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7 Dec 1998

Volume 73, Issue 23, pp. 3321-3467

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Platinum nanodot formation by atomic point contact with a scanning tunneling microscope platinum tip

D. H. Huang, T. Nakayama, and M. Aono

Appl. Phys. Lett. 73, 3360 (1998); http://dx.doi.org/10.1063/1.122769 (3 pages) | Cited 14 times

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Using a platinum tip of a scanning tunneling microscope, ultrasmall nanodots of about 1 to 2 nm in diameter are reproducibly created on the Si(111)7×7 surface at room temperature by applying appropriate voltage pulses between tip and sample. Dynamic processes of the nanodot formation have been monitored by means of the displacement of the tip and the current through the tip. The experimental data suggest that a nanometer-scale bridge is formed between tip and sample, and that the created nanodot is a part of the nanobridge left on the surface. We have also observed relaxation of the tip apex and the created nanodots after the nanobridge is broken. © 1998 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Ion induced disordering and dissolution of Ni3Al precipitates

J. C. Ewert, G. Schmitz, F. Harbsmeier, M. Uhrmacher, and F. Haider

Appl. Phys. Lett. 73, 3363 (1998); http://dx.doi.org/10.1063/1.122770 (3 pages) | Cited 3 times

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The disordering of homogeneous Ni3Al and decomposed Ni(Al) alloys under irradiation with 300 keV 58Ni ions is studied at room temperature. In order to determine the development of the long-range order parameter, electron diffraction patterns are quantitatively evaluated taking into account dynamical diffraction effects. Although postulated by a recent model based on the thermal spike concept, no finite rest order is observed in the high-dose limit. The disordering rate of Ni3Al precipitates is much higher than that of homogeneous Ni3Al which is explained by the additional chemical dissolution of the particles due to ballistic mixing. © 1998 American Institute of Physics.
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64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Activation fields in ferroelectric thin film capacitors: Area dependence

T. K. Song, S. Aggarwal, Y. Gallais, B. Nagaraj, R. Ramesh, and J. T. Evans

Appl. Phys. Lett. 73, 3366 (1998); http://dx.doi.org/10.1063/1.122771 (3 pages) | Cited 37 times

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We report the activation field characteristics of (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 capacitors with areas varying from 13 to 9600 μm2. Switching properties such as maximum current and switching time depend on the capacitor area and measuring circuit elements, but the activation field is independent of capacitor area and measuring circuit parameters. Area independence of activation fields is also confirmed in (Pb,La)(Zr,Ti)O3 thin film capacitors. Two different approaches have been used to determine the activation field, yielding similar results. It is concluded that activation field is an intrinsic property and is a good quantitative measure of the ferroelectric switching properties. © 1998 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.80.Fm Switching phenomena

Room-temperature diffusivity of self-interstitials and vacancies in ion-implanted Si probed by in situ measurements

Salvatore Coffa and Sebania Libertino

Appl. Phys. Lett. 73, 3369 (1998); http://dx.doi.org/10.1063/1.122753 (3 pages) | Cited 13 times

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We have determined the room-temperature diffusivity of self-interstitials and vacancies in Si. Silicon p+−n junctions were realized in n-type epitaxial Si wafers, having an O and C content ⩽ 1015/cm3, and implanted at room temperature with 2.5 MeV He ions to fluences in the range 1×109–1×1012/cm2. The junctions were reverse biased at −30 V, in order to embody the entire damage profile of the ion in the depletion layer, and in situ leakage measurements were performed during and just after implantation. It is found that the leakage current increases monotonically during implantation while, at the beam turn off, it decreases by about a factor of 2 for times as long as 1 day. Ex situ deep level transient spectroscopy measurements show that the main contribution to leakage current is due to the deep levels introduced in the band gap by phosphorous–vacancy and divacancy complexes. This allowed us to associate the leakage current reduction at the beam turn off to the recombination of vacancy-type complexes by residual free interstitials. When, for a fixed fluence, the ion flux is increased, an initial faster transient, lasting up to ∼1000 s, is observed and has been attributed to the annihilation of residual free vacancies. Diffusivity values of 1.5×10−15 and 3.0×10−13 cm2/s for interstitials and vacancies, respectively, have been achieved from the analysis of these data. © 1998 American Institute of Physics.
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66.30.J- Diffusion of impurities
66.30.Lw Diffusion of other defects
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology

A method for liquid crystal alignment using in situ ultraviolet exposure during imidization of polyimide

Jae-Hoon Kim, Bharat R. Acharya, Satyendra Kumar, and Ki Ryong Ha

Appl. Phys. Lett. 73, 3372 (1998); http://dx.doi.org/10.1063/1.122754 (3 pages) | Cited 17 times

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Homogeneous alignment of liquid crystals can be achieved by a technique using polyimide films and in situ exposure to linearly polarized ultraviolet (LPUV) light during imidization. The alignment layers prepared by this method exhibit higher thermal stability while requiring shorter processing time than the conventional UV alignment method which employs UV exposure after the imidization of polyimide is complete. Multidomain cells can be easily fabricated with the use of a photomask and multistep in situ LPUV exposure during hard bake. © 1998 American Institute of Physics.
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61.30.-v Liquid crystals
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
82.35.-x Polymers: properties; reactions; polymerization
68.60.Dv Thermal stability; thermal effects

Metal–insulator transition in SrRuO3 induced by ion irradiation

Z. Sefrioui, D. Arias, M. A. Navacerrada, M. Varela, G. Loos, M. Lucía, J. Santamaría, F. Sánchez-Quesada, and M. A. López de la Torre

Appl. Phys. Lett. 73, 3375 (1998); http://dx.doi.org/10.1063/1.122772 (3 pages) | Cited 15 times

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We have studied the effect of He+ irradiation on the electrical resistivity and Curie temperature of ferromagnetic SrRuO3 thin films. An evolution from metallic to insulating behavior is observed when He+ ion fluence is increased, suggesting a metal–insulator transition. Damage by ion irradiation produces a strong decrease of the Curie temperature. On the other hand, no significant change in Tc (∼160 K) takes place in fresh samples grown at different substrate temperatures. We discuss the possible correlation between structural changes induced by irradiation, which reflect in an increase of the pseudocubic lattice parameter, and the observed depression of Tc.© 1998 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
71.30.+h Metal-insulator transitions and other electronic transitions
61.80.Jh Ion radiation effects
75.70.Ak Magnetic properties of monolayers and thin films

Hydrogen desorption and adsorption measurements on graphite nanofibers

C. C. Ahn, Y. Ye, B. V. Ratnakumar, C. Witham, R. C. Bowman, and B. Fultz

Appl. Phys. Lett. 73, 3378 (1998); http://dx.doi.org/10.1063/1.122755 (3 pages) | Cited 76 times

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Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying, and gas condensation. The nanofibers were grown by passing ethylene and H2 gases over the catalysts at 600 °C. Hydrogen desorption and adsorption were measured using a volumetric analysis Sieverts’ apparatus, and the graphite nanofibers were characterized by transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis. The absolute level of hydrogen desorption measured from these materials was typically less than the 0.01 H/C atom, comparable to other forms of carbon. © 1998 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
61.46.-w Structure of nanoscale materials

Transient thermochromism during ArF excimer laser ablation of poly(3-dodecylthiophene) films

Katsunori Tsunoda, Keiko Kakinuma, Hirofumi Yajima, and Tadahiro Ishii

Appl. Phys. Lett. 73, 3381 (1998); http://dx.doi.org/10.1063/1.122773 (3 pages)

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The photothermal effects involved in ArF (193 nm) laser ablation of poly(3-dodecylthiophene) (PDT) films, which have the characteristics of fusibility and thermochromism, were studied using atomic force microscopy and transient absorption spectroscopy. A molten layer was observed in the irradiated region of the PDT films. The behavior of the transient absorption spectra corresponding to the thermochromism showed a rapid increase in temperature during laser duration. A heating rate of approximately 5×109 deg/s was obtained. The obtained findings reveal that photothermal effects are significantly involved in the ablation process. © 1998 American Institute of Physics.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
79.20.Ds Laser-beam impact phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics

Scale dependence of submicron polycrystals due to configurational entropy

Qiang Yang and Wei Yang

Appl. Phys. Lett. 73, 3384 (1998); http://dx.doi.org/10.1063/1.122774 (3 pages) | Cited 5 times

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It is well known that polycrystals exhibit abnormal Hall-Petch dependence when their grain sizes fall into the submicron range. A plausible explanation is that the scale dependence of the yield stress of submicron polycrystals is mediated not only by the internal energy of the dislocation patterns, but also by their configurational entropy. Two-level dislocation arrangements are explored which naturally embed a grain size. Detailed calculations of the internal energy and the configurational entropy are facilitated by the dislocation pileup theory and the Ashby model of geometric necessary dislocations. It is shown that the present model is capable of interpreting the abnormal Hall-Petch dependence for grain sizes in the submicron range. © 1998 American Institute of Physics.
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65.20.-w Thermal properties of liquids
65.40.gd Entropy
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations

Thermal diffusivity measurements of sub-micron organic dye thin films using a high temperature superconductor bolometer

Steven M. Savoy, Cyndi A. Wells, John T. McDevitt, and Timothy A. Rhodes

Appl. Phys. Lett. 73, 3387 (1998); http://dx.doi.org/10.1063/1.122775 (3 pages)

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The thermal diffusivity of a thin organic dye layer deposited atop thin films of the high temperature superconductor YBa2Cu3O7−δ is measured using a pulsed laser flash method. Here, the underlying superconductor acts as a highly sensitive temperature transducer after appropriate conversion of the transient voltage response from 7 ns optical pulses. Film surface temperature decays for several thicknesses of the dye layers were evaluated; these decays exhibited a linear dependence of the time at half temperature maximum versus thickness squared. Three dimensional finite difference modeling was used to study and extract the thermal diffusivity values of the thin organic layers as well as to investigate the transient temperature distributions within the dye and superconductor areas. © 1998 American Institute of Physics.
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07.20.-n Thermal instruments and apparatus
68.60.Dv Thermal stability; thermal effects
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
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