Sensors

Radiation detectors, which convert radiation into measurable light signals, currently come in fixed shapes like blocks or cylinders because they are made by growing crystals at extremely high temperatures – around 1700 °C. These rigid shapes make it difficult to measure radiation doses accurately around irregularly shaped tumors or in tight spaces. Previous attempts to create detectors in custom shapes have focused on plastic materials that can be easily molded, but these plastic detectors perform poorly because they lack the heavy elements needed to efficiently capture radiation. Scientists have tried mixing metal particles into plastics to improve their detection ability, but this often results in uneven distribution of the particles and poor overall performance.

A research team from several institutions in Italy and Switzerland has now developed a new approach using stereolithography (SLA), a precise form of 3D printing that builds objects by hardening light-sensitive liquid materials layer by layer. This marks the first successful use of SLA to fabricate 3D-printed scintillators, a breakthrough in radiation detection technology. The team mixed microscopic crystals of cesium lead bromide (Cs₄PbBr₆), a perovskite material, into a liquid resin that hardens when exposed to ultraviolet light. Perovskites have gained significant attention in recent years because they efficiently convert various forms of energy into light. Their crystal structure, which contains heavy elements like lead, makes them particularly effective at detecting radiation.

Researchers from the Chinese Academy of Sciences (CAS), Beihang University and Imperial College London have developed an on-chip integrated polarization photodetector (pol-PD), drawing inspiration from the unique polarization vision of desert ants.

Working mechanism diagram of the single-shot on-chip pol-PD. Image from Science Advances

Pol-PDs have widespread applications in geological remote sensing, machine vision and biological medicine. However, commercial pol-PDs usually require bulky and complicated optical components and are difficult to miniaturize and integrate. The researchers observed that desert ants can navigate back to their nests across barren landscapes without landmarks, thanks to their compound eyes' ability to detect polarized sunlight. They aimed to mimic this capacity with their pol-PD.

Researchers from China's Jiangxi Normal University, Chinese Academy of Sciences (CAS) and City University of Hong Kong have developed a self-driven X-ray detection device using high resistivity zero-dimensional lead-free perovskite ferroelectric single-crystal (NMP)₃Sb₂Br₉. The device exhibits an excellent self-driven X-ray detection performance, with an ultra-low detection limit of 84.1 nGyair/s, approximately 60 times lower than that of commercial α-Se (5500 nGyair/s).

The self-driven detection mode without external bias has been proven to be an effective means of reducing the limit of detection (LoD) due to its low current noise characteristics. Additionally, the zero-dimensional distinctive isolated framework results in a high resistivity of 1.39 × 1011 W cm, which effectively reduces the current noise and suppresses ion migration. 

Researchers from King Abdullah University of Science and Technology (KAUST), the University of Manchester and Marvell Semiconductor have developed an innovative high-speed photodetector design utilizing ultrathin two-dimensional metal halide perovskites (2D-MHP), coupled with a planar nanocavity to significantly enhance optical absorptance—achieving more than a fourfold increase in a solution-processed 10-nm-thick 2D-MHP film. 

This integration facilitates an exceptional response time (30 ns) alongside a high responsivity of 2.12 A W⁻¹. The method is said to overcome traditional constraints related to thickness and absorption, thereby optimizing device speed and dark noise features through active area variation.

Researchers from China's Dongguan University of Technology and Xi'an Jiaotong University have developed a spontaneous cooling strategy with a hot-pressing technique that enables the production of high-purity, wafer-scale, pinhole-free perovskite wafers with a reflective surface. 

This method can, according to the team, be extended to a variety of perovskite wafers, including organic-inorganic, 2D, and lead-free perovskites. The size of the wafer (with diameters of 10, 15, and 20 mm) can be tailored by changing the mold.

An NSW Smart Sensing Network Grand Challenge Fund project is hoping to eliminate the reliance of sensors on disposable batteries by testing the fast production of perovskite photovoltaic (PV) cells, in the hope of creating a more sustainable sensor power source. The NSW Smart Sensing Network, a consortium of eight leading universities across NSW and the ACT, is a not-for-profit innovation network that brings together universities, industry and government to translate world-class research into innovative smart sensing solutions that create value for NSW and beyond.

The Revolutionizing Indoor Sensor Power: Rapid Microwave Annealing for Ultra-low-cost Perovskite Solar Cells project is being led by Dr. Binesh Veettil, a Senior Lecturer in the School of Engineering at Macquarie University. “Perovskite cells offer continuous power, and are ideal for harvesting indoor light to power low-power sensors,” Dr. Veettil says. “They are cost-effective when mass manufactured and they are suitable for roll-to-roll manufacturing as they can be screen-printed, slot-die coated, or spray-painted. Unfortunately the lengthy annealing time required is a challenge to be addressed to enable their widespread adoption.”

Interface engineering is widely used to enhance the efficiency and stability of photodetectors (PDs). Researchers from China's Guangxi University have explained that although fluorine-containing materials are ideal for interface modification, they are seldom used at the NiOx/perovskite interface. Their recent paper reports on the use of Tris(pentafluorophenyl)borane (BCF) and 2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane (F4-TCNQ)-modified NiOx HTL to achieve high-efficiency and high-stability PDs. 

This work shows that BCF and F4-TCNQ interact to provide better doping ability, form Lewis adducts with Pb²⁺, and enhance the crystallinity of their perovskites. Interaction with nickel oxide optimizes the Ni³⁺/Ni²⁺ ratio, thus improving conductivity and charge transport capability. The F4-TCNQ:BCF modification effectively reduces interface defects, improves carrier mobility, and enhances both the performance and stability of PDs in ambient air. 

Researchers from Queen Mary University of London and QinetiQ could pave the way for faster discovery of novel perovskite materials with desirable properties for applications in wireless communication and biosensors. The recent research introduces an automated platform for rapid sintering and dielectric characterization of perovskite solid solutions. This innovative approach integrates machine learning (ML) for material screening with robotic synthesis and high-throughput characterization.

The scientists stated that while accelerating perovskite solid solution discovery and sustainable synthesis is crucial for addressing challenges in wireless communication and biosensors, the vast array of chemical compositions and their dependence on factors such as crystal structure and sintering temperature require time-consuming manual processes. To overcome these constraints, they introduced an automated materials discovery approach encompassing machine learning (ML) assisted material screening, robotic synthesis, and high-throughput characterization. 

Researchers from China's Shaanxi Normal University, Zhejiang Normal University, China Institute of Radiation Protection and Chinese Academy of Sciences have developed lead-free photoferroelectric hybrid metal halide perovskite flexible membranes for wearable detectors, that offer excellent X-ray response with high sensitivities, low detection limit and impressive imaging capabilities. 

Demonstration and application potential for lead-free photoferroelectric perovskite membrane (LFPPM). a) Optical images of the LFPPM. b) Schematic diagram of LFPPM wearable X-ray dosimeter. c) Schematic diagram of the working principle of wearable X-ray dosimeter. (Image credit: Nanowerk)

High-sensitivity wearable radiation detectors are important for personnel protection in radiation environments such as defense, nuclear facilities, and medical fields. Traditional detectors using bulk crystals tend to lack flexibility. Hybrid metal halide perovskites have shown promise for next-generation radiation detection as they can efficiently absorb high-energy radiation and convert it into electrical signals. However, there are concerns of lead toxicity. More recent efforts have explored lead-free alternatives, but these have generally suffered from poor charge transport properties, reducing their effectiveness as radiation detectors.

Researchers from Gwangju Institute of Science and Technology (GIST) and Institute for Basic Science (IBS) have developed a perovskite-based camera, inspired by the structures and functions of birds' eyes, specializing in object detection. 

Schematic illustration showing the visual ecology of birds. Image from Science Robotics

The eyes of different organisms in the natural world have evolved and been optimized to suit their habitat and the environment in which they survive. As a result of countless years of evolutionary adaptation to the environment of living and flying at high altitudes, bird eyes also have unique structures and visual functions. In the retina of an animal's eye, there is a small pit called the fovea that refracts the light entering the eye. Unlike the shallow foveae found in human eyes, bird eyes have deep central foveae, which refract the incoming light to a large extent. The region of the highest cone density lies within the foveae, allowing the birds to clearly perceive distant objects through magnification. This specialized vision is known as foveated vision.