Quantitative Cathodoluminescence Mapping: A CdMgSeTe Thin-Film Case Study.

Full-spectrum cathodoluminescence (CL) mapping provides a point-by-point spatial measurement of the apparent band gap of a semiconductor thin film. In most studies, analysis of the electrical film properties from CL is presented as color mapping images. We have developed a spectra data analysis algorithm to functionalize, analyze, and generate statistical measurements of the luminescence data to provide additional insights. This algorithm was coded in the R language program, and a set of CdMgSeTe films were studied as an application case study. CL maps were measured for samples with different luminescent responses. A quantitative measure of the heterogeneity of the films was generated by statistical analysis of luminescent intensity and wavelength, spectra type curves, frequency distributions of peak wavelength, and relative intensity maps. The final CL analysis facilitates the investigation of the CdMgSeTe films and has potential applications for many semiconductor films.

Microscopy Visualization of Carrier Transport in CdSeTe/CdTe Solar Cells.

Solar cells are essentially minority carrier devices, and it is therefore of central importance to understand the pertinent carrier transport processes. Here, we advanced a transport imaging technique to directly visualize the charge motion and collection in the direction of relevant carrier transport and to understand the cell operation and degradation in state-of-the-art cadmium telluride solar cells. We revealed complex carrier transport profiles in the inhomogeneous polycrystalline thin-film solar cell, with the influence of electric junction, interface, recombination, and material composition. The pristine cell showed a unique dual peak in the carrier transport light intensity decay profile, and the dual peak feature disappeared on a degraded cell after light and heat stressing in the lab. The experiments, together with device modeling, suggested that selenium diffusion plays an important role in carrier transport. The work opens a new forum by which to understand the carrier transport and bridge the gap between atomic/nanometer-scale chemical/structural and submicrometer optoelectronic knowledge.

Molecular plasma deposited peptides on anodized nanotubular titanium: an osteoblast density study.

A large amount of work is currently being conducted to design, fabricate, and characterize materials coated or immobilized with bioactive molecules for tissue engineering applications. Here, a novel method, molecular plasma deposition (MPD), is introduced with can efficiently coat materials with numerous bioactive peptides. Specifically, here, RGDS (arginine-glycine-aspartic acid-serine), KRSR (lysine-arginine-serine-arginine), and IKVAV (isoleucine-lysine-valine-alanine-valine) were coated on anodized nanotubular titanium using MPD. The anodized nanotubular titanium surfaces were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle measurements. Peptide coatings were examined by X-ray photoelectron spectroscopy (XPS) and an amine reactive fluorescence molecule, 3-(4 carboxybenzoyl)quinoline 2-carboxaldehyde (CBQCA). Electrospray ionization (ESI) was used to confirm peptide integrity. Osteoblast (bone-forming cell) density was determined on the materials of interest. Results confirmed peptide coatings and showed that the MPD RGDS and KRSR coatings on anodized nanotubular titanium increased osteoblast density compared with uncoated substrates and those coated with IKVAV and a control peptide (RGES) after 4 h and 7 days. SEM confirmed differences in the morphology of the attached cells. These results, to the best of our knowledge, are the first reports using MPD to efficiently create peptide coatings to increase osteoblast density on metals commonly used in orthopedics. Since MPD represents a quick, inexpensive, and versatile technique to coat implants with peptides, it should be further studied for numerous implant applications.