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8 Aug 2005

Volume 87, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 061103 (2005); http://dx.doi.org/10.1063/1.2008357 (3 pages)

Y. C. Zhong, S. A. Zhu, H. M. Su, H. Z. Wang, J. M. Chen, Z. H. Zeng, and Y. L. Chen
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Selective oxidation of an individual layer in a magnetic tunnel junction through the use of thermodynamic control

Peter F. Ladwig, J. Joshua Yang, Ying Yang, Y. Austin Chang, Feng Liu, Bharat B. Pant, and Allan E. Schultz

Appl. Phys. Lett. 87, 061901 (2005); http://dx.doi.org/10.1063/1.2007863 (3 pages) | Cited 3 times

Online Publication Date: 1 August 2005

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Oxidation of an ultrathin metal layer (less than 1 nm) to form a tunnel barrier oxide, without oxidizing adjacent layers, is of critical importance in making nanoscale devices such as magnetic tunnel junctions. It is extremely difficult, if not impossible, to achieve this objective using conventional methods that rely on kinetic control of the oxidation process. We present an alternative approach using a gas mixture with a fixed chemical potential of oxygen as the oxidizing medium. This mixture, chosen with thermodynamic calculations, tends to uniformly oxidize the tunnel barrier to the thermodynamically favored stoichiometry without oxidizing the adjacent layers. Experiments on a model system show that a thin-film layer such as Al can be oxidized without oxidizing common ferromagnetic alloys, such as Co–Fe, using a mixture of CO2/CO or H2/H2O. The chemical states of the Al and Co–Fe based example were characterized using x-ray photoelectron and synchrotron-source Fourier transform infrared spectroscopy.
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81.65.Mq Oxidation
75.50.Bb Fe and its alloys
78.66.Bz Metals and metallic alloys
78.30.Er Solid metals and alloys
79.60.Bm Clean metal, semiconductor, and insulator surfaces
65.40.G- Other thermodynamical quantities

Linear viscoelasticity in aluminum thin films

Seungmin Hyun, Tejpal K. Hooghan, Walter L. Brown, and Richard P. Vinci

Appl. Phys. Lett. 87, 061902 (2005); http://dx.doi.org/10.1063/1.2008383 (3 pages) | Cited 8 times

Online Publication Date: 1 August 2005

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We have found that thin aluminum films at room temperature exhibit changes in elastic modulus of 25% or more over periods of an hour under stress by using a novel capacitance bulge system. Furthermore, we have strong evidence that this change is due to linear viscoelasticity. Such large changes in modulus can affect the stability and performance of microelectromechanical systems structures and need to be understood and controlled. These results are also proof that linear viscoelastic analysis is as appropriate for thin metal films as it is for many polymer systems.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Brillouin imaging

K. J. Koski and J. L. Yarger

Appl. Phys. Lett. 87, 061903 (2005); http://dx.doi.org/10.1063/1.1999857 (3 pages) | Cited 9 times

Online Publication Date: 1 August 2005

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Using an angle-dispersive Fabry-Perot interferometer in a confocal backscattering geometry, we have obtained Brillouin images of several liquid and polymer materials. One- and two-dimensional images of heterogeneous samples are presented using longitudinal Brillouin frequency shifts and acoustic attenuation for contrast. The experimental resolution of the images is 20 μm.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering

Nb clusters formation in Nb-doped magnesium hydride

R. Checchetto, N. Bazzanella, A. Miotello, C. Maurizio, F. D’Acapito, P. Mengucci, G. Barucca, and G. Majni

Appl. Phys. Lett. 87, 061904 (2005); http://dx.doi.org/10.1063/1.2007866 (3 pages) | Cited 10 times

Online Publication Date: 2 August 2005

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Extended x-ray absorption fine structure spectroscopy, x-ray diffraction and transmission electron microscopy were used to analyze the Nb coordination and clustering in Nb-doped (5 at. %) h-Mg film samples deposited by rf magnetron sputtering. Results show that the catalytic effect of the Nb doping in the H2 absorption and desorption kinetics is connected with the formation of Nb nanoclusters dispersed in the host matrix. The H2 desorption from β-MgH2 is favored by local elastic stresses produced by β-NbH0.89 clusters on the MgH2 matrix that reduces the stability of the hydride phase and by preferential paths in the nanocomposite hydride.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.46.-w Structure of nanoscale materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
78.70.Dm X-ray absorption spectra
68.37.Lp Transmission electron microscopy (TEM)

The role of Al on Ohmic contact formation on n-type GaN and AlGaN/GaN

B. Van Daele, G. Van Tendeloo, W. Ruythooren, J. Derluyn, M. R. Leys, and M. Germain

Appl. Phys. Lett. 87, 061905 (2005); http://dx.doi.org/10.1063/1.2008361 (3 pages) | Cited 13 times

Online Publication Date: 2 August 2005

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A standard metallization scheme for the formation of Ohmic contacts on n-type GaN does exist. It has the following multilayer structure: Ti/Al/metal/Au. Ti is known to extract N out of the GaN. This leaves a high density of N vacancies (donors) near the interface pinning the Fermi level. The created tunnel junction is responsible for an Ohmic contact behavior. Au is deposited as the final metal layer to exclude oxidation of the contact and the metal should limit the diffusion of Au into the layers below and vice versa. Al in the metallization scheme is known to improve the contact resistance, but the reason why has not been reported yet. We studied Ti and Ti/Al contacts on GaN and AlGaN/GaN as a function of annealing temperature by transmission electron microscopy. The role of Al in the metal multilayer, and of Al in the AlGaN on the Ohmic contact formation, has been determined. The latter result indicates that the standard metallization scheme for GaN cannot be simply transferred to AlGaN/GaN structures.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
68.37.Lp Transmission electron microscopy (TEM)

Enhancement of phase separation in the InGaN layer for self-assembled In-rich quantum dots

Il-Kyu Park, Min-Ki Kwon, Sung-Ho Baek, Young-Woo Ok, Tae-Yeon Seong, Seong-Ju Park, Yoon-Seok Kim, Yong-Tae Moon, and Dong-Joon Kim

Appl. Phys. Lett. 87, 061906 (2005); http://dx.doi.org/10.1063/1.2008365 (3 pages) | Cited 21 times

Online Publication Date: 2 August 2005

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The enhancement of phase separation in the InGaN layer grown on a GaN layer with a rough surface was investigated for the formation of self-assembled In-rich quantum dots (QDs) in the InGaN layer. Transmission electron microscopy images showed that In-rich QDs with a size of 2–5 nm were formed even in an InGaN layer with a low indium content, and a layer thickness less than the critical thickness. The room-temperature photoluminescence (PL) spectrum of this layer showed emission peaks corresponding to In-rich QDs. The temperature-dependent PL spectra showed dominant peak shifts to the lower energy side, indicating that the self-assembled In-rich QDs are formed in the InGaN layer grown on a rough GaN surface and that the carriers are localized in In-rich QDs.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
64.75.-g Phase equilibria
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effect of barrier thickness on electromigration reliability of Cu/porous low k interconnects

Jung Woo Pyun, Xia Lu, Jayhoon Chung, Sean Yoon, Paul S. Ho, Neil Henis, Kyle Neuman, Larry Smith, and Klaus Pfeifer

Appl. Phys. Lett. 87, 061907 (2005); http://dx.doi.org/10.1063/1.2008382 (3 pages) | Cited 1 time

Online Publication Date: 2 August 2005

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The effects of Ta barrier thickness on electromigration reliability of dual-damascene Cu/porous methylsilsesquioxane interconnects were investigated. With decreasing Ta barrier thicknesses, the threshold product of current density and line length (jL)c was found to be reduced due to less structural confinement from thinner barriers. The effect can be accounted for by the effective modulus of the structure except for the 75-Å Ta barrier where the (jL)c product is reduced more than expected, probably due to the presence of defects in the barrier. Results from the early failure test structures revealed a bimodal failure distribution for samples with the 75-Å and l00-Å barriers. Focused ion beam microprobe and transmission electron microscopy observations revealed that the weak-mode early failure was caused by Cu outdiffusion through structural defects in the thin Ta barrier.
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77.84.Jd Polymers; organic compounds
85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
68.37.Lp Transmission electron microscopy (TEM)

Improved photoluminescence of 1.26 μm InGaAs/GaAs quantum wells assisted by Sb surfactant and indium-graded intermediate layers

Yi-An Chang, Hao-Chung Kuo, Ya-Hsien Chang, and Shing-Chung Wang

Appl. Phys. Lett. 87, 061908 (2005); http://dx.doi.org/10.1063/1.2009048 (3 pages) | Cited 5 times

Online Publication Date: 2 August 2005

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We have grown high-quality InGaAs/GaAs quantum wells (QWs) with emission wavelength range of 1.2–1.26 μm by metalorganic chemical vapor depositions. By incorporating Sb surfactant and the indium-graded intermediate layers into InGaAs/GaAs QWs, the photoluminescence (PL) intensity of the 1.26-μm In0.45Ga0.55As/GaAs QW is enhanced by a factor of 20 and the full width at half maximum value is reduced from 60.4 meV to 35.9 meV. The good crystalline quality is proved by temperature-dependent PL, which shows that the activation energies of In0.45Ga0.55As and Sb-assisted indium-graded In0.45Ga0.55As QWs are 20.87 meV and 27.09 meV.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Optical and electrical properties of nanostructured LaCoO3 thin films

Maria Losurdo, Alberto Sacchetti, Pio Capezzuto, Giovanni Bruno, Lidia Armelao, Davide Barreca, Gregorio Bottaro, Alberto Gasparotto, Cinzia Maragno, and Eugenio Tondello

Appl. Phys. Lett. 87, 061909 (2005); http://dx.doi.org/10.1063/1.2009057 (3 pages) | Cited 2 times

Online Publication Date: 2 August 2005

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Nanostructured lanthanum cobaltite thin films have been grown on silica substrates by hybrid chemical vapor deposition/sol-gel approaches. The refractive index and the extinction coefficient of the specimens have been determined in the spectral range of 0.75–6.5 eV by spectroscopic ellipsometry. The conductivity of the films as a function of temperature has been also investigated, highlighting the different electrical behavior of LaCoO3 nanosystems as a function of the adopted synthetic strategy.
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78.66.Nk Insulators
73.61.Ng Insulators
81.07.Bc Nanocrystalline materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.63.-b Electronic transport in nanoscale materials and structures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Surface relief grating formation on a single crystal of 4-(dimethylamino)azobenzene

Hideyuki Nakano, Takahiro Tanino, and Yasuhiko Shirota

Appl. Phys. Lett. 87, 061910 (2005); http://dx.doi.org/10.1063/1.2009065 (3 pages) | Cited 21 times

Online Publication Date: 2 August 2005

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Surface relief grating (SRG) formation on an organic single crystal by irradiation with two coherent laser beams has been demonstrated by using 4-(dimethylamino)azobenzene (DAAB). It was found that the SRG formation was greatly depending upon both the coordination of the crystal and the polarization of the writing beams. The dependence of the polarization of writing beams on the SRG formation using the single crystal was found to be quite different from that reported for amorphous polymers and photochromic amorphous molecular materials, suggesting that the mechanism of the SRG formation on the organic crystal is somewhat different from that on amorphous materials.
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61.82.Pv Polymers, organic compounds
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.66.Hq Organic compounds

Three-dimensional organization of rare-earth atoms at grain boundaries in silicon nitride

Graham B. Winkelman, Christian Dwyer, Toby S. Hudson, Duc Nguyen-Manh, Markus Döblinger, Raphaelle L. Satet, Michael J. Hoffmann, and David J. H. Cockayne

Appl. Phys. Lett. 87, 061911 (2005); http://dx.doi.org/10.1063/1.2009067 (3 pages) | Cited 30 times

Online Publication Date: 2 August 2005

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Used in the preparation of Si3N4 components, rare-earth elements promote the growth of needlelike grains essential to elevated toughness; evidently, La is significantly more effective than Lu. To explore this difference, we determine the three-dimensional organization of rare-earth atoms in the amorphous phase near prismatic interfaces in La- and Lu-containing Si3N4 using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and image processing. Evidence is presented for substantial atomic structure in notionally amorphous volumes. While the atomic arrangement in the amorphous phase conforms to the periodicity of the terminating crystal plane in both cases, the attachment sites are very different.
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61.72.Mm Grain and twin boundaries
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.Ct Interface structure and roughness

Gold based bulk metallic glass

Jan Schroers, Boonrat Lohwongwatana, William L. Johnson, and Atakan Peker

Appl. Phys. Lett. 87, 061912 (2005); http://dx.doi.org/10.1063/1.2008374 (3 pages) | Cited 81 times

Online Publication Date: 3 August 2005

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Gold-based bulk metallic glass alloys based on Au–Cu–Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5 mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644 K, a glass transition temperature of 401 K, and a supercooled liquid region of 58 K. The Vickers hardness of the alloys in this system is ∼ 350 Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Micro-x-ray absorption near-edge structure imaging for detecting metallic Mn in GaN

G. Martínez-Criado, A. Somogyi, A. Homs, R. Tucoulou, and J. Susini

Appl. Phys. Lett. 87, 061913 (2005); http://dx.doi.org/10.1063/1.1989446 (3 pages) | Cited 11 times

Online Publication Date: 3 August 2005

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In this study, we report the application of a synchrotron radiation microprobe to the analysis of Mn valencies in GaN. X-ray absorption near-edge structure (XANES) images taken around Mn K-edge in fluorescence detection mode reveal the concentration of oxidation states of Mn centers. By fitting the XANES curve for each point of the image, the distributions of the Mn0, Mn2+, and Mn3+ oxidation states are obtained. At low Mn concentrations, there is a homogeneous mixture of Mn2+ and Mn3+ centers, while at high Mn content strong spatial-dependent Mn0 and Mn2+ distributions characterize the XANES maps. In a supplementary way with respect to Mn2+, the Mn0 pattern suggests the presence of specific cluster-like features, indicating surface segregation of metallic Mn centers.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.70.Dm X-ray absorption spectra
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors

Photoinduced changes of surface order in coumarin side-chain polymer films used for liquid crystal photoalignment

G. Bergmann, P. O. Jackson, J. H. C. Hogg, T. Stirner, M. O’Neill, W. L. Duffy, S. M. Kelly, and G. F. Clark

Appl. Phys. Lett. 87, 061914 (2005); http://dx.doi.org/10.1063/1.2009070 (3 pages) | Cited 1 time

Online Publication Date: 3 August 2005

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Specular x-ray reflectivity probes morphological changes in a crosslinkable coumarin photoalignment polymer film resulting from ultraviolet irradiation. An ordered surface layer with density oscillations compatible with planar side-chain alignment is obtained before irradiation. The ordering is enhanced in the early stages of crosslinking. This is attributed to the photoinduced increase of mobility of the side-chains resulting from the creation of free volume by the crosslinking process. The expansion of the thin film confirms that free volume is created. The surface ordering decreases with prolonged ultraviolet irradiation because of increased material viscosity resulting from a high crosslinked density. The implications of surface ordering on liquid crystal photoalignment are discussed.
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61.30.Vx Polymer liquid crystals
61.25.H- Macromolecular and polymers solutions; polymer melts
82.35.-x Polymers: properties; reactions; polymerization
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
68.47.Mn Polymer surfaces
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds
66.20.-d Viscosity of liquids; diffusive momentum transport

Experimental and theoretical evidence for vacancy-clustering-induced large voids in Czochralski-grown germanium crystals

S. Hens, J. Vanhellemont, D. Poelman, P. Clauws, I. Romandic, A. Theuwis, F. Holsteyns, and J. Van Steenbergen

Appl. Phys. Lett. 87, 061915 (2005); http://dx.doi.org/10.1063/1.2009830 (2 pages) | Cited 10 times

Online Publication Date: 3 August 2005

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Optical inspection of polished Czochralski-grown Ge wafers typically reveals the presence of surface pits similar to the Crystal Originated Particles (COP’s) observed in silicon but in a wider variety of sizes and shapes. Computer simulation of vacancy clustering during the Cz germanium crystal growth suggests that the surface pits originate from large voids formed by the diffusion-limited clustering of an excess of vacancies.
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61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Conducting In-doped CdTe oxide thin films grown by pulsed-laser deposition

R. Castro-Rodríguez, J. L. Peña, F. Leccabue, B. E. Watts, and E. Melioli

Appl. Phys. Lett. 87, 061916 (2005); http://dx.doi.org/10.1063/1.2005391 (3 pages) | Cited 2 times

Online Publication Date: 3 August 2005

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Conducting transparent oxide semiconductor In-doped CdTe oxide (ICTO) thin films ( ∼ 200 nm thick) have been deposited by pulsed-laser deposition on glass substrates without a postdeposition anneal. The electrical, structural, and optical properties of these films have been investigated as a function of O2 partial pressures during the deposition. Films were deposited at substrate temperature of 420 °C in oxygen partial pressures between 15 and 55 mTorr. The resistivity is very sensitive to the oxygen deposition pressure; at 28.5 mTorr the films show electrical resistivities as low as 9.4×10−3 Ω cm, an average visible transmittance of ∼ 75.5%, and an optical band gap of 2.74 eV.
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81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Bulk-like pentacene epitaxial films on hydrogen-terminated Si(111)

Toshihiro Shimada, Hiroyuki Nogawa, Tetsuya Hasegawa, Ryusuke Okada, Hisashi Ichikawa, Keiji Ueno, and Koichiro Saiki

Appl. Phys. Lett. 87, 061917 (2005); http://dx.doi.org/10.1063/1.2008371 (3 pages) | Cited 11 times

Online Publication Date: 4 August 2005

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The epitaxial growth of pentacene on hydrogen-terminated Si(111) is reported. Reflection high energy electron diffraction (RHEED) revealed that the crystal packing resembles that in the bulk crystal even at a monolayer thickness, which was maintained in multilayers. A ripening effect was clearly observed by atomic force microscopy (AFM). These results are important to obtain oriented crystalline films of pentacene combined with silicon microdevices with reduced defect densities.
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81.05.Hd Other semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Atomic structure in Zr70Cu29Pd1 metallic glass

L. Yang, J. Z. Jiang, T. Liu, T. D. Hu, and T. Uruga

Appl. Phys. Lett. 87, 061918 (2005); http://dx.doi.org/10.1063/1.2009827 (3 pages) | Cited 14 times

Online Publication Date: 4 August 2005

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Local atomic structures of Pd, Cu, and Zr atoms in an as-prepared Zr70Cu29Pd1 glassy alloy and the annealed samples containing icosahedral quasicrystal have been investigated by Pd, Cu, and Zr K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that Cu and Zr atoms have an icosahedral atomic surrounding. Cu atoms could locate at both center position and shell sites while Zr atoms most likely occupy the shell sites of icosahedron. Pd atoms neither substitute Zr atoms nor Cu atoms. They sit at octahedral interstices, which link up icosahedron and promote the growth of icosahedron into long-range-order icosahedral quasicrystal in the ternary Zr70Cu29Pd1 glassy alloy during annealing treatment.
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61.43.Fs Glasses
78.70.Dm X-ray absorption spectra
81.40.Gh Other heat and thermomechanical treatments

Ag9TlTe5: A high-performance thermoelectric bulk material with extremely low thermal conductivity

Ken Kurosaki, Atsuko Kosuga, Hiroaki Muta, Masayoshi Uno, and Shinsuke Yamanaka

Appl. Phys. Lett. 87, 061919 (2005); http://dx.doi.org/10.1063/1.2009828 (3 pages) | Cited 41 times

Online Publication Date: 4 August 2005

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We studied a high-performance thermoelectric material whose chemical formula is Ag9TlTe5. Ag9TlTe5 is simple and easy to prepare. Its highest dimensionless figure of merit (ZT) value is 1.23, obtained at 700 K. The values of individual thermoelectric properties at 700 K are 2.63×10−4 Ω m for electrical resistivity, 319 μV K−1 for Seebeck coefficient, and 0.22 W m−1 K−1 for thermal conductivity. Ag9TlTe5 is a unique material combining extremely low thermal conductivity and relatively low electrical resistivity.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Determination of thermal and optical parameters of melanins by photopyroelectric spectroscopy

J. E. de Albuquerque, C. Giacomantonio, A. G. White, and P. Meredith

Appl. Phys. Lett. 87, 061920 (2005); http://dx.doi.org/10.1063/1.2009833 (3 pages) | Cited 8 times

Online Publication Date: 4 August 2005

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Photopyroelectric spectroscopy (PPE) was used to study the thermal and optical properties of melanins. The photopyroelectric intensity signal and its phase were independently measured as a function of wavelength and chopping frequency for a given wavelength in the saturation part of the PPE spectrum. Equations for both the intensity and the phase of the PPE signal were used to fit the experimental results. From these fits we obtained for the first time, with great accuracy, the thermal diffusivity coefficient, the thermal conductivity, and the specific heat of the samples, as well as a value for the condensed phase optical gap, which we found to be 1.70 eV.
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87.14.-g Biomolecules: types
87.15.M- Spectra of biomolecules
87.15.Vv Diffusion

Rapid stress-driven grain coarsening in nanocrystalline Cu at ambient and cryogenic temperatures

Kai Zhang, J. R. Weertman, and J. A. Eastman

Appl. Phys. Lett. 87, 061921 (2005); http://dx.doi.org/10.1063/1.2008377 (3 pages) | Cited 98 times

Online Publication Date: 5 August 2005

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There have been long-standing concerns about the stability of the internal structure of nanocrystalline metals. In this letter we examine grain growth in nanocrystalline Cu under the microhardness indenter, examining the influence of temperature of indentation and sample purity. Surprisingly, it is found that grain coarsening is even faster at cryogenic temperatures than at room temperature. Sample purity is seen to play an important role in determining the rate of grain growth. Fast grain coarsening can affect the outcome of mechanical tests, especially if they involve large stresses and high-purity samples.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
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

Tunable uniaxial vs biaxial in-plane strain using compliant substrates

Haizhou Yin, R. L. Peterson, K. D. Hobart, S. R. Shieh, T. S. Duffy, and J. C. Sturm

Appl. Phys. Lett. 87, 061922 (2005); http://dx.doi.org/10.1063/1.2006215 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2005

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In this letter, the relaxation of strained rectangular islands on compliant substrates is used to achieve semiconductor thin films with either uniaxial stress or uniaxial strain in the plane of the film over an area of tens of microns. The work is demonstrated using silicon and silicon–germanium alloy single-crystal thin films, with uniaxial strain values approaching 1%. The biaxially strained SiGe or SiGe/Si films on borophosphorosilicate glass (BPSG) were fabricated by a wafer bonding and layer transfer process. When the viscosity of BPSG drops at high temperatures for short times, films patterned in a rectangular shape can move laterally to relieve stress only in one in-plane direction. Thus one can tailor the strain from biaxial to uniaxial in the thin films.
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81.05.Cy Elemental semiconductors
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.A- Nucleation and growth
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