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  • 1
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    Online Resource
    Temperature dependent valence states and magnetic properties of lithium delithiated Li0.59FePO4
    AIP Publishing ; 2010
    In:  Journal of Applied Physics Vol. 107, No. 9 ( 2010-05-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 107, No. 9 ( 2010-05-01)
    Abstract: Polycrystalline samples of Li0.59FePO4 were prepared by oxidation reaction of pure LiFePO4, and temperature dependent valence states and magnetic properties were studied. X-ray diffraction patterns showed a biphasic olivine-type orthorhombic structure (space group: Pnma) where triphylite (LiFePO4) and heterosite (FePO4) coexisted. Also, we have observed the biphasic antiferromagnetic ordering of triphylite and heterosite with different antiferromagnetic to paramagnetic ordering transition temperatures. Mössbauer spectra of Li0.59FePO4 showed a two-phase asymmetrical eight line pattern due to the different electric quadrupole interactions in triphylite and heterosite. The iron ions of triphylite and heterosite are at Fe2+ (3d6) and the Fe3+ (3d5) valence state. Also the large value of ΔEQ for the triphylite phase was originated from the asymmetric charge distribution of FeO6. These results indicate that the charge distributions around the Fe nucleus in the triphylite are more asymmetric because of the contribution from the crystal field and the ion valence state.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3337680
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
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    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 2
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    Electrochemical analysis of transparent oxide-less photovoltaic cell with perforation patterned metal substrate
    AIP Publishing ; 2013
    In:  Applied Physics Letters Vol. 102, No. 18 ( 2013-05-06)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 102, No. 18 ( 2013-05-06)
    Abstract: In terms of electrochemical behaviour, a transparent conductive oxide (TCO)-less dye-sensitized solar cell (DSSC) with two metal foils was compared with those of a metal foil-based DSSC with a TCO-coated substrate. By virtue of electrochemical impedance spectroscopy, intensity modulated photocurrent spectroscopy, intensity modulated photovoltage spectroscopy, open-circuit voltage decay, and photocurrent transient measurements, it was clearly confirmed that the limited performance of the TCO-less DSSC was caused by the restricted transport of ion species in the electrolyte due to the perforation patterned metal foil.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.4804987
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 3
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    Structural and magnetic phase transition of mixed olivines Li x Fe1− y Ni y PO4 by lithium deintercalation
    AIP Publishing ; 2012
    In:  Journal of Applied Physics Vol. 111, No. 7 ( 2012-04-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 111, No. 7 ( 2012-04-01)
    Abstract: The structural and magnetic phase transitions of LixFe1–yNiyPO4 were investigated by x-ray diffraction (XRD), superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. Rietveld refinement of XRD patterns of LiFe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) revealed that the lattice parameters a0 = 10.328, b0 = 6.007, and c0 = 4.692 Å for LiFePO4 changed linearly to a0 = 10.154, b0 = 5.923, and c0 = 4.687 Å for LiFe0.4Ni0.6PO4 with the substitution of Ni ions. Also, the fully lithium-deintercalated Fe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) series had enhanced lattice distortions along the c axis compared to LiFe1-yNiyPO4 because the Jahn–Teller distortion changed as the unit cell volume decreased due to lithium ion deintercalation. LiFe1–yNiyPO4 has an antiferromagnetic order; the magnetic Nèel temperature (TN) decreased from 51 K for LiFePO4 to 36 K for LiFe0.4Ni0.6PO4. Fully deintercalated Fe1–yNiyPO4 has strong antiferromagnetic order; TN decreased from 114 K for FePO4 to 62 K for Fe0.4Ni0.6PO4 due to the charge transition of Fe2+/Fe3+ and Ni2+/Ni3+, mediated by lithium ion vacancies in an olivine structure. The Mössbauer spectra below the TN of LixFe1–yNiyPO4 (x = 0, 1, 0.0 ≤ y ≤ 0.6) were fitted with eight asymmetrical Lorentzian functions. The electric quadrupole splitting value (ΔEQ) of LiFe1–yNiyPO4 is larger than that of Fe1–yNiyPO4 due to more asymmetric charge distributions around Fe2+ (3d6) than Fe3+ (3d5) in FeO6 sites.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3678468
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 4
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    Phase transition studies of sodium deintercalated Na2− x FePO4F (0 ≤   x   ≤ 1) by Mössbauer spectroscopy
    AIP Publishing ; 2011
    In:  Journal of Applied Physics Vol. 109, No. 7 ( 2011-04-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 109, No. 7 ( 2011-04-01)
    Abstract: The phase transition in sodium deintercalated Na2−xFePO4F (0 ≤ x ≤ 1) polycrystalline samples was studied by x-ray diffraction and Mössbauer spectroscopy. Sodium deintercalated samples were obtained by chemical deintercalation of pure Na2FePO4F. From the refined x-ray diffraction patterns, the crystalline structure of Na2FePO4F was determined to be orthorhombic with the space group Pbcn. The structure of fully sodium deintercalated NaFePO4F is identical to that of pure Na2FePO4F, differing only in the cell parameters. The changes in the unit cell parameters and atomic positions in Na2−xFePO4F (x = 0, 1) samples originated from a Na2 ion deficiency in the interlayer spaces. The room-temperature Mössbauer spectra of Na2−xFePO4F (x = 0, 1) were fitted with one set of the Fe2+ /3+ doublets. A decrease in the absorption area of Fe2 + in Na2FePO4F with increasing sodium deintercalation was observed in the Mössbauer spectra of Na2−xFePO4F, whereas the area of the Fe3+ doublet in NaFePO4F increased. The large value of ΔEQ for the Fe2+ doublet phase was due to the asymmetric charge distribution of FeO4F2 arising from different lattice and valence state contributions.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3561798
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 5
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    Temperature dependent magnetic structure of lithium delithiated Li x FeSO4F ( x  = 0, 1) by Mössbauer spectroscopy
    AIP Publishing ; 2012
    In:  Journal of Applied Physics Vol. 111, No. 7 ( 2012-04-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 111, No. 7 ( 2012-04-01)
    Abstract: Recently, lithium iron sulfate compounds have been highly considered for a positive electrode material for lithium ion batteries. In this work, LiFeSO4F and the fully delithiated FeSO4F were prepared by the ionothermal process and chemical oxidation reaction method. The LixFeSO4F (x = 0, 1) samples show the triclinic structure with P-1 space group. In the case of delithiated FeSO4F, changes in lattice parameters were observed due to the disappearance of the Li site while maintaining the triclinic structure. Temperature-dependent magnetic susceptibility curves show the antiferromagnetic (AFM) structure with the ordering temperature of 28 K for LiFeSO4F and 99 K for FeSO4F. Also, temperature-dependent Mössbauer spectra of LiFeSO4F below TN were fitted with two-sets of eight Lorentzian indicating the existence of two different types of Fe2+ ions due to the different hyperfine and electric quadrupole interactions. With the lithium delithiated, the Fe3+ iron ions in FeSO4F exhibit two-sets of six-line patterns due to the electron transfer in FeO4F2 site by lithium delithiation. These suggest that the different AFM ordering in LixFeSO4F can be originated from the Fe2+/Fe3+ magnetic ions with different charge distributions and spin contributions.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3677865
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 6
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    Determination of the space-charge field in polymeric photorefractive material
    AIP Publishing ; 2002
    In:  Journal of Applied Physics Vol. 91, No. 10 ( 2002-05-15), p. 6471-6475
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 91, No. 10 ( 2002-05-15), p. 6471-6475
    Abstract: We proposed a method for measuring the magnitude of the space-charge field of the polymeric photorefractive materials. In the case of polymeric photorefractive material with low glass transition temperature, optically anisotropic chromophores are known to be reoriented under space-charge field. Simply by adding a pair of crossed polarizer units to a conventional degenerated four wave mixing setup, we could measure the birefringence of the photorefractive materials induced by a newly formed space-charge field. Since the birefringence of a given material is governed by the applied electric field, the space-charge field can be determined from the variation of birefringence using the oriented gas model.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.1471580
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2002
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 7
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    Mössbauer analysis of silicate Li2FeSiO4 and delithiated Li2− x FeSiO4 ( x  = 0.66) compounds
    AIP Publishing ; 2013
    In:  Journal of Applied Physics Vol. 113, No. 17 ( 2013-05-07)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 113, No. 17 ( 2013-05-07)
    Abstract: Lithium iron silicate compounds of Li2FeSiO4 and partially delithiated Li2−xFeSiO4 (x = 0.66) were synthesized by vacuum-sealed solid-state and chemical delithiation reactions, and their magnetic properties were characterized based on Mössbauer analysis. Crystal structures of both Li2FeSiO4 and Li2−xFeSiO4 (x = 0.66) compounds are found to be γs-type (P21/n) monoclinic structures with difference in the lattice parameters due to lithium delithiation. Mössbauer spectrum of Li2FeSiO4 below TN1 = 20 K exhibits eight Lorentzians of Fe2+ with antiferromagnetic ordering. However, the spectrum of intermediate Li2−xFeSiO4 (x = 0.66) compound shows the appearance of magnetically ordered Fe3+ sextet below TN2 = 28 K. The temperature-dependent isomer shift of Li2−xFeSiO4 indicates the coexistence of nonequivalent Fe2+/Fe3+ valence states with the partial oxidation of FeO4, enhanced by the lithium ion deficiency. Also, we have observed a considerable change in electric quadrupole interaction between Fe2+/Fe3+ ions in Li2−xFeSiO4, when compared to that of Li2FeSiO4, due to the different lattice and valence electron contributions, being originated from crystalline and valence transitions caused by the lithiation/delithiation process.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.4799153
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 8
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    Online Resource
    Organic memory device with self-assembly monolayered aptamer conjugated nanoparticles
    AIP Publishing ; 2013
    In:  Applied Physics Letters Vol. 103, No. 8 ( 2013-08-19)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 103, No. 8 ( 2013-08-19)
    Abstract: An organic memory structure using monolayered aptamer conjugated gold nanoparticles (Au NPs) as charge storage nodes was demonstrated. Metal-pentacene-insulator-semiconductor device was adopted for the non-volatile memory effect through self assembly monolayer of A10-aptamer conjugated Au NPs, which was formed on functionalized insulator surface with prostate-specific membrane antigen protein. The capacitance versus voltage (C-V) curves obtained for the monolayered Au NPs capacitor exhibited substantial flat-band voltage shift (ΔVFB) or memory window of 3.76 V under (+/-)7 V voltage sweep. The memory device format can be potentially expanded to a highly specific capacitive sensor for the aptamer-specific biomolecule detection.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.4819336
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 9
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    229 nm UV LEDs on aluminum nitride single crystal substrates using p-type silicon for increased hole injection
    AIP Publishing ; 2018
    In:  Applied Physics Letters Vol. 112, No. 8 ( 2018-02-19)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 112, No. 8 ( 2018-02-19)
    Abstract: AlGaN based 229 nm light emitting diodes (LEDs), employing p-type Si to significantly increase hole injection, were fabricated on single crystal bulk aluminum nitride (AlN) substrates. Nitride heterostructures were epitaxially deposited by organometallic vapor phase epitaxy and inherit the low dislocation density of the native substrate. Following epitaxy, a p-Si layer is bonded to the heterostructure. LEDs were characterized both electrically and optically. Owing to the low defect density films, large concentration of holes from p-Si, and efficient hole injection, no efficiency droop was observed up to a current density of 76 A/cm2 under continuous wave operation and without external thermal management. An optical output power of 160 μW was obtained with the corresponding external quantum efficiency of 0.03%. This study demonstrates that by adopting p-type Si nanomembrane contacts as a hole injector, practical levels of hole injection can be realized in UV light-emitting diodes with very high Al composition AlGaN quantum wells, enabling emission wavelengths and power levels that were previously inaccessible using traditional p-i-n structures with poor hole injection efficiency.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.5011180
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 211245-0
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  • 10
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    Quasi-Electrostatic Modes in Axisymmetric Tori
    AIP Publishing ; 1970
    In:  The Physics of Fluids Vol. 13, No. 9 ( 1970-09-01), p. 2385-2390
    Details
    In: The Physics of Fluids, AIP Publishing, Vol. 13, No. 9 ( 1970-09-01), p. 2385-2390
    Abstract: The effect of the magnetic perturbations on the drift instabilities in the axisymmetric tori is studied. The dispersion relations and growth rates are calculated for the various frequency ranges of physical interest. An unstable mode exists for which the characteristic frequency of the oscillations ω is greater than the electron bounce frequency ωbe. This instability can be suppressed by the average favorable curvature. For the case, ωbe  & gt; ω  & gt; ωbi, the drift ballooning and drift universal modes are far more unstable than in the electrostatic case. The oscillations are always electrostatic for ω  & lt; ωbi.
    Type of Medium: Online Resource
    ISSN: 0031-9171
    URL: Article
    DOI: 10.1063/1.1693248
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1970
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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