(Pb)SCCO 2 2 2 3 superconducting phase. Samples with the nominal composition of up to three F atoms per formula were synthesized. A number of experimental methods have been used to characterize the samples and to trace the phase transformations during the preparation process: DTA/TGA, XRD, EPMA (WDS and EDS), atomic absorption, potentiometry with fluoride selective electrode, resistance and inductive measurements. Fluorine was shown to enhance considerably the formation of the 2 2 2 3 phase. Thermodynamic calculations of P-T-X equilibrium in the Bi-Pb-Sr-Ca-Cu-O-F-C-H-N system were made in a wide temperature range to determine the composition of the vapours coexisting with the solid phases at different stages of the preparation process.A part of the results was presented at the M²S-HTSC IV Conference in Grenoble, France, 1994.     

The effect of wheat grain composition, cuticular lipids and kernel surface microstructure on feeding, egg-laying, and the development of the granary weevil, Sitophilus granarius (L.)

Adult feeding intensity, oviposition, and larval development of Sitophilus granarius (Coleoptera: Curculionidae) were observed on grain from three Polish wheat varieties (Begra, Korweta, and LGR 896/64a) washed with petroleum ether to remove cuticular lipids. Extraction of lipids did not cause any statistically significant changes in the physicochemical, biochemical and technological (milling, rheological and baking) properties of the wheat grain studied. Wheat grain washed with petroleum ether did not show any visible changes in the surface and morphology of the outer layer of the wheat grain. However, differences were noted in the microstructure of the kernel surface. Grain with a thicker seed coat (LGR 896/64a) was infested at a lower rate than the other varieties. Of the 18 hydrocarbons extracted from the grain surface, three compounds - n-heptacosane (C₂₇), n-nonacosane (C₂₉) and n-hentriacontane (C₃₁) - were found in significant amounts. In general, beetles produced 64-95% less dust and laid 7-16% fewer eggs in kernels from which cuticular lipids had been removed. This implies that these compounds have a major role in food selection and the search for an oviposition site prior to grain infestation.     

High on/off ratios in bilayer graphene field effect transistors realized by surface dopants

The unique property of bilayer graphene to show a band gap tunable by external electrical fields enables a variety of different device concepts with novel functionalities for electronic, optoelectronic, and sensor applications. So far the operation of bilayer graphene-based field effect transistors requires two individual gates to vary the channel's conductance and to create a band gap. In this paper, we report on a method to increase the on/off ratio in single gated bilayer graphene field effect transistors by adsorbate doping. The adsorbate dopants on the upper side of the graphene establish a displacement field perpendicular to the graphene surface breaking the inversion symmetry of the two graphene layers. Low-temperature measurements indicate that the increased on/off ratio is caused by the opening of a mobility gap.     

Layer intermixing and related long-term instability in heavily carbon-doped AlGaAs/GaAs superlattices

Superlattices (SLs) of Al_o.3Ga_o.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CClp₄ were annealed for 24 h at 825° C under a variety of ambient and surface encapsulation conditions. Photoluminescence atT = 1.7 K has been employed to determine approximate Al-Ga interdiffusion coefficients (D _Ai-Ga) for different annealing conditions. For all encapsulants studiedD _Al-Ga increases with increasing As₄ pressure in the annealing ampoule. This result disagrees with trends reported for Mg-doped crystals, and with predictions of the charged point-defect (Fermilevel) model. The Si₃N₄ cap provides the most effecitve surface sealing against ambientstimulated layer interdiffusion (D _Al-Ga ≈ 1.5-3.9 x 10^-19 cm²/sec). The most extensive layer intermixing has occurred for an uncapped SL annealed under As-rich ambient (D _Al-Ga ≈ 3.3 x 10^-18 cm²/sec). These values are up to ~40 times greater than those previously reported for nominally undoped AIGaAs/GaAs SLs, implying that theC _As doping slightly enhances layer intermixing, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental data and the model are discussed. Pronounced changes in the optical properties of the annealed SLs with storage time at room temperature are also reported. These changes may indicate a degraded thermal stability of the annealed crystals due to high-temperature-induced lattice defects. A possibly related effect of the systematic failure to fabricate buried heterostructure quantum well lasers via impurity-induced layer disordering in similarly doped AIGaAs/GaAs crystals is discussed.     

Current saturation and voltage gain in bilayer graphene field effect transistors

The emergence of graphene with its unique electrical properties has triggered hopes in the electronic devices community regarding its exploitation as a channel material in field effect transistors. Graphene is especially promising for devices working at frequencies in the 100 GHz range. So far, graphene field effect transistors (GFETs) have shown cutoff frequencies up to 300 GHz, while exhibiting poor voltage gains, another important figure of merit for analog high frequency applications. In the present work, we show that the voltage gain of GFETs can be improved significantly by using bilayer graphene, where a band gap is introduced through a vertical electric displacement field. At a displacement field of -1.7 V/nm the bilayer GFETs exhibit an intrinsic voltage gain up to 35, a factor of 6 higher than the voltage gain in corresponding monolayer GFETs. The transconductance, which limits the cutoff frequency of a transistor, is not degraded by the displacement field and is similar in both monolayer and bilayer GFETs. Using numerical simulations based on an atomistic p(z) tight-binding Hamiltonian we demonstrate that this approach can be extended to sub-100 nm gate lengths.     

The sesquiterpene composition of leaf cuticular neutral lipids of ten Polish varieties of Solanum tuberosum

The sesquiterpene composition of leaf cuticular neutral lipids of potato (Solanum tuberosum) varieties was investigated by GC, GC-MS and HPLC. The distribution of sesquiterpenes varied between varieties with the major components being β-caryophyllene, trans-β-farnesene, germacrene D, β-sesquiphellandrene and germacrene D-4-ol. cis-β-Farnesene and bicyclogermacrene were identified in potato for the first time. The amount of sesquiterpenes was 10–60% of the cuticular neutral lipids depending on variety. The sesquiterpenes and alkanes were the major groups of components in the waxes investigated. © 1998 SCI.     

Use of changes in ST segment elevation for prediction of infarct artery recanalization in acute myocardial infarction

BACKGROUND: The role of the ECG in evaluating reperfusion status after thrombolytic treatment in acute myocardial infarction is not clear. Dramatic ST segment changes have been observed during recanalization of an infarct-related artery, but ST criteria have not been definitively established for prediction of coronary artery patency. Differences in ST segment changes in relation to infarct localization have not been evaluated, and further investigation is required into reciprocal ST depression, which provides information independent from ST elevation. Therefore, the aim of this study was to evaluate how early changes in ST segment elevations and depressions predict vessel patency after fibrinolysis for patients with anterior and inferior/lateral infarcts. METHODS AND RESULTS: Two hundred patients with a Pardee wave in the ECG and chest pain of less than 6 h duration were given thrombolytic treatment. The result of the therapy was assessed simultaneously with coronary angiography. Patients were divided into two groups: I (50 patients) without recanalization (TIMI grade 0, 1 or 2), and II (150 patients) with successful recanalization (TIMI grade 3). Before and after therapy, analysis of the 12 lead ECG included maximum ST elevation measurement (H1, H2 respectively), the sum of ST elevations (sigma H1, sigma H2), the sum of ST segment depressions (sigma h1, sigma h2), and the ratios of ST segment changes (R1 = H2:H1, R2 = sigma H2:sigma H1, R3 = sigma h2:sigma h1). The mean interval from the first to the second ECG was 3.5 +/- 1 h. Successive values of R1 and R2 were examined to find that which best distinguished between the two groups. The best values for prediction of reperfusion were: (1) For anterior wall infarct [table: see text] (2) For inferior and lateral infarct [table: see text] In 13 patients with a complete right or left bundle branch block in the first or second ECG, the result of treatment was predicted in 11 patients using criteria for factor R1 and in 12 patients using criteria for R2. Analysis of ST segment depressions revealed a significant correlation between normalization of ST segment depressions and elevations (R3 vs R1: r = 0.60, P < 0.05; R3 vs R2 r = 0.59, P < 0.05). Multivariate discriminant analysis showed an independent value of R3 for discrimination between the two groups, but only in patients with inferior/lateral infarcts. The overall accuracy of the common algorithm in predicting reperfusion was significantly better in patients with inferior/lateral infarcts (Chi2 test, P = 0.0078). When separate algorithms were used, there was no significant difference between patients with anterior or inferior/lateral infarcts because of the significant improvement in prediction of reperfusion in patients with anterior infarcts (McNemar's test: P = 0.041). CONCLUSIONS: We conclude that analysis of ST segments on the standard 12-lead ECG offers valuable help in the early identification of successful recanalization of infarct-related arteries after thrombolytic therapy in patients with acute myocardial infarction. Use of the ratio of ST segment normalization according to the separate criteria for anterior and inferior/lateral infarcts gives the test a high sensitivity and specificity, even in the presence of interventricular conduction disturbances.     

Identification of branched alkanes in lipids ofLeptinotarsa decemlineata say andTribolium destructor by GC-MS: A comparison of main-beam and link-scanned spectra

Branched hydrocarbons were identified in the lipids ofLeptinotarsa decemlineata Say andTribolium destructor by gas chromatography, ordinary electron impact mass spectrometry, and linked, scanned, daughterion monitoring. This methodology allowed us to revise our earlier results based only on GC-MS data confirming the existence of only monomethyl-, dimethyl-, and trimethylalkanes in the hydrocarbons ofL. decemlineata Say. The hydrocarbons fromTribolium destructor consist ofn-alkanes, 3-methylalkanes, internally branched monomethylalkanes and dimethylalkanes. Daughter-ion monitoring can be particularly important for distinguishing between incidentally overlapped GC peaks of hydrocarbons from different series. A trace, for example, of dimethylalkane coeluating withn-alkane was easily identified in GC peak of hydrocarbon mixture ofT. destructor. Link scans confirmed also molecular weights for the compounds without molecular ions in the mass spectra. Structural assignment of the compounds were verified by comparison of the experimental and calculated values of the GC retention Kovats indexes (KI).