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9 Apr 2001

Volume 78, Issue 15, pp. 2095-2255

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Electron energy loss near-edge structures of cubic Si3N4

Isao Tanaka, T. Mizoguchi, T. Sekine, Hongliang He, K. Kimoto, T. Kobayashi, Shang-Di Mo, and W. Y. Ching

Appl. Phys. Lett. 78, 2134 (2001); http://dx.doi.org/10.1063/1.1360232 (3 pages) | Cited 35 times

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Electron energy loss near-edge structures of the newly discovered cubic-Si3N4 at the Si L2,3, edge and N K edge have been measured. The same edges were calculated using a first-principles supercell approach, including the core–hole interaction. The experimental spectra at the two edges were satisfactorily reproduced by the calculations, confirming that the present calculation has sufficient predictive power. The difference in spectral shapes between c-Si3N4 and β-Si3N4 is more clear for the Si L2,3, edge. However, the difference cannot be simply explained by the difference in coordination numbers of Si. © 2001 American Institute of Physics.
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79.20.Uv Electron energy loss spectroscopy
71.20.Ps Other inorganic compounds

Compositional dependence of the strain-free optical band gap in InxGa1−xN layers

S. Pereira, M. R. Correia, T. Monteiro, E. Pereira, E. Alves, A. D. Sequeira, and N. Franco

Appl. Phys. Lett. 78, 2137 (2001); http://dx.doi.org/10.1063/1.1358368 (3 pages) | Cited 50 times

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The effect of strain on the compositional and optical properties of a set of epitaxial single layers of InxGa1−xN was studied. Indium content was measured free from the effects of strain by Rutherford backscattering spectrometry. Accurate knowledge of the In mole fraction, combined with x-ray diffraction measurements, allows perpendicular strain (ϵzz) to be evaluated. Optical band gaps were determined by absorption spectroscopy and corrected for strain. Following this approach, the strain free dependence of the optical band gap in InxGa1−xN alloys was determined for x ⩽ 0.25. Our results indicate an “anomalous,” linear, dependence of the energy gap on the In content, at room temperature: Eg(x) = 3.39–3.57x eV. Extension of this behavior to higher concentrations is discussed on the basis of reported results. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.55.Nq Composition and phase identification

Semimagnetic self-organized Cd1−xMnxTe quantum dots generated by postgrowth thermal annealing

G. Prechtl, W. Heiss, S. Mackowski, and E. Janik

Appl. Phys. Lett. 78, 2140 (2001); http://dx.doi.org/10.1063/1.1362199 (3 pages) | Cited 13 times

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We demonstrate the possibility to fabricate self-organized semimagnetic quantum dots by the growth of two-dimensional layers and subsequent thermal annealing. In particular, CdTe/CdMgTe quantum-well samples containing four narrow MnTe barriers are characterized by optical methods. After annealing well above the growth temperature, from time-resolved photoluminescence (PL), PL experiments under selective excitation, as well as micro-PL measurements, we find clear evidence for the presence of quantum dots. For a sample with a average Mn content of 5%, the dot luminescence shows a redshift of 18 meV under an applied magnetic field of 4 T, due to the giant Zeeman effect. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
75.50.Pp Magnetic semiconductors
78.67.Hc Quantum dots
61.72.Cc Kinetics of defect formation and annealing
78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.20.Ls Magneto-optical effects

Near infra-red radiation squeezing through 20 nm voids in obliquely deposited metal films

G. B. Smith, A. K. M. Hossain, and A. Gentle

Appl. Phys. Lett. 78, 2143 (2001); http://dx.doi.org/10.1063/1.1359489 (2 pages) | Cited 1 time

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Obliquely deposited metal films which are nearly continuous, displaying several unexpected solar optical properties. Transmittance intensity, spectral character, preferred direction of incidence, and polarization sensitivity, infer processes which effective-medium models based solely on “interior” properties cannot describe. Amplified transmittance through voids around 20 nm wide involving near surface excitations can explain the data. © 2001 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
42.50.Dv Quantum state engineering and measurements
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Kinetics of the glass-transition and crystallization process of Fe72−xNbxAl5Ga2P11C6B4 (x = 0, 2) metallic glasses

N. Mitrovic, S. Roth, and J. Eckert

Appl. Phys. Lett. 78, 2145 (2001); http://dx.doi.org/10.1063/1.1361099 (3 pages) | Cited 37 times

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The kinetics of the glass-transition and the crystallization process of multicomponent ferromagnetic Fe72−xNbxAl5Ga2P11C6B4 (x = 0, 2) metallic glasses have been investigated by constant-rate heating differential scanning calorimetry at different heating rates. The glass-transition temperature Tg and the crystallization peak temperature Tp shift to higher temperatures with increasing heating rate. The apparent activation energy and the frequency factor are evaluated by the Kissinger method, and the rate constant of the crystallization process is estimated by an Arrhenius law. The kinetics of the glass-transition process have been analyzed in terms of a Vogel–Fulcher–Tammann equation describing the heating rate dependence of the glass-transition temperature. The effect of the niobium addition on the glass-forming ability has been investigated with respect to the glass-transition and crystallization kinetics, revealing that substitution of Nb for Fe does not improve the glass-forming ability and it lowers the thermal stability of the material. © 2001 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses

Photoluminescence of nanostructured PbTiO3 processed by high-energy mechanical milling

E. R. Leite, L. P. S. Santos, N. L. V. Carreño, E. Longo, C. A. Paskocimas, J. A. Varela, F. Lanciotti, C. E. M. Campos, and P. S. Pizani

Appl. Phys. Lett. 78, 2148 (2001); http://dx.doi.org/10.1063/1.1362200 (3 pages) | Cited 25 times

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This letter reports on a process to prepare nanostructured PbTiO3 (PT) at room temperature with photoluminescence (PL) emission in the visible range. This process is based on the high-energy mechanical milling of ultrafine PbTiO3 powder. The results suggest that high-energy mechanical milling modifies the particle’s structure, resulting in localized states in an interfacial region between the crystalline PT and the amorphous PT. These localized states are believed to be responsible for the PL obtained with short milling times. When long milling times are employed, the amorphous phase that is formed causes PL behavior. An alternative method to process nanostructured wide-band-gap semiconductors with active optical properties such as PL is described in this letter. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.20.Wk Machining, milling
81.07.Wx Nanopowders
73.22.-f Electronic structure of nanoscale materials and related systems
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
71.55.Jv Disordered structures; amorphous and glassy solids

Argon inclusion in sputtered films and the effect of the gas on molybdenum field emitter arrays

Babu R. Chalamala and Robert H. Reuss

Appl. Phys. Lett. 78, 2151 (2001); http://dx.doi.org/10.1063/1.1361281 (3 pages) | Cited 6 times

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Residual gas analysis of a number of field emission displays showed that argon desorbed from molybdenum metal lines was the dominant gas in sealed vacuum packages. We present experimental results on the emission characteristics of molybdenum field emitter arrays in argon ambient. In argon, the emission current dropped rapidly similar to that in oxygenic gas ambients. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest a model based on shallow implantation of argon into the field emitter tips that increases the effective width of the tunneling barrier. Experimental support for this model comes from the following observations: emission current degraded only when the device was turned on; after gas exposure, significant current recovery which followed diffusion type behavior was noted; degradation and recovery rates were functions of partial pressure; and no detectable effects associated with sputtering were observed. This mechanism is also consistent with ion pumping known to occur in field emission displays. © 2001 American Institute of Physics.
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85.45.Fd Field emission displays (FEDs)
68.43.Mn Adsorption kinetics
79.70.+q Field emission, ionization, evaporation, and desorption
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.80.-d Chemical analysis and related physical methods of analysis

Multiplet structures of tetrahedrally coordinated Cr4+ and Cr5+ in Y3Al5O12

Takugo Ishii, Kazuyoshi Ogasawara, Hirohiko Adachi, and Isao Tanaka

Appl. Phys. Lett. 78, 2154 (2001); http://dx.doi.org/10.1063/1.1364655 (3 pages) | Cited 2 times

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Multiplet structures of tetrahedrally coordinated Cr4+ and Cr5+ in Y3Al5O12 (yttrium aluminum garnet) were calculated with use of the ab initio electronic-structure calculation method. The calculated absorption spectrum of Cr4+ showed that two bands at the near-infrared and visible spectral regions originated from the same 3T1 parent multiplet term. The calculated levels originating from Cr5+ in the near-infrared region overlapped with the levels originating from Cr4+. Both the lowest-spin-allowed transitions of Cr4+ and Cr5+ were revealed to have the same polarization dependence. The result indicated that confusion on the assignment of the peaks could be ignored if the Cr5+ state really exists. © 2001 American Institute of Physics.
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75.50.Gg Ferrimagnetics
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
71.55.Ht Other nonmetals

Transmission electron microscopy studies of the effect of A-site cation size mismatch and disorder on charge ordering behavior in (La1−xYx)0.5(Ca1−ySry)0.5MnO3

Y. Q. Wang, X. F. Duan, Z. H. Wang, and B. G. Shen

Appl. Phys. Lett. 78, 2157 (2001); http://dx.doi.org/10.1063/1.1364505 (3 pages) | Cited 6 times

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The effects of A-site cation mismatch and disorder on the charge ordering (CO) behavior in the manganites (La1−xYx)0.5(Ca1−ySry)0.5MnO3 have been studied by transmission electron microscopy. The presence of the size mismatch and disorder suppresses the CO transition. Incommensurate CO modulations are observed in three samples with 0 ⩽ σ2 ⩽ 0.003. Structural models, based on the selected area electron diffraction and high-resolution electron microscopy observation, are suggested for such kinds of incommensurate modulations. © 2001 American Institute of Physics.
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64.70.Rh Commensurate-incommensurate transitions
71.45.-d Collective effects
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