Showing papers by "Philips published in 1975"

Anomalous transit-time dispersion in amorphous solids

Abstract: Measurements of the transient photocurrent $I(t)$ in an increasing number of inorganic and organic amorphous materials display anomalous transport properties. The long tail of $I(t)$ indicates a dispersion of carrier transit times. However, the shape invariance of $I(t)$ to electric field and sample thickness (designated as universality for the classes of materials here considered) is incompatible with traditional concepts of statistical spreading, i.e., a Gaussian carrier packet. We have developed a stochastic transport model for $I(t)$ which describes the dynamics of a carrier packet executing a time-dependent random walk in the presence of a field-dependent spatial bias and an absorbing barrier at the sample surface. The time dependence of the random walk is governed by hopping time distribution $\ensuremath{\Psi}(t)$. A packet, generated with a $\ensuremath{\Psi}(t)$ characteristic of hopping in a disordered system [e.g., $\ensuremath{\Psi}(t)\ensuremath{\sim}{t}^{\ensuremath{-}(1+\ensuremath{\alpha})}$, $0l\ensuremath{\alpha}l1$], is shown to propagate with a number of anomalous non-Gaussian properties. The calculated $I(t)$ associated with this packet not only obeys the property of universality but can account quantitatively for a large variety of experiments. The new method of data analysis advanced by the theory allows one to directly extract the transit time even for a featureless current trace. In particular, we shall analyze both an inorganic ($a\ensuremath{-}{\mathrm{As}}_{2}{\mathrm{Se}}_{3}$) and an organic (trinitrofluorenone-polyvinylcarbazole) system. Our function $\ensuremath{\Psi}(t)$ is related to a first-principles calculation. It is to be emphasized that these $\ensuremath{\Psi}(t)$'s characterize a realization of a non-Markoffian transport process. Moreover, the theory shows the limitations of the concept of a mobility in this dispersive type of transport.

On the heat of formation of solid alloys

Abstract: We demonstrated recently that the available experimental data on the heat of formation of solid alloys of transition metals can be accounted for by means of a cellular model. The energy effect is derived from two contributions; a negative one, arising from the difference in chemical potential, ϑ∗, for electrons at the two types of atomic cells, and a second term, which reflects the discontinuity in the density of electrons, n ws , at the boundary between dissimilar atomic cells. Expressed as a formula, ΔH ~ [-Pe(Δϑ∗) 2 + Q(Δn ws ) 2 ] . In this paper we demonstrate that the second term is preferably to be written as Q 0 (Δn 1 3 ws ) 2 . Values for P and Q 0 can be derived from basic arguments. The advantage of this alteration is that the values for P and Q 0 are now nearly the same for widely different alloy systems (i.e., as different as intermetallic compounds of two transition metals, and liquid alloys of two non-transition metals). It is demonstrated that the description (and hence the predictions) for heats of formation of alloys of transition metals is sufficiently accurate to be of practical interest. The present model conflicts strongly with descriptions of heats of formation of transition metal alloys in terms of the Engel-Brewer theory.

On-the-fly garbage collection: an exercise in cooperation

Abstract: As an example of cooperation between sequential processes with very little mutual interference despite frequent manipulations of a large shared data space, a technique is developed which allows nearly all of the activity needed for garbage detection and collection to be performed by an additional processor operating concurrently with the processor devoted to the computation proper. Exclusion and synchronization constraints have been kept as weak as could be achieved; the severe complexities engendered by doing so are illustrated.

Magneto-optic spectra and the dielectric tensor elements of bismuth-substituted iron garnets at photon energies between 2.2-5.2 eV

Abstract: Optical and magneto-optical measurements have been performed at room temperature on both polycrystalline samples and thin single-crystal films of bismuth-substituted iron garnets. Kerr rotation, ellipticity, and reflectivity are given for polycrystalline samples of composition ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Bi}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ ($0lx\ensuremath{\le}1$) between 2.0 and 5.2 eV (wavelengths between 0.6 and 0.24 \ensuremath{\mu}m). The absorption and the Faraday rotation and ellipticity of epitaxial films with $0lxl0.5$ were measured up to 3.5 eV. The experimental results have been used to calculate the diagonal and off-diagonal elements of the dielectric tensor at optical frequencies. Strong magneto-optic active transitions have been found at 2.8, 3.3, 4.1, and 4.9 eV, apart from the weaker crystal-field transitions. The bands at 2.8 and 3.3 have been studied in more detail: The oscillator strengths and splittings due to spin-orbit coupling were calculated, both increase with bismuth substitution. The large splitting of the band at 3.3 eV for the bismuth-substituted compounds is concluded to be the origin of the anomalous Faraday rotation of these compounds. The assignment of these bands in terms of an energy level scheme is discussed.

Optical and electrical properties of doped In2O3 films

Abstract: Sn doped In2O3 films are electrically conductive and transparent in the visible range of the spectrum. Films with a plasma wavelength in the 1 μm region have been prepared by spraying a solution of InCl3 and SnCl4 onto a heated substrate. The free electron concentration is observed to increase with the Sn content up to a maximum. A tentative explanation of this maximum is presented. The optical constants of the films are compared with theoretical values obtained from electrical data. At long wavelengths the experimental results are in good agreement with the classical dispersion formula of a free electron gas. At wavelengths in the region of and shorter than the plasma wavelength the damping is found to be smaller than that predicted by classical theory. Films with a rough surface, typical dimensions of the roughness being 10−5 cm, exhibit an additional surface plasmon absorption. In conjunction with the shift of the plasma edge to shorter wavelengths with increasing free electron density, a shift of the UV-absorption edge to shorter wavelengths is observed, corresponding to the rise of the Fermi level within a parabolic conduction band. Consequences for the valence band structure are discussed. Sn-dotierte In2O3-Schichten sind elektrisch leitend und im Sichtbaren transparent. Schichten mit einer Plasmawellenlange im 1 μm-Bereich wurden durch Spruhen einer Losung von InCl3 und SnCl4 auf ein erhitztes Substrat hergestellt. Mit dem Sn-Gehalt steigt die Konzentration freier Elektronen bis zu einem Maximum, fur welches eine mogliche Erklarung gegeben wird. Die optischen Konstanten der Schichten werden mit theoretischen Werten verglichen, die aus den elektrischen Daten zu erwarten sind. Bei grosen Wellenlangen lassen sich die experimentellen Ergebnisse gut mit der klassischen Dispersionsformel fur freie Elektronen wiedergeben. Im Wellenlangenbereich kleiner und gleich der Plasmawellenlange findet man abweichend von der klassischen Theorie eine geringere Dampfung. Schichten mit einer rauhen Oberflache – typisch sind Dimensionen von 10−5 cm – zeigen zusatzlich eine Oberflachenplasmonen-Absorption. Gleichzeitig mit einer Verschiebung der Plasmakante zu kleineren Wellenlangen durch eine gesteigerte Dichte freier Elektronen wird eine Verschiebung der UV-Absorptionskante zu kleineren Wellenlangen beobachtet, was einem Anheben des Fermi-Niveaus in und innerhalb eines parabolischen Leitungsbandes entspricht. Konsequenzen fur die Valenzbandstruktur werden hieraus abgeleitet.

The structure of borosilicate glasses studied by Raman scattering

Abstract: Raman spectra of alkali and alkaline earth borosilicate glasses are reported. These spectra are used to discuss the molecular structure of the glasses. The influence of Al 2 O 3 additions on the structure of borosilicate glass is also discussed. It is shown that the same type of groups are present in borosilicate glasses as in borate and silicate glasses. The presence of large borate groups such as tetraborate and metaborate groups is strongly suggested by the Raman spectra. It appears that boron ions are hardly taken up in the silicon-oxygen network. Our results suggest that the region of phase separation is larger than the region presently acknowledged.

The mirror-matrix tube: A novel light valve for projection displays

Abstract: A completely sealed-off electron beam-addressed light valve offering high reliability, low thermal impedance, and low-voltage operation is described. It is suitable for projection displays and is capable of producing bright high-contrast images with full gray-scale range and long-term storage. The light valve is contained as the faceplate in an otherwise standard, sealed-off 1½-in diameter vidicon tube and utilizes conventional focusing and deflection components. The target, which is fabricated of refractory materials using high-yield semiconductor-processing techniques, is composed of a dense matrix (500 elements/in) of aluminized silicon-dioxide membranes (~ 3000-A thickness) which are supported centrally on small silicon posts (4-5 µm high) above a transparent sapphire faceplate. These flat, stress-free oxide membranes can be deflected electrostatically (up to 4°) when addressed with the electron beam. Thus an intensity-modulated display of the deposited charge pattern on the "mirror matrix" is produced when this type of light valve is used in conjunction with reflective schlieren optical arrangement, Mechanical and optical considerations have led to a special 4-leaf geometry of the mirror elements, enabling operation at low-voltage levels (175 V) and a high optical gating efficiency (~ 50 percent) to be achieved. Large-screen (2½-by 3½-ft) displays with up to 35-fL highlight brightness ( ×5 screen gain), 15:1 contrast ratio, and 400 TV lines resolution have been demonstrated. In addition, single-frame displays (1/30-s writetime) with full gray scale storage (of many hours) have been achieved. Preliminary studies using higher density mirror matrices (1000 elements/in) show that the display resolution can be extended to 600 TV lines/picture height.

Device physics of integrated injection logic

Abstract: After a brief review of relevant device parameters, characterizing the inversely operating multicollector n-p-n transistor and the lateral p-n-p transistor which make up an I^{2}L basic cell, some electronic circuit properties of this gate are discussed quantitively. Analytic expressions are derived for the transfer characteristics, the noise margin and the propagation delay time per gate in relation to the cell geometry, fan-out, doping profiles, and recombination properties. These expressions are compared with experimental and numerical circuit simulation results.

Dynamic behaviour of semiconductor lasers

Abstract: It will be shown that spontaneous emission in a semiconductor injection laser has an important effect on the response of the laser to a step current. Simple analytical approximations of the description of the transient response, also useful for the study of the response to other current waveforms, are derived.

The barber pole, a linear magnetoresistive head

Abstract: A short review of bias methods for the magnetoresistive head (MRH), all based on the rotation of the magnetization, is given, and the properties of the various methods are discussed. A novel bias method is proposed which avoids many disadvantages of the former since it is based on the rotation of the current with the aid of slanted conductors, covering the MRH. Measured and calculated static curves are given for this new configuration, for which the name "Barber Pole" is proposed. The Barber Pole turns out to be more linear than a field-biassed MRH. The wavelength response of a Barber Pole is calculated and found to be very similar to that of a normal MRH; this is confirmed by measurements. A two terminal track sensing head, based on the new biassing principle is described.

Concentration profiles of boron implantations in amorphous and polycrystalline silicon

Abstract: Boron was implanted in amorphous silicon at energies in the range 30–200 keV and in polycrystalline silicon at energies in the range 70–800 keV. The boron distributions were measured with secondary ion mass spectrometry. By comparing the boron distributions in amorphous silicon and in polycrystalline silicon it was found that the used polycrystalline silicon behaves similarly to amorphous silicon for the boron stopping process. It was found that with the first four moments of the experimental distributions, an analytic description of the experimental distributions can be given by distributions of the Pearson system. The moments are determined by curve fitting of Pearson distributions to experimental distributions. In this way a systematic extrapolation of the low energy distributions outside the surface is automatically obtained. The moments are compared with the moments calculated by Winterbon and others. A satisfactory correspondence between the experimental and theoretical average ranges and s...

Modulation and filtering device

Abstract: A digital data transmitter is described, whose line carrier frequency need not be an integral multiple of one half the clock frequency of the digital input signal. Use is made of a digital filter for increasing the sampling frequency to a value which is twice the modulator carrier wave frequency.

Hydrogen absorption in intermetallic compounds of thorium

Abstract: The formation of ternary hydrides has been studied for 15 intermetallic compounds of thorium, (five compounds in each of the systems Th-Ni, Th-Co and Th-Fe). With the exception of the compounds richest in 3 d -metal, they all form hydrides by reaction with hydrogen gas at room temperature. The hydrides prepared include the compounds ThCoH 4 , ThNi 2 H 5 and Th 7 Ni 3 H 28 - Some compounds (Th 2 Co 7 H 4 , Th 2 Fe 7 H 5 ) have equilibrium hydrogen pressures near to 1 atmosphere at 300 K. The results are discussed in terms of a model that predicts the enthalpy of formation of a ternary hydride from the knowledge of ΔH for the corresponding binary hydrides and binary intermetallic compounds. In addition we discuss experimental results on hydrogen absorption in LaNi 5 and related compounds, published earlier. The agreement between model predictions and experiment is quite convincing.

Apparatus for reading a disc-shaped record carrier with plural scanning spots for stable radial tracking

Abstract: An apparatus for reading a disc-shaped record carrier on which information is stored in a preferably spiral-shaped track. Said information is read optically with the aid of a radiation beam, which via a directing system transfers the information contained in the scanning point of the record carrier to a read detector. The radial position of the scanning point is controlled with the aid of a control system which via a first pattern of radiation spots which is projected onto the record carrier receives information about said radial position and by means thereof controls the directing system. In order to ensure that the system is stable under all conditions use is made of a second pattern of radiation spots which are projected onto the record carrier, which pattern is radially shifted relative to the first pattern, and from which a control signal is derived with which the transfer function of the control system is varied so as to stabilize the control system.

Possibly Mixed Valency of Uranium in U Ni 5 − x Cu x

Abstract: This paper reports the lattice constant at room temperature and the susceptibility, specific heat, electrical resistivity, and absolute Seebeck coefficient of compounds $\mathrm{U}{\mathrm{Ni}}_{5\ensuremath{-}x}{\mathrm{Cu}}_{x}$ ($0\ensuremath{\le}x\ensuremath{\le}5$) as a function of temperature It is suggested that the drastic change in the properties of these compounds when $x$, increasing from 0, comes into the range of 4 to 5 is caused by a change of the uranium ions from a ${\mathrm{U}}^{4+}$ to a mixed ${\mathrm{U}}^{4+}$-${\mathrm{U}}^{3+}$ state

Device for measuring local radiation absorption in a body

Abstract: A device for measuring the spatial distribution of radiation absorption in a body wherein a multiplicity of radiators are regularly distributed about a circle surrounding the body, each radiator emitting a wedge-shaped beam of radiation in the plane of the circle toward a different arc portion of the circle between two other radiators, a multiplicity of adjoining detectors in each arc portion measuring radiation from the radiator emitting radiation to that arc portion, the spatial distribution of radiation absorption being calculated from the measured radiation values of all the detectors.

On the stability of the forced response of digital filters with overflow nonlinearities

Abstract: The forced response of a general type of digital filter, implemented with overflow nonlinearities, is studied. A definition of stability of this forced response is given. It is indicated that this stability can be studied by means of the zero-input behavior of a system, with the same structure but with time-varying nonlinearities. A theorem is derived giving sufficient conditions for the stability of the forced response of a digital system. Some results of the application of this theorem to wave digital filters are given.

Injection syringe with telescopic assembly between cartridge and vial

Abstract: An injection syringe having a cartridge with a hollow injection needle attached thereto; a vial which contains a medicament, closed by a pierceable stopper; and a telescopic assembly which detachably connects the cartridge to the vial. The telescopic assembly consists of two telescopic members, the inner member being detachably connected by an inner and an outer collar to the cartridge, and the outer member being connected to the vial by a snap connection.

Substrate holder for etching thin films

Abstract: Substrate holder for etching thin films by means of an ion beam in which a driving device moves the surface of a substrate placed on a turntable with respect to the ion beam, which holder includes a friction disk which rotates in rolling contact with a surface of a driving disk carrying the turntable and is spaced from the axis of the driving disk by a distance equal to that at which the point of impact of the ion beam on the substrate is located.

Magnetic measurements on particles in suspension

Abstract: Acicular magnetic particles up to about 25 nm thick can be suspended permanently and individually in a liquid. Their orientation by dc and ac magnetic fields can be followed through the induced optical birefringence (Cotton-Mouton effect). Analysis of the field dependencies yields the average magnetic dipole moment of the particles and the width of the distribution, the magnetic anisotropy field, and the distribution of switching fields.