Lead Iodide (PbI
) is a large bandgap 2D layered material that has potential for semiconductor applications. However, atomic level study of PbI
monolayer has been limited due to challenges in ...obtaining thin crystals. Here, we use liquid exfoliation to produce monolayer PbI
nanodisks (30-40 nm in diameter and > 99% monolayer purity) and deposit them onto suspended graphene supports to enable atomic structure study of PbI
. Strong epitaxial alignment of PbI
monolayers with the underlying graphene lattice occurs, leading to a phase shift from the 1 T to 1 H structure to increase the level of commensuration in the two lattice spacings. The fundamental point vacancy and nanopore structures in PbI
monolayers are directly imaged, showing rapid vacancy migration and self-healing. These results provide a detailed insight into the atomic structure of monolayer PbI
, and the impact of the strong van der Waals interaction with graphene, which has importance for future applications in optoelectronics.
We study the atomic structure and dynamics of defects and grain boundaries in monolayer Pd2Se3 using annular dark field scanning transmission electron microscopy. The Pd2Se3 monolayers are ...reproducibly created by thermally induced phase transformation of few-layered PdSe2 films in an in situ heating holder in the TEM to promote Se loss. A variety of point vacancies, one-dimensional defects, grain boundaries (GBs), and defect ring complexes are directly observed in monolayer Pd2Se3, which show a series of dynamics triggered by electron beam irradiation. High mobility of vacancies leads to self-healing of point vacancies by migration to the edge and subsequent edge etching under beam irradiation. Specific defects for Pd2Se3 are stabilized by the formation of Se–Se bonds, which can shift in a staggered way to buffer strain, forming a wave-like one-dimensional defect. Bond rotations are also observed and play an important role in defect and grain boundary dynamics in Pd2Se3 during vacancy production. The GBs form in a meandering pathway and migrate by a sequence of Se–Se bond rotations without large-scale vacancy formation. In the GB corners and tilted GBs, other highly symmetric vacancy defects also occur to adapt to the orientation change. These results give atomic level insights into the defects and grain boundaries in Pd2Se3 2D monolayers.
The solid progress in the study of a single two-dimensional (2D) material underpins the development for creating 2D material assemblies with various electronic and optoelectronic properties. We ...introduce an asymmetric structure by stacking monolayer semiconducting tungsten disulfide, metallic graphene, and insulating boron nitride to fabricate numerous red channel light-emitting devices (LEDs). All the 2D crystals were grown by chemical vapor deposition (CVD), which has great potential for future industrial scale-up. Our LEDs exhibit visibly observable electroluminescence (EL) at both 5.5 V forward and 7.0 V backward biasing, which correlates well with our asymmetric design. The red emission can last for at least several minutes, and the success rate of the working device that can emit detectable EL is up to 80%. In addition, we show that sample degradation is prone to happen when a continuing bias, much higher than the threshold voltage, is applied. Our success of using high-quality CVD-grown 2D materials for red light emitters is expected to provide the basis for flexible and transparent displays.
Heterophase homojunction formation in atomically thin 2D layers is of great importance for next-generation nanoelectronics and optoelectronics applications. Technologically challenging, controllable ...transformation between the semiconducting and metallic phases of transition metal chalcogenides is of particular importance. Here, we demonstrate that controlled laser irradiation can be used to directly ablate PdSe2 thin films using high power or trigger the local transformation of PdSe2 into a metallic phase PdSe2–x using lower laser power. Such transformations are possible due to the low decomposition temperature of PdSe2 and a variety of stable phases compared to other 2D transition metal dichalcogenides. Scanning transmission electron microscopy is used to reveal the laser-induced Se-deficient phases of PdSe2 material. The process sensitivity to the laser power allows patterning flexibility for resist-free device fabrication. The laser-patterned devices demonstrate that a laser-induced metallic phase PdSe2–x is stable with increased conductivity by a factor of about 20 compared to PdSe2. These findings contribute to the development of nanoscale devices with homojunctions and scalable methods to achieve structural transformations in 2D materials.
Transmission electron microscopy (TEM) has long been used as the ultimate characterization technique for nanomaterials at the atomic level. Herein, the importance of the use of graphene in TEM is ...also presented to introduce the properties that make it indispensable for the characterization of other nanomaterials and study their properties and van der Waals interactions. A broad overview of the importance of using TEM for the study of nanomaterials and the rise of graphene as a superior substrate for the study of different kinds of low‐dimensional materials is provided. A review of the study of morphology, properties, and behavior of a range of nanomaterials is presented, with a specific focus on how graphene facilitates these studies due to its unique influence and interaction with the specific materials under TEM. This review presents an overview of the various studies and characterization that have been carried out on a range of nanomaterials using TEM with the use of graphene, and discusses the future challenges and engineering applications.
Graphene as the ultimate electron transparent support for transmission electron microscopy is reviewed, showing how weak scattering molecules and nanomaterials can be supported and imaged with structure resolved with contrast improvements beyond conventional carbon supports. Graphene supports enable direct imaging using lower doses and opens opportunities to study delicate molecules.
Photoswitching behavior of individual organic molecules was imaged by annular dark-field scanning transmission electron microscopy (ADF-STEM) using a highly electron beam transparent graphene ...support. Photoswitching azobenzene derivatives with ligands at each end containing single transition-metal atoms (Pt) were designed (Pt-complex), and the distance between the strong ADF-STEM contrast from the two Pt atoms in each Pt-complex is used to track molecular length changes. UV irradiation was used to induce photoswitching of the Pt complex on graphene, and we show that the measured Pt–Pt distances within isolated molecules decrease from ∼2.1 nm to ∼1.4 nm, indicative of a trans-to-cis isomerization. Light illumination of the Pt-complex on the graphene support also caused their diffusion out from initial clusters to the surrounding area of graphene, indicating that the light-activated mobilization overcomes the intermolecular van der Waals interactions. This approach shows how individual isolated heavy metal atoms can be included as markers into complex molecules to track their structural changes using ADF-STEM on graphene supports, providing an effective method to study a diverse range of complex organic materials at the single molecule level.
Fullerenes have a unique structure, capable of both encapsulating other molecules and reacting with those on the exterior surface. Fullerene derivatives have also been found to have enormous ...potential to address the challenges of the renewable energy sector and current environmental issues, such as in the production of n-type materials in bulk heterojunction solar cells, as antimicrobial agents, in photocatalytic water treatment processes, and in sensor technologies. Endohedral metallofullerenes, in particular, can possess unpaired electron spins, driven by the enclosed metal atom or cluster, which yield valuable magnetic properties. These properties have significant potential for applications in molecular magnets, spin probes, quantum computing, and devices such as quantum information processing,, atomic clocks, and molecular magnets. However, the intrinsically low yield of endohedral fullerenes remains a huge obstacle, impeding not only their industrial utilization but also the synthesis and characterization essential for exploring novel applications. The low yield and difficulty in separation of different types of endohedral fullerenes results in the usage of a large amount of solvents and energy, which is detrimental to the environment. In this paper, we analyse the methodologies proposed by various researchers and identify the critical synthesis parameters that play a role in increasing the yields of fullerenes.
Purpose
To evaluate the effect of tube shunt type Ahmed (AGV) versus Baerveldt (BGI) on the frequency of tube-cornea touch and corneal decompensation after tube shunt surgery.
Methods
This ...retrospective comparative study included 145 eyes of 130 patients with uveitic glaucoma who underwent AGV (75 eyes) or BGI (70 eyes) implantations. Electronic medical records were reviewed to document demographic factors, intraocular pressure (IOP) reduction, frequency of tube-cornea touch, corneal decompensation, and need for subsequent corneal transplantation.
Results
The mean follow-up was 27.7±3.3 months for AGV and 32.8±3.8 months for BGI (
p
=0.30). Tube-cornea touch was observed in 5 eyes after BGI and 1 eye in the AGV group (
p
=0.08). The BGI group reported a significantly higher rate of corneal decompensation (9 versus 0;
p
=0.001) and transplantation (6 versus 0;
p
=0.01) compared to the AGV group. Previous trabeculectomy was a significant risk factor for corneal complications in eyes undergoing BGI implantation (odds ratio OR= 8.17, 95% confidence interval CI=1.78–37.45,
p
=0.007).
Conclusion
Similar rates of tube-cornea touch were observed in both shunt types; BGI shunts were associated with a greater incidence of corneal complications and transplantation as compared to AGV in this retrospective series of uveitic glaucoma cases.
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