bluuebunny/crossref_metadata_2025 huggingface dataset:
Overview and Characteristics of Tourism Seasonality in Ohrid
Authors: Trajkov Aleksandar , Biljan Jovanka , Andreeski Cvetko
Published: March 2017

Tourism research has always been an imperative for the scientists and policy creators, so they can maximise its socioeconomic effects. In that order, all the factors that influence the tourism industry must be taken into consideration. One of the biggest characteristics of tourism and challenges for researchers is its seasonality. It is a temporary imbalance of tourism activities caused by many factors and can have many social, economic and environmental consequences. Seasonal component of tourism becomes more important with its development. This paper analyses tourism seasonality in Ohrid as the most popular tourist destination in Macedonia. Findings and conclusions are based on several research methods like: Descriptive statistics, Seasonality coefficient, Gini coefficient and Seasonal Indicator. Research results determine Ohrid as a tourist destination with a strong seasonality caused by natural factors. Paper outcomes can be useful for tourism policy creators and tourism practitioners for further planning and carrying of all tourism activities. Also, findings and presented methodologies can be used in further similar researches or in further analyses of overall tourism seasonality in the country.
The Transformation of The Serbian Labour Market from a Gender Perspective
Authors: Stanković Sunčica
Published: March 2017

In conditions of great social changes that have affected the entire world since the beginning of 1980, there is the emergence of new social risks such as difficult labour market entry, stable employment problem, the problem of outdated qualifications, affecting both women and men. In the competitive race for employment, differences between men and women in the market are conditioned by their starting position. The position of women is required by expectations which exist in regard to their gender role. Women are additionally burdened by establishing a balance between work and family responsibilities, especially childcare and with caring for elderly family members.Men are more often employed in areas that are better paid and socially valued, while women are mainly employed in the service sector. The purpose of this paper is to analyse the quality of labour force in the Republic of Serbia and changes in the gender wage gap during the observed period. The main indicators of gender inequality show significant differences in the status of women compared to men in the labour market. Analysis of labour market trends over the past decade has illustrated that the position of women is constantly deteriorating.
Baylisascaris procyonis roundworm infection patterns in raccoons (Procyon lotor) from Missouri and Arkansas, USA
Authors: Al-Warid H. S. , Belsare A. V. , Straka K. , Gompper M. E.
Published: March 2017

Baylisascaris procyonis is a helminth parasite of raccoons Procyon lotor and represents a health concern in paratenic hosts, including humans and diverse domestic and wildlife species. In North America the helminth is expanding its geographic range. To better understand patterns of infection in the Ozark region of the USA, raccoons (n = 61) were collected in 2013-2014 from five counties in Missouri and Arkansas, USA and necropsied. We documented B. procyonis in all surveyed locations. The overall prevalence of B. procyonis was 44.3 % (95 % CI = 31.9 - 57.4) and was significantly higher in females than males. There were also significant differences in prevalence among raccoons sampled north and south of the Missouri River. Mean intensity was 9.9 (CI = 5.44 - 17.22), and parasites were highly aggregated among hosts such that approximately 20 % of hosts harbor 90 % of parasites. These levels of parasitism indicate that B. procyonis is common in the region and its impacts on paratenic hosts could be qualitatively similar to effects observed in other localities.
A comprehensive mathematical model of heat and moisture transfer for wood convective drying
Authors: Zhao Jingyao , Cai Yingchun
Published: March 2017

The focus of this study is the development of a specific drying model for the design and operation of drying systems for stacked lumber in drying chambers. Namely, a comprehensive three-dimensional (3D) mathematical model of heat and moisture transfer in stacked wood has been developed, where the wood was subjected to convective drying that accounts for the effect of the surrounding fluid flow. In developing the model, the characteristics of wood and fluid flow, i.e. velocity, pressure, temperature, relative humidity (RH) and moisture content (MC) are described by the conservation equations of mass, momentum and energy as well as thermodynamic relations. The model presented was solved numerically by means of the commercial software COMSOL Multiphysics. The simulation results were validated against experimental data under laboratory conditions. Air current circulation was found to be non-uniform during drying, which accounts for the different rates of temperature and MC in wood. At the initial stage of drying, this difference was relatively large but reduced gradually with the drying process. Meanwhile, the transient gathered phenomenon related to humidity around the stacked wood in the chamber was observed in response to air current circulation and evaporation rate of moisture. Finally, sources of error incurred in numerical calculations and actual detection were identified and discussed.
Male smokers with HLA-B27 positivity, SI joints inflammation have more radiological damages and higher prevalence of AS while females have higher BASDAI scores: observations from cluster analyses of a group of SpA patients
Authors: Chan Shirley Chiu Wai , Tsang Helen Hoi Lun , Lau Chak Sing , Chung Ho Yin
Published: March 2017

Objectives

To describe the clinical characteristics and the relations with disease activity, functional status, and syndesmophytes formation in patients with axial spondyloarthritis (AxSpA) by categorizing them into different groups.

Methods

One hundred and sixty three patients with AxSpA were recruited. Clinical and blood parameters were collected. Patients were asked to complete the self-assessment questionnaires, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), and Bath Ankylosing Spondylitis Functional Index (BASFI). Spinal mobility was measured according to Bath Ankylosing Spondylitis Metrology Index (BASMI). Radiographs of cervical and lumbosacral spine were performed for modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Radiological sacroiliitis was scored for ankylosing spondylitis (AS). Magnetic resonance imaging (MRI) of the sacroiliac (SI) joints was performed for spondyloarthritis research consortium of Canada (SPARCC) MRI inflammation score. Two-way cluster analyses were performed to determine the relationships between the parameters.

Results

Two cluster models were built using SPARCC scores of different scorers. Results were similar. The group of patients with highest mSASSS (20.33 vs 20.33) and prevalence radiological AS (85% vs 86%) were male patients (75% vs 75%), positive for HLA-B27 (70.0% vs 66.7%), smokers (87.5% vs 97.2%), and higher SPARCC SI joints score (5.32 vs 3.17). Higher BASDAI was observed among female sex. BASMI varies little but the group with highest BASMI (3.60 vs 3.62) also had highest mSASSS (20.33 vs 20.33).

Conclusion

Our data showed that male smokers with HLA-B27 positivity and SI joints inflammation have more radiological damage and higher prevalence of AS, consistent with known poor prognosis factors.
Effect of Core Training on Male Handball Players’ Throwing Velocity
Authors: Manchado Carmen , García-Ruiz José , Cortell-Tormo Juan Manuel , Tortosa-Martínez Juan
Published: March 2017

In handball, throwing velocity is considered to be one of the essential factors in achieving the ultimate aim of scoring a goal. The objective of the present study was to analyze the effect of a core training program on throwing velocity in 30 handball players (age 18.7 ± 3.4 years, body height 179.3 ± 7.0 cm, body mass 78.9 ± 7.7 kg), 16 of whom were in the junior category and 14 of whom were in the senior category. The 30 players were randomly divided into two groups, the control group (n = 15) and the experimental group (n = 15). For a period of ten weeks, both groups attended their regular handball training sessions (four per week), but in addition, the experimental group participated in a program specifically aimed at progressively strengthening the lumbo-pelvic region and consisting of seven exercises performed after the general warm-up in each regular session. Pre- and post-tests were carried out to analyze each player’s throwing velocity from different throwing positions and thus assess the effects of this specific training program. Statistically significant differences (p ≤ 0.05) in throwing velocity were observed between the experimental group, which presented a percentage improvement of 4.5%, and the control group, which did not show any improvement. The results seem to indicate that an increase in the strength and stability of the lumbo-pelvic region can contribute to an improvement in the kinetic chain of the specific movement of throwing in handball, thus, increasing throwing velocity.
Judging a tumor cell by its cover: a matter of mitochondrial contact sites
Authors: Lakshminarayanan Sowmya , Scorrano Luca
Published: March 2017

Glioblastoma is a highly aggressive brain tumor constituted by glioma stem cell and differentiated cell populations with distinct susceptibility to cytotoxic T lymphocytes crucial for tumor immune surveillance. In this issue of The EMBO Journal, Bassoy et al () show that the surface expression of certain glycans that favor recognition and killing by T cells depends on mitochondrial contacts with the endoplasmic reticulum, extending the function of this interface even to immune recognition.
Reactions of eosinophilic granulocytes in the sputum and peripheral blood of children suffering from bronchial asthma with signs of eosinophilic and non-eosinophilic inflammation of the bronchi
Authors: Koloskova O. K. , Bilous T. M. , Dikal M. V. , Lomakina U. V. , Kopchuk T. G. , Lobanova T. O.
Published: March 2017

The aim of research was to improve the management of bronchial asthma in children by examining the peculiarities and diagnostic value of reaction markers of eosinophil granulocytes in the sputum and peripheral blood of patients with signs of eosinophil and non-eosinophil phenotypes of this disease. A cohort of 118 school-age children suffering from BA was examined during a period free from attacks. Group I (the main group ) included 61 schoolchildren with signs of eosinophil phenotype (EP) of asthma detected by the character of bronchial inflammation with eosinophil granulocytes present in the sputum at a level of >3%, group II (the comparison group) included 57 patients with a lower number of eosinophils in the sputum (non-eosinophil phenotype (NP) of BA). The average index of the relative content of eosinophils in the peripheral blood among the representatives of group I was 5.82 ± 0.63%, and in children with the signs of NPBA – 6.02 ± 0.74% (P > 0.05), and average indices in the groups of absolute eosinophil number in the blood were 0.37 ± 0.04 and 0.41 ± 0.05 respectively (P > 0.05). The negative reserve of NBT eosinophils in the sputum as a test to verify EPBA showed the following diagnostic values: specificity – 83.3%, predicted value of a positive result – 95.6%. IL-5 content in the blood serum of children with EPBA was 5.99 ± 1.74 ng/ml, in patients of group ІІ – only 1.99 ± 0.49 ng/ml (P < 0.05). Eosinophil cationic protein (ЕСР) in the sputum of patients of group I reached 2.72 ± 0.35 ng/ml, and in the comparison group – only 1.74 ± 0.34 ng/ml (P < 0.05), when the content of ECP in sputum was >1.0 ng/ml the risk of EPBA showed a statistically significant increase: OR = 4.13, RR = 2.02, and AR – 0.34. The efficacy of the standardized basic anti-inflammatory therapy in patients of clinical group I was higher as compared to the children with the signs of NPBA, which was illustrated by the reduced risk of inadequate control of the disease: the index of absolute risk decrease was 31.7%, relative risk – 57.1% with necessary minimal number of patients – 1.75.
Pathogenic specifics of development of vegetative dysfunction in adolescents in relation to their morphological status
Authors: Skyba O.
Published: March 2017

Exploring the mechanisms of vegetative regulation in children and adolescents of different somatotypes has a prognostic value in regard to the character of adaptive reactions of the organism, as it facilitates the identification of the risk factors of pathological processes and states of vegetative systems, which may cause chronic illness in adulthood. The author defines the pathogenic specifics of development of vegetative dysfunction in adolescents in relation to their morphological status. Cardiointervalography and anthropometric, mathematical and statistical methods of research were used. Based on the results of cardiointervalography, the structure of initial vegetative tonus was established, which was characterized by prevalence of eutonia (38.4 ± 4.9%). The specific weight with background eutonia of adolescent boys and girls tended to be higher among the representatives of the thoracic and muscular somatotypes, compared to adolescents of the alimentive and osseous somatotypes (Р < 0.001–0.05). The established specifics indicate that thoracic and muscular somatotypes ensure optimal adaptation of organisms to the environment. Sympathicotonia was measured among the majority of boys of extreme constitutional variants (alimentive and osseous somatotypes) (36.3% and 30.0% respectively), which demonstrates the activation of adaptive mechanisms in the abovementioned category of examined adolescents, while among girls this phenomenon was evident among the representatives of the osseous and thoracic somatotypes (38.5% and 30.8% respectively). We found that the majority of examined adolescents (53.4%) had a normal vegetative reactivity. Gender differences in the structure of vegetative reactivity of adolescents could well be explained by the higher number of girls of asympaticotonic type (19.2%) compared to boys (7.3%, Р < 0.05). Furthermore, we found that hypersympathicotonic and asympathicotonic types of vegetative reactivity were characteristic of the majority of representatives of the alimentive and osseous somatotypes irrespective of the gender, which indicates activation of functioning of the cardiovascular system, decreased adaptive capacity of the organism among the examined group. The research shows that the group at risk of developing functional deviations in vegetative systems is formed by the representatives of the alimentive and osseous somatotypes.
Coherence of EEG frequency components during manual movements executed by the subdominant hand in women
Authors: Korzhyk O. V. , Pavlovych O. S. , Morenko A. H.
Published: March 2017

The academic community is paying more and more attention to the question of the individual characteristics of the brain processes which ensure the manual motor programming of movements performed not only by the leading, but also by the subdominant hand. Researchers do not exclude the existence of the particular parameters of the human brain correlating with manual motor activities. This study involved 136 women at the age of 19–21 years. The testees were divided into two groups according to high and low values of the EEG modal α-frequency determined individually and in a motionless state. We evaluated the coherence status of the EEG frequency components in the motionless state and during movements performed by fingers of the subdominant (left) hand in response to rhythmic sound signals. The testing stages involved the sequential execution of motor tasks including clamping and unclamping performed by the fingers of the subdominant hand (such as grasping movements) without effort. The testees also performed fingering (a manual response to each stimulus) at in different times and not by all the fingers of the hand simultaneously, but separately, one by one, in a given sequence). Clamping and unclamping was executed by the fingers subject to power loading the (additional load on the fingers being 10H). Execution of manual movements by means of the subdominant hand in response to the sensory signals was accompanied by an increase in coherence in the EEG frequency components, especially in the frontal, temporal, and parietal cortexes of the central areas. Women with a low individual α-rate of such a regularity had significantly increased scores at the high (α3-, β-) frequencies of the EEG spectrum. At the same time, women in both groups mainly showed a decrease in the coherence coefficients of θ-, α1- and α3-activity in the frontal cortex leads in terms of the execution of the sequential finger movements and movements under power loading. The analysis of differences proved that women with a low IαF had relatively higher coherence of the EEG frequency components in the frontal lobes. However, relatively higher frequency components of EEG coherence in the central, posterior temporal and parietal leads were set in women with high IαF. Changes in cortical activity were established during different movements performed by fingers of the subdominant hand, namely, grasping movements of common occurrence, successive movements and movements under power loading. They differ from each other in their low specificity. Thus, the factor of motor performance of tests by means of the subdominant hand had obviously more decisive importance in the nature of the organization of brain activity than for the actual specifics of manual movements.
The Role of Hydrogen for Disordered Silicon
Authors: Nickel N. H.
Published: March 2017

The properties of hydrogen in disordered silicon are of great interest due to its beneficial and deleterious aspects. This paper highlights some of the manifold properties of hydrogen in silicon. The influence of dopants on hydrogen diffusion in poly-Si, laser-induced dehydrogenation and crystallization of amorphous silicon, and hydrogen bonding in a-Si:H, poly-Si, and c-Si are reviewed.
Low Temperature Oxynitridation of SiGe in NO/N2O Ambients
Authors: Dasgupta Anindya , Takoudis Christos G.
Published: March 2017

X-Ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and spectral ellipsometry have been used to study sub-35 Å low temperature oxynitrides of SiGe. The oxynitridations steps have been performed at 550°C and 650°C, while the oxynitridation feed gases have been preheated to 900°C and 1000°C, respectively, before entering the reaction zone. XPS and SIMS data suggests that NO-assisted oxynitridation incorporates more nitrogen than the N2O-assisted one, while there is minimal Ge segregation towards the dielectric/substrate interface in both oxynitridation processes. SIMS data suggests that the nitrogen is distributed throughout the film in contrast to high temperature Si oxynitridation where nitrogen incorporation takes place near the dielectric/substrate interface. Spectral Ellipsometry has been used to measure the final thickness of the oxynitrides film. These results are discussed in the context of an overall mechanism of the oxynitridation of SiGe.
PECVD Silicon Nitride for Damascene Applications
Authors: Lee Albert , Rajagopalan Nagarajan , Le Maggie , Kim Bok Heon , M'Saad Hichem
Published: March 2017

A Pecvd silicon nitride film, Damascene Nitride™, is deposited in a PECVD chamber with a hollow cathode faceplate using silane and ammonia as precursor gases. Various techniques (FTIR, RBS-HFS, SIMS, TDS and BTS) were used to characterize the structure, composition, density and wet etch rate of the film. FTIR analysis indicates that Damascene Nitride is very similar to a high density plasma (HDP) nitride film. HFS analysis shows the film's hydrogen content to be 13%,∼6% less than other PECVD nitride films, leading to a 20% improvement in etch selectivity to FSG. The film wet etch rate is 2 times slower than that of other PECVD nitrides, and the dielectric constant k was measured to be 6.8, which is lower compared to other PECVD nitrides and HDP CVD nitrides where k∼ 7.0 and 7.5, respectively. SIMS analysis shows that Cu diffusion is <250Å in the nitride, and low leakage current (10-10 A) is confirmed through BTS testing. The higher density of Damascene Nitride leads to higher etch selectivity and better Cu barrier properties, allowing a thinner nitride film to be used. Thinner nitride layers, in addition to the lower k of Damascene Nitride, leads to a 5-6% reduction in RC delay when Damascene Nitride is used with low k dielectric materials.
Passivation of Defect States in Amorphous and Crystalline Si by use of Cyanide Treatment and Improvement of Solar Cell Characteristics
Authors: Kobayashi Hikaru , Fujiwara Naozumi , Fujinaga Tetsushi , Niinobe Daisuke , Maida Osamu , Takahashi Masao
Published: March 2017

We have developed a new method of eliminating defect states in Si. This method called cyanide treatment simply includes immersion of Si in KCN solutions followed by the rinse. The contamination by potassium ions can be completely prevented by the inclusion of 18-crown-6 in the KCN solutions (crown-ether cyanide treatment). When the crown-ether cyanide treatment was performed on intrinsic amorphous Si (a-Si) films, decreases in the photo-and dark current densities with the irradiation time were completely prevented. When cyanide treatment using aqueous KCN solutions was applied to pin-junction a-Si solar cells, the conversion efficiencies measured before and after light-induced degradation became higher than those with no treatment. These improvements are attributed to the elimination of defect and defect precursor states by the reaction with cyanide ions, resulting in the formation of Si-CN bonds. From density functional calculations, Si-CN bonds are found to possess a high bond energy of 4.5 eV. Due to the high bond energy, the bonds are not ruptured by heat treatment at 800°C and upon irradiation, resulting in the thermal and irradiation stability of the cyanide treatment.
Temperature and Frequency Dependencies of Charging and Discharging Properties in Mos Memory Based on Nanocrystalline Silicon Dot
Authors: Huang Shaoyun , Banerjee Souri , Oda Shunri
Published: March 2017

Temperature and frequency dependencies of the electrical properties of SiO2/nanocrystalline Si (nc-Si)/SiO2 sandwich structures have been studied. A clear positive shift in capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics suggests electron trapping in nc-Si dots. The role of interface states and deep traps in these devices has also been examined, which shows that they have little effect on the overall device performance.
Amorphous Silicon Vertical Thin Film Transistor for High Density Integration
Authors: Chan Isaac , Nathan Arokia
Published: March 2017

This paper presents a fabrication process for vertical thin film transistors (VTFT) based on hydrogenated amorphous silicon (a-Si:H) technology. This process yields VTFTs with an ON/OFF ratio of 105 and a leakage current of the order of 10-13A for a channel length of 1 μm. The device structure, because of significant undercutting formed after dry-etch process (reactive ion etching or RIE), has a channel profile that is skewed as opposed to vertical. This serves to compromise the structural integrity and the electrical performance of the device. Therefore, an anisotropic dry-etch process for this channel profile is being developed. It is found that a CF4/20%H2 gas mixture yields a sharp vertical sidewall profile. In addition, a modified masking process has been developed to produce a rectangular photoresist profile so as to achieve an anisotropic etch profile for the channel region. The effects of the photoresist geometry on the anisotropic dry-etch process will be discussed.
High Voltage Amorphous Silicon Solar Cells by Hot-Wire Chemical Vapor Deposition
Authors: Wang Qi , Iwaniczko Eugene
Published: March 2017

We have achieved the best open-circuit voltage (Voc = 0.94 V) to-date in hydrogenated amorphous silicon (a-Si:H) photovoltaic cells deposited entirely by hot-wire chemical vapor deposition. The fill factor (FF = 0.74) remained high and a current density of 8-9 mA/cm2 with about 1800 Å i-layer was obtained in our n-i-p cells on untextured stainless-steel substrates. The Voc improvement of about 60 mV in compared to our previous best Voc was obtained by incorporating materials grown with H-dilution close to the phase transition from amorphous to microcrystalline silicon in the i-layer and at the i-p interface. A low substrate temperature of 150°C for the i-layer was also essential, most likely to widen the bandgap of the i-layer. A brief atomic H-treatment after grown the i-layer increases the Voc further by improving the p-i interface. The last 60 Å of the i-layer before p-layer is extremely close to the transition to microcrystallinity, though it remains mainly amorphous. Our p-layers are also close to the phase transition.
Charge-trapping Metastability in p-Type Hydrogenated Amorphous Silicon: Meyer-Neldel Rule and Entropy Change
Authors: Crandall Richard S.
Published: March 2017

Measurements of capacitance transients due to charge carrier emission from metastable defects in p-type hydrogenated amorphous silicon (a-Si:H) p/n junction structures, show that both holes and electrons can be metastably trapped in the p layer. At 350 K electrons and holes are emitted at the same rate defining the isokinetic temperature (Tiso) for the Meyer-Neldel rule. The enthalpy changes for hole and electron emission are 0.94 and 0.51 eV, respectively. The entropy changes for hole and electron emission are 31 and 16 Boltzmann constant, respectively. Charge emission rates are measured, for the first time, above and below Tiso. Below Tiso electrons are emitted faster than holes and above Tiso the reverse is true. These relative changes in emission rates are a direct consequence of the large entropy changes in the defect reactions. Tiso, within experimental error is the same as the H glass equilibration temperature (360 K) measured by others in p-type a-Si:H, suggesting that the defect reactions measured here are involved in H glass equilibration. Activation and deactivation of B atoms with accompanying charge emission likely govern both processes.
On the Surface Roughness Evolution During a-Si:H Growth
Authors: van de Sanden M.C.M. , Smets A.H.M. , Kessels W.M.M.
Published: March 2017

The surface roughness evolution during a-Si:H film growth from a SiH3 beam under purely chemical deposition conditions is discussed. The data is explained in terms of the different universality classes proposed in literature. It is argued that roughness evolution during a-Si:H growth shows great similarity with MBE growth, which belongs to a universality class studied extensively by Das Sarma and coworkers. The activation energy for surface diffusion extracted from simulating the growth exponent β vs. temperature reveals an activation energy of about 1 eV. This result suggests that the surface roughness evolution is not controlled by the weakly adsorbed SiH3 radical.
The Use of Seed Layers in Hot Wire Chemical Vapor Deposition of Microcrystalline Silicon Films
Authors: Zaharias G.A. , Mahan A.H. , Schropp R.E.I. , Xu Y. , Williamson D.L , Al-Jassim M.M. , Romero M.J. , Gedvilas L.M.
Published: March 2017

The effect of thin seed layers on the subsequent growth of thick, high growth rate bulk μc-Si is investigated by XRD, SEM and cross sectional TEM. All layers were deposited by hotwire chemical vapor deposition (HWCVD). When the seed layer as observed by XRD is highly crystalline, made by using high H2 dilution (H2:SiH4 100:1), the amorphous incubation layer typical of μc-Si growth is virtually eliminated. Furthermore, with this seed layer, bulk layer deposition conditions that would otherwise produce highly amorphous material enable a composite film with significant crystallinity. When the seed layer is predominantly amorphous, made using a much lower H2 dilution (10:1), there is evidence that very small crystallites, undetected by XRD, still facilitate immediate nucleation and enable the formation of larger grains in the subsequent bulk layer. In concurrence with other HWCVD results, lowering the filament temperature results in significant improvements in film compactness, photoresponse and grain size, while maintaining significant crystallinity. Such films have been incorporated into high deposition rate solar cells.
Amorphous to Microcrystalline Transition in Thickness-graded Hot-Wire CVD Silicon Films
Authors: Wang Qi , Perkins John , Moutinho Helio , To Bobby , Branz Howard M.
Published: March 2017

We study the amorphous to microcrystalline silicon phase transition in hot-wire chemical vapor deposition thin-film silicon by depositing a series of unique, thickness-graded, samples on a glass substrate at 200°C. By inserting or withdrawing a motor-driven shutter during growth, we make samples that vary from 200 to about 2000 Å thick across each 5-cm along stripe. Each stripe is grown at a different dilution ratio of hydrogen to silane in the source gas. The phase composition at various locations was determined by Raman and ultraviolet-reflectivity measurements. Atomic force microscopy (AFM) images of topology reveal that the surface changes from a rather smooth a-Si phase to more granular microcrystalline-Si (rms roughness increases from 10 to 47 Å).
Epitaxial Growth in Dislocation-Free Strained Alloy Films
Authors: Huang Zhi-Feng , Desai Rashmi C.
Published: March 2017

The morphological and compositional instabilities in the heteroepitaxial strained alloy films have attracted intense interest from both experimentalists and theorists. To understand the mechanisms and properties for the generation of instabilities, we have developed a nonequilibrium, continuum model for the dislocation-free and coherent film systems. The early evolution processes of surface pro.les for both growing and postdeposition (non-growing) thin alloy films are studied through a linear stability analysis. We consider the coupling between top surface of the film and the underlying bulk, as well as the combination and interplay of different elastic effects. These e.ects are caused by filmsubstrate lattice misfit, composition dependence of film lattice constant (compositional stress), and composition dependence of both Young's and shear elastic moduli. The interplay of these factors as well as the growth temperature and deposition rate leads to rich and complicated stability results. For both the growing.lm and non-growing alloy free surface, we determine the stability conditions and diagrams for the system. These show the joint stability or instability for film morphology and compositional pro.les, as well as the asymmetry between tensile and compressive layers. The kinetic critical thickness for the onset of instability during.lm growth is also calculated, and its scaling behavior with respect to misfit strain and deposition rate determined. Our results have implications for real alloy growth systems such as SiGe and InGaAs, which agree with qualitative trends seen in recent experimental observations.
Computational Modeling of Homogeneous Nucleation and Particle Growth During Chemical Vapor Deposition of Silicon Films from Silane Plasmas
Authors: Warthesen S , Bhandarkar U , Girshick S , Kortshagen U
Published: March 2017

We have been developing a model to study the nucleation and growth of particles in silane plasmas. Presently we are experimenting with parameters that could potentially be important. It has been found that an increase in the heavy species gas temperature leads to a delay in the nucleation of particles in low pressure silane plasmas. This effect could be useful in tailoring processes for the manufacture of new materials such as polymorphous silicon. We have made an effort to study this effect using a plasma chemistry model. The model includes gas temperature dependent electron attachment and vibrational relaxation of excited species with a view to study their importance in relation to the gas temperature. Preliminary simulation results predict that these two processes do not contribute substantially to slowing the nucleation process when the gas temperature is increased. Extra efforts must be made to study this potentially important effect.
Surface Roughness Evolution of PECVD Cathodic and Anodic a-Si:H.
Authors: Dalakos George T. , Plawsky Joel L. , Persans Peter D.
Published: March 2017

Surface or interface roughness can impact optical, electronic, and MEMS applications of thin a-Si:H films. Deposition at lower temperatures can be advantageous for some applications of a-Si:H, but lower temperature deposition generally leads to rougher films. We have found that the evolution of surface roughness growth can be modified substantially by ion bombardment due to the self-bias of the plasma during Plasma-Enhanced Chemical Vapor Deposition (PECVD). Notable differences in the surface roughness evolution and deposition rate are shown for films deposited in “cathodic” versus “anodic” mode – where the substrate is placed on the powered and grounded electrode respectively. Suppression of surface roughness growth of a-Si:H can be achieved under conditions of relatively high ion bombardment even at deposition temperatures as low as 75 C. Atomic force microscopy (AFM) was used to measure the relative surface roughness profile as a function of deposition time. Analysis of the power spectral density of the roughness yielded important statistical surface parameter information. Based on these observations, insight is given into growth mechanisms under the two deposition conditions.
Microwave Plasma Assisted VHF-PECVD of Micro-Crystalline Silicon
Authors: Soppe Wim , Bailat Julien , Droz Corinne , Graf Urs , Kroll Ulrich , Meier Johannes , Shah Arvind
Published: March 2017

Growth of intrinsic micro-crystalline silicon layers by means of VHF-PECVD, assisted by remote microwave (MW) plasma has been investigated. The aim of the MW plasma is to enhance the deposition rate by introducing excited hydrogen and Ar atoms from the MW plasma in the VHF deposition zone. For this purpose a remote microwave plasma source was constructed in which a H2/Ar plasma is generated in a 20 mm diameter quartz tube. A gasshower has been constructed for homogeneous distribution of the flow of excited gas species from the microwave source into the deposition zone of the VHF-PECVD reactor where the dissociation of silane takes place. In a first series of experiments we applied high microwave power (< 500 W) and pure hydrogen in the MW source. This resulted in a larger deposition rate, but all layers – even grown at low silane concentrations – were amorphous and had a high oxygen content. The oxygen contamination was partly due to reduction of the quartz tube by the hydrogen plasma. In a second series of experiments Ar dilution and reduced MW power were used to eliminate the effect of etching of the tube by the microwave hydrogen plasma. In this series of experiments an increase of the growth rate of micro-crystalline silicon by about 15 % due to assistance of the microwave plasma was found. Optical emission spectroscopy indicates that – in these experiments – the main mechanism for the increased dissociation of silane is through molecular quenching reaction of Ar* metastables.
Effects of Substrate Temperature and Atomic Hydrogen Flow on the Mircocrystallinity of Evaporated Hydrogenated silicon Films
Authors: Stoltz A.J. , Mason Whitney , Benson J.D. , Dinan J.H. , McCormack K. , Kaleczyc A.
Published: March 2017

As a first step toward an understanding of the chemical and structural role of hydrogen in hydrogenated amorphous silicon, we utilized electron beam evaporation in an ultra high vacuum environment to deposit films of amorphous silicon and systematically dosed these films with atomic hydrogen during deposition. Secondary Ion Mass Spectroscopy (SIMS) data indicated that hydrogen concentration can be varied from the detection limit of SIMS to a value in excess of 1021 atoms cm-3. The intentional addition of hydrogen caused the concentration to fall from in an excess of 1021 atoms*cm-3 to below 1018 atoms*cm-3.
Magnetic Resonance Probes Of Band Tail States And Defects In Tetrahedrally Coordinated Amorphous Semiconductors
Authors: Taylor P. C.
Published: March 2017

Recent electron spin resonance (ESR) results relating to (1) recombination processes for optically excited electrons and holes in tetrahedrally coordinated amorphous semiconductors and (2) kinetics of metastable defects (dangling bonds associated with the Staebler-Wronski effect) in hydrogenated amorphous silicon (a-Si:H). With regard to recombination processes, ESR measurements have been performed over a wide range of excitation intensities (nW/cm2 to W/cm2) on hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous germanium (a-Ge:H). The kinetics can be studied down to carrier densities as low as 1014 cm-3. The longtime decay curves show that at large carrier separation (1) the random distribution of optically excited electrons and holes is subject to the condition of charge neutrality, and (2) the decays are universal and independent of the densities of localized, band-tail states. With regard to the metastable defects in a-Si:H, the kinetics of the production and thermal annealing of silicon dangling bonds have been measured at temperatures between 25 and 480 K using ESR. Below about 150 K the measurement of the dangling bonds is masked by long-lived, band tail carriers that accumulate with time. The production rate for silicon dangling bonds decreases with decreasing temperature and is nearly temperature independent below approximately 100 K. Defects created by 10 hours of irradiation below 100 K anneal almost completely at 300 K. In a- Ge:H, the first measurements of optically induced, metastable germanium dangling bonds have been made.
Generation-Recombination Noise in a-Si:H Studied by Device Simulations
Authors: Bakker J.P.R. , Capel P.J.S. van , Fine B.V. , Dijkhuis J.I.
Published: March 2017

An attempt is made to interpret low-frequency noise measured in a-Si:H n-i-n devices based on the assumption that the noise is due to generation-recombination (g-r) processes. The interpretation is based on a spatial distribution of recombination lifetimes of electrons obtained with the help from the AMPS-1D device simulation program. These lifetimes have the same order of magnitude as that of the noise observed. Further, a distribution of lifetimes naturally results from band bending. Simulations of noise spectra are obtained by multiplication of a phenomenological weight factor to the Lorentzian spectral contribution corresponding to the local electron lifetime. There are, however, two problems with this interpretation: (i) we were not able to come up with a reasonable noise description, where the relatively long electron lifetimes were not overshadowed by much shorter times (ii) the current description, where variance is included in a weight factor, is still incomplete, and therefore we can not explain the shape of the weight factor yet.
Lifetime Regime in the Electrically-Detected Transient Grating Method Applied to Amorphous and Microcrystalline Silicon Films
Authors: Sanguino P. , Niehus M. , Koynov S. , Brogueira P. , Schwarz R. , Conde J.P. , Chu V. , Schiff E.A.
Published: March 2017

The minority-carrier diffusion length in thin silicon films can be extracted from the electrically-detected transient grating method, EDTG, by a simple ambipolar analysis only in the case of lifetime dominated carrier transport. If the dielectric relaxation time, τdiel, is larger than the photocarrier response time, τR, then unexpected negative transient signals can appear in the EDTG result. Thin silicon films deposited by hot-wire chemical vapor deposition (HWCVD) near the amorphous-to-microcrystalline transition, where τR varies over a large range, appeared to be ideal candidates to study the interplay between carrier recombination and dielectric response. By modifying the ambipolar description to allow for a time-dependent carrier grating build-up and decay we can obtain a good agreement between analytical calculation and experimental results.
Transient Photocurrents in Microcrystalline Silicon Films
Authors: Reynolds Steve , Smirnov Vladimir , Main Charlie , Carius Reinhard , Finger Friedhelm
Published: March 2017

Transient photoconductivity in microcrystalline silicon thin films prepared by VHF PECVD over a range of [silane]: [silane + hydrogen] concentrations γ from 3 to 6.3% has been measured as a function of temperature (210 K - 390 K) and laser pulse density (1013 – 1016 cm3). The behavior of highly crystalline films (γ ∼ 3%) bears certain similarities to n-type amorphous silicon, where the power law decay at long times is controlled by hole rather than electron kinetics. As γ approaches 6% the decay begins to resemble that of intrinsic amorphous silicon, consistent with structural studies which indicate a transition from crystalline to amorphous character. Transient photocurrent density of states spectroscopy on transitional films suggests a similar deep defect density to high-quality amorphous silicon, but a larger conduction band tail energy of some 30 meV and a tenfold increase in localised state density at a depth of about 0.4 eV.
Transient Decay from the Steady-State in Microcrystalline Silicon
Authors: Brüggemann R. , Reynolds S. , Main C.
Published: March 2017

We measured the transient photocurrent decay from the steady state in microcrystalline silicon from plasma-enhanced chemical vapor deposition and hot-wire chemical vapour deposition. Samples exhibiting a range of photoconductive properties in terms of both the majority and minority carrier mobility-lifetime products or sub-gap absorption coefficients were studied. Measurements were made over a wide range of steady-state photogeneration rates for which we detail the variation with generation rate of the decay time. Samples with a short steady-state photocarrier lifetime show a long decay time. We relate the slow decay process to the much larger density of traps in the band gap in the poor-quality samples. Trapped carriers are released, undergo emission and trapping processes and eventually recombine in these samples, on a much longer time-scale than in the higher-quality samples so that the decay time cannot be taken as a fingerprint for photo-electronic quality. Analytical and numerical modeling indicate bimolecular recombination behavior during the decay. Results are in agreement with free-carrier interaction with exponentially distributed band-tail states.
The Meyer-Neldel Rule in Conductivity of Microcrystalline Silicon
Authors: Ram Sanjay K. , Kumar Satyendra , Cabarrocas P. Rocai
Published: March 2017

The dark conductivity (σd) has been measured from 300 to 440K on undoped hydrogenated microcrystalline silicon (μc-Si:H) films having different thicknesses. The carrier transport is found to be thermally activated with single activation energy (Ea) in all the samples. The Ea increases as the film thickness decreases. At the same time logarithmic of dark conductivity prefactor (σo) is found to follow a linear relation with activation energy, known as the Meyer-Neldel rule (MNR). Results are explained in terms of increased degree of disorder in thinner samples. Thus change in Ea with the film thickness is directly related to the density of localized states at the Fermi level in grain boundary (GB). Therefore varying the film thickness and, hence, the exponential density of states induces a statistical shift of Fermi level which gives rise to the observed MNR.
The Effect of Aging on Tungsten Filament Surface Kinetics in Hot-Wire Chemical Vapor Deposition of Silicon
Authors: Holt Jason K. , Swiatek Maribeth , Goodwin David G. , Atwater Harry A. , Watson Thomas J.
Published: March 2017

Wire-desorbed radicals present during hot-wire chemical vapor deposition growth have been measured by quadrupole mass spectrometry. For wire temperatures in excess of 1500 K, Si is the predominant radical desorbed from a new wire, with a minor contribution from SiH3. Aged wires showed profoundly different radical desorption kinetics, consistent with evaporation of Si from liquid silicon. It is proposed that this aging is related to silicide formation at the surface of the wire.
Mapping the Phase-Change Parameter Space of Hot-Wire CVD Si:H Films Using In-Situ Real Time Spectroscopic Ellipsometry
Authors: Levi Dean H. , Nelson Brent P. , Perkins John D.
Published: March 2017

In-situ real-time spectroscopic ellipsometry (RTSE) provides detailed information on the evolution of the structural and optical properties of Si:H films during film growth. We have used in-situ RTSE to characterize the film morphology and crystallinity of hot-wire CVD (HWCVD) Si:H films as a function of hydrogen dilution R=[H]/[H+SiH4], substrate temperature Ts, and film thickness db. Transitions from one mode of film growth to another are indicated by abrupt changes in the magnitude of the surface roughness during film growth. The degree of crystallinity of the film can be determined from the bulk dielectric function. We have studied the growth parameter space consisting of R from 0 to 12, Ts from 150°C to 550°C, and db from 0 to 1 um. For each set of R and Ts values, the structural evolution of the film can be characterized by the shape of the surface roughness thickness ds versus bulk thickness db curve. In contrast to studies done by Collins et al on PECVD growth of Si:H films, our studies of HWCVD growth find no conditions where ds remains constant after coalescence of the initial nucleation centers. Most of the films grown within the range of parameters studied exhibit a secondary nucleation and coalescence signature. The transition between a-Si:H and uc-Si:H growth is near the R=3 to R=4 dividing line. Initial coalescence of purely uc-Si:H material doesn't occur until R>8. We have verified the RTsE crystallinity classification using ex-situ Raman scattering.
High Rate Deposition of Microcrystalline Silicon Solar Cells Using 13.56 MHz PECVD – Prerequisites and Limiting Factors
Authors: Roschek Tobias , Repmann Tobias , Kluth Oliver , Müller Joachim , Rech Bernd , Wagner Heribert
Published: March 2017

Microcrystalline silicon (μìc-Si:H) solar cells were prepared in a wide range of deposition parameters using high pressure 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD). Focus was on the influence of deposition pressure, electrode distance and the application of a pulsed plasma on high rate deposition of solar cells. At electrode distances between 5 and 20 mm solar cells with efficiencies >8 % were prepared. A medium electrode distance of 10 mm yielded best device performance. Pulsed plasma deposition leads to good results at medium deposition rates of ∼5 Å/s, for higher rates a strong decrease of efficiency was observed. The highest efficiencies in a small area reactor were 8.9 % for CW and 8.4 % for pulsed plasma. We also succeeded in preparing μc-Si:H and a-Si:H/μc-Si:H solar cells in a 30x30 cm2 reactor with efficiencies of 9 % and 12.5 %, respectively.