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3 Dec 2001

Volume 79, Issue 23, pp. 3749-3889

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Thermal stability of stacked high-k dielectrics on silicon

J. P. Chang and Y.-S. Lin

Appl. Phys. Lett. 79, 3824 (2001); http://dx.doi.org/10.1063/1.1419030 (3 pages) | Cited 38 times

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The thermal stability of ZrO2/ZrSixOy and ZrO2/ZrSixOy/SiNx thin films on silicon was examined by synchrotron radiation ultraviolet photoemission spectroscopy. The ZrO2/ZrSixOy layer deposited by atomic-layer-controlled deposition is stoichiometric, uniform, amorphous, and has an equivalent oxide thickness of ∼1 nm and a dielectric constant of ∼18 with low leakage current. These ZrO2/ZrSixOy samples are thermally stable in vacuum up to 880 °C at which the film decomposed to form ZrSi2, the most thermodynamically stable metal silicide at a per zirconium atom basis, and the desorption of SiO(g) and ZrO(g) accounted for the greatly reduced oxygen and zirconium photoemission intensities. The thermal stability of ZrO2/ZrSixOy is improved to 950 °C when deposited on a 0.5–0.7 nm SiNx film. © 2001 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.60.Dv Thermal stability; thermal effects
79.60.Dp Adsorbed layers and thin films
79.60.Ht Disordered structures
77.22.Ch Permittivity (dielectric function)
68.43.Vx Thermal desorption
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

X-ray diffraction and Raman scattering study of SrBi2Ta2O9 ceramics and thin films with Bi3TiNbO9 addition

J. S. Zhu, H. X. Qin, Z. H. Bao, Y. N. Wang, W. Y. Cai, P. P. Chen, W. Lu, H. L. W. Chan, and C. L. Choy

Appl. Phys. Lett. 79, 3827 (2001); http://dx.doi.org/10.1063/1.1421642 (3 pages) | Cited 7 times

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Good ferroelectric properties have previously been reported for both the (1−x)SrBi2Ti2O9–xBi3TiNbO9 bulk ceramics and thin films. In this work, x-ray diffraction and Raman scattering were used to investigate the effect of the incorporation of Bi3TiNbO9 into SrBi2Ta2O9 bulk ceramics and thin films. A better crystallization, larger grain size and larger displacement of the Ta–O(4) or Ta–O(5) ions are the origin for the good ferroelectric properties of (1−x)SrBi2Ta2O9–xBi3TiNbO9 with x = 0.3–0.4. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.30.Hv Other nonmetallic inorganics
77.80.-e Ferroelectricity and antiferroelectricity
68.55.-a Thin film structure and morphology
85.50.Gk Non-volatile ferroelectric memories
63.20.-e Phonons in crystal lattices
78.66.Nk Insulators

Stress-induced depolarization of (Pb, La)TiO3 ferroelectric thin films by nanoindentation

M. Algueró, A. J. Bushby, M. J. Reece, R. Poyato, J. Ricote, M. L. Calzada, and L. Pardo

Appl. Phys. Lett. 79, 3830 (2001); http://dx.doi.org/10.1063/1.1418258 (3 pages) | Cited 14 times

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Electrical depolarization has been observed in lanthanum-modified lead titanate ferroelectric thin films stressed by nanoindentation. A spherical metallic indenter was used as a top electrode to locally pole the films and then to measure the depolarization current intensity. The current intensity had distinctive maxima at given indentation forces. These are related to the stress thresholds for the depolarization mechanism, which is probably 90° domain wall movements. Knowledge of the depolarization stresses is necessary for the design of microelectromechanical systems that include a ferroelectric layer. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
68.60.Bs Mechanical and acoustical properties
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
77.80.Dj Domain structure; hysteresis
62.20.M- Structural failure of materials

Effects of tantalum adhesion layer on the properties of SrBi2Ta2O9 ferroelectric thin films

Ching-Chich Leu, Ming-Che Yang, Chen-Ti Hu, Chao-Hsin Chien, Ming-Jui Yang, and Tiao-Yuan Huang

Appl. Phys. Lett. 79, 3833 (2001); http://dx.doi.org/10.1063/1.1423405 (3 pages) | Cited 10 times

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The effects of tantalum (Ta) adhesion layer on the ferroelectric and microstructural properties of sol-gel-derived SrBi2Ta2O9 (SBT) films are reported in this study. Compared to the traditional titanium (Ti) adhesion layer, the Ta adhesion layer results in more favorable, highly (115) textural structure of SBT films and therefore higher polarization and dielectric constant. The remnant polarization value of the SBT films crystallized at 750 °C increases from 11.1 to 14.2 μC/cm2 at 5 V, and the dielectric constant increases from 175 to 225. The observed improvement in the electrical properties of SBT films is ascribed to the superior microstructure of Pt thin film on Ta, which has been characterized by x-ray diffraction spectrum (XRD). XRD patterns clearly indicate that the Ti adhesion layer favors c-axis crystalline structure that is undesirable for ferroelectric properties. Moreover, secondary ion mass spectrometer profiles strongly indicate that Ti atoms diffuse deeply into the bulk of SBT thin films after crystallization annealing. By using Ta as the adhesion layer material, this inhomogeneous interdiffusion phenomenon can be effectively suppressed, eliminating the formation of TiOx interfacial layer, and possibly decreasing the occurrence of undesirable second phase compound. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.35.Np Adhesion
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
61.72.Cc Kinetics of defect formation and annealing
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology

Soft phonon modes in Ba0.5Sr0.5TiO3 thin films studied by Raman spectroscopy

D. A. Tenne, A. M. Clark, A. R. James, K. Chen, and X. X. Xi

Appl. Phys. Lett. 79, 3836 (2001); http://dx.doi.org/10.1063/1.1424463 (3 pages) | Cited 18 times

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We have studied vibrational properties of Ba0.5Sr0.5TiO3 thin films grown by pulsed laser deposition on SrTiO3 and LaAlO3 substrates with SrRuO3 buffer layers by Raman spectroscopy over the temperature range from 5 to 300 K. The soft phonon modes were observed. The temperature dependence of the soft phonon frequency and the splitting of the triply degenerated soft mode into two components of A and E symmetries indicate the ferroelectric phase transition. The E soft mode is overdamped over a broad range of temperatures, and the A soft mode intensity decreases gradually in this range. This indicates a broad ferroelectric phase transition in the thin films. A comparison of results obtained from films deposited on SrTiO3 and LaAlO3 substrates shows that strain shifts the ferroelectric phase transition temperatures. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.66.Nk Insulators
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
77.80.B- Phase transitions and Curie point
81.15.Fg Pulsed laser ablation deposition
78.30.Hv Other nonmetallic inorganics
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Temperature increase and charging current in polyethylene film during application of high voltage

Chao Zhang, Kazue Kaneko, and Teruyoshi Mizutani

Appl. Phys. Lett. 79, 3839 (2001); http://dx.doi.org/10.1063/1.1421625 (3 pages)

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Temperature increase in a low density polyethylene film during the application of high dc voltage was estimated by measuring the sound velocity with a pulsed electroacoustic method. The temperature shows no change under the electric field of 50 MVm−1 at ambient temperature of 30 °C. However, the temperature increases with time, and rises to 63.7 °C in 90 min of the voltage application at ambient temperature of 60 °C. The temperature increase was caused by Joule heating and it resulted in the increase of charging current during the application of high dc voltage. The increase in charging current calculated from the temperature increase agreed well with the experimental one. © 2001 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
62.65.+k Acoustical properties of solids
73.50.Rb Acoustoelectric and magnetoacoustic effects
77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds

Higher-order nonlinear dielectric microscopy

Yasuo Cho and Koya Ohara

Appl. Phys. Lett. 79, 3842 (2001); http://dx.doi.org/10.1063/1.1421645 (3 pages) | Cited 17 times

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A higher-order nonlinear dielectric microscopy technique with higher lateral resolution than conventional nonlinear dielectric imaging is investigated. The proposed scheme involves the measurement of higher-order nonlinear dielectric constants, with sensitivity to the first 0.75 nm in depth for LiNbO3 substrate surface. This technique is demonstrated to be very useful for observing surface layers of the order of unit cell thickness on ferroelectric materials. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
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Temperature-induced change from p to n conduction in metallofullerene nanotube peapods

P. W. Chiu, G. Gu, G. T. Kim, G. Philipp, S. Roth, S. F. Yang, and S. Yang

Appl. Phys. Lett. 79, 3845 (2001); http://dx.doi.org/10.1063/1.1415770 (3 pages) | Cited 22 times

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Metallofullerene nanotube peapods were prepared by introducing DyC82 into the interior space of single-walled carbon nanotubes. Transport measurements show that the DyC82 molecules function as electron donors and transfer charge to the carbon nanotube host. The amount of charge transferred varies with the temperature. At room temperature, the doped nanotube shows p-type behavior as seen from the response to a back gate. As the temperature decreases, the conductance becomes n type and at T<215 K metallic behavior is observed, indicating the degenerate state by doping. Below about 75 K, single-electron charging phenomena dominate the transport and show irregular Coulomb blockade oscillation, implying that the insertion of DyC82 splits the tube into a series of several quantum dots. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
72.80.Rj Fullerenes and related materials
72.60.+g Mixed conductivity and conductivity transitions
73.22.-f Electronic structure of nanoscale materials and related systems

Alignment of self-assembled magnetic nanostructures: Co dot chains and stripes on grooved Ru(0001)

Chengtao Yu, Dongqi Li, J. Pearson, and S. D. Bader

Appl. Phys. Lett. 79, 3848 (2001); http://dx.doi.org/10.1063/1.1421624 (3 pages) | Cited 21 times

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We have deposited 0–60 nm Co with a wedge-shaped thickness gradient onto a grooved Ru(0001) substrate by means of molecular-beam epitaxy at 350 °C. The resultant epitaxial Co island (dot) structure was characterized ex situ using atomic- and magnetic-force microscopy and the magneto-optic Kerr effect. The dots self-assemble with ∼ 70–500 nm diameter, ∼ 1–7 nm height, and align into linear chains along the grooves with spacings in the chains to decrease from ∼ 1 μm until they form continuous stripes, depending on dosage and groove structure. The dots have magnetic single domains with in-plane easy axes. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films

Tunneling current through a quantum dot array

David M.-T. Kuo, G. Y. Guo, and Yia-Chung Chang

Appl. Phys. Lett. 79, 3851 (2001); http://dx.doi.org/10.1063/1.1420775 (3 pages) | Cited 12 times

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The tunneling current through a quantum dot array (QDA) is studied theoretically. Strong electron correlation effect is taken into account in the QDA in which the quantum dots provide a strong three-dimensional confinement effect. A mixed Hubbard and Anderson model is used to simulate the system. It is found that Coulomb charging splits the band resulting from interdot coupling into two subbands. The tunneling current is thus influenced significantly by both Coulomb charging and interdot coupling. © 2001 American Institute of Physics.
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73.21.La Quantum dots
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling

Faceting evolution during self-assembling of InAs/InP quantum wires

H. R. Gutiérrez, M. A. Cotta, and M. M. G. de Carvalho

Appl. Phys. Lett. 79, 3854 (2001); http://dx.doi.org/10.1063/1.1424476 (3 pages) | Cited 26 times

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The self-assembling of InAs quantum wires on (001) InP substrates during chemical beam epitaxy has been studied. The samples were characterized by reflection high-energy electron diffraction (RHEED), atomic force microscopy, and high-resolution transmission electron microscopy (HRTEM). By monitoring the RHEED chevron structures along the [1math0] direction, we studied the facets formation during the initial states of InAs growth. The facets angles measured by HRTEM are in perfect agreement with the angles between chevron streaks. A time dependence of the chevron streaks angles is reported and correlated to the wire formation. These results can be interpreted using nonequilibrium models existing in literature. © 2001 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
81.16.Dn Self-assembly
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Controlled striped phase formation on ultraflat Si(001) surfaces during diborane exposure

J.-F. Nielsen, J. P. Pelz, H. Hibino, C.-W. Hu, I. S. T. Tsong, and J. Kouvetakis

Appl. Phys. Lett. 79, 3857 (2001); http://dx.doi.org/10.1063/1.1421084 (3 pages) | Cited 2 times

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We have used low-energy electron microscopy to study spontaneous step formation in “striped” domains on ultraflat Si(001)-(2×1) surfaces during B2H6 exposure at elevated temperatures. We show that the size and arrangement of striped domains are kinetically limited, and propose that the limiting factor is the supply of diffusing Si surface adatoms. By adding controlled amounts of extra Si to ultraflat terraces, it is possible to foster the formation of very large (>5 μm) single-domain striped regions with adjustable stripe widths. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Nq Low energy electron microscopy (LEEM)
68.35.Md Surface thermodynamics, surface energies
68.35.Fx Diffusion; interface formation

Dipole-assisted self-assembly of light-emitting p-nP needles on mica

F. Balzer and H.-G. Rubahn

Appl. Phys. Lett. 79, 3860 (2001); http://dx.doi.org/10.1063/1.1424071 (3 pages) | Cited 74 times

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We report on dipole-assisted, self-assembled formation of p-6P and p-5P needles on cleaved and heated mica (0001) surfaces. Low-energy electron diffraction (LEED) reveals that the needles are single crystalline with the (1mathmath) face parallel to the surface, consisting of parallel stacks of laying molecules oriented along the direction of microscopic dipoles on the mica surface. They have submicrometer cross-sectional dimensions and lengths as large as millimeters. Moreover, due to the strong dipole confinement of individual molecules, the needles form large domains with parallel oriented entities. A pronounced optical dichroism agrees with the findings from LEED. © 2001 American Institute of Physics.
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68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)

Adsorption of NH3 and NO2 molecules on carbon nanotubes

Hyunju Chang, Jae Do Lee, Seung Mi Lee, and Young Hee Lee

Appl. Phys. Lett. 79, 3863 (2001); http://dx.doi.org/10.1063/1.1424069 (3 pages) | Cited 122 times

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Adsorption of NH3 and NO2 molecules on semiconducting single-walled carbon nanotubes is investigated using density functional theory. Both NH3 and NO2 molecules are found to bind to carbon nanotubes via physisorption. Electron charge transfer is found to be a major mechanism determining the conductivity change in carbon nanotubes upon exposure to NH3 and NO2 molecules. The calculated density of states is also considered to elucidate the differences in the NO2 and NH3 gas detection mechanism of carbon nanotubes. © 2001 American Institute of Physics.
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68.43.Fg Adsorbate structure (binding sites, geometry)
68.43.Mn Adsorption kinetics
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Creation of nanodiamonds by single impacts of highly charged ions upon graphite

T. Meguro, A. Hida, M. Suzuki, Y. Koguchi, H. Takai, Y. Yamamoto, K. Maeda, and Y. Aoyagi

Appl. Phys. Lett. 79, 3866 (2001); http://dx.doi.org/10.1063/1.1424047 (3 pages) | Cited 26 times

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The local modification of the electronic states of highly oriented pyrolytic graphite (HOPG) surfaces using highly charged ion (HCI) irradiation has been demonstrated as a promising technique in the design of nanoscale materials. The high potential energy of HCI and subsequent surface treatment by either electron injection from a scanning tunneling microscopy (STM) tip or by He–Cd laser irradiation provide a localized transition from sp2 to sp3 hybridization in HOPG, resulting in the formation of nanoscale diamond-like structures (nanodiamond). It is of interest that a single impact of HCI creates one nanodiamond structure without inducing any defects in the area surrounding the impact region, suggesting potential applications of HCI in nanoscale material processing. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.At Surface states, band structure, electron density of states
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Stiction-controlled locking system for three-dimensional self-assembled microstructures: Theory and experimental validation

Vincent Agache, Emmanuel Quévy, Dominique Collard, and Lionel Buchaillot

Appl. Phys. Lett. 79, 3869 (2001); http://dx.doi.org/10.1063/1.1418031 (3 pages) | Cited 7 times

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The premise of our study lies in the controlled use of the phenomenon of stiction to lock three-dimensional self-assembled polycrystalline silicon (polysilicon) microstructures. The stiction refers to the permanent adhesion of the microstructures to adjacent surfaces. It can occur either during the final stage of the micromachining process, that is to say the releasing of the microstructural material, or after the packaging of the device, due to overrange input signals or electromechanical instability. As a result, we often regard stiction as a major failure issue in the microelectromechanical systems fabrication. This letter reports both the theory of our stiction-controlled locking system operation mode and the validation of our original concept through the stiction-locking of a three-dimensional self-assembled device. © 2001 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.Cy Elemental semiconductors
81.16.Dn Self-assembly
46.55.+d Tribology and mechanical contacts
68.35.Af Atomic scale friction
68.35.Gy Mechanical properties; surface strains
81.40.Pq Friction, lubrication, and wear
68.35.Np Adhesion
07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling
85.30.-z Semiconductor devices

Improving efficiency by balancing carrier transport in poly(9,9-dioctylfluorene) light-emitting diodes using tetraphenylporphyrin as a hole-trapping, emissive dopant

Alasdair J. Campbell, Donal D. C. Bradley, Tersilla Virgili, David G. Lidzey, and Homer Antoniadis

Appl. Phys. Lett. 79, 3872 (2001); http://dx.doi.org/10.1063/1.1421415 (3 pages) | Cited 39 times

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Unbalanced carrier transport is known to strongly affect the efficiency of polymer light-emitting diodes. Here, we report the results of time-of-flight (TOF), current density–voltage, and electroluminescence (EL) quantum efficiency measurements on single-layer poly(9,9-dioctylfluorene) (PFO) devices doped with the red-emitter tetraphenylporphyrin (TPP). TOF shows that PFO is a unipolar conductor, with hole transport much better than electron transport. At a field of 5×105 V/cm, a nondispersive hole mobility of 4×10−5–5×10−4 cm2/V s, dependent on sample morphology, is obtained. Upon the addition of 5% by weight TPP, hole transport becomes as highly dispersive as electron transport, having no measurable average mobility. This results in a decrease in the current for a given applied bias but an increase in the external EL quantum efficiency. TPP acts as a strong hole trap, reducing the dominant hole current and producing more balanced carrier transport. At TPP concentrations above 6%, the device characteristics start to revert to those found at lower TPP concentrations. This is due to the onset of efficient hole transport between the dopant molecules that reestablishes a transport imbalance. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices

Robust microfabricated field-effect sensor for monitoring molecular adsorption in liquids

E. B. Cooper, J. Fritz, G. Wiegand, P. Wagner, and S. R. Manalis

Appl. Phys. Lett. 79, 3875 (2001); http://dx.doi.org/10.1063/1.1423776 (3 pages) | Cited 6 times

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We show that a microfabricated field-effect sensor located at the terminus of a freestanding cantilever can detect surface potential changes resulting from the adsorption of charged molecules in an aqueous environment. The charge sensitive region, defined by lightly doped silicon, is embedded within the heavily doped silicon cantilever. Since both the electrical trace and sensitive region are passivated with thermally diffused silicon dioxide, the entire cantilever can be immersed in buffer solutions and cleaned with strong acids without degrading its electrical response. As an example, we demonstrate that the device can reproducibly detect adsorption of positively charged poly-L-lysine (PLL) on silicon dioxide. We also demonstrate that PLL adsorption and pH can be measured in discrete solutions by scanning the cantilever through parallel, distinct streams within a microfluidic channel array. © 2001 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
68.43.Mn Adsorption kinetics
82.80.Fk Electrochemical methods
87.85.Va Micromachining
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Three-dimensional thermal noise imaging

Christian Tischer, Stephan Altmann, Samo Fisinger, J. K. Heinrich Hörber, Ernst H. K. Stelzer, and Ernst-Ludwig Florin

Appl. Phys. Lett. 79, 3878 (2001); http://dx.doi.org/10.1063/1.1423404 (3 pages) | Cited 22 times

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We present a scanning probe microscope based on optical tweezers for three-dimensional imaging of the topology of transparent material in the nanometer range. A spherical nanoparticle serves as a probe. An optical trap moves it through the sample (e.g., a polymer network), while the position of the particle center is recorded by three-dimensional interferometry. Accessible volumes are reconstructed from the histogram of thermal position fluctuations of the particle. The resolution in determining the position of surfaces in three dimensions is about 20 nm. © 2001 American Institute of Physics.
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07.79.-v Scanning probe microscopes and components
87.64.Dz Scanning tunneling and atomic force microscopy

Insulating behavior for DNA molecules between nanoelectrodes at the 100 nm length scale

A. J. Storm, J. van Noort, S. de Vries, and C. Dekker

Appl. Phys. Lett. 79, 3881 (2001); http://dx.doi.org/10.1063/1.1421086 (3 pages) | Cited 166 times

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Electrical transport measurements are reported for double-stranded DNA molecules located between nanofabricated electrodes. We observe the absence of any electrical conduction through these DNA-based devices, both at the single-molecule level as well as for small bundles of DNA. We obtain a lower bound of 10 TΩ for the resistance of a DNA molecule at length scales larger than 40 nm. It is concluded that DNA is insulating. This conclusion is based on an extensive set of experiments in which we varied key parameters such as the base-pair sequence [mixed sequence and homogeneous poly(dG)⋅poly(dC)], length between contacts (40–500 nm), substrate (SiO2 or mica), electrode material (gold or platinum), and electrostatic doping fields. Discrepancies with other reports in the literature are discussed. © 2001 American Institute of Physics.
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85.65.+h Molecular electronic devices
87.14.G- Nucleic acids
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Porosity characterization by beam-based three-photon positron annihilation spectroscopy

Mihail P. Petkov, Marc H. Weber, Kelvin G. Lynn, and Kenneth P. Rodbell

Appl. Phys. Lett. 79, 3884 (2001); http://dx.doi.org/10.1063/1.1421090 (3 pages) | Cited 33 times

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We present a straightforward and fast positron annihilation spectroscopy (PAS) technique for measuring the 2 to 3 photon annihilation ratio of Ps (electron-positron) atoms (3γ PAS), utilized here for the nondestructive characterization of mesoporous (pore size >1 nm) dielectric films. Examples are given for ∼1-μm-thick foamed methyl-silsesquioxane (MSSQ) films, produced by mixing MSSQ (0–90 wt % fraction) with a sacrificial foaming agent (porogen). Probing these films as a function of depth allows one to monitor Ps escape from interconnected pores and to determine the threshold for pore interconnectivity to the film surface. A classical treatment of Ps diffusion is used to calculate the open and closed porosity fractions as a function of the initial porogen load. © 2001 American Institute of Physics.
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78.70.Bj Positron annihilation
61.80.Fe Electron and positron radiation effects
61.82.Pv Polymers, organic compounds
77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
82.70.Rr Aerosols and foams
36.10.Dr Positronium
78.66.Qn Polymers; organic compounds

Probing the confined dynamics of a spherical colloid close to a surface by combined optical trapping and reflection interference contrast microscopy

François Nadal, Alexandre Dazzi, Françoise Argoul, and Bernard Pouligny

Appl. Phys. Lett. 79, 3887 (2001); http://dx.doi.org/10.1063/1.1423790 (3 pages) | Cited 2 times

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A reflection interference contrast microscope and a two-beam optical trap have been combined to measure the interaction force between a colloidal particle (latex) and a solid wall (quartz plate). The particle-wall separation is measured with a nanometric resolution. The technique reveals the film drainage effect when the particle gets close to the wall and allows deducing the particle-wall equilibrium force profile, in the 0.1 to 10 pN range. © 2001 American Institute of Physics.
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82.70.Dd Colloids
07.60.Ly Interferometers
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
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