bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurocognitive functioning of preschool children with uncomplicated epilepsy
Authors: Rantanen Kati , Nieminen Pirkko , Eriksson Kai
Published: June 2009

Only few studies are available on the cognitive functioning of preschool children with uncomplicated epilepsy. The aim of this study was to describe the neurocognitive functioning of 3–6‐year‐old children with uncomplicated epilepsy. A subgroup of children with uncomplicated epilepsy from a population based cohort of preschool children with active epilepsy (N = 64) participated in the study. The neurocognitive functioning of these children (N = 13) was compared to that of matched healthy controls (N = 13). The Wechsler's Primary and Preschool Scale of Intelligence ‐ Revised and the Developmental Neuropsychological Assessment were administered. The intellectual functioning of the children with uncomplicated epilepsy was within normal range, but differed significantly from that of healthy controls, which was contrary to expectations. Statistically significant differences emerged between the study and the control group in Verbal IQ and Full Scale IQ, but no differences were found in Performance IQ. The children with uncomplicated epilepsy also had minor neurocognitive difficulties in verbal short‐term memory (p <.01) compared to healthy children. The result suggests that uncomplicated epilepsy in preschool children may interfere with language and verbal short‐term memory functions. Further studies with detailed neuropsychological assessments and follow‐up time are needed to gain more insight into the developmental course of children with uncomplicated epilepsy. Also, because of the developmental risks reported in this study, psychological screening and detailed neuropsychological assessment are recommended in clinical practice.
Comparative Analysis of PCR-Based Biomarker Assay Methods for Colorectal Polyp Detection from Fecal DNA
Authors: Ausch Christoph , Kim Young-Ho , Tsuchiya Karen D , Dzieciatkowski Slavomir , Washington Mary K , Paraskeva Christos , Radich Jerry , Grady William M
Published: June 2009

Background: Aberrantly methylated genes are promising biomarkers for the detection of colon adenomas and colorectal cancers (CRCs). The optimal assay type and specific methylated genes for these assays remain to be determined.

Methods: We used genomewide microarray-based assays to identify methylated genes as candidate biomarkers for colon neoplasms. The frequency of aberrant methylation of these genes in primary tumors was assessed with methylation-specific PCR (MSP). The limits of detection and specificities for different types of PCR-based assays were then assessed with the most promising genes identified in this screen. Finally, we assessed the best-performing MSP assay as an early-detection marker using fecal DNA samples.

Results: ITGA4 [integrin, alpha 4 (antigen CD49D, alpha 4 subunit of VLA-4 receptor)] was identified as a novel gene frequently methylated in CRC. Methylated ITGA4 is present in 75% of colon adenomas (n = 36) and 92% of colon adenocarcinomas (n = 75). Comparison of end point MSP, end point MSP with clamped primers, and quantitative fluorescent MSP (qMSP) approaches revealed that both types of end point MSP assays could routinely detect as little as 70 pg DNA, whereas the qMSP assay could routinely detect as little as 7 pg. A fecal DNA qMSP assay for methylated ITGA4 can detect 69% of individuals with colon adenomas (n = 13) with a diagnostic specificity of 79% (n = 28).

Conclusions: Methylated ITGA4 is a promising marker gene for the early detection of colonic neoplasms. qMSP has the lowest limit of detection of the MSP assay types tested, and a qMSP assay that detects methylated ITGA4 has potential as an early-detection assay for colon neoplasms.
CYP2D6 Genotyping for Functional-Gene Dosage Analysis by Allele Copy Number Detection
Authors: Hosono Naoya , Kato Mamoru , Kiyotani Kazuma , Mushiroda Taisei , Takata Sadaaki , Sato Hiroko , Amitani Hanae , Tsuchiya Yumiko , Yamazaki Keiko , Tsunoda Tatsuhiko , Zembutsu Hitoshi , Nakamura Yusuke , Kubo Michiaki
Published: June 2009

Background: Cytochrome P450 2D6 (CYP2D6), one of the most important drug-metabolizing enzymes, has been reported to possess variation in the encoding CYP2D6 gene (cytochrome P450, family 2, subfamily D, polypeptide 6) that affects enzymatic activity. For the pharmacogenetic study of CYP2D6, accurate measurement of the dosage of the functional gene is essential; however, current genotyping techniques are insufficient because of their inability to provide the exact copy number of functional CYP2D6 genes.

Methods: We developed 3 quantitative real-time PCR (qPCR) assays for estimating the total copy number of the CYP2D6 gene, as well as 24-multiplex PCR-based real-time Invader assays (mPCR-RETINAs) for estimating the allele ratio at each variation locus. After determining the allele copy number at each locus, we estimated the frequencies of CYP2D6 alleles in a population and the diplotype in each individual by a CNVphaser (copy number variation phaser). The qPCR assays and RETINAs used for HapMap Japanese and Chinese samples were applied to 455 Japanese individuals.

Results: Forty-two individuals (9.2%) had one CYP2D6 gene copy, 207 (45.5%) had 2 copies, 161 (35.4%) had 3 copies, 40 (8.8%) had 4 copies, and 5 (1.1%) had 5 copies of the CYP2D6 gene. We found 16 different CYP2D6 alleles, with frequencies similar to those described in previous reports. In the diplotype analysis, we observed that CYP2D6*1/*1 and *1/*10-*36 were the most common diplotypes (approximately 20%) in our population.

Conclusions: Our method is the first to determine the exact number of functional CYP2D6 gene copies. We believe our method will facilitate and accelerate the detailed pharmacogenetic analysis of CYP2D6.
Asymmetric Dimethylarginine Reference Intervals Determined with Liquid Chromatography–Tandem Mass Spectrometry: Results from the Framingham Offspring Cohort
Authors: Schwedhelm Edzard , Xanthakis Vanessa , Maas Renke , Sullivan Lisa M , Schulze Friedrich , Riederer Ulrich , Benndorf Ralf A , Böger Rainer H , Vasan Ramachandran S
Published: June 2009

Background: Accumulating evidence links higher circulating asymmetric dimethylarginine (ADMA) to greater risk of cardiovascular disease (CVD). Relatively small differences in ADMA concentrations between healthy individuals and those with disease underscore the need to formulate reference intervals that may aid risk stratification of individuals.

Methods: We formulated reference intervals for plasma ADMA concentrations using a community-based reference sample from the Framingham Offspring Study consisting of 1126 nonsmoking individuals [mean (SD) age 56 (9) years; 60% women] who were free of clinical CVD, hypertension, diabetes, and obesity and who attended a routine examination at which ADMA was assayed. ADMA concentrations were determined using a validated tandem mass spectrometry–liquid chromatography assay.

Results: In the study sample, the mean ADMA concentration was 0.52 (0.11) μmol/L, and the reference limits were 0.311 and 0.732 (2.5th and 97.5th percentile). The sex-specific reference limits were 0.310 and 0.745 in men and 0.313 and 0.721 μmol/L in women. In multivariable regression analysis, ADMA plasma concentrations were positively correlated with age and total plasma homocysteine (both P < 0.001).

Conclusions: Reference limits calculated for circulating ADMA in our large community-based healthy reference sample confirm the previous observation of a relatively narrow distribution of concentrations. This suggests a tight physiological control of ADMA plasma concentrations, presumably by dimethylarginine dimethylaminohydrolase (DDAH) metabolism of ADMA.
Multiplex Detection of 60 Hepatitis B Virus Variants by MALDI-TOF Mass Spectrometry
Authors: Luan Ju , Yuan Jing , Li Xiaohe , Jin Shengnan , Yu Ling , Liao Mingfeng , Zhang Hongmei , Xu Cheng , He Qing , Wen Bin , Zhong Xunhua , Chen Xinchun , Chan Henry L Y , Sung Joseph J Y , Zhou Boping , Ding Chunming
Published: June 2009

Background: Variations in the hepatitis B virus (HBV) genome may develop spontaneously or under selective pressure from antiviral therapy. Such variations may confer drug resistance or affect virus replication capacity, resulting in failure of antiviral therapy.

Methods: A duplex PCR was used to amplify the region of the reverse transcriptase gene, the precore promoter, and the basal core promoter of the HBV genome. Four multiplex primer-extension reactions were used to interrogate 60 frequently observed HBV variants during antiviral therapy. Automated MALDI-TOF mass spectrometry (MS) was used for mutation detection. Capillary sequencing was used to confirm the MS results.

Results: The limit of quantification was 1000 HBV copies/mL for multiplex detection of HBV variants. Fifty-three variants (88.3%) were analyzed successfully in at least 90% of the sera from 88 treatment-naive patients and 80 patients with virologic breakthrough. MS was able to detect twice as many minor variants as direct sequencing while achieving close to full automation. MS and direct sequencing showed only 0.1% discordance in variant calls.

Conclusions: This platform based on multiplex primer extension and MALDI-TOF MS was able to detect 60 HBV variants in 4 multiplex reactions with accuracy and low detection limits.
Contribution of the Bituminous Mortar and Stone Skeleton to the Resistance to Permanent Deformation in Asphalt Mixtures
Authors: Muraya P. M. , Molenaar A. A. A. , van de Ven M. F. C.
Published: June 2009

This paper describes the results of a research that was conducted to investigate the contribution of the different components in an asphalt mixture to the resistance to permanent deformation. As part of this research, extensive triaxial tests were performed on the stone skeletons of dense, stone mastic, and porous asphalt concrete. An extensive characterization of the bituminous mortar was also performed using the dynamic shear rheometer and the direct tension tests. The results showed that aggregate skeletons exhibit a high tendency to dilate implying tensile stresses and strains in the bituminous mortar. The results also showed that plastic deformation is much more important than viscous deformation for the stone skeleton mixtures and that viscous deformation is more important for the dense mixture. The findings of the research were used to analyze the permanent deformation that occurred in accelerated pavement test sections.
"Hang Them if They Have to be Hung": Mitigation Discourse, Black Families, and Racial Stereotypes
Authors: Lane Alycee
Published: June 2009

This article examines how mitigation discourse fails to address the racial implications of presenting to white jurors a narrative of a black capital defendant's dysfunctional family life. Given the plethora of racist configurations in the public sphere of "the black family"—signified most perniciously through the figure of the "welfare queen"—the telling of a black defendant's dysfunctional family life may in fact reinforce what white jurors "already know" about black families. Indeed, since "the black family" figures not as an object of sympathy but of contempt, presenting uncritically mitigating evidence of a black capital defendant's family story may, in the end, provide to a white-dominated capital jury an opportunity to punish not only the black defendant but also "the black family" writ large.
Government investment in a small open economy
Authors: Major K. , Szilágyi K.
Published: June 2009

In this article the effects of government infrastructure investment in a small open economy environment are analysed. Apart from enhancing the country’s output directly, government spending on capital — modelled here as development of public infrastructure — creates positive externalities in the production process of the private sector. Short- and long-run effects of ambitious development programs, depending on the source of financing (transfers or loans from abroad), are addressed. The empirical relevance of the quantitative conclusions to be derived from the present stylised form of the model is admittedly limited. However, the qualitative conclusions can add some new insights and contribute to the lively debate on the expected effects of government investments and EU transfers on macroeconomic development.
Similarities and differences of human resource management in private and public sector organisations in the light of new public management in international comparison
Authors: Poór J. , Karoliny Zs. , Musztyné Bártfai B. , Pótó Zs. , Farkas F.
Published: June 2009

This paper seeks to address the similarities and differences between HR practices and policies of private and public sector organisations by reporting the results of our analysis based on the CRANET database. In our paper detailed statistical analysis is made for the three geographical subsets (New Public Management Countries, Eastern Europe, and All Other Countries) of the CRANET Survey 2004–2005. In light of CRANET data we review whether public sector reforms driven by radical structural changes, privatisation of certain government functions, or adaptation of New Public Management technologies could have or could not have eliminated the most important distinguishing features of public and private sector organisations in the field of HRM.
Infrared Photoconductivity in Heavily Nitrogen Doped a-Si:H
Authors: Shelton David J , Ginn James C , Coffey Kevin R , Boreman Glenn D
Published: June 2009

The generation of high frequency steady-state photoconductivity in nitrogen doped hydrogenated amorphous silicon (a-Si:H-N) films has been demonstrated at infrared (IR) frequencies of 650 to 2000 cm-1 or 15 to 5 μm in wavelength. This allows IR photoconductivity to be observed using a simple thermal source. In order to produce high frequency photoconductivity effects the plasma frequency must be increased to the desired device operation frequency or higher as described by the Drude model. IR ellipsometry was used to measure the steady-state permittivity of the a-Si:H-N films as a function of pump illumination intensity. The largest permittivity change was found to be Δεr = 2 resulting from a photo-carrier concentration on the order of 1022 cm-3. IR photoconductivity is shown to be limited by the effective electron mobility at IR frequencies.
SIMULATION OF PLASMONIC CRYSTAL ENHANCEMENT OF THIN FILM SOLAR CELL ABSORPTION
Authors: Biswas Rana , Zhou Dayu , Garcia Luis
Published: June 2009

Light management and enhanced photon harvesting is a critical area for improving efficiency of thin film solar cells. Red and near infrared photons with energies just above the band edge have large absorption lengths in amorphous silicon and can not be efficiently collected. We previously demonstrated that a photonic crystal back reflector involving a periodically patterned ZnO layer can enhance absorption of band edge photons. We propose and design alternative new plasmonic crystal structures that enhance absorption in thin film solar cell structures. These plasmonic crystals consist of a periodically patterned metal back reflector with a periodic array of holes An amorphous/nanocrystalline silicon layer resides on top of this plasmonic crystal followed by a standard anti-reflecting coating. We have found plasmonic crystal structures enhance average photon absorption by more than 10%, and by more than a factor of 10 at wavelengths just above the band edge, and should lead to improved cell efficiency. The plasmonic crystal diffracts band edge photons within the absorber layer, increasing their path length and dwell time. In addition there is concentration of light within the plasmonic crystal. Design simulations are performed with rigorous scattering matrix simulations where both polarizations of light are accounted for.
Light Trapping in Thin-film μc-Si:H Solar Cells using Self-ordered 2D Grating Reflector
Authors: Sai Hitoshi , Kanamori Yoshiaki , Kondo Michio
Published: June 2009

Effect of back reflectors on light trapping in μc-Si:H cells has been investigated with self-ordered Al substrates obtained by anodic oxidation. With increasing the period of the patterned substrates from 0 to 1.1 μm, 1-μm-thick μc-Si:H cells on the patterned substrates have shown a significant enhancement of spectral response in the near infrared region, giving an increment of the short circuit current density from 18 to 24 mA/cm2. This enhanced light trapping effect are attributed to the improved reflectivity of the rear side and effective light scattering at the front side, as well as light scattering at the rear side.
Amorphous Semiconductors Studied by First-principles Simulations: Structure and Electronic Properties
Authors: Jarolimek Karol , de Groot Robert A. , de Wijs Gilles A. , Zeman Miro
Published: June 2009

Atomistic models of amorphous solids enable us to study properties that are difficult to address with experimental methods. We present a study of two amorphous semiconductors with a great technological importance, namely a- Si:H and a-SiN:H. We use first-principles density functional theory (DFT), i.e. the interatomic forces are derived from basic quantum mechanics, as only that provides accurate interactions between the atoms for a wide range of chemical environments (e.g. brought about by composition changes). This type of precision is necessary for obtaining the correct short range order. Our amorphous samples are prepared by a cooling from liquid approach. As DFT calculations are very demanding, typically only short simulations can be carried out. Therefore most studies suffer from a substantial amount of defects, making them less useful for modeling purposes. We varied the cooling rate during the thermalization process and found it has a considerable impact on the quality of the resulting structure. A rate of 0.02 K/fs proves to be sufficient to prepare realistic samples with low defect concentrations. To our knowledge these are the first calculations that are entirely based on first-principles and at the same time are able to produce defect-free samples. Because of the high computational load also the size of the systems has to remain modest. The samples of a-Si:H and a-SiN:H contain 72 and 110 atoms, respectively. To examine the convergence with cells size, we utilize a large cell of a-Si:H with a total of 243 atoms. As we obtain essentially the same structure as with the smaller sample, we conclude that the use of smaller cells is justified.
Although creating structures without any defects is important, on the other hand a small number of defects can give valuable information about the structure and electronic properties of defects in a-Si:H and a-SiN:H. In our samples we observe the presence of both the dangling bond (undercoordinated atom) and the floating bond (over-coordinated atom). We relate structural defects to electronic defect states within the band gap. In a-SiN:H the silicon-silicon bonds induce states at the valence and conduction band edges, thus decreasing the band gap energy. This finding is in agreement with measurements of the optical band gap, where increasing the nitrogen content increases the band gap.
High Temperature Post-deposition Annealing Studies of Layer-by-layer (LBL) Deposited Hydrogenated Amorphous Silicon Films
Authors: Tong Goh Boon , Gani Siti Meriam Ab. , Muhamad Muhamad Rasat , Rahman Saadah Abdul
Published: June 2009

High temperature post-deposition annealing studies were done on hydrogenated amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) using the layer-by-layer (LBL) deposition technique. The films were annealed at temperatures of 400 °C, 600 °C, 800 °C and 1000 °C in ambient nitrogen for one hour. Auger electron spectroscopy (AES) depth profiling results showed that high concentration of O atoms were present at the substrate/film interface and at film surface. Very low concentration of O atoms was present separating silicon layers at regular intervals from the film surface and the substrate due to the nature of the LBL deposition and these silicon oxide layers were stable to high annealing temperature. Reflectance spectroscopy measurements showed that the onset of transformation from amorphous to crystalline phase in the LBL a-Si:H film structure started when annealed at temperature of 600 °C but the X-ray diffraction (XRD) and Raman scattering spectroscopy showed that this transition only started at 800 °C. The films were polycrystalline with very small grains when annealed at 800 °C and 1000 °C. Fourier transform infrared spectroscopy (FTIR), measurements showed that hydrogen was completely evolved from the film at the on-set of crystallization when annealed at 800 °C. The edge of the reflectance fringes shifted to longer wavelength decrease in hydrogen content but shifted to shorter wavelength with increase in crystallinity.
Polysilicon Films Formed on Metal Sheets by Aluminium Induced Crystallization of Amorphous Silicon: Barrier Effect
Authors: Pathi Prathap , Tüzün Ozge , Slaoui Abdelilah
Published: June 2009

Polycrystalline silicon (pc-Si) thin films have been synthesized by aluminium induced crystallization (AIC) of amorphous silicon (a-Si) at low temperatures (≤500°C) on flexible metallic substrates for the first time. Different diffusion barrier layers were used to prepare stress free pc-Si films as well as to evaluate the effective barrier against substrate impurity diffusion. The layers of aluminum (Al) and then amorphous silicon with the thickness of 0.27 μm and 0.37 μm were deposited on barrier coated metal sheets by means of an electron beam evaporation and PECVD, respectively. The bi-layers were annealed in a tube furnace at different temperatures (400-500°C) under nitrogen flow for different time periods (1-10hours). The degree of crystallinity of the as-grown layers was monitored by micro-Raman and reflectance spectroscopies. Structure, surface morphology and impurity analysis were carried out by X-ray diffraction, scanning electron microscopy (SEM) and EDAX, respectively. The X-ray diffraction measurements were used to determine the orientation of grains. The results show that the AIC films on metal sheets are polycrystalline and the grains oriented in (100) direction preferentially. However, the properties of AIC films are highly sensitive to the surface roughness.
Improving Silicon Crystallinity by Grain Reorientation Annealing
Authors: Saenger Katherine L. , de Souza Joel P. , Inns Daniel , Fogel Keith E. , Sadana Devendra K.
Published: June 2009

Demand for high efficiency, low-cost solar cells has led to strong interest in post-deposition processing techniques that can improve the crystallinity of thick (1 to 40 μm) silicon films deposited at high growth rates. Here we describe a high temperature grain reorientation annealing process that enables the conversion of polycrystalline silicon (poly-Si) into a single crystal material having the orientation of an underlying single crystal Si seed layer. Poly-Si films of thickness 0.5 to 1.0 μm were deposited by low pressure chemical vapor deposition (LPCVD) on substrates comprising a surface thermal oxide or a 100-oriented single crystal silicon-on-insulator (SOI) layer. After annealing at 1300 °C for 1 hour, poly-Si on oxide shows very significant grain growth, as expected. In contrast, the poly-Si deposited on SOI showed no grain boundaries after annealing, transforming into a single crystal material with a fairly high density of stacking faults. Possible uses and drawbacks of this approach for solar cell applications will be discussed.
Optimization of p-type Nanocrystalline Silicon Thin Films for Solar Cells and Photodiodes
Authors: Vygranenko Yuri , Fathi Ehsanollah , Sazonov Andrei , Vieira Manuela , Heiler Gregory , Tredwell Timothy , Nathan Arokia
Published: June 2009

We report on structural, electronic, and optical properties of boron-doped, hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) at a substrate temperature of 150°C. Film properties were studied as a function of trimethylboron-to-silane ratio and film thickness. The film thickness was varied in the range from 14 to 100 nm. The conductivity of 60 nm thick films reached a peak value of 0.07 S/cm at a doping ratio of 1%. As a result of amorphization of the film structure, which was indicated by Raman spectra measurements, any further increase in doping reduced conductivity. We also observed an abrupt increase in conductivity with increasing film thickness ascribed to a percolation cluster composed of silicon nanocrystallites. The absorption loss of 25% at a wavelength of 400 nm was measured for the films with optimized conductivity deposited on glass and glass/ZnO:Al substrates. A low-leakage, blue-enhanced p-i-n photodiode with an nc-Si p-layer was also fabricated and characterized.
Hydrogenated Amorphous Silicon Based Solar Cells: Optimization Formalism and Numerical Algorithm
Authors: Shkrebtii Anatoli , Kryuchenko Yuriy , Sachenko Anaroliy , Sokolovskyi Igor , Gaspari Franco
Published: June 2009

Thin film hydrogenated amorphous silicon (a-Si:H) is widely used in photovoltaics. In order to get the best possible performance of the a-Si:H solar cells it is important to optimize the amorphous film and solar cells in terms their parameters such as mobility gap,p-,i- andn-layer doping levels, electron and hole lifetime and their mobilities, resistance of p-, i- and n-layers, contact grid geometry and parameters of the transparent conducting and antireflecting layers, and others. To maximize thin a-Si:H film based solar cell performance we have developed a general numerical formalism of photoconversion, which takes into account all the above parameters for the optimization. Application of the formalism is demonstrated for typical a-Si:H based solar cells before Staebler-Wronski (SW) light soaking effect. This general formalism is not limited to a-Si:H based systems only, and it can be applied to other types of solar cells as well.
Junction Capacitance Study of a-SiGe:H Solar Cells Grown at Varying RF and VHF Deposition Rates
Authors: Hugger Peter G. , Lee JinWoo , Cohen David J. , Yue Guozhen , Xu Xixiang , Yan Baojie , Yang Jeff , Guha Subhendu
Published: June 2009

Significant advances have been made in increasing the deposition rate of hydrogenated silicon germanium alloys (a-SiGe:H) using a modified VHF glow discharge deposition method while also maintaining good electronic properties important for its application in photovoltaic devices. We examine the electrical and optical properties of these alloys deposited either by RF (13.56MHz) or the modified VHF methods over deposition rates varying from 1 to 10 Å/s. The electronic properties of a series of 1.4 eV optical gap a-SiGe:H i-layers, in many cases in solar cell device configurations, were characterized. Drive-level capacitance profiling was used to determine the deep defect densities, and transient photocapacitance measurements allowed us to determine the Urbach energies. Results were obtained for both the annealed and light-soaked degraded states and these results were correlated to the cell performance parameters. In general the a-SiGe:H layers deposited using the modified VHF excitation exhibited improved electronic properties at higher growth rates than the RF deposited samples.
Passivation of Silicon Surfaces Using Atomic Layer Deposited Metal Oxides
Authors: Wang Jun , Farrokh Baroughi Mahdi , Shanmugam Mariyappan , Samadzadeh-Tarighat Roohollah , Sivoththaman Siva , Paul Sanjoy
Published: June 2009

Surface passivation of silicon substrates using atomic layer deposited Al2O3 and HfO2 thin films are assessed. Al2O3 and HfO2 dielectric layers with various thicknesses were deposited on both sides of n-type (100) FZ-Si substrates (resistivity 4 – 6 Ω-cm) at 200°C by atomic layer deposition (ALD) system. The effective excess carrier lifetime of as-deposited oxide/Si/oxide structure was measured by microwave-photoconductivity-decay (MWPCD) measurement technique and it was observed that the thicker ALD dielectrics lead to higher effective excess carrier lifetime and better surface passivation. The measurements showed average excess carrier lifetime values of 302 μs and 347 μs for as-deposited Al2O3 and HfO2 passivated Si substrates with 150 ALD cycles, respectively. MWPCD and capacitance-voltage (C-V) measurements suggest that as-deposited ALD HfO2 layer leads to a better surface passivation compared to as-deposited ALD Al2O3 layer. Further, the results suggest that there exist fixed negative charges in the bulk of the ALD dielectrics and this contributes to the field effect passivation of the silicon surfaces.
Highly Transparent and High Haze ZnO:Al film For Front TCO of a-Si:H and μc-Si:H Solar Cells by Controlling Oxygen Flow
Authors: Kang Dong-Won , Kuk Seung-Hee , Ji Kwang-Sun , Ahn Seh-Won , Han Min-Koo
Published: June 2009

We fabricated highly transparent and high haze ZnO:Al film for front TCO of amorphous and microcrystalline silicon solar cells. We have sputtered ZnO:Al film of 1.3 μm on the thin seed layer of about 60nm which was previously sputtered on the glass substrate by using 4% dilution of oxygen to argon gas. The ZnO:Al film grown on the seed layer had much higher crystalline phase than one without any seed layer. Our bi-layer ZnO:Al film showed low resistivity of 2.66×10-4 Ω•cm and sheet resistance of 2.08 Ω/⇐ while conventional ZnO:Al film showed resistivity of 3.24×10-4 Ω•cm and sheet resistance of 2.46 Ω/⇐. After surface texturing by 0.5% HCl wet-chemical etching, the transmittance of ZnO:Al film was increased from 83.7% to 88.1% at wavelength of 550nm through the seed layer. Also the transmittance at 800nm was increased from 82.3% to 88.9%. Especially, haze values of the ZnO:Al film were drastically increased from 58.7% to 90.6% at wavelength of 550nm by employing the seed layer. Also haze values at 800nm were increased from 22.1% to 68.1%. It is expected that the seed layer method to improve the quality of ZnO:Al film will contribute to an increase of solar cell efficiency due to the high capability of light trapping and low electrical resistivity.
Optics in Thin-film Silicon Solar Cells with Integrated Lamellar Gratings
Authors: Dewan Rahul , Madzharov Darin , Raykov Andrey , Knipp Dietmar
Published: June 2009

Light trapping in microcrystalline silicon thin-film solar cells with integrated lamellar gratings was investigated. The influence of the grating dimensions on the short circuit current and quantum efficiency was investigated by numerical simulation of Maxwell’s equations by a Finite Difference Time Domain approach. For the red and infrared part of the optical spectrum, the grating structure leads to scattering and higher order diffraction resulting in an increased absorption of the incident light in the silicon thin-film solar cell. By studying the diffracted waves arising from lamellar gratings, simple design rules for optimal grating dimensions were derived.
Voltage Controlled Amorphous Si/SiC Phototransistors and Photodiodes as Wavelength Selective Devices: Theoretical and Electrical Approaches
Authors: Vieira Manuel Augusto , Vieira Manuela , Louro Paula , Fernandes Miguel , Fantoni Alessandro , Barata Manuel
Published: June 2009

In this paper single and stacked structures that can be used as wavelength selective devices, in the visible range, are analysed. Two terminal heterojunctions ranging from p-ií-n to p-i-n-p-i’-n configurations are studied. Three terminals double staked junctions with transparent contacts in-between are also considered to increase wavelength discrimination. The color discrimination was achieved by ac photocurrent measurement under different externally applied bias. Experimental data on spectral response analysis and current –voltage characteristics are reported.
A theoretical analysis and an electrical simulation procedure are performed to support the wavelength selective behaviour. Good agreement between experimental and simulated data was achieved. Results show that in the single p-i-n configuration the device acts mainly as an optical switch while in the double ones, due to the self bias effect, the input channels are selectively tuned by shifting between positive and negative bias. If the internal terminal is used the inter-wavelength cross talk is reduced and the S/N increased.
Photoelectron Spectroscopy Measurements of Valence Band Discontinuities for a-Si:H/c-Si Heterojunction Solar Cells
Authors: Kaneko Tetsuya , Kondo Michio
Published: June 2009

The valence band discontinuity (offset) between a-Si:H-based intrinsic thin layers and c-Si substrates was estimated using ultraviolet photoelectron spectroscopy (UPS) in combination with x-ray photoelectron spectroscopy (XPS). A core level shift measured by XPS was utilized to correct the shifts of UPS spectra after UV light illumination. Thin films of a-Si:H, a-SiO:H and a-SiC:H were prepared by plasma-enhanced chemical vapor deposition (PECVD) using SiH4, CO2 and CH4 gases. The valence band offset of 0.11 eV was obtained from the a-Si:H/c-Si heterojunction, whereas 0.27 eV was obtained from the a-SiO:H/c-Si heterojunction. Moreover, the valence band offset between the c-Si and the a-SiC:H deposited with [CH4]=10 SCCM and [CH4]=20 SCCM were determined to be 0.25 eV and 0.36 eV, respectively. The c-Si-based heterojunction solar cells with estimated i layer in this study were fabricated, reduction of FF with increasing the valence band offset was observed. It is likely that increasing of the valence band offset contributes to the reduction of FF.
High efficiency amorphous and nanocrystalline silicon based multi-junction solar cells deposited at high rates on textured Ag/ZnO back reflectors
Authors: Yue Guozhen , Sivec Laura , Yan Baojie , Yang Jeff , Guha Subhendu
Published: June 2009

We report our recent progress on nc-Si:H single-junction and a-Si:H/nc-Si:H/nc-Si:H triple-junction cells made by a modified very-high-frequency (MVHF) technique at deposition rates of 10-15 Å/s. First, we studied the effect of substrate texture on the nc-Si:H single-junction solar cell performance. We found that nc-Si:H single-junction cells made on bare stainless steel (SS) have a good fill factor (FF) of ˜0.73, while it decreased to ˜0.65 when the cells were deposited on textured Ag/ZnO back reflectors. The open-circuit voltage (Voc) also decreased. We used dark current-voltage (J-V), Raman, and X-ray diffraction (XRD) measurements to characterize the material properties. The dark J-V measurement showed that the reverse saturated current was increased by a factor of ˜30 when a textured Ag/ZnO back reflector was used. Raman results revealed that the nc-Si:H intrinsic layers in the two solar cells have similar crystallinity. However, they showed a different crystallographic orientation as indicated in XRD patterns. The material grown on Ag/ZnO has more random orientation than that on SS. These experimental results suggested that the deterioration of FF in nc-Si:H solar cells on textured Ag/ZnO was caused by poor nc-Si:H quality. Based on this study, we have improved our Ag/ZnO back reflector and the quality of nc-Si:H component cells and achieved an initial and stable active-area efficiencies of 13.4% and 12.1%, respectively, in an a-Si:H/nc-Si:H/nc-Si:H triple-junction cell.
Microcrystalline Silicon Thin-Film Transistors for Ambipolar and CMOS Inverters
Authors: Chan Kah-Yoong , Gordijn Aad , Stiebig Helmut , Knipp Dietmar
Published: June 2009

Microcrystalline silicon (μc-Si:H) thin-film transistors (TFTs) have lately gained much attention due to their high charge carrier mobilities. We report on top-gate μc-Si:H TFTs fabricated by plasma-enhanced chemical vapor deposition at process temperatures below 180 °C with high electron and hole charge carrier mobilities exceeding 50 cm2/Vs and 12 cm2/Vs, respectively. Based on the μc-Si:H TFTs different thin-film inverters were realized including ambipolar and complimentary metal-oxide-semiconductor (CMOS) inverters. Microcrystalline CMOS inverters exhibit high voltage gains exceeding 22, whereas ambipolar inverters show reduced voltage gains of 10 at low operating voltages. The electrical characteristics of the μc-Si:H CMOS and ambipolar thin-film inverters will be discussed in terms of the voltage transfer curve, the voltage gain and the power dissipation.
Carrier drift-mobilities and solar cell models for amorphous and nanocrystalline silicon
Authors: Schiff Eric A
Published: June 2009

Hole drift mobilities in hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) are in the range of 10-3 to 1 cm2/Vs at room-temperature. These low drift mobilities establish corresponding hole mobility limits to the power generation and useful thicknesses of the solar cells. The properties of as-deposited a-Si:H nip solar cells are close to their hole mobility limit, but the corresponding limit has not been examined for nc-Si:H solar cells. We explore the predictions for nc-Si:H solar cells based on parameters and values estimated from hole drift-mobility and related measurements. The indicate that the hole mobility limit for nc-Si:H cells corresponds to an optimum intrinsic-layer thickness of 2-3 μm, whereas the best nc-Si:H solar cells (10% conversion efficiency) have thicknesses around 2 μm.
Bulk-heterojunction Based on Blending of Red and Blue Luminescent Silicon Nanocrystals and P3HT Polymer
Authors: Švrček Vladimir , Kondo Michio
Published: June 2009

Blending of red and blue photoluminescent silicon nanocrystals (Si-ncs) with poly(3-hexylthiophene (P3HT) conjugated polymer is demonstrated. The room temperature luminescent and ambient conditions stable Si-ncs prepared by electrochemical etching and laser ablation in water are used for the blend fabrication. Furthermore photo-electric properties in parallel configuration on platinum interdugitated contact are shown. Both types of Si-ncs results the bulk-heterojunction formation and photoconductivity is observed when the blends are irradiated AM1.5. The increase in photoconductivity is rather the same and ratio between photo- and dark-conductivity is about 1.7. The nanocrystal oxidation during laser ablation fabrication process in water hinders the transport properties of the blend.
Imaging Electron Transport across Grain Boundaries in an Integrated Electron and Atomic Force Microscopy Platform: Application to Polycrystalline Silicon Solar Cells
Authors: Romero Manuel J , Liu Fude , Kunz Oliver , Wong Johnson , Jiang Chun-Sheng , Al-Jassim Mowafak , Aberle Armin G
Published: June 2009

We have investigated the local electron transport in polycrystalline silicon (pc-Si) thin-films by atomic force microscopy (AFM)-based measurements of the electron-beam-induced current (EBIC). EVA solar cells are produced at UNSW by EVAporation of a-Si and subsequent solid-phase crystallization–a potentially cost-effective approach to the production of pc-Si photovoltaics. A fundamental understanding of the electron transport in these pc-Si thin films is of prime importance to address the factors limiting the efficiency of EVA solar cells. EBIC measurements performed in combination with an AFM integrated inside an electron microscope can resolve the electron transport across individual grain boundaries. AFM-EBIC reveals that most grain boundaries present a high energy barrier to the transport of electrons for both p-type and n-type EVA thin-films. Furthermore, for p-type EVA pc-Si, in contrast with n-type, charged grain boundaries are seen. Recombination at grain boundaries seems to be the dominant factor limiting the efficiency of these pc-Si solar cells.
Blue/White Emission from Hydrogenated Amorphous Silicon Carbide Films Prepared by PECVD
Authors: Ivashchenko Volodymyr , Vasin Andrey , Ivashchenko L. A. , Skrynskyy P. L.
Published: June 2009

Photoluminescence (PL) from hydrogenated silicon carbide (SiC:H) films is studied at room temperature. The films were deposited by plasma-enhanced chemical vapor (PECVD) technique with and without substrate bias using methyltrichlorosilane as a main precursor. After the deposition the samples were annealed at various temperatures in vacuum. The films were characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The samples deposited without substrate bias (series A) were amorphous, whereas the samples deposited with negative substrate bias -100V (series B) were nanocrystalline. The one-peak (470 nm) and double-peak (415 and 437 nm) PL structures of the as-deposited samples A and B were observed, respectively. Annealing strongly enhanced intensity of PL of the samples B and trandformed PL spectrum from double-peak into broad featureless band with intensity at about 470 nm. The blue PL in as-deposited films B is supposed to be assigned to the radiative recombination in the sites located at the nanocrystallite surface, whereas the photo excitation of carries mostly occurs in nanocrystallite cores. A further increase in annealing temperature causes hydrogen effusion, which leads to an increase of the concentration of non-raidative recombination centers associated with dangling-bonds and as a result, to the quenching of PL.
Characterization of Microcrystalline Silicon by High Wavenumber Raman Scattering
Authors: Johnson Erik V , Kroely Laurent , Moreno Mario , Roca i Cabarrocas Pere
Published: June 2009

One of the primary challenges in the application of hydrogenated microcrystalline silicon (μc-Si:H) to photovoltaic cells is achieving high growth rates while maintaining good material quality over a wide process window. The rapid characterization of the material without generating a complete cell is thus a useful tool to determine said process window. Infrared absorption due to the various vibrational modes of the material has been used as a coarse tool towards this purpose, but the use of FTIR to perform this diagnosis limits the substrates upon which the analysis can be performed. We report on the use of high wave-number (1800-2200 cm-1) Raman scattering to perform a similar role of telltale peak detection directly on solar cells and on substrates suitable for thin-film photovoltaics. We evaluate material grown from SiF4 by RF-PECVD and from SiH4 by Matrix Distributed Electron Cyclotron Resonance (MDECR-) PECVD.
Properties of Nano-crystalline Silicon-Carbide Films Prepared Using Modulated RF- PECVD
Authors: Zhu Feng , Hu Jian , Matulionis Ilvydas , Kunrath Augusto , Madan Arun
Published: June 2009

We report on the fabrication of nano-crystalline silicon-carbide (nc-SiC) using pulse modulated RF-PECVD technique, from silane (SiH4) and methane (CH4) gas mixtures which is highly diluted in hydrogen (H2). The microstructure of nc-SiC material is nanometer-size silicon crystallites embedded in amorphous silicon-carbide (a-SiC) matrix. As carbon incorporation in nc-Si film increases, the bandgap is enlarged from 1.1eV to 1.55eV as measured by Photothermal Deflection Spectroscopy (PDS) while the crystalline volume fraction decreases from 70% to about 20%. It is found that the crystalline volume fraction, grain size and dark conductivity of nc-SiC films can be enhanced with applying a negative DC bias to substrate during deposition.
Ion Assisted ETP-CVD a-Si:H at Well Defined Ion Energies
Authors: Wank Michael A. , van Swaaij René , van de Sanden M.
Published: June 2009

Hydrogenated amorphous silicon (a-Si:H) was deposited with the Expanding Thermal Plasma-CVD (ETP CVD) method utilizing pulse-shaped substrate biasing to induce controlled ion bombardment during film growth. The films are analyzed with in-situ real time spectroscopic ellispometry, FTIR spectroscopy, as well as reflection-transmission and Fourier transform photocurrent spectroscopy (FTPS) measurements. The aim of this work is to investigate the effect ion bombardment with well defined energy on the roughness evolution of the film and the material properties.

We observe two separate energy regimes with material densification and relatively constant defect density below ˜ 120-130 eV and a constant material density at increasing defect density > 120-130 eV substrate bias. We discuss our results in terms of possible ion – surface atom interactions and relate our observations to reports in literature.
Phosphorus and Boron Doping Effect on Nanocrystalline Formation in Hydrogenated Amorphous and Nanocrystalline Mixed-phase Silicon Thin Films
Authors: Jiang Chunsheng , Yan Yanfa , Moutinho Helio R. , Al-Jassim Mowafak , Yan Baojie , Sivec Laura , Yang Jeff , Guha Subhendu
Published: June 2009

Phosphorus and Boron doping effects on the microstructure of nanocrystallites in hydrogenated amorphous and nanocrystalline mixed-phase silicon films were investigated using Raman spectroscopy, secondary ion mass spectrometry, cross-sectional transmission electron microscopy, atomic force microscopy, and conductive atomic force microscopy. The characterizations revealed the following observations. First, the mixed-phase Si:H films can be heavily doped in ˜1021/cm3 by adding PH3 and BF3 in the precursor gases. Second, the intrinsic and doped films can be made in a similar crystalline volume fraction by adjusting hydrogen dilution ratio. The hydrogen dilution ratio is much higher for P-doped films than for the intrinsic film with the similar crystallinity. Third, the doping impacts the nanostructures in the films significantly. Nanograins aggregate to form cone-shaped clusters in the intrinsic and B-doped films but isolate and randomly distribute in amorphous tissues in the P-doped films. The cones in the intrinsic and B-doped films are also different. The cone-angle is smaller and the nanograin density is lower in the B-doped films than in the intrinsic films. These P- and B-doping effects on the nanocrystalline formation are interpreted in terms of diffusions of Si-related radicals during the film growth.
Effects of a Bias Voltage During Hydrogenation on Passivation of the Defects in Polycrystalline Silicon for Solar Cells
Authors: Saito Yoji , Kohata Hayato , Sano Hideyuki
Published: June 2009

The short circuit current and conversion efficiency of the poly(multi)-crystalline solar cells are increased by the passivation process using hydrogen plasma. The passivation rate apparently increases at a reverse bias voltage near 0.6V during the hydrogenation process. The effects of the bias voltage on the passivation are large at the substrate temperatures between 200C and 250C. The phenomena are likely due to the existence of positively-ionized hydrogen, H+. The H+ ions can be accelerated from the surface into the bulk by the electric field with the negative bias. The possibility of the H+ ions in the bulk silicon has been predicted in the previous reports. The increase of the incorporated hydrogen is confirmed by IR absorption measurements. The enhanced diffusion of hydrogen induced by the reverse bias is supported by the results of spectral response characteristics of the hydrogenated solar cells.
Optical Processing Devices for Optical Communications: Multilayered a-SiC:H Architectures
Authors: Louro Paula , Vieira Manuela , Vieira M. A. , Fernandes Miguel , Fantoni Alessandro , Lavareda G. , Carvalho C. N.
Published: June 2009

In this paper three multilayered architectures based on a-SiC:H with voltage controlled spectral selectivity in the visible spectrum range are analyzed. Multiple simultaneous modulated communication channels (red, green and blue or their polychromatic mixtures) were transmitted together at different frequencies. The combined optical signal was analyzed by reading out the photocurrent signal generated by the devices, under different applied voltages. Results show that the multiplexed signal depends on the device architecture and is balanced by the wavelength and transmission speed of each input channel, keeping the memory of the incoming optical carriers. In the single graded p-i’i-n configuration the device acts mainly as an optical switch while in two stacked p-i’-n-(ITO)-p-i-n configurations, the input channels are selectively tuned by shifting between forward and reverse bias. An electrical model, supported by a numerical simulation gives insight into the device operation.