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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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Asynchronous optical sampling terahertz time-domain spectroscopy for ultrahigh spectral resolution and rapid data acquisition

Takeshi Yasui, Eisuke Saneyoshi, and Tsutomu Araki

Appl. Phys. Lett. 87, 061101 (2005); http://dx.doi.org/10.1063/1.2008379 (3 pages) | Cited 35 times

Online Publication Date: 1 August 2005

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We propose a terahertz time-domain spectrometer based on asynchronous optical sampling. The spectrometer features ultrahigh spectral resolution equivalent to a laser mode-locked frequency and rapid data acquisition. The proposed method requires no mechanical translation stages for time-delay scanning, and hence, overcomes the inherent tradeoff between frequency resolution and data acquisition time. Time evolution of the picosecond terahertz pulse with a temporal window of 12.1 ns is measured directly on an oscilloscope using a time-scale magnification of 764 815. A frequency resolution of 82.6 MHz is achieved at a measurement time of 10 s. The effectiveness of the proposed method is confirmed by comparing it with conventional stage-scanning terahertz time-domain spectroscopy.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
02.50.-r Probability theory, stochastic processes, and statistics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Seeded amplification of colored conical emission via spatiotemporal modulational instability

Heping Zeng, Kun Wu, Han Xu, and Jian Wu

Appl. Phys. Lett. 87, 061102 (2005); http://dx.doi.org/10.1063/1.2009059 (3 pages) | Cited 5 times

Online Publication Date: 1 August 2005

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Seeded amplification of colored conical emission was realized by means of parametric wave mixing via spatiotemporal modulational instabilities in a thick β-barium borate crystal, where an accurately synchronized white-light supercontinuum seed pulse obtained exponential growth along the conical angle under infrared fundamental pump, leading to the generation of a broadband upconverted pulse.
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42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Photonic crystal with diamondlike structure fabricated by holographic lithography

Y. C. Zhong, S. A. Zhu, H. M. Su, H. Z. Wang, J. M. Chen, Z. H. Zeng, and Y. L. Chen

Appl. Phys. Lett. 87, 061103 (2005); http://dx.doi.org/10.1063/1.2008357 (3 pages) | Cited 20 times

Online Publication Date: 2 August 2005

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In this letter, we report a diamondlike structure. Our theoretical analysis reveals that a large complete band gap exists between the second and third bands with only a very low refractive index is needed (n ≥ 2.05) to open the complete band gap for this inverse structure. Large-scale and high-quality three-dimensional structures with this diamondlike symmetry are fabricated by a holographic lithography method using four laser beams incident from the same half-space. The beam geometry is similar to that for the face-centered cubic (fcc) structure except that the central beam is circularly polarized and the polarizations of the three outer beams must be optimized, which is critical to construct this diamondlike interference pattern.
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42.70.Qs Photonic bandgap materials
42.40.Kw Holographic interferometry; other holographic techniques
42.86.+b Optical workshop techniques

Anisotropic thermal properties of monoclinic Yb:KLu(WO4)2 crystals

Jianxiu Zhang, Kunpeng Wang, Jiyang Wang, Huaijin Zhang, Wentao Yu, Xuping Wang, Zhengping Wang, Qingming Lu, Mingfang Ba, D. G. Ran, Z. C. Ling, and H. R. Xia

Appl. Phys. Lett. 87, 061104 (2005); http://dx.doi.org/10.1063/1.2008360 (3 pages) | Cited 19 times

Online Publication Date: 2 August 2005

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Yb:KLu(WO4)2 (KLuW) crystals with large size and good optical quality have been grown by the top-seeded solution growth (TSSG) method. The melting point and specific heat, anisotropic thermal expansion and thermal conductivity have been measured. The Jackson factor α of a series of observed faces (hkl) on Yb:KLuW crystals have been calculated. In addition, the microhardness has also been measured. We find that the thermal expansion anisotropy of Yb:KLuW is weaker than KGd(WO4)2 (KGW) and KYb(WO4)2 (KYbW) and the thermal conductivity is up to 4.4 W m−1 k−1 along [205] directions at 25 °C, which is the greatest in their family.
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65.40.Ba Heat capacity
65.40.De Thermal expansion; thermomechanical effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.10.Dn Growth from solutions
64.70.D- Solid-liquid transitions
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Electric field controlled polarization grating based on a hybrid structure “photosensitive polymer-liquid crystal”

L. M. Blinov, G. Cipparrone, A. Mazzulla, C. Provenzano, S. P. Palto, M. I. Barnik, A. V. Arbuzov, and B. A. Umanskii

Appl. Phys. Lett. 87, 061105 (2005); http://dx.doi.org/10.1063/1.2009064 (3 pages) | Cited 8 times

Online Publication Date: 2 August 2005

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An investigation was carried out on a hybrid structure consisting of a photosensitive polymer in contact with a nematic liquid crystal (NLC) layer. Before assembling the structure, holographic gratings of different periods were recorded in the photopolymer by two laser beams with opposite circular polarization. Such gratings are known for their unique asymmetric diffraction in case of elliptically polarized light and can be used in optical polarization devices. Due to a spatial modulation of the direction of the local optical axis, the photopolymer modulates the anchoring conditions for NLC in a similar way. As a result, a new grating is induced in NLC with the enhanced diffraction efficiency (in a particular experiment it was four orders of magnitude higher than that of the photopolymer). The NLC grating also shows the characteristic asymmetric diffraction for the reconstructing beams of opposite circular polarizations. The diffraction efficiency is easily controlled by an external electric field.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
42.70.Jk Polymers and organics

Theoretical and experimental investigation of strongly localized plasmons on triangular metal wedges for subwavelength waveguiding

D. F. P. Pile, T. Ogawa, D. K. Gramotnev, T. Okamoto, M. Haraguchi, M. Fukui, and S. Matsuo

Appl. Phys. Lett. 87, 061106 (2005); http://dx.doi.org/10.1063/1.1991990 (3 pages) | Cited 87 times

Online Publication Date: 3 August 2005

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We report numerical analysis and experimental observation of strongly localized plasmons guided by a triangular metal wedge. Dispersion and dissipation of such wedge plasmons are analyzed using the finite-difference time-domain algorithm. Experimental observation is conducted by the end-fire excitation and near-field detection of the predicted plasmons on a 40° silver nanowedge. Good agreement with the theoretically predicted propagation distances is demonstrated. Differences between the theoretical and experimental field distribution are explained by insufficient resolution of the near-field optical probe.
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78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
42.79.Gn Optical waveguides and couplers

Experimental demonstration of complete photonic band gap in two-dimensional photonic crystal slabs

Sei-ichi Takayama, Hitoshi Kitagawa, Yoshinori Tanaka, Takashi Asano, and Susumu Noda

Appl. Phys. Lett. 87, 061107 (2005); http://dx.doi.org/10.1063/1.2009060 (3 pages) | Cited 29 times

Online Publication Date: 3 August 2005

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The realization of a photonic band gap (PBG)—not only for transverse electric (TE), but also transverse magnetic (TM)-like polarization modes in two-dimensional photonic crystal slab—is of interest for various applications. Such a complete PBG has been investigated theoretically in two-dimensional structures of which thickness is infinity. However, a complete PBG has not been demonstrated in feasible two-dimensional slab structure. In this letter, we propose two-dimensional photonic crystal slabs consisting of a triangular lattice of triangular air holes to achieve a complete PBG, and report the transmission spectra of fabricated samples. The results indicate that the degeneracy between the first and second band at the J point for TM-like polarization mode is solved, and PBG for TM-like polarization mode is obtained. Finally, we confirm the overlap of PBG between TE- and TM-like polarization modes.
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42.70.Qs Photonic bandgap materials

Enhancement of terahertz radiation from photoconductors by elliptically focused excitation

Dae Sin Kim and D. S. Citrin

Appl. Phys. Lett. 87, 061108 (2005); http://dx.doi.org/10.1063/1.2009080 (3 pages) | Cited 1 time

Online Publication Date: 4 August 2005

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Based on simulations from a detailed Monte Carlo Poisson solver, we show that the effects of photoinduced screening of the bias field as a function of optical spot shape for ultrafast excitation of photoconductors to generate terahertz transients leads to alteration of the temporal shape of the terahertz transients related to the photoexcited carrier drift velocity. The results of the simulations demonstrate that given the same photoexcited carrier density, a line focus parallel to the direction of the bias field suppresses saturation at high optical fluence due to space-charge screening and enhances the peak terahertz power in the time domain.
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72.40.+w Photoconduction and photovoltaic effects
02.50.Ng Distribution theory and Monte Carlo studies

Probe of the Si nanoclusters to Er3+ energy transfer dynamics by double-pulse excitation

M. Falconieri, E. Borsella, L. De Dominicis, F. Enrichi, G. Franzò, F. Priolo, F. Iacona, F. Gourbilleau, and R. Rizk

Appl. Phys. Lett. 87, 061109 (2005); http://dx.doi.org/10.1063/1.2001753 (3 pages) | Cited 5 times

Online Publication Date: 4 August 2005

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In this letter the dynamics of the energy transfer (ET) process from amorphous silicon nanoclusters (Si-nc) to Er3+ ions is investigated in co-doped silica glasses. Using a double pulse setup the recovery time of the sensitizing effect is monitored and direct evidence is found for the occurrence of a fast (few hundreds ns) ET process in a sample containing large (2 nm) aggregates, while a slower transfer time of few microseconds is revealed in a sample containing very small (<1 nm) aggregates.
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78.55.−m
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.47.-p Spectroscopy of solid state dynamics
81.40.Tv Optical and dielectric properties related to treatment conditions

Highly efficient and bright electroluminescent Ru(bpy)3(ClO4)2/Alq3 device

Chong-Yang Liu and Allen J. Bard

Appl. Phys. Lett. 87, 061110 (2005); http://dx.doi.org/10.1063/1.2009079 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2005

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Electroluminescent devices of indium tin oxide (ITO)/Alq3(212 nm)/Ru(bpy)3(ClO4)2(100 nm)/Ga:In were fabricated and showed high external quantum and power efficiencies, of 6.4% and 5.3%, respectively, at an optical output power of 0.4 mW/cm2 under a bias of 2.3 V. At a higher bias voltage (>2.7 V), the output power was well above 10 mW/cm2, but with a lower efficiency. Light emission occurred at the interface between Alq3 and Ru(bpy)3(ClO4)2, whose relative energies of both excited and ground states were offset, ideal for confining both charge carriers and minimizing the quenching of the Ru(bpy)32+ excited state. By comparison, in a single layer device without Alq3, the emission zone was located at the ITO interface where excited states were quenched and electron injection from the reduced molecules to the ITO contact produced a unipolar current and thus lower efficiency.
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85.60.Jb Light-emitting devices

Silicon membrane resonant-cavity-enhanced photodetector

B. W. Cheng, C. B. Li, F. Yao, C. L. Xue, J. G. Zhang, R. W. Mao, Y. H. Zuo, L. P. Luo, and Q. M. Wang

Appl. Phys. Lett. 87, 061111 (2005); http://dx.doi.org/10.1063/1.2009822 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2005

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A Si resonant-cavity-enhanced (RCE) photodiode was fabricated on a silicon membrane. The Si membrane was formed by etching from the back side of the silicon-on-insulator substrate with the buried SiO2 layer as etch-stop layer. A gold layer was deposited serving as an electrode layer and bottom mirror of the RCE photodiode. The photodiode had an external quantum efficiency of 33.8% at the resonant wavelength of 848 nm and a full width at half maximum (FWHM) of 17 nm. The responsivity was 4.6 times that of a conventional Si p‐i‐n photodiode with the same absorption layer thickness.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
81.65.Cf Surface cleaning, etching, patterning

Side-chain electro-optic polymer modulator with wide thermal stability ranging from −46 °C to 95 °C for fiber-optic gyroscope applications

Seong-Ku Kim, Yu-Chueh Hung, Byoung-Joon Seo, K. Geary, W. Yuan, B. Bortnik, H. R. Fetterman, C. Wang, W. H. Steier, and C. Zhang

Appl. Phys. Lett. 87, 061112 (2005); http://dx.doi.org/10.1063/1.2009807 (3 pages) | Cited 8 times

Online Publication Date: 5 August 2005

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Electro-optic (EO) polymer modulators with a wide range of thermal stability from −46 °C to 95 °C for fiber-optic gyroscope applications are reported. The synthesized EO side-chain polymer used has a glass transient temperature (Tg) of 200 °C and a large EO coefficient of 25.2 pm/V in a real device measurement. Mach–Zehnder (MZ) intensity and optical phase modulators are implemented based on this high-Tg side-chain EO polymer, exhibiting ∼ 3.75 V half-wave voltage with 1.5 cm interaction length and 2.3 cm total length at 1.55 μm wavelength. The optical fiber-to-lens insertion loss is ∼ 7.5 dB in the MZ interferometers and ∼ 6 dB in the straight waveguides. We examine the long-term thermal stability of these devices and demonstrate their ability to meet the strict requirements of various EO device applications, particularly fiber-optic gyroscopes.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Jk Polymers and organics
07.60.Ly Interferometers
42.81.Pa Sensors, gyros
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
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Work function reduction of graphitic nanofibers by potassium intercalation

V. S. Robinson, T. S. Fisher, J. A. Michel, and C. M. Lukehart

Appl. Phys. Lett. 87, 061501 (2005); http://dx.doi.org/10.1063/1.2009052 (3 pages) | Cited 6 times

Online Publication Date: 3 August 2005

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Materials with low work functions hold great potential for improving the performance of thermionic energy converters and other thermionic emission devices. Thermionic electron energy distributions (TEEDs) of graphitic carbon nanofibers (GCNFs) with and without intercalated potassium are used to characterize performance under realistic operating conditions. TEEDs of intercalated GCNFs at temperatures of 600 and 700 °C reveal an effective work function of 2.2 eV, a reduction of 2.5 eV from the work function of the GCNF without intercalate. In addition, consistent with other published work, a narrowing of the electron energy spectrum’s width occurs with intercalation. This narrower energy distribution may indicate emission from hybridized carbon–potassium states.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.40.+z Thermionic emission
61.46.-w Structure of nanoscale materials

Transition from diffuse to filamentary domain in a 9.5 GHz microwave-induced surface discharge

S. Popović, R. J. Exton, and G. C. Herring

Appl. Phys. Lett. 87, 061502 (2005); http://dx.doi.org/10.1063/1.2009068 (3 pages) | Cited 8 times

Online Publication Date: 3 August 2005

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The transition from the low-pressure diffuse to the high-pressure filamentary domain of a 9.5 GHz microwave-induced surface discharge in air is recorded. The discharge employs several half-wavelength initiators that locally enhance the electric field to achieve breakdown in the higher-pressure subcritical region. Visible light imaging illustrates the qualitative changes in discharge morphology over the pressure range 4.5 to 760 Torr (0.6 to 100 kPa).
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52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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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
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