Development of a low-cost silica-titania optical platform for integrated photonics applications.

This paper investigates a highly attractive platform for an optical waveguide system based on silica-titania material. The paper is organized into two parts. In the first part, an experimental study on the development of an optical waveguide system is conducted via the sol-gel dip-coating method, and the optical characterization of the waveguide system is performed at a visible wavelength. This system is capable of operating from visible to near-IR wavelength ranges. The experimental results prove the dominance of this waveguide platform due to its low-cost, low loss, and easy to develop integrated optics systems. The numerical analysis of a one-dimensional Photonic crystal waveguide optical filter based on the silica-titania platform is considered in the second part of the paper by utilizing the 2D-finite element method (2D-FEM). A Fabry-Perot structure is also analyzed for refractive index sensing applications. We believe that the results presented in this work will be valuable in the realization of low-cost photonic integrated circuits based on the silica-titania platform.

In Situ Formation of Free-Standing Single-Atom-Thick Antiferromagnetic Chromium Membranes.

Compared to van der Waals two-dimensional (2D) layers with lateral covalent bonds, metallic bonding systems favor close-packed structures, and thus, free-standing 2D metals have remained, for the most part, elusive. However, a number of theoretical studies suggest a number of metals can exist as 2D materials and a few early experiments support this notion. Here we demonstrate free-standing single-atom-thick crystalline chromium (Cr) suspended membranes using aberration-corrected transmission electron microscopy and image simulations. Density functional theory studies confirm the 2D Cr membranes have an antiferromagnetic ground state making them highly attractive for spintronic applications. Moreover, the work also helps consolidate the existence of a new family of 2D metal layers.

Electron-beam induced synthesis of nanostructures: a review.

As the success of nanostructures grows in modern society so does the importance of our ability to control their synthesis in precise manners, often with atomic precision as this can directly affect the final properties of the nanostructures. Hence it is crucial to have both deep insight, ideally with real-time temporal resolution, and precise control during the fabrication of nanomaterials. Transmission electron microscopy offers these attributes potentially providing atomic resolution with near real time temporal resolution. In addition, one can fabricate nanostructures in situ in a TEM. This can be achieved with the use of environmental electron microscopes and/or specialized specimen holders. A rather simpler and rapidly growing approach is to take advantage of the imaging electron beam as a tool for in situ reactions. This is possible because there is a wealth of electron specimen interactions, which, when implemented under controlled conditions, enable different approaches to fabricate nanostructures. Moreover, when using the electron beam to drive reactions no specialized specimen holders or peripheral equipment is required. This review is dedicated to explore the body of work available on electron-beam induced synthesis techniques with in situ capabilities. Particular emphasis is placed on the electron beam-induced synthesis of nanostructures conducted inside a TEM, viz. the e-beam is the sole (or primary) agent triggering and driving the synthesis process.

Chemical vapor deposition of twisted bilayer and few-layer MoSe2 over SiO(x) substrates.

The chemical vapor deposition of monolayer and few-layer transition metal dichalcogenides is a rapidly developing area of materials science due to the exciting electrical, optical, thermal and mechanical properties of transition metal dichalcogenides in their layered form. These properties make these innovative materials potentially relevant to wide-ranging commercial applications. One of these promising materials is MoSe2; however, just recently, a few research groups have been able to demonstrate its synthesis via chemical vapor deposition. Moreover, only oriented few-layer MoSe2 has been exhibited by synthetically formed material using chemical vapor deposition thus far. Here, we confirm twisted-layer MoSe2 can also form during chemical vapor deposition. Twisted-layer transition metal dichalcogenides alter their properties as compared to their oriented counterparts. Therefore, twisted-layer structures are of interest because they can tune their properties.

Retro-fitting an older (S)TEM with two Cs aberration correctors for 80 kV and 60 kV operation.

For the characterization of light materials using transmission electron microscopy, a low electron acceleration voltage of 80 kV or even 60 kV is attractive due to reduced beam damage to the specimen. The concomitant reduction in resolving power of the microscope can be restored when using spherical aberration (C(s) ) correctors, which for the most part are only available in the latest and most expensive microscopes. Here, we show that upgrading of existing TEMs is an attractive and cost-effective alternative. We report on the low-voltage performance on graphitic material of a JEOL JEM-2010F built in the early 1990s and retro-fitted with a conventional imaging C(s) corrector and a probe C(s) corrector. The performance data show C(s) retro-fitted instruments can compete very favourably against more modern state-of-the-art instruments in both conventional imaging (TEM) and scanning (STEM) modes.

Delivery of carboplatin by carbon-based nanocontainers mediates increased cancer cell death.

Since the activity of several conventional anticancer drugs is restricted by resistance mechanisms and dose-limiting side-effects, the design of nanocarriers seems to be an efficient and promising approach for drug delivery. Their chemical and mechanical stability and their possible multifunctionality render tubular nanomaterials, such as carbon nanotubes (CNTs) and carbon nanofibres (CNFs), promising delivery agents for anticancer drugs. The goal of the present study was to investigate CNTs and CNFs in order to deliver carboplatin in vitro. No significant intrinsic toxicity of unloaded materials was found, confirming their biocompatibility. Carboplatin was loaded onto CNTs and CNFs, revealing a loading yield of 0.20 mg (CNT-CP) and 0.13 mg (CNF-CP) platinum per milligram of material. The platinum release depended on the carrier material. Whereas CNF-CP marginally released the drug, CNT-CP functioned as a drug depot, constantly releasing up to 68% within 14 days. The cytotoxicity of CNT-CP and CNF-CP in urological tumour cell lines was dependent on the drug release. CNT-CP was identified to be more effective than CNF-CP concerning the impairment of proliferation and clonogenic survival of tumour cells. Moreover, carboplatin, which was delivered by CNT-CP, exhibited a higher anticancer activity than free carboplatin.

Advances in engineering of diameter and distribution of the number of walls of carbon nanotubes in alcohol CVD.

A detailed study on the influence of the substrate loading (relative to the catalyst content) and supply pressure of the feedstock on the diameter and distribution of the number of walls in carbon nanotubes in alcohol chemical vapor deposition (CVD) is presented. Here we show how one can modify the technique for the bulk formation of high quality desired nanotube types: single-walled, double-walled or multi-walled CNTs. The influence of the concentration of the catalysts with respect to the substrate concentration was examined to select the optimal conditions in terms of the sample quality. Resonance Raman spectroscopy and high resolution transmission electron microscopy have been applied to characterize the samples.