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2 Aug 2004

Volume 85, Issue 5, pp. 701-848

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 807 (2004); http://dx.doi.org/10.1063/1.1777817 (3 pages)

Henry J. Liu and Kyeongjae Cho
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Finite size effects in stress analysis of interconnect structures

I. C. Noyan, Conal E. Murray, Jay S. Chey, and Charles C. Goldsmith

Appl. Phys. Lett. 85, 724 (2004); http://dx.doi.org/10.1063/1.1776331 (3 pages) | Cited 12 times

Online Publication Date: 27 July 2004

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Conventional formulations of thermal stress evolution in interconnect structures usually ignore the interface integrity between the various levels. In this letter we present thermal and residual stress versus temperature data from simple copper thin-film structures on silicon. The results indicate that interconnection models which assume fully elastic behavior and perfectly bonded interfaces may yield inaccurate predictions of the thermo-mechanical response for feature sizes smaller than 10 μm.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Gh Other heat and thermomechanical treatments
68.35.Ct Interface structure and roughness

Evaluation of the discrete energy levels of individual ZnO nanorod single-quantum-well structures using near-field ultraviolet photoluminescence spectroscopy

T. Yatsui, J. Lim, M. Ohtsu, S. J. An, and G.-C. Yi

Appl. Phys. Lett. 85, 727 (2004); http://dx.doi.org/10.1063/1.1776338 (3 pages) | Cited 19 times

Online Publication Date: 27 July 2004

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Spatially and spectrally resolved photoluminescence imaging of individual ZnO∕ZnMgO nanorod single-quantum-well structures (SQWs) with a spatial resolution of 55 nm was performed using the optical near-field technique with a metallized UV fiber probe. Using excitation power density-dependent photoluminescence spectra of a ZnO∕ZnMgO SQW nanorod, we observed the discrete energy levels in a ZnO quantum-well layer.
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73.21.Fg Quantum wells
68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials

Disorder and Urbach energy in hydrogenated amorphous carbon: A phenomenological model

G. Fanchini and A. Tagliaferro

Appl. Phys. Lett. 85, 730 (2004); http://dx.doi.org/10.1063/1.1776633 (3 pages) | Cited 26 times

Online Publication Date: 27 July 2004

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We develop a phenomenological model describing the structural and topological effects of the disorder in hydrogenated amorphous carbons (a-C:H), through the analysis of the Raman G-peak width and the optical absorption spectra, providing information on the densities of electronic π ad π* states (πDOS). We show that the Urbach energy is not related to topological disorder but to the Gaussian width (σπ) of the πDOS, peaked at ±Eπ energies above∕below the Fermi level. σπ, on its turn, is not related in a straightforward manner to the disorder. The disorder is better represented by the σπ∕Eπ ratio, expressing the disorder-induced narrowing of the Tauc optical gap.
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71.23.An Theories and models; localized states
73.20.At Surface states, band structure, electron density of states
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Deformation behavior of ion-irradiated polyimide

S. O. Kucheyev, T. E. Felter, M. Anthamatten, and J. E. Bradby

Appl. Phys. Lett. 85, 733 (2004); http://dx.doi.org/10.1063/1.1776618 (3 pages) | Cited 8 times

Online Publication Date: 27 July 2004

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We study nanoindentation hardness, Young’s modulus, and tensile strength of polyimide (Kapton H) films bombarded with MeV light ions in the predominantly electronic stopping power regime. Results show that, for all the ion irradiation conditions studied, bombardment increases the hardness and Young’s modulus and decreases the tensile strength. These changes depend close to linearly on ion fluence and superlinearly (with a power-law exponent factor of ∼1.5) on electronic energy loss. Physical mechanisms of radiation-induced changes to mechanical properties of polyimide are discussed.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.20.D- Elasticity
61.80.Jh Ion radiation effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains

Determination of cations distribution in Mn3O4 by anomalous x-ray powder diffraction

Yanan Xiao, Dale E. Wittmer, Fujio Izumi, Susan Mini, Tim Graber, and P. James Viccaro

Appl. Phys. Lett. 85, 736 (2004); http://dx.doi.org/10.1063/1.1776326 (3 pages)

Online Publication Date: 27 July 2004

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The oxidation states of Mn at two different crystallographic sites in the distorted spinel structure of Mn3O4 were determined by the approach of anomalous synchrotron x-ray powder diffraction. The real parts of anomalous scattering factors for the two Mn sites were refined from a series of powder diffraction patterns collected at the vicinity of K absorption edge of Mn. The results of Rietveld refinements showed that the two distinct cation sites can obviously be distinguished from each other and that Mn2+ ions occupy the tetrahedral site and Mn3+ ions are located at the octahedral site.
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61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra

Anisotropic thermoelectric properties in layered cobaltite AxCoO2 (A=Sr and Ca) thin films

Tsutomu Kanno, Satoshi Yotsuhashi, and Hideaki Adachi

Appl. Phys. Lett. 85, 739 (2004); http://dx.doi.org/10.1063/1.1776310 (3 pages) | Cited 17 times

Online Publication Date: 27 July 2004

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We have fabricated epitaxial thin films of layered cobaltite AxCoO2 (A=Sr and Ca) on sapphire substrates by rf magnetron sputtering. The grown phase in the AxCoO2 films was found to be a monoclinic β-phase of primitive layered cobaltites and the epitaxial orientation of the film could be controlled by the surface plane of the substrates. The resistivity parallel to the CoO2 layers ρ∥ for the β-SrxCoO2 is as low as 2 mΩ cm at room temperature and shows metallic behavior. The ratio of perpendicular resistivity ρ⊥ to ρ∥ increases from 20 at room temperature to 90 at 3 K. More isotropic nature was observed in the Seebeck coefficient. Parallel Seebeck coefficients S∥ of AxCoO2 are approximately 60 μV∕K at room temperature and the perpendicular S⊥ are about half of S∥.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
73.50.Lw Thermoelectric effects
68.55.A- Nucleation and growth

Photovoltage characterization of CuAlO2 crystallites

Th. Dittrich, L. Dloczik, T. Guminskaya, M. Ch. Lux-Steiner, N. Grigorieva, and I. Urban

Appl. Phys. Lett. 85, 742 (2004); http://dx.doi.org/10.1063/1.1776611 (3 pages) | Cited 21 times

Online Publication Date: 27 July 2004

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The delafossite phase of CuAlO2 has been prepared by ion exchange reaction at 475°C. The samples were characterized by x-ray diffraction, transmission electron microscopy, electron diffraction, transient and spectral photovoltage (PV), and diffuse reflectance spectroscopy. The produced CuAlO2 crystallites are p-type and of high electronic quality, i.e., no electronic transitions induced by deep states in the forbidden gap have been observed by PV. The temperature dependence of the optical band gap of CuAlO2 was measured between 80 and 600 K. The band gap of CuAlO2 approximated to 0 K amounts to 3.61 eV. The quenching of the PV signal is thermally activated with an activation energy of 1.8 eV.
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72.40.+w Photoconduction and photovoltaic effects
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments
68.37.Lp Transmission electron microscopy (TEM)

Evidence from atomistic simulations of fluctuation electron microscopy for preferred local orientations in amorphous silicon

S. V. Khare, S. M. Nakhmanson, P. M. Voyles, P. Keblinski, and J. R. Abelson

Appl. Phys. Lett. 85, 745 (2004); http://dx.doi.org/10.1063/1.1776614 (3 pages) | Cited 14 times

Online Publication Date: 27 July 2004

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Simulations from a family of atomistic structural models for unhydrogenated amorphous silicon suggest that fluctuation electron microscopy experiments have observed orientational order of paracrystalline grains in amorphous silicon. This order may consist of correlations in the orientation of nearby paracrystalline grains or anisotropy in the grain shape. This observation makes a natural connection to the known growth modes of microcrystalline silicon and may be useful for other materials systems.
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68.55.-a Thin film structure and morphology
61.43.Bn Structural modeling: serial-addition models, computer simulation

Structure formation upon reactive direct current magnetron sputtering of transition metal oxide films

J. M. Ngaruiya, O. Kappertz, S. H. Mohamed, and M. Wuttig

Appl. Phys. Lett. 85, 748 (2004); http://dx.doi.org/10.1063/1.1777412 (3 pages) | Cited 22 times

Online Publication Date: 27 July 2004

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A comparative study of reactive direct current magnetron sputtering for different transition metal oxides reveals crystalline films at room temperature for group 4 and amorphous films for groups 5 and 6. This observation cannot be explained by the known growth laws and is attributed to the impact of energetic particles, originating from the oxidized target, on the growing film. This scenario is supported by measured target characteristics, the evolution of deposition stress of the films, and the observed backsputtering.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.05.cm X-ray reflectometry (surfaces, interfaces, films)

Sphalerite–rock salt phase transition in ZnMnSe heterostructures

D. Litvinov, D. Gerthsen, A. Rosenauer, B. Daniel, and M. Hetterich

Appl. Phys. Lett. 85, 751 (2004); http://dx.doi.org/10.1063/1.1775285 (3 pages) | Cited 6 times

Online Publication Date: 27 July 2004

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We report on the investigation of epitaxial MnSe layers grown on ZnSe by transmission electron microscopy. MnSe∕ZnSe superlattices (SLs) with different nominal MnSe thicknesses tMnSe between 2 and 20 monolayers (MLs) were investigated, which were grown by molecular-beam epitaxy on GaAs(001) substrates. Composition profiles of the SLs were evaluated by the measurement of local (002) lattice parameters in growth direction. A MnSe deposition between 2 and 4 MLs on ZnSe leads to the formation of intermixed Zn1−xMnxSe layers with sphalerite structure and a Mn concentration x increasing from 50% to 90%. For MnSe layers with a thickness between 6 and 20 ML, we observe 5–10 nm small MnSe inclusions with a rock salt structure embedded in sphalerite Zn1−xMnxSe with approximately 90%Mn.
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68.65.Cd Superlattices
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
68.55.A- Nucleation and growth
64.70.K- Solid-solid transitions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Effective optical manipulation of the charge state and emission intensity of the InAs∕GaAs quantum dots by means of additional infrared illumination

E. S. Moskalenko, K. F. Karlsson, V. Donchev, P. O. Holtz, B. Monemar, W. V. Schoenfeld, and P. M. Petroff

Appl. Phys. Lett. 85, 754 (2004); http://dx.doi.org/10.1063/1.1773374 (3 pages)

Online Publication Date: 27 July 2004

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InAs quantum dots (QDs) at different levels of density have been studied by means of photoluminescence, when in addition to the main laser, a second infrared (IR) laser is employed to excite the QD. It is demonstrated that the IR laser considerably affects the QD charge state as well as the emission intensity level (an increase greater than fivefold was observed). These effects are explained in terms of separate generation of excess electrons and holes provided under dual-laser excitation. However, these effects progressively vanish with increasing QD density. The results obtained unambiguously imply that the emission intensity from the QD can be effectively enhanced by purely optical means.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots
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