Laser-induced Strain Research Articles

Laser-Induced Graphene Strain Sensors for Body Movement Monitoring.

To enable the development of artificial intelligence of things, the improvement of the strain sensing mechanisms and optimization of the interconnections are needed. Direct laser writing to obtain laser-induced graphene (LIG) is being studied as a promising technique for producing wearable, lightweight, highly sensitive, and reliable strain sensors. These devices show a higher degree of flexibility and stretchability when transferred to an elastomeric substrate. In this article, we manufactured polydimethylsiloxane (PDMS)-encapsulated LIG piezoresistive strain sensors with a quasi-linear behavior and a gauge factor of 111. The produced LIG was morphologically characterized via Raman spectroscopy and scanning electron microscopy before and after the electromechanical characterization and before and after the LIG transfer to PDMS. The results from these analyses revealed that the integrity of the material after the test was not affected and that the LIG volume in contact with the substrate increased after transfer and encapsulation in PDMS, leading to the improvement of the sensor performance. The sensors' capability for measuring bend angles accurately was demonstrated experimentally, making them useable in a wide range of applications for human body movement monitoring as well as for structural health monitoring. Regarding body monitoring, a PDMS-encapsulated LIG sensor for knee bending angle detection was proposed. This device showed unaffected performance of 1500 cycles under 8% uniaxial deformation and with response times in the range of 1-2 s.

Controlling effective field contributions to laser-induced magnetization precession by heterostructure design

Nanoscale heterostructure design can control laser-induced heat dissipation and strain propagation, as well as their efficiency for driving magnetization precession. Here, we incorporate MgO layers into the experimental platform of metallic Pt-Cu-Ni heterostructures to block the propagation of hot electrons. We show via ultrafast x-ray diffraction the capability of our platform to control the spatio-temporal shape of the transient heat and strain. Time-resolved magneto-optical Kerr experiments with systematic tuning of the magnetization precession frequency showcase control of the magnetization dynamics in the Ni layer. Our experimental analysis highlights the role of quasi-static strain as a driver of precession when the magnetic material is rapidly heated via electrons. The effective magnetic field change originating from demagnetization partially compensates the change induced by quasi-static strain. The strain pulses can be shaped via the nanoscale heterostructure design to efficiently drive the precession, paving the way for opto-magneto-acoustic devices with low heat energy deposited in the magnetic layer.

Laser-Induced Graphene Strain Sensor for Conformable Lip-Reading Recognition and Human–Machine Interaction

Laser-Induced Graphene Strain Sensor for Conformable Lip-Reading Recognition and Human–Machine Interaction

Optical-acoustic excitation of broadband terahertz antiferromagnetic spin waves

We propose an optical-acoustic means to excite broadband terahertz antiferromagnetic (AFM) spin wave in a metal/insulator/antiferromagnet heterostructure. The AFM spin wave is excited by an ultrafast strain wave triggered by a femtosecond pulsed laser based on photoacoustic conversion. This spin wave comprises an AFM exchange spin wave and a magnetoelastic spin wave. Their dispersion curves are overlapped in a wide frequency range by manipulating the Dzyaloshinskii–Moriya interaction, which is accompanied by lifting the degeneration of the spin-wave modes with opposite chirality. This optical-acoustic excitation of spin waves exploits the laser-induced ultrafast strain waves and avoids the thermal effect from the laser. It paves a way to develop novel AFM devices that can apply for ultrafast information processing and communication.

Ultrahigh strain rate-activated superplastic forming of aluminum and gold nanometals

Commonly, the increased free surface of nanometals results in completely different mechanical behaviors from their bulk counterparts. At present, studies on the plasticity behavior of nanometals is widely carried out under quasi-static states. Understanding the plasticity mechanism of nanometals during a high-speed forming process is largely unexplored. This study explored the rate dependence of the forming behaviors of Al and Au nanofilms using laser-induced ultrahigh strain rate forming processes. The results showed that the superplastic behavior of the nanofilms can be activated above a critical value of the strain rate (>2.0E8 s−1). The Al nanofilm exhibited a maximum vertical strain of ∼ 567% at a strain rate of 8.1E8 s−1, and that of the Au nanofilm was ∼ 620% at a strain rate of 8.8E8 s−1. The superplastic forming mechanism mediated by interstitials was revealed for the first time. Further, the potential contribution of the interstitial-mediated plasticity mechanism in breaking through grain size limit and constitutive model modification was discussed. The discovery of this particular mechanism supplements the deformation mechanism diagram and constitutive relationship of nanometals, and is thus of great significance to the study of material responses in extreme conditions and manufacturing process analysis and optimization.

Evolution of laser-induced strain in a Ge crystal for the [111] and [100] directions probed by time-resolved X-ray diffraction

Ultra-short laser-pulse-induced strain propagation in a Ge crystal is studied in the [111] and [100] directions using time-resolved X-ray diffraction (TXRD). The strain propagation velocity is derived by analysis of the TXRD signal from the strained crystal planes. Numerical integration of the Takagi–Taupin equations is performed using open source code, which provides a very simple approach to estimate the strain propagation velocity. The present method will be particularly useful for relatively broad spectral bandwidths and weak X-ray sources, where temporal oscillations in the diffracted X-ray intensity at the relevant phonon frequencies would not be visible. The two Bragg reflections of the Ge sample, viz. 111 and 400, give information on the propagation of strain for two different depths, as the X-ray extinction depths are different for these two reflections. The strain induced by femtosecond laser excitation has a propagation velocity comparable to the longitudinal acoustic velocity. The strain propagation velocity increases with increasing laser excitation fluence. This fluence dependence of the strain propagation velocity can be attributed to crystal heating by ambipolar carrier diffusion. Ge is a promising candidate for silicon-based optoelectronics, and this study will enhance the understanding of heat transport by carrier diffusion in Ge induced by ultra-fast laser pulses, which will assist in the design of optoelectronic devices.

Ultrafast laser-induced strain waves in thin ruthenium layers

We report on the time-dependent optical diffraction from ultra-high frequency laser-induced acoustic waves in thin layers of ruthenium deposited on glass substrates. We show that the thermo-optic and strain-optic effects dominate the optical response of Ru layers to a traveling longitudinal strain wave. In addition, we show the generation and detection of acoustic waves with a central frequency ranging from 130 GHz to 750 GHz on ultra-thin layers with thicknesses in the range of 1.2 - 20 nm. For these ultra-thin layers we measure a strong dependency of the speed of sound on the layer thickness and, thus, the frequency. This frequency-dependent speed of sound results in a frequency-dependent acoustic impedance mismatch between the ruthenium and the glass substrate, leading to a faster decay of the measured signals for increasing frequency. Furthermore, for these extremely high-frequency oscillations, we find that the frequency and phase remain constant for times longer than about 2 ps after optical excitation. Back extrapolation of the acquired acoustic signals to t = 0 gives a starting phase of -π/2. As this seems unlikely, we interpret this as an indication of possible dynamic changes in the phase/frequency of the acoustic wave in the first 2 ps after excitation.

Ultrafast control of lattice strain via magnetic circular dichroism

Using ultrafast x-ray diffraction, we directly monitor the lattice dynamics induced by femtosecond laser pulses in nanoscale thin films of bismuth iron garnet in external magnetic fields ${H}_{\mathrm{ext}}$. We control the ultrafast laser-induced lattice strain amplitude by changing the laser pulse helicity. The strength of ${H}_{\mathrm{ext}}$ is used as an external parameter to switch the helicity dependence on and off, respectively. Based on magneto-optical spectroscopic measurements, we explain these phenomena by magnetic circular dichroism. Our findings highlight an important approach for ultrafast manipulation of lattice strain in magnetic materials, in particular insulators, and open exciting perspectives towards ultrafast control of lattice strain and heat-induced magnetization switching and spin waves in bismuth substituted iron garnets using the polarization of light.

Controllable wrinkling patterns on liquid crystal polymer film/substrate systems by laser illumination

Smart soft materials, because of their mechanical flexibility and quick response to multi-physics stimuli, have drawn considerable attention over the past few years. Here, we present controllable wrinkling patterns of a liquid crystal polymer film attached on a soft substrate, controlled by laser illumination that holds unique optical characteristics of high coherence and irradiance. To analyze the mechanical response of liquid crystal polymer film/substrate systems under laser illumination, we develop a mathematical model by introducing laser-induced strain that has continuous Gaussian distribution, into the Föppl–von Kármán nonlinear plate theory. We explore effects of photo illumination areas and light-induced bending moments on pattern formation and selection, and discuss the inherent difference compared with uniform illumination. We find that the critical wrinkling strain is independent of laser decay distance, while pattern formation and pattern evolution are primarily determined by this parameter and the half width of laser irradiation. Novel wrinkling patterns, including horseshoe-shaped and spiral modes, are observed upon laser illumination. Furthermore, we provide phase diagrams on pattern selection and bifurcation diagrams on pattern evolution, which could quantitatively guide the effective design of multi-functional surfaces and precisely remote control of diverse surface morphology.

A study of laser-induced surface defects in silicon and impact on electrical properties

Laser processing of silicon solar cells has unique advantages that offer the potential for low-cost high-efficiency photovoltaic devices. The understanding, monitoring, and control of laser-induced defects in silicon become important challenges that limit photovoltaic efficiency. In this work, the fundamental investigation of laser-induced defects was achieved by identifying defect types and origins at different laser-fluence regimes, assessing defect concentrations, and evaluating their impact on surface electrical properties and photovoltaic device performance. Studies showed that below laser melting, little degradation of electrical properties is observed, but no defects are identified; between laser melting and ablation, point defects and oxygen incorporation mainly occur; above laser ablation, dislocations and strain are primarily generated. Laser-induced dislocation density and strain are found likely to increase exponentially with laser fluence, and laser-induced strain is identified to be a possible major source of dislocation generation. In order to understand carrier recombination and charge transport in laser-processed silicon surface, we quantified the drift mobility, conductivity, carrier lifetime, and leakage current at various laser fluences and dislocation levels. The laser-defect induced degradation of surface electrical properties is governed by a probable exponential relationship with laser fluence, suggesting that laser-processing fluences near silicon melting should be carefully chosen for minimizing induced defects and electrical property degradation. Finally, the control of laser-induced defects was demonstrated through laser or furnace post annealing of laser-processed solar cell devices. After two laser-annealing steps, the open circuit voltage, fill factor, series resistance, and shunt resistance were significantly improved, resulting in an increased photovoltaic efficiency.

Coherent Acoustic Phonon and Its Chirping in Dirac Semimetal Cd3As2**Supported by the National Key Research and Development Program of China under Grant Nos 2017YFA0303603, 2016YFA0300303, 2017YFA0302901 and 2016YFA0300604, the National Natural Science Foundation of China under Grant Nos 11774408, 11574383 and 11774399, the External Cooperation Program of Chinese Academy of Sciences under Grant No GJHZ1826, and the Interdisciplinary Innovation Team

Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal Cd3As2 is carried out. An acoustic phonon (AP) mode with central frequency f = 0.037 THz (i.e., 1.23 cm−1 or 0.153 meV) is unambiguously generated and detected, which we attribute to laser-induced thermal strain. An AP chirping (i.e., variation of the phonon frequency) is clearly detected, which is ascribed to heat capacity variation with time. By comparing our experimental results and the theoretical model, we obtain a chirping time constant, which is 31.2 ps at 6 K and 19.8 ps at 300 K, respectively. Significantly, we identify an asymmetry in the AP frequency domain peak and find that it is caused by the chirping, instead of a Fano resonance. Moreover, we experimentally demonstrate that the central frequency of AP is extremely stable with varying laser fluence, as well as temperature, which endows Cd3As2 application potentials in thermoelectric devices.

Formation of uniform high-density and small-size Ge/Si quantum dots by scanning pulsed laser annealing of pre-deposited Ge/Si film

The capability to fabricate Ge/Si quantum dots with small dot size and high dot density uniformly over a large area is crucial for many applications. In this work, we demonstrate that this can be achieved by scanning a pre-deposited Ge thin layer on Si substrate with a line-focused pulsed laser beam to induce formation of quantum dots. With suitable setting, Ge/Si quantum dots with a mean height of 2.9 nm, a mean diameter of 25 nm, and a dot density of 6×1010 cm−2 could be formed over an area larger than 4 mm2. The average size of the laser-induced quantum dots is smaller while their density is higher than that of quantum dots grown by using Stranski-Krastanov growth mode. Based on the dependence of the characteristics of quantum dots on the laser parameters, a model consisting of laser-induced strain, surface diffusion, and Ostwald ripening is proposed for the mechanism underlying the formation of the Ge/Si quantum dots. The technique demonstrated could be applicable to other materials besides Ge/Si.

Low-Temperature Diffusion at Ni/SiC Interface with the Aid of Femtosecond Laser-Induced Strain

Low-Temperature Diffusion at Ni/SiC Interface with the Aid of Femtosecond Laser-Induced Strain

17aAB-5 ナノ秒時間分解X線回折法を用いたシリコン単結晶における光誘起格子歪の測定

17aAB-5 ナノ秒時間分解X線回折法を用いたシリコン単結晶における光誘起格子歪の測定

Layer separation driven by laser-induced strain in semiconductor thin film

The scribing of the semiconductor layer in thin-film solar cells is here achieved by means of laser induced thermal gradient and mechanical strain. We experimentally demonstrate the scribing by separating one layer from a underlying layer without a substantial melting phase. The modeling of the process was used to predict the spatio-temporal distribution of the induced effects, the resulting scribed channel is confined and the process has a good repeatability. We envisage a parallelization of the process for simultaneous cell formation on the panel.

Laser-induced dynamic strain measurements in granular rocks and minerals

Laser-induced dynamic strain measurements in granular rocks and minerals

Visualizing laser-induced strain and fracture dynamics in crystals

Visualizing laser-induced strain and fracture dynamics in crystals

激光诱导2024铝合金表面动态应变检测

激光诱导2024铝合金表面动态应变检测

Picosecond dynamics of laser-induced strain in graphite

We report on the use of grazing-incidence time-resolved x-ray diffraction to investigate the evolution of strain in natural graphite excited by femtosecond-laser pulses in the fluence range of 6--35 mJ$/$cm${}^{2}$. Strains corresponding to up to \ensuremath{\sim}2.8% $c$-axis expansion were observed. We show that the experimental data is in good agreement with calculations based on the Thomsen strain model in conjunction with dynamical diffraction theory. Furthermore we find no evidence of nonthermal lattice expansion as reported in recent ultrafast electron-diffraction studies of laser-excited graphite conducted under comparable excitation conditions.

Laser-induced picosecond lattice oscillations in submicron gold crystals

We report direct observations of structural changes in submicron-sized gold crystals and gold films on a fused-quartz substrate using picosecond time-resolved x-ray diffraction. The femtosecond laser-induced expansion waves in 400 and 800 nm irradiation generated a lattice vibration inside the gold nanocrystals. This laser-induced strain wave repeatedly propagated and reflected to the finite-sized gold nanocrystals on the substrate. These longitudinal strain waves generated lattice vibrations in corresponding appropriately sized gold nanocrystals. In addition, each of the two laser-induced lattice oscillation modes in the polydispersed size distribution for 400 and 800 nm excitation was shown over a duration of a few hundred picoseconds.