http://nanomechanics.mit.edu/sites/default/files/documents/Kumar_03.pdf

Mechanical behavior of nanocrystalline metals and alloys

This paper presents an overview of the strain hardening and strain rate hardening behavior of nanostructured and ultrafine-grained metals. The experimental findings obtained in our laboratory are summarized, with some recent data for ultrafine-grained Cu presented as a model case. Due to the diminishing strain hardening capacity and inadequate strain rate hardening, plastic instabilities in the form of inhomogeneous and localized deformation such as necking and shear banding often contribute to the low ductility of nanostructured and ultrafine-grained metals at room temperature (RT). The observed grain size dependence of the strain rate sensitivity is also discussed in terms of its implications for new deformation mechanisms when the grain size is in the nanocrystalline (nc) and ultrafine regime.

Strain hardening, strain rate sensitivity, and ductility of nanostructured metals

A commercial aluminum alloy, 5083, was processed using a cryomilling synthesis approach to produce powders with a nanostructured grain size. The powders were subsequently degassed, hot isostatically pressed, and extruded. The grain size at each processing step was measured utilizing both X-ray diffraction and transmission electron microscopy (TEM). The mechanical properties of the n-5083 extruded material were determined utilizing ASTM E8-93, Standard Test Methods for Tension Testing of Metallic Materials. This processing technique was found to produce a thermally stable nanostructured aluminum alloy which maintained an average grain size of 30 to 35 nm through several processing steps up to 0.61 T
 mp
 . The thermal stability was attributed to Zener pinning of the grain boundaries by AIN and Al2O3 particles and solute drag of numerous atomic species. The nanostructured 5083 was found to have a 30 pct increase in yield strength and ultimate strength over the strongest commercially available form of 5083, with no corresponding decrease in elongation. The enhanced ductility is attributed to the presence of a few large, single-crystal aluminum grains acting as crack-blunting objects.

Mechanical behavior and microstructure of a thermally stable bulk nanostructured Al alloy

Development of ion-implanted optical waveguides in optical materials: A review

Energetic ion beams with diverse energies, species and beam dimensions have been extensively utilized to modify the properties of materials to achieve versatile applications in many aspects of industry, agriculture and scientific research. In optics, the ion-beam technology has been applied to fabricate various micro- and submicrometric guiding structures on a wide range of optical crystals through the efficient modulation of the refractive indices or structuring of the surface, realizing various applications in many branches of photonics. The ion-beam fabricated optical waveguides and other photonic structures have shown good guiding performance as well as properties related to the materials, suggesting promising potential for many aspects of photonics. This paper gives the state-of-the-art review of fabrication, characterization and application on the ion-beam-processed micro- and submicrometric photonic structures by highlighting the most recent research progress. A brief prospect is presented by focusing on a few potential spotlights.

Micro- and submicrometric waveguiding structures in optical crystals produced by ion beams for photonic applications

ZnO/Mg0.16Zn0.84O (ZnO/MgZnO) films are fabricated on x-cut and z-cut LiNbO3 (LN) substrates by radio-frequency magnetron sputtering. High transparencies are confirmed by a spectrophotometer. X-ray diffraction (XRD) spectra show that all the films are c-axis oriented. The waveguiding properties, as well as the refractive indices and thickness of the films are demonstrated and determined by prism coupling. Both transverse electric (TE) and transverse magnetic (TM) modes are measured at λ=0.633 µm and 1.539 µm, respectively. The waveguide loss is measured at λ=0.633 µm with a fiber probe technique. The experimental results show that high optical quality ZnO films can be obtained with MgZnO buffer layers.

Formation of c-axis oriented ZnO optical waveguides by radio-frequency magnetron sputtering

A model is presented to explain the refractive-index changes in the ion-implanted $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ waveguides that indicates that the lattice damage may be the main factor for the refractive-index changes. The model indicates that a slight enhancement may occur for the extraordinary refractive index in the ion-implanted $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ waveguides with lattice damage ratios of less than 65%, and a maximum positive change $(\ensuremath{\Delta}n=0.0338)$ occurs at a damage ratio of 33%. The model explains both the positive refractive-index changes observed in waveguides formed using $500\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ ${\mathrm{Si}}^{+}$-ion implantation and the refractive-index changes observed in ${\mathrm{He}}^{+}$-ion-implanted waveguides.

Model of refractive-index changes in lithium niobate waveguides fabricated by ion implantation

Erbium doping into potassium titanyl phosphate (KTiOPO4 or KTP) was performed by pulsed laser deposition. Waveguide laser film in Er-doped KTiOPO4 was formed using both KTiOPO4 and erbium as targets and optically polished KTiOPO4 as a substrate. Rutherford backscattering, photoluminescence spectrometry, x-ray diffraction, and prism coupling method are used to investigate the properties of Er-doped KTiOPO4. The results show that (1) Er-doped KTiOPO4 emits the characteristic photoluminescence of Er3+ around 1.54 μm corresponding to transition between the 4I13/2 and 4I15/2 manifolds of the Er3+ ions in KTiOPO4 host. (2) two bright modes in Er-doped KTiOPO4 were observed. This approach may be useful for direct fabrication of thin film waveguide laser for other optoelectrical materials.

Waveguide laser film in erbium-doped KTiOPO4 by pulsed laser deposition

Tm+, Er+ and Yb+ have been implanted into LiNbO3 and quartz crystal (SiO2) in the energy range 100–400 keV. The profile of implanted ions was measured by Rutherford backscattering of MeV He ions. The mean projected range and range straggling obtained were compared with TRIM code. The result shows that (1) The mean projected range and range straggling are in well agreement with TRIM prediction except for 100 keV for LiNbO3 (2) The mean projected range is in good agreement with TRIM prediction within 8%, but the experimental range straggling is higher than the calculated value by TRIM code for quartz crystal. After 800°C annealing for 30 min, it is found that there is no obvious diffusion for the case of 300 keV Er+, but for the case of 300 keV Yb+ the diffusion occurs and the diffusion coefficient D estimated is 2.77×10−15 cm2 s−1.

Range and thermal behaviour studies of Tm+, Er+ and Yb+ implanted into LiNbO3 and quartz crystal

Reconstruction of extraordinary refractive index profiles of optical planar waveguides with single or double modes fabricated by O2+ ion implantation into lithium niobate

Fei Lu

Papers

Formation of c-axis oriented ZnO optical waveguides by radio-frequency magnetron sputtering

Model of refractive-index changes in lithium niobate waveguides fabricated by ion implantation

Waveguide laser film in erbium-doped KTiOPO4 by pulsed laser deposition

Range and thermal behaviour studies of Tm+, Er+ and Yb+ implanted into LiNbO3 and quartz crystal

Reconstruction of extraordinary refractive index profiles of optical planar waveguides with single or double modes fabricated by O2+ ion implantation into lithium niobate