Precisely Positioned CsPbBr3 Nano-Light Sources Advance On-Chip Optical Technologies

Scientists are tackling the challenge of integrating high-quality light sources into nanoscale devices, a crucial step towards advanced on-chip optical technologies .Tomoyasu Fujimaru, Kanta Hirai, and Masato Inamata, from Kyushu University, alongside et al., have demonstrated a novel method for precisely positioning nano-light sources within a stable host material. Their research reveals that focused electron beam irradiation can locally generate CsPbBr3 nanoparticles directly within a Cs4PbBr6 film , effectively creating perovskite nano-light sources where they are needed. This breakthrough addresses a key limitation of halide perovskite nanoparticles, namely their instability, and paves the way for creating densely packed, submicron-spaced arrays with potential applications in next-generation photonics and optoelectronics.

The study reveals that by carefully controlling the electron beam, researchers can create arrays of perovskite nano-light sources with submicron spacing, offering unprecedented control over light emission positioning. This process effectively transforms the host material into a platform for generating localized light sources with high precision. Characterization of the films involved low-dose STEM-based analysis, ensuring minimal disruption during observation, and revealed the formation of new light-emitting centres upon irradiation.

Experiments showed that the initial Cs4PbBr6, CsBr film, devoid of CsPbBr3, underwent a transformation under the focused electron beam. Bright-field STEM imaging and cathodoluminescence (CL) mapping confirmed the generation of light-emitting nanoparticles at the irradiated locations. CL spectra obtained from these newly formed nanoparticles exhibited a peak wavelength of 526nm, closely matching the emission characteristics of established CsPbBr3 particles. Furthermore, the research establishes a robust method for creating perovskite nano-light source arrays with submicron spacing, a critical requirement for advanced optical applications.
By precisely controlling the electron beam’s path, the team demonstrated the ability to define the location of each nano-light source, opening possibilities for complex optical designs and quantum information processing. The use of Cs4PbBr6 as a host material is particularly advantageous, as it provides both chemical stability and effective passivation of surface defects, enhancing the performance and longevity of the generated nanoparticles. This breakthrough unlocks the potential for halide perovskites to become key components in next-generation optoelectronic devices and quantum technologies .

Perovskite Nanoparticle Generation via Electron Beam Irradiation

The study pioneered a two-step thermal evaporation process to create the requisite halide films. Initially, a CsPbBr3, Cs4PbBr6 nanocomposite film was annealed in vacuum at 250°C for 30 minutes, resulting in well-separated Cs4PbBr6 and CsPbBr3 grains, these served as reference materials for subsequent analysis. A second film, composed solely of Cs4PbBr6 and CsBr, was also fabricated, ensuring the absence of pre-existing CsPbBr3 nanoparticles. Crucially, all STEM-based analyses were conducted at a low dose rate of 0.4 electrons per nanometer squared per nanosecond, with a total dose not exceeding 2x 10⁷ electrons per nanometer squared, to prevent premature light source generation during characterization.

Experiments employed bright-field STEM imaging to observe the formation of pores in the annealed CsPbBr3, Cs4PbBr6 film, a consequence of the annealing process itself. Electron energy-loss spectroscopy (EELS) was used to definitively identify the generated nanoparticles, while cathodoluminescence (CL) spectroscopy characterized the emitted light from these newly formed nano-light sources. This innovative approach leverages the significant bandgap difference between Cs4PbBr6 (~3.9 eV) and CsPbBr3 (~2.3 eV) to confine charge carriers within the generated nanoparticles, enhancing their luminescence. Previous work demonstrated photoluminescence yields exceeding 90% from CsPbBr3 nanoparticles embedded in Cs4PbBr6, and electroluminescence from nanocomposites further motivated this position-controlled nano-light source generation. The ability to directly generate these light emitters, rather than relying on pre-existing particles or indirect methods, represents a substantial advancement in on-chip optical control and nanophotonic device fabrication.

Electron Beam Creates CsPbBr3 Nanoparticles in Host Matrix

Specifically, CL spectra obtained from irradiated areas exhibited a peak wavelength of 526nm, closely matching previously measured values from micrometer-scale CsPbBr3 particles. The team meticulously controlled the experimental parameters, performing STEM-based analysis at a low dose rate of 0.4 e/nm2/ns and a total dose of 2 × 107 e/nm2, ensuring accurate observation of the nanoparticle generation process. Further investigation involved fabricating two distinct halide films via thermal evaporation. One film, created by annealing a CsPbBr3, Cs4PbBr6 nanocomposite, contained separated CsPbBr3 and Cs4PbBr6 grains, with the estimated CsPbBr3 volume ratio being 23% based on CL map analysis.

The second film, composed of Cs4PbBr6 and CsBr, was designed to be free of the initial CsPbBr3 phase. CL maps of this second film revealed submicron- to micrometer-sized grains exhibiting brightness levels significantly lower than those of pure CsPbBr3 grains, but still discernable from the surrounding material. EELS and EDS analyses confirmed the chemical composition of these grains, showing the absence of lead and an increased density of cesium, consistent with the presence of CsBr. ADF-STEM imaging showed these “slightly bright grains” appearing darker than the surrounding Cs4PbBr6, further supporting their distinct composition.