In this work, large-scale molecular dynamics simulations are conducted to explore the thermal and mechanical phenomena in surface nanostructuring with a laser-assisted scanning tunnelling microscope. Employing a super parallel computer, more than 200 million atoms are modelled to provide substantial details about how the localized thermal and mechanical perturbations result in surface nanostructures. Extremely localized stress accumulation beneath the sample surface leads to an explosion of the melted/vaporized material, leaving a nanoscale hole in the sample surface. Normal and shear stress development are observed. Stress propagation in space is strongly influenced by the anisotropic nature of the crystal. The high pressure in the melted/vaporized region pushes the melt adjacent to the solid to move, thereby forming a protrusion at the edge of the hole. More importantly, visible sub-surface nanoscale structural damages are observed in a direction 45˚with respect to the axial direction. Detailed study of the lattice structure reveals atomic dislocations in the damaged regions. Both temporary and permanent structural damages are observed in the material. The temporary structural damage is featured with a formation, propagation and disappearing procedure.

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The substituent effect on the self-thiylation of 2-thiophenethiols was studied. Experimental results and quantum chemical calculations suggested possible mechanisms for this reaction dependent on the reaction conditions.We have already discovered the self-thiylation of 2-thiophenethiol (Ia) to give a dimeric dithiolactone (Ha) [1][2][3][4]. Subsequently, we obtained products of the reaction of Ha with hydrazine (Ilia) and its derivatives (IVa-h) as well as with hydroxylamine OVi) (see our previous work [5] and present communication).Similar to dithiolactone IIa, 3,-dithiobutyrolactone reacts with hydrazine hydrate and acetone monohydrazone to give III (V, R = H) and IV (VI, R = H, X = N=CMe2), respectively (see Scheme 1).

Selenophenethiols have been synthesized by a modified organolithium method. The structures of the products were established by their autothiylation and reaction with phenylhydrazine.We showed previously that 2-thiophenethiol and 2-furanthiol autothiylate spontaneously into 4-(2-thienylthio)tetrahydrothiophene-2-thione and 4-(2-furylthio)tetrahydrofuran-2-thione respectively [1, 2]. The aim of the present work was to ascertain whether 2-selenophenethiol underwent a similar reaction.Unsubstituted 2-selenophenethiol (Ia) was synthesized by the sequential treatment of 2-bromoselenophene with butyllithium, sulfur, and acid. The tendency of the product to thicken rapidly was noted. It was concluded on the basis of PMR and IR spectroscopy that thiol (Ia) exists in equilibrium with the tautomeric 5H-selenophene-2-thione [3].Our attempts to synthesize thiol (Ia) by treating unsubstituted selenophene (IIa) with butyllithium and then sulfur with subsequent acidification proved unsuccessful. Neither the target product (Ia) nor the initial selenophene were detected in the reaction mixture. It is possible that this is linked with inadequate cooling at the lithiation step which leads to destruction of the selenophene ring.The use of phenyllithium as lithiating agent proved to be more successful. After treating the lithium derivates of selenophene (IIa) with sulfur and alkylating the thiolate formed with methyl iodide 2-(methylthio)selenophene (IIb) was obtained in 37% yield. To synthesize 2-selenophenethiols (Ia, b) we treated a solution of the appropriate lithium 2-selenophenethiolate not with acid but with chlorotrimethylsilane which led to trimethylsilyl ether (IIIa, b) stable on storage. When needed the latter compound is converted readily and almost quantitatively into (Ia, b) by hydrolysis with a strictly stoichiometric quantity of water (this method was used by us previously when investigating the autoconversions of furanthiols and -selenols, and also of 2-thiopheneselenol [2, 4] Investigation of a freshly distilled sample of compound (Ia) by PMR showed that in CDC13 it exists solely in the thiol form. Catalytic addition of HC1 and warming to -50~ only affected the position and width of the SH group signal.On leaving in the air or by the action of a catalytic quantity of triethylamine the thiol (Ia) is autothiylated with the formation of 4-(2-selenienylthio)tetrahydroselenophene-2-thiol (IVa). The substituted thiol (Ib) is not converted under the conditions indicated into the analogous thione (IVb). However derivatives of the corresponding thiones (IVa) and (IVb), viz. the hydrazones (Va) and Vb), are obtained on treating compounds (Ia, b) with phenylhydrazine.