Laser-induced Voltage Signals Research Articles

Epitaxial growth of c-axis inclined Sr3YCo4O10.5+ δ thin film: Insights into laser-induced voltage signals arising from magnetic anisotropy

We report the laser-induced voltage (LIV) signals in cubic phase Sr3YCo4O10.5+δ (CP-SYCO) thin films with a c-axis tilted and discuss the relationship between the LIV signals and magnetic anisotropy. CP-SYCO thin films were epitaxially deposited on 0°, 5°, 10°, 15°, and 20° miscut LaAlO3 (001) substrates using pulsed laser deposition (laser energy of 200 mJ, post-annealed at 760 °C). The peak voltage of the LIV for the 15° tilted CP-SYCO film is 310 mV (under laser energy of 400 mJ/pulse), with a rising edge of 26 ns. Compared with G-type antiferromagnetic ordered tetragonal phase Sr3YCo4O10.5+δ(OT-SYCO, deposited at a laser energy of 300 mJ, post-annealed at 790 °C) film, the CP-SYCO exhibits much stronger magnetization anisotropy along in-plane and out-plane due to the possible A-type antiferromagnetic moment arrangement. CP-SYCO films also demonstrate significant thermoelectric anisotropy, supporting the transverse thermoelectric effect, which is partially attributed to the contribution of spin entropy. This study provides an understanding of the anisotropic behavior in atomic layer thermoelectric stack materials and explores magnetic anisotropic material systems.

Ultrafast ultraviolet laser-induced voltage of air

In this work, the time-scale laser-induced voltage (LIV) of air was investigated under KrF excimer laser irradiation. The LIV response was fitted by a sum of three exponential functions, where the fitted parameters were influenced by the bias voltage Vb and the laser energy Ein. Higher Vb produced significant LIV. An exponential relationship was observed between the Ein and LIV signal amplitude (Vp). After decreasing the adjustable resistor, the LIV trace was almost triangular and symmetrical due to the impedance effect with the response time which was completely limited by the laser pulse duration. As a potential application, the LIV of air presented a viable method for single-pulse laser detection.

Optimizing Laser-Induced Voltage Signal in SnO2 Thin Films by Changing Oxygen Pressure

Laser-induced voltage (LIV) effect of the thin film can be applied for the laser energy measurement and millimeter-wave detection. The amplitude and corresponding velocity of LIV signals depended on the film material and preparation process. In the study, the effect of oxygen pressure on the LIV signals of SnO2 thin films was studied and got the surprised result that the maximum LIV peak reach about 4.02 V and response time with only 98 ns when oxygen pressure was 30 Pa. The crystal quality of the films was analyzed by X-ray diffraction (XRD) and LIV measurements, and a linear relationship between LIV peak voltage and laser energy was also disclosed. Those findings indicate that the laser energy/power meters designed with SnO2 thin film with optimized oxygen pressure would have the merits high precision, high sensitivity, and fast response.

Pulsed laser deposition preparation and laser-induced voltage signals of TiO2 thin films

TiO2 thin films were deposited on two different kinds of substrates (α-Al2O3 and LaAlO3) by pulsed laser deposition. The crystal structure and laser-induced voltage (LIV) signal in the films were analyzed through X-ray diffraction and LIV measurements respectively. It was established that the films on the α-Al2O3 substrate were found growing epitaxial to the [100] direction of the rutile structure and remained structure stabilization after intense laser operating, in contrast to the films produced on LaAlO3 were [001] oriented of the anatase phase and had weak structure stability. The magnitude of the LIV signals increases linearly with laser energy density developing in TiO2 thin films, and the films exhibited the best LIV performance of 1.37 V at 0.1 mJ/cm2 with a laser wavelength of 248 nm. The results demonstrate that the TiO2 film deposited on α-Al2O3 is a potential candidate for detecting laser radiations, especially in ultraviolet laser detection.

Characterization of wax appearance temperature of model oils using laser-induced voltage

As a component of crude oils, wax plays an important part in the flowability of waxy oils. The deposition of waxes poses a significant challenge in petroleum production. This paper proposes laser-induced voltage (LIV) to measure the wax appearance temperature (WAT). With a decreased temperature, the peak of the LIV signal (VP) decreases with a greater slope until the inflection point (TLIV) after that wax precipitates from the oil. After which, VP changes more slowly. Thus, the TLIV is confirmed as the WAT. Furthermore, the WAT was measured using conventional differential scanning calorimetry, and the results of the two methods are consistent. When a laser irradiates the oil sample, plasma is generated in the liquid due to cascade ionization and multiphoton absorption. The plasma moves based on the effects of an external electric field and generates the LIV. However, temperature changes influence variations in the LIV for waxy oils. In addition, when paraffin precipitates from the oil, it exits as sediment at the bottom of a cuvette, which can impede plasma movement. Therefore, there will be significant differences in the trends before and after WAT. This study demonstrates that LIV offers a way to measure WAT in waxy oils.

Characterizing the laser drilling process of oil shale using laser-induced voltage

In this study, the oil shale surface was irradiated using an ultraviolet (UV) laser. Since the UV photon energy exceeded the band-gap of the oil shale, the photoexcited carriers were generated and the inter-band transition was induced. Thus the laser-induced voltage (LIV) occurred under an application of bias voltage. The peak value of LIV signal strongly depended on the drilling time. The voltage waveforms were fitted well by the double-exponential function. The whole drilling process was divided into two distinct stages corresponding to surface spallation and rock puncture, respectively. The results indicated that LIV can be employed to characterize the laser drilling process of oil shale.

Target effects on electrical properties and laser induced voltages of La0.72Ca0.28MnO3 thin films prepared by pulsed laser deposition

La0.72Ca0.28MnO3 thin films were deposited on untilted and 15° tilted LaAlO3 (100) single crystalline substrates by pulsed laser deposition. The polycrystalline targets used in the deposition process were synthesized by sol–gel and coprecipitation methods, respectively. The structure, electrical transport properties and surface morphology of the targets and films were studied. It is found that, compared with coprecipitation method, the sol–gel target has more homogeneous components and larger density and grain size, thus the higher insulator–metal transition temperature and larger temperature coefficient of resistivity. The thin film prepared by sol–gel target has a uniform grain size and higher quality. The metal–insulator transition temperature is higher and the laser induced voltage signal is larger. Preparing the target by sol–gel method can largely improve the properties of corresponding thin films in pulsed laser deposition process.

Electrical transport properties and laser-induced voltage effect in La0.8Ca0.2MnO3 epitaxial thin films

La0.8Ca0.2MnO3 (LCMO) thin films about 200 nm thickness were grown on untilted and tilted (5°, 10° and 15°) LaAlO3 (100) single crystal substrates by pulsed laser deposition technique. Electrical properties of the epitaxial thin films were studied by conventional four-probe technique and the anisotropic thermoelectric properties of the films grown on the tilted substrates have been investigated by laser-induced voltage (LIV) measurements. X-ray diffraction analysis and atomic force microscopy results show that the prepared LCMO thin films have a single phase and high crystalline quality. The remarkably large temperature coefficient of resistance (TCR) values (above 11 %/K) are observed in the all films. TCR value reaches 18 %/K on the film grown on 10° tilted substrate. The intensity of LIV signals monotonously increases with the tilting angles, and the largest signal is 148 mV with the fast time response 229 ns for the film grown on 15° tilted substrate.

Effects of substrate-induced-strain on the electrical properties and laser induced voltages of tilted La0.67Ca0.33MnO3 thin films

La0.67Ca0.33MnO3 thin films have been prepared on vicinal cut LaAlO3, (LaAlO3)0.3-(SrAlTaO6)0.7, and SrTiO3 (001) substrates by pulsed laser deposition. The influence of the substrate on the electrical transport properties and laser induced voltage (LIV) effect of the films was investigated. The high insulator to metal transition temperature Tp (263.6 K) and large peak voltage of LIV signal (2.328 V) were observed in the film grown on LaAlO3 substrate. The compressive strain and large Seebeck coefficient anisotropy ΔS (3.62 μV/K) induced by LaAlO3 are thought to be responsible for this result.

Effects of crystallinity on laser-induced voltage effect from Zn0.9Co0.1O thin film

Co-doped ZnO epilayer films were grown by pulsed laser deposition (PLD) on vicinal cut silicon and sapphire substrates. Changes in deposition time were observed as a moderate effect on the quality of the films, and the influence of the thickness on thermoelectric signals from Zn0.9Co0.1O thin films were discussed. The effect of one of the main deposition parameters, the deposition time, on the crystallinity and electron mobility properties of the Zn0.9Co0.1O thin films grown on sapphire was investigated by means of X-ray diffraction (XRD) and laser-induced voltage (LIV) effect. It shown that the XRD rocking curve full-width half-maximun (FWHM) decreased as time increasing, and the LIV signals were observed along the tilting angle of the substrate orientation when the pulsed KrF excimer laser of 248 nm were irradiated on the films. When the films illuminated in pulse lasers, the highest signals occurred in the films with best crystalline quality, and the signals were higher in the films grown on sapphire than those on silicon substrates. It suggested that the electrical resistivity and electron mobility have close relations with not only the crystallinity but also with the interface of the thin films.

Laser-induced voltage effect in Pb(Zr0.3Ti0.7)O3 ferroelectric thin film

Pb(Zr0.3Ti0.7)O3(PZT)thin films have been grown by pulsed laser deposition (PLD) on LaSrAlTaO3 (LSATO),LaAlO3(LAO) and SrTiO3(STO) single crystal vicinal cut substrates. Laser-induced voltage(LIV) effect was also found in PZT thin films grown on the three vicinal cut substrates for the first time. LIV signals increased with the single-pulse laser energy following the linear relation in case of c-axis orientation of thin film; but this linear relation was not followed obviously in case of a-axis orientation of thin film. This result shows that the LIV effect in PZT thin film is the atomic layer thermopile effect, in the which anisotropy of Seebeck coefficient plays an important role. Through realizing impedance-matching of thin films and transmission line, LITV signal response time has been optimized, the time of rising edge dropped from 60 ns to 26 ns, the full width at half maximum dropped from 260 ns to 38 ns.

Thermoelectric signals from Si/SiGe superlattices

p-Si/Si0.5Ge0.5 superlattices (SLs) grown on a vicinal-cut p-type silicon single crystalline substrate by molecular beam epitaxy (MBE) were irradiated by a KrF excimer laser. Two types of transient laser induced voltage (LIV) signals were observed, among which the signals of 0.3 V in amplitude with time response ∼40 ns showed up along the tilted directions, while voltage signals of ∼10 mV with a time response of tens of microseconds presented along the untilted directions which were perpendicular to the tilted direction. The results demonstrate that the observed photoelectric signals of 0.3V amplitude are laser induced thermoelectric voltages (LITV) due to the tilting angle relation. The observed LIV signals implied that these SLs exhibited anisotropic Seebeck components. It was also found that the LIV signals increased with the p-type doping level in the Si layer, which was coincident with the expectation of the laser induced thermoelectric effect. According to the measured signals and the theoretical formula, one can calculate the physical parameters of the SLs. The calculated effective Seebeck anisotropy coefficients (Sab − Sc) for samples with 1018 cm−3 and 1020 cm−3 are approximately 11.2 µV K−1 and 18.2 µV K−1, respectively.

Laser induced voltage in CMR thin films and its device application

A laser induced voltage (LIV) effect was observed in La 1− x Ca x MnO 3 thin films deposited on tilted LaAlO 3 substrates. The dependence of the LIV signals on the irradiated laser intensity and different doping levels was measured and compared with that measured from thin films on SrTiO 3. Based on the new effect, we designed a novel room-temperature laser power meter. The optical response of this device to the pulsed and modulated continuous laser was measured from the infrared to ultraviolet band.