Photopyroelectric response of PTCa/PEEK composite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Voltage responsivity of pyroelectric sensor

Composites polymer-ceramic using castor oil-based polyurethane (PU) as non-ferroelectric matrix and Lead Zirconate Titanate (PZT) as ceramic powder have been prepared at thin films form by spin coating. The samples are poled by appropriated electric field to show piezo and pyroelectric activity. The pyroelectric coefficient p(T) at 343 K is obtained to be equal 5.8 X 10(-5) C m(-2) K-1 for a composite with 32 vol.% of ceramic. The figure of merit of this composite is six times higher than of PZT ceramic. The voltage responsivity of the pyroelectric is reduced when the thickness of the sample increases. It was used modulated white light as radiation source to excite the sensor film. The electric signal of the sensor decreases with the light modulation frequency by 1/f. (C) 1999 Elsevier B.V. S.A. All rights reserved.

Nonresonant third-order nonlinearity of antimony glasses at telecom wavelengths

We report measurements of the nonresonant nonlinear refractive index n(2) in antimony glasses at telecom wavelengths. The measurements were performed using the Z-scan technique with a 130 fs pulsed laser operating at five wavelengths in the range of 1400-1600 nm. Values of n(2)approximate to 10(-15) cm(2)/W were measured and a negligible two-photon absorption coefficient (< 0.003 cm/GW) was estimated for all glasses compositions. The samples present a good figure of merit for ultrafast all-optical switching. (c) 2006 American Institute of Physics.

Near-infrared third-order nonlinearity of PbO-GeO(2) films containing Cu and Cu(2)O nanoparticles

We report measurements of the nonlinear (NL) refractive index n(2) of lead-germanium films (LGFs) containing Cu and Cu(2)O nanoparticles (NPs). The thermally managed eclipse Z-scan technique with 150 fs pulses from a laser operating at 800 nm was used. The NL refractive index measured, n(2)=6.3x10(-12) cm(2)/W has electronic origin and the NL absorption coefficient alpha(2) is smaller than 660 cm/GW. The figure of merit n(2)/lambda alpha(2) is enhanced by more than two orders of magnitude in comparison with the result for the LGFs without the copper based NPs. (C) 2008 American Institute of Physics.

Photoluminescence of core-shell nanoparticles made from yttrium stabilized zirconia powder grain coated with alumina

A YSZ@Al2O3 nanocomposite was obtained by Al 2O3 coating on the surface of yttrium stabilized zirconia via a polymeric precursor method. The resulting core-shell structures were characterized by X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and PL spectra. The TEM micrographs clearly show a homogeneous Al2O3 shell around the ZrO2 core. The observed PL is related to surface-interface defects. Such novel technologies can, in principle, explore materials which are not available in the bulk single crystal form but their figure-of-merit is dramatically dependent on the surface-interface defect states. © 2013 This journal isThe Royal Society of Chemistry.

Near-infrared nonlinearity of a multicomponent tellurium oxide glass at 800 and 1,064 nm

We report on the nonlinear (NL) optical properties of glassy TeO2-GeO2-K2O-Bi2O3 at lambda = 800 nm and lambda = 1,064 nm. Using the Kerr gate technique with a laser delivering 150 fs pulses at 800 nm, we demonstrated the fast NL response of the samples. The modulus of the NL refractive index, n (2), at 800 nm was similar to 10(-15) cm(2)/W. The Z-scan technique was used to determine n (2) a parts per thousand +10(-15) cm(2)/W, at 1,064 nm with pulses of 17 ps. The two-photon absorption coefficient, alpha (2), was smaller than the minimum that we can measure (< 0.003 cm/GW). The figure of merit n (2)/alpha (2) lambda was calculated and indicates that this glass composition has large potential to be used for all-optical switching.

Non-destructive thermal wave method applied to study thermal properties of fast setting time endodontic cement

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Presentation Remarks: Gamma Sigma Delta Award of Merit

I am really pleased to have this opportunity to present the 2008 Gamma Sigma Delta Award of Merit to Alan Baquet. Being here to say "Congratulations, Alan," is a special treat for me - and I do say, "Congratulations, Alan." You are very deserving of this honor.

Optimization of x-ray spectra in digital mammography through Monte Carlo simulations

In this work, a Monte Carlo code was used to investigate the performance of different x-ray spectra in digital mammography, through a figure of merit (FOM), defined as FOM = CNR2/(D) over bar (g), with CNR being the contrast-to-noise ratio in image and (D) over bar (g) being the average glandular dose. The FOM was studied for breasts with different thicknesses t (2 cm <= t <= 8 cm) and glandular contents (25%, 50% and 75% glandularity). The anode/filter combinations evaluated were those traditionally employed in mammography (Mo/Mo, Mo/Rh, Rh/Rh), and a W anode combined with Al or K-edge filters (Zr, Mo, Rh, Pd, Ag, Cd, Sn), for tube potentials between 22 and 34 kVp. Results show that the W anode combined with K-edge filters provides higher values of FOM for all breast thicknesses investigated. Nevertheless, the most suitable filter and tube potential depend on the breast thickness, and for t >= 6 cm, they also depend on breast glandularity. Particularly for thick and dense breasts, a W anode combined with K-edge filters can greatly improve the digital technique, with the values of FOM up to 200% greater than that obtained with the anode/filter combinations and tube potentials traditionally employed in mammography. For breasts with t < 4 cm, a general good performance was obtained with the W anode combined with 60 mu m of the Mo filter at 24-25 kVp, while 60 mu m of the Pd filter provided a general good performance at 24-26 kVp for t = 4 cm, and at 28-30 and 29-31 kVp for t = 6 and 8 cm, respectively.

Development of a slow-wave MEMS phase shifter on CMOS technology for millimeter wave frequencies

We propose a slow-wave MEMS phase shifter that can be fabricated using the CMOS back-end and an additional maskless post-process etch. The tunable phase shifter concept is formed by a conventional slow-wave transmission line. The metallic ribbons that form the patterned floating shield of this type of structure are released to allow motion when a control voltage is applied, which changes the characteristic impedance and the phase velocity. For this device a quality factor greater than 40 can be maintained, resulting in a figure of merit on the order of 0.7 dB/360 degrees and a total area smaller than 0.14 mm(2) for a 60-GHz working frequency. (C) 2011 Elsevier B.V. All rights reserved.

Photoluminescence of core-shell nanoparticles made from yttrium stabilized zirconia powder grain coated with alumina

A YSZ@Al2O3 nanocomposite was obtained by Al2O3 coating on the surface of yttrium stabilized zirconia via a polymeric precursor method. The resulting core–shell structures were characterized by X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and PL spectra. The TEM micrographs clearly show a homogeneous Al2O3 shell around the ZrO2 core. The observed PL is related to surface–interface defects. Such novel technologies can, in principle, explore materials which are not available in the bulk single crystal form but their figure-of-merit is dramatically dependent on the surface–interface defect states.

Electronic structure and physical properties of Heusler compounds for thermoelectric and spintronic applications

This thesis focuses on synthesis as well as investigations of the electronic structure and properties of Heusler compounds for spintronic and thermoelectric applications.rnThe first part reports on the electronic and crystal structure as well as the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co2MnGe. The crystalline structure was examined in detail by extended X-ray absorption fine structure spectroscopy and anomalous X-ray diffraction. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab-initio calculations. Transport measurements and hard X-ray photoelectron spectroscopy (HAXPES) were performed to explain the electronic structure of the compound.rnA major part of the thesis deals with a systematical investigation of Heusler compounds for thermoelectric applications. Few studies have been reported on thermoelectric properties of p-type Heusler compounds. Therefore, this thesis focuses on the search for new p-type Heusler compounds with high thermoelectric efficiency. The substitutional series NiTi1−xMxSn and CoTi1−xMxSb (where M = Sc, V and 0 ≤ x ≤ 0.2) were synthesized and investigated theoretically and experimentally with respect to electronic structure and transport properties. The results show the possibility to create n-type and p-type thermoelectrics within one Heusler compound. The pure compounds showed n-type behavior, while under Sc substitution the system switched to p-type behavior. A maximum Seebeck coefficient of +230 μV/K (at 350 K) was obtained for NiTi0.26Sc0.04Zr0.35Hf0.35Sn, which is one of the highest values for p-type thermoelectric compounds based on Heusler alloys up to now. HAXPES valence band measurement show massive in gap states for the parent compounds NiTiSn, CoTiSb and NiTi0.3Zr0.35Hf0.35Sn. This proves that the electronic states close to the Fermi energy play a key role for the behavior of the transport properties. Furthermore, the electronic structure of the gapless Heusler compounds PtYSb, PtLaBi and PtLuSb were investigated by bulk sensitive HAXPES. The linear behavior of the spectra close to εF proves the bulk origin of Dirac-cone type density of states. Furthermore, a systematic study on the optical and transport properties of PtYSb is presented. The compound exhibits promising thermoelectric properties with a high figure of merit (ZT = 0.2) and a Hall mobility μh of 300 cm2/Vs at 350 K.rnThe last part of this thesis describes the linear dichroism in angular-resolved photoemission from the valence band of NiTi0.9Sc0.1Sn and NiMnSb. High resolution photoelectron spectroscopy was performed with an excitation energy of hν = 7.938 keV. The linear polarization of the photons was changed using an in-vacuum diamond phase retarder. Noticeable linear dichroism is found in the valence bands and this allows for a symmetry analysis of the contributing states. The differences in the spectra are found to be caused by symmetry dependent angular asymmetry parameters, and these occur even in polycrystalline samples without preferential crystallographic orientation.rnIn summary, Heusler compounds with 1:1:1 and 2:1:1 stoichiometry were synthesized and examined by chemical and physical methods. Overall, this thesis shows that the combination of first-principle calculations, transport measurements and high resolution high energy photoelectron spectroscopy analysis is a very powerful tool for the design and development of new materials for a wide range of applications from spintronic applications to thermoelectric applications.rn

Thermoelectric properties of TiNiSn and Zr 0.5 Hf 0.5 NiSn thin films and superlattices with reduced thermal conductivities

Durch steigende Energiekosten und erhöhte CO2 Emission ist die Forschung an thermoelektrischen (TE) Materialien in den Fokus gerückt. Die Eignung eines Materials für die Verwendung in einem TE Modul ist verknüpft mit der Gütezahl ZT und entspricht α2σTκ-1 (Seebeck Koeffizient α, Leitfähigkeit σ, Temperatur T und thermische Leitfähigkeit κ). Ohne den Leistungsfaktor α2σ zu verändern, soll ZT durch Senkung der thermischen Leitfähigkeit mittels Nanostrukturierung angehoben werden.rnBis heute sind die TE Eigenschaften von den makroskopischen halb-Heusler Materialen TiNiSn und Zr0.5Hf0.5NiSn ausgiebig erforscht worden. Mit Hilfe von dc Magnetron-Sputterdeposition wurden nun erstmals halbleitende TiNiSn und Zr0.5Hf0.5NiSn Schichten hergestellt. Auf MgO (100) Substraten sind stark texturierte polykristalline Schichten bei Substrattemperaturen von 450°C abgeschieden worden. Senkrecht zur Oberfläche haben sich Korngrößen von 55 nm feststellen lassen. Diese haben Halbwertsbreiten bei Rockingkurven von unter 1° aufgewiesen. Strukturanalysen sind mit Hilfe von Röntgenbeugungsexperimenten (XRD) durchgeführt worden. Durch Wachstumsraten von 1 nms 1 konnten in kürzester Zeit Filmdicken von mehr als einem µm hergestellt werden. TiNiSn zeigte den höchsten Leistungsfaktor von 0.4 mWK 2m 1 (550 K). Zusätzlich wurde bei Raumtemperatur mit Hilfe der differentiellen 3ω Methode eine thermische Leitfähigkeit von 2.8 Wm 1K 1 bestimmt. Es ist bekannt, dass die thermische Leitfähigkeit mit der Variation von Massen abnimmt. Weil zudem angenommen wird, dass sie durch Grenzflächenstreuung von Phononen ebenfalls reduziert wird, wurden Übergitter hergestellt. Dabei wurden TiNiSn und Zr0.5Hf0.5NiSn nacheinander abgeschieden. Die sehr hohe Kristallqualität der Übergitter mit ihren scharfen Grenzflächen konnte durch Satellitenpeaks und Transmissionsmikroskopie (STEM) nachgewiesen werden. Für ein Übergitter mit einer Periodizität von 21 nm (TiNiSn und Zr0.5Hf0.5NiSn jeweils 10.5 nm) ist bei einer Temperatur von 550 K ein Leistungsfaktor von 0.77 mWK 2m 1 nachgewiesen worden (α = 80 µVK 1; σ = 8.2 µΩm). Ein Übergitter mit der Periodizität von 8 nm hat senkrecht zu den Grenzflächen eine thermische Leitfähigkeit von 1 Wm 1K 1 aufgewiesen. Damit hat sich die Reduzierung der thermischen Leitfähigkeit durch die halb-Heusler Übergitter bestätigt. Durch die isoelektronischen Eigenschaften von Titan, Zirkonium und Hafnium wird angenommen, dass die elektrische Bandstruktur und damit der Leistungsfaktor senkrecht zu den Grenzflächen nur schwach beeinflusst wird.rn