Journal of Materials Research

Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.

As the technology for diamond film preparation by plasma-assisted CVD and related procedures has advanced, Raman spectroscopy has emerged as one of the principal characterization tools for diamond materials. Cubic diamond has a single Raman-active first order phonon mode at the center of the Brillouin zone. The presence of sharp Raman lines allows cubic diamond to be recognized against a background of graphitic carbon and also to characterize the graphitic carbon. Small shifts in the band wavenumber have been related to the stress state of deposited films. The effect is most noticeable in diamond films deposited on hard substrates such as alumina or carbides. The Raman line width varies with mode of preparation of the diamond and has been related to degree of structural order. The Raman spectrum of hexagonal diamond (lonsdaleite) is distinct from that of the cubic diamond and allows it to be recognized.

It was found that montmorillonite cation exchanged for 12-aminolauric acid (12-montmorillonite) was swollen by ∊-caprolactam to form a new intercalated compound. Caprolactam was polymerized in the interlayer of montmorillonite, a layer silicate, yielding a nylon 6-clay hybrid (NCH). The silicate layers of montmorillonite were uniformly dispersed in nylon 6. The carboxyl end groups of 12-aminolauric acid in 12-montmorillonite initiated polymerization of ∊-caprolactam, and as 12-montmorillonite content became larger, the molecular weight of nylon was reduced. From the result of end-group analysis, carboxyl end groups were more than amino end groups. The difference between the carboxyl and the amino end groups was attributed to ammonium cations (-NH₃⁺) of nylon molecules, because the difference agreed with the anion site concentration of the montmorillonite in NCH. It is suggested that the ammonium cations in nylon 6 interact with the anions in montmorillonite.

Bài báo này tổng quan về quá khứ, hiện tại và tương lai của các vật liệu sinh học dựa trên hydroxyapatit (HAp) từ góc độ chế tạo các cấy ghép thay thế mô cứng. Các tính chất của mô cứng cũng được mô tả. Độ tin cậy cơ học của gốm HAp nguyên chất là thấp, do đó nó không thể được sử dụng làm răng hoặc xương nhân tạo. Vì lý do này, các loại composite dựa trên HAp đã được chế tạo, nhưng chỉ có hợp kim titan phủ HAp là đã tìm thấy ứng dụng rộng rãi. Trong số các loại khác, gốm HAp được điều khiển vi cấu trúc như HAp gia cường bằng sợi hoặc râu, polymer gia cường bằng HAp sợi, hay composite HAp/collagen chế tạo sinh học có vẻ là những vật liệu gốm phù hợp nhất cho các cấy ghép thay thế mô cứng trong tương lai.

Results of Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space are used to show that a simple relationship exists among the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch. The generality of the relationship has important implications for the measurement of mechanical properties using load and depth sensing indentation techniques and in the measurement of small contact areas such as those encountered in atomic force microscopy.

The hardness of thick, high-purity, epitaxially grown silver on sodium chloride is found to be dependent on the size of the indentation for sizes below ≃10 μm. The measurement of the size effect has been made in two ways. In one, the hardness has been calculated from the load-displacement curve obtained from an instrumented microhardness testing machine and assuming a geometric self-similarity in the indenter shape. In the other measurement, the hardness was obtained from the load exerted by the microhardness tester divided by the indentation impression area as measured by atomic force microscopy. The observed variation in microhardness with indentation size is consistent with a simplified strain gradient plasticity model in which the densities of the geometrically necessary and statistically stored dislocations are fitting parameters. An equally good fit can also be made with a simple geometric scaling relationship. Transmission electron microscopy observations of a thin (≃50 nm) epitaxial gold film embedded in the silver layers revealed that the deformation was primarily restricted to the sharp edges of the indentation. In addition, deformation twinning within the indentation impression was observed on the {1H} planes.

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising technology that uses sunlight and water to produce renewable hydrogen with oxygen as a by-product. In the expanding field of PEC hydrogen production, the use of standardized screening methods and reporting has emerged as a necessity. This article is intended to provide guidance on key practices in characterization of PEC materials and proper reporting of efficiencies. Presented here are the definitions of various efficiency values that pertain to PEC, with an emphasis on the importance of solar-to-hydrogen efficiency, as well as a flow chart with standard procedures for PEC characterization techniques for planar photoelectrode materials (i.e., not suspensions of particles) with a focus on single band gap absorbers. These guidelines serve as a foundation and prelude to a much more complete and in-depth discussion of PEC techniques and procedures presented elsewhere.

Finite element simulation of conical indentation of a wide variety of elastic-plastic materials has been used to investigate the influences of pileup on the accuracy with which hardness and elastic modulus can be measured by load and depth-sensing indentation techniques. The key parameter in the investigation is the contact area, which can be determined from the finite element results either by applying standard analysis procedures to the simulated indentation load-displacement data, as would be done in an experiment, or more directly, by examination of the contact profiles in the finite element mesh. Depending on the pileup behavior of the material, these two areas may be very different. When pileup is large, the areas deduced from analyses of the load-displacement curves underestimate the true contact areas by as much as 60%. This, in turn, leads to overestimations of the hardness and elastic modulus. The conditions under which the errors are significant are identified, and it is shown how parameters measured from the indentation load-displacement data can be used to identify when pileup is an important factor.

Carbon nanofibers (sometimes known as carbon filaments) can be produced in a relative large scale by the catalytic decomposition of certain hydrocarbons on small metal particles. The diameter of the nanofibers is governed by that of the catalyst particles responsible for their growth. By careful manipulation of various parameters it is possible to generate carbon nanofibers in assorted conformations and at the same time also control the degree of their crystalline order. This paper is a review of the recent advances made in the development of these nanostructures, with emphasis both on the fundamental aspects surrounding the growth of the material and a discussion of the key factors which enable one to control their chemical and physical properties. Attention is also given to some of the possible applications of the nanostructures which center around the unique blend of properties exhibited by the material.