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17 Aug 1998

Volume 73, Issue 7, pp. 865-1010

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Effects of ion irradiation on the residual stresses in Cr thin films

A. Misra, S. Fayeulle, H. Kung, T. E. Mitchell, and M. Nastasi

Appl. Phys. Lett. 73, 891 (1998); http://dx.doi.org/10.1063/1.122029 (3 pages) | Cited 11 times

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Cr films sputtered onto {100} Si substrates at room temperature were found to be under residual tension, as revealed by wafer curvature measurements. A 150 nm thick Cr film was bombarded with 300 keV Ar ions after deposition. The intrinsic residual tensile stress increased slightly and then decreased with further increase in the ion dose. For ion doses >1×1015 ions/cm2, the stress in the film became compressive and increased with increasing dose. Transmission electron microscopy revealed that the grain boundaries in as-deposited Cr have columnar porosity. A Cr film, ion irradiated to a dose of 5×1015 ions/cm2, showed no grain boundary porosity. The changes in the residual stress during ion irradiation are explained by considering Ar incorporation in the film and the manner in which irradiation may change the interatomic distances and forces. © 1998 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
61.72.Mm Grain and twin boundaries

Combinatorial synthesis and evaluation of epitaxial ferroelectric device libraries

I. Takeuchi, H. Chang, C. Gao, P. G. Schultz, X.-D. Xiang, R. P. Sharma, M. J. Downes, and T. Venkatesan

Appl. Phys. Lett. 73, 894 (1998); http://dx.doi.org/10.1063/1.122030 (3 pages) | Cited 43 times

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Combinatorial libraries of parallel-plate capacitors, consisting of Pt and La0.5Sr0.5CoO3 electrodes and a doped BaxSr1−xTiO3 dielectric layer, have been fabricated and analyzed to systematically study the effects of dopants on device performance. Epitaxial heterostructure libraries with sharp interfaces were generated from amorphous layers on LaAlO3 substrates. Two hundred and forty different host/dopant combinations were synthesized on a 1/2 in. by 1/2 in. substrate, with 23 capacitors for each combination. Addition of 1.5 mol % W was found to increase the figure of merit (ϵ/Ileak) 220-fold and reduce the high-frequency (MHz and GHz) loss tangent by fourfold. © 1998 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Improvement in performance of electrically tunable devices based on nonlinear dielectric SrTiO3 using a homoepitaxial LaAlO3 interlayer

Q. X. Jia, A. T. Findikoglu, D. Reagor, and P. Lu

Appl. Phys. Lett. 73, 897 (1998); http://dx.doi.org/10.1063/1.122031 (3 pages) | Cited 35 times

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Improved structural and dielectric properties of nonlinear dielectric SrTiO3 thin films on LaAlO3 substrates were accomplished by incorporating a homoepitaxial LaAlO3 interlayer between the substrate and the dielectric film. Using this interlayer, the quality factor of SrTiO3 films with high-temperature superconducting YBa2Cu3O7−x electrodes on LaAlO3 substrates was improved by more than 50% at 4.2 GHz and 4 K. This improvement, combined with no change in nonlinearity, led to greater than a 50% enhancement of the finesse factor (defined as the product of the quality factor and the fractional shift resonant frequency) for the coplanar waveguide microwave resonators. The reduced planar defect density in the SrTiO3 films was attributed to this improvement. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
68.35.Ct Interface structure and roughness
74.72.-h Cuprate superconductors
84.40.Az Waveguides, transmission lines, striplines
61.72.-y Defects and impurities in crystals; microstructure
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Mechanism of low temperature C54 TiSi2 formation bypassing C49 TiSi2: Effect of Si microstructure and Mo impurities on the Ti–Si reaction path

J. A. Kittl, M. A. Gribelyuk, and S. B. Samavedam

Appl. Phys. Lett. 73, 900 (1998); http://dx.doi.org/10.1063/1.122032 (3 pages) | Cited 22 times

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X-ray diffraction, high resolution transmission electron microscopy, and resistivity measurements were used to demonstrate a modification of the Ti/Si reaction path consisting of direct nucleation followed by diffusion limited growth of low resistivity C54 TiSi2 without nucleation of high resistivity C49 TiSi2, for the reaction of Ti with Mo doped polycrystalline or Mo doped amorphous Si by rapid thermal processing at 650 °C. We also report the mechanism of early C54 nucleation. We demonstrate that MoSi2 and an unidentified silicide phase lattice matched to C54 TiSi2, with spacings of 4.15 and 2.26 Å, nucleate along the Ti/Si interface at early stages of the reaction and act as templates on which C54 TiSi2 nucleates and grows epitaxially. In contrast, the conventional phase sequence, nucleation and growth of C49 TiSi2 preceding nucleation of C54 TiSi2, was observed for the Ti/Mo doped single crystal (100) Si reaction and for all samples without Mo. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
73.40.Ns Metal-nonmetal contacts

Ferroelectric characterization of highly (0001)-oriented YMnO3 thin films grown by chemical solution deposition

Woo-Chul Yi, Joon-Seon Choe, Chang-Rok Moon, Sook-Il Kwun, and Jong-Gul Yoon

Appl. Phys. Lett. 73, 903 (1998); http://dx.doi.org/10.1063/1.122443 (3 pages) | Cited 42 times

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Highly (0001)-oriented thin films of YMnO3 were grown directly on Si substrates by chemical solution deposition. The crystallinity of the films was investigated by using x-ray diffraction: θ–2θ scan, rocking curve, and pole figure. Analysis of the x-ray photoelectron spectroscopy data and Rutherford backscattering spectroscopy spectrum showed that the films had a single phase of stoichiometric YMnO3. The ferroelectric properties of YMnO3 were investigated by measuring the temperature dependence of the capacitance–voltage characteristics in the metal/ferroelectric/semiconductor structure. Screening of the ferroelectricity of YMnO3 thin film at room temperature was discussed in conjunction with the charge effects. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.-e Ferroelectricity and antiferroelectricity
68.55.-a Thin film structure and morphology
79.60.Dp Adsorbed layers and thin films
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Coherent x-ray scattering from an optical grating

Binhua Lin, Mark L. Schlossman, Mati Meron, Scott M. Williams, Zhengqing Huang, and P. James Viccaro

Appl. Phys. Lett. 73, 906 (1998); http://dx.doi.org/10.1063/1.122033 (3 pages) | Cited 1 time

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X-ray speckles due to scattering of partially (transverse) coherent x rays from an optical reflection grating are observed. The speckles indicate the presence of surface inhomogeneities of the grating that are otherwise undetectable with either visible laser light or transversely incoherent x-ray scattering. Qualitative analysis of the speckle patterns provide information on the surface morphology of the grating. The underlying order due to the periodicity of the grating enhances the detection of the speckles. © 1998 American Institute of Physics.
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42.79.Dj Gratings
78.70.Ck X-ray scattering
68.35.B- Structure of clean surfaces (and surface reconstruction)

Recover the phases from intensity data of x-ray diffraction

Gu Xu

Appl. Phys. Lett. 73, 909 (1998); http://dx.doi.org/10.1063/1.122034 (3 pages) | Cited 1 time

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For many years, people believed that in conventional x-ray crystallography one can only record the scattering intensities but not the phases. In order to study structures at the atomic scale, one has to use multibeam measurement or to rely on additional knowledge such as bonding length and to fit the intensity data by trial structure models. In this letter, however, we show that the phases are in fact hidden in the intensity data and can be recovered by studying the peak shoulders. To demonstrate, the x-ray diffraction data of aluminum powder were used to recover the phases and to reconstruct the electron density map. © 1998 American Institute of Physics.
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61.05.C- X-ray diffraction and scattering
61.05.cf X-ray scattering (including small-angle scattering)
78.70.Ck X-ray scattering
61.05.cp X-ray diffraction

Wavelength dependence of 4-dimethylamino-4′-nitrostilbene polymer thin film photodegradation

Qiang Zhang, Michael Canva, and George Stegeman

Appl. Phys. Lett. 73, 912 (1998); http://dx.doi.org/10.1063/1.122035 (3 pages) | Cited 15 times

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The polymeric electro-optical stilbene material, 4-dimethylamino-4′-nitrostilbene (DANS), was illuminated at wavelengths ranging from the visible to near-infrared in order to quantify its photodegradation processes. Photodegradation due to one-photon and two-photon absorption was studied. The quantum efficiency of the chromophore degradation is found to be strongly wavelength and absorption mechanism dependent. This suggests that, in different regions of the spectrum, different excited states or different mechanisms are involved in the degradation process. In the near-infrared spectral region, operation lifetimes of electro-optic devices made from this chromophore are expected to be around only few hundreds hours, dramatically shorter than it was previously believed. © 1998 American Institute of Physics.
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82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
61.41.+e Polymers, elastomers, and plastics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.35.-x Polymers: properties; reactions; polymerization

Influence of negative dc bias voltage on structural transformation of carbon nitride at 600 °C

Y. K. Yap, S. Kida, T. Aoyama, Y. Mori, and T. Sasaki

Appl. Phys. Lett. 73, 915 (1998); http://dx.doi.org/10.1063/1.122036 (3 pages) | Cited 39 times

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Carbon nitride (CN) thin films were prepared at 600 °C by rf plasma pulsed laser deposition. As we increased the magnitude of the negative dc bias voltage, the CN bonds were transformed from a mixture of sp2 C–N and sp3 C–N states into a CN phase predominated by tetrahedral CN bonds. A biasing threshold of this transformation occurred due to the annihilation of the graphite microstructure, which coincided with a threshold of significant nitrogen incorporation. We found that suppression of graphite supersaturation appeared to be important for the formation of the tetrahedral sp3 C–N bonds. The nitrogen content of these films is stable upon annealing at 800 °C in vacuum. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments

Field emission from single-wall carbon nanotube films

Jean-Marc Bonard, Jean-Paul Salvetat, Thomas Stöckli, Walt A. de Heer, László Forró, and André Châtelain

Appl. Phys. Lett. 73, 918 (1998); http://dx.doi.org/10.1063/1.122037 (3 pages) | Cited 364 times

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We report on the field emission properties of single-wall carbon nanotube films, with emphasis on current–versus–voltage (I–V) characteristics and current stability. The films are excellent field emitters, yielding current densities higher than 10 mA cm−2 with operating voltages that are far lower than for other film emitters, but show a significant degradation of their performances with time. The observed deviations from the Fowler-Nordheim behavior in the I–V characteristics point to the presence of a nonmetallic density of states at the tip of the nanotubes. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption
71.20.Tx Fullerenes and related materials; intercalation compounds

Three-dimensional orientational control of molecules by slantwise photoirradiation

Kunihiro Ichimura, Shin’ya Morino, and Haruhisa Akiyama

Appl. Phys. Lett. 73, 921 (1998); http://dx.doi.org/10.1063/1.122038 (3 pages) | Cited 30 times

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When a film of poly[2-(4-phenylazophenyloxy)ethyl methacrylate] is subjected to irradiation with nonpolarized 436 nm light for n-π∗ excitation at an oblique incident angle with respect to a film surface, dichroism is induced as a result of the reorientation of azobenzene chromophores. The orientational direction is determined reversibly by an incident plane of the light while azobenzene residues reorient in a direction parallel with the light propagation. This procedure is applicable to the generation of tilt angles of nematic liquid crystals assisted by obliquely photoirradiated films as a function of exposure doses, maintaining homogeneous alignment during photoirradiation. © 1998 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
78.20.Fm Birefringence

X-ray diffraction analysis of SiGe/Si heterostructures on sapphire substrates

P. M. Mooney, J. A. Ott, J. O. Chu, and J. L. Jordan-Sweet

Appl. Phys. Lett. 73, 924 (1998); http://dx.doi.org/10.1063/1.122039 (3 pages) | Cited 6 times

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Si/Si1−xGex heterostructures on improved silicon-on-sapphire substrates were grown epitaxially by ultrahigh vacuum chemical vapor deposition for application as p-channel field effect transistors. High-resolution triple-axis x-ray diffraction was used to analyze these structures quantitatively and to evaluate their thermal stability. Outdiffusion of Ge from the strained Si1−xGex quantum well was observed after annealing at 850 °C. The amount of outdiffusion was comparable to that observed in Si1−xGex structures on bulk Si wafers. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
85.30.Tv Field effect devices
68.60.Dv Thermal stability; thermal effects
61.72.Cc Kinetics of defect formation and annealing
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