500 keV Ar2+ ion irradiation induced anatase to brookite phase transformation and ferromagnetism at room temperature in TiO2 thin films

Bharati, B.; Mishra, N. C.; Kanjilal, D.; Rath, Chandana

doi:10.1016/j.apsusc.2017.09.070

Cited by 24 publications

(9 citation statements)

References 32 publications

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“…Raman spectroscopy is a powerful technique useful in the microstructural analysis of materials at the nanoscale. − In recent years, the optical Raman modes of titanium dioxide (TiO 2 ) nanocrystals have been object of intense research because of the wide range of applications of these materials in photocatalysis, solar cells, chemical sensors, identification of art heritage falsification, and glass coating and self-cleaning materials. − TiO 2 exists mainly in three different crystalline phases: rutile (tetragonal), anatase (tetragonal), and brookite (orthorhombic). Rutile is the thermodynamically stable form in the bulk, whereas bulk anatase and brookite are metastable. − However, in the synthesis of TiO 2 nanomaterials, the surface energy plays an important role, and anatase is the phase normally found in the sol–gel synthesis of nanocrystalline TiO 2 , with brookite often observed as a byproduct when synthesis is carried out in acidic medium. − …”

Section: Introductionmentioning

confidence: 99%

Influence of Brookite Impurities on the Raman Spectrum of TiO₂ Anatase Nanocrystals

et al. 2018

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Synthesis of TiO2 anatase nanocrystals by hydrothermal methods often results in the formation of small quantities of brookite, which is difficult to eliminate by tuning the reaction conditions and is usually present in the final nanomaterial. The effect of this impurity on the Raman spectrum in anatase nanomaterials has not been fully explored. In this work, a study on the effect of reaction temperature on the position and line shape of the low-wavenumber Raman peak is presented. A comparison of the spectra of nanomaterials of pure anatase and anatase with brookite impurity (4–13 nm), synthesized by hydrothermal microwave heating, is made. It is shown that the low-wavenumber Raman peak (100–300 cm–1) for pure anatase nanocrystals is strongly dependent on the nanocrystal size and that the peak position is well described by the phonon confinement model (PCM). For anatase nanocrystals with 15% brookite impurity, the spectrum shows an asymmetric band, which is formed mainly by the contributions of the anatase Eg and brookite A1g modes, with the brookite B1g and B3g peaks further broadening the band. In addition, the PCM no longer describes the peak position. These results show that even a small amount of brookite can have a strong influence on the Raman spectra of anatase/brookite-impurity samples.

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Section: Introductionmentioning

confidence: 99%

Influence of Brookite Impurities on the Raman Spectrum of TiO₂ Anatase Nanocrystals

et al. 2018

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“…These strategies provide a new way to improve the HER performance of MoSe 2 -based electrocatalysts. Ion beam irradiation is a common technology to introduce structural defects such as point defects, grain boundaries, and native vacancies in compounds, which can tailor the electronic, magnetic, and optical properties of the materials obviously. − Therefore, it is expected that ion beam irradiation method could introduce structural defects in the basal plane of MoSe 2 to provide additional active sites and activate the inert basal plane. Herein, we introduced an amount of multivacancies in MoSe 2 basal plane by Ar 2+ beam irradiation with different doses and demonstrated the apparent enhancement of electrocatalytic performance in MoSe 2 nanosheets.…”

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confidence: 99%

Ar²⁺ Beam Irradiation-Induced Multivancancies in MoSe₂ Nanosheet for Enhanced Electrochemical Hydrogen Evolution

et al. 2018

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Poor electronic conductivity and an inert basal plane restrict the further enhancement of hydrogen evolution reaction (HER) in 2H-phase MoSe 2 . Herein, we synthesized MoSe 2 nanosheet arrays on carbon cloth and induced multivacancies in their basal plane via high-energy Ar 2+ beam irradiation, which are confirmed by Raman, electron spin resonance, X-ray photoelectron spectroscopy, and highresolution transmission electron microscopy analyses. Electrical measurement results indicate that these vacancies in the MoSe 2 basal plane can effectively improve their electrocatalytic performance, where the lowest overpotential of −171 mV at the current density of −100 mA/cm 2 and Tafel slope of 35 mV/dec were achieved in Ar 2+ -irradiated (dose of 5 × 10 15 ions/cm 2 ) MoSe 2 nanosheets. First-principles calculation results reveal that different cases of native vacancies in the MoSe 2 basal plane could effectively enhance the conductivity of MoSe 2 and produce more catalytic active sites for hydrogen evolution, giving rise to the better electrocatalytic capacity in the HER process. This finding opens the strategy of vacancy engineering for efficient hydrogen evolution in other transition metal dichalcogenide-based electrocatalysts.

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“…We therefore observed the appearance of amorphous phase at the fluence of 5 × 10 12 ions cm −2 . On subsequent irradiation, this amorphous phase could not facilitate the high quenching rate due to low thermal conductivity and the resulting slower cooling rate can facilitate the recrystallization of the matrix . It is assumed that many subcritical quasicrystalline nuclei or much reduced crystallites may be present in the each layer .…”

Section: Resultsmentioning

confidence: 77%

Effect of 120 MeV Au⁹⁺ ion irradiation on the structure and surface morphology of ZnO/NiO heterojunction

Das

Biswal

Choudhary

et al. 2018

Surface & Interface Analysis

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ZnO/NiO thin films, each of thickness 100 nm, were deposited on Si(100) substrate by pulsed laser deposition method. The resulting heterojunction, ZnO/NiO/Si, was irradiated by 120 MeV Au 9+ ions and characterized by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, and atomic force microscopy (AFM). The GIXRD confirmed the presence of both NiO and ZnO in the samples. Ion irradiation induced suppression of crystalline nature, and the recrystallization of the same occurred at the fluence of 1 × 10 13 ions cm −2 . The occurrence of most intense band at 302 cm −1 in Raman spectra corresponds to the symmetric stretching vibration of ZnO. The linear shift of stretching mode of ZnO with ion fluence could be associated with the effect of compressive stress in the material. AFM analysis of the films indicated that the rms roughness increased when the film is irradiated at a fluence of 1 × 10 12 ions cm −2 .Beyond this fluence, the value of roughness decreased up to fluence of 1 × 10 13 ions cm −2 and increased thereafter. To see the effect of the stress of buffer layer on the surface layer, we calculated the stress for NiO layer with ion fluence form the lattice parameter. Comparing the stress of buffer layer with roughness of surface layer at the given fluence, we can say that the compressive stress in the buffer layer could possibly control the roughness of the surface layer. KEYWORDS atomic force microscope, heterostructure, ion irradiation, stress 1 | INTRODUCTION Heterojunction devices, formed by combining semiconductors with different band gap and closely matching lattice parameters, have attracted much attention in optoelectronics. 1 ZnO is a wide-band gap (3.37 eV) semiconductor of the II-VI group. 2 It exhibits intrinsic n-type semiconducting property due to oxygen vacancies and zinc interstitials. It exhibits several properties like large exciton binding energy, 3 good transparency, 4 high electron mobility, 5 high thermal conductivity, 6 and strong room-temperature luminescence 7 for various device applications like liquid crystal displays, transparent conducting electrodes in solar cells, light emitting diodes, thin film transistors, gas sensors, and spintronic applications. 8 NiO is another wide band gap semiconductor that shows p-type behaviour due to the vacancy at Ni 2+ sites. NiO is widely used for applications such as transparent conductive films, 9 anode material, 10 and electrochromic devices. 11 Heterojunctions formed out of two layers (n-type ZnO and p-type NiO) can exhibit the potential of both the materials, in addition to the junction characteristics. In 2003, Ohta et al., 12 first reported the preparation of transparent NiO/ZnO heterojunction by pulsed laser deposition (PLD) combined with a solid-phase-epitaxy technique. Since then, many developments have been reported on the preparation and application of this heterojunction. These include methods like sol-gel spin coating, 13 chemical bath deposition, 4 hydrothermal method, 14and PLD. 15 On the application front, use of the hete...

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500 keV Ar2+ ion irradiation induced anatase to brookite phase transformation and ferromagnetism at room temperature in TiO2 thin films

Cited by 24 publications

References 32 publications

Influence of Brookite Impurities on the Raman Spectrum of TiO₂ Anatase Nanocrystals

Influence of Brookite Impurities on the Raman Spectrum of TiO₂ Anatase Nanocrystals

Ar²⁺ Beam Irradiation-Induced Multivancancies in MoSe₂ Nanosheet for Enhanced Electrochemical Hydrogen Evolution

Effect of 120 MeV Au⁹⁺ ion irradiation on the structure and surface morphology of ZnO/NiO heterojunction

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500 keV Ar2+ ion irradiation induced anatase to brookite phase transformation and ferromagnetism at room temperature in TiO2 thin films

Cited by 24 publications

References 32 publications

Influence of Brookite Impurities on the Raman Spectrum of TiO2 Anatase Nanocrystals

Influence of Brookite Impurities on the Raman Spectrum of TiO2 Anatase Nanocrystals

Ar2+ Beam Irradiation-Induced Multivancancies in MoSe2 Nanosheet for Enhanced Electrochemical Hydrogen Evolution

Effect of 120 MeV Au9+ ion irradiation on the structure and surface morphology of ZnO/NiO heterojunction

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Product

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Influence of Brookite Impurities on the Raman Spectrum of TiO₂ Anatase Nanocrystals

Influence of Brookite Impurities on the Raman Spectrum of TiO₂ Anatase Nanocrystals

Ar²⁺ Beam Irradiation-Induced Multivancancies in MoSe₂ Nanosheet for Enhanced Electrochemical Hydrogen Evolution

Effect of 120 MeV Au⁹⁺ ion irradiation on the structure and surface morphology of ZnO/NiO heterojunction