C. Falcony

Structural and photoluminescent characteristics of yttrium–aluminum oxide films doped with Tb, Eu or Ce

Abstract The structural and room temperature luminescent characteristics of rare earth doped yttrium–aluminum oxide films deposited by the spray pyrolysis technique at low temperatures have been studied as a function of the deposition parameters such as substrate temperature and dopant concentration. The spraying solution is prepared by mixing yttrium and aluminum chlorides in water, and the incorporation of the rare earth dopants is achieved by adding chloride salts of these elements to this solution. The photoluminescent emission from Tb- and Eu-doped films have the spectral characteristics typical of radiative transitions among the electronic energy levels associated with the 3+ ionized states of these atoms. The Ce doped films, on the other hand, present a blue emission that is associated with transitions within the energy states of the CeCl 3 molecule used for the doping process of the film. The X-ray diffraction measurements of these films indicated poor crystallinity in general, with small crystalline peaks and a broad amorphous component that tend to be reduced as the deposition temperature is increased.

Duality metal oxide semiconductor–PN junction in the Al/silicon rich oxide/Si structure as a radiation sensor

In this work the possibilities of using the induced PN junction as a photon detector in the Al/silicon rich oxide/Si devices is investigated. The devices were fabricated on high resistivity silicon substrates, the chemical vapor deposition (CVD) silicon rich oxide reactive gases ratio used was 20. Experimental results show that this device is sensitive to visible light, and that is possible, in a controlled and simple manner, to use the PN-induced junction as a detector.

Optical, electrical, and structural characteristics of yttrium oxide films deposited on plasma etched silicon substrates

Yttrium oxide thin films were deposited on Si(100) substrates using the rf-sputtering technique at low power density and low temperatures (up to 300 °C). Previous to deposition, the substrates were plasma etched during different lengths of time. The characteristics of these films and the effect of surface etching on the substrate were studied by ellipsometry, x-ray diffraction at grazing angle, atomic force microscopy, and x-ray energy dispersive spectroscopy (EDS). The deposited films were polycrystalline, presenting cubic and/or monoclinic phases. The deposition rate, refractive index, surface roughness, and degree of crystallinity were strongly dependent on etching time of the substrate, especially for low deposition temperatures. The electrical characterization of the films incorporated in a metal–oxide–semiconductor structure showed a good dielectric constant value (up to 11), surface states densities as low as 6.7×1011 cm−2 eV−1 at midgap and breakdown strength in the range of 1.16–4.84 MV/cm. EDS m...

Metal oxide Co and Co-Fe-Cr films deposited on glass substrates from a metal-organic aerosol atomised by means of ultrasonic excitations

Abstract Thin films of metal oxides of Co and the Co -Fe -Cr system were deposited on a commercial soda-lime-silica float gray glass from an aerosol generated by ultrasonic excitation, using acetylacetonates as the source of the aerosol. Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) studies performed prior to the film deposition revealed a principal difference between the thermal decomposition of acetylacetonates and the nitrates used previously, influencing greatly the properties of the synthesised films. Deposited films were characterised by the measurement of their optical properties that are vital for privacy purposes (i.e., reflectance, transmittance), and of their surface roughness and thickness measurements. Crystallinity of films has been investigated and chemical durability tests have been performed. Results of these investigations are presented and the properties of films are compared with those obtained from films deposited previously from a nitrate aerosol generated either pneumatically or by means of ultrasonic excitation.

Preliminary studies of thin metal oxide films prepared by deposition of an aerosol generated ultrasonically from aqueous nitrate solutions

Abstract Thin Co, Co-Fe and Co-Fe-Cr metal oxide films were prepared by deposition of an aerosol generated by ultrasonic excitations from aqueous nitrate solutions. Commercial gray glass has been used as substrates. Thermogravimetric (TG and DTG) measurements of initial nitrate components as well as their homogenized mixtures were performed and optical properties, i.e. reflectance and transmittance of the deposited films in the UV-visible and near-infrared regions up to 4761 nm, were measured. The surface roughness of the films was also measured and their chemical durability tested. The reflectance values obtained for 550 nm radiation wavelength were 25–33% for Co-oxide films compared to 20–30% for films deposited by us from a pneumatic aerosol, or values of 10–15% reported by others. The reflectance was 21–28% for Co:Fe = 15:1 films and up to 26% and 30% for Co:Fe:Cr = 15:1:0.25 and Co:Fe:Cr = 12:3:1 films, respectively. The reflectance of the uncoated reference glass was 5%. The surface roughness values of films deposited from ultrasonic aerosol dropped to about 50–60% of the value measured for films deposited from pneumatic aerosol. At the same time the chemical durability of films deposited from ultrasonic aerosol has approximately doubled.

Influence of substrate and precursor film composition on morphology and superconducting transition of Tl-2212 thin films characterized by microwaves

Abstract An influence of various substrates (MgO, LaAlO 3 , SrTiO 3 , YSZ, CeO 2 /r-sapphire) and Ba–Ca–Cu precursor chemical composition (212, 223) upon morphology and microwave quality of Tl 2 Ba 2 CaCu 2 O 8 (Tl-2212) thin films has been studied. Under the same thalliation conditions, Tl-2212 phase has been synthesized in all films independently of the initial precursor film chemical composition (212, 223) with almost the same T c values. However, the film surface morphology and, thus, the microwave surface impedance, both were found to be strongly dependent from the type of substrate used as well as from the precursor chemical composition. Films with sharp transition to the superconducting state were prepared when 212 precursors were deposited on the MgO and/or LaAlO 3 substrates.

RBS characterization of MgB2 superconducting films annealed ex situ and in situ

The elemental composition and depth profiles of MgB2 films prepared by successive e-beam evaporation as well as by thermal co-deposition of Mg and B components were investigated by Rutherford backscattering spectrometry (RBS). In the case of films deposited by e-beam evaporation we studied both Mg-B precursors and appropriate MgB2 films grown on glassy carbon, Si(100) and J-sapphire substrates annealed in situ. For the films co-deposited by thermal evaporation on R-sapphire substrates and annealed ex situ we investigated superconducting MgB2 films only. The Tco values of all MgB2 films ranged from 21 to 30 K. Because of a very fine granular structure of the annealed films, confirmed also by SEM observations, we could not identify any MgB2 phase from x-ray diffraction (XRD) patterns. On the other hand, Mg2Si phase has been detected by XRD on the film–substrate interface for the superconducting film deposited on Si(100) substrate. The RBS measurements were performed with a 3.1 MeV 4He+ beam. Under these conditions, the 16O(α,α)16 elastic resonance allowed us to detect oxygen in all studied samples especially in B layers. The depth profiles of precursors prepared by successive e-beam evaporation showed clearly the multilayer film structure consisting of B and Mg layers. A strong interdiffusion between B and Mg layers may be observed after an in situ annealing, but still some degree of non-homogeneous component distribution may be observed. On the other hand, the MgB2 films co-deposited by thermal evaporation and annealed ex situ are much more homogeneous, but a higher content of oxygen is present.

Characterization of SiOxNy films deposited from SiCI4 by remote plasma-enhanced chemical vapor deposition

Abstract Silicon oxynitride films have been deposited with SiCl4 by remote-plasma enhanced chemical vapor deposition and a substrate temperature of 250°C. Different mixtures of O2 and NH3 were used to obtain different oxynitride compositions ranging from SiO2 to a stoichiometry close to that of silicon nitride. Rutherford backscattering spectrometry was used to determine the stoichiometry of the SiOxNy films. Also, the behavior of the IR absorption spectra as well as the refractive index measured by ellipsometry were used to estimate the effect of the different deposition parameters. It was found that the IR spectra show a shift of the characteristic peak associated with the stretching vibration mode of the Si–O–Si bonds towards lower wave numbers as the relative concentration of ammonia was increased with respect to oxygen. No double peaks associated with silicon oxide and silicon nitride were observed, indicating the formation of an homogeneous alloy. The IR spectra did not show any presence of water or hydrogen related impurities in the films. The effect of a hydrogen flow added during the deposition process on the films was studied. Atomic force microscopy measurements on these films show that the hydrogen flow added during deposition results in a reduction of the film roughness, which might be very significant for applications of silicon oxynitrides in very large scale integration microelectronics. Dielectric parameters as well as the dc conductivity of the films under the effect of an external sinusoidal electric field have been calculated in order to complete the structural characterization of the films.

Study of the superconducting MgB2 films by ion beam analysis methods

Superconducting MgB 2 films were prepared by sequential e-beam evaporation of boron and magnesium on randomly oriented sapphire, glassy carbon and silicon substrates followed by an in-situ annealing. Ion beam analysis (IBA) methods using a 2530 keV 3 He + beam were applied to obtain the Mg and B film profiles by Rutherford backscattering (RBS) and nuclear reaction analysis (NRA). It was found that Mg and B diffuse rather deeply into the substrates due to the annealing process. A presence of O and C in the MgB 2 films was detected, apparently as formation of MgO and eventually B 2 O 3 . The zero resistance critical temperatures T co values were 28 K for MgB 2 /Al 2 O 3 and 25 K for MgB 2 /C samples. Because of a rather high annealing temperature of 700 °C, we obtained T co = 8 K only in the case of MgB 2 /Si(111) sample.

Low-energy particle treatment of GaAs surface

Abstract Modification of high-doped GaAs surface by the interaction with RF plasma and a monoenergetic beam of similar chemical composition (Ar with a low content of H 2 ) was investigated via the evolution of optical, electrical and structural properties. A reduction in the free charge concentration in the GaAs surface region of ∼100 nm in thickness is concluded from Raman spectroscopy. In the processed samples, the surface electric field strength induced by a laser beam (photoreflectance technique) continually decreases with both the energy and fluence of impinging particles. The same results were obtained by evaluation of quasistatic C – V curves of corresponding MOS structures. They confirmed that longer exposure caused the formation of ∼100-nm-thick modified near-surface region with a decreased donor concentration. After the plasma irradiation, an ∼10-nm-thick outermost insulating layer was created in situ. The formation of textured polycrystalline grains with (100) orientation in the surface region was observed by X-ray diffraction.