R.C. da Silva

Characterisation of corrosion products in Cr implanted Mg surfaces

In this work we used medium and high fluence Cr implantation, 5×1016 and 5×1017/cm2 in an attempt to promote the formation of a Mg–Cr surface system with enhanced corrosion resistance, in particular under neutral and acid conditions. It is also the aim of this work to contribute to the study of the influence and role of the implanted ions in the corrosion progress and mechanisms. Unimplanted and Cr implanted magnesium surfaces were submitted to accelerated corrosion tests by the immersion technique. Concentration depth profiles of the implanted ions were obtained by use of Rutherford backscattering spectrometry (RBS). Information about the H and O contents and depth profiles were obtained by, respectively, elastic recoil detection and RBS, before and after immersion of the unimplanted and implanted surfaces in a 3 wt.% NaCl solution saturated with Mg(OH)2, for different periods of time. The elemental composition and surface distribution of the corroded surfaces were characterised by RBS and proton induced X-ray emission maps obtained with an ion microprobe, and complemented with electron microprobe analysis. Morphology of the affected surfaces was accessed by scanning electron microscopy.

Magnetism in Ar-implanted ZnO

ZnO single crystals were implanted with Ar ions with an energy of 100 keV and different fluences. Ferromagnetic behaviour is observed at room temperature after implantation. This behaviour is suppressed after consecutive annealings at 400 and 500 °C. Although trace transition metal impurities have been identified in the virgin samples, it is shown that they cannot account for the observed magnetic behaviour that is assigned to the presence of implantation-induced lattice defects.

Nonlinear optical properties of gold nanoparticles synthesized by ion implantation in sapphire matrix

Single crystal Al2O3 substrates have been implanted with 160-keV Au+ to a dose of 0.6 × 1017 or 1.0 × 1017 cm−2, with a postimplantation annealing for 1 h at 800°C in air. The obtained composite layers were studied by the method of linear optical reflection; the nonlinear optical characteristics were determined by the RZ-scan technique using picosecond radiation pulses of an Nd:YAG laser operating at 1064 nm. The appearance of a characteristic surface optical plasmon resonance band in the linear reflection spectra was indicative of the formation of gold nanoparticles in a subsurface layer of ion-irradiated Al2O3. It is shown that the synthesized particles are responsible for the observed manifestations of nonlinear refraction. The composite layers were characterized by the nonlinear refractive index (n2) and the real part of the third-order nonlinear susceptibility (Reϰ (3)).

Formation of Al13Cr2 intermetallic phase by Cr ion implantation

Abstract In this work, the formation of Al 13 Cr 2 intermetallic phase during high-fluence, high-temperature implantation with Cr ions is reported. It is also shown that it is possible to form the same phase by implantation at lower temperatures, with low fluence, provided that it is followed by a proper annealing. The phase formed is crystalline and it is embedded in the surrounding aluminum matrix.

Structural and optical studies of Co and Ti implanted sapphire

Abstract Single crystals of α-Al 2 O 3 with different orientations were implanted with several fluences of Ti and Co ions. For low fluences both Ti and Co ions are fully incorporated in Al lattice sites and remain stable up to annealing temperatures of 1000 °C. For fluences of 5×10 16 cm −2 the implanted region becomes completely disordered (amorphous) for samples implanted with Ti while for Co the same condition is achieved only for higher fluences (2×10 17 Co + /cm 2 ). The recovery of the implantation damage is almost complete after annealing at 1000 °C in either oxidizing or reducing atmospheres for fluences below 5×10 16 cm −2 . For higher fluences annealing in a reducing ambient promotes the precipitation of crystalline metallic Co and Ti particles, as revealed by TEM and RBS. These precipitates retard the damage recovery. The presence of oxygen during annealing leads to the formation of mixed Co and Al oxides through the entire implanted region. Annealing at 1000 °C promotes the formation of a spinel phase (Al 2 CoO 4 ) and the blue or green coloration of sapphire, depending on the Co fluence. Moreover, narrow red emission lines were observed. For Ti the oxides concentrate at the surface and optical absorption measurements show the presence of a broad absorption band centered at 325 nm. This band is absent in the samples annealed in a reducing atmosphere. Photoluminescence measurements reveal the presence of an emission band centered near 840 nm.

Ion synthesis and optical properties of gold nanoparticles in an Al2O3 matrix

Single-crystal Al2O3(0001) and Al2O3(1120) substrates are implanted by 160-keV Au+ ions with doses from 1015 to 1017 cm−2. Some of the implanted samples are air-annealed at 800–1200°C. The properties of the synthesized composite layers are studied by Rutherford backscattering and linear optical reflection measurements, and their nonlinear optical characteristics are examined by RZ-scanning using a picosecond Nd: YAG laser operating at a wavelength of 1064 nm. The Rutherford backscattering spectra indicate that the implanted impurity concentrates near the surface of the Al2O3. The formation of gold nanoparticles in the Al2O3 can be judged from the characteristic optical plasmon resonance band in the reflectance spectra of the samples irradiated to a dose higher than 6.0 × 1016 cm−2. The synthesized particles are shown to be responsible for nonlinear optical refraction in the samples. The nonlinear refractive index, n2, and the real part of the third-order susceptibility, Rex(3), of the composite layers are determined.

Investigation of the Nonlinear Optical Characteristics of Composite Materials Based on Sapphire with Silver, Copper, and Gold Nanoparticles by the Reflection Z -Scan Method

The nonlinear optical characteristics of silver, copper, and gold nanoparticles synthesized in a sapphire matrix by ion implantation are studied. The measurements are performed by the RZ-scan method with optical reflection at the radiation wavelength of a picosecond Nd:YAG laser (λ = 1064 nm). The nonlinear refractive indices and the real parts of the third-order nonlinear susceptibility of the composites are determined. It is shown that the nonlinear refraction in the samples is caused by the Kerr effect.

High temperature phase transitions and critical exponents of Samarium orthoferrite determined by in situ optical ellipsometry

Determining phase transitions has always been a great challenge in material science due to their important fundamental and technological aspects. Recently, iron-based perovskites (RFeO3), exhibiting phase transitions at high temperatures, have attracted much interest for their functional properties at room temperature, such as multiferroicity (BiFeO3) and ultrafast spin dynamics (TmFeO3). In this family of materials, Samarium orthoferrite (SmFeO3) is a weak ferromagnet, ordering at high temperatures and exhibiting an intrinsic spin reorientation transition above room temperature, which is “hidden” in macroscopic magnetization measurements in polycrystalline samples. In the present article, we show that the related magnetic high temperature phase transitions can be studied through their dielectric functions by spectroscopic ellipsometry in situ and without any need for an applied external magnetic field. The presence of this intrinsic spin reorientation transition is demonstrated for textured SmFeO3 films ...

Optical and mechanical properties of MgO crystals implanted with lithium ions

Defect profile induced by implantation of Li+ ions with an energy of 175 keV and a fluence of 1×1017 ions/cm2 in MgO single crystals was characterized by Rutherford backscattering and optical absorption measurements. Several absorption bands at 5.0, 3.49, 2.16, and 1.27 eV, identical to those found in neutron irradiated crystals, were observed and have been previously associated with oxygen vacancies and higher-order point defects involving oxygen vacancies. Despite the high fluence of Li+ ions, no evidence was found for the formation of Li nanocolloids during implantation. Nanoindentation experiments demonstrated that both the hardness and Young’s modulus were higher in the implanted layer than in the sample before implantation. The maximum values were H=(17.4±0.4) and E=(358±9) GPa, respectively, at a contact depth of ≈165 nm. Thermal annealings in flowing argon at increasing temperatures improved the crystalline quality of the implanted layer. After annealing at 500 K, two extinction bands at ≈2.75 and...

Nitrogen and argon doped zinc oxide.

In this work argon and nitrogen were implanted into ZnO single crystals in order to compare the influence of these non-magnetic elements in the magnetic and electrical behaviour of zinc oxide. The results indicate that both nitrogen and argon implantations induce magnetic defects in ZnO, although these do not remain stable upon annealing. The comparison between the electrical behaviour of argon and nitrogen implanted crystals indicates that mobile charge carriers exist in the argon implanted sample after annealing, but were not detected in the nitrogen implanted sample.