In this paper, the effect of ion irradiation on nanoscale hardness of ZnO microcones is reported. The hardness of ZnO cones determined by nanoindentation using atomic force microscope initially increases from 4.7±1.4 to 9.5±1.6 GPa after irradiation with 1.2 MeV Ar+8 ions at an ion fluence of 1015 ions cm−2 and then decreases with increasing ion fluence. This change in mechanical hardness has been correlated with the residual stress of the sample revealed by Raman peak shift in the E2(H) mode. These results show that the generally reported radiation-hard nature of ZnO depends critically on irradiation conditions, especially the irradiation temperature.

Radiation induced modification in nanoscale hardness of ZnO cone structures

The dispersion capacity of MoO3 on the surface of muscovite powder was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The results indicated that MoO3 can disperse onto the surface of a support as a sub-monolayer. The dispersion capacity was 5.88 mg MoO3
(g muscovite)−1, or 3.24 Mo atoms nm−2. The diffusing process of MoO3 on muscovite wafer was investigated by means of Synchrotron Radiation excited Total-reflection X-Ray Fluorescence spectroscopy (SR-TXRF). A stripe of MoO3 on the muscovite wafer was used as the diffusion source. After thermal treatment in air or dry N2, MoO3 diffuses onto the surface of muscovite and forms a sub-monolayer. Sublimation of MoO3 was also detected during the diffusion process. The diffusion rate in two heating atmospheres differed significantly. The diffusion rate of MoO3 on muscovite in dry N2 was greater than that in air. A possible explanation of the phenomena is that surface diffusion onto the muscovite surface plays a more important role in the process than transportation via gas phase during the diffusion of MoO3.

Study of monolayer dispersion of MoO3 on muscovite powder and diffusing behavior of MoO3 on muscovite wafer by SR-TXRF

Метою даної роботи є оцінка енергетичної сприятливості утворення різних молібдатних груп (≡Si‑O‑)2Mo(=O)2 та =Si(‑O‑)2Mo(=O)2 під час термічно ініційованого диспергування MoO3 на гідроксильованій поверхні SiO2. Для цього було здійснено квантовохімічне моделювання реакції O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O в температурному інтервалі 300–1100 K із використанням обмеженого методу Хартрі-Фока (наближення ЛКАО) з валентним базисом SBKJC (Stevens-Basch-Krauss-Jasien-Cundari). Кластер O12Si10(OH)16, який являє собою структурний фрагмент кристала β‑кристобаліту, був використаний як модель високогідроксильованої поверхні кремнезему. Ми розглянули дві структури молібдатних груп (≡Si‑O‑)2Mo(=O)2, прикріплених до кремнеземного кластера O12Si10(OH)16 через силанольні групи. Молібдатні групи (Etot ‑584.60147 Hartree), прикріплені до кремнеземного кластера через віддалені силанольні групи, виявляються більш енергетично вигідними, ніж молібдатні групи (Etot ‑584.56565 Hartree), прикріплені до кремнеземного кластера через сусідні силанольні групи. Енергія молібдатних груп =Si(‑O‑)2Mo(=O)2 (Etot ‑584.48399 Hartree), прикріплених до кремнеземного кластера O12Si10(OH)16 через силандіольні групи, менш енергетично вигідні в порівнянні з подібними групами, прикріпленими через силанольні групи, через більше напруження кута між зв’язками. Знайдено, що реакція O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O в температурному інтервалі 300–1100 K, змодельована шляхом квантовохімічних розрахунків, свідчить, що процес диспергування MoO3 на гідроксильованій поверхні SiO2 є енергетично вигідним. Експ The aim of the present work is to evaluate the energetic favourability of the formation of different molybdate species (≡Si‑O‑)2Mo(=O)2 and =Si(‑O‑)2Mo(=O)2 during the thermally induced MoO3 dispergation on hydroxylated SiO2 surface. In order to do this a quantum chemical modelling of the reaction O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O within the temperature interval of 300–1100 K was undertaken using the Restricted Hartree-Fock method (the LCAO approximation) with the SBKJC (Stevens-Basch-Krauss-Jasien-Cundari) valence basis set. The cluster O12Si10(OH)16 which represents a structural fragment of a β‑cristobalite crystal was used in this work as a model of highly hydroxylated silica surface. We considered two structures of molybdate (≡Si‑O‑)2Mo(=O)2 species attached to O12Si10(OH)16 silica cluster via silanol groups. Molybdate species (Etot ‑584.60147 Hartree) attached to silica cluster via distant silanols appeared more energetically favourable than molybdate species (Etot ‑584.56565 Hartree) attached to silica cluster via nearby silanols. The energy of molybdate =Si(‑O‑)2Mo(=O)2 species (Etot ‑584.48399 Hartree) attached to O12Si10(OH)16 silica cluster via silanediol group is less favourable energetically in comparison with those attached via silanol groups because of higher bond angle straining. The reaction O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O in the temperature interval of 300–1100 K which simulates by quantum chemical calculations the dispergation of MoO3 on hydroxylated SiO2 surface was found to be energetically favourable. The experimentally optimised temperature of ca. 800 K required for dispergation of MoO3 on hydroxylated SiO2 surface is determined by MoO3 evaporation and transportation via the gas phase. ериментальна оптимальна температура (близько 800 K), потрібна для диспергування MoO3 на гідроксильованій поверхні SiO2, визначається випаровуванням та перенесенням MoO3 в газовій фазі.

Quantum Chemical Simulation of MoO3 Dispergation on Hydroxylated SiO2 Surface

The diffusion process Of MoO3 and ZnO on stable oxide thin films (SiO2, Al2O3, TiO2) was investigated mainly by means of synchrotron-radiation-excited total reflection x-ray fluorescence spectroscopy (SR-TXRF). A stripe Of MoO3 or ZnO on the oxide thin film was used as the diffusion source. After thermal treatment, MoO3 diffused onto the surface of those films and formed a monolayer or a submonolayer. The diffusion capacity and the diffusion rate Of MoO3 on each film differed significantly. Sublimation of MoO3 also was detected during the diffusion process. A possible explanation for all the phenomena is the combination of surface diffusion onto the surface of the support and transportation via the gas phase. By contrast, ZnO hardly diffuses onto the surface of the film due to its high melting point. Copyright (C) 2001 John Wiley & Sons, Ltd.

Study of the diffusion behaviour of MoO3 and ZnO on oxide thin films by SR-TXRF†

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Study of the diffusion behaviour of MoO3 and ZnO on oxide thin films by SR-TXRF†