Computational Modeling of Extracellular Matrix Protein Stamping on Hard Substrates for Biomedical Micro-Devices.

We model the direct transfer of ECM protein to hard substrates that are relevant to biomedical micro devices. To better understand the processes involved in the contact and transfer of protein, mechanics model and finite element simulations were used to simulate the protein transfer process over hard substrates with different stamped–strike layer thickness ratios. We also considered the direct transfer of the ECM protein to bare substrates.  Interfacial fracture analyses are used to determine the minimum stamping pressure required for direct transfer. A conservative model is also presented for the stamping of ECM protein on hard substrate. This provides the opportunity for better designs of new stamps and optimization of existing ECM Stamps Keywords: ECM Protein, stamp, Substrates

Development of Sustainable and Eco-Friendly Materials from Termite Hill Soil Stabilized with Cement for Low-Cost Housing in Chad

This paper explores the effects of cement stabilization (5, 10, 15 and 20 wt%) on the structural and mechanical properties (compressive/flexural strengths and fracture toughness) of abandoned termite mound soil. The crystal structures and crystallinity of the constituents were determined using X-ray diffraction (XRD), while the microstructure was characterized via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The functional groups were also identified using Fourier transform infra-red spectroscopy (FTIR). The compressive/flexural strengths of the stabilized and un-stabilized termite mound soil were also studied after curing for 7, 14 and 28 days. The fracture toughness mechanism was analyzed with the aid of the R-curve method. Additionally, the underlying deformation and cracking mechanisms are elucidated via in-situ/ex-situ optical and scanning electron microscopy. The stabilized termite mound soil displayed the highest mechanical properties of 13.91 MPa, 10.25 MPa and 3.52 kPa·m1/2 for compressive strength, flexural strength and fracture toughness, respectively. Besides displaying good mechanical properties and being locally available at no cost, renewable and an eco-friendly material, the termite mound soil will contribute to lowering the cost of housing in Sub-Saharan Africa, particularly in Chad

Optical properties of ZnO/Al/ZnO multilayer films for large area transparent electrodes

This study presents the optical properties of layered ZnO/Al/ZnO composite thin films that are being explored for potential applications in solar cells and light emitting devices. The composite thin films are explored as alternatives to ZnO thin films. They are produced via radio frequency magnetron sputtering. The study clarifies the role of the aluminum mid-layer in a ZnO (25 nm)/Al/ZnO (25 nm) film structure. Multilayers with low resistivity ∼362 µΩ cm and average transmittances between ∼85 and 90% (in the visible region of the solar spectrum) are produced. The highest Haacke figure of merit of 4.72 × 10−3 Ω−1 was obtained in a multilayer with mid-layer Al thickness of 8 nm. The combined optical band gap energy of the multilayered films increased by ∼0.60 eV for mid-layer Al thicknesses between ∼1 and 10 nm. The observed shifts in the optical absorption edges to shorter wave lengths of the spectrum are shown to be in agreement with the Moss–Burstein effect

Synthesis and Characterization of Alkylamine-Functionalized Si(111) for Perovskite Adhesion With Minimal Interfacial Oxidation or Electronic Defects

We investigated synthetic strategies for the functionalization of Si(111) surfaces with organic species containing amine moieties. We employed the functionalized surfaces to chemically “glue” perovskites to silicon with efficient electron transfer and minimal oxidation leading to deleterious recombination at the silicon substrate. A two-step halogenation-alkylation reaction produced a mixed allyl–methyl monolayer on Si(111). Subsequent reactions utilized multiple methods of brominating the allyl double bond including reaction with HBr in acetic acid, HBr in THF, and molecular bromine in dichloromethane. Reaction with ammonia in methanol effected conversion of the bromide to the amine. X-ray photoelectron spectroscopy (XPS) quantified chemical states and coverages, transient-microwave photoconductivity ascertained photogenerated carrier lifetimes, atomic force microscopy (AFM) quantified perovskite–silicon adhesion, and nonaqueous photoelectrochemistry explored solar-energy-conversion performance. The HBr bromination followed by the amination yielded a surface with ∼10% amine sites on the Si(111) with minimal oxide and surface recombination velocity values below 120 cm s^–1, following extended exposures to air. Importantly, conversion of amine sites to ammonium and deposition of methylammonium lead halide via spin coating and annealing did not degrade carrier lifetimes. AFM experiments quantified adhesion between perovskite films and alkylammonium-functionalized or native-oxide silicon surfaces. Adhesion forces/interactions between the perovskite and the alkylammonium-functionalized films were comparable to the interaction between the perovskite and native-oxide silicon surface. Photoelectrochemistry of perovskite thin films on alkylammonium-functionalized n⁺-Si showed significantly higher <i>V</i>_oc than n⁺-Si with a native oxide when in contact with a nonaqueous ferrocene^+/0 redox couple. We discuss the present results in the context of utilizing molecular organic recognition to attach perovskites to silicon utilizing organic linkers so as to inexpensively modify silicon for future tandem-junction photovoltaics