Electron Beam Excitation Research Articles

Effect of Eu Ions Concentration in Y2O3-Based Transparent Ceramics on the Electron Irradiation Induced Luminescence and Damage

Eu3+-doped Y2O3-based luminescent materials can be used as a scintillator for electron or high energy β-ray irradiation, which are essential for applications such as electron microscopy and nuclear batteries. Therefore, it is essential to understand their defect mechanisms and to develop materials with excellent properties. In this paper, Y2O3-based transparent ceramics with different Eu3+ doping concentrations were prepared by solid-state reactive vacuum sintering. This series of transparent ceramic samples exhibits strong red emission under electron beam excitation at the keV level. However, color change appears after the high-energy electron irradiation due to the capture of electrons by the traps in the Y2O3 lattice. Optical transmittance, laser-excited luminescence, X-ray photoelectron spectroscopy (XPS), and other analyses indicated that the traps, or the color change, mainly originate from the residual oxygen vacancies, which can be suppressed by high Eu doping. Seen from the cathodoluminescence (CL) spectra, higher doping concentrations of Eu3+ showed stronger resistance to electron irradiation damage, but also resulted in lower emissions due to concentration quenching. Therefore, 10% doping of Eu was selected in this work to keep the high emission intensity and strong radiation resistance both. This work helps to enhance the understanding of defect formation mechanisms in the Y2O3 matrix and will be of benefit for the modification of scintillation properties for functional materials systems.

Self-hybridisation between interband transitions and Mie modes in dielectric nanoparticles

Abstract We discuss the possibility of self-hybridisation in high-index dielectric nanoparticles, where Mie modes of electric or magnetic type can couple to the interband transitions of the material, leading to spectral anticrossings. Starting with an idealised system described by moderately high constant permittivity with a narrow Lorentzian, in which self-hybridisation is visible for both plane-wave and electron-beam excitation, we embark on a quest for realistic systems where this effect should be visible. We explore a variety of spherical particles made of traditional semiconductors such as Si, GaAs, and GaP. With the effect hardly discernible, we identify two major causes hindering observation of self-hybridisation: the very broad spectral fingerprints of interband transitions in most candidate materials, and the significant overlap between electric and magnetic Mie modes in nanospheres. We thus depart from the spherical shape, and show that interband–Mie hybridisation is indeed feasible in the example of GaAs cylinders, even with a simple plane-wave source. This so-far unreported kind of polariton has to be considered when interpreting experimental spectra of Mie-resonant nanoparticles and assigning modal characters to specific features. On the other hand, it has the potential to be useful for the characterisation of the optical properties of dielectric materials, through control of the hybridisation strength via nanoparticle size and shape, and for applications that exploit Mie resonances in metamaterials, highly-directional antennas, or photovoltaics.

Inactivation of pathogenic microorganisms in water by electron beam excitation multi-wavelength ultraviolet irradiation: Efficiency, influence factors and mechanism

Due to the limitations of traditional ultraviolet (UV) in microbial inactivation in water, it is necessary to explore a more suitable and efficient UV disinfection method. In this study, an electron beam excitation multi-wavelength ultraviolet (EBE-MW-UV) system was established and aims to analyze its differential microbial inactivation capabilities in comparison to single-wavelength UV-LEDs in waterborne applications. Furthermore, the inactivation mechanisms of this system on microorganisms were explored. The results showed that EBE-MW-UV had significantly higher inactivation effects on the Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Candida albicans in water compared to UV-LEDs (p＜0.05), and the inactivation effect of EBE-MW-UV on Escherichia coli and Pseudomonas aeruginosa at the same UV dose was 3.8 and 1.9 log higher than that of UV-LEDs, respectively, EBE-MW-UV exhibited better inactivation effects on Gram-negative bacteria. Further research found that, under the majority of irradiation doses, neither EBE-MW-UV nor UV-LEDs were significantly affected by the concentration of suspended solids (5 and 20 mg/L) or humic acids (2 and 5 mg/L) in the water. Mechanism analysis revealed that during the disinfection process of EBE-MW-UV, microbial DNA and proteins were initially damaged, which prevented the occurrence of dark repair and led to bacterial inactivation. In addition, UV irradiation led to the production of additional reactive oxygen species (ROS) inside the cells, increasing cell membrane permeability and exacerbating membrane damage. This was accompanied by a decrease in energy metabolism and depletion of ATP, ultimately resulting in microbial inactivation. Therefore, EBE-MW-UV demonstrated more effective disinfection than single-wavelength UV-LEDs, showing great potential. Our research gives new insights into the characteristics of multiple wavelength ultraviolet, and provides scientific basis for the selection of new light sources in the field of ultraviolet disinfection.

Cationic substitution engineering induced Multi-Color light emitting of bismuth in Tantalate used for WLED

Revealing and predicting the photoluminescence behavior of trivalent bismuth activated phosphors is very important for exploiting high-quality photoluminescent materials and modulating their luminescence properties, since it commonly performs multi-type electronic transitions. In this work, the chosen matrix of Gd3TaO7, which contains only one highly symmetrical cationic crystallographic site, is favorable for analyzing luminescence behavior of Bi3+ ions, and Bi3+-activated Gd3TaO7 can emit bright green light under the near-ultraviolet (NUV) light or low voltage electron beam excitation. The cationic substitution engineering of rare earths Ln (Ln = Lu, Y and La) replacing Gd3+ ions was carried out for further regulation of spectra, and multi-color light emitting was successfully realized. However, their unusual photoluminescence properties bring a novel comprehension for the photoluminescence behavior of Bi3+ ions in this system. For well rationalizing this phenomenon, the first-principles calculation was carried out for revealing their electronic structure, combined with their geometry optimization. The results indicate multi factors have contribution in modulating the luminescence behavior of Bi3+ ions, especially the interaction between 3P1 state, metal-to-metal charge transfer state and Bi-Bi dimers. The result is favorable for us to exactly adjust the luminescence properties of Bi3+ ions.

Donor-acceptor pair transitions in MgAl2O4 spinel

The luminescence of the well-known spinel-structured functional compound MgAl2O4 was studied at cryogenic temperatures below 10 K in a wide spectral range from near-IR to VUV under synchrotron radiation and electron beam excitation. The most intense luminescence band at ∼5 eV, which origin remained largely unknown up to now, showed characteristic behaviour of the donor-acceptor pair (DAP) centres and was assigned to the so-called antisite defects. The antisite DAPs are formed by position-swapped cations AlMg● and MgAl′, which define the inversion degree of the spinel structure and, to the best of our knowledge, always exceed 10% (>1.5 × 1021 cm−3) in the synthetic solids. Full data set allowed confirming that extremely high concentration of these intrinsic defects is the main reason for the strong 5-eV luminescence, which mechanism includes the electron transfer from MgAl′ to AlMg● (excitation) following by that from VO● to MgAl× (emission). Irradiation with He + ions up to fluences of 1017 cm−2 randomly displaced cations to empty sites of the spinel lattice resulting in more intragap defect levels, which induce a non-radiative energy relaxation channel quenching closely spaced while unaffecting distant DAP luminescence.

Sub-to-super-Poissonian photon statistics in cathodoluminescence of color center ensembles in isolated diamond crystals

Abstract Impurity-vacancy centers in diamond offer a new class of robust photon sources with versatile quantum properties. While individual color centers commonly act as single-photon sources, their ensembles have been theoretically predicted to have tunable photon-emission statistics. Importantly, the particular type of excitation affects the emission properties of a color center ensemble within a diamond crystal. While optical excitation favors non-synchronized excitation of color centers within an ensemble, electron-beam excitation can synchronize the emitters excitation and thereby provides a control of the second-order correlation function g 2(0). In this letter, we demonstrate experimentally that the photon stream from an ensemble of color centers can exhibit g 2(0) both above and below unity, thereby confirming long standing theoretical predictions by Meuret et al. [S. Meuret, L. H. G. Tizei, T. Cazimajou, et al., “Photon bunching in cathodoluminescence,” Phys. Rev. Lett., vol. 114, no. 19, p. 197401, 2015.]. Such a photon source based on an ensemble of few color centers in a diamond crystal provides a highly tunable platform for informational technologies operating at room temperature.

Chiral Smith–Purcell Radiation Light Source

AbstractSmith–Purcell radiation (SPR) with broadly tunable spectra has attracted attention in light emission, and this free‐electron‐driven source shows great potential in illumination fields, such as terahertz sources, ultra‐compact light sources, free‐electron lasers, etc. However, it remains difficult to control the polarization properties of SPR and realize a free‐electron chiral light source. In this work, the chiral SPR with the maximum chirality (>40%) is acquired in a periodic stacked nanosquare light‐well, and the radiation chirality is manipulated by variations of the designed electron beam excitation positions. Furthermore, this work reveals that the chiroptical effect originates in the superposition of SPRs with different phases and polarization, which are derived from adjacent sidewalls. This work may deepen the comprehension of electron‐matter interaction and facilitate the development of compact electron‐driven chirality‐tunable source‐on‐chip, highlighting potential applications in photonic integration and binary data processing.

Multicolor tunable luminescence and energy transfer mechanism in Gd2O2S: Dy3+, Sm3+ phosphors

High quality single-phase multicolor emission phosphor is a prerequisite for efficient luminescence devices, but the system design and quantity preparation are still facing substantial challenges. Herein, Gd2O2S-based phosphors with high crystallinity, good dispersibility, and relatively good size uniformity were obtained by optimizing the type and components of flux based on the conventional solid-state method. By single-doping system study, the emission properties of matrix and activated ions are expounded, meanwhile the composition and co-excitation wavelength of co-doping system are designed. In the co-doping system, we mainly realized adjustable emission, interionic energy transfer, and application performance analysis. Firstly, multicolor emission in the range of yellow, orange and white was achieved through the modulation of dopant type and concentration as well as excitation wavelength. Secondly, the phenomena of spectral overlap (between Dy3+ and Sm3+), fluorescence intensity change (606 nm of Sm3+) and the monotonically decreasing fluorescence lifetime (Dy3+ at 578 nm) were evidence of energy transfer in the co-doping system. The theoretical fitting demonstrates that the energy transfer process of Dy3+→Sm3+ is primarily based on the quadrupole-quadrupole interaction mechanism. In addition, the cathodoluminescence spectra, temperature-dependent emission spectra, and magnetic properties tests have demonstrated the characteristics of multicolor adjustable emission (electron-beam excitation), excellent thermal stability, and good paramagnetic properties of the co-doping phosphors, further indicating that the Gd2O2S:Dy3+/Sm3+ system phosphors have potential as an excellent optical-magnetic bifunctional material in the fields of luminescence and bioimaging.

Surface morphologies, chemical compositions and luminescent properties of ZnO thin films flattened by ion milling procedure

The luminescent properties of ZnO thin films have been developed to form a nanometric light source for an electron beam-excitation assisted optical microscope. Spatial uniformity of the electron-induced luminescence is important when using this luminescent ZnO film-based light source. In this work, ZnO thin film surfaces have been flattened using broad ion beam polishing with Ar+ ions at a grazing angle of incidence. Atomic force microscopy and electron microscopy confirmed transformation of needle-like ZnO surface structures into scale-like morphologies during ion irradiation. The root-square-mean roughness, corresponding to the height distribution decreased dramatically from 32 to 8 nm after 5 keV Ar+ ion irradiation for 60 min. X-ray photoelectron spectroscopy and Monte Carlo simulations revealed changes in the chemical state and lattice defects during ion irradiation. Positive shifts in the binding energies of the Zn 2p and O 1s spectra suggested preferential Zn atom sputtering and chemical composition change from oxygen-deficient to stoichiometric ZnO. The ultraviolet region luminescent intensity improved after ion irradiation for 60 min. Valence band electron redistribution was considered to influence the ZnO thin film’s luminescent properties. We propose that homogeneous luminescence over a specified area with flat surfaces can be accomplished by repeated short-duration ion irradiation.

Hyperspectral mapping of nanoscale photophysics and degradation processes in hybrid perovskite at the single grain level.

With solar cells reaching 26.1% certified efficiency, hybrid perovskites are now the most efficient thin film photovoltaic material. Though substantial effort has focussed on synthesis approaches and device architectures to further improve perovskite-based solar cells, more work is needed to correlate physical properties of the underlying film structure with device performance. Here, using cathodoluminescence microscopy coupled with unsupervised machine learning, we quantify how nanoscale heterogeneity globally builds up within a large morphological grain of hybrid perovskite when exposed to extrinsic stimuli such as charge accumulation from electron beams or milder environmental factors like humidity. The converged electron-beam excitation allows us to map PbI2 and the emergence of other intermediate phases with high spatial and energy resolution. In contrast with recent reports of hybrid perovskite cathodoluminescence, we observe no significant change in the PbI2 signatures, even after high-energy electron beam excitation. In fact, we can exploit the stable PbI2 signatures to quantitatively map how hybrid perovskites degrade. Moreover, we show how our methodology allows disentangling of the photophysics associated with photon recycling and band-edge emission with sub-micron resolution using a fundamental understanding of electron interactions in hybrid perovskites.

Luminescence of yttrium tantalate doubly activated with europium and terbium under x-ray and electron beam excitations

This paper reports the luminescence spectra of YTaO4 activated with rare-earth ions, such as Eu3+ and Tb3+. The effect of these rare-earth ions on the luminescence of yttrium tantalate phosphors is studied. The luminescent properties are studied under X-ray and electron beam excitations. It is found that, under these excitations, the emission centers of the rare-earth activators (Eu3+, Tb3+) efficiently contribute to the overall luminescence. Color cathodoluminescence images clearly show the dependence of chromaticity on the different activators. These rare-earth activated phosphors exhibiting various luminescence chromaticities are promising materials for optoelectronic applications and for X-ray intensifying screens in medical diagnosis, because they provide a broad variation of visible photoluminescence from blue to red.

Lanthanoid-doped quaternary garnets as phosphors for high brightness cathodoluminescence-based light sources

Gadolinium-yttrium- aluminum-gallium garnets (GYAGG) doped and codoped with Eu, Tb, and Ce were manufactured as ceramics to develop long-wavelength phosphors for high-brightness white light sources based on cathodoluminescence (CL). The CL light yield (LY) of Tb-doped ceramics at high-intensity electron beam excitation is shown to be more than twice as high as that of the conventional phosphor YAG:Ce, whereas codoping with Eu to redshift the chromaticity results in reducing the LY approximately to the level of YAG:Ce. The LY might be substantially improved by using a mix of Tb- and Eu-doped GYGAG powders instead of a single codoped GYGAG to produce ceramic phosphor. The high LY is explained by favorable contribution of Gd sublattice in excitation transfer to activator ions. Chromaticity of phosphors GYGAG:Tb, Eu can be tuned in a wide range by varying the ratio of Tb to Eu concentration. They are radiation resistant and stabile in the temperature range from 300 to 450 K.

Novel Dy incorporated Ca3Y2B4O12 phosphor: Insights into the structure, broadband emission, photoluminescence and cathodoluminescence characteristics

This study reports cathodoluminescence (CL) and photoluminescence (PL) properties of undoped borate Ca3Y2B4O12 and Ca3Y2B4O12:x Dy3+ (x = 0.5, 1, 2, 3, 5, and 7) synthesized by gel combustion method. Micro-X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), CL and PL under electron beam and 359 nm pulse laser excitation, respectively were used to investigate characterization and luminescence studies of synthesized samples in the visible wavelength. As-prepared samples match the standard Ca3Y2BO4 phase that belongs to the orthorhombic system with space group Pnma (62) based on XRD results. Under electron beam excitation, this borate host shows a broad band emission from about 250 to 450 nm, peaked at 370 nm which is attributed to NBHOC. All as-prepared phosphors exhibited the characteristic PL and CL emissions of Dy3+ ions corresponding to 4F9/2→6HJ transitions when excited with laser at 359 nm. The CL emission spectra of phosphors were identical to those of the PL spectra. Concentration quenching occurred when the doping concentration was 1 mol% in both the CL and PL spectra. The underlying reason for the concentration quenching phenomena observed in the discrete orange-yellow emission peaked at 574 nm of Dy3+ ion-doped Ca3Y2B4O12 phosphor is also discussed. According to these data, we can infer that this new borate can be used as a yellow emitting phosphor in solid-state illumination.

High Spatial Resolution Ion Imaging by Focused Electron-Beam Excitation with Nanometric Thin Sensor Substrate.

We developed a high spatially-resolved ion-imaging system using focused electron beam excitation. In this system, we designed a nanometric thin sensor substrate to improve spatial resolution. The principle of pH measurement is similar to that of a light-addressable potentiometric sensor (LAPS), however, here the focused electron beam is used as an excitation carrier instead of light. A Nernstian-like pH response with a pH sensitivity of 53.83 mV/pH and linearity of 96.15% was obtained. The spatial resolution of the imaging system was evaluated by applying a photoresist to the sensing surface of the ion-sensor substrate. A spatial resolution of 216 nm was obtained. We achieved a substantially higher spatial resolution than that reported in the LAPS systems.

Electron beam chiral diffraction radiation in isosceles right triangle light-well

<sec>Electron beam diffraction radiation source has the advantages of small size, wavelength tunability, and polarization controllability, showing great potential applications in nanophotonic circuits. However, studies of optical chirality of electron beam diffraction radiation are relatively scarce. The optical chirality of electron beam diffraction radiation in isosceles right triangle light-well is realized and demonstrated in this work. The light-well consists of twelve alternating layers of gold and silicon dioxide, and the electron beam diffraction radiation originates from oscillating dipole sources within the light-well. In the case of the electron beam injected at the geometrically asymmetric position within the structure, the diffraction radiation signal with a maximum chirality of more than 40% can be obtained. By changing the injection position of the electron beam, the state of the optical chirality can be effectively controlled, and even the inversion of the chirality can be realized.</sec><sec>By analyzing the vacuum electromagnetic mode in the system and the dynamic evolution of charge distribution in the gold layer, a reasonable theoretical explanation is provided for the generation of the chiral optical effect. A semi-analytical model for explaining the optical chirality of electron beam diffraction radiation is given by solving the incident electromagnetic field and the waveguide modes in the light-well. The observed difference between left-handed circularly polarized and right-handed circularly polarized signals originates from the asymmetry between left-handed and right-handed electromagnetic modes in the light-well caused by the geometrically asymmetric positional excitation, which ultimately leads to far-field chiral radiation determined by the electromagnetic field within the light-well. In addition, the simulation results of the surface charge distribution of the top gold film of the light-well reveal the correlation between the dynamic evolution of the surface charge distribution and the radiation chirality.</sec><sec>The advantages of nanoscale focusing and moving of electron beam excitation source make the optical chirality of electron beam diffraction radiation have more flexible adjustment potential. The proposed physical mechanism and unique experimental platform not only provide new ideas for manipulating optical chirality on a nanoscale, but also lay the foundation for binary information processing and integration in nanophotonic circuits and chiral nano-light-sources in the future.</sec>

Electron beam chiral diffraction radiation in an isosceles right triangle light-well

Electron beam diffraction radiation sources have the advantages of small size, wavelength tunability, and polarization controllability, showing great application potential in nanophotonic circuits. However, studies on optical chirality of electron beam diffraction radiation are relatively scarce. The optical chirality of electron beam diffraction radiation in isosceles right triangle light-well is realized and demonstrated in this work. The light-well consists of twelve alternating layers of gold and silicon dioxide, and the electron beam diffraction radiation originates from oscillating dipole sources within the light-well. In the case of the electron beam injecting at the geometrically asymmetric position within the structure, the diffraction radiation signal with a maximum chirality of more than 40% can be obtained. By changing the injection position of the electron beam, the state of the optical chirality can be effectively controlled, and even the inversion of the chirality can be realized.<br>By analyzing the vacuum electromagnetic mode in the system and the dynamic evolution of charge distribution in the gold layer, a reasonable theoretical explanation is provided for the generation of the chiral optical effect. A semi-analytical model for explaining the optical chirality of electron beam diffraction radiation is given by solving the incident electromagnetic field and the waveguide modes in the light-well. The observed difference between left-handed circularly polarized and right-handed circularly polarized signals originates from the asymmetry between left-handed and right-handed electromagnetic modes in the light-well caused by the geometrically asymmetric positional excitation, which ultimately leads to far-field chiral radiation determined by the electromagnetic field within the light-well. In addition, the simulation results of the surface charge distribution of the top gold film of the light-well reveal the correlation between the dynamic evolution of the surface charge distribution and the radiation chirality.<br>The advantages of nanoscale focusing and moving of electron beam excitation source make the optical chirality of electron beam diffraction radiation have more flexible adjustment potential. The proposed physical mechanism and unique experimental platform not only provide new ideas for manipulating optical chirality at the nanoscale, but also lay the foundation for binary information processing and integration in nanophotonic circuits and chiral nano-light-sources in the future.

Cathodoluminescence in Ultrafast Electron Microscopy.

Implementing the modern technologies of light-emitting devices, light harvesting, and quantum information processing requires the understanding of the structure-function relations at spatial scales below the optical diffraction limit and time scales of energy and information flows. Here, we distinctively combine cathodoluminescence (CL) with ultrafast electron microscopy (UEM), termed CL-UEM, because CL and UEM synergetically afford the required spectral and spatiotemporal sensitivities, respectively. For color centers in nanodiamonds, we demonstrate the measurement of CL lifetime with a local sensitivity of 50 nm and a time resolution of 100 ps. It is revealed that the emitting states of the color centers can be populated through charge transfer among the color centers across diamond lattices upon high-energy electron beam excitation. The technical advance achieved in this study will facilitate the specific control over energy conversion at nanoscales, relevant to quantum dots and single-photon sources.

Near white light and near-infrared luminescence in perovskite Ga:LaCrO3

We report the realization of near-white light emission (near-WLE) and the selective tuning to the near-infrared (NIR) luminescence from Ga substituted lanthanum chromite perovskite with electron-beam excitation for the first time. The near-WLE in Cathodoluminescence (CL), arises from the combination of 4T1(F)→4A2(blue), 4T1(P)→4A2(green) and 4T2→4A2(red) spin allowed transitions and 2E→4A2 spin forbidden transitions from the Cr3+ ion. The spin allowed transitions from the Cr3+ ions is rare, however can be accomplished by adjusting the Cr3+/Ga3+ ion concentration in the host lattice. The NIR emission originates from the selective 2E→4A2 transition, which increases with the increasing concentration of Ga3+ions. Moreover, the Density Functional Theory (DFT) calculations point out the presence of extra electronic states in the NIR region with Ga substitution, which elucidates the observation of NIR emission in Ga substituted samples.

Study on Localized Surface Plasmon Coupling with Many Radiators.

Localized surface plasmon (LSP) coupling with many radiators are investigated. The LSP is generated by excitation of laser or electron beam on the random Ag nano particles (NPs) and arrayed ones embedded in the p-GaN of green LEDs. They couple with the excitons or radiative recombination in the quantum well (QW) and electron beam, which enhance or suppress the luminescence of the radiators. The photoluminescence (PL) intensity of periodic Ag NPs can get as much as 4.5 times higher than that of bare LED. In addition to the periodic structure, the morphology of Ag NPs also affects the localized SP (LSP) resonance intensity and light scattering efficiency. In the finite difference time domain (FDTD) simulation, five x-polarized dipoles are approximated to five quantum wells. Considering the interaction between the five dipoles and their feedback effect on LSP, the enhancement effect of SP dipole coupling with Ag NPs is amplified and the energy dissipation is reduced. The enhancement of cathodoluminescence (CL) was also found in green LEDs with Ag NPs. The three-body model composed of two orthogonal dipoles and an Ag NP is used for 3D FDTD simulation. The LSP-QWs coupling effect is separated from the electron beam (e-beam)-LSP-QW system by linear approximation. Under the excitation of electron beam, the introduction of z-dipole greatly reduces the energy dissipation. In the cross-sectional sample, z-polarized dipoles in QWs show more coupling strength to the dipole and quadrupole modes of LSP. The perturbation theory is used to separate the LSP coupling effects to x-dipole and z-dipole. At last, the resonator and the antenna effects are discussed for LSP coupling at different positions to the Ag NP.

Chirality Affecting Reaction Dynamics of HgS Nanostructures Simultaneously Visualized in Real and Reciprocal Space.

Chirality involved reactions enable to probe features in the fields of asymmetric synthesis and catalysis, which allow to gain insight into the fundamental mechanisms of topochemically controlled reactions. However, in situ observation of the chirality-associated reaction dynamics with simultaneous structural determination of microscopic features has been lacking. Here, we report the direct visualization of the electron-beam-stimulated reaction dynamics of HgS nanostructures with chiral and achiral morphologies simultaneously in both real and reciprocal space. Under the electron-beam excitation of HgS nanostructures, the formation and evaporation dynamics of Hg nanodroplets were vividly pictured, while the reciprocal space imaging revealed the structural transformation from monocrystalline to polycrystalline. Interestingly, such induced changes were size dependent, which were slowed when involving the chirality in the nanostructures. The finding offers a fundamental understanding of topochemically controlled reaction mechanisms and holds promise of tuning asymmetric synthesis for catalysis-related applications.