Temperature measurement during laser heating of thin films using a temperature-sensitive phosphor

A phosphor with temperature-dependent lifetime has been used to measure the temperature distribution produced by laser heating of a thin film surface. A gold thin film deposited on a quartz substrate is coated with 40 m film of the phosphor material. A cw argon ion laser (476 nm) beam is split into two beams, with the more intense beam focused to 15 m (1/e² radius) to heat the film through the quartz substrate. The weaker probe beam is chopped and focused tightly using a microscope objective to excite the phosphor from the other side. The spatial variation in lifetime, and hence the temperature distribution, is obtained by scanning the probe beam over the heated region. The temperature distribution measured for different film thickness's is compared with calculations using a finite element model. The calculated temperatures at the gold surface near the laser beam are higher than the experimentally measured values, and agree only when the heat-sinking effect of the phosphor material is taken into account. The results suggest that a phosphor layer thinner than a micron will be required (for 15 m laser spot size) so as not to perturb the temperature of the gold layer.     

Electrocaloric response of a ferroelectric capacitor to a periodic electric field

The electrocaloric response of a ferroelectric capacitor to a periodic electric field has been analyzed in terms of the nonstationary heat conduction equation. A linear physical model is considered for an electrocaloric element in which one end (x = 0) is thermally insulated and a constant temperature T ₀ is maintained at the boundary x = l. The effect of a periodic electric field on the capacitor gives rise to temperature oscillations about a decreasing average value that reaches saturation. A relatively simple analytic expression is derived for the temperature distribution along the electrocaloric element and the heat flux density under stationary conditions. The calculations are carried out using the results obtained from measurements performed for a PMN-PT relaxor ferroelectric in the temperature range of the phase transition. A temperature gradient and a heat flux of ～150 W/cm² are observed in an electric field of 2.4 V/μm at a frequency of 10 Hz.     

Excimer-laser-assisted RF glow-discharge deposition of amorphous and microcrystalline silicon thin films

We combine the deposition of Hydrogenated amorphous Silicon (a-Si:H) by rf glow discharge with XeCl-excimer laser irradiation of the growing surface in order to obtain different kinds of silicon films in the same deposition system. In-situ UV-visible ellipsometry allows us to measure the optical properties of the films as the laser fluence is increased from 0 up to 180 mJ/cm² in separate depositions. For fixed glow-discharge conditions and a substrate temperature of 250° C we observe dramatic changes in the film structure as the laser fluence is increased. With respect to a reference a-Si:H film (no laser irradiation) we observe at low laser fluences (15–60 mJ/cm²) that the film remains amorphous but demonstrates enchanced surface roughness and bulk porosity. At intermediate fluences (80–165 m/Jcm²), we obtain an amorphous film with an enhanced density with respect to the reference film. Finally, at high fluences (165–180 mJ/cm²), we obtain microcrystalline films. The in-situ ellipsometry measurements are complemented by ex-situ measurements of the dark conductivity, X-ray diffraction, and Elastic Recoil Detection Analysis (ERDA). Simulation of the temperature profiles for different film thicknesses and for three laser fluences indicates that crystallization occurs if the surface temperature reaches the melting point of a-Si:H ( 1420 K). The effects of laser treatment on the film properties are discussed by taking into account the photonic and thermal effects of laser irradiation.Presented at LASERION 93, Munich, June 21–23, 1993     

Pyroelectric behavior and dielectric properties of linear copolysiloxane/eicosylamine superlattice

The pyroelectric behavior and dielectric properties of a superlattice containing a Langmuir-Blodgett (LB) film of alternately monomeric eicosylamine and linear copolysiloxane substituted with aromatic acid side chains have been investigated in the temperature range of C. The pyroelectric coefficient of the superlattice increases with temperature, exhibiting the highest coefficient of 6.2 ± 0.2 cm K-1 at 29 °C. The dielectric behavior of the superlattice is investigated by examining the dielectric loss and capacitance in the frequency range of 102 to 105 Hz. The maximum loss values for all temperatures in the range occur at a frequency ∼5000 Hz which correspond to a relaxation time of 3.18 × 10-5 s. The Cole-Cole plots obtained experimentally are found to be broad and fall inside the semicircle derived from the Debye relaxation theory. However, they agree fit with the semi-empirical Cole-Cole relaxation model. The parameter α obtained from the Cole-Cole relaxation model decreases with temperature indicating the rise in the internal degrees of freedom of the dipole in the superlattice.     

Laser Stabilisation for the Measurement of Thermal Noise

In order to measure the thermal noise of a mirror suspended in a vacuum it is necessary for the length measurement error due to intensity and frequency noise of the probe laser to be reduced below the thermal noise level. Here we report on an experiment to reduce the frequency and intensity noise of a 40mW Nd:YAG laser for this purpose. The frequency is stabilised using the standard reflection locking technique. To stabilise the laser intensity a technique which uses the properties of an in loop light field has been developed. This technique is capable of suppressing the intensity noise below the shot noise limit without reducing the useful laser power. A servo based on this technique has been designed and tested. The experimental results indicate that the laser noise can be reduced to a level which will allow a displacement sensitivity of 1.5 × 10^-19m/ Hz for the detection of thermal noise in a frequency band of 10 to 500Hz.     

Spectroscopic trace-gas sensor with rapidly scanned wavelengths of a pulsed quantum cascade laser for in situ NO monitoring of industrial exhaust systems

Development of a pulsed quantum cascade laser (QCL)-based spectroscopic trace-gas sensor for sub-part-per-million detection of nitric oxide (NO) and capable of monitoring other molecular species such as CO₂, H₂O, and NH₃ in industrial combustion exhaust systems is reported. Rapid frequency modulation is applied to the QCL to minimize the influence of fluctuating non-selective absorption. A novel method utilizes only a few laser pulses within a single wavelength scan to probe an absorption spectrum at precisely selected optical frequencies. A high-temperature gas cell was used for laboratory evaluation of the NO sensor performance. A noise-equivalent sensitivity (1) of 100 ppb × m/ at room temperature and 200 ppb × m/ at 630 K was achieved by measuring the NO R(6.5) absorption doublet at 1900.075 cm^–1.     

Transient thermal characterization of micro/submicroscale polyacrylonitrile wires

In this work, the thermal diffusivity of single polyacrylonitrile (PAN) wires with diameters from 4.62 μm down to 324 nm is measured by using our recently developed transient electro-thermal technique. The wires span from 23 μm to 126.2 μm in our measurement. Since PAN wires are dielectric, a thin Au film is coated on the surface of the wires to make them conductive. In the experiment, a step current (with ∼2 μs rising time) is fed to the sample. The sample is heated and takes a certain time to reach its steady thermal state. The temperature rising response of the sample is sensed by measuring the resistance change of the thin Au coating. From the average temperature evolution of the sample, the thermal diffusivity can be extracted. Three PAN wires with different diameters are synthesized using the electro-spinning technique and are measured to obtain their thermal diffusivities (around 1.53×10^-7 m²/s), which are slightly smaller than the bulk value. PACS 65.80.+n; 66.30.Xj; 44.10.+i     

Asymptotic properties of a simple random motion

A random walker in ^N is considered. At each step the walker picks a point in ^N from a fixed finite set of destination points. Having chosen the point, the walker moves a fractionr (r<1) of the distance toward the point along a straight line. Assuming that the successive destination points are chosen independently, it is shown that the asymptotic distribution of the walker's position has the same mean as the destination point distribution. An estimate is obtained for the fraction of time the walker stays within a ball centered at the mean value for almost every destination sequence. Examples show that the asymptotic distribution could have intricate structure.     

Characterization of superconducting YBaCuO-films by low temperature scanning electron microscopy

Low-temperature scanning electron microscopy has been performed for imaging the spatial distribution of the critical current densityj _c(x,y) and of the critical temperatureT _c(x,y) in polycrystalline superconducting YBaCuO films. Strongly inhomogeneous behavior has been observed, and the spatial resolution limit has been found to be 1–2 m. The local temperature increment in the specimen film caused by the electron beam scanning has been demonstrated experimentally as the underlying mechanism of the imaging principle, and the beam-induced thermal perturbation of the high-T _c film/substrate configuration is discussed in detail. The radiation hardness of the sample films against the electron beam irradiation in our imaging experiments has been evaluated. No radiation damage could be detected up to the maximum applied dose of well above 10²⁰ electrons/cm² for a typical beam energy of 26 keV.     

Time-resolved thermal microscopy with fluorescent films

A technique is experimentally demonstrated, allowing one, with a time resolution of a few ns, to remotely measure the temperature distribution on surfaces that are accessible to light. The surfaces are coated with a polymer containing fluorescing dye. When excited at the desired moment with a flashlight this is induced to fluoresce. As the fluorescence yield is temperature dependent, the temperature distribution during the fluorescence decay time can be uniquely determined. The fluorescence is recorded first in thermal equilibrium and then at the elevated temperature for which knowledge of the temperature distribution is desired. From the ratio of the spatially resolved fluorescence yields the temperature distribution can be evaluated. With spatial resolutions down to 2 m, temperatures in the range 20°–120°C are measured with accuracies of ±1°C, where the measurement intervals are as short as 18 ns.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Thermal conductivity of the Nb3Ge layer prepared by the continuous deposition method

The paper describes the measurement of thermal conductivity of the stainless steel tape on which the superconductive Nb₃Ge layer was vapour-deposited on both sides by the continuous method. The stainless steel 50 m substrate covered by the 2 m Nb layer was deposited with the layer of Nb₃Ge of the thickness of 10 m. Thermal conductivity in the temperature range within 5 up to 80 K was measured in lengthwise direction using the thermopotentiometric method in the bath cryostat. In the same experimental arrangement the measurement of thermal conductivity of the substrate and of the tape with the deposited layer of Nb₃Ge was performed. Specific thermal conductivity of the Nb₃Ge layer was calculated on the basis of measured values.     

Temperature measurement of a single ion in a Penning trap

The present work is concerned with the association of a temperature to a single ion stored in a Penning ion trap. Several methods are described which allow to determine the temperature by measurements of the ions cyclotron and axial trapping frequencies. Recent results of a measurement on a hydrogen-like carbon ion ¹²C^{5 +} by use of mode coupling are presented and possible further applications are discussed.Received: 8 July 2004, Published online: 6 December 2004PACS: 07.20.-n. Thermal instruments and apparatus - 07.20.Dt. Thermometers - 42.50.Lc Quantum fluctuations - 42.50.Vk Mechanical effects of light on ions     

Infrared photography in liquid films by thermocapillary convection

A thermal imaging system using a liquid-liquid interface has been studied, which utilizes the extreme temperature sensitivity of surface tension (Marangoni Effect). Theoretical considerations for the design and the operating conditions of the device are given. The experimental results using a detection by polarization interferometer indicate that the limitations on such a device are primarily due to the finite film thickness of the upper solution (on the order of 50–80 m). This system was able to image 1°C with a limiting resolution of ten lines pair per millimeter.     

Numerical Simulations of Screened Coulomb Systems. A Comparison Between Hyperspherical and Periodic Boundary Conditions

Numerical simulations or Coulomb systems can be performed in various geometries, for instance in a cube with periodic boundary conditions ( ³) or on the surface of a hypersphere or on the surface of a hypersphere ( ³). We show how to extend these methods of simulations to the case of screened (Yukawa) potentials. We make a detailed comparison between the properties of Yukawa systems in these two geometries and derive the correct configurational energies of some models such as the Yukawa restricted primitive model and the Yukawa one component plasma.     

The possibility of using a semiconductor thermal probe to investigate the power flow distribution in waveguides

Conclusions

1. The temperature profile of an absorbing film for a given microwave power flux distribution has been considered.
2. The conditions under which agreement is found between the temperature relief and the flux distribution has been clarified.
3. An experimental investigation has been carried out of the temperature profile in a matched film for the TE₁₀ mode.
4. The possibility of using a semiconductor thermal probe to investigate the microwave power flux distribution has been demonstrated.

     

Lateral growth rates in laser CVD of microstructures

Lateral growth rates of Ni spots deposited on absorbing substrates by decomposition of Ni(CO)₄ with visible Kr⁺ laser light have been measured. The experimental data are consistent with the calculated temperature distributions. The mechanism of decomposition is thermal with an apparent chemical activation energy of 22±3 kcal/mole for the temperature range 350 KT500 K.     

Photon counting statistics of the superposition of coherent and chaotic light of arbitrary spectrum passed through the turbulent atmosphere or a Gaussian medium

We derive the approximate photon counting distribution and its factorial moments of arbitrary order for the superposition of coherent and chaotic light of arbitrary spectrum and for arbitrary counting time intervals passing through the turbulent atmosphere or a Gaussian scattering medium; the frequency of coherent light and the mean frequency of chaotic light need not coincide. It is shown by discussion of numerical results for various levels of turbulence and various values of the parameter, which is the halfwidth of the Lorentzian spectrum of chaotic light multiplied by the detection time, that peaks of the photon counting distributions are decreasing (the distributions are broadening) with increasing level of turbulence, they are shifted to lower number of counts and values of the normalized factorial moments are rapidly increasing; these values tend to a limit given by the level of turbulence for.Leninova 26, Olomouc, Czechoslovakia.The authors thank Dr. Z. Braunerová of the Computer Centre of the Palacký University for performing the numerical calculations.     

Analysis of ionic fragments from 308 nm photoablation of polyimide

The ionic products from excimer laser photoablation (=308 nm) of polyimide (Kapton) film have been studied as a function of fluence. Large ion masses up to about 900a.m.u. are easily observed, the mass distribution depending strongly on the fluence. Velocities of the emitted particles lie between 1400 and 10 000 ms^–1, again dependent on the fluence. A mechanism to explain the high velocities is suggested consisting of ionisation of the surface polymer molecules followed by a Coulomb explosion combined with expansion of the high density gas formed by the photoablation.     

Pyroelectric infrared detector for precision earth sensor

Two new types of infrared detectors have been developed for the precision earth sensor in the three axis stabilized satellite, Engineering Test Satellite VI (ETS-VI). Both detectors have a pair of infrared sensing elements, each of which is made of a pyroelectric material and mounted on an immersion lens. A-type element is a flake of lead titanate ceramic, and B-type is a sputtered epitaxial film of calcium-modified lead titanate.The precision earth sensor consists of a scanning mirror and an infrared telescope containing an objective lens, plus either type of infrared detector.Detectivity of each type at 120Hz, which is the nominal frequency of the earth sensor's signal, is 1.5×10⁹Hz^1/2/W(A-type) and 2.7×10⁹Hz^1/2/W(B-type) at 1416.25m. Each value is 2.5 and 4.5 times as high as the previous model in ETS-V.A-type detector passed the space environmental test and the random error cf attitude measurement was 0.03 deg with the preliminary model of the earth sensor being ahead of the breadboard model. This measurement accuracy is nearly equal to that of the foremost earth sensor. A-type was chosen as the detector for ETS-VI.The random error of the earth sensor with B-type detector is 0.012deg, smaller than a half of the A-type sensor's error. Investigation of B-type is being continued in order to confirm its reliability for space use.     

Current transport in Pd2Si/n-Si(100) Schottky barrier diodes at low temperatures

The forward current-voltage (I–V) characteristics of Pd₂Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height ( _b0) and an increase of the ideality factor () with decreasing temperature. Further, the changes in _b0 and become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and T ₀-effect fail to account for the temperature dependence of the barrier parameters. The 1n(I _s /T ²) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd₂Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 10⁴ A m^–2 K^–2 against the theoretical value of 1.12 × 10⁶ A m^–2 K^–2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.