Microscopic investigation of single-crystal diamond following ultrafast laser irradiation

We present a structural investigation of single-crystal diamond following ultrafast laser irradiation of the surface and the bulk material. Optical microscopy, atomic force microscopy, scanning electron microscopy, and focused-ion beam and transmission electron microscopy techniques were utilized to selectively examine the final state of the samples. Laser induced periodic surface structures (LIPSS) with high- and low-spatial frequencies were obtained with multiple-pulse surface irradiation under both stationary and translated target conditions. High magnification transmission electron microscopy analysis of cross sections of the LIPSS revealed modified layers of a few tens of nanometers in thickness capping the crystalline diamond matrix. Sub-surface irradiation of diamond at high laser fluences led to damaged regions and cracks in the bulk material. When translational bulk irradiation of the diamond was performed, substantially sub-wavelength periodic structures were observed at the unpolished side facet of the diamond plate where the laser focus was translated out of the bulk. Spatial periods were 140 nm and the structures largely consisted of single-crystal diamond with a 10 nm modified layer. Finally, preliminary studies of single-shot laser ablation craters at high laser fluences exhibited suppression of material removal for peak values above 45 J/cm².     

The first semiquinone-bridged bisdithiazolyl radical conductor: a canted antiferromagnet displaying a spin-flop transition

The alternating ABABAB π-stacked bis-1,2,3-dithiazolyl radical 2a (2, R(2)=Ph) has a conductivity σ of 3×10(-5) S cm(-1) at 300 K, and orders as a spin-canted antiferromagnet (T(N)=4.5 K) which undergoes a spin-flop transition to a field-induced ferromagnetic state saturating (at 2 K) at H ～20 kOe.     

Convenient preparation and full characterization of a synthetically useful salt of the dithianitronium cation, SNSSbF6, from readily available starting materials

The synthetically useful SNSSbF6 is prepared, in good yield, from the reactions of S3N2Cl2 or S3N3Cl3 with stoichiometric amounts of AgSbF6 and S8 in liquid SO2. SNSSbF6 crystallizes monoclinic in space group C2/m (a = 9.740(2) A, b = 6.644(2) A, c = 5.334(1) A, beta = 90.58(2) degrees , Z = 2). The crystal structure was determined by standard methods and refined to R1 = 0.019 and wR2 = 0.048. The structure consists of discrete linear centrosymmetric SNS+ cations [S-N = 1.4871(10) A] and almost octahedral SbF6- anions, with weak cation-anion interactions. The lattice energy of SNSSbF6 was determined from the volume-based method as 525 +/- 32 KJ mol(-1) and the heat of formation of SNSSbF(6(s)) has been estimated as -1566 +/- 24 KJ mol(-1). The FT-IR, Raman, and (14)N NMR spectra are reported, as well as an in situ study of the reaction of S3N2Cl2 with AsF5 in SO2 solution.     

Low-Valent Germanylidene Anions: Efficient Single-Site Nucleophiles for Activation of Small Molecules

Rare mononuclear and helical chain low-valent germanylidene anions supported by cyclic (alkyl)(amino)carbene and hypermetallyl ligands were synthesised by stepwise reduction from corresponding germylene precursors via stable and isolable germanium radicals. The electronic structures of the anions can be described with ylidene and ylidone resonance forms with the Ge−C π-electrons capable of binding even weak electrophiles. The germanylidene anions reacted with CO₂ to give μ-CO₂-κC:κO complexes, a rare coordination mode for low-valent germanium and inaccessible for the related neutral germylones. These results implicate low-valent germanylidene anions as efficient single-site nucleophiles for activation of small molecules.     

Simultaneous determination of thioridazine and its S-oxidized and N-demethylated metabolites using high-performance liquid-chromatography on radially compressed silica

A method for simultaneously quantifying thioridazine, northioridazine, thioridazine-2-sulfoxide, thioridazine-2-sulfone and thioridazine-5-oxide in serum and plasma is described. Following solvent extraction these compounds were separated by high-performance liquid chromatography on radially compressed silica gel and detected by UV absorbance at 254 nm. Chromatography time is less than 7 min. The relative retention of these compounds as a function of the methanol and methylamine content of the mobile phase is discussed. Practical limits of detection, based upon on assayed plasma or serum volume of 1 ml, were 20 ng/ml for thioridazine-5-oxide and 10 ng/ml for the other compounds. The coefficient of variation for all compounds was less than 13%. The method is compared with more conventional high-performance liqiud chromatographic and gas chromatographic methodology.     

A prototype hybrid 7π quinone-fused 1,3,2-dithiazolyl radical

Reaction of 1,4-naphthoquinone and SNSMF(6) (M = As, Sb) in SO(2) solution in a 1 : 2 molar ratio led to the naphthoquinone fused 1,3,2-dithiazolylium salts, 3MF(6) quantitatively by multinuclear NMR (87% isolated yield of 3SbF(6)) via the cycloaddition and oxidative dehydrogenation chemistry of SNS(+) with formation of NH(4)SbF(6) and S(8). The product 3SbF(6) was fully characterized by IR, Raman, multinuclear {(1)H, (13)C, (14)N} NMR, elemental analysis, cyclic voltammetry and single crystal X-ray crystallography. The reduction of 3SbF(6) with ferrocene (Cp(2)Fe) in refluxing acetonitrile (CH(3)CN) led to the first isolation of a fused quinone-thiazyl radical, 3˙ in 73% yield. The prototype hybrid quinone-thiazyl radical 3˙ was fully characterized by IR, Raman microscopy, EI-MS, elemental analysis, solution and solid state EPR, magnetic susceptibility (2-370 K) and was found to form π*-π* dimers in the solid state as determined by single crystal X-ray crystallography. Furthermore, the thermal decomposition of 3˙ led to a novel quinone-fused 1,2,3,4-tetrathiine, 10 (x = 2) and the known 1,2,5-thiadiazole, 11. The energetics of the cycloadditon and oxidative dehydrogenation chemistry of SNS(+) and 1,4-naphthoquinone leading to 3SbF(6) were estimated in the gas phase and SO(2) solution by DFT calculations (PBE0/6-311G(d)) and lattice enthalpies obtained by the volume based thermodynamic (VBT) approach in the solid state. The gas phase ion energetics (ionization potential (IP) and electron affinity (EA)) of 3˙ are compared to related 1,3,2- and 1,2,3-dithiazolyl radicals.     

Crossing the insulator-to-metal barrier with a thiazyl radical conductor

The layered-sheet architecture of the crystal structure of the fluoro-substituted oxobenzene-bridged bisdithiazolyl radical FBBO affords a 2D π-electronic structure with a large calculated bandwidth. The material displays high electrical conductivity for a f = 1/2 system, with σ(300 K) = 2 × 10(-2) S cm(-1). While the conductivity is thermally activated at ambient pressure, with E(act) = 0.10 eV at 300 K, indicative of a Mott insulating state, E(act) is eliminated at 3 GPa, suggesting the formation of a metallic state. The onset of metallization is supported by infrared measurements, which show closure of the Mott-Hubbard gap above 3 GPa.