bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative analyses of chloroplast genomes in ‘Red Fuji’ apples: low rate of chloroplast genome mutations
Authors: Miao Haoyu , Bao Jinbo , Li Xueli , Ding Zhijie , Tian Xinmin
Published: February 2022

Background

Fuji is a vital apple cultivar, and has been propagated clonally for nearly a century. The chloroplast genome variation of Fuji apples in China has not been investigated.

Methods

This study used next-generation high-throughput sequencing and bioinformatics to compare and analyze the chloroplast genome of 24 Red Fuji varieties from nine regions in China.

Results

The results showed that the 24 chloroplast genomes were highly conserved in genome size, structure, and organization. The length of the genomes ranged from 160,063 to 160,070 bp, and the GC content was 36.6%. Each of the 24 chloroplast genomes encoded 131 genes, including 84 protein-coding genes, 37 tRNA genes, and eight rRNA genes. The results of repeat sequence detection were consistent; the most common sequence was forward repeats (53.1%), and the least common sequence was complementary repeats (4.1%). The chloroplast genome sequence of Red Fuji was highly conserved. Two indels were detected, but the PI value was 0, and there were no SNP loci. The chloroplast genome variation rate of Red Fuji was low.
Papillary Thyroid Carcinoma- Variants and Associated Disorders
Authors: Ravindra Savithri , Kavyashri HB
Published: February 2022

Introduction: Papillary Thyroid Carcinoma (PTC) is a malignant epithelial tumour. It is the most common form of thyroid cancer. Several variants have been described like classic, follicular, tall cell, diffuse sclerosing, papillary microcarcinoma and others. Aim: To study the variants of PTC and to evaluate the presence of associated disorders. Materials and Methods: Total of 41 cases of PTC were studied retrospectively from January 2016 to December 2018 in the Department of Pathology, Kempegowda Institute of Medical Sciences, Bengaluru, Karnataka, India. Demographic data and clinical findings were retrieved from case files. The histopathological slides were studied and the results were analysed using Fischer’s-exact test using R (Robert Gentleman and Ross Ihaka) statistical Software version 4.0.0. Results: Total data of 41 cases of PTC was collected and analysed. The patient age range between 20 to 70 years with mean age of 47 years. Female preponderance was noted. Among 41 cases, most were classic variant (31, 75.6%) followed by follicular variant (6, 14.6%), papillary microcarcinoma (3, 7.31%) and diffuse sclerosing variant (1, 2.4%). Multinodular goiter was associated with 8 cases of PTC and Hashimoto’s thyroiditis was associated with 5 cases of PTC. Among 13 cases of associated disorders, only 6 had preoperative diagnosis of PTC and remaining 7 cases were diagnosed on histopathological examination. Conclusion: Classic variant is the most common type of PTC. All thyroidectomies done for multinodular goiter and Hashimoto’s thyroiditis should be screened thoroughly for PTC especially microcarcinoma.
Animal-Assisted Therapy- A Potential Tool for Management of Dental Anxiety in Children: A Questionnaire-based Cross-sectional Study
Authors: Nalini Bashyam
Published: February 2022

Introduction: Animal-Assisted Therapy (AAT) is being developed as an alternative approach to reduce the anxiety and comfort the apprehensive patients. Hence, to evaluate the child’s and parental acceptance of pets in dental operatory, their favourite pet, child’s choice of live pet over soft toy, their preference of own pet vs therapy, more hairy pets vs less hairy pets, play area vs child’s lap, the present study is undertaken. Aim: To evaluate the influence of pets in reducing anxiety of children in the dental operatory and acceptance of this technique by the children and the parents. Materials and Methods: This questionnaire-based crosssectional study was conducted on 65 children of age group 3-12 years and their parents who attended the Department of Pedodontics and Preventive Dentistry, GITAM Dental college and Hospital, Visakhapatnam, Andhra Pradesh, India for a period of two weeks in the month of July 2018. They were assessed for anxiety and the influence of pets on anxiety levels using questionnaire and picture cards. The data was statistically analysed using Chi-square test. Results: An 83.3% of parents and 75.4% of children felt that pets in the dental operatory are useful in reducing the anxiety. A 58.5% of children preferred live pets whereas only 33.3% parents preferred them. Dog was found to be the most favourite pet for very young children (31.6%) whereas older children preferred rabbit (43.5%). Conclusion: Animal-assisted therapy was found to be useful in reducing the anxiety of children during dental visit.
Anxiety and Coping Strategies Among Medical Students During COVID-19 Pandemic: A Cross-sectional Study
Authors: Reddy C Ruth EstherTaruni , Tekulapally Kranti
Published: February 2022

Introduction: COVID-19 pandemic has impacted the mental health of medical students due to multiple factors like the fear of getting infected, the stress of maintaining the preventive measures, the demands of the online classes, and the uncertainty of the future. Aim: To assess the anxiety levels of the medical students and strategies, they used to cope up with the anxiety during the pandemic. Materials and Methods: A cross-sectional study was carried out among all the first and final year MBBS students of a Women’s Medical College and Teaching Hospital in Hyderabad, Telangana, India. The questionnaire contained a total of 25 questions- three questions to collect the demographic data, a 7-item Generalised Anxiety Disorder Scale (GAD), and 15 questions assessing their coping strategies; was distributed to all the study participants as a Google form. Data from completed questionnaires were entered into an excel sheet and analysed using Jamovi software version 1.6.23.0. Results: A total of 164 students completed the questionnaire59.1% first year MBBS students and 40.8% final year MBBS students. Mean age of the participants was 19.4 years among the first year MBBS students, and 21.7 years among the final year MBBS students. Majority of the participants had mild anxiety (43.2%). There was no statistically significant difference in the anxiety levels of the first year MBBS and final year MBBS students. The most commonly used coping strategy factor was putting trust in the god (59.7% of first year MBBS, and 62.6% of final year MBBS) while the least commonly used coping strategy was substance abuse-use of alcohol or drugs to feel better (0 among first year MBBS and 2.9% among the final year MBBS). There was statistically significant association between one of the coping strategy and anxiety-I can adjust to the situation and deal with the changes and anxiety levels (p=0.010). Conclusion: COVID-19 pandemic has impacted the mental health of medical students by causing anxiety. There is a need to mitigate these negative effects by introducing supportive programs in the form of educational programs, yoga and meditation to relieve anxiety and maintain mental health of medical students.
Seroprevalence of IgG Antibodies against Rubella in Young Females in a Medical College in Chennai, India
Authors: Nandhini KJ , Lakshmanan Anandhi , Mane Manisha S , Saraswathy MP
Published: February 2022

Introduction: Rubella being a mild infection, rarely causes any complications in childhood, will cause adverse effects during pregnancy ranging from miscarriage to a child born with congenital rubella syndrome. Females of reproductive age group must be immune to rubella to prevent infection during pregnancy. Medical students and healthcare workers should have sufficient immunity to rubella as there are increased chances of them getting exposed to the infection. To estimate the immune status against rubella, measurement of Immunoglobulin G (IgG) antibody titer will be helpful. Aim: To detect the level of IgG antibodies specific to rubella in the sera of young female students in a medical college in Chennai, Tamil Nadu, India and to determine the proportion of anti-rubella IgG seropositivity. Materials and Methods: A cross-sectional study was conducted at ESIC Medical College and PGIMSR, KK Nagar, Chennai, Tamil Nadu, India, from July 2019 to August 2019. A total of 90 female students of the age group 19-26 years were selected by random sampling method. After obtaining informed consent, their blood samples were collected. The IgG antibody titer in the serum was estimated by indirect Enzyme Linked Immuno Sorbent Assay (ELISA). Statistical analysis was done using Statistical Package for the Social Sciences (SPSS) version 26.0. Results: Based on the test results, 62 (68.9%) were immune, 25 (27.8%) were not immune, and 3 (3.3%) had indeterminate results. No association was found between the age of the participants and their immune status. Conclusion: Through this study, it can be concluded that there was a low level of seropositivity of protective rubella antibodies among females, particularly the medical students who were the study population.
Agronomic Yield Performance of Rape and Assessment of Discrimination of Soil Fertilizer Amendments on Genotypic Responses
Authors: Mayuniyuni Marshal , Tembo Langa
Published: February 2022

Aim: The objectives of the study were to (i) assess agronomic performance of rape (Brassica napus L.) genotypes under different soil amendments and seasons and (ii) identify the most discriminating soil fertilizer amendment on genotypic responses of rape.

Study Design: The experiment was laid as a split plot design with 3 replications in each season.

Place and Duration of Study: The study was undertaken in Monze district, southern province, Zambia in winter and summer periods of 2020/2021 cropping season.

Methodology: The soil fertilizer amendment combinations were the main plots and rape varieties (English Giant [ENG], Hobson [HOB] and Rampart [RAM]) were laid as subplots. Giving a total of 54 experimental units per season. The amendments constituted combinations of raw dung type and artificial fertilizer. The quantitative data, on biomass, breadth, height and leaf count were measured at six weeks after transplanting.

Results: Across seasons, soil amendment and genotypic main effects exhibited significantly responses with regards to biomass and leaf count (P = 0.05). Furthermore, the agronomic genotypic performance showed that RAM was the worst performer. The genotypic response to measured agronomic parameters was better in Raw Cow-Dung plus Cow- Dung Ash (RCD + CDA) soil fertilizer amendment than others. Interestingly RCD + CDA was the common discriminating amendment in summer and winter trials.

Conclusion: Rape genotypes performed relatively better in summer than in winter season. The genotype English giant rape and Hobson were better performers across seasons and soil fertilizer amendments. The combination of RCD + CDA was the common discriminating amendment in both summer and winter trials.
Microbial Changes During the Fermentation of Aerial Potato (Discorea bulbifera Linn)
Authors: Daniel A. B. , Akinyele B. J. , Akinyosoye F. A.
Published: February 2022

Dioscorea bulbifera is one of the under-utilized tubers in Nigeria both for food and medical purposes. Microbial changes during the fermentation of aerial potato after being subjected to different treatment were monitored using standard methods, the changes in microbial load and type of microorganisms was reported. It was observed that unpeeled backslopping fermented samples had the highest total viable bacterial count (7.06±0.05 x 105 cfu/g), lactic acid bacterial count (67.74±1.17 x 107 cfu/g) and fungal count (0.81±0.16 x 106 sfu/g), while total viable bacterial, LAB and fungal in peeled samples were 30.40±2.00 x 1010 cfu/g, 298.17±2.36 x 107 cfu/g and 133.30±0.15 x 106 sfu/g at 120 hour of fermentation respectively. Some of the bacteria isolated include Shigella flexneri, Escherichia coli, Staphylococcus aureus, Lactobacillus delbrueckii, Lactobacillus fermentum, Lactobacillus plantarum, Lactococcus lactis, while the fungal isolates were Fusarium oxysporum, Geomyces pannorum, Geotrichum candidum, Penicillium brevicompactum, Penicillium corylophilum, Saccharomyces cerevisiae, Candida tropicalis and others species. The treatment methods employed had a significant effects on the microbial load of fermented aerial potato. The fermentation methods employed have significant effects on the microbial load and type of microorganisms in the fermented aerial potato. Fermentation can be used as a food processing method to eliminate unwanted microorganisms in fermented food, which will enhance the food shelf life.
Evaluation of Nutritional Status of Haemodialysis Patients Using Malnutrition Inflammation Score
Authors: Elgamasy Mona M. , Omar Ahmed A. Abo , A. Hodeib Hossam , T. Gabr Mostafa
Published: February 2022

Background: One of the common problems of maintenance dialysis patients is malnutrition especially Protein-Energy Malnutrition (PEM) and several studies have revealed that PEM is associated with increased morbidity, mortality, and impaired quality of life. The aim of this work was to evaluate the nutritional status in hemodialysis patients using malnutrition inflammation score (MIS).

Methods: This cross-sectional study was carried out on 100 patients on regular hemodialysis. Patients were classified in to two groups according to MIS status; group A which were well nourished and group B which were malnourished. Patients included were subjected to; through history taking, laboratory investigations [CBC, Blood glucose level, Kidney function, Livre function tests, Lipid profile (cholesterol- triglycerides-HDL-LDL), Sodium-Potassium- phosphorus, C-reactive protein, ESR, Iron study (serum iron-serum ferritin-total iron binding capacity)], malnutrition-inflammation questionnaire and malnutrition-inflammation score.

Results: There was a statistically significant difference regarding blood hemoglobin, TIBC, creatinine, sodium, HDL, ESR, and CRP between two groups as they all decreased in group B more than group A, except CRP and ESR, creatinine and HDL they increased in group B more than group A (P value <0.05).

Conclusions: It is important to incorporate MIS in the care of hemodialysis patients for early detection of malnutrition and for medical nutrition therapy to optimize patients' nutritional status for better outcomes.
A Comprehensive Review on Therapeutic Perspectives of Morinda citrifolia (Indian Noni) to Combat Cancer
Authors: Rekha U. Vidhya , Bhuminathan S. , Shankar P. Ravi
Published: February 2022

Back ground: Indian Noni (Morinda citrifolia L.) is a large shrub or small evergreen tree, also known as Indian mulberry. It is a medicinal plant that has been used as conventional medicine and food additives for a long time. As a drug, plant bioactivity is attributed to its secondary metabolites. M.citrifolia has very rich nutrients and consists of over 100 varieties of chemical compounds which have been isolated so far from the plant. In disorders such as skin ailments, respiratory infections, gastritis, menstrual, abortion, diabetes, and venereal diseases, it also shows beneficial effects.

Materials and Methods: The relation of noni juice or its extract (fruit, leaves or root) to anticancer and/or immunostimulant properties was investigated in this study. A Medline quest was performed along with cross-referencing using the main search terms 'Morinda citrifolia and cancer'.

Results: According to our search results for scientific studyM. citrifolia is used in literature for more than 40 forms of ailments. Crude extract is recorded from various plant and fruit juice components. There are records of amino acids, anthraquinones, fatty acids, flavonoids, iridoids, lignans, polysaccharides, sterols, carbohydrates, terpenoids, etc. in the crude extract of different sections of plant and fruit juice that are therapeutically beneficial for a wide range of pathological conditions.

Conclusion: Literature indicates that Nonii pharmacologically active and used in various cancer types (Colon, breast, esophageal, colorectal Cancers, cardiovascular disorders, diabetes, hypertension, arthritis). This plant's high potential classifies the compounds as the noteworthy medication of the future, and clinical trials are needed to demonstrate their effect on life-threatening diseases such as cancer. Further analysis warrants the isolation of the active components. These properties can be substantiated by the preclinical or/and clinical investigations.
A Survey on Jaw Correction in Aesthetical Aspects
Authors: Safiya S. Nehal , Premavathy Dinesh
Published: February 2022

Introduction: Orthognathic surgery helps in adjusting your bite, correcting conditions that affect the symmetry of your face etc. Corrective jaw surgery or is designed to correct conditions of the jaw and lower face.

Aim: The aim of this study is to pass on the knowledge and information about Jaw correction in aesthetical aspects

Materials and Methods: The present study was a questionnaire based survey. The data was entered and analyzed using a software program called SPSS Statistics version 23.

Result: From the responses obtained, about 40 percent of the respondents belonged to the age group of 23-25 whereas about 35 percent belonged to the age group of 17-19 and the rest of 25 percent belonged to the age group of 20-22

Conclusion: The present study thus concluded that the knowledge of jaw correction in aesthetical aspects was passed on to the undergraduates students.
Comparative Evaluation of 0.5% Levobupivacaine V/S 0.5% Levobupivacaine Mixed with 20µG Dexmedetomidine in Mandibular Iii Molar Surgeries – A Double Blind Randomised Controlled Trial
Authors: Patil Shweta , Bhola Nitin
Published: February 2022

Background: Mandibular third molars (M3M) are the most common impacted teeth in the human dentition. Removal or extraction of these teeth is frightening for the patients owing to the perception of pain. As a result, pain control mechanism like anesthesia is the major factor that needs to be executed appropriately. Using newer local anesthetic drugs minimizes side effects and drug interactions. Levobupivacaine (Levo) is a congener of bupivacaine thereby minimizing the cardiotoxic effects of bupivacaine. Dexmedetomidine (Dex) is an alpha agonist which alongwith Levo is capable of providing prolonged duration of anesthesia decreasing the need for rescue analgesics.

Aim: This study will compare the anesthetic effectiveness between Levo and Levo alongwith Dex during the extraction of impacted M3M.

Methodology: A total of 50 consecutive systemically healthy patients requiring unilateral surgical extraction of impacted M3M with similar orientations will be divided into two groups randomly, one group (L) will receive nerve block with levo while the second group (LD) will receive Levo plus Dex during the extraction procedure.

Results: ‘Students t-test’ will be used to analyse and evaluate. The patients will be evaluated based on different parameters. The patient will be asked to reciprocate about the first bout of pain experience based on the Visual Analog Scale that will be handed over to patient after the procedure. The other parameters that will be evaluated are Onset on Anesthesia, Depth of Anesthesia, Hemodynamics, Oxygen saturation level, Sedation level and duration of post-operative analgesia. The patient will be evaluated over the time duration after which the patient had to take a rescue analgesic.

Conclusion: Levo with Dex is more efficient than Levo in providing prolonged duration of anesthesia and has prolonged duration of postoperative analgesia.
Redox state dependency of HERGS631C channel pharmacology: relation to C‐type inactivation
Authors: Ulens Chris , Tytgat Jan
Published: July 2002

The S631C mutation in human ether‐à‐go‐go‐related gene (HERG) channels has previously been reported to disrupt C‐type inactivation and ion‐selectivity when Cys‐631 is in the oxidized state. In this study, we report the relation between pharmacology and C‐type inactivation for HERGS631C channels. We demonstrate that HERGS631C in its reduced state is fully blocked by 1 μM astemizole, terfenadine and dofetilide, similar to wild‐type HERG channels. In contrast, oxidized HERGS631C is insensitive for these blockers. Our results suggest that an interaction with HERG channels in the inactivated state might be a common mechanism to a variety of drugs known to block HERG channels with high affinity.
Stoichiometry, Kinetics, and Regulation of Glucose and Amino Acid Metabolism of a Recombinant BHK Cell Line in Batch and Continuous Cultures
Authors: Linz Monika , Zeng An‐Ping , Wagner Roland , Deckwer Wolf‐Dieter
Published: July 2002

Batch and continuous cultures were carried out to study the stoichiometry, kinetics, and regulation of glucose and amino acid metabolism of a recombinant BHK cell line, with particular attention to the metabolism at low levels of glucose and glutamine. The apparent yields of cells on glucose and glutamine, lactate on glucose, and ammonium on glutamine were all found to change significantly at low residual concentrations of glucose (<5 mmol/L) and glutamine (<1 mmol/L) . The uptake rates of glucose and glutamine were markedly reduced at low concentrations, leading to a more effective utilization of these nutrients for energy metabolism and biosynthesis and reduced formation rates of lactate and ammonium. However, the consumption of other amino acids, especially the essential amino acids leucine, isoleucine, and valine and the nonessential amino acids serine and glutamate, was strongly enhanced at low glutamine concentration. Quantitatively, it was shown that the cellular yields and rates associated with glucose metabolism were primarily determined by the residual glucose concentration, while those associated with glutamine metabolism depended mainly on the residual glutamine. Both experimental results and analysis of the kinetic data with models showed that the glucose metabolism of BHK cells is not affected by glutamine except for a slight influence under glucose limitation and glutaminolysis not by glucose, at least not significantly under the experimental conditions. Compared to hybridoma and other cultured animal cells, the recombinant BHK cell line showed remarkable differences in terms of nutrient sensitivity, stoichiometry, and amino acid metabolism at low levels of nutrients. These cell‐line‐specific stoichiometry and nutrient needs should be considered when designing an optimal medium and/or feeding strategy for achieving high cell density and high productivity of BHK cells. In this work, a cell density of 1.1 × 107 cells/mL was achieved in a conventional continuous culture by using a proper feed medium.
Factors associated with cirrhosis development in chronic hepatitis C patients from an area of low prevalence
Authors: Verbaan H. , Widell A. , Bondeson L. , Andersson K. , Eriksson S.
Published: July 2002

The aim of this study was to evaluate the importance of different endogenous and exogenous factors associated with cirrhosis development among heptatitis C virus (HCV)‐positive individuals from an area of low prevalence. We studied 106 consecutive HCV RNA positive patients who had undergone liver biopsy. Each patient was assessed with special attention to risk factors for hepatitis C infection, average daily alcohol consumption and analysis of plasma levels of α1‐antitrypsin (α1AT) and α1‐antichymotrypsin (α1ACT). Viral RNA, amplified from serum with the polymerase chain reaction (PCR) technique, was used for genotyping. Liver biopsies were assessed according to conventional histopathological criteria, and for necroinflammatory activity (grade) and fibrosis (stage) according to a numerical scoring system. The presence of cirrhosis (stage 4) was used as the dependent variable in multivariate logistic regression analysis. Alcohol abuse (P=0.007), age at entry (P<0.001), immigrant status (P=0.017) and a low α1ACT level (P=0.008) were all independent determinants of progression to cirrhosis whereas HCV genotype 1, estimated duration of HCV infection and positivity for antibodies to hepatitis B core antigen (HBcAb) were not. Cirrhosis occurred at a significantly younger age (P=0.005) among alcohol abusers. Hence, both endogenous and exogenous factors such as subnormal α1ACT levels and alcohol appear to contribute to the rate of progression to cirrhosis among HCV‐positive patients.
Isozyme Variation and Ploidy Levels within the Apomictic Ranunculus auricomus Complex: Evidence for a Sexual Progenitor Species in Southeastern Austria
Authors: Hörandl E. , Greilhuber J. , Dobeš C.
Published: July 2002

Abstract: Allozyme variation of 11 enzymes in each of three populations of the diploid species Ranunculus notabilis and the tetraploid R. variabilis of the predominantly apomictic R. auricomus complex has been studied by horizontal starch gel electrophoresis. Genetic interpretation of electrophoretic patterns is supported by chromosome counts and densitometric ploidy level determination. R. notabilis is confirmed as diploid (2 n = 16), and R. variabilis as tetraploid (2 n = 32). Two triploids and one tetraploid individual were sorted out as putative hybrids. Genetic variability measures based on both allelic frequencies and genotype frequencies were calculated for 13 polymorphic loci. Allelic and genotypic variation in R. notabilis is similar to other sexual plants, and the species is shown to be an outbreeder and not a dihaploid apomict. Corresponding values in R. variabilis confirm a previously assumed clonal population structure. A higher frequency of observed heterozygotes in R. variabilis indicates its hybridogenous origin and the lack of meiosis. Putative hybrids showed combinations of morphological phenotype and electrophoretic patterns of both species. Genetic identity is high among species (0.905), but still lower than within species (R. notabilis: 0.965, R. variabilis: 0.940); corresponding distance values allow a clear separation of the two species in a dendrogram. Genetic identity and distance values between R. notabilis and R. variabilis resemble those of other progenitor‐derivative species pairs. The results favour the hypothesis that R. notabilis is an ancient sexual species of the R. auricomus complex and also one progenitor of the presumably allopolyploid R. variabilis.
Characterization of semi-insulating GaAs wafers by room-temperature EL2-related photoluminescence
Authors: Tajima Michio
Published: July 2002

Deep level photoluminescence (PL) associated with the dominant midgap donor EL2 in semi-insulating (SI) GaAs crystals has been observed for the first time at room temperature. A broad emission band with a peak at 0.65 eV was observed always in commercial undoped SI GaAs wafers. The association of the 0.65 eV band with the EL2 level has been verified on the basis of the semiquantitative agreement of the distribution on wafers between the PL intensity and the EL2 absorption. Room-temperature PL spectroscopy can be used as a powerful tool to investigate the nonuniformity of the EL2 distribution on commercial wafers with a high spatial resolution.
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u substrate-surface cleaning for very low temperature silicon epitaxy by low-kinetic-energy particle bombardment
Authors: Ohmi T. , Ichikawa T. , Shibata T. , Matsudo K. , Iwabuchi H.
Published: July 2002

A very low temperature in situ substrate-surface cleaning process utilizing low-kinetic-energy particle bombardment has been developed. Dramatic improvements have been achieved in the crystallinity of epitaxial silicon films grown by the newly developed low-kinetic-energy particle process, in which argon ions having precisely controlled energies are continuously bombarding the film surface during the entire growth operation. With the optimized substrate-surface cleaning conditions, in which the contaminants on the surface of silicon substrates are removed without introducing any damages to the substrates, the epitaxial silicon layer with a perfect crystallinity has been obtained at such very low temperatures below 350 °C.
Buried GaInAs/InP layers grown on nonplanar substrates by one-step low-pressure metalorganic vapor phase epitaxy
Authors: Galeuchet Yvan D. , Roentgen Peter , Graf Volker
Published: July 2002

Growth of GaInAs/InP layers on nonplanar substrates by low-pressure metalorganic vapor phase epitaxy has been investigated using InP substrates patterned with [011] and [011̄] oriented grooves and mesas. For a wide range of growth parameters we find that GaInAs does not grow on {111}A and {111}B surfaces whereas InP grows on all available crystal planes. This allows very narrow GaInAs layers to be embedded in InP within one growth step. We find that the growth rate on the (100) surface of a mesa increases for both materials when the mesa width is reduced below ∼2 μm. The results are explained with a growth model where crystal facet-dependent surface catalyzed reactions dominate the growth on a microscopic scale. These lead to blocking of low growth rate planes for the adsorption of arriving species and to local redistribution of adsorbed molecules by surface diffusion.
Low-noise modular microsusceptometer using nearly quantum limited dc SQUIDs
Authors: Awschalom D. D. , Rozen J. R. , Ketchen M. B. , Gallagher W. J. , Kleinsasser A. W. , Sandstrom R. L. , Bumble B.
Published: July 2002

A flexible combination of superconducting integrated circuits was used to construct a low-temperature magneto-optic microsusceptometer utilizing a dc superconducting quantum inteference device (SQUID) detector operating near the quantum limit (coupled energy sensitivity of 1.7ℏ). Miniature pick-up loop assemblies on transparent substrates were joined by superconducting interchip connections to a thin-film dc SQUID, which is in turn read out by a second dc SQUID connected to room-temperature electronics. Measurements on an 8.5-μm-diam titanium dot evaporated directly into the pick-up loop demonstrate a spin sensitivity of ∼103 spins/(Hz)1/2 at T=290 mK.
Tunneling lifetime broadening of the quantum well intersubband photoconductivity spectrum
Authors: Levine B. F. , Bethea C. G. , Choi K. K. , Walker J. , Malik R. J.
Published: July 2002

We have measured, for the first time, the continuous infrared (λ∼10 μm) photoconductivity spectrum, for an intersubband absorption photoexcited tunneling quantum well detector. The line shape is broadened and asymmetrical with respect to the zero-bias Lorentzian absorption spectrum. We show that this is a result of the uncertainty principle lifetime broadening due to the rapid tunneling escape of the photoexcited electrons.
Ion beam enhanced diffusion of B during Si molecular beam epitaxy
Authors: Pukite P. R. , Iyer S. S. , Scilla G. J.
Published: July 2002

Enhanced diffusion of B is observed during the growth of ion bombarded epitaxial layers by Si molecular beam epitaxy. Ion-assisted methods are generally required for high levels of n-type doping, and we find that the damage caused by the low-level ion bombardment is responsible for the enhanced diffusion of B. Furthermore, the concentration profiles of as-grown and post-growth annealed samples show that the diffusion is a transient effect that occurs at the growth temperature of 600–700 °C. Simulation of the diffusion process demonstrates that nearly all of the B is participating in the diffusion and that the built-in electric field at the p-n junction leads to a further smearing of the B profile.
Surface morphological microstructures of poly(ethylene 2,6-naphthalate) modified by excimer laser ablation
Authors: Niino Hiroyuki , Yabe Akira , Nagano Shozaburo , Miki Tetsuro
Published: July 2002

KrF excimer laser photoablation of semicrystalline poly(ethylene 2,6-naphthalate) showed characteristic microstructures on the surface. These stable and well-defined structures were investigated with scanning electron microscopy, transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy. The results of TEM analysis have revealed that the debris of the microstructures is composed of a polymer with a higher density.
Optical evidences of assisted tunneling in a biased double quantum well structure
Authors: Liu H. W. , Ferreira R. , Bastard G. , Delalande C. , Palmier J. F. , Etienne B.
Published: July 2002

Experimental evidences of electron and hole resonant tunnelings are obtained in a biased double quantum well system using optical methods. Calculations of the defect-induced tunneling rates are performed and compared with experiments.
Role of vanadium in organometallic vapor phase epitaxy grown GaAs
Authors: Hobson W. S. , Pearton S. J. , Swaminathan V. , Jordan A. S. , Kanber H. , Kao Y. J. , Haegel N. M.
Published: July 2002

The electrical and photoluminescent properties of vanadium incorporated into GaAs epitaxial layers from a VO(OC2H5)3 source during organometallic vapor phase epitaxy were examined. The vanadium concentration in the GaAs was controllably varied from 1016 to 1018 atoms cm−3. Deep level transient spectroscopy showed the presence of an electron trap at Ec−0.15 eV which increased in concentration with vanadium content of the epitaxial layers. A maximum value of 8×1015 cm−3 for this trap was obtained. There were no midgap electron traps associated with vanadium. In intentionally Si-doped epitaxial layers, co-doping with vanadium was observed to have no effect in reducing the carrier density when the Si concentration was ≥4×1016 cm−3. The net carrier concentration profiles resulting from 29Si implantation into GaAs containing 1018 cm−3 of total V had sharper tails than for similar implantation into undoped material, indicating the presence of less than 1016 cm−3 V-related acceptors. Photoluminescent spectra exhibited the characteristic V+3 intracenter emission at 0.65–0.75 eV. No other deep level photoluminescence was detected. For a V concentration of 1016 cm−3 only 2.5×1013 cm−3 was electrically active. Over the entire V concentration investigated this impurity was predominantly (≥99%) inactive.
Characterization of very thin Si oxynitride films produced by rapid thermal processing
Authors: Novkovski N. , Aizenberg I. , Goin E. , Fullin E. , Dutoit M.
Published: July 2002

The electrical properties of thin films of SiO2 can be improved by nitridation and reoxidation. They are very sensitive to the nitrogen profile, as well as to other impurities, such as hydrogen or water, for example, which makes it necessary to carefully adjust processing parameters. The purpose of this work is to characterize very thin oxynitride films produced by rapid thermal processing (RTP) and to optimize their electrical properties in view of applying them in electrically erasable programmable read-only memories (EEPROMs). We propose a novel etch-back and test oxidation technique that is very sensitive to traces of nitrogen at the oxynitride/Si interface. We show a strong correlation between the oxidation resistance of the interface and the electrical properties of metal-oxide-silicon (MOS) capacitors fabricated with these films. Nitridation conditions that give a maximal resistance to oxidation (for example, 4 s at 1100 °C) also provide the lowest values of interface charges and traps after reoxidation. Using these processing parameters, we achieve a significant increase in charge to breakdown.
Crystalline diamond growth in thin films deposited from a CH4/Ar rf plasma
Authors: Amaratunga Gehan , Putnis Andrew , Clay Kim , Milne William
Published: July 2002

Observation of single-crystal diamond growth in thin films obtained from the rf decomposition of a CH4/Ar plasma is reported. The films were deposited on Si substrates which were kept at 20 °C. Polycrystalline diamond grains are seen over the entire film. Single-crystal diffraction patterns obtained from larger grains all show {111} twinning.
Low-temperature deposition of diamond films for optical coatings
Authors: Ong T. P. , Chang R. P. H.
Published: July 2002

A low-temperature (≊400 °C) plasma-enhanced chemical vapor deposition process has been developed to grow diamond films for optical coatings application. Films with fine grains (≤3000 Å) have been obtained by controlling diamond nucleation. The surface roughness of the films is on the order of 50–200 Å. The optical transparency of the films is over 60% in the range 0.6–2 μm wavelength, which is comparable to that of Type IIa natural diamond. Using a block-on ring tribotester, it is found that the diamond films adhere well to quartz substrates.
Photoluminescence and Raman studies of residual stresses in GaAs directly grown on InP
Authors: Freundlich A. , Grenet J. C. , Neu G. , Landa G. , Carles R.
Published: July 2002

We report first-order Raman spectroscopy and low-temperature photoluminescence (PL) studies of GaAs layers grown by metalorganic vapor phase epitaxy (MOVPE) on InP (100) substrates. From both the shift of the longitudinal-optical phonons in the Raman spectra and the splitting and shift of band-edge exciton lines in PL, the epilayers are found to be under (100) coplanar tensile stress, which is consistent with the difference between the thermoelastic properties of the two materials. The PL analysis shows that carbon is the main residual acceptor impurity in MOVPE-grown GaAs/InP.
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u measurements of critical layer thickness and optical studies of InGaAs quantum wells grown on GaAs substrates
Authors: Elman B. , Koteles Emil S. , Melman P. , Jagannath C. , Lee Johnson , Dugger D.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) intensity oscillations have been used during molecular beam epitaxy (MBE) to accurately determine threshold layer thicknesses for two-dimensional (2D) growth of InxGa1−xAs on GaAs for a wide range of substrate temperatures and indium compositions. InxGa1−xAs/GaAs single quantum wells were also grown by MBE and studied using low-temperature photoluminescence (PL) spectroscopy. PL peak energy, intensity, and linewidth measurements provided information on the critical layer thicknesses for the formation of dislocations which, under our experimental conditions, were the same as the threshold layer thicknesses for 2D growth measured from the damping behavior of RHEED intensity oscillations.
Interface study of hydrogenated amorphous silicon nitride on hydrogenated amorphous silicon by x-ray photoelectron spectroscopy
Authors: Beaudoin M. , Arsenault C. J. , Izquierdo R. , Meunier M.
Published: July 2002

The interface between near stoichiometric hydrogenated amorphous silicon nitride (a-SiNx :H) deposited on hydrogenated amorphous silicon (a-Si:H) is studied using x-ray photoelectron spectroscopy as a function of the electron escape angle. This method allows the study of a-SiNx :H overlayers of about 40 Å thickness which is typical of the thicknesses used for well and barrier layers in superlattices and quantum well structures. Within the instrument’s resolution, subnitride components constitute less than 1% of the interface bonds. It is therefore concluded that the interface is atomically abrupt.
Short time electron cyclotron resonance hydrogenation of polycrystalline silicon thin-film transistor structures
Authors: Ditizio R. A. , Liu G. , Fonash S. J. , Hseih B.-C. , Greve D. W.
Published: July 2002

Electron cyclotron resonance plasmas have been used to produce the most effective, shortest time plasma hydrogenation of thin-film polycrystalline silicon transistors yet reported. We demonstrate that significant improvement in device characteristics can be achieved with these plasmas using exposure times of the order of only 1 min and that 5 min exposures give saturated characteristics of a 2 V threshold voltage, a 65 cm2/V s mobility, and a 107 on/off ratio. We also explore the pressure and power level dependence of this passivation, as well as the effects of shielding with a grid, and show that the more efficient and more stable electron cyclotron resonance hydrogen exposures are at lower pressures.
Generation of femtosecond electromagnetic pulses from semiconductor surfaces
Authors: Zhang X.-C. , Hu B. B. , Darrow J. T. , Auston D. H.
Published: July 2002

We have generated electromagnetic beams from a variety of semiconductors. When a bare semiconductor wafer was illuminated by femtosecond optical pulses, electromagnetic waves radiate from the surface and form collinear diffraction-limited electromagnetic beams in the inward and outward directions. The amplitude and phase of the radiated field depend on carrier mobility, the strength and polarity of the static internal field at the semiconductor surface.
Realization and analysis of GaAs/AlAs/In0.1Ga0.9As based resonant tunneling diodes with high peak-to-valley ratios at room temperature
Authors: Kapre R. , Madhukar A. , Kaviani K. , Guha S. , Rajkumar K. C.
Published: July 2002

Investigations of pseudomorphic resonant tunneling diodes based on the GaAs/AlAs/In0.1Ga0.9As material system reveal that the use of undoped In0.1Ga0.9As spacer layers gives rise to a significantly enhanced peak-to-valley ratio of 3.2 and 14 at 300 and 77 K, respectively, as opposed to 2 and 5 obtained with the use of conventional GaAs spacers in an otherwise identical structure. This is achieved without any significant degradation of the peak current density but rather through reduction of the undesired nonresonant valley current. Comparison of the experimental results with calculations done using the Airy function transfer matrix approach indicates that the Γ-X discontinuity at the GaAs/AlAs and In0.1Ga0.9 As/AlAs interface is relevant for electron tunneling, along with the smaller transverse effective mass of 0.19m0 in the AlAs X valley. We also find that In0.1Ga0.9As layers grown under an excess As-stabilized growth condition give better results than those grown under a barely As-stabilized condition.
Influence of spacer layer thickness on the current-voltage characteristics of AlGaAs/GaAs and AlGaAs/InGaAs resonant tunneling diodes
Authors: Yoo H. M. , Goodnick S. M. , Arthur J. R.
Published: July 2002

We have investigated the dependence of the current-voltage characteristics of AlGaAs/GaAs and AlGaAs/InGaAs resonant tunneling diodes (RTDs) on spacer layer thickness. The measured peak to valley current ratio of the RTDs studied here is shown to improve while the current density through the RTDs decreases with increasing spacer layer thickness below a critical value. We find significant differences in the effect of the spacer layer thickness between AlGaAs/InGaAs and AlGaAs/GaAs RTDs, which we believe to be related to the relative quasi-bound state energies of the two systems.
High coercivity in mechanically alloyed Sm-Fe-V magnets with a ThMn12 crystal structure
Authors: Schultz L. , Schnitzke K. , Wecker J.
Published: July 2002

Microcrystalline Sm-Fe-V magnets with a ThMn12 crystal structure were prepared by mechanical alloying and a subsequent reaction heat treatment. In Sm15Fe70V15 a coercivity of 11.7 kOe is obtained. This is the best value reported so far for 1:12 magnets. As expected from their high anisotropy fields, the 1:12 magnets, therefore, show coercivities which are common in the Nd-Fe-B system.
Quantum-confined field-effect wavelength tuning in a three-terminal double quantum well laser
Authors: Huang F. Y.
Published: July 2002

A three-terminal quantum-confined field-effect double quantum well laser device is proposed. The wavelength shift scheme caused by the field-induced change in the energy levels is demonstrated. With the current injected and the electric field applied to different wells, wide range wavelength shift can be achieved by changing the applied field.
Effects of carrier mass differences on the current-voltage characteristics of resonant tunneling structures
Authors: Ohno H. , Mendez E. E. , Wang W. I.
Published: July 2002

We show that the current-voltage characteristics of resonant tunneling structures are drastically influenced by the difference of electronic effective masses between the electrodes and the quantum well. In particular, if the mass in the well is larger than that in the emitter, the current peak is shifted to lower voltages, relative to the more conventional case of equal masses. This situation is illustrated experimentally with GaAs/AlAs/GaAs heterostructures, in which Γ electrons emitted from GaAs tunnel resonantly through the AlAs X point, where the mass is considerably heavier.
Nanometer resolution in luminescence microscopy of III-V heterostructures
Authors: Abraham D. L. , Veider A. , Schönenberger Ch. , Meier H. P. , Arent D. J. , Alvarado S. F.
Published: July 2002

In a scanning tunneling microscope experiment, the luminescence induced by the recombination of holes with electrons tunneling into cleaved (110) GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.
Cross-section transmission electron microscopy study of carbon-implanted layers in silicon
Authors: Wong H. , Lou J. , Cheung N. W. , Kvam E. P. , Yu K. M. , Olson D. A. , Washburn J.
Published: July 2002

We have used cross-section transmission electron microscopy (XTEM) to study microstructures of carbon-implanted silicon layers after high-temperature annealing. It was found that the threshold dose for extended defect formation was much higher for carbon implantation than for other ion species such as B, P, and O. In 2.4 MeV carbon-implanted layers, no dislocations were formed for doses as high as 2×1016 cm−2 after annealing at 1000 °C for 1 h. The threshold was found to be lower for low-energy implantation (100 keV): at a dose of 2×1016 cm−2, when an amorphous layer was formed, microtwins were formed near the projected range upon annealing. Microprecipitates around 50 Å in size were observed in low-energy carbon-implanted samples and the precipitates appeared to be under strain.
Role of step-flow dynamics in interface roughening and in the spontaneous formation of InGaAs/InP wire-like arrays
Authors: Cox H. M. , Aspnes D. E. , Allen S. J. , Bastos P. , Hwang D. M. , Mahajan S. , Shahid M. A. , Morais P. C.
Published: July 2002

We investigate a morphological instability that causes an InGaAs/InP multiquantum well structure grown on a vicinal (001) InP surface to spontaneously evolve into an array of InGaAs quasi-one-dimensional filaments buried in an InP matrix. To explain this behavior, we propose a step-flow growth model involving different lateral growth velocities for heteroepitaxy and homoepitaxy. A computer simulation based on the model agrees closely with the experiment.
Epitaxial ferromagnetic τ-MnAl films on GaAs
Authors: Sands T. , Harbison J. P. , Leadbeater M. L. , Allen S. J. , Hull G. W. , Ramesh R. , Keramidas V. G.
Published: July 2002

We report the growth of epitaxial τ-MnAl ferromagnetic films on GaAs substrates by molecular beam epitaxy (MBE). Reflection high-energy electron diffraction and x-ray diffraction show that the τ-phase films grow with the c axis of the tetragonal unit cell normal to the {100}GaAs substrate surface. In the bulk, τ-MnAl is a metastable ferromagnetic phase with uniaxial magnetocrystalline anisotropy. The large hysteresis observed in the Hall resistance versus applied magnetic field suggests that the easy magnetization direction is indeed parallel to the c axis in the MBE-grown films. The growth of these ferromagnetic films with perpendicular magnetization on compound semiconductor substrates creates the possibility of novel devices that combine magnetic memory and magneto-optic functions with semiconductor electronics and photonics.