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15 Apr 2002

Volume 91, Issue 8, pp. 4791-5508

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Ultraviolet light assisted oxygenation process for submicron YBa2Cu3O7−δ thin film devices

F. Herbstritt, T. Kemen, A. Marx, and R. Gross

J. Appl. Phys. 91, 5411 (2002); http://dx.doi.org/10.1063/1.1459599 (8 pages) | Cited 6 times

Online Publication Date: 29 March 2002

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We have successfully fabricated superconducting nanobridges and grain-boundary junctions from epitaxial YBa2Cu3O7−δ thin films with thickness between 20 and 30 nm and width down to ∼100 nm. The patterning process turned out to severely deteriorate the transport properties resulting in structural damage, corrosion, and oxygen loss. The most crucial steps are the baking procedure used to cure the electron beam resist, the resist development, and the ion beam etching process. By optimizing these steps and applying a suitable post-treatment procedure a significant enhancement of the sample quality could be achieved. An ultraviolet light assisted oxygenation procedure after the patterning process enabled us to achieve superconducting transition temperatures between 80 and 87 K and critical current densities at 4.2 K up to 4×107 A cm−2 for the nanobridges and 5×103–2×105 A cm−2 for the grain boundary junctions. At 4.2 K junctions with width down to 100 nm corresponding to a junction area down to 2.3×10−3 μm2 showed superconductivity. © 2002 American Institute of Physics.
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85.25.-j Superconducting devices
74.78.-w Superconducting films and low-dimensional structures
81.65.Cf Surface cleaning, etching, patterning
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
74.10.+v Occurrence, potential candidates

Propagation and post-acceleration of a pseudospark-sourced electron beam

H. Yin, A. W. Cross, A. D. R. Phelps, D. Zhu, W. He, and K. Ronald

J. Appl. Phys. 91, 5419 (2002); http://dx.doi.org/10.1063/1.1459757 (4 pages) | Cited 3 times

Online Publication Date: 29 March 2002

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Propagation and post-acceleration of a pseudospark-sourced electron beam from a three-gap pseudospark discharge chamber were studied in recent experiments. The pseudospark produced an electron beam of two phases, an initial 22 kV, 50 A hollow cathode phase beam of brightness 109−10 Am−2 rad−2 followed by a 200 V, 200 A conductive phase (CP) beam of brightness 1011−12 Am−2 rad−2. The aim of these experiments was to post accelerate the lower-voltage, higher-current CP beam using an acceleration unit driven by a 40 kV, 125 ns voltage pulse produced by a cable Blumlein. The experiments were realized by attaching an acceleration unit to the downstream side of the anode of the discharge chamber. Both the pseudospark discharge and the cable Blumlein were triggered to ensure time correlation between initiation of the pseudospark discharge and post-acceleration of the beam. © 2002 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
29.27.Eg Beam handling; beam transport
29.27.Bd Beam dynamics; collective effects and instabilities
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.59.-f Intense particle beams and radiation sources
52.80.Hc Glow; corona
29.25.Bx Electron sources

Enhanced thermally induced stress effect on an ultrathin gate oxide

Jiann-Liang Su, Chao-Chi Hong, and Jenn-Gwo Hwu

J. Appl. Phys. 91, 5423 (2002); http://dx.doi.org/10.1063/1.1452763 (6 pages) | Cited 7 times

Online Publication Date: 29 March 2002

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The effects of thermal stress on the electrical characteristics of metal–oxide–semiconductor diodes with oxides in an ultrathin regime were studied. By centering a quartz ring as a heat sink beneath the silicon wafer, the introduced temperature gradient results in a corresponding hat-like shape thickness distribution for an oxide grown on the wafer with a rapid thermal processing system. The enhanced exterior tensile and compressive thermal stresses due to introduced temperature gradient make the oxides exhibit less and more substrate injection saturation current Jsat, respectively, in comparison to control oxides. Their flatband voltage VFB data also clearly show the dependency of effective charge number density Neff on exterior thermal stress. A stress distribution model is proposed to explain the observation. Co-60 irradiation was also performed on the stressed samples to observe this stress extent by examining the variation of electrical characteristics. It was found that an oxide grown on a wafer in exterior compression exhibited better radiation hardness than one in tension. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
73.61.Ng Insulators

Observation of the growth mode of TiN during magnetron sputtering using synchrotron radiation

J. Bøttiger, J. Chevallier, J. H. Petersen, N. Schell, W. Matz, and A. Mücklich

J. Appl. Phys. 91, 5429 (2002); http://dx.doi.org/10.1063/1.1459749 (5 pages) | Cited 14 times

Online Publication Date: 29 March 2002

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The heteroepitaxial growth of TiN on MgO(001), deposited by reactive magnetron sputtering, has been studied in situ. Using real-time specular x-ray reflectivity, layer-by-layer growth was observed, with the surface roughening decreasing with an increase in the deposition temperature. Higher temperatures also resulted in lower growth rates. The film thickness was measured with specular x-ray reflectivity. Using off-plane Bragg–Brentano as well as grazing incidence in-plane wide angle scattering, the pseudomorphic growth of TiN to the underlying MgO(001) was established. Transmission electron microscopy reveals atomic planes passing through the MgO–TiN boundary, thus confirming heteroepitaxial growth. © 2002 American Institute of Physics.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Stable field emission with low threshold field from amorphous carbon films due to layer-by-layer hydrogen plasma annealing

Jun Xu, Xiaohui Huang, Wei Li, Kunji Chen, and Jianbin Xu

J. Appl. Phys. 91, 5434 (2002); http://dx.doi.org/10.1063/1.1464211 (4 pages) | Cited 1 time

Online Publication Date: 29 March 2002

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The layer-by-layer hydrogen plasma treatment method, alternatively repeating the process of nanometer thickness film deposition and hydrogen plasma chemical annealing, was applied to fabricate amorphous carbon (a-C) films. It was shown that hydrogen plasma treatment reduced the size of sp2 clusters and resulted in the increase of the optical band gap. Consequently, a stable vacuum electron emission with a low threshold field was achieved from layer-by-layer hydrogen plasma annealed a-C films compared with that from conventionally deposited samples. The threshold electric field was as low as 2 V/μm. The improvement of field emission characteristics could be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
52.77.Dq Plasma-based ion implantation and deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.-j Plasma applications

Fokker–Planck approach to impact ionization distributions in space and time

Biju Jacob, P. N. Robson, J. P. R. David, and G. J. Rees

J. Appl. Phys. 91, 5438 (2002); http://dx.doi.org/10.1063/1.1458054 (4 pages) | Cited 8 times

Online Publication Date: 29 March 2002

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A Fokker–Planck equation for carrier transport in semiconductors is derived from the Boltzmann transport equation by expanding in Legendre polynomials and assuming the phonon energy exchanged at momentum randomizing collisions is small compared with the mean carrier energy. The method is used to compute impact ionization probability distributions in space and time and the results agree well with those generated by an equivalent Monte Carlo model over a wide range of electric fields from 300 kV/cm to 1 MV/cm. © 2002 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
72.10.Bg General formulation of transport theory

Role of hydrogen in controlling the growth of μc-Si:H films from argon diluted SiH4 plasma

Madhusudan Jana, Debajyoti Das, and A. K. Barua

J. Appl. Phys. 91, 5442 (2002); http://dx.doi.org/10.1063/1.1454201 (7 pages) | Cited 18 times

Online Publication Date: 29 March 2002

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Hydrogenated microcrystalline silicon thin films have been prepared by the rf glow discharge method using argon as a diluent of SiH4 to achieve a high growth rate. μc-Si:H film having conductivity ∼10−5 S cm−1 was achieved at a deposition rate of 36 Å/min at a moderate power density of 90 mW/cm2, without hydrogen dilution. Micrograins were identified with several well defined crystallographic orientations. Inhomogeneity and porosity at the grain boundary zone have a significant effect on the electrical properties of the films due to adsorption when exposed to atmosphere. However, by adding hydrogen to the Ar-diluted SiH4 plasma, a homogeneous and improved network structure without having any effect of adsorption was obtained at a reduced deposition rate. Highly conducting (σD∼10−3 S cm−1) undoped μc-Si:H film was prepared at a deposition rate of 15 Å/min having 90% crystalline volume fraction. The energy released by the de-excitation of Ar∗ in the plasma initiates rapid nucleation in the Si network and atomic hydrogen in the plasma helps in the defect elimination, structural reorientation, and grain growth. © 2002 American Institute of Physics.
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81.05.Cy Elemental semiconductors
52.77.Dq Plasma-based ion implantation and deposition
68.55.A- Nucleation and growth
81.05.Rm Porous materials; granular materials
61.72.Mm Grain and twin boundaries
61.43.Gt Powders, porous materials

Correlation between magnetic properties of layered ferromagnetic/dielectric material and tunable microwave device applications

Erwan Salahun, Patrick Quéffélec, Gérard Tanné, Anne-Lise Adenot, and Olivier Acher

J. Appl. Phys. 91, 5449 (2002); http://dx.doi.org/10.1063/1.1461066 (7 pages) | Cited 24 times

Online Publication Date: 29 March 2002

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Layered dielectric / ferromagnetic materials are extensively explored for microwave applications. Indeed, these materials combine the large saturation magnetization of ferromagnetic material with the low loss of dielectrics. Here, our aim was to integrate a layered ferromagnetic composite in a microwave propagation structure since the main advantage of such a material is the large impedance for one polarization. Thus, in order to predict the transmission response of the device, we carried out an electromagnetic analysis to determine how the field pattern of a microstrip line and the microwave-induced demagnetizing fields disturb the material behavior. We also explored the use of the propagation structure in two dc magnetic field-dependent devices: a tunable band stop filter and a magnetic switch. The stop-band function presented a large tunability of more than 50% with a minimal insertion loss of 3 dB when 250 Oe field was applied. Moreover, a magnetic switch using a dc field perpendicular to the easy axis of the ferromagnetic material was manufactured. © 2002 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
84.40.Dc Microwave circuits
84.30.Vn Filters
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
77.55.-g Dielectric thin films

Molecular engineering versus energy level alignment: Interface formation between oligothiophene derivatives and a metal substrate studied with photoemission spectroscopy

A. J. Mäkinen, I. G. Hill, M. Kinoshita, T. Noda, Y. Shirota, and Z. H. Kafafi

J. Appl. Phys. 91, 5456 (2002); http://dx.doi.org/10.1063/1.1464209 (6 pages) | Cited 11 times

Online Publication Date: 29 March 2002

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Two series of thin films of oligothiophene derivatives grown on Ag substrates have been studied with photoelectron spectroscopy. The oligothiophenes were end-capped with either electron-deficient (dismesitylboryl) or electron-rich (diphenyltolylamine) moieties to create molecules with electron-accepting or -donating properties, respectively. The position of the highest occupied molecular orbital (HOMO) at the metal/organic interface is found to be strongly dependent on the effective π-conjugation length of the oligothiophenes capped with dimesitylboryl groups, whereas in the oligothiophenes capped with diphenyltolylamine, the position of the HOMO is independent of the molecular length. The difference in the observed HOMO characteristics is attributed to the different make-up of the frontier orbitals in the two molecular series. This will particularly affect the overall energy barrier for charge injection at the conductor/organic interface in a device structure, such as an organic light-emitting diode, utilizing the investigated molecules for carrier injection and transport. © 2002 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states

Laser ablation of thin films with very high induced stresses

H. Dömer and O. Bostanjoglo

J. Appl. Phys. 91, 5462 (2002); http://dx.doi.org/10.1063/1.1462850 (6 pages) | Cited 5 times

Online Publication Date: 29 March 2002

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The ablation of chromium films by nanosecond laser pulses was tracked by triple-frame high-speed transmission electron microscopy and selected area diffraction (exposure time ≈7–11 ns, frame spacings 20 ns–10 μs). At lower fluences the films were shattered during heatup and cooldown, producing debris with huge in-plane accelerations up to 1010 m/s2 and rotations with 106 rps. At higher fluences the ablation is proceeded by a domain-patterned evaporation. These effects are responsible for the high damage in laser-produced patterns in chromium films. They were all explained as being due to stress waves, launched by an extremely fast nonthermal 3%–4% expansion/contraction of the bcc lattice constant during heating/cooling. © 2002 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys

Structural properties and stability of Zr and Ti germanosilicides formed by rapid thermal annealing

V. Aubry-Fortuna, O. Chaix-Pluchery, F. Fortuna, C. Hernandez, Y. Campidelli, and D. Bensahel

J. Appl. Phys. 91, 5468 (2002); http://dx.doi.org/10.1063/1.1462855 (6 pages) | Cited 3 times

Online Publication Date: 29 March 2002

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Because of their good ohmic and rectifying properties, silicides are routinely used in Si technology. This approach has been recently extended to the novel devices produced using Si1−xGex alloys. Here, we study the Zr and Ti germanosilicides produced in the low thermal budget contact formation during Si/Si1−xGex heterodevice processing. Phase formation was monitored by combining a range of spectrometries with electron microscopy and x-ray diffraction techniques, while sheet resistance measurements allowed correlation of phase formation with film conductance. After completion of the reaction, the final crystalline phase was either C49–Zr(Si1−yGey)2 in the entire Ge composition (x) range, or C54–Ti(Si1−yGey)2 in the Ge composition range 0–0.47. In the Zr–Si–Ge system, the C49–Zr(Si1−yGey)2 formation temperature (Tf) decreases as x increases, and films formed at this temperature are continuous. Excess heating (above Tf) produces islanded films with embedded grains. A most significant feature of the results was that no Ge segregation was detected at any annealing temperature and that the Ge content in the C49 phase (y) remained equal to x for all x. This is in contrast to results on the C54–Ti(Si1−yGey)2 films, which were discontinuous when x>0.10, and in which Ge segregation occurred in the form of Ge-rich SiGe decorations separating the germanosilicide grains. The Ge content in the final C54 phase (y) was always lower than the value of x in the initial SiGe alloy, and the measured sheet resistance of the corresponding contacts was large. Our results indicate that the alloys formed between Zr and Si1−xGex are good candidates as stable contacts on Si1−xGex, and hence that Zr should be preferred for contacting in Ge-rich SiGe-based applications. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
61.72.Cc Kinetics of defect formation and annealing
61.66.Bi Elemental solids
61.66.Dk Alloys
73.40.Ns Metal-nonmetal contacts
73.61.-r Electrical properties of specific thin films

Three-dimensional position detection of optically trapped dielectric particles

Alexander Rohrbach and Ernst H. K. Stelzer

J. Appl. Phys. 91, 5474 (2002); http://dx.doi.org/10.1063/1.1459748 (15 pages) | Cited 45 times

Online Publication Date: 29 March 2002

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A theory is presented together with simulation results that describe three-dimensional position detection of a sphere located in a highly focused beam by back-focal plane interferometry. This technique exploits the interference of scattered and unscattered light, which is projected on a quadrant photodiode placed in the back-focal plane of a condenser lens. Due to the Gouy-phase shift inherent in focused beams, it is not only possible to determine the lateral but also the axial position of a spherical particle with nanometer accuracy. In this paper we describe the calculation of arbitrary focused electromagnetic fields, the Gouy phase shift, Mie scattering by focused beams and the resulting position signals using the angular momentum representation. The accuracy and the sensitivity of the detection system are investigated theoretically for various sphere parameters. Both accuracy and sensitivity depend on the incident light distribution as well as on the particle’s properties and position. It is further shown that the maximum capture angle of the detection lens influences the detector’s sensitivity in a nonlinear manner. Additionally, for optical trapping applications the influence of the laser power is taken into account and is considered through a noise analysis. For all investigated trapping conditions the reconstructed position deviates on average <1 nm laterally and <5 nm axially from the actual particle position. © 2002 American Institute of Physics.
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42.50.-p Quantum optics
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly Interferometers
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