Nanoscale Encapsulation of Perovskite Nanocrystal Luminescent Films via Plasma-Enhanced SiO2 Atomic Layer Deposition

Atomic-scale stress modulation of nanolaminate for micro-LED encapsulation

Micro/nano-LEDs for augmented reality (AR) and virtual reality (VR) applications face the challenge that the edge effect in micro-LEDs becomes significant as the size of devices shrinks. This issue can be effectively addressed through thin-film encapsulation, where zero stress of the thin film is a crucial factor, apart from the barrier property. Herein, a stress-modulation strategy was developed through a binary-cycle atomic-layer deposition (ALD) process combining PEALD SiO2 (compressive stress) and thermal ALD Al2O3 (tensile stress) in the same process window. The hybrid ALD process allows avoiding extra thermal stress generation and enables precise modulation of the atomic-scale thickness, thereby allowing the fabrication of nanolaminates with modulated stress. The optical nanolaminate developed herein achieved a stress level of near-zero, representing one of the best among reported studies. The structural design, characterized by a high-low refractive index, tortuous permeation path, and ultra-thin thickness, remarkably improved the optical transmittance and barrier properties (8.68 × 10-6 g m-2 day-1) of the nanolaminate. Moreover, the micro-LED encapsulated with SA2/1 exhibited excellent stability under thermal cycling, damp heat, and applied stress conditions. The mechanical stability of the nanolaminate was due to the strong interaction between Si-O and Al-O and the abundance of Si-O-Al bonding in the interface. Overall, the ALD-coating process provides a new avenue for accurately controlling the stress on nanolaminates, and has potential application to bolster the reliability of optoelectronic devices.

One-Step Ultrasonic Preparation of Stable Bovine Serum Albumin-Perovskite for Fluorescence Analysis of L-Ascorbic Acid and Alkaline Phosphatase

Halide lead perovskite has attracted increased attention due to its excellent optical properties. However, the poor stability of the halide lead perovskite nanocrystals has been a major obstacle to their application in biosensing. Here, we proposed a method to synthesize CsPbBr3/BSA NCs perovskite using bovine serum albumin (BSA) as a zwitterion ligand. Then, a fluorescent sensor for alkaline phosphatase determination based on CsPbBr3/BSA NCs was successfully built via the interaction of L-ascorbic acid (AA) with BSA on the perovskite surface. Under optimal conditions, the sensor showed a linear concentration range from 50 to 500 μM with a detection limit of 28 μM (signal-to-noise ratio of 3) for AA, and demonstrated a linear concentration range from 40 to 500 U/L with a detection limit of 15.5 U/L (signal-to-noise ratio of 3) for alkaline phosphatase (ALP). In addition, the proposed fluorescent biosensor exhibited good selectivity and recovery in the determination of ALP in human serum. This strategy offers an innovative way for enhancing the water stability of lead halide perovskite and promoting their application in biosensing areas.

In situ growth of lead-free halide perovskites into SiO2 sub-microcapsules toward water-stable photocatalytic CO2 reduction

Halide perovskites (HPs) are highly susceptible to heat, light, or moisture and are easily decomposed even in an ambient environment, which greatly hinders their practical applications. Herein, an in situ growth strategy is presented for implanting an inorganic lead-free HP, Cs₂AgBiBr₆, into SiO₂ sub-microcapsules to form a Cs₂AgBiBr₆@SiO₂ yolk-shell composite. The SiO₂ sub-microcapsule endows Cs₂AgBiBr₆ with good thermal and light stability, as well as excellent corrosion resistance against polar solvents. Furthermore, when employed as a lead-free perovskite photocatalyst, the composite exhibits a higher visible-light-driven CO₂-to-CO rate (271.76 μmol g^-1 h^-1) and much better stability than Cs₂AgBiBr₆ in water. The formation of a Cs₂AgBiBr₆/SiO₂ heterostructure using an in situ growth method alleviates water binding on the perovskites, supported by density functional theory calculations, which is the key to an improvement in the stability of the composite. The in situ growth strategy developed here sheds light on the design and development of HP-based materials for applications involving polar solvents.

Plasma-Assisted Nanofabrication: The Potential and Challenges in Atomic Layer Deposition and Etching

The growing need for increasingly miniaturized devices has placed high importance and demands on nanofabrication technologies with high-quality, low temperatures, and low-cost techniques. In the past few years, the development and recent advances in atomic layer deposition (ALD) processes boosted interest in their use in advanced electronic and nano/microelectromechanical systems (NEMS/MEMS) device manufacturing. In this context, non-thermal plasma (NTP) technology has been highlighted because it allowed the ALD technique to expand its process window and the fabrication of several nanomaterials at reduced temperatures, allowing thermosensitive substrates to be covered with good formability and uniformity. In this review article, we comprehensively describe how the NTP changed the ALD universe and expanded it in device fabrication for different applications. We also present an overview of the efforts and developed strategies to gather the NTP and ALD technologies with the consecutive formation of plasma-assisted ALD (PA-ALD) technique, which has been successfully applied in nanofabrication and surface modification. The advantages and limitations currently faced by this technique are presented and discussed. We conclude this review by showing the atomic layer etching (ALE) technique, another development of NTP and ALD junction that has gained more and more attention by allowing significant advancements in plasma-assisted nanofabrication.

Acid-mediated phase transition synthesis of stable nanocrystals for high-power LED backlights

Perovskite nanocrystals (PNCs) have excellent optical and optoelectronic properties, but their intrinsic instability hampers their practical applications. Herein, stable CsPbBr₃ nanocrystals (NCs) are fabricated with triethylaluminium (TMA, a Lewis acid) and hydrobromic acid by the co-assisted transformation of Cs₄PbBr₆ NCs. TMA forms a cross-linked alumina (AlO_x) encapsulation layer on the nanocrystal surface to suppress the deformation and ion migration. The introduction of hydrobromic acid acts as a binding ligand, and the acidified reaction environment provides conditions for the water-triggered phase transformation of Cs₄PbBr₆ NCs into CsPbBr₃ NCs. The synergistic effect of TMA and hydrobromic acid improves the stability of CsPbBr₃ NCs. The obtained CsPbBr₃ NC film maintains a high photoluminescence (PL) intensity after immersion in water. When stored in the atmosphere for over 30 days, the PL intensity of the CsPbBr₃ NC film hardly decreases. The proposed acid co-assisted phase transformation strategy provides a new avenue for the stabilization of PNCs which exhibits wider application prospects in backlight displays.

Soft, Pressure-Tolerant, Flexible Electronic Sensors for Sensing under Harsh Environments

Energy-efficient, miniaturized electronic ocean sensors for monitoring and recording various environmental parameters remain a challenge because conventional ocean sensors require high-pressure chambers and seals to survive the large hydrostatic pressure and harsh ocean environment, which usually entail a high-power supply and large size of the sensor system. Herein, we introduce soft, pressure-tolerant, flexible electronic sensors that can operate under large hydrostatic pressure and salinity environments, thereby eliminating the need for pressure chambers and reducing the power consumption and sensor size. Using resistive temperature and conductivity (salinity) sensors as an example for demonstration, the soft sensors are made of lithographically patterned metal thin films (100 nm) encapsulated with soft oil-infused elastomers and tested in a customized pressure vessel with well-controlled pressure and temperature conditions. The resistance of the temperature and pressure sensors increases linearly with a temperature range of 5-38 °C and salinity levels of 30-40 Practical Salinity Unit (PSU), respectively, relevant for this application. Pressure (up to 15 MPa) has shown a negligible effect on the performance of the temperature and salinity sensors, demonstrating their large pressure-tolerance capability. In addition, both temperature and salinity sensors have exhibited excellent cyclic loading behaviors with negligible hysteresis. Encapsulated with our developed soft oil-infused elastomer (PDMS, poly(dimethylsiloxane)), the sensor has shown excellent performance under a 35 PSU salinity water environment for more than 7 months. The soft, pressure-tolerant and noninvasive electronic sensors reported here are suitable for integration with many platforms including animal tags, profiling floats, diving equipment, and physiological monitoring.

Tb3+/Sm3+ co-doped double perovskite: synthesis, exfoliation and luminescence properties

Tb³⁺/Sm³⁺ co-doped double perovskite K[K_1.5(Tb_1-xSm_x)_0.5]Ta₃O₁₀ (denoted as KKT_1-xS_xTO) was prepared, which exhibited typical Tb³⁺ and Sm³⁺ photoluminescence emissions and tunable colours. After protonation and subsequent exfoliation processes, unilaminar KT_1-xS_xTO nanosheets with a lateral size of ∼300 nm and thickness of ∼2.7 nm were obtained.

Atomic-Layer-Deposited SiOx/SnOx Nanolaminate Structure for Moisture and Hydrogen Gas Diffusion Barriers

High-density SnO_x and SiO_x thin films were deposited via atomic layer deposition (ALD) at low temperatures (100 °C) using tetrakis(dimethylamino)tin(IV) (TDMASn) and di-isopropylaminosilane (DIPAS) as precursors and hydrogen peroxide (H₂O₂) and O₂ plasma as reactants, respectively. The thin-film encapsulation (TFE) properties of SnO_x and SiO_x were demonstrated with thickness dependence measurements of the water vapor transmission rate (WVTR) evaluated at 50 °C and 90% relative humidity, and different TFE performance tendencies were observed between thermal and plasma ALD SnO_x. The film density, crystallinity, and pinholes formed in the SnO_x film appeared to be closely related to the diffusion barrier properties of the film. Based on the above results, a nanolaminate (NL) structure consisting of SiO_x and SnO_x deposited using plasma-enhanced ALD was measured using WVTR (H₂O molecule diffusion) at 2.43 × 10^-5 g/m² day with a 10/10 nm NL structure and time-lag gas permeation measurement (H₂ gas diffusion) for applications as passivation layers in various electronic devices.

Bioinspired Oil-Infused Slippery Surfaces with Water and Ion Barrier Properties

Encapsulation materials play an important role in many applications including wearable electronics, medical devices, underwater robotics, marine skin tagging system, food packaging, and energy conversation and storage devices. To date, all the encapsulation materials, including polymer layers and inorganic materials, are solid materials. These solid materials suffer from limited barrier lifetimes due to pinholes, cracks, and nanopores or from complicated fabrication processes and limited stretchability for interfacing with complex 3D surfaces. This paper reports a solution to this material challenge by demonstrating bioinspired oil-infused slippery surfaces with excellent waterproof property for the first time. A water vapor transmission test shows that locking a thin layer of oil on the silicone elastomer improves the water vapor barrier performance by three orders of magnitude. Accelerated lifetime tests suggest robust water barrier characteristics that approach 226 days at 37 °C even under severe mechanical damage. A combination of temperature- and thickness-dependent experimental measurements and reaction-diffusion modeling reveals the key waterproof property. In addition to serving as a barrier to water, the oil-infused surface demonstrates an attractive ion barrier property. All these exceptional properties suggest the potential applications of slippery surfaces as encapsulation materials for medical devices, underwater electronics, and many others.