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X-ray photoelectron spectroscopy examination shows that after laser cutting under ambient condition, the upper surface of diamond consists of a heavy oxidized layer consisting of a variety of carbon–oxygen chemical states comprising –C═O, –C–O–C– and –C–O–H species. The thickness of the oxide layer was estimated to be ∼22 Ǻ. Upon vacuum annealing to 700 °C the thickness of the oxide layer decreases to ∼10 A and the upper surface layer becomes more diamond-like through desorption of C–O species. Exposure of the laser cut diamond surface to a microwave hydrogen (MW-H) plasma results in removal of the oxide layer and exposure of the diamond phase. This is evidenced by the appearance of characteristic diamond surface and bulk plasmons which accompanied the C (1s) X-ray photoelectron peak. Our studies show that the surface chemical composition and thermal stability of the laser cut and polished surfaces both after MW-H exposure are nearly similar. The morphology of the laser cut surface shows an ill-defined laminar structure without any characteristic features which is not significantly affected by MW-H plasma exposure. This is in contrast to the polished surfaces for which exposure to the MW-H may result in its planarization.

It is shown that exposure of polished single crystal diamond surfaces to microwave hydrogen plasma at optimized conditions may be applied as a very efficient method for the smoothing out of single crystal diamond surfaces. The effect of microwave (MW) hydrogen plasma exposure on the morphology of mechanically polished natural single crystal (100) oriented diamond type 2a surfaces is reported. It is shown that the surface morphology is very sensitive to plasma power and exposure time. Under appropriate plasma exposure conditions the diamond surfaces smooth out as reflected in the decrease in the number and depth of the polishing scratches or lines. However adverse effects on the surface morphology through the formation of pits were found to occur upon long exposure times and high plasma power. A systematic study of the influence of hydrogen microwave plasma power and exposure time on the diamond surface morphology is presented. The morphology of the diamond surfaces at the different stages was monitored with sub-nano-metric resolution by atomic force microscopy and scanning electron spectroscopy.

The effect of microwave hydrogenated (MW-H) plasma exposure on the morphology of mechanically polished natural single crystal (100) oriented diamond type 2a surfaces is reported. It is shown that the surface morphology is very sensitive to plasma power and exposure time. Under appropriate plasma exposure conditions the diamond surfaces smooth out as reflected in the decrease in the number and depth of the polishing lines. A systematic study of the influence of hydrogen MW plasma power and exposure time on the diamond surface morphology is presented. The morphology of the diamond surfaces at the different stages was monitored with sub-nanometric resolution by atomic force microscopy and scanning electron spectroscopy.

Scanning tunneling spectroscopy in the shell-filling regime was carried out at room temperature to investigate the size dependence of the band gap and single-electron charging energy of single Si quantum dots (QDs). The results are compared with model calculation. A 12-fold multiple staircase structure was observed for a QD of about 4.3 nm diameter, reflecting the degeneracy of the first energy level, as expected from theoretical calculations. The systematic broadening of the tunneling spectroscopy peaks with decreasing dot diameter is attributed to the reduced barrier height for smaller dot sizes and to the splitting of the first energy level.

Oxide removal processes for InSb(100) and GaSb(100) substrates utilizing exposure to molecular hydrogen at moderate temperatures were studied in an experimental UHV chamber and were compared to the common method of thermal oxide desorption (TOD). Molecular hydrogen cleaning (MHC) deoxidizes the substrate surfaces effectively at temperatures of ∼100 and ∼200°C lower than that in TOD of GaSb and InSb, respectively. Closely related hydrogen based procedures for the cleaning of these materials before molecular beam epitaxial growth were developed. In these procedures a very low flux of atomic hydrogen was used in order to achieve short, yet mild, deoxidation of the substrates both with and without an Sb flux. These mild atomic hydrogen cleaning (MAHC) methods give smoother, cleaner, and more perfect InSb and GaSb surfaces after a shorter cleaning cycle at temperatures of 100–200°C lower than that in TOD. An Sb flux is not necessary in MAHC, but if used it gives a smoother substrate surface, and a well ordered...

In this paper the surface roughness and topography of low-pressure chemical vapor deposition amorphous silicon films grown on (001) silicon substrates after phosphorus/argon/arsenic ion implantation, after annealing at 850 °C in an ambient N2 environment and after further annealing to 1070 °C in O2 environment have been investigated. The influence of the different treatments on the sample surface topography was examined by atomic force microscopy in the noncontact mode. The surface composition of the films was analyzed by x-ray photoelectron spectroscopy for annealed and unannealed phosphorus implanted wafers. It was found that the surface roughness of the films is affected by implantation and annealing and mostly by implantation followed by annealing. Only implantation reduced the surface roughness while only annealing results in an increase of surface roughness. Implantation followed by annealing results in a drastic increase of surface roughness. “Bumps” which appeared following annealing seem to consi...

The surface roughness and topography of low-pressure chemical vapor deposited (LPCVD) silicon films have been investigated by atomic force microscopy (AFM) in the non-contact mode. Deposition parameters were varied and various post-deposition treatments tested. The morphology of poly-silicon and amorphous-silicon were compared as well as morphology modification due to different amorphous-silicon deposition temperatures. The effects of post-deposition treatments: ion implantation and oxidation have been investigated. A significant difference in morphology between poly-silicon and amorphous-silicon films was revealed. Poly-silicon roughness was an order of magnitude higher than amorphous-silicon roughness. The surface morphology of amorphous-silicon layers was strongly affected by the deposition temperature. Asperity concentration and height were highly sensitive to the deposition temperature in the range of 545–560 °C. Phosphorous, argon and arsenic ion implantation decreased the roughness of amorphous-silicon films. On the other hand, the oxidation process caused an increase of roughness. Moreover, implantation followed by oxidation resulted in a drastic increase of the surface roughness, with a pronounced dose dependence.

Nanocrystalline carbon films possessing a prevailing diamond character are deposited by a direct current glow discharge chemical vapor deposition method using a 9:91 vol % methane to hydrogen gas mixture. In the present work the evolution and properties of nanodiamond films deposited by this method onto silicon substrates as a function of time were studied by various complementary techniques. Our analysis showed that prior to formation and growth of continuous films of a predominantly nanodiamond character, a graphitic phase is formed. After the nanodiamond phase is stabilized, near edge x-ray adsorption fine structure measurements proved the predominant diamond character of the film to be about 80%. By electron energy loss spectroscopy analysis the sp2-like character of the nanodiamond grain boundaries has been determined. The nanodiamond films were found to be thermally stable up to temperatures of ∼950 °C as established by vacuum heating. By scanning electron microscopy and atomic force microscopy the ...

Photodynamically induced oxygen depletion has been measured in an Ehrlich ascites mouse tumor cell line using a Clark-type electrode. Cells are loaded with aluminum phthalocyanines, sulfonated to different degrees (AlPcSn, n = 0,2,3,4) and consisting of various isomeric species. Different cell lines and incubation procedures are used in order to investigate the cellular uptake mechanism. Uptake (in units of molecules/cell), post-irradiation redistribution and AlPcSn photodegradation are measured using spectroscopic techniques. For a given sensitizer, the oxygen depletion rate per cell increases sublinearly with uptake and superlinearly with cell density. In order to compare oxygen depletion rates of different compounds, we have defined the biological quantum yield (BQY) as the number of oxygen molecules that disappear per absorbed photon. The BQY is independent of uptake and cell density; therefore, it denotes the intrinsic photoactivity of a sensitizer. Sensitizers with high BQY show efficient post-irradiation intracellular redistribution. Photodegradation during irradiation is similar for all sensitizers (20–30%).

Aluminium phthalocyanines sulfonated to a different degree ( AlPcS n) and consisting of various isomeric species were studied by spectroscopic techniques to determine their tendencies to form dimers and aggregates. These characteristics were compared with the cell-penetrating properties of the species, using the Ehrlich ascites mouse tumor cell line, to arrive at structure-activity relationships. AlPcS n preparations consisting of the least number of isomeric species exhibited the highest tendency to form dimers and aggregates, whereas the more complex preparations, consisting of many isomeric products, showed more consistent monomeric features in aqueous environments. Uptake in cells was shown to correlate well with the overall hydrophobicity of the preparation and inversely with its degree of aggregation in the extracellular environment. Among the purified, single isomeric AlPcS n the amphiphilic disulfonated AlPcS 2a , enriched in positional isomers featuring sulfonate groups on adjacent phthalic subunits, showed the best membrane-penetrating properties. Even higher cell uptake was observed for the AlPcS 2mix reflecting a combination of optimal lipophilicity and a low degree of aggregation. Similarly, in the case of AlPcS 4, the pure isomeric compound showed less cell uptake than the mixed isomeric preparation of similar hydrophobicity, reflecting the higher degree of aggregation invoked by its symmetrical structure. Our data indicate that mixed sulfonated phthalocyanine preparations may exert higher photodynamic efficacy in biological applications as compared to the pure isomeric constituents.

The roughness evolution of carbon films deposited from hyperthermal species was investigated by AFM. 10 eV C deposition at normal incidence angle starts with formation of 10 nm high islands followed by continuous, sp2 rich films at larger doses with essentially the same feature height and film roughness. 40 eV C deposition at normal incidence angle (0°) forms sp3 rich, atomically smooth films, which become sp2 rich and rough at oblique angles (≥60°). The limitations of currently available molecular dynamic simulations prevent their use to describe the island formation during 10 eV C bombardment. Dedicated calculations probing the effect of incidence angle on 40 eV C deposition exhibit similar trends to the experimental data i.e. decrease of the sp3 fraction and increase of the roughness with increasing incidence angle. The results are in accord with the “subplantation” scheme, linking roughness and sp2 bonding to surface entrapment. Implications on recent works discussing growth mechanisms or surface smoothening are given.

In this paper we formulate and analyze a continuum model for the vibration of a noncontacting atomic force microscope (AFM) microbeam in air that consistently incorporates nonlinear geometric and inertia effects, localized atomic interaction, viscoelastic damping and quadratic drag. We investigate a controlled set of experiments that include both free vibration decay of a large Silicon beam and forced vibration response of an AFM Silicon microbeam mapping a Silicon sample for various initial interaction distances. Nonlinear frequency and damping backbone curves are obtained from free vibration decay data and equivalent damping ratios are deduced from forced vibration frequency response. Estimation of the system linear viscoelastic parameters and nonlinear drag parameters is enabled by comparison of the experimental backbone curves with those of a nonlinear modal dynamical system deduced from the continuum model. The calibration results without sample interaction include both a slight softening effect for small amplitude response due to nonlinear inertia and viscoelastic damping and a hardening effect for large amplitude response governed by nonlinear geometric effects and drag. Validation of the nonlinear model is enabled by comparison with the measured forced vibration AFM frequency response below the dynamic jump-to-contact threshold.Copyright © 2007 by ASME

Photodynamic efficacy of four tetrakis (methoxyethyl) porphycene (TMPn) derivatives encapsulated in liposomes, was studied in vitro and in vivo. Fluorescence and absorption measurements were used to determine aggregation in dipalmitoyl phosphatidylcholine (DPPC) liposomes; no spectral changes were found when dissolving in an organic solution or in an aqueous dispersion of DPPC liposomes. This indicates that the porphycenes were located in the lipophilic bilayer of the liposomes. Fluorescence quenching experiments with I- showed, specifically, that porphycenes located in the liposome bilayer at various depths, according to the hydrophilicity of the porphycene side chains. Dose-response relations were established: increasing porphycene concentration or light dose enhanced the damage proportionally. In cultured MDCK cells, photodynamic damage was in accordance with location: a porphycene 'buried' inside the bilayer did not cause damage to the cell culture. PDT efficacy was tested also in vivo by the damage to blood vessels of the chorioallantoic membrane (CAM) of the fertilized chick embryo. Unlike in the in vitro case, the porphycene 'buried' inside the bilayer did cause significant photodynamic damage in vivo. This difference suggests that in vitro photodynamic action follows contact-mediated sensitizer transfer to cell membranes from liposomes, which remain distinct from cells, whereas in vivo the photosensitizer is delivered to tissue via fusion of liposomes with endothelial cell membranes.

The preparation of InSb (001) oxygen-free surfaces by thermal annealing at relatively low temperatures under molecular hydrogen flow is reported. This process is compared with thermal oxide desorption (TOD) at 400°C under ultrahigh vacuum conditions. Molecular hydrogen cleaning (MHC) at substrate temperature of 250°C and at hydrogen pressure of 5×10−6Torr resulted in complete desorption of the native oxide layer. Furthermore, no carbon contamination was observed on the surface following this treatment. The surface morphology of the samples following this process was found to be very smooth without any droplet structure. The In:Sb surface stoichiometry was nearly 1:1 along the MHC process. In addition, annealing the sample at 400°C in vacuum after oxide removal by MHC maintains the smoothness and the stoichiometry of the surface. In contrast, TOD at 400°C of an oxidized InSb surface in vacuum does not result in complete oxide removal from the surface. Furthermore, small droplets associated with In are prod...

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We report that annealing of an oxidized InSb (100) single-crystal sample at 250°C under molecular hydrogen flow [molecular hydrogen cleaning (MHC)] results in complete desorption of the surface oxides. Following this process, the surface morphology is found to be very smooth at the nanometric scale without any droplet structure and a nearly 1:1 In:Sb stoichiometry. MHC was applied to remove the native oxide of an epi-ready InSb(100) substrate used for molecular beam epitaxy growth of InSb films. These results suggest that MHC of InSb can be used as a very effective cleaning process for epitaxial film growth.

The influence of thermal oxidation on the composition of silicon nitride films in SiO2∕Si3N4∕SiO2 stacks for advanced nonvolatile memories is reported. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses lead to the conclusion that wet thermal (pyrogenic) oxidation of silicon nitride enhances the incorporation of oxygen into the silicon nitride layer and creates a silicon oxynitride layer. In the oxynitride layer formed by wet oxidation, O is mostly bonded to N, whereas in the native oxynitride at the silicon nitride surface, O is preferentially bonded to Si. Dry oxidation (1200°C) results in an even higher amount of oxygen incorporation into the silicon nitride layer as compared with the pyrogenic process. After both pyrogenic and dry oxidation, hydrogen concentration decreases in the bulk of the silicon nitride layer. Following wet oxidation, hydrogen was found to accumulate at the surface layers of the grown oxynitride film. Oxygen penetration into the nitride l...

Time-of-flight secondary ion mass spectrometry (SIMS) depth profiling was used to study nitrogen distribution in SiO2∕Si3N4∕SiO2 (ONO) structures employed in advanced semiconductor memories. We have investigated different factors that affect nitrogen accumulation at the Si∕SiO2 interface of the ONO structure. To isolate the impact of ion beam enhanced nitrogen diffusion towards the Si∕SiO2 interface in SIMS measurements, the top silicon oxide and silicon nitride layers were chemically etched before the SIMS procedure. Thermal diffusion effects were investigated by comparing specimens with different thermal budgets and different thickness of layers in the ONO stack. Our results unambiguously suggest that nitrogen can be accumulated at the Si∕SiO2 interface during ONO fabrication.

The evolution of the surface topography and microstructure of silicon films deposited near the amorphous-to-polycrystalline transition was investigated, and was found to be accompanied by the appearance of crystalline aggregates whose density and size distribution strongly depend on deposition parameters. The films were deposited by low-pressure chemical vapor deposition, and the parameters varied were temperature, pressure, film thickness, and substrate material. Both temperature and pressure have a dramatic effect on the density and size of surface aggregates. A transition from amorphous to polycrystalline silicon at the critical temperature, T C 580°C, is evident from the abrupt change in surface roughness. This effect was far more pronounced for thin (55 nm) silicon films than for their thicker (150 nm) counterparts and was generally larger for films grown directly on c-Si rather than on SiOx substrates. Evidence for nanocrystalline silicon particles embedded into the amorphous matrix below T C was found. In this study, it is suggested that the amorphous-polycrystalline silicon transition and consequently the surface topography evolution of the films is fluctuation assisted. The transition manifests itself in an enhanced population of Si nucleation centers, which are mostly formed at the upper surface of the deposited film.

The roughness of the poly/interpoly oxide interface plays a most important role in the performance of devices; it is expected that for a smoother interface, the double-polysilicon structure will present better electrical properties, such as higher breakdown voltage, and will be more reliable. To obtain the best electrical properties of the oxide layer, it is, therefore, essential to control the polysilicon morphological properties. The overall performances will be affected by the postdeposition process: implantation (dose, energy, and ion), oxidation (temperature, time, ambient), and preoxidation cleaning procedures. In this study, polysilicon and amorphous silicon films were produced under different controlled process conditions and were analyzed using atomic force microscopy (AFM). Significant differences in morphology between polysilicon and amorphous silicon films were obtained. Polysilicon roughness is an order of magnitude higher than amorphous silicon. Roughness of amorphous silicon films increased...