A high-performance laser energy meter based on anisotropic Seebeck effect in a strongly correlated electronic thin film

We have developed a high-performance laser energy meter based on anisotropic Seebeck effect in a strongly correlated electronic (SCE) thin film. SCE thin films, typically represented by high-temperature superconductor (HTS) cuprate and colossal magnetoresistance (CMR) manganite thin films, demonstrate tremendous anisotropic Seebeck effect. In this study, a La_2/3Ca_1/3MnO₃ thin film grown on a tilted LaAlO₃ substrate is tested with the fundamental, the second, the third, and the fourth harmonics (1064, 532, 355, 266 nm, respectively) of a Q-switched Nd:YAG laser over a wide range of temperatures from room temperature to 16 K. The peak-value of the laser-induced thermoelectric voltage signal shows a good linear relationship with the laser energy per pulse in the measured wavelength and temperature ranges. The combined advantages over other commercial laser detectors such as nanosecond-order response and spectrally broad and flat response over a wide range of temperatures, in situ real-time measurement, and energy savings, make the device an ideal candidate for next-generation laser detectors and laser power/energy meters.     

Pb(Zr0.3Ti0.7)O3铁电薄膜激光感生电压效应

采用脉冲激光沉积(PLD)技术在LaSrAlTaO₃(LSATO),LaAlO₃(LAO)和SrTiO₃(STO)的单晶倾斜衬底上成功制备了Pb(Zr_0.3Ti_0.7)O₃(PZT)薄膜,在三种倾斜衬底上生长的PZT薄膜中都首次发现了LIV效应.对PZT/LSATO薄膜在a,c轴两种不同取向择优生长下的LIV效应做了研究,发现在薄膜c轴取向择优生长 关键词： 激光感生电压效应 铁电薄膜 薄膜生长取向 原子层热电堆     

Ag掺杂的La0.67Pb0.33MnO3薄膜中激光感生热电电压效应

采用脉冲激光沉积法在倾斜LaAlO₃衬底上制备了Ag掺杂的La_0.67Pb_0.33MnO₃(LPMO)系列薄膜，发现该类薄膜中有激光感生热电电压(LITV)效应.随着掺Ag量x(x为Ag的质量与LPMO的质量之比)从0.00增加到0.10，LPMO薄膜中的LITV信号的响应时间先递减后递增，但始终小于未掺Ag的薄膜，掺Ag量x=0.06时响应时间最小.研究发现LPMO薄膜存在一个最佳厚度，在这一厚度下可使得LITV信号 关键词： 3薄膜')" href="#">LaPbMnO₃薄膜 激光感生热电电压 各向异性Seebeck系数 响应时间     

A novel time-integral type laser energy meter based on anisotropic Seebeck effect

We have posed the design of a time-integral type laser energy meter based on anisotropic Seebeck effect for the first time. Anisotropic Seebeck effect is responsible for the laser-induced thermoelectric voltage effect in high temperature superconductor (HTSC) cuprates and colossal magnetoresistance (CMR) manganites thin films grown on tilted single crystal substrates. In this study, for an example, an epitaxial La_2/3Ca_1/3MnO₃ thin film prepared on a tilted LaAlO₃ substrate by standard pulsed-laser deposition (PLD) method is tested with a 1064-nm Q-switched Nd:YAG laser and its 2nd (532 nm), 3rd (355 nm), and 4th (266 nm) harmonics from room temperature to 16 K. The integral of the voltage signal with time shows a good linear relation with the laser energy per pulse in the measured wavelength and temperature range, which confirms the theoretical analysis given in this letter and can be used to design a time-integral type laser energy meter. The sensitivity increases as the film thickness increases or as the thermal diffusion constant decreases, which makes the time-integral type laser energy meter low cost as compared with the peak-voltage type. It operates with fast (nanosecond range) and broad-spectrum (from infrared to ultraviolet) response in wide temperature range (from room temperature to 10s K), and can be useful replacements for pyroelectric power/energy meters.     

The transverse laser induced thermoelectric voltages in step flow growth （1-x）Pb(Mg1/3Nb2/3)O3-xPbTiO3 thin films

This paper reports that the transverse laser induced thermoelectric voltages (LITV) are observed for the first time in the step flow growth (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT,x = 0.20, 0.33, 0.50) thin films deposited on vicinal-cut strontium titanate single crystal substrates. Because lead magnesium niobate-lead titanate is a solid solution of lead magnesium niobate (PMN) and lead titanate (PT), there are two types of signals. One is wide with a time response of a microsecond, and the other superimposed with the wide signal is narrow with a time response of a nanosecond. The transverse LITV signals depend on the ratio of PMN to PT drastically. Under the irradiation of 28-ns pulsed KrF excimer laser with the 248-nm wavelength,the largest induced voltage is observed in the 0.50Pb(Mg1/Nb2/3)O3-0.50PbTiO3 films. Moreover, the effects of film thickness, substrates, and tilt angles of substrates are also investigated.     

退火氧压对YBa2Cu3O7-x薄膜中的激光感生热电电压效应的影响

测量了在不同氧压下退火生长的YBa₂Cu₃O_7-x(YBCO)薄膜中的激光感生热电电压(LITV)信号,发现随退火氧压的增大可使LITV信号的峰值有2—4倍的增强,并且变化趋势与薄膜热电势的各向异性随氧含量的变化规律相同.波长在473—808nm范围内的连续激光辐照,在5000Pa的氧压下退火生长的YBCO薄膜中探测到的LITV信号最大;而紫外脉冲激光辐照时,LITV信号的最大值出现在退火氧压为10⁵Pa 关键词： 2Cu₃O_7-x薄膜')" href="#">YBa₂Cu₃O_7-x薄膜 激光感生热电电压 各向异性的Seebeck系数 氧含量     

LaCaMnO3 thin film laser energy/power meter

A prototype laser energy/power meter was designed based on the anisotropic Seebeck effect of LaCaMnO₃ thin film grown on vicinal cut LaAlO₃ substrate. The optical response of this device to the pulsed laser and the chopped CW laser was measured from infrared to ultraviolet. The peak voltage of the measured signal shows a good linear relation to the laser energy and power in the measured range. It was shown that at 1064 nm wavelength, this prototype device demonstrates higher sensitivity than that of commercial device.     

Effect of Ca doping level on the laser-induced voltages in tilted La1−x Ca x MnO3 (0.1 ≤ x ≤ 0.7) thin films

Tilted La_1?x Ca _x MnO₃ (0.1 ≤ x ≤ 0.7) thin films have been grown on vicinal cut LaAlO₃ (100) substrate by pulsed laser deposition. The laser-induced voltage effect was studied at room temperature with the KrF excimer laser using as the thermal source. The relationships between Ca doping level and voltage signal, response time and anisotropy Seebeck coefficient were established. The voltage signal and anisotropy Seebeck coefficient increase at first with increasing Ca doping level, reach a maximum at the same Ca content around x = 0.5, and then decrease. The respond time decreases with the Ca concentration increasing, and changes very little after x = 0.5. The figure of merit F _m was also the largest at this doping level, indicating a potential good performance of the photodetector devices. The variation of intrinsic structural and transport anisotropy induced by the change of Ca concentration has been proposed to account for the different LIV effects observed in LCMO thin films.     

Laser-induced voltage (LIV) enhancement of La2/3Sr1/3MnO3 films with Ag addition

La_2/3Sr_1/3MnO₃:Ag _x (LSMO:Ag _x , x=0, 0.04, 0.08, 0.10, 0.20, 0.30) films were grown on vicinal cut LaAlO₃ (LAO) substrates by pulsed laser deposition technique (PLD). It is found that laser-induced voltage (LIV) of LSMO:Ag _x films is improved and enhanced by Ag addition. With x increasing, figure of merit (F _m ) and anisotropic Seebeck coefficient (ΔS) of LSMO:Ag _x (x=0.08) films reach the maximum values of 28.25 mV/ns and 0.38 μV/K, respectively. The results suggest that the LIV enhancement of LSMO:Ag _x films is due to the anisotropy of the Seebeck tensor, which is produced by long range cooperative Jahn–Teller distortions with Ag addition.     

Influence of pulse laser energy on laser-induced voltage in La2/3Ca1/3MnO3:Ag0.04 films

With various pulse laser energy (E _pulse), La_2/3Ca_1/3MnO₃:Ag _x [La_1?x Ca _x MnO₃ (LCMO):Ag _x , x = 0.04, wt%] films were prepared on vicinal cut LaAlO₃ substrates by the pulsed laser deposition technique. It is found that laser-induced voltage (LIV) of LCMO:Ag_0.04 films was improved and enhanced by E _pulse. With E _pulse increasing, figure of merit (F _m) and anisotropic Seebeck coefficient (ΔS) of LCMO:Ag_0.04 films reached the maximum value of 109.8 mV/ns and 0.29 μV/K for E _pulse = 300 mJ. The results suggested that the LIV enhancement of LCMO:Ag_0.04 films was due to Seebeck tensor improvement, the high crystallization and oxygen balance in LCMO:Ag_0.04 films.     

Interaction of ultra-short laser pulses with CIGS and CZTSe thin films

The thin-film solar cell technologies based on complex quaternary chalcopyrite and kesterite materials are becoming more attractive due to their potential for low production costs and optimal spectral performance. As in all thin-film technologies, high efficiency of small cells might be maintained with the transition to larger areas when small segments are interconnected in series to reduce photocurrent and related ohmic losses in thin films. Interconnect formation is based on the three scribing steps, and the use of a laser is here crucial for performance of the device. We present our simulation and experimental results on the ablation process investigations in complex CuIn_1?x Ga _x Se₂ (CIGS) and Cu₂ZnSn(S,Se)₄ (CZTSe) cell’s films using ultra-short pulsed infrared (~1 μm) lasers which can be applied to the damage-free front-side scribing processes. Two types of processes were investigated—direct laser ablation of ZnO:Al/CIGS films with a variable pulse duration of a femtosecond laser and the laser-induced material removal with a picosecond laser in the ZnO:Al/CZTSe structure. It has been found that the pulse energy and the number of laser pulses have a significantly stronger effect on the ablation quality in ZnO:Al/CIGS thin films rather than the laser pulse duration. For the thin-film scribing applications, it is very important to carefully select the processing parameters and use of ultra-short femtosecond pulses does not have a significant advantage compared to picosecond laser pulses. Investigations with the ZnO:Al/CZTSe thin films showed that process of the absorber layer removal was triggered by a micro-explosive effect induced by high pressure of sublimated material due to a rapid temperature increase at the molybdenum-CZTSe interface.     

Transverse laser induced thermoelectric voltage effect in tilted La0.5Sr0.5CoO3 thin films

The transverse laser induced thermoelectric voltage effect has been investigated in tilted La_0.5Sr_0.5CoO₃ thin films grown on vicinal cut LaAlO₃ (1 0 0) substrates when films are irradiated by pulse laser at room temperature. The detected voltage signals are demonstrated to originate from the transverse Seebeck effect as the linear dependence of voltage on tilted angle in the range of small tilted angle. The Seebeck coefficient anisotropy ΔS of 0.03 μV/K at room temperature is calculated and its distorted cubic structure is thought to be responsible for this. Films grown on a series of substrates with different tilted angles show the optimum angle of 19.8° for the maximum voltage. Film thickness dependence of voltage has also been studied.     

Development of a high-throughput thermoelectric screening tool for combinatorial thin film libraries

We have developed a high-throughput thermoelectric screening tool for the study of combinatorial thin films. This tool consists of a probe to measure resistance and Seebeck coefficient on an automated translation stage. A thin film library of the (Ca_1−x−ySr_xLa_y)₃Co₄O₉ ternary system has been fabricated on a Si (1 0 0) substrate, using combinatorial pulsed laser deposition by the natural-composition-spread method. We have demonstrated successful mapping of the resistance and Seebeck coefficient of this film library. The mapping indicates that the substitution of La for Ca results in an increase of both resistance and Seebeck coefficient, and that of Sr results in a decrease of resistance. The screening tool allows us to measure 1080 data points in 6 h.     

Critical thickness and stress relaxation in YBaCuO (123) strained epitaxial layers and YBaCuO based strained superlattices

An energy model has been used to calculate the critical thickness h _c of YBaCuO thin films and YBaCuO based superlattices within an isotropic or anisotropic approximation. The critical thickness of single layers calculated from the anisotropic model (16 nm) is in good agreement with the previously published experimental values which are spread out from 4 to 20 nm. In the case of superlattices, relaxation appears to be governed by the critical thickness of the elementary sub-layers and is then better evaluated through the calculation performed for YBaCuO single layers. XRD measurements on YBa₂Cu₃O₇/PrBa₂Cu_3?xGa_xO₇ superlattices grown on {100{ SrTiO₃ have evidenced a tetragonal stress in the YBaCuO ab plane which remains expanded when the YBaCuO elementary layer thickness is lower than 4.8 nm (4 YBaCuO cells). However the critical temperature of the shortest period superlattices is only slightly affected by this expanded stress in contrast to the effect of an elastic stress externally applied along the ab plane of YBaCuO thin films.     

Effects of UV photon irradiation on SiOx (0 < x < 2) structural properties

Thin films of a-SiO_x (0 < x < 2) were prepared by reactive r.f. magnetron sputtering from a polycrystalline-silicon target in an Ar/O₂ gas mixture. The oxygen partial pressure in the deposition chamber was varied so as to obtain films with different values of x. The plasma was monitored, during depositions, by optical emission spectroscopy (OES) system. Energy dispersive X-ray (EDX) measurements and infra-red (IR) spectroscopy were used to study the compositional and structural properties of the deposited layers.Structural modifications of SiO_x thin films have been induced by UV photons’ bombardment (wavelength of 248 nm) using a pulsed laser. IR spectroscopy and X-ray photoemission spectroscopy (XPS) were used to investigate the structural changes as a function of x value and incident energy. SiO_x phase separation by spinodal decomposition was revealed. The IR peak position shifted towards high wavenumber values when the laser energy is increased. Values corresponding to the SiO₂ material (only Si⁴⁺) have been found for laser irradiated samples, independently on the original x value. The phase separation process has a threshold energy that is in agreement with theoretical values calculated for the dissociation energy of the investigated material.For high values of the laser energy, crystalline silicon embedded in oxygen-rich silicon oxide was revealed by Raman spectroscopy.     

［（SrTiO3）n/（SrTi0.8Nb0.2Ｏ3）m］20/LaAlO3超晶格的制备及其激光感生热电电压效应

采用脉冲激光沉积（PLD）镀膜技术在倾斜10°的LaAlO₃（100）单晶衬底上制备了（SrTiO₃）_n/（SrTi0.8Nb_0．2Ｏ₃）_m系列超晶格.在超晶格薄膜的XRD图谱中清楚地观察到周期调制的卫星峰结构.从卫星峰的分布计算了超周期,进而得到了在生长SrTiO₃和SrTi_0．8Nb_{0．2< 关键词： 3}）_n/（SrTi_0．8Nb_0．2Ｏ₃）_m］20/LAO（100）超晶格')" href="#">［（SrTiO₃）_n/（SrTi_0．8Nb_0．2Ｏ₃）_m］20/LAO（100）超晶格 激光感生热电电压 各项异性Seebeck系数 原子层热电堆     

Nd:YAG laser ablation characteristics of thin CIGS solar cell films

This work reports that the ablation characteristics of thin CuIn_1?x Ga _x Se₂ (CIGS) solar cell film differ significantly with elemental composition and laser pulse energy. From in situ shadowgraphs measured during Nd:YAG laser (1,064 nm) irradiation of CIGS films and crater morphologies, it was found that strong surface evaporation is dominant for low Ga concentration films of which band gap is well below the photon energy. As the band gap of CIGS film becomes close to or over the laser photon energy due to increased Ga content, surface absorption diminishes and at low laser energy, laser heating of the film plays an important role. It is demonstrated that for the CIGS films with Ga/(Ga + In) ratio being approximately over 0.2, the laser irradiation leads to solid phase removal of the film due to thermomechanical fracture at low laser energy but to ablative evaporation at elevated energy.     

Optical parameters of In–Se and In–Se–Te thin amorphous films prepared by pulsed laser deposition

The thin films of materials based on In–Se are under study for their applicability in photovoltaic devices, solid-state batteries and phase-change memories.The amorphous thin films of In₂Se_3−xTe_x (x=0–1.5) and InSe were prepared by pulsed laser deposition method (PLD) using a KrF excimer laser beam (λ=248 nm, 0.5 J cm⁻²) from polycrystalline bulk targets. The compositions of films verified by energy-dispersive X-ray analysis (EDX) were close to the compositions of targets. The surfaces of PLD films containing small amount of droplets were viewed by optical and scanning electron microscopy (SEM).The optical properties (transmittance and reflectance spectra, spectral dependence of index of refraction, optical gap, single-oscillator energy, dispersion energy, dielectric constant) of the films were determined.The values of index of refraction increased with increasing substitution of Te for Se in In₂Se₃ films, the values of the optical gap decreased with increasing substitution of Te for Se in In₂Se₃ films.     

Effect of substrate annealing on the quality of pulsed laser deposited Zn1−xMgxO thin films

The annealing effects of sapphire substrate before deposition on the quality of epitaxial Zn_1−xMg_xO thin films grown by pulsed laser deposition are reported. Our Experimental results indicate that the surface quality of Zn_1−xMg_xO thin films and hexagonal columnar growth is improved on the annealed sapphire substrate at high temperatures due to formation of atomic terraces on the substrate surface. The photoluminescence signals also increases with the increasing annealing temperature of the substrate.