arXiv subjects

Mingyu Xie

Publications and source records attributed to Mingyu Xie.

8 recordsLinked to original sources

arXiv2026

Wavelength-dependent photo-creep in halide perovskite single crystals

Halide perovskites are promising optoelectronic materials, but their time-dependent permanent deformation under illumination (i.e., photo-creep) is poorly understood, limiting their mechanical stability. Here we report wavelength-dependent photo-creep phenomena in CsPbBr3 and FAPbBr3 single crystals, studied by constant-load nanoindentation under controlled light with various wavelengths. Compared with creep in dark, continuous green light (near-bandgap) suppresses creep by 19% in CsPbBr3 and 10% in FAPbBr3, whereas violet (far above-bandgap) light enhances creep by 16% in CsPbBr3 and 8% in FAPbBr3. In contrast, when light is onset during creep, blue light enhances creep most prominently, whereas green light exhibits minimal influence. Such photo-creep behavior in halide perovskites are distinct with photo-plasticity phenomenon in conventional semiconductors. By combining the photoluminescence and photocurrent measurements, we unveil that ion migration promotes dislocation climb and creep, while carrier trapping suppresses dislocation glide and related creep in halide perovskites. Such competition between carrier trapping and ion migration tuned by wavelength governs the photo-creep response. Our findings uncover a photomechanical effect in halide perovskites and highlight how coupled carrier and ion dynamics under illumination affect their device reliability.

cond-mat.mtrl-sci↗

arXiv2025

Unveiling competitions between carrier recombination pathways in semiconductors via mechanical damping

The total rate of carrier recombination in semiconductors has conventionally been expressed using an additive model, r_total = \Sigma r_i , which rules out the interactions between carrier recombination pathways. Here we challenge this paradigm by demonstrating pathway competitions using our newly developed light-induced mechanical absorption spectroscopy (LIMAS), which allows us to probe genuine recombination dynamics in semiconductors via mechanical damping. We show that the total recombination rate in zinc sulfide (ZnS), a model semiconductor material, follows a multiplicative weighting model, r_total \propto \Pi r_i ^(w_i) with \Sigma w_i=1. Under both steady-state and switch-on illuminations, the weighting factors w_i for each recombination pathway-direct, trap-assisted, and sublinear-are dictated by the carrier generation mechanism: (i) interband transition favors direct recombination; (ii) single-defect level-mediated generation promotes trap-assisted recombination; (iii) generation involving multiple saturated defect levels gives rise to sublinear recombination. Upon light switch-off, localized state changes drive a dynamic evolution of w_i, altering pathway competitions. These findings reshape our fundamental understanding of carrier dynamics and provide a new strategy to optimize next-generation optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Radiation-induced Instability of Organic-Inorganic Halide Perovskite Single Crystals

Organic-inorganic halide perovskites (OIHPs) are promising optoelectronic materials, but their instability under radiation environments restricts their durability and practical applications. Here we employ electron and synchrotron X-ray beams, individually, to investigate the radiation-induced instability of two types of OIHP single crystals (FAPbBr3 and MAPbBr3). Under the electron beam, we observe that 3-point star-style cracks grow on the surface of FAPbBr3, and bricklayer-style cracks are formed on the surface of MAPbBr3. Under the X-ray beam, a new composition without organic components appears in both FAPbBr3 and MAPbBr3. Such cracking and composition changes are attributed to the volatilization of organic components. We propose a volume-strain-based mechanism, in which the energy conversion results from the organic cation loss. Using nanoindentation, we reveal that beam radiations reduce the Youngs modulus and increase the hardness of both OIHPs. This study provides valuable insights into the structural and mechanical stabilities of OIHP single crystals in radiation environments.

cond-mat.mtrl-sci↗

arXiv2024

Existence of solution to modified Gursky-Streets equation

We solve the modified Gursky-Streets equation, which is a fully nonlinear equation arising in conformal geometry with uniform $C^{1, 1}$ estimates when (i) $\gamma > 0$ and $1 \leq k \leq n$ or (ii) $r > 0$ and $2 s k \leq r n$. We also prove the existence of a Lipschitz continuous viscosity solution when $r \neq 0$.

math.AP↗

arXiv2024

StreetNav: Leveraging Street Cameras to Support Precise Outdoor Navigation for Blind Pedestrians

Blind and low-vision (BLV) people rely on GPS-based systems for outdoor navigation. GPS's inaccuracy, however, causes them to veer off track, run into obstacles, and struggle to reach precise destinations. While prior work has made precise navigation possible indoors via hardware installations, enabling this outdoors remains a challenge. Interestingly, many outdoor environments are already instrumented with hardware such as street cameras. In this work, we explore the idea of repurposing existing street cameras for outdoor navigation. Our community-driven approach considers both technical and sociotechnical concerns through engagements with various stakeholders: BLV users, residents, business owners, and Community Board leadership. The resulting system, StreetNav, processes a camera's video feed using computer vision and gives BLV pedestrians real-time navigation assistance. Our evaluations show that StreetNav guides users more precisely than GPS, but its technical performance is sensitive to environmental occlusions and distance from the camera. We discuss future implications for deploying such systems at scale.

cs.HC↗

arXiv2022

Elastic, piezoelectric coefficients, and internal frictions of a single alpha-quartz crystal determined by partial-electrode electromechanical impedance spectroscopy

In this work, all the independent elastic coefficients, piezoelectric coefficients, and internal frictions of a single alpha-quartz crystal are determined using our recently proposed partial-electrode electromechanical impedance spectroscopy (PE-EMIS) at 25 centigrade. In PE-EMIS, the rectangular parallelepiped quartz sample with two small partial electrodes fabricated on a corner is self-excited/sensed. The conductance spectrum (equivalent to the resonance spectrum) measured by an impedance analyzer under a true free boundary condition is noiseless, allowing the first 100 eigenmodes ranging from 50 to 310kHz to be accurately fitted. To avoid mode misidentification, the off-plane displacement distributions of the quartz sample under different eigenmodes are determined using a scanned-laser vibrometer. The resonance spectrum measured using a commercial sandwich-like RUS apparatus is also presented for comparison, and the results show that the clamping force in sandwich-like RUS shifts the sample's resonance frequencies, causing 13% and 75% overestimations for the piezoelectric coefficients e11 and e14, respectively. In comparison to the RUS, our proposed PE-EMIS is more effective and convenient, and will be widely used for characterization of piezoelectric crystals.

physics.app-ph↗

arXiv2021

Detecting fatigue in aluminum alloys based on internal friction measurement using an electromechanical impedance method

Detecting mechanical fatigue of metallic components is always a challenge in industries. In this work, we proposed to monitor the low-cycle fatigue of a 6061 aluminum alloy based on internal friction (IF) measurement, which is realized by a quantitative electromechanical impedance (Q-EMI) method using a small piezoelectric wafer bonded on the specimen. Large strain amplitude (3.3*10^-3) was employed thus the fatigue life can always be below 10^5 cycles. It was found that except for the initial testing stage, the IF always increases steadily with the increasing fatigue cycles. Before the fatigue failure, the IF can reach 2.5 to 3.4 times of the initial value, which is thought to be caused by the micro-cracks forming and growing. In comparison, the resonance frequency of the specimen just drops less than 2% compared with the initial value. Finally, a general fatigue criterion based on IF measurement is suggested for all the metallic materials.

physics.app-ph↗

arXiv2018

Quick and repeatable shear modulus measurement based on torsional resonance and torsional wave propagation using a piezoelectric torsional transducer

Shear modulus is one of the fundamental mechanical properties of materials, while its quick and accurate measurement is still a challenge. Here we proposed two methods for shear modulus measurement based on torsional resonance and torsional wave propagation using a same piezoelectric torsional transducer. Firstly, the torsional transducer was introduced which consists of two thickness poled, thickness shear (d15) piezoelectric half-rings. Secondly, the equivalent circuit of the transducer-cylindrical specimen system is derived and the shear modulus can be explicitly obtained using the torsional resonance frequency. The internal friction can also be obtained, which is calculated by using an approximate formula. Then, the principle of shear modulus and internal friction measurement based on torsional wave propagation were presented. Finally, shear modulus and internal friction measurement on four materials including 1045 steel, aluminum, quartz glass and PMMA, were conducted. Results indicate that the measured shear moduli using these two methods are very close to each other, and consistent with the reference values in literatures. The resonance method is quite convenient and highly repeatable, but is typically not suitable for long specimens where the first torsional resonance may not be visible. The wave propagation method is especially suitable for long specimens and high frequency measurement is suggested. The internal frictions measured by these two methods were also close to each other, and the simple wave attenuation method is suggested. The two shear modulus measurement methods proposed in this work are quite reliable and can be widely used in near future.

physics.app-ph↗