C. Marques

Luminescence and structural studies of iron implanted α-Al2O3

Abstract Transition metal ions (TM) are typically contaminants of growth processes in wide band gap materials. In Al2O3 (Eg∼9 eV) Cr, Fe and Ti are responsible for red, yellow and blue colored sapphire. While the R-lines from Cr3+ have been extensively studied by photoluminescence (PL) the optical characterization of other transition metal ions is less known. In this work we studied by PL, transmission electron microscopy (TEM) and RBS/channeling measurements a series of iron implanted α-Al2O3 samples. In the red region a sharp emission line at 1.833 eV with a lifetime of ∼1 ms is identified at low temperature. For temperatures above 35 K and on the high energy side a new thermally populated emission line occurs at 1.843 eV. Structural analysis performed by RBS/channeling, TEM and X-ray measurements indicates that metallic iron precipitates as well as iron oxide complexes are present in the samples. Combining the temperature dependence of luminescence and decay times with the results obtained from structural analysis a model for the optical center is discussed.

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)).

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.

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.

Structural and optical characterization of topaz implanted with Fe and Co

Natural single crystalline colourless topaz (Al2SiO4(F, OH)2) samples were implanted at room temperature with Fe and Co ions with fluences in the range of 5×1016–2×1017 ions/cm2. Following implantation, the implanted region becomes amorphous in all cases studied and significant changes occur in the absorption spectra. Irradiated samples were subjected to thermal annealings up to 900 °C in steps of 100 °C. At 700 °C almost all F is lost from the implanted region and the implanted ions diffused into the bulk. In contrast, when virgin samples undergo the same thermal treatments, the fluorine loss is not observed. At higher annealing temperatures the implanted ions segregate to the surface. After annealing at 700 °C the samples implanted with the higher concentration of Co do not present colour changes but develop absorption bands centred at 450 and 740 nm. On the contrary, high dose Fe implanted samples submitted to similar annealing protocol show absorption at 280, 350 and 455 nm, becoming yellow. We propose that the absorption bands are related with the crystal field splitting of the transition metal 3d orbitals, probably in a new compound.

Study of new surface structures created on sapphire by Co ion implantation

Abstract Single crystalline α-Al2O3 was implanted with several fluences of Co ions. Detailed angular scans performed after implantation indicate incorporation of the Co ions into substitutional Al sites for fluences up to 1×10 15 cm −2 . For higher fluences a large amount of defects are produced and new compounds start to form in the implanted region. At a fluence of 5×10 17 cm −2 the samples displayed both metallic conduction and ferromagnetic behaviour. Annealing in an oxidising atmosphere promote the diffusion of Co into the bulk leaving a Co-rich thin layer at the surface and leading to the formation of a Co–Al–O compound that extends to a depth of 250 nm. After this annealing the magnetic behaviour disappears and the samples become insulating. Annealing in a reducing atmosphere produces a Co-rich layer in the topmost 80 nm of the surface without loss of the ferromagnetic behaviour and the metallic conductivity.

Annealing behaviour of natural topaz implanted with W and Cr ions

Abstract Single crystalline samples cleaved from natural topaz were implanted with W and Cr ions with fluences in the range 5×1015–3×1017 ions/cm2. After implantation the implanted region becomes amorphous in all the samples and the absorption spectra reveal significant changes in the near infrared region in the wavelength range 2000–3000 nm. For the lowest doses the transmission has a maximum in this wavelength region. The stoichiometry of the implanted surface changes due to the loss of fluorine after annealing at 600°C. This loss is not observed in virgin samples. Chromium starts to diffuse into the bulk after annealing at 600°C while W profile remains stable up to 800°C. After annealing at 800°C the optical absorption shows a reduction while the damage profile remains without any noticeable change.

Luminescence studies in colour centres produced in natural topaz

Luminescence emission bands originating in colour centres produced in natural topaz have been detected. These bands are studied by steady-state and time-resolved photoluminescence spectroscopy. We found that the energy of the emitting bands are different in colourless samples and in samples submitted to treatment and depend on the treatment itself. Also, there is an emission present in long-lived detection regimes, indicating the possible presence of non-radiative processes. These results are analysed and a possible correlation between structural and colour changes resulting from the irradiation and annealing treatment is addressed.

Features of the pulsed treatment of silicon layers implanted with erbium ions

The formation of thin-film solid solutions of erbium in silicon and synthesis of erbium silicides were performed using continuous implantation of silicon with erbium ions followed by pulsed ion-beam treatment. Structural and optical properties of formed Si:Er layers were studied by Rutherford backscattering, transmission electron microscopy, and low-temperature photoluminescence. The dependences of erbium redistribution, the microstructure of Si:Er layers, and their photoluminescence in the near-IR region on the erbium concentration and pulsed treatment conditions were determined.

Optical changes induced by high fluence implantation of Co ions on sapphire

Abstract Surface properties of single crystalline α-Al 2 O 3 were changed by the implantation of high doses of Co ions. Colorless and transparent (0001) and (1120) sapphire samples were implanted at room temperature with 150 keV cobalt ions with fluences in the range of 10 16 to 5×10 17 Co + /cm 2 . For the highest dose the surface displays a metallic-like behavior after implantation. The absorption spectra reveal the presence of the 200 nm band due to the implantation damage. Annealing in an oxidizing atmosphere promotes the diffusion of Co leading to the formation of a Co–Al–O compound that extends to a depth of 250 nm. This new structure is responsible for the blue and green coloration of the samples, depending on the Co fluence. Annealing in reducing atmosphere produces a Co-rich layer in the first 80 nm of the surface and the samples remain with the dark brown coloration characteristic of the implantation damage.