P. Lu

Ion-irradiation-induced phase transformation in rare earth sesquioxides (Dy2O3,Er2O3,Lu2O3)

Polycrystalline pellets of cubic C-type rare earth structure (Ia3¯) Dy2O3, Er2O3, and Lu2O3 were irradiated at cryogenic temperature (120K) with 300keV Kr++ ions to a maximum fluence of 1×1020Kr∕m2. Irradiated specimens were examined using grazing incidence x-ray diffraction and transmission electron microscopy. Ion irradiation leads to different radiation effects in these three materials. First, Dy2O3 begins to transform to a monoclinic B-type rare earth structure (C2∕m) at a peak dose of ∼5 displacements per atom (dpa), (corresponding to a fluence of 2×1019Kr∕m2). This transformation is nearly complete at a peak dose of 25 dpa (a fluence of 1×1020Kr∕m2). Er2O3 also transforms to the B-type structure, but the transformation starts at a higher irradiation dose of about 15–20 dpa [a fluence of about (6–8)×1019Kr∕m2]. Lu2O3 was found to maintain the C-type structure even at the highest irradiation dose of 25 dpa (a fluence of 1×1020Kr∕m2). No C-to-B transformation was observed in Lu2O3. The irradiation dose...

Damage evolution in Xe-ion irradiated rutile (TiO2) single crystals

Abstract Rutile (TiO 2 ) single crystals with (1xa01xa00) and (1xa00xa00) orientations were irradiated with 360 keV Xe 2+ ions at 300 K to fluences ranging from 1×10 17 to 5×10 20 Xe/m 2 . Irradiated samples were analyzed using Rutherford backscattering spectroscopy combined with ion channeling analysis (RBS/C) and transmission electron microscopy (TEM). RBS/C results showed that much of the instantaneous displacement damage produced under ion irradiation is recovered under ambient temperature irradiation conditions. Upon irradiation to a fluence of 2×10 19 Xe/m 2 , the radiation damage-induced microstructure was observed by TEM to consist of three distinct layers: (1) a layer near surface (thickness about 12 nm) exhibiting relatively homogeneous TEM contrast; (2) a second layer with a low density of relatively large-sized defects; and (3) a third layer consisting of a high concentration of small defects. After the fluence was increased to 5×10 19 Xe/m 2 , a buried amorphous layer was observed by TEM. The thickness of the amorphous layer was found to increase with increasing Xe ion fluence. The uppermost damage layer, which accounts for the surface subpeak in RBS/C spectra, was found to be polygonized by ion irradiation.

Heavy ion irradiation-induced phase transformation in polycrystalline Dy2O3

Radiation damage effects in polycrystalline pellets of the rare earth sesquioxide Dy2O3 irradiated with 300u2009keV Kr2+ ions were studied by combining grazing incidence X-ray diffraction (GIXRD) with transmission electron microscopy (TEM). Radiation damage was introduced using 300u2009keV Kr2+ ions to fluences up to 1u2009×u20091020u2009Kru2009m−2 at cryogenic temperature. GIXRD and cross-sectional TEM observations revealed that the crystal structure of the irradiated Dy2O3 transformed from a cubic, so-called C-type rare earth sesquioxide structure to a monoclinic, B-type rare earth sesquioxide structure upon ion irradiation. In addition, TEM and high-resolution electron microscopy (HREM) indicated that the transformed surface Dy2O3 layer adopts an epitaxial orientation relationship with the substrate Dy2O3.

Order-disorder phase transformation in ion-irradiated rare earth sesquioxides

An order-to-disorder (OD) transformation induced by ion irradiation in rare earth (RE) sesquioxides, Dy2O3, Er2O3, and Lu2O3, was studied using grazing incidence x-ray diffraction and transmission electron microscopy. These sesquioxides are characterized by a cubic C-type RE structure known as bixbyite. They were irradiated with heavy Kr++ ions (300keV) and light Ne+ ions (150keV) at cryogenic temperature (∼120K). In each oxide, following a relatively low ion irradiation dose of ∼2.5 displacements per atom, the ordered bixbyite structure was transformed to a disordered, anion-deficient fluorite structure. This OD transformation was found in all three RE sesquioxides (RE=Dy, Er, and Lu) regardless of the ion type used in the irradiation. The authors discuss the irradiation-induced OD transformation process in terms of anion disordering, i.e., destruction of the oxygen order associated with the bixbyite structure.

Effect of heavy ion irradiation on near-surface microstructure in single crystals of rutile TiO2

Abstract Radiation damage near the surface of rutile (TiO2) single crystals irradiated with 360 keV Xe2+ ions has been studied by combining Rutherford back-scattering spectroscopy and ion channelling (RBS/C) analyses with direct observations using transmission electron microscopy (TEM). lrradiations were performed at ambient temperature on TiO2 single crystal surfaces with (110) and (100) orientations, using ion fluences of up to 7 × 1019 Xe ions m−2. The RBS/C spectra revealed two damage peaks: one peak due to a surface damage layer and a second peak due to a buried damage layer near the mean projected range of the implanted ions. Cross-sectional TEM and high-resolution electron microscopy revealed that the surface damage layer consists of TiO2 crystallites with different orientations compared with the original single crystal.

Damage Evolution in Xe-Ion Irradiated Rutile (TiO 2 ) Single Crystals

Rutile (TiO 2 ) single crystals with (110) orientation were irradiated with 360 keV Xe 2+ ions at 300K to fluences ranging from 2×10 19 to 1×10 20 Xe/m 2 . Irradiated samples were analyzed using: (1) Rutherford backscattering spectroscopy combined with ion channeling analysis (RBS/C); and (2) cross-sectional transmission electron microscopy (XTEM). Upon irradiation to a fluence of 2×1O 19 Xe/m 2 , the sample thickness penetrated by the implanted ions was observed to consist of three distinct layers: (1) a defect-free layer at the surface (thickness about 12 nm) exhibiting good crystallinity; (2) a second layer with a low density of relatively large- sized defects; and (3) a third layer consisting of a high concentration of small defects. After the fluence was increased to 7×10 19 Xe/m 2 , a buried amorphous layer was visible by XTEM. The thickness of the amorphous layer was found to increase with increasing Xe ion fluence. The location of this buried amorphous layer was found to coincide with the measured peak in the Xe concentration (measured by RBS/C), rather than with the theoretical maXimum in the displacement damage profile. This observation suggests the implanted Xe ions may serve as nucleation sites for the amorphization transformation. The total thickness of the damaged microstructure due to ion irradiation was always found to be much greater than the projected range of the Xe ions. This is likely due to point defect migration under the high stresses induced by ion implantation.

Microstructure of heteroepitaxially grown RuO2 thin films on MgO by pulsed-laser deposition

Abstract Conductive ruthenium oxide (RuO2) thin films with a room-temperature resistivity of 35μΩcm and a residual resistivity ratio above 5 have been heteroepitaxially grown on MgO(100) substrates by pulsed-laser deposition. The heteroepitaxial growth of RuO2 on MgO is confirmed by both the strong in-plane and the strong out-of-plane orientation of the film with respect to major axes of the substrate. The orientation relationship between the RuO2 film and the MgO substrate, deduced from both X-ray and electron diffraction, is (110)RuO2 ∥ (100)MgO and [001]RuO2 ∥ [011]MgO) (and [110]RuO ∥ [01 1]MgO). High-resolution electron microscopy reveals that the epitaxial RuO2 film contains two variants that are consistent with the X-ray diffraction measurement.