bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of mechanical properties and microstructure of weld nugget between weld-bonded and spot-welded dual-phase steel
Authors: Zhang Y S , Sun H T , Chen G L , Lai X M
Published: June 2009

Weld bonding, which is a combination of resistance spot welding and adhesive bonding, is finding application in vehicle structures that involve advanced high-strength steels. The strength of weld-bonded specimens is attributed to the strength of the weld nugget and adhesive strength. The existence of an insulating epoxy adhesive layer causes a rise in contact resistance and current density during the welding stage, and thus enhances the heat input. The aim of the present study is to explore the mechanical properties and microstructure of the weld nugget in weld-bonded dual-phase steel by means of comparison with a spot-welded nugget. Tensile-shear tests, weld lobe determination, microstructural characterization, and microhardness tests of weld-bonded and spot-welded specimens were conducted. The results of tensile-shear tests show that the weld nuggets of weld-bonded specimens have a higher tensile-shear force and energy absorption, and exhibit button-pullout fracture more easily at lower welding current. The weld lobe of weld-bonded dual-phase steel is too narrow. The results of microstructural characterization and microhardness tests indicate that, compared with resistance spot welding specimens, weld-bonded specimens have a larger nugget size at lower current; finer martensite and lower hardness in the heat-affected zone; and slightly more ferrite and lower hardness in the fusion zone. The comparative results are useful for optimizing the processing parameters and improving the weld quality of weld bonding.
Diffusion model for thin layer drying process of corn
Authors: Hacihafizoğlu O , Cihan A , Kahveci K , Korkmaz C
Published: June 2009

In this study, single-layer drying behaviour of corn is simulated by liquid diffusion model by using the experimental data for drying temperatures between 40 and 70 °C and for a drying rate of 2 m/s. Three different geometries representing a corn grain, slab, sphere, and cylinder are taken into consideration to specify the geometry which yields best results. The drying curves are obtained by minimizing the sum of squared differences between experimental data and theoretical predictions. Results show that drying behaviour of corn can be modelled reasonably by liquid diffusion model and that the solution based on sphere geometry is in better agreement with the experimental drying behaviour as compared with other geometries. The results also show that the temperature and the movement velocity of moisture from the inner part of corn grains towards the outer part have a quite significant effect on the drying rate.
On minimizing derailment risks and consequences for passenger trains at higher speeds
Authors: Brabie D , Andersson E
Published: June 2009

The first part of this article deals with the possibility of preventing wheel climbing derailments after an axle journal failure by implementing mechanical restrictions between the wheelsets and the bogie. A multi-body system (MBS) computer model is developed to account for such an axle failure condition, which is successfully validated by comparing the pre-derailment sequence of events with two authentic cases. An extensive parameter analysis on the maximum vertical and longitudinal play between the wheelset and the bogie, required to prevent a high-speed power or trailer car to derail, is performed for various combinations of running conditions in curves.

Once an actual derailment has occurred on conventional passenger trains at 200 km/h, extensive MBS simulations are performed on the feasibility of utilizing alternative substitute guidance mechanisms, such as low-reaching parts of bogie frame, axle box, or brake disc, as means of minimizing the lateral deviation. Results are presented in terms of geometrical parameters that lead to a successful engagement with the rail for a total of 12 different derailment scenarios. These are caused by an axle journal failure, an impact with a small object on the track, or a high rail failure. Minimizing the lateral deviation is also investigated by means of restraining the maximum coupler yaw angle and altering the bogie yaw stiffness. Time-domain simulations are also performed in terms of lateral track forces and derailment ratio when negotiating a tight horizontal ‘ S-curve’. Further, the articulated train concept is investigated in terms of the post-derailment vehicle behaviour after derailments on tangent and curved track at a speed of 200 km/h. In this respect, a trainset consisting of one power car and four articulated passenger trailer cars is modelled in the MBS software. Results in terms of lateral deviation and maximum carbody roll angle are presented as a function of different inter-carbody damper characteristics and running gear features. The feasibility of these damper characteristics is also tested in terms of lateral track forces and derailment ratio when negotiating a tight horizontal S-curve.
A genetic-algorithm-based approach for scheduling the renewal of railway track components
Authors: Zhao J , Chan A H C , Burrow M P N
Published: June 2009

This article describes a procedure that may be used to help synchronize the renewal of railway track components so that the costs of the renewal processes are minimized. To this end a model has been developed to maximize the cost benefit by combining renewal activities for a section of track. As the problem may be considered to be a mixed integer program with constrains, a genetic algorithm (GA)-based approach was used to find the solution. Techniques that may be used to reduce the computational effort required to perform the analysis are also described. The applicability of the approach to optimize the renewal of railway track components is shown by means of an example.
The application of a systematic approach to material selection for the lightweighting of metro vehicles
Authors: Carruthers J J , Calomfirescu M , Ghys P , Prockat J
Published: June 2009

With reduced operational energy consumption as the primary driver, a cross-industry consortium of vehicle manufacturers has explored some of the issues surrounding the introduction of lightweight materials into metro vehicles. Taking today's vehicles as the starting point, the aim of the study was to examine the current barriers that need to be removed or overcome in order to realize the economic and environmental benefits of lightweight materials.

From a technical perspective, the use of a systematic approach to material selection is described that matches the design requirements and constraints of a given application to potentially suitable candidate materials within a large database. The approach is illustrated by a case study in which a 57 per cent mass saving is achieved for a metro vehicle interior grab rail.

Estimates are also provided for the magnitude of the operational energy and cost savings that can be achieved through metro vehicle lightweighting. For the particular scenario considered in this article, a 10 per cent reduction in vehicle mass was estimated to equate to a 7 per cent saving in energy consumption and a corresponding 100 000 € annual operational cost saving per vehicle. Such data can now be used to support decision making with respect to the benefits of lightweighting.
Fuzzy variable structure control based on a Takagi-Sugeno model for permanent-magnet synchronous motors
Authors: Zhang X Z , Wang Y N
Published: June 2009

A fuzzy variable structure control (FVSC) scheme based on a Takagi-Sugeno (T-S) model is proposed in this paper for a permanent-magnet synchronous motor (PMSM) drive system in order to solve the speed tracking problem. A T-S fuzzy model is first formed to represent the non-linear system of the PMSM. To convert the tracking control into a stabilization problem, a new control design is proposed to define the internal desired states. Then, an FVSC controller for the PMSM system with parameter variation and load disturbances is designed on the basis of this fuzzy model. The FVSC scheme can drive the dynamics of the PMSM into a designated sliding surface in finite time, and guarantee the property of asymptotical stability. It is also shown that information on the upper bound of modelling errors, as well as on perturbations, is not required when using the FVSC controller. The performance of the proposed controller is verified by simulation and experimental results on a PMSM system.
Fully coupled seakeeping, slamming, and whipping calculations
Authors: Tuitman J T , Malenica Š
Published: June 2009

This paper presents a methodology to solve the seakeeping, slamming, and whipping problems coupled within a single calculation. The coupled problem is solved within a partly non-linear time domain seakeeping program. The elastic modes used in this hydroelastic problem can be calculated using a beam model or full three-dimensional (3D) finite element model of the ship structure.

The slamming loading is calculated by a two-dimensional (2D) method. The main focus of this paper is the creation of an accurate and consistent coupling between the 3D seakeeping program and the 2D slamming calculation. Differences in timescale and integration methods make this coupling complex.

A large container ship is used to illustrate the application of the presented methodology. The contribution of the non-linearities and the whipping response to the expected maximum bending moment and fatigue damage of this ship for a full-wave scatter diagram is calculated. The results show that the slamming-induced whipping response has a significant contribution to both the ultimate bending moment and the fatigue loading of the ship.
Experimental study of compensation for the effect of temperature on a silicon micromachined gyroscope
Authors: Zhu X-H , Chu H-J , Shi Q , Qiu A-P , Su Y
Published: June 2009

The drift rate temperature sensitivity Dt of a silicon micromachined gyroscope can be greatly reduced by compensation, so that the gyroscope can achieve high performance over a wide temperature range. A new experimental process for establishing the temperature—voltage model of the gyroscope used in compensation is introduced. First, a temperature sensor is placed inside the silicon micromachined gyroscope and the gyroscope is placed in a temperature-controlled chamber. Second, the ambient temperature of the gyroscope is changed by adjusting the temperature in the chamber, and the temperature inside the gyroscope and the gyroscope output voltage are acquired simultaneously. Finally, the temperature—voltage model of the gyroscope used in compensation can be established by the data obtained. By the above experimental process, the experiment time may be greatly shortened. A temperature-sensing system for implementing the given experiment for a silicon micromachined gyroscope is established, and a compensation model is developed on the basis of the numerous experimental data acquired during this process. Through compensation, the gyroscope sensitivity Dt is reduced from 229.1°/h per°C (before compensation) to 35.7°/h per°C (after compensation), that is, by 84.4 per cent, and the turn-on time of the gyroscope is reduced, with improved bias stability.
Ultimatum Deadlines
Authors: Tang Wenjie , Bearden J. Neil , Tsetlin Ilia
Published: June 2009

An important characteristic of any offer is the deadline at which it expires. We consider an ultimatum deadline game in which the proposer's decision variable is the offer deadline, while the responder faces a standard finite-horizon search problem. We show that the responder's strategy is characterized by a shortest acceptable deadline: at the time of deadline, he accepts an offer if the deadline is longer than his shortest acceptable deadline, and rejects it otherwise. If the proposer has all information available to the responder, the optimal deadline is the responder's shortest acceptable deadline. If the proposer is uncertain about the responder's situation, the optimal deadline gets longer, unless this uncertainty is very large. After normative analysis of the deadline setting problem, we present results from a behavioral study of the game. The average shortest acceptable deadline set by the responders equals the one that would maximize the expected value, whereas the proposers tend to set deadlines that are too short. The prescriptive conclusion for a proposer, emerging from the model and the experiment, is that in case of uncertainty it is better to set a deadline longer than what would be optimal if uncertainty were ignored.
Direct and indirect effects of parents' education on reading achievement among third graders in Sweden
Authors: Myrberg Eva , Rosén Monica
Published: June 2009

Background Cultural capital in families and especially, the educational level of parents, has during the last decades been found to be the most important dimension of socio‐economic influence on school performance. How the transmission of cultural capital over generations is concretized is however not yet fully investigated.

Aims The aim is to unfold the influence of home background and more specifically, to reveal some important mediating factors between the educational levels of parents and the reading achievement levels of children.

Sample Data comes from the Swedish participation in Progress in International Reading Literacy Study 2001 conducted by the The International Association for the Evaluation of Educational Achievement and comprises some 10,000 students in grade 3.

Methods The effects of parents' education on reading achievement are estimated with structural equation modelling.

Results The results reveal that the total effect of parents' education is substantial and that almost half of this effect is mediated through other variables, i.e. the number of books at home, early literacy activities, and emergent literacy abilities at the time for school start. The article thus identifies some of the mechanisms through which parents' education exert an influence on children's literacy development.

Conclusions Cultural reproduction starts in the very early childhood, in informal settings where reading aloud is an important activity. The knowledge of written language that children have at the time for school‐start influences further reading acquisition.
Performance of First-Trimester Screening between Gestational Weeks 7 and 13
Authors: Tørring Niels
Published: June 2009

Background: Screening for fetal chromosome abnormalities in the first trimester includes analysis of the serological markers pregnancy-associated plasma protein A (PAPP-A) and free β human choriogonadotropin (free β hCG). The blood sample is traditionally taken around week 12 of gestation, but the performance of earlier blood sampling is not well documented.

Methods: We studied 44 537 singleton pregnancies. Complete first-trimester screening took place between November 2003 and March 2009, and blood samples were taken between 7 weeks + 5 days and 13 weeks + 6 days.

Results: Of 120 cases of trisomy 21, 108 were diagnosed in the first-trimester screening (detection rate 90%). When the blood sample was taken before gestational week 10, the detection rate of trisomy 21 was 97% (70 of 72), whereas 80% were detected (38 of 48) after week 10 (χ2 = 0.0035). For trisomy 18, trisomy 13, and triploidy, 65% (13 of 20) were detected before gestational week 10, and 73% (11 of 15) after (not significant). All 6 cases of triploidy before and after gestational week 10 were detected. The screen positive rate and the maternal age were similar before and after week 10 of gestation.

Conclusions: Screening for fetal aneuploidy can be performed with good results with the blood sample taken as early as week 7 of gestation. Blood samples taken before gestational week 10 showed a high detection rate of fetal trisomy 21, with no difference in the detection of fetal trisomy 18, trisomy 13, or triploidy.
Is a Man's Car More Important than a Battered Woman's Body? Human Rights and Punishment for Violent Crimes against Female Spouses
Authors: First Anat , Agmon-Gonnen Michal
Published: June 2009

The study examines, through textual analysis, the narrative of verdicts in violent crimes of men against their female spouses in Israel, and compares them with vehicle-related crimes through an examination of human rights discourse. The comparison with vehicle-related crimes, taken from other legal discourse of property crimes, was selected in order to examine whether the rights to life and dignity include women, or whether women are perceived as property akin to a vehicle. Moreover, the article clarifies whether the position of women in legal discourse in Israel has changed from subject to object, whereas vehicles have changed from object to subject.
A New Systematic Explanation of the Types and Mitigating Effects of Exculpatory Defenses
Authors: Staihar Jim
Published: June 2009

When someone performs a criminal act, there is a rebuttable presumption that she is particularly blameworthy and liable to a particularly severe punishment for the act. The presumption is rebutted when the criminal actor has an exculpatory defense. Such defenses mitigate how much a criminal actor is blameworthy and liable to be punished for her act. In this paper, I begin by spelling out a taxonomy of the main types of exculpatory defenses. Then I argue that a restorative signaling theory of punitive desert best explains why such defenses have their mitigating effects. According to the theory, how much someone is blameworthy and deserves to be punished for performing a criminal act corresponds to the severity of the burdens she is obligated to undertake to restore the conditions of trust she undermined by performing the act. The theory explains the mitigating effects of exculpatory defenses by explaining why they mitigate the severity of burdens that a criminal actor must undertake to fulfill the obligation of restoration she incurs from performing her act.
Thirst perception and arginine vasopressin production in a kindred with an activating mutation of the type 2 vasopressin receptor: the pathophysiology of nephrogenic syndrome of inappropriate antidiuresis
Authors: Gupta S , Cheetham T D , Lambert H J , Roberts C , Bourn D , Coulthard M G , Ball S G
Published: June 2009

Background

Activating mutations of the vasopressin receptor gene on the X chromosome cause the nephrogenic syndrome of inappropriate antidiuresis (NSIAD). We describe a male child who presented with persistent hyponatraemia and whose mother was also found to be hyponatraemic. She had learnt to avoid excess fluid consumption because of associated malaise. Both individuals had a subnormal ability to excrete a water load with mother also demonstrating a heightened sense of thirst at low serum osmolalities.

Results

Mother and child were found to have the previously characterised activating mutation (p.Arg137Cys) of the arginine vasopressin receptor type 2 gene (AVPR2), but had measurable levels of AVP when hyponatraemic.

Conclusions

We conclude that female carriers of activating mutations of the vasopressin receptor are susceptible to hyponatraemia and therefore need to be provided with advice regarding fluid intake. An altered thirst perception may increase susceptibility to hyponatraemia. We confirm that the presence of measurable amounts of AVP in patients with hyponatraemia does not exclude the diagnosis of  NSIAD.
FGF2 is crucial for the development of bovine luteal endothelial networks in vitro
Authors: Woad Kathryn J , Hammond Amanda J , Hunter Morag , Mann George E , Hunter Morag G , Robinson Robert S
Published: June 2009

The development of the corpus luteum requires angiogenesis, and involves the complex interplay between factors such as vascular endothelial growth factor A (VEGFA), fibroblast growth factor 2 (FGF2) and platelet-derived growth factor (PDGF). However, the relative role of these factors remains to be elucidated. This study used a new physiologically relevant mixed luteal cell culture system to test the hypotheses that: a) FGF2 and VEGFA are critical for bovine luteal angiogenesis; and b) local luteal PDGF signalling stimulates the formation of endothelial networks. Cells were treated with receptor tyrosine kinase inhibitors against VEGFA (SU1498), FGF2 (SU5402) or PDGF (AG1295) activity. After 9 days in culture, endothelial cells were immunostained for von Willebrand factor (VWF) and quantified by image analysis. Highly organised intricate endothelial networks were formed in the presence of exogenous VEGFA and FGF2. The inhibition of FGF2 activity reduced the total area of VWF staining versus controls (>95%;P<0.001). Inhibition of VEGF and PDGF activity reduced the endothelial network formation by more than 60 and 75% respectively (P<0.05). Progesterone production increased in all treatments from day 1 to 7 (P<0.001), and was unaffected by FGF2 or PDGF receptor kinase inhibition (P>0.05), but was reduced by the VEGF receptor inhibitor on days 5 and 7 (P<0.001). In conclusion, this study confirmed that VEGF signalling regulates both bovine luteal angiogenesis and progesterone production. However, FGF2 was crucial for luteal endothelial network formation. Also, for the first time, this study showed that local luteal PDGF activity regulates bovine luteal endothelial network formationin vitro.
Ca2+-stores in sperm: their identities and functions
Authors: Costello Sarah , Michelangeli Francesco , Nash Katherine , Lefievre Linda , Morris Jennifer , Machado-Oliveira Gisela , Barratt Christopher , Kirkman-Brown Jackson , Publicover Stephen
Published: June 2009

Intracellular Ca2+stores play a central role in the regulation of cellular [Ca2+]iand the generation of complex [Ca2+] signals such as oscillations and waves. Ca2+signalling is of particular significance in sperm cells, where it is a central regulator in many key activities (including capacitation, hyperactivation, chemotaxis and acrosome reaction) yet mature sperm lack endoplasmic reticulum and several other organelles that serve as Ca2+stores in somatic cells. Here, we review i) the evidence for the expression in sperm of the molecular components (pumps and channels) which are functionally significant in the activity of Ca2+stores of somatic cells and ii) the evidence for the existence of functional Ca2+stores in sperm. This evidence supports the existence of at least two storage organelles in mammalian sperm, one in the acrosomal region and another in the region of the sperm neck and midpiece. We then go on to discuss the probable identity of these organelles and their discrete functions: regulation by the acrosome of its own secretion and regulation by membranous organelles at the sperm neck (and possibly by the mitochondria) of flagellar activity and hyperactivation. Finally, we consider the ability of the sperm discretely to control mobilisation of these stores and the functional interaction of stored Ca2+at the sperm neck/midpiece with CatSper channels in the principal piece in regulation of the activities of mammalian sperm.
Structural change without trust: Reform cycles in Hungary and Slovakia
Authors: Győrffy D.
Published: June 2009

The recent admission of Slovakia into the Economic and Monetary Union (EMU) stands in sharp contrast with the considerable difficulties faced by Hungary with the fulfilment of the Maastricht criteria. This is a puzzling development for two reasons: first, during the early phase of the transition process Hungary was ahead of Slovakia, and second, the high level of political polarisation and general public disillusionment are shared characteristics of the two countries and not conducive to reforms in either case. In order to address these contradictions a theoretical framework is developed examining the conditions of structural reforms in a low-trust environment, where promises about long-term benefits for short-term costs are not believed. After the identification of three potential factors — perception of crisis, emergence of credible reformers, elite consensus — that can help to overcome the gap in credibility, the theoretical framework is applied to the transition history of the two countries. It is shown that while in the past decade all three factors had been present in Slovakia, the former success of Hungary strongly contributed to the absence of such special circumstances. The continued divergence of the two countries, however, cannot be taken for granted as in both cases reform cycles rather than sustainable progress can be observed. In order to ensure sustainability the difficult tasks of consensus- and trust-building cannot be avoided.
Effect of disutility on prices together with income changes in the context of a durable goods monopoly
Authors: Maçãs Nunes P.
Published: June 2009

In this article, we study the effect of disutility of consumers who do not buy certain durable goods at the present time with income variations on the behaviour over time of prices in the context of a Durable Goods Monopoly facing a continuous demand. If consumers do not foresee future changes in their income, price always decreases. However, greater disutility contributes to softening the price fall in the present, never reaching marginal cost at that moment. Consumers’ perspective for future changes to income has two major implications: 1) the durable goods monopoly, depending on disutility, can set a price equal to marginal cost at the present time if the perspective is for income growth in the future, something which never happens if reduced income is foreseen; and 2) it increases the tendency of a rise in price depending on disutility. We conclude that a price rise may be obtained for quite small disutility when the predicted increase in income is moderate and for moderate disutility, when the predicted increase in income is high.
Photonic Crystal Back Reflector in Thin-film Silicon Solar Cells
Authors: Isabella Olindo , Lipovšek Benjamin , Krč Janez , Zeman Miro
Published: June 2009

One-dimensional photonic crystals having desired broad region of high reflectance (R) were fabricated by alternating the deposition of amorphous silicon and amorphous silicon nitride layers. The effect of the deposition temperature and angle of incidence on the optical properties of photonic crystals deposited on glass substrate was determined and an excellent matching was found with the simulated results. The broad region of high R of photonic crystals deposited on flat and textured ZnO:Al substrates decreases when compared to the R of photonic crystals de-posited on glass. The performance of amorphous silicon solar cells with 1-D photonic crystals integrated as the back reflector was evaluated. The external quantum efficiency measurement demonstrated that the solar cells with the photonic crystals back reflector had an enhanced re-sponse in the long wavelength region (above 550 nm) compared to the cells with the Ag reflector.
Modeling the Grain Size Distribution during Solid Phase Crystallization of Silicon
Authors: Bill Andreas , Teran Anthony V , Bergmann Ralf B
Published: June 2009

We analyze the grain size distribution during solid phase crystallization of Silicon thin films. We use a model developed recently that offers analytical expressions for the time-evolution of the grain size distribution during crystallization of a d-dimensional solid. Contrary to the usual fit of the experimental results with a lognormal distribution, the theory describes the data from basic physical principles such as nucleation and growth processes. The theory allows for a good description of the grain size distribution except for early stages of crystallization. The latter case is expected and discussed. An important outcome of the model is that the distribution at full crystallization is determined by the time-dependence of the nucleation and growth rates of grains. In the case under consideration, the theory leads to an analytical expression that has the form of a lognormal-type distribution for the fully crystallized sample.
Low-temperature Fabrication of a Crystallized Si Film Deposited on a Glass Substrate using an Yttria-stabilized Zirconia Seed Layer
Authors: Herman Sukreen Hana , Horita Susumu
Published: June 2009

We have been investigating fabrication of a crystallized Si (c-Si) film deposited on a glass substrate at low temperature, using a poly-yttria-stabilized zirconia (poly-YSZ) film as a seed layer. It can be expected that the crystallographic information of the YSZ layer transmits to the deposited Si film so that it stimulates its crystallization even at lower temperature. To reduce the crystallization temperature further, we focused on the surface treatment of the YSZ layer, in which it was dipped in the HF solution, followed by rinsing with deionized water (DIW) or with ethanol.

After depositing the poly-YSZ layer by reactive magnetron sputtering on the quartz glass substrate, the Si film was deposited directly on it by e-beam vacuum evaporation in <10-6 Pa. The Raman spectra of the Si films deposited at 430 °C on the ethanol-rinsed glass without YSZ layer and on the DIW-rinsed YSZ layer showed amorphous phase. However, on the ethanol-rinsed YSZ layer, they showed a strong peak of c-Si of the deposited film, even at 350 °C, and indicated the beginning of the crystallization at 320 °C. This means that the YSZ layer enhanced the Si film crystallization, and that the ethanol-rinse was effective for low-temperature crystallization. The crystalline fraction of the Si film varied with the yttria content and the surface treatment of the YSZ layer prior to the Si film deposition. From the XPS results, we found out that fluorine F were adsorbed on the surface and were bonded with the Y. The Y 3d and F 1s peaks observed from the ethanol-rinsed YSZ were higher than those of the DIW rinse, which suggests that the Y and adsorbed F on the surface were removed by the DIW rinse, but remained even after the ethanol rinse. Based on the Raman and XPS results, we can speculate that the excessive amount of F on the YSZ layer surface prior to the Si film deposition play an important role on the Si film crystallization. We observed the surface of the Secco-etched Si/YSZ films deposited at 320, 350, and 430 °C by SEM. The number of crystallized Si grains was denser at higher temperature than that of lower temperature. That is, the Si film deposited at 430 °C was crystallized thoroughly on the whole substrate, but some regions of the Si films deposited at 350 and 320 °Cwere amorphous and removed by the Secco etching. The grain sizes were in the range from 20 to 40 nm, and the size at the lower deposition temperature was more uniform than the higher temperature. From SIMS observation, it was found that Zr atoms diffuse from the interface with the YSZ layer.
Observation of the Evolution of Etch Features on Polycrystalline ZnO:Al Thin-Films
Authors: Owen Jorj Ian , Hüpkes Jürgen , Bunte Eerke
Published: June 2009

The transparent conducting oxide (TCO) ZnO:Al is often used as the window layer and a source of light trapping in thin-film silicon solar cells. Light scattering in sputtered zinc oxide is achieved by wet chemical etching, which results in craters distributed randomly over the ZnO surface. To gain a better understanding of the etching process on ZnO thin films, a method for atomic force microscope (AFM) realignment between etching steps is developed. Using this method, the evolution of the HCl etch on a polycrystalline ZnO thin-film is observed. Results showed that this observation method did not modify the etching behavior, nor did stopping and restarting the etching change the points of attack, indicating that the points of HCl attack are built into the films as they are grown. Additionally, we investigated the evolution of the HCl etch on a ZnO surface previously etched in KOH, and found that the etch sites for both the acidic and basic solution are identical. We conclude that “peculiar” defects, which induce accelerated etching, are built into the film during growth, and that these defects can extend part or all the way though the thin-film in a similar way as screw dislocations in single crystalline ZnO.
In-Situ Observation of High Deposition Rate Hydrogenated Polymorphous Silicon Cell Degradation through Variable Intensity Method Measurements
Authors: Johnson Erik V , Kim Ka-Hyun , Roca i Cabarrocas Pere
Published: June 2009

The efficiencies of hydrogenated polymorphous silicon (pm-Si:H) solar cells have been previously demonstrated to show superior stability under light-soaking. This stability arises due to the fact that the decrease they show in fill factor (FF) is partially offset by an accompanying increase in open circuit voltage (VOC). Recently, high-deposition rate (9Å/s) pm-Si:H material deposited by standard RF-PECVD at 13.56MHz has been investigated as the intrinsic layer in photovoltaic modules as it has shown excellent electronic properties. The degradation behaviour of these high-deposition rate cells, however, differs significantly from that of lower deposition rate material. In particular, no beneficial increase in Voc is observed during light soaking. We investigate the degradation dynamics of solar cells made from this high growth rate material using a Variable Illumination Method (VIM) during light soaking to quantify the changes to these high-rate cells during light-soaking and directly contrast them with those of low-rate (1.5Å/s) cells. In particular, we discuss the importance of bulk recombination effects vs interface quality changes, as well as the dynamics of changes in VOC.
Low Temperature Si Homoepitaxy by a Reactive CVD with a SiH4/F2 Mixture
Authors: Minowa Akihisa , Kondo Michio
Published: June 2009

Single crystalline Si thin films on insulating substrates (SOI) have a variety of potential applications to such as high mobility TFT and to high efficiency and low cost solar cells. Since the SOI is limited to a thin layer, it is needed to develop a low temperature epitaxial growth technology to form active layers thicker than several micorns at low temperatures. The purpose of this study is to develop a deposition technique of single crystalline Si thin films by a reactive CVD method [1] at temperatures less than 600○C utilizing gas-phase reaction (SiH4, F2).
Deposition of Si films was performed on a single crystalline Si (100) wafer.
Substrate-temperature was varied between 100 and 700○C, reaction-pressure 1 and 500mTorr, flow-rate between SiH4/F2 = 1/1 and 1/3, and the geometry of the substrate and the gas-outlet were optimized.
First, it was found that deposition rate was sensitive to the distance between the
gas-outlet and the substrate and to the total pressure. For four different combinations of pressures, 250 and 500 mTorr and distances, 50 and 150 mm. The deposition took place only for the combination of 500 mTorr and 50 mm, and otherwise the deposition rate was significantly lower or etching of Si wafer was observed. The deposition rate for gas flow ratio, SiH4/F2 of 1/1 was 1.7 nm/s at a substrate-temperature of 400○C, while for higher F2 flow rate ratio, SiH4/F2 = 1/2 and 1/3, the deposition rates were 8.3×10-3 nm/s and etching, respectively.
Raman measurements show that crystallinity depends on the substrate-temperature; broad amorphous signal appears at 300, microcrystalline signal at 300 and 500○C and sharp crystalline at 400○C. RHEED observation shows a halo-pattern of amorphous-Si at 200○C, a mixed pattern of streak and spot without 2×1 superstructure at 300○C, a 2×1 streak-pattern at 400○C and a spot-pattern at 500○C. The reason of the narrow temperature window for epitaxial layer is a characteristic feature of low temperature epitaxy as reported before [2]. It is noteworthy the deposition rate of epitaxy obtained in this work is quite high, 1.7 nm/s even at 400○C.
These observations are ascribed to the gas phase reaction between SiH4 and F2 and successive surface reactions. The SiH4 and F2 cause an exothermic reaction in the gaseous phases to generate radicals such as SiHx, H and F. The SiHx acts as a film precursor and others act as etchant. Under the conditions which radical density ratio SiHx/F increases, therefore, the deposition rate decreases or etching occurs. The material properties also will be discussed in relation to the growth mechanism.
[1]J. Hanna et al., J. Non-Crst. Solids 114 (1989) 172-174
[2]T. Kitagawa, M. Kondo et al, Appl. Surf. Sci. 159-160 (2000) 30-34
Device Physics of Heterojunction with Intrinsic Thin Layer (HIT) Solar Cells
Authors: Kanevce Ana , Metzger Wyatt K.
Published: June 2009

Heterojunction with intrinsic thin layer (HIT) solar cells have achieved conversion efficiencies higher than 22%. Yet, many questions concerning the device physics governing these cells remain unanswered. We use numerical modeling to analyze the role of a-Si:H layers and tunneling on cell performance. For cells with n-type c-Si (n-HIT cells), incorporating the indium-tin-oxide (ITO) as an n-type semiconductor creates an n+/p/n structure. Most device simulations do not work with this structure. Our modeling indicates that the n+/p/n device often produces irregular S-shaped current density–voltage (J-V) curves, which have been observed experimentally but were not previously understood. However, if tunneling is included, there are specific conditions where the n+/p/n structure performs as a robust solar cell with efficiencies exceeding 20%. Additional analysis examines voltage-dependent carrier collection in n-HIT cells, as well as material and interface properties that limit fill factor.
In p-HIT cells, modeling the ITO layer as a semiconductor, rather than as a metallic contact, significantly reduces the impact of a-Si:H layer parameters on device performance. In p-HIT cells, the a-Si:H layers adjacent to the ITO layer play the role of a buffer that reduces interface recombination at the a-Si:H/c-Si interface and prevents tunneling of electrons from the ITO layer to the c-Si absorber. Tunneling through the a-Si:H layers adjacent to the back contact is important to attain regular J-V curves.
High Performance n- and p-channel Strained Single Grain Silicon TFTs using Excimer Laser
Authors: Baiano Alessandro , Ishihara Ryoichi , Beenakker Kees
Published: June 2009

In this paper we investigate the carriers mobility enhancement of the n- and p-channel single-grain silicon thin-film transistors (SG-TFTs) by μ-Czochralski process at low-temperature process (< 350 °C). The high laser energy density nearby the ablation phenomenon that completely melts the silicon layer during the crystallization is responsible for high tensile strain and good crystal quality of the silicon grains, which lead carriers mobility enhancement.
Raman Characterization of Protocrystalline Silicon Films
Authors: Syllaios A. J. , Ajmera S. K. , Tyber G. S. , Littler C. L. , Hollingworth R. E.
Published: June 2009

An increasingly important application of thin film hydrogenated amorphous silicon (α-Si:H) is in infrared detection for microbolometer thermal imaging arrays. Such arrays consist of thin α-Si:H films that are integrated into a floating thermally isolated membrane structure. Among the α-Si:H material properties affecting the design and performance of microbolometers is the microstructure. In this work, Raman spectroscopy is used to study changes in the microstructure of protocrystalline p-type α-Si:H films grown by PECVD as substrate temperature, dopant concentration, and hydrogen dilution are varied. The films exhibit the four Raman spectral peaks corresponding to the TO, LO, LA, and TA modes. It is found that the TO Raman peak becomes increasingly well defined (decreasing line width and increasing intensity), and shifts towards the crystalline TO energy as substrate temperature is increased, H dilution of the reactants is increased, or as dopant concentration is decreased.
Structural Properties of a-Si:H Films with Improved Stability against Light Induced Degradation
Authors: van Elzakker Gijs , Ŝutta Pavel , Zeman Miro
Published: June 2009

X-ray diffraction (XRD) analysis of thin silicon films was carried out using both the symmetric Bragg-Brentano and asymmetric thin-film attachment geometries. The asymmetric configuration allows quantitative phase analysis of the films and reveals that amorphous silicon films deposited from silane diluted with hydrogen have the strongest peak in the XRD patterns located around 27.5 degrees. This peak corresponds to the signal from ordered domains of tetragonal silicon hydride and not from cubic silicon crystallites. The full width at half maximum (FWHM) of this peak narrows from 5.1 to 4.8 degrees as the ratio of hydrogen to silane flow (R) increases to 20 and does not change significantly for higher hydrogen dilutions. The amorphous silicon films fabricated at different hydrogen dilution were applied as absorber layers in single-junction solar cells. Degradation experiments confirm a substantial reduction of the degradation when the dilution ratio is increased from R=0 to R=20. The light induced degradation of solar cells with absorber layers prepared at R > 20 is not further reduced by increasing R.
Fine Tuning of the Spectral Sensitivity in a-SiC:H Stacked p-i'i-n Graded Cells
Authors: Fantoni Alessandro , Fernandes Miguel , Louro Paula , Lavareda Guilherme , Carvalho Carlos N , Vieira Manuela
Published: June 2009

It is presented in this work a p(a-SiC:H)/i(a-SiC:H)/i((a-Si:H)/ n(a-Si:H) single junction for application in color sensing domain produced with the PECVD technique. The interest of this device resides in its simplicity of realization and utilization, as it takes advantage from the well known properties of the a-Si:H p-i-n junctions together with the possibility of color filtering by tailoring the optical gap of a-Si:H with the introduction of a small percentage of Carbon. The thicknesses of the i(200 nm) and i (1000 nm) layers are optimized for light absorption in the blue and red ranges, respectively. Measurements of the spectral response under forward and reverse polarization show a dependence of the wavelength of the maximum absorption on the intensity of the applied bias. A comparison of the photocurrent reading with and without a 650 nm background DC optical bias permits a complete separation of blue and red color under reverse and forward applied bias, respectively. The application of the LSP technique (AC regime of the optical bias) permits a complete RGB reading of the incoming light.
Simulation results obtained with the program ASCA will support and explain the measurements about spectral response and photocurrent reading under DC and AC regimes.
Laser-Induced Crystallization of SiGe MEMS Structural Layers Deposited at Temperatures Below 250°C
Authors: El-Rifai Joumana , Sedky Sherif , Wasfi Rami , Van Hoof Chris , Witvrouw Ann
Published: June 2009

This work is a step towards a viable process for poly-SiGe MEMS structural layers deposited at substrate temperatures below 250°C. Laser annealing was used for post-deposition layer treatment to realize poly-SiGe structural layers with the desired electrical and mechanical properties at low substrate temperatures. The technique uses a pulsed excimer laser beam for the local thermal treatment of a SiGe layer deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) at 210°C. By tuning the laser treatment and the film deposition conditions, 1-1.8 μm thick films having an electrical resistivity as low as 14.1 mΩ∙cm and optimal strain gradient in the range of -4.3×10-6to +6.8×10-6μm-1were realized.
The effect of active-layer thickness on the characteristic of nanocrystalline silicon thin film transistor
Authors: Kim Sun-Jae , Han Sang-Myeon , Kuk Seung-Hee , Lee Jeong-Soo , Han Min-Koo
Published: June 2009

We fabricated nc-Si TFTs in order to investigate the effect of the active-layer thickness on the characteristic of the nc-Si TFT. Bottom gate nc-Si TFTs were fabricated at 350°C using ICP-CVD. The thicknesses of the nc-Si layer were remained to 700, 1200 and 1700 Å. As the active-layer thickness increases, the mobility and the on-current level were not altered. However, the off-current level increased considerably and on/off ratio decreased. It may be attributed to highly doped characteristic of thick nc-Si film. As the nc-Si film thicker, the conductivity increases considerably and the Fermi level approaches to the conduction band minimum, which indicates the increases of doping level. The oxygen concentration shows high level of unintentional doping. Also, columnar growth of nc-Si film makes that the crystallinity of top region is much higher than that of bottom region. So, the conductivity of thick nc-Si film becomes high compared to that of thin nc-Si film. The structure of the nc-Si TFT with thick nc-Si film can be similar to the serial connection of N+, N- and N+ resistance, so that it suffers difficulty to suppress the off current and to secure high on/off ratio. Therefore, the off current can be suppressed by thinning of the high conducting active nc-Si layer and nc-Si TFT with channel thickness of 700 Å shows good on/off characteristic. It is deduced that bottom gate nc-Si TFT is necessary to have intrinsic channel layer as well as thin channel layer to reduce the leakage current.
1H NMR Study Of Hydrogenated Nanocrystalline Silicon Thin Films
Authors: Kiriluk Kristin G. , Bobela David C. , Su Tining , Yan Baojie , Yang Jeff , Guha Subhendu , Reyes Arneyl , Kuhns Philip , Taylor Craig
Published: June 2009

Hydrogenated nano-crystalline silicon (nc-Si:H) is a promising material for multi-junction solar cells. We investigated the local hydrogen environments in nano-crystalline silicon thin films by nuclear-magnetic-resonance (NMR). At room temperature, 1H NMR spectra have broader components than those observed in standard device grade hydrogenated amorphous silicon (a-Si:H). As the temperature decreases, the 1H NMR exhibits a broadening of the line shape attributed to hydrogen atoms at the interfaces between the amorphous silicon (a-Si) and the crystalline silicon (c-Si) regions. These results suggest that the local hydrogen structure in nc-Si:H is very different from that in a-Si:H. In particular, the hydrogen clusters contributing to broadened spectra may exist on the surfaces of the a-Si/c-Si interfaces which do not exist in the more dense matrix of a-Si:H and may contribute to certain unique optoelectronic properties of these nc-Si:H thin films. The dependence of the spin-lattice relaxation time (T1) on temperature, however, is very similar to that in a-Si:H, which indicates the spin-lattice relaxation mechanism, i.e via spin diffusion through molecular hydrogen, is common to both systems.
Near Infrared Fluorescent and Phosphorescent Organic Light-Emitting Devices
Authors: Yang Yixing , Farley Richard , Steckler Timothy , Sommer Jonathan , Eom Sang Hyun , Graham Kenneth , Reynolds John , Schanze Kirk , Xue Jiangeng
Published: June 2009

Organic light-emitting devices (OLEDs) emitting near-infrared (NIR) light have many potential applications, yet the efficiency of these devices remains very low, typically ˜0.1% or less. Here we report efficiency NIR OLEDs based on two fluorescent donor-acceptor-donor oligomers and a phosphorescent Pt-containing organometallic complex. External quantum efficiencies in the range of 0.5–3.8% with emission peak ranging from 700 to 890 nm have been achieved.
Spin Transport and Magneto-Resistance in Organic Semiconductors
Authors: Yunus Mohammad , Ruden P. P. , Smith Darryl L.
Published: June 2009

Calculated results for spin injection, transport, and magneto-resistance (MR) in organic semiconductors sandwiched between two ferromagnetic contacts are presented. The carrier transport is modeled by spin dependent device equations in drift-diffusion approximation. In agreement with earlier results, spin injection from ferromagnetic contacts into organic semiconductors can be greatly enhanced if (spin-selective) tunneling is the limiting process for carrier injection. Modeling the tunnel processes with linear contact resistances yields spin currents and MR that tend to increase with increasing bias. We also explore the possibility of bias dependent contact resistances and show that this effect may limit MR to low bias.