B. Amov’s research while affiliated with Bulgarian Academy of Sciences and other places

In the present work plasma polymer films obtained from hexamethyldisiloxane have been implanted by carbon ions at three different doses. The photoluminescent properties of the implanted polymers were investigated. The optical transmission of these polymer layers was investigated in the visible spectral region. Their electrical parameters were also measured. It was found that the resulting changes do not worsen the protective properties of the implanted polymer layer. The variations in the properties studied might be ascribed to the nanostructured carbon clusters formed on the polymer surface. The results obtained could form the basis for further optimization of the polymer structure by carbon ion implantation in view of applications in electroluminescent display structures.

Rutherford backscattering spectroscopy in combination with channelling have been applied to investigate the surface structural changes of silicon implanted with low-soluble species (Zn and Pb) and subsequently thermally and ion beam annealed. For the fast diffusing Zn complete recrystallization during annealing of layers amorphized by ion implantation was observed, while for the slow diffusing Pb incomplete recrystallization took place. The results are discussed with respect to the corresponding experimental conditions.

The behaviour of Fe implanted into Si(100) during subsequent pulsed ion - beam treatment (PIBT) has been studied. A two-step 56Fe+ ion implantation at energies of 60 and 20 keV and total doses of 1016 - 2×1017 cm-2 was used. As crystallization due to PIBT took place, Fe segregated towards the surface of the samples for the lower dose used (1016 cm-2) and diffusion into the bulk of the Si samples ccured for higher doses (1×1017 cm-2 and 2×1017 cm-2). The Fe concentration profile was shifted rigidly, without Fe losses. Both the movement of the Fe layer and the maximum concentration of Fe in the Si crystallized region were characterized by Rutherford backscattering spectroscopy (RBS) in combination with channelling (RBS/C).

The Mg2Si phase was fabricated using ion beam synthesis with high doses of 24 Mg+ implantation in Si substrates, followed by rapid thermal annealing. The chemical composition of the as-implanted and of samples annealed under different conditions was studied by X-ray energy dispersive spectroscopy. The effect of the different doses and annealing time on the surface morphology was investigated by scanning electron microscopy and atomic force microscopy.

The ion-beam synthesis (IBS) of Mg2Si to overcome the low condensation coefficient of magnesium and the limited Mg2Si film thickness is discussed. The compound had a cubic structure with a large lattice parameter. An ion accelerator type ILU-4 which allowed a high current density was used for the implantation of 24Mg+ ions. It was found that the lower the implanted dose, the stronger is the influence of the annealing time on the IR spectra behavior.

The implantation of heavy atoms is of great interest since it is a basis when creating electronic and optoelectronic devices for operation under a high temperature or reactive environment. Corresponding surface irradiation effects such as laser annealing are extensively applied, since it leads to quite appropriate modification of the surface. In our experiment, using transmission and scanning electron microscopy applied in combination with sensitive analytical methods, the microstructure of Bi+-implanted and laser-annealed silicon is characterized. Recrystallisation of Bi-implanted silicon is recorded, after laser annealing. The obtained experimental results on bismuth-implanted silicon up to very high bismuth fluence, are of special interest due to the recorded Bi nanocrystal formation in amorphized silicon layers. Optical characteristics of specimens are also measured using a tunable laser control system.

The electrical and optical properties of hydrogenated amorphous silicon-carbide alloy films (a-Si1-xCx:H), modified by Fe+ ion implantation (D = 1×1016 - 1×1017 cm-2), have been investigated. Optical transmission spectra have been measured in the visible range (400-900 nm) and considerable absorption edge shift to the longer wavelength region has been registered, together with well-defined decrease of transmittance in the whole measured range. These effects are increased with the dose and are similar for samples with different carbon content (x1=0.08 and x2=0.15). Room temperature (RT) surface electrical conductivity is also increased by Fe+ implantation and the effect is most pronounced for the highest doses (D ~ 1017cm-2). The temperature dependence of the conductivity was measured in the temperature range from RT to 250 oC. The activation energy is considerably reduced and the effect is again strongest for the highest doses. From the above results we conclude that high doses Fe+ implantation in a-Si1-xCx:H affects both the localised states deep in the gap and the shallow states in the band tails.

Results are presented on the dc and ac conductivity and dielectric loss, tan δ, of thin amorphous chalcogenide films in the AsSe system, implanted with C+ at different doses and of the same films after thermal annealing. Investigations of the temperature dependence of the diffuse reflectivity in the near infrared (λ = 800 nm) have been performed to obtain supplementary data on the optical properties of the implanted films. X-ray photoelectron spectroscopy studies confirm the presence of a high concentration of C+ and its partial transformation from the sp3 into the sp2 state.

Lead stocks of wooden-lead anchors found along the Bulgarian Black Sea coast and typologically dated VI c. B.C.-III c. A. D. have been analyzed for chemical composition and lead isotope ratios by INAA, AAS and mass spectrometry. Using multivariate methods for analysis as well as simple bivariate plots the lead for production of the stocks was localized as originating from Laurion, Thassos, Troas, Chalkidike and the Rhodopes. In general, the chemical composition is not recommended to be used for provenance study of lead artefacts. Combining the results from this study with the existing typological classification certain conclusions about the production and distribution of lead anchors in the Aegean region are made.

The isotopic composition of lead in normal and metal-rich black shales and associated volcanogenic rocks has been studied in the Barrandian Upper Proterozoic of the Bohemian Massif, which is a part of the Central European Variscan Belt. These rocks played an important role in the metallogeny of the Bohemian Massif. The Late Proterozoic age of metamorphism is evidenced by the slope of the secondary isochron of the uranogenic lead corresponding to the age of 635 ± 45 Ma, and by the model age of 540–590 Ma of thorogenic lead in the samples with low Th/U ratios. In most of the samples, the leached Pb is less radiogenic than the residual Pb. No correlation was established between the presence of more radiogenic samples and the distance towards Variscan granitoids. The samples are mostly associated with the Upper Proterozoic volcano-sedimentary sequences far from Variscan intrusions and only some occur in the exocontacts of Variscan plutons. This suggest that most of the uranium was introduced into rocks during Cadomian metamorphism rather than Variscan tectonomagmatic phases. However, a possible contribution of radiogenic lead in connection with the latter events as well as some heterogeneity in U/Pb and Th/Pb ratios from the time between sedimentation and metamorphism cannot be excluded. The comparatively low ratios indicate that thorium was not mobilized by the metamorphic fluids, and testifies that Th is less mobile under metamorphic conditions. The values (15.57–15.63) of less radiogenic lead in the rocks are close to those of galenas from different Variscan polymetallic mineralizations in the Bohemian Massif, which suggests a common source from a well-mixed reservoir as observed in ore leads in mature island arcs or at active boundaries between continental and oceanic plates.