A. Paoletti

Growth of diamond films: General correlation between film morphology and plasma emission spectra

We have studied the emission spectra from plasmas excited in several compositions of three different gas mixtures useful for the growth of diamond films, namely CH4‐H2 (the classical one), CH4‐CO2 and C2H2‐CO2 (not previously reported by other authors). In all three cases we find the same correlation between the quality of the obtained diamond films and some spectral features: in particular, the yield of the best diamond films corresponds to the presence of the emission line at wavelength 431 nm ascribed to CH, in the absence of the emission band at 505–517 nm attributed to C2. The appearance and the progressive increase of the latter corresponds to a gradual worsening of the diamond film quality. We propose such spectral features of the plasma as a general and practical gauge of the diamond film growth conditions, for any gas mixture used.

Compositional and spectroscopic study of the growth of diamond films from several gaseous mixtures

A critical experimental test of the empirical unifying scheme recently proposed by Bachmann, Leers, and Lydtyn [Diamond and Related Mater. 1, 1 (1991)] about the gas compositions useful to grow diamond films by plasma‐assisted chemical‐vapor deposition has been performed. The data confirm the main concept of the Bachmann scheme, namely, the existence of a single compositional ‘‘diamond domain’’ in a C‐O‐H triangular diagram, in which the overall gas compositions are plotted; however, quantitatively, the shape and the borders of such a diamond domain are rather different from those assumed in the work of Bachmann and co‐workers. For all the gas mixtures investigated, the changes in the plasma optical emission spectra consequent to crossing the border from the ‘‘no‐growth zone’’ into the ‘‘diamond domain’’ have been studied. These changes show universal features, which point to the presence of the same growth mechanisms over all the diamond domain, independent of the identity of the initial chemical species.

Growth of textured films of Bi2Sr2CaCu2O8+x from KCl solution

Films of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+//sub x/ have been grown from KCl solution. Gadolinium gallium garnet substrates (1 1 1) oriented have been used. The films resulted highly textured with the c axis perpendicular to the substrate surface. The onset of the resistive transition was 85 K, while zero resistance was obtained at 50 K. This technique is particularly promising in view of the possibility to grow large epitaxial films of both the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+//sub x/ and the Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+//sub x/ phases.Films of Bi2Sr2CaCu2O8+x have been grown from KCl solution. Gadolinium gallium garnet substrates (1u20091u20091) oriented have been used. The films resulted highly textured with the c axis perpendicular to the substrate surface. The onset of the resistive transition was 85 K, while zero resistance was obtained at 50 K. This technique is particularly promising in view of the possibility to grow large epitaxial films of both the Bi2Sr2CaCu2O8+x and the Bi2Sr2Ca2Cu3O10+x phases.

Electrical transport properties of artificially layered films of [BaCuO2](2)/[(Sr,Ca)CuO2](n)

In this letter we show that SrCuO2/BaCuO2 and CaCuO2/BaCuO2 based artificial structures of very good crystallographic quality can be grown by pulsed laser deposition. We demonstrate that the most important parameters which determine the superconductive properties are the chemical composition, the oxygen growth pressure, and the CO2 contamination. A major difference is found in the behavior of resistivity between films containing Sr and Ca, respectively. Namely [BaCuO2]2/[SrCuO2]n films never show any trace of superconductivity, while [BaCuO2]2/[CaCuO2]n films result in having, for growth oxygen pressures PO2⩾0.2 mbar, a full transition with Tc (zero resistance) up to 46 K. Furthermore we demonstrate that even a tiny amount of CO2 in the oxygen growth atmosphere can suppress completely the superconducting properties of these artificial structures.

Effect of gas composition on texture of diamond films

Textured diamond films have been deposited on single‐crystal silicon substrates by microwave plasma‐enhanced chemical vapor deposition. Several unconventional gas mixtures (CO2–CH4, CO2–C2H6, and CO2–C2H4) were used in order to study the texturing formation within the diamond stability region in the C–O–H phase diagram. Optical emission spectroscopy was used to monitor the compositional dependence of the plasma emission. The obtained diamond films were characterized by scanning electron microscopy and x‐ray diffraction. Diamond films deposited with all the gas mixtures showed very similar surface morphologies and (100) texturing was achieved only within a very narrow compositional range. Finally, a correlation was found between texturing conditions and CH and C2 line intensities in the plasma emission spectra.

Fast growth of Bi2Sr2Ca2Cu3O10+x and Bi2Sr2CaCu2O8+x thin crystals at the surface of KCl fluxes

We report a novel technique to grow crystals of the high‐temperature superconductor Bi2Sr2Ca2Cu3O10+x and Bi2Sr2CaCu2O8+x (2223 and 2212 BSCCO phases), both pure and Pb substituted. The technique, based on chemical transport in a thermal gradient in molten KCl, is simple and inexpensive, and yields a continuous output of crystals, with growth times of a few minutes, i.e., orders of magnitude shorter than conventional flux methods. Depending on melt aging, crystals of either the pure 2223 or the pure 2212 BSCCO phases are obtained, having zero‐resistance temperature of 105 and 90 K, respectively, and a transport critical current density of 104 Au2009cm−2 at liquid nitrogen temperature.

Epitaxial LiNbO3 thin films grown by pulsed laser deposition for optical waveguides

We have grown good-quality epitaxial LiNbO3 thin films on (0001) sapphire substrates using a pulsed laser deposition technique. The growth conditions permitted us to deposit c-axis oriented films avoiding the problem of the LiNb3O8 Li-deficient phase. The chemical composition of thin films was investigated by secondary ion mass spectrometry and resulted to coincide with the target composition. Guided propagation was demonstrated at 632 and 488 nm with thin films (∼1200 A).

PULSED LASER DEPOSITION OF SRCUO2/CACUO2 SUPERLATTICES

We have shown that the pulsed laser deposition (PLD) technique, with no in situ diagnostic, can be used to grow good quality superlattices based on the infinite layer compounds SrCuO2 and CaCuO2. We demonstrated that the major source of disorder in these superlattices, grown at temperatures lower than 600u2009°C, comes from random discrete thickness fluctuations. However the random discrete thickness fluctuations affect essentially only one unit cell. This makes the PLD technique very attractive for the growth of new artificial high‐Tc structures based on the infinite layers compounds.

Transport critical current density in epitaxial Bi2Sr2CaCu2O8+x films: Effects of the substrate twinning

Epitaxial Bi2Sr2CaCu2O8+x films have been grown by the liquid phase technique on twinned LaGaO3 and untwinned SrTiO3 substrates. Crystallographic properties and transition temperatures are comparable, but the transport critical current density Jc depends dramatically on the substrate. Films grown on SrTiO3 have Jc comparable with single crystals, while films grown on LaGaO3 have Jc values extrapolated at 4.2 K in the 104–105 Au2009cm−2 range. This effect is demonstrated to be a consequence of the presence of twinning domains in the substrate.

Superconducting properties of [ BaCuO x ] 2 / [ CaCuO 2 ] n artificial structures with ultrathick CaCuO 2 blocks

The electrical transport properties of