RF/Microwave Non-Destructive Measurements of Electrical Properties of Semiconductor Wafers for Thermophotovoltaic Applications

A radio-frequency/microwave measurement system has been designed for non-contacting determination of sheet resistance and excess carrier lifetime of low-bandgap materials and junctions, specifically GaSb-based alloys for thermophotovoltaic (TPV) applications. The design incorporates RF circuitry in the 100--500 MHz frequency range and utilizes a Q-switched YAG laser at 1.32 microns to photo-generate electron-hole pairs and conductivity modulate the material and/or junction under test. Supplementary measurements with a GaAs pulsed diode laser at 904 nm provides a faster transient response with near-surface photogeneration. Initial measurements on GaSb substrates, Zn-diffused materials and epitaxially grown layers are presented and discussed

Patients' perceived needs of osteoarthritis health information: A systematic scoping review

Background: Optimal management of osteoarthritis requires active patient participation. Understanding patients’ perceived health information needs is important in order to optimize health service delivery and health outcomes in osteoarthritis. We aimed to review the existing literature regarding patients’ perceived health information needs for OA. Methods: A systematic scoping review was performed of publications in MEDLINE, EMBASE, CINAHL and PsycINFO (1990–2016). Descriptive data regarding study design and methodology were extracted and risk of bias assessed. Aggregates of patients’ perceived needs of osteoarthritis health information were categorized. Results: 30 studies from 2876 were included: 16 qualitative, 11 quantitative and 3 mixed-methods studies. Three areas of perceived need emerged: (1) Need for clear communication: terms used were misunderstood or had unintended connotations. Patients wanted clear explanations. (2) Need for information from various sources: patients wanted accessible health professionals with specialist knowledge of arthritis. The Internet, whilst a source of information, was acknowledged to have dubious reliability. Print media, television, support groups, family and friends were utilised to fulfil diverse information needs. (3) Needs of information content: patients desired more information about diagnosis, prognosis, management and prevention. Conclusions: Patients desire more information regarding the diagnosis of osteoarthritis, its impact on daily life and its long-term prognosis. They want more information not only about pharmacological management options, but also non-pharmacological options to help them manage their symptoms. Also, patients wanted this information to be delivered in a clear manner from multiple sources of health information. To address these gaps, more effective communication strategies are required. The use of a variety of sources and modes of delivery may enable the provision of complementary material to provide information more successfully, resulting in better patient adherence to guidelines and improved health outcomes

PP/ABS Blends with Carbon Black: Morphology and Electrical Properties

Phase morphology of melt-mixed polypropylene (PP)/acrylonitrile-butadiene-styrene (ABS) blends was found to be blend ratio dependent, viz., matrix-particle dispersed type of morphology which was observed up to 30 wt% of ABS level beyond which the morphology showed co-continuous type. The domain size of 80/20 PP/ABS blends was found to decrease significantly at 10 wt% carbon black (CB) level, and in case of 70/30 blends morphology was transformed into co-continuous type in the presence of CB, which was retained up to 60 wt% ABS. The finer morphological features were associated with the compatibilizing action of CB particles. Continuous network was achieved through aggregated CB particles predominantly in the PP phase wherein one could find CB-rich PP phase and CB-less PP phase. Solution experiments further supported the existence of CB particles preferentially in the PP phase. AC electrical conductivity measurements indicated a 3D network-like structure of CB aggregates in the co-continuous compositions which showed enhanced electrical conductivity as compared to the matrix-dispersed type of morphology in 80/20 PP/ABS blends which exhibited insulating behavior. On increasing ABS content in the blends the electrical conductivity decreased progressively due to a difficulty in retaining 3D continuous network of CB aggregates especially at 40/60 composition. Increased processing temperature led to a higher electrical conductivity in the respective blends. Dielectric measurements revealed the existence of metallic type of conduction in the co-continuous compositions. However, 80/20 blends showed low epsilon' value. Overall, structure property relationship studies were conducted in PP/ABS blends with CB. (C) 2009 . J Appl Polym Sci 112: 998-1004, 200

Blends of Polypropylene and Ethylene Octene Comonomer with Conducting Fillers: Influence of State of Dispersion of Conducting Fillers on Electrical Conductivity

Blends of polypropylene/ethylene octene comonomer (PP/EOC) with conducting fillers viz., carbon black (CB) and multiwall carbon nanotubes (MWNT) were prepared using melt mixing technique with varying filler concentration and blend compositions. Thermo gravimetric analysis studies indicated that presence of filler enhanced the thermal stability of PP/EOC blends. Morphological analysis revealed the formation of matrix-dispersed droplet and co-continuous type of morphology depending on the blend compositions. Significant reduction in droplet size and finer ligament thickness in co-continuous structure were observed in the blends with filler due to compatibilization action. Fillers were found to be aggregated in the EOC phase irrespective of blends compositions and could be related to the affinity of the fillers toward EOC phase. The electrical conductivity of PP/EOC blends with CB and MWNT was found to be highest for 80/20 composition and decreased as EOC content increased. The percolation threshold of CB was between 10 and 15 wt% for the 80/20 and 70/30 blends whereas it was 15-20 wt% for blends with EOC content higher than 30 wt%. The percolation threshold was 2-3 wt% MWNT for PP/EOC blends. This was attributed to the aggregated filler network preferentially in the EOC phase. The melt-rheological behavior of PP/EOC blends was significantly influenced in presence of both the fillers. POLYM. ENG. SCI., 49:1502-1510, 2009. (C) 2009 Society of Plastics Engineer

Highly Transparent Thermoplastic Elastomer From Isotactic Polypropylene and Styrene/Ethylene-Butylene/Styrene Triblock Copolymer: Structure-Property Correlations

Polypropylene (PP) is one of the most useful general purpose plastics. However, the poor transparency and brittleness of PP restricts its applications in the field of medical and personal care where silicone and polyvinyl chloride (PVC) are presently used. This work concentrates on developing highly transparent elastomeric PP blends and also thermoplastic elastomer by blending isotactic polypropylene (I-PP) with styrene/ethylene-butylene/styrene (SEBS) triblock copolymer. PP/SEBS blend derived from high melt flow index (MFI) PP and high MFI SEBS exhibit remarkable transparency (haze value as low as 6%) along with good percentage of elongation and processability. The reduction in difference of refractive index (RI) between PP and SEBS has been observed by blending SEBS with PP. The wide angle X-ray diffraction studies show that there is significant reduction in the percentage crystallinity of PP by the addition of SEBS block copolymer. Temperature-dependent polarized light microscopy studies reveal the reduction in spherulites size by the addition of SEBS block copolymer. Transmission electron micrographs show that the SEBS polymer forms a fine lamellar structure throughout the PP matrix with phase inversion at higher SEBS concentration. Development of phase morphology, crystalline morphology, and crystallinity in different blends has been analyzed and microstructure-haze correlations have been developed. POLYM. ENG. SCI., 50:331-341, 2010. (C) 2009 Society of Plastics Engineer

RF photoreflectance characterization of binary and quasi-binary substrates and antimonide-based TPV devices

Both starting substrates and complete TPV device structures have been characterized using a radio-frequency (RF) photoreflectance technique, in which a Nd-YAG pulsed laser is used to excite excess carriers, and the short-pulse response and photoconductivity decay are monitored with an inductively-coupled non-contacting RF probe. The initial exponential transient decay, indicative of bulk recombination and surface recombination mechanisms as demonstrated previously for doubly-capped sample structures, is approximately 30--40 ns for GaSb substrates, with the decay constant increasing with increasing optical excitation (similar to Shockley-Read-Hall (SRH) high injection behavior). In the InGaAsSb quasi-binary substrates two distinct decays are observed, an initial decay transient of 15--20 ns which is independent of optical intensity and a subsequent decay of 30--60 ns which decreases with increasing optical intensity. This latter dependence on optical intensity was observed with doubly-capped epitaxial layers and is indicative of radioactive recombination. Similar measurements on quaternary device structures indicate that both the pulse amplitude and initial decay are reduced significantly without a front-surface capping layer that reduces surface recombination velocity. With reduction of the front surface recombination velocity, initial decays of 20--25 ns were obtained under open-circuit conditions. These results indicate that the RF photoreflectance technique can be useful in characterizing and qualifying starting substrates and can be used to qualify epitaxial structures as well, particularly when doubly-capped standards are available for initial understanding of recombination processes in the material systems being investigated

RF Photoreflectance Characterization of Binary and Quasi-Binary Substrates and Antimonide-Based TPV Devices

Both starting substrates and complete TPV device structures have been characterized using a radio-frequency (RF) photoreflectance technique, in which a Nd-YAG pulsed laser is used to excite excess carriers, and the short-pulse response and photoconductivity decay are monitored with an inductively-coupled non-contacting RF probe. The initial exponential transient decay, indicative of bulk recombination and surface recombination mechanisms as demonstrated previously for doubly-capped sample structures, is approximately 30--40 ns for GaSb substrates, with the decay constant increasing with increasing optical excitation (similar to Shockley-Read-Hall (SRH) high injection behavior). In the InGaAsSb quasi-binary substrates two distinct decays are observed, an initial decay transient of 15--20 ns which is independent of optical intensity and a subsequent decay of 30--60 ns which decreases with increasing optical intensity. This latter dependence on optical intensity was observed with doubly-capped epitaxial layers and is indicative of radioactive recombination. Similar measurements on quaternary device structures indicate that both the pulse amplitude and initial decay are reduced significantly without a front-surface capping layer that reduces surface recombination velocity. With reduction of the front surface recombination velocity, initial decays of 20--25 ns were obtained under open-circuit conditions. These results indicate that the RF photoreflectance technique can be useful in characterizing and qualifying starting substrates and can be used to qualify epitaxial structures as well, particularly when doubly-capped standards are available for initial understanding of recombination processes in the material systems being investigated

Propriedades mecânicas e morfologia de blendas de polipropileno com Tpes Morphology and mechanical properties of polypropylenes/Tpes blends

Blendas de polipropileno e elastômeros termoplásticos (TPEs), estireno-b-butadieno-b-estireno (SBS) e estireno-b-etileno-co-butileno-b-estireno(SEBS) foram preparadas com o objetivo de avaliar a influência do tipo e da concentração do elastômero nas propriedades mecânicas e na morfologia das blendas. Foram utilizados dois tipos de polipropileno, um homopolímero de propileno (PP-H) e um copolímero randômico de propileno-etileno (PP-R), sendo avaliado também o efeito das características da matriz termoplástica. O elastômero termoplástico aumentou a resistência ao impacto do PP, e a variação da rigidez das blendas foi dependente somente da quantidade de TPE adicionada, sendo estas comparativamente mais rígidas que aquelas com igual teor de elastômero convencional, tipo EPDM e EPR. A blenda com melhor balanço rigidez-impacto foi aquela de PP-R com 10% de SEBS. As blendas do copolímero de propileno-etileno com os TPEs apresentaram maior deformação do que aquelas com o homopolímero, devido à natureza menos cristalina da matriz do copolímero de propileno. As blendas tanto do homo quanto do copolímero de propileno com SEBS ficaram mais homogêneas em função da maior afinidade do bloco central poliolefínico EB (etileno-co-butileno) do primeiro com a região amorfa da matriz, sendo esta mais significativa no PP-R.<br>Blends of polypropylene and thermoplastic elastomers (TPEs) of styrene-butadiene-styrene (SBS) and styrene-ethylene-co-butene-styrene (SEBS) triblock copolymers were prepared to evaluate the effect of the elastomer and its concentration on the material properties. For this purpose, a polypropylene homopolymer (PP-H) and a propylene-ethylene random copolymer (PP-R) were used to evaluate the matrix effect on the tensile properties and morphology of the blends. The addition of TPEs to PP promotes increase on impact resistance and the PP-R/SEBS 10%wt blend showed the best balance in stiffness-impact resistance. The morphology of binary blends was similar to elastomeric domains dispersed into the PP matrix and changed as the TPE type and concentration varied. The size of SEBS domains was more homogeneous than the SBS' in both PP matrices due to the high affinity between the polyolefinic EB (ethylene-butene) middle block of the SEBS with the PP amorphous fraction