Pyroelectric Research Articles

Mechanism of energy conversion of ferroelectric in pyroelectric cycle

<p indent="0mm">“Waste heat” in the environment can be converted into electric energy by the Seebeck effect of semiconductor and pyroelectric effect of ferroelectrics ascribed to induction effect of polarization by electric field applied, energy conversion originates from the difference of polarization hysteresis electric field (<italic>P-E</italic>) loops between two different temperatures. Two isothermal processes and two iso-electric field processes form a pyroelectric cycle. By absorbing and releasing heat between two thermal reservoirs, a ferroelectric change its polarization successively so as to convert heat into electricity in a thermal-electric cycle, similar to the Carnot cycle. Output electric energy is the area enclosed by the cycle. For a constant high temperature environment, how to design a ferroelectric with proper Curie temperature and how to set cycling condition to match the temperatures to enlarge the area of a cycle are the two crucial problems. Experiment researches on pyroelectric energy conversion have been performed since the 1960s. The theoretic research was limited on simple expressions due to the difficulty on solving <italic>P-E</italic> loop. The <italic>P-E</italic> loop of ferroelectrics stems from rotation of dipoles and polarization hysteresis. In three-dimensional ferroelectrics, Gibbs free energies in the orientation directions of dipoles change with applied electric field differently, which causes changes in probabilities of dipole in different directions, i.e., rotation effect of dipoles. By introducing a coupling factor in the parallel dipoles the hysteresis effect was solved. The above solutions are extended to pyroelectric cycle to solve the problems referring to two isothermal processes and two iso-electric field processes with different initial condition. By combining the rotation effect and coupling effect that the coupling strength between dipoles is proportional to the rotated dipoles in the field direction during the field increasing process and persists to the same value in the field withdrawing process, mechanisms of polarization hysteresis are derived as several formulae. By editing a software program, numerical simulation method is used by setting values to the parameters to obtain evolution of polarization in the four processes of a cycle. Simulated result provides path of a cycle, depending on the maximal electric field (<italic>E</italic>_max). For a <italic>P-E</italic> loop in the first quadrant, there is a middle-curve rises from zero point to the top point of the loop, and an up-curve reduces from the top point to the remnant polarization at the zero field. In a cycle for a large enough <italic>E</italic>_max, the iso-low temperature process passes along the up-curve in the opposite direction, while for a smaller <italic>E</italic>_max, the process starts between the middle-curve and the up-curve and then transforms to the up-curve with the increase in the field because of impact of the small remnant polarization produced by <italic>E</italic>_max. The efficiency of pyroelectric cycling depends on cycling temperatures relative to Curie temperature and magnitude of the fields. High temperature is set above or below Curie temperature, and low temperature is set much below Curie temperature. Results show that when the low temperature is closer to Curie temperature, and high temperature is slightly higher than Curie temperature, pyroelectric energy conversion efficiency is higher and stable. When the high and low temperatures are close to the Curie temperature, the maximum pyroelectric conversion efficiency is obtained, but it decreases with the increase of the high temperature rapidly. A scaled efficiency, the efficiency relative to the Carnot cycle, decreases with the increase of temperature.

Miniature quartz tuning fork-based broad spectral coverage and high detectivity infrared spectroscopy

This paper reports a type of detector based on the thermoelastic effect of a miniature quartz tuning fork (mQTF) for infrared spectroscopy applications. Instead of using a pyroelectric infrared detector, a mQTF with a resonant frequency of ∼45 kHz was adopted as a detector for infrared light signal collection. To explore the capabilities of this technique, measurement of infrared absorption spectra of samples was conducted, and the effect of scattered light on the sensitivity was investigated. The experimental results indicate that the mQTF detector is sensitive to infrared radiation within a wide range of wavelengths, and packaging the mQTF could increase the sensitivity and signal-to-noise ratio (SNR) by 2.54, and 2.87 times, respectively. The infrared transmission spectrum of polystyrene (PS), polyethylene (PE) have been measured by the mQTF detector, and the experimental data show that the infrared characteristic absorption peaks appears in the same position as commercial pyroelectric detector. Finally, mid-infrared spectroscopy of acetone gas was measured by the mQTF with highprecision. It is worth noting that this is the first study of using the mQTF-based photodetector for gas phase infrared spectroscopy, the mQTF exhibits its cost-effectiveness, sensitivity, and broadband optical response advantages, could be used for qualitative analysis of components by the infrared spectrum.

Voltage Response of a Pyroelectric Detector to a Single Rectangular Optical Radiation Pulse.

In this paper, a mathematical description of the voltage response of a pyroelectric detector to a single rectangular pulse of optical radiation is presented. Mathematical procedures leading to the derivation of the dependencies describing the detector response for the cases, taking into account the duration of the radiation pulse absorbed by the detector and the relations between values of the electrical and thermal time constants of the detector, are shown in detail. The analytical results are compared and verified by experimental studies carried out using a commercially available pyroelectric detector (model PE10-S-Q) manufactured by the company Ophir. Comparison of the experimentally obtained data with analytical calculations showed good agreement.

Miniaturized CO2 Gas Sensor Using 20% ScAlN-Based Pyroelectric Detector.

NDIR CO2 gas sensors using a 10-cm-long gas channel and CMOS-compatible 12% doped ScAlN pyroelectric detector have previously demonstrated detection limits down to 25 ppm and fast response time of ∼2 s. Here, we increase the doping concentration of Sc to 20% in our ScAlN-based pyroelectric detector and miniaturize the gas channel by ∼65× volume with length reduction from 10 to 4 cm and diameter reduction from 5 to 1 mm. The CMOS-compatible 20% ScAlN-based pyroelectric detectors are fabricated over 8-in. wafers, allowing cost reduction leveraging on semiconductor manufacturing. Cross-sectional TEM images show the presence of abnormally oriented grains in the 20% ScAlN sensing layer in the pyroelectric detector stack. Optically, the absorption spectrum of the pyroelectric detector stack across the mid-infrared wavelength region shows ∼50% absorption at the CO2 absorption wavelength of 4.26 μm. The pyroelectric coefficient of these 20% ScAlN with abnormally oriented grains shows, in general, a higher value compared to that for 12% ScAlN. While keeping the temperature variation constant at 2 °C, we note that the pyroelectric coefficient seems to increase with background temperature. CO2 gas responses are measured for 20% ScAlN-based pyroelectric detectors in both 10-cm-long and 4-cm-long gas channels, respectively. The results show that for the miniaturized CO2 gas sensor, we are able to measure the gas response from 5000 ppm down to 100 ppm of CO2 gas concentration with CO2 gas response time of ∼5 s, sufficient for practical applications as the average outdoor CO2 level is ∼400 ppm. The selectivity of this miniaturized CO2 gas sensor is also tested by mixing CO2 with nitrogen and 49% sulfur hexafluoride, respectively. The results show high selectivity to CO2 with nitrogen and 49% sulfur hexafluoride each causing a minimum ∼0.39% and ∼0.36% signal voltage change, respectively. These results bring promise to compact and miniature low cost CO2 gas sensors based on pyroelectric detectors, which could possibly be integrated with consumer electronics for real-time air quality monitoring.

Fabrication of integrated polysilicon waveguides for mid-infrared absorption sensing

Abstract. The increasing popularity of environments equipped with sensors for convenience and with safety features, as in, for example, smart homes, greenhouses, or the interior of modern cars, demands a variety of sensor systems. In this respect, the sensing of ambient gases in the sense of air quality monitoring or leakage detection is one of the prominent applications. However, even though there are many different systems already available, the trend goes towards smaller and rather inconspicuous sensors which are embedded in the environment. We present the fabrication and characterization of integrated waveguides, which constitute an interesting platform for absorption spectroscopy in the mid-infrared (mid-IR) using the evanescent field of guided modes interacting with the analyte, thus leading to the absorption-induced attenuation of the mode. Corresponding simulations, characterizing the efficiency of the desired interaction, predict values for the confinement factor Γ and the intrinsic damping D for a waveguide geometry, which is then characterized by measurements. Furthermore, we discuss how these waveguides could be part of an integrated, non-dispersive, mid-IR sensor system fully integrated on a single chip. In this context, we present a way to maintain the quality of waveguides throughout the entire workflow needed to integrate a pyroelectric IR detector based on aluminum nitride (AlN).

Enhanced performance of self-powered ultraviolet photodetectors coupled with the photovoltaic-pyroelectric effect based on ZnO/CuBO2 core-shell nanorod arrays

An innovative self-powered ultraviolet photodetector based on ZnO/CuBO 2 core-shell nanorod arrays was fabricated using cost-efficient and scalable preparation technologies, including a chemical hydrothermal method and an impregnation technique. The ZnO/CuBO 2 core-shell heterostructure exhibits significant diode behavior with a rectification ratio approaching 7016 at± 1 V because of the type-II band alignment formed at the heterojunction interface, acquiring a maximum responsivity of 165 mA /W1 with an external quantum efficiency of 55.3% (370 nm, 65 mW cm −2 ) and specific detectivity (4.13 ×10 12 cm Hz 1/2 W −1 ) under zero bias. Simultaneously, by applying an external bias to adjust the photovoltaic and pyroelectric effects and delving into the operating mechanisms, the photodetector based on the ZnO/CuBO 2 heterostructure achieves enhanced performance. The decay time has been shortened, and the responsivity has reached up to 38.82 A W −1 (apparent quantum efficiency ~ 13,010%) at − 2.5 V. Moreover, the effects of the power density on the photocurrent response and temperature induced by the photovoltaic-pyroelectric effect are discussed. This study reveals the potential of CuBO 2 (one of the Cu-delafossite families) as a hole transport layer in optoelectronic devices, broadens the application prospects of core-shell nanorod arrays based on the photovoltaic-pyroelectric effect, and provides a direction for modulating the performance of such devices. • CuBO 2 , as a p-type layer of copper delafossite, was firstly used to covered ZnO nanorods forming a core-shell structure. • The facile, convenient and low-cost processes were demonstrated to fabricate original self-powered ZnO NRs/CuBO 2 core-shell heterojunctions. • The performance of the photodetector has been enhanced by modulating photovoltaic and pyroelectric effects. • The curves of output current I pyr+pho , proportion of I pyr and temperature varying with the incident light power densities were fitted with the power-law I&T = AP α . • Significant excellent performance, e.g., R=165 mA W −1 @0 V, 38.82 A W −1 @-2.5 V (370 nm, 65 mW cm −2 ), D* λ =4.13×10 12 cm Hz 1/2 W −1 , RR=7016 at±1 V, was achieved for self-powered ultraviolet photodetectors with ZnO NRs/CuBO 2 core-shell sturcture.

Doping Sr and Introducing Oxygen Vacancies in Ba0.7Sr0.3TiO3‐X Synergistically Promote the Pyro‐Photo‐Electric Catalysis Performance

AbstractThe low utilization of light and the severe recombination of charge carriers have always restricted the development of photoelectric catalysis. In this work, the photoelectric catalytic performance is tuned by doping Sr in BaTiO3 pyroelectric material and simultaneously introducing oxygen vacancies to form double‐type defects, combined with pyroelectric polarization. Under the light and 20–50 °C cold‐heat cycle, the current density of Ba0.7Sr0.3TiO3‐X reaches the maximum of 0.92 mA ⋅ cm−2, which is higher than the current density of Ba0.7Sr0.3TiO3‐X under only light (0.69 mA ⋅ cm−2). Under light alone, the current density of Ba0.7Sr0.3TiO3‐X is higher than that of BaTiO3 (0.19 mA ⋅ cm−2) and Ba0.7Sr0.3TiO3 (0.44 mA ⋅ cm−2). This is because the incorporation of Sr can introduce the Fermi level, improve the utilization rate of solar energy, and improve the pyroelectric polarization effect with volume shrinkage, and promote the separation and transfer of carriers. Oxygen vacancies can be used as reactive centers for excited electrons to suppress the recombination of excited electron‐hole pairs. Furthermore, the generation of photogenerated and pyrogenerated carriers increases the overall carrier concentration. This provides ideas for the modification of traditional photoelectrodes for photoelectric catalysis water splitting.

Pyroelectric metamaterial millimeter-wave detector

We present experimental demonstration of a multi-functional metamaterial absorber, which operates as an efficient detector of millimeter wave radiation at room temperature. Intimate integration of a pyroelectric crystal directly within the metamaterial unit cell enables an efficient large area sensing element made up of repeating unit cells that are nearly ten times smaller than the operational wavelength. An un-amplified intrinsic responsivity of 3.90 V/W is demonstrated at 91.5 GHz, which is close to the peak of the spectral absorption at 97.8 GHz. Numerical full-wave electromagnetic simulations match well to experiments and clarify the underlying absorption mechanism, while thermal simulations permit optimization of the responsivity. The demonstrated results show that the monolithic pyroelectric metamaterial geometry well functions as a detector and represents an ideal device platform for realization of novel and compact room temperature millimeter wave sensing and imaging components.

Design of Self‐Powered Sensors with Excellent Thermal and UV–Light Detections by 0.94(Bi0.5Na0.5)TiO3‐0.06Ba(Zr0.25Ti0.75)O3 Nanoparticles

AbstractFerroelectric materials provide a new pathway to convert thermal energy into electricity based on the pyroelectric effect. How to modulate the pyroelectric property of ferroelectric materials through UV–light is still an urgent problem that needs to be solved. Here, a self‐powered sensor is demonstrated based on 0.94(Bi0.5Na0.5)TiO3‐0.06Ba(Zr0.25Ti0.75)O3 nanoparticles, exhibiting high output electric performance under temperature variation and UV–light illumination conditions. Compared with a purely pyroelectric system, the corresponding current peaks of “UV–light + heating” and “UV–light + cooling” states are 88.6% higher and 37.3% smaller in the coupled system. The fabricated pyroelectric system shows excellent performance with detection sensitivities of 0.9 (heating) and 1.48 nA K−1 (cooling) with 0.7 × 10−3 and 0.2 × 10−3 nA lux−1 illuminated by 395 nm UV–light as a temperature sensor. Furthermore, a self‐powered sensor that is suitable for detecting both UV–light and temperature variations by recording the output current signals are demonstrated, which provides a basis for the development of the next generation of UV–light‐modulated ferroelectric devices.

Inducing photocarrier separation via 3D porous faveolate cross-linked carbon to enhance photothermal/pyroelectric property

The CdS/Bi2S3 supported three-dimensional (3D) porous faveolate carbon structure (CdS/Bi2S3@C) composite photocatalyst was constructed. Bi2S3 nanoparticles are regarded as photothermal agents and pyroelectric materials to absorb near infrared light (NIR) and convert it into heat. 3D porous faveolate of carbon acts as incubator to reduce heat loss and optimize photothermal effects. There is a greater fluctuating temperature difference (ΔΤ) between photothermal effect of Bi2S3 and cold photocatalytic system. This enhances the pyroelectric effect that Bi2S3 undergoes spontaneous polarization and releases the surface charge. Therefore, the separation of electrons and holes in the CdS photocatalyst can be induced. The COMSOL simulation results show that, the higher pyroelectric potential producted by larger ΔΤ is more favorable to the photocatalytic process. The hydrogen evolution rate of CdS/Bi2S3@C photocatalyst can reach 5.88 ​mmol·g−1·h−1 with excellent cycle stability.

Electrocaloric studies of bulk materials and multilayer structures by dynamic infrared radiometry

A new experimental approach to the complex study of electrocaloric, pyroelectric, and thermal effects associated with the bulk and local electrical conductivity of ferroelectrics and related materials is proposed. The key to this approach is the analysis of the dynamics of the sample temperature response to an arbitrary external action, including long-term electrical impacts. The metrological justification of the experimental technique is based on direct non-contact high-speed monitoring of the sample temperature using an IR photodiode sensor designed by Ioffe Institute. Its efficiency is confirmed by numerous experimental data on electrocaloric properties of ferroelectrics, relaxors, and relaxors-based multilayer structures.

Construction of NaNbO3/CdS nanorods composites with pyroelectric effect for enhanced pyrocatalytic and antibacterial activity under room-temperature cold-hot cycles

In the present study, NaNbO3-CdS nanorods composites with pyroelectric effect were used to degrade RhB solution and sterilize Salmonella under room-temperature cold-hot cycles. The pyrocatalytic decomposition rate of NaNbO3-CdS reached 90 % under 45 cold-hot (25–55 °C) cycles while the antibacterial rate of NaNbO3-CdS also achieved 90 % under 45 cold-hot (17–37 °C) cycles. Compared with the pyrocatalytic effect of single NaNbO3, with the hole’s radicals and superoxide radicals as the main active species, the pyrocatalytic effect of the NaNbO3-CdS was significantly enhanced. It is mainly attributed to its surface electrons being captured by CdS, thereby reducing the recombination probability of electron pairs. After four repeated experiments, the high pyrocatalytic activity still maintained, which indicated that the property of NaNbO3-CdS composites was stable. The composite nanocatalyst has potential in the degradation of dye pollution and sterilization by temperature difference.

High-performing UV photodetectors by thermal-coupling transparent photovoltaics

Understanding of light-driven electric power (photovoltaics) and thermally–induced electric (pyroelectric) effect is crucial for the next-generation of optoelectronics, emphasizing sustainability and portability with improved performance. Herein, we report the high-performing thermal-coupling transparent photovoltaics for ultrafast photodetection. Optically transparent photovoltaic device has p–n heterojunction, with n-ZnO and two different p-type metal oxides (Cu2O or NiO). The ZnO based photodetector is highly transparent with average visible transmittance of 51%. Importantly, significant enhancement of device sensitivity toward ultraviolet (UV) light (λ = 365 nm) is obtained via tuning the pyroelectric effect of ZnO. The pyro-current is originated from polarization charges due to thermal variation, thus the control of heat flow in ZnO is the origin to enhance pyro-current. The lower thermal conductivity of Cu2O (4.5 W m−1 K−1) is more effective rather than the case of NiO to shape the well-confined heat in ZnO thermal reservoir, resulting in the significantly enhanced pyro-current (176.3%). The transparent ZnO/Cu2O photodetector exhibits the extremely-high responsivity of 0.98 A W−1 and detectivity of 1.62 × 1013 Jones, with μs response speed at zero bias condition due to the photovoltaic operation. This will bring the self-support transparent electronics for versatile see-through platforms without bulky power system. One day people will get information quickly and wireless without loss of vision.

Application of Temperature Compensation Combined with Neural Network in Infrared Gas Sensor

Due to the state of the gas to be measured, the detection mechanism of the pyroelectric detector and the temperature drift of the peripheral circuit components and the detection of the ambient temperature will interfere with the measurement accuracy of the nondispersive infrared gas sensor from many aspects. This paper proposes a temperature compensation method based on the BP neural network. The compensation function of the gas sensor is realized by programming the various functional parameters in the neural network through the program provided in the Matlab neural network toolbox. Experimental simulation results show that the proposed method effectively reduces the influence of external temperature on the gas sensor output and improves its accuracy and stability.

Performance and mechanism of hydrogen evolution from room-temperature thermal catalytic water splitting by α-phase Si3N4

Because α-Si3N4 has a noncentrosymmetrical crystal pattern capable of self-polarizing point groups, it is theoretically pyroelectric. When the ambient temperature changes, the surface of a pyroelectric semiconductor will produce abundant compensationary charges q+ and q-, which theoretically can be used into hydrogen evolution from water splitting. In this study, the piezoelectric and pyroelectric performances of α- Si3N4were validated by piezoelectric force microscopy and potassium permanganate reduction experiments. Based on the pyroelectric performance of α- Si3N4 and with methanol as the sacrificial agent, hot–cold cycles were conducted from room temperature (27 °C) to 60 °C. Per gram of catalysts can produce 12.32 μmol/g hydrogen after 20 cycles, and the hydrogen yields after repeated experiments did not significantly decrease, proving that Si3N4 has high stability and that the pyroelectric effect is highly potential for hydrogen production from water splitting.

Chemical Nature of Heterogeneous Electrofreezing of Supercooled Water Revealed on Polar (Pyroelectric) Surfaces.

ConspectusThe ability to control the icing temperature of supercooled water (SCW) is of supreme importance in subfields of pure and applied sciences. The ice freezing of SCW can be influenced heterogeneously by electric effects, a process known as electrofreezing. This effect was first discovered during the 19th century; however, its mechanism is still under debate. In this Account we demonstrate, by capitalizing on the properties of polar crystals, that heterogeneous electrofreezing of SCW is a chemical process influenced by an electric field and specific ions. Polar crystals possess a net dipole moment. In addition, they are pyroelectric, displaying short-lived surface charges at their hemihedral faces at the two poles of the crystals as a result of temperature changes. Accordingly, during cooling or heating, an electric field is created, which is negated by the attraction of compensating charges from the environment. This process had an impact in the following experiments. The icing temperatures of SCW within crevices of polar crystals are higher in comparison to icing temperatures within crevices of nonpolar analogs. The role played by the electric effect was extricated from other effects by the performance of icing experiments on the surfaces of pyroelectric quasi-amorphous SrTiO3. During those studies it was found that on positively charged surfaces the icing temperature of SCW is elevated, whereas on negatively charged surfaces it is reduced. Following investigations discovered that the icing temperature of SCW is impacted by an ionic current created within a hydrated layer on top of hydrophilic faces residing parallel to the polar axes of the crystals. In the absence of such current on analogous hydrophobic surfaces, the pyroelectric effect does not influence the icing temperature of SCW. Those results implied that electrofreezing of SCW is a process influenced by specific compensating ions attracted by the pyroelectric field from the aqueous solution. When freezing experiments are performed in an open atmosphere, bicarbonate and hydronium ions, created by the dissolution of atmospheric CO2 in water, influence the icing temperature. The bicarbonate ions, when attracted by positively charged pyroelectric surfaces, elevate the icing temperature, whereas their counterparts, hydronium ions, when attracted by the negatively charged surfaces reduce the icing temperature. Molecular dynamic simulations suggested that bicarbonate ions, concentrated within the near positively charged interfacial layer, self-assemble with water molecules to create stabilized slightly distorted “ice-like” hexagonal assemblies which mimic the hexagons of the crystals of ice. This occurs by replacing, within those ice-like hexagons, two hydrogen bonds of water by C–O bonds of the HCO3– ion. On the basis of these simulations, it was predicted and experimentally confirmed that other trigonal planar ions such as NO3–, guanidinium+, and the quasi-hexagonal biguanidinium+ ion elevate the icing temperature. These ions were coined as “ice makers”. Other ions including hydronium, Cl–, and SO4–2 interfere with the formation of ice-like assemblies and operate as “ice breakers”. The higher icing temperatures induced within the crevices of the hydrophobic polar crystals in comparison to the nonpolar analogs can be attributed to the proton ordering of the water molecules. In contrast, the icing temperatures on related hydrophilic surfaces are influenced both by compensating charges and by proton ordering.

Nonmetallic surface plasmon resonance coupling with pyroelectric effect for enhanced near-infrared-driven CO2 reduction

Plasmonic semiconductors with both features of metals and semiconductors are expected materials for solar light harvesting. Here, plasmonic semiconductor heterostructures were constructed by coupling pyroelectric black phosphorus (BP) and plasmonic tungsten oxides (WO) as photocatalyst for CO2 reduction. Intriguingly, under visible and near-infrared (NIR) light irradiation, the plasmonic BP/WO heterostructures with optimal composition exhibit high-selective 26.1 μmol g-1h−1 CO generation (98 %), which is 7- and 17-fold higher than those of plasmonic WO and pyroelectric BP, respectively. The interface bonds (P-O-W) were detected by FTIR spectra and demonstrated by density functional theory (DFT) calculations as dominant channels for electron transfer from BP to WO. Plasmonic thermal effect of WO can increase the local temperature to 86 °C under visible and NIR light irradiation, triggering pyroelectric effect of BP and generating pyroelectric carriers, which enhance the electron transfer from BP to WO. Therefore, continuous electron injection from pyroelectric BP to WO enhances surface plasmon resonance for high-selective CO2 reduction. This work provides clear proofs to demonstrate that constructing pyroelectric effect on plasmonic heterostructures is one useful strategy to promote NIR-harvesting for artificial photosynthesis.

Peculiarities of the electrocaloric effect in relaxors

A comprehensive study and detailed analysis of pyroelectric and electrocaloric effects in relaxor ferroelectrics based on lead magnesium niobate as a promising object for such investigations have been carried out. It was found that even at the maximum values of pyroelectric coefficients the electrocaloric response inextricably linked with the pyroelectric effect does not exceed 1 °C in the temperature range from 10 to 60 °C under DC electric field up to 60 kV/cm. These conditions are the most demanded for the operation of electrocaloric cooling devices. Vision for the future as to increasing the efficiency of the main elements for such devices is discussed.

Femto Seconds Laser Based Efficient THz Generation from Different Temperature Annealed CdTe Thin Films and Effects of Carrier Concentration and Phase Transition on Efficiency of Generation

The paper reports the thermal evaporation based growth process of CdTe thin films on glass substrates. These films were annealed between room temperature to 200, 300 and 400 oC, respectively. The XRD characterization of these films revealed the change in crystalline phase from cubic to triclinic above 200 oC. Finally, these films were subjected to 800 nm wavelength of 35fs pulsed obtained from Ti: sapphire amplifier at 1kHz repetition rate. The incident power of the laser was focused and tuned between 150-350 mW range and generated THz signals were recorded using calibrated Pyroelectric detector at 22.5 Hz frequency. The highest power of the THz signal was 80nW for 200 oC annealed film with respect to incident power of 300mW. The highest efficiency of THz signal was of the order of 3.11E-5%. We have also explained the effect of carrier concentration and phase transition with respect to different annealed temperature for efficient generation of THz signal.

Measurement of stress distribution at the nanoscale: Towards stress nanotomography

We develop an experimental method for the in-situ stress measurement at the nanoscale. It provides a stress distribution in a contact zone between a probe and a pyroelectric crystal, based on the piezoelectric effect. We elaborate a theory of the method and demonstrate that the continuum theory of elasticity and piezoelectricity remains valid at the nanoscale. We show that the stress in the bulk of the contacting bodies may be also reconstructed, thus paving a way to 3D stress nanotomography.