Thermal Excitation Model Research Articles

Large-Scale Crosstalk-Corrected Thermo-Optic Phase Shifter Arrays in Silicon Photonics

We introduce a thermo-optic phase shifter (TOPS) array architecture with independent phase control of each phase shifter for large-scale and high-density photonic integrated circuits with two different control schemes: pulse amplitude modulation (PAM) and pulse width modulation (PWM). We realize a compact spiral TOPS and a 288-element high-density row-column TOPS array with this architecture and drive TOPS with waveforms of both control schemes and of different array sizes. We present a thermal excitation model and a finite difference method-based simulation to simulate large-scale TOPS arrays and compare both schemes experimentally and theoretically. We also analyze the effects of thermal crosstalk in the realized TOPS array and implement a thermal crosstalk correction algorithm with the developed model. The high-density TOPS array architecture and the thermal crosstalk correction algorithm pave the way for high-density TOPS arrays with independent phase control in large-scale photonic integrated circuits interfaced with electronics limited in voltage swing and bandwidth.

Kinetics of Thermal Excitation of a Molecule in a Condensed Medium

A microscopic model of thermal excitation of the vibrational ground state of a molecule interacting with a condensed medium is developed. The master equation for the evolution of occupancies of vibrational levels is derived. The rate constant limiting the process of molecular thermal excitation is determined analytically. It is shown that while this quantity is independent of the temperature at low temperatures, by coinciding with a rate speed limit for quantum transitions due to the uncertainty principle, it rises rather linearly with the temperature at high temperatures according to the Einstein's relation for adiabatic transitions.

Влияние механических напряжений на поведение лазерных ультразвуковых сигналов вблизи отверстия в керамике нитрида кремния

An experimental study of the behavior of laser ultrasonic signals near a hole in a plate from dielectric silicon nitride ceramics under the action of external compressive stresses is carried out. A fundamental discrepancy between the results obtained and similar results obtained by us earlier for metals and a quantitative discrepancy with the predicted thermodynamic model of the formation of thermoelastic signals from stressed materials is shown. An explanation of the observed discrepancies is proposed using the model of thermal excitation of lattice defect states that we proposed earlier.

Synthesis and Investigation of Al/Sn/La2O3 Nanocomposite for Gate Dielectric Applications

In this research, TGA technique was used for determining thermal and gravimetrical stability of Al/Sn/La2O3 nanostructures prepared by sol-gel and spin-coating methods. Structural properties and surface morphology of the films were investigated by different analysis methods. Energy dispersive X-ray spectroscopy and a map were used to make a quantitative chemical analysis of unknown materials. Electrical properties of the samples were measured by metal-dielectric-semiconductor through capacitance–voltage and current rate–voltage. The conduction mechanism in the electrical field below 0.12 MV/cm and in the temperature range of 335 K < T < 420 K was found to be ohmic emission. A model of thermal excitation is proposed to explain the mechanism of ohmic conduction current. The highest value of dielectric constant (k) was ~32 at T1 = 200°C with almost amorphous structure. The results showed that at T1 = 200°C the Al/Sn/La2O3 nanostructure has lower leakage current rate and higher capacitance than those for other samples because of almost amorphous structure.

Transition between Efros–Shklovskii and Mott variable-range hopping conduction in polycrystalline germanium thin films

We report on the electrical transport properties of polycrystalline germanium thin films which are grown by the DC magnetron sputtering method. The temperature dependent resistance of seven devices are measured from 290 K down to 10 K. The thermal excitation model dominating the transport properties at the high temperature regime (above ∼60 K) is demonstrated and the low temperature electron transport is governed by the variable-range hopping (VRH) mechanism. Moreover, we observed a transition from Efros–Shklovskii to Mott VRH at ∼25 K over the entire VRH conduction regime, which is well described by a universal scaling law.

Structural and Electrical Properties of Zr x Y1−x O y Nanocomposites for Gate Dielectric Applications

The possibility of ultrathin ZrxY1−xOy films was investigated as a good gate dielectric structure for metal–oxide–semiconductor field-effect transistors (MOSFETs). Zr-doped Y2O3 nanocrystallites were synthesized by the sol–gel method. The nanocrystallite size was determined using the Scherrer equation and x-ray powder method from the main peak of the sample phase observed in x-ray diffraction patterns. Moreover, qualitative elemental analysis was performed by energy-dispersive x-ray spectroscopy. The nanocrystallite properties were characterized by scanning electron microscopy. The nanocrystallite morphology was determined by atomic force microscopy, showing that the grain size of the nanoparticles observed at the surface depends on the type of metal dopant and the annealing temperature. The capacitance–voltage and current density–voltage characteristics of the ZrxY1−xOy/Si structures were analyzed. The results indicate that the Zr0.1Y0.9Oy nanocomposite can be used as a good gate dielectric for next-generation MOSFET devices. The conduction mechanism in electrical fields below 0.25 MV/cm and the temperature range of 333 K < T < 423 K was found to be ohmic emission. A thermal excitation model is proposed to explain the ohmic current conduction mechanism.

Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume.

We present the first data from individual C60 impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for C(n)(-) clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimental yields of C(n)(-) with those of C(n)(0) from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for C(n)(-) emission can also explain the emission of electrons. The interaction of C60 with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta.

Temperature dependence of the key electro-optical characteristics for midinfrared emitting quantum cascade lasers

The equations for threshold-current density Jth, differential quantum efficiency ηd, and maximum wallplug efficiency ηwp,max for quantum-cascade lasers (QCLs) are modified for electron leakage and backfilling. A thermal-excitation model of “hot” injected electrons from the upper laser state to upper active-region states is used to calculate leakage currents. The calculated characteristic temperature T0 for Jth is found to agree well with experiment for both conventional and deep-well (DW) QCLs. For conventional QCLs ηwp,max is found to be strongly temperature dependent; explaining experimental data. At 300 K for optimized DW-QCLs, front-facet, continuous-wave ηwp,max values &amp;gt;20% are projected.

Current-voltage characteristics of individual conducting polymer nanotubes and nanowires

We report the current-voltage (I–V) characteristics of individual polypyrrole nanotubes and poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires in a temperature range from 300 K to 2 K. Considering the complex structures of such quasi-one-dimensional systems with an array of ordered conductive regions separated by disordered barriers, we use the extended fluctuation-induced tunneling (FIT) and thermal excitation model (Kaiser expression) to fit the temperature and electric-field dependent I–V curves. It is found that the I–V data measured at higher temperatures or higher voltages can be well fitted by the Kaiser expression. However, the low-temperature data around the zero bias clearly deviate from those obtained from this model. The deviation (or zero-bias conductance suppression) could be possibly ascribed to the occurrence of the Coulomb-gap in the density of states near the Femi level and/or the enhancement of electron-electron interaction resulting from nanosize effects, which have been revealed in the previous studies on low-temperature electronic transport in conducting polymer films, pellets and nanostructures. In addition, similar I–V characteristics and deviation are also observed in an isolated K0.27MnO2 nanowire.

Current–Voltage Characteristics in Individual Polypyrrole Nanotube, Poly(3,4-ethylenedioxythiophene) Nanowire, Polyaniline Nanotube, and CdS Nanorope

In this paper, we focus on current–voltage (I–V) characteristics in several kinds of quasi-one-dimensional (quasi-1D) nanofibers to investigate their electronic transport properties covering a wide temperature range from 300 down to 2 K. Since the complex structures composed of ordered conductive regions in series with disordered barriers in conducting polymer nanotubes/wires and CdS nanowires, all measured nonlinearI–Vcharacteristics show temperature and field-dependent features and are well fitted to the extended fluctuation-induced tunneling and thermal excitation model (Kaiser expression). However, we find that there are surprisingly similar deviations emerged between theI–Vdata and fitting curves at the low bias voltages and low temperatures, which can be possibly ascribed to the electron–electron interaction in such quasi-1D systems with inhomogeneous nanostructures.

Simulations of glitches in isolated pulsars

Many radio pulsars exhibit glitches wherein the star's spin rate increases fractionally by $\sim 10^{-10} - 10^{-6}$. Glitches are ascribed to variable coupling between the neutron star crust and its superfluid interior. With the aim of distinguishing among different theoretical explanations for the glitch phenomenon, we study the response of a neutron star to two types of perturbations to the vortex array that exists in the superfluid interior: 1) thermal motion of vortices pinned to inner crust nuclei, initiated by sudden heating of the crust, (e.g., a starquake), and 2) mechanical motion of vortices, (e.g., from crust cracking by superfluid stresses). Both mechanisms produce acceptable fits to glitch observations in four pulsars, with the exception of the 1989 glitch in the Crab pulsar, which is best fit by the thermal excitation model. The two models make different predictions for the generation of internal heat and subsequent enhancement of surface emission. The mechanical glitch model predicts a negligible temperature increase. For a pure and highly-conductive crust, the thermal glitch model predicts a surface temperature increase of as much as $\sim$ 2%, occurring several weeks after the glitch. If the thermal conductivity of the crust is lowered by a high concentration of impurities, however, the surface temperature increases by $\sim$ 10% about a decade after a thermal glitch. A thermal glitch in an impure crust is consistent with the surface emission limits following the January 2000 glitch in the Vela pulsar. Future surface emission measurements coordinated with radio observations will constrain glitch mechanisms and the conductivity of the crust.

Evidence for the Breakdown of Simple Classical Pictures of Organic Molecule-Based Ferrimagnetics: Low-Temperature Crystal Structure and Single-Crystal ESR Studies of an Organic Heterospin System

A model compound for purely organic ferrimagnets has been studied by single-crystal cw-ESR spectroscopy. A heterospin system under study is composed of two kinds of nitronylnitroxide molecules with the ground states of S = 1/2 and S = 1. These molecules are stacked in an alternating chain in the crystal. The cw-ESR signal of the compound was found to split into two signals below 10 K, which were reproduced by the superposition of two Lorentzian signals. The X-ray measurements at 9.6 K disclosed that the crystal structure remained unchanged at low temperatures, indicating that the origin of the ESR line splitting is not attributable to symmetry reduction associated with structural change but to some change in the spin state: Two distinguishable paramagnetic species are found from the ESR spectra. The appearance of two kinds of paramagnetic species in the alternating chain at finite temperature is expected as a primitive model of thermal excitation in the ferrimagnetic chain which is based on a theoretical calculation. The present experimental results demonstrate that the classical picture of ferrimagnetic spin state (antiparallel alignment of adjacent spins with different spin quantum numbers) is invalidated to describe organic molecule-based exchange-coupled spin systems and overlooks an essential part of the nature of ferrimagnetics.

Magnetoresistance in NiFebCo/Cu/Co/Cu Multilayers

AbstractMultilayer films of glass/[3 nm NiFeCo/dCuCu/3 nm Co]10, dCu = 0.5 to 24 nm are prepared by an electron beam evaporation method under a pressure of ≈ 1.3 × 10−4 Pa. The magnetoresistance for these multilayers is investigated in the temperature range between 4.2 and 300 K. The temperature dependence of magnetoresistance is discussed based on the model of thermal excitation of magnons and also the two‐current model.

Thermoluminescence in Polymers

The major developments in the study of thermoluminescence in organic polymers over the last ten or eleven years are reviewed. These include attempts to describe quantitatively the escape of electrons from traps using a barrier tunnelling model, rather than the usual thermal excitation model, increased sophistication of data analysis involving distributions of trap activation energies (rather than single or discrete values) and more precise definitions of the kinetic order of the thermoluminescence emission mechanism.

Detection of CH3OH J = 5 to 4 lines around 242 GHz from OMC-1

Sixteen methanol lines have been detected at a frequency of 242 GHz from OMC-1. They correspond to the J = 5..-->..4, ..delta..k = 0 transitions of CH/sub 3/OH A and E. With the assumption of reproduced with a thermal excitation model using one temperature, T/sub exc/ = 90 K, and using a column density of N(CH/sub 3/OH) = 5 x 10/sup 16/ cm/sup -2/. All lines appear to be optically thin. Collisional excitation of the J = 5 levels requires gas densities of n(H/sub 2/)> or =4 x 10/sup 6/ cm/sup -3/. Some of the detected methanol lines are also observed at a position 2' south of OMC-1 and in DR 21, M17(SW), and W3(OH).

Two new methanol transitions in Orion A

Emission from the 11(1) - 10(2) (A-) and 5(0) - 4(1) (E) transitions of CH3OH at rest frequencies of 76,247.4 and 76,509.9 MHz, respectively, has been detected toward Orion A. The velocity widths of the two transitions are estimated to be approximately 3 km/s, which is consistent with other methanol lines in Orion. It is noted that the 117.5-kayser upper-state energy of the 11(1) - 10(2) (A-) transition is the highest yet reported for methanol in any source. The observed intensity is shown to be consistent with the 90-K thermal excitation model that seems to be appropriate for all other reported CH3OH lines in Orion A. Total column densities of 3 x 10 to the 16th per sq cm for the 11(1) - 10(2) (A-) transition and of 2 x 10 to the 16th per sq cm for the 5(0) - 4(1) (E) transition are calculated.

A search for emission from vibrationally excited H2

view Abstract Citations (4) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A search for emission from vibrationally excited H2. Traub, W. A. ; Carleton, N. P. ; Black, J. H. Abstract A search has been conducted for the 8150-A emission line of interstellar H2 in Orion, in NGC 7027, and in the Rho Oph region, with negative results. In order that the results be consistent with the recently reported observations of H2 emission lines near 2 microns in Orion, the visual extinction must be greater than 10 mag for a 2500-K thermal-excitation model, or greater than 6-11 mag for a shock-excitation model. Finally, an ultraviolet-excitation model is introduced. Publication: The Astrophysical Journal Pub Date: July 1978 DOI: 10.1086/156244 Bibcode: 1978ApJ...223..140T Keywords: Astronomical Spectroscopy; Emission Spectra; Hydrogen Clouds; Nebulae; Astronomical Models; Interstellar Extinction; Molecular Excitation; Molecular Oscillations; Molecular Spectra; Astrophysics; Interstellar Matter:Molecular Hydrogen; Molecular Hydrogen:Orion Nebula full text sources ADS | data products SIMBAD (1)

An attempt to understand secondary photon emission

If excited neutrals which are sputtered from bombarded solids have a thermal origin, the yields of photons emitted by these excited neutrals will be governed by a Boltzmann factor. This idea was tested experimentally with Be, BeO, Al, Al 2O 3, Sc, GaAs, Y, In, and Tl. A Boltzmann factor was in fact obeyed but the inferred temperatures were insensitive to the variation of target mass, ion mass, ion energy, and target crystallinity. It is concluded that a thermal-excitation model accounts for many of the details of excited-state production but that the inferred temperatures have an origin other than in conventional thermal spikes.

On the problem of whether excited states amongst sputtered particles are of thermal origin

Abstract Two models of a thermal nature are currently advocated to explain the presence of ions amongst sputtered particles. In so far as these models are valid, one must consider the possibility that excited neutrals amongst sputtered particles also have a thermal origin, whence that the yields of photons emitted by these excited neutrals will be given by Yield α (ω i /Q) exp(-e i /kT). Here ω i is the degeneracy of a state which lies ε i above the ground state and Q is the internal partition function. We have tested the above equation experimentally and can summarize the results as follows: (a) The equation was satisfactorily obeyed by Be, BeO, Al, Al2 O3, Sc, GaAs, Y, In, and Tl, the inferred temperatures lying in the interval 3600–5900 K. (b) The range of temperatures agrees with four independent estimates from other work, (c) The temperatures are, on the other hand, insensitive to the variation of target mass from 9 to 204 u, ion mass from 20 to 84 u, ion energy from 4 to 16 keV, and target crystallinity, results which are in disagreement with conventional thermal-spike theory. It is concluded that the thermal-excitation model accounts for many of the details of excited-state production but that the inferred temperatures have an origin other than in conventional thermal spikes.

Mechanism of the intrinsic magnetic aftereffect

Measurements of the magnetization M and dM/dt have been made as a function of magnetic field and temperature in materials based on the composition DyCo 2. The results are compared with the tunnelling model of Egami and a simple thermal excitation model.