bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial Intelligence-based tools in the context of Open Science
Authors: Faber Hege Charlotte Lysholm , Gasparini Andrea Alessandro , Grote Michael
Published: November 2022

This poster presents possibilities and issues concerning the new wave of Artifical Intelligence (AI)-based services and tools entering academia aimed to help researchers and students. Iris.ai, semanticscholar.org, yewno.com, connectedpapers.com, researchrabbit.ai, www.paper-digest.com, openknowled-gemaps.org, and keenious.com, are all examples of services part of a complex landscape of educational and research support resources driven by AI. Unfortunately, researchers and students have very few arenas to learn about all the aspects of using those resources. Trust, ethics, interpretability and reliability, are all topics to be addressed when using those tools (Guidotti et al., 2018). Moreover, the lack of possibility to test and influence how literature is analyzed and new knowledge created by AI-based services, is an emerging concern in various academic libraries (Gasparini & Kautonen, 2016). The increasing production of fake science in AI-based papermills implies new challenges for academic quality control and for the accountability and reliability of research as a whole (Løkeland-Stai, 2022).
The poster proposes to use the site PhD-on-track (https://www.phdontrack.net/, Faber et al., 2018), one of the preferred starting points for new PhD candidates and early career researchers, to contextualize AI-based services in researchers’ literature search and analysis. PhD on Track aims to enable PhD candidates from all academic fields to easily access information on different aspects of open science and support academic integrity in their research practices. By addressing AI-based services and tools in an early stage, PhD on Track will contribute to avoid opacity and clarify non-intuitive aspects of the use of technology in research. Furthermore, we argue for the possibility that these technical innovations will change the workflows of researchers and students. Academia needs to react to this development, offer a framework and support a shift of focus on AI-based services from the micro level (users) to a wider institutional one (the university).
The poster will present the following issues and questions, with respective possible reactions and solutions: 

What is the minimum level of competence PhD candidates should have about machine learning and deep learning? 
How should PhD candidates choose reliable AI-based services? 
When and where should PhD candidates and researchers gather reliable information about AI-based services? 
How should academic libraries support access to repositories of Open Access articles? 
How should universities ensure the correct use of AI-based tools? 
How can universities and academic libraries address ethical questions which may be raised by the increasing availability and use of AI-based tools?
Linking the dots
Authors: Cheng Chieh-Chih Estelle , Marín-Arraiza Paloma
Published: November 2022

One of the key concepts in open science is sharing, but this may not be in place without open research infrastructure. Openness is one of the key ORCID values, and we work with the global community and partners to build and sustain a technology infrastructure that not only allows the sharing of research information between systems but also enables the open creation of linkages between researchers, research institutions, publishers, and funding organisations. The global publishing community is one of the earliest ORCID adopters and has been one of the most significant contributors to the data in the ORCID Registry. Although substantial publishers have implemented ORCID into the publishing workflow, their practices vary due to various reasons, such as the capacities of the publishing systems they use or their levels of support for ORCID.
To maximise the benefits of ORCID in the publishing workflow will require publishers to follow the best practices of ORCID adoptions. By implementing deeper workflows with ORCID, researchers and organisations benefit from ‘trust markers’ to advance trusted research worldwide and improve the integrity of the research process. This is achieved through affiliation data added by the institutions, contributions on the researcher records that other publishers or repositories have added, and funding history or additional data such as other person identifiers and organisation identifiers. This trusted data can then be used further downstream in the community’s workflows.
Treatment for dental erosion: a systematic review of in vitro studies
Authors: Né Yago Gecy de Sousa , Souza-Monteiro Deiweson , Frazão Deborah Ribeiro , Alvarenga María Olimpia Paz , Aragão Walessa Alana Bragança , Fagundes NatháliaCarolina Fernandes , Souza-Rodrigues Renata Duarte de , Lima Rafael Rodrigues
Published: November 2022

Background

Dental erosion is a chemical loss of the mineralized dental tissue caused by exposure to nonbacterial acids. Different treatment protocols have been adopted with the use of fluoride compounds to promote the formation of a layer of mineral precipitation in eroded lesions.

Aim

This systematic review aimed to evaluate the main treatments for dental erosion.

Methodology

This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and recorded in the Open Science Framework database (OSF) under DOI 10.17605/OSF.IO/XMFNZ. The searches were conducted in six electronic databases (Pubmed, Embase, Web of Science, Cochrane, Scopus, Lilacs) and two grey literature sources (Google Scholar and OpenGrey). The eligibility criteria included in vitro studies that evaluated eroded teeth under treatment with some topical agent. Risk of bias assessment and qualitative synthesis were performed using the Cochrane collaboration’s tool for assessing risk of bias modified for in vitro studies.

Results

A total of 522 studies were identified, and only four studies that fulfilled our eligibility criteria were included in this review. Among these studies, three were considered to have a low risk of bias, and one to have a high risk of bias. Two studies evaluated the anti-erosion effect of fluoride toothpaste, and the other two assessed the action of casein phosphopeptide–amorphous calcium phosphate (CPP-ACP) on the surface of human teeth. Among the products analyzed, CPP-ACP was the only one that promoted a significant increase in enamel microhardness and reduced tooth wear.

Conclusion

Based on the in vitro studies included in this review, there was no anti-erosion effect after using different fluoride toothpaste. However, it should be considered that one of these studies presented a high risk of bias. On the other hand, studies with CPP-ACP showed anti-erosion efficacy when applied before or after erosive wear.
In silico ATP Synthase Inhibition Activity and Antibacterial Activity of Selected Essential Oil against Escherichia coli and Resistant Acinetobacter baumannii
Authors: Boddupalli Bindu Madhavi , Ramani Ramalingam , Jacob Barnabas Mwambua , Ramaiah Sivakumar , Mungoma Micheal , Wanaina Samwel
Published: November 2022

The rise in the resistant strains has ignited the investigation of the ability of these essential oils to have an effect against them. The aim of this study was to investigate the antibacterial activity of clove oil, oregano oil and tea tree oil against Escherichia coli and resistant patient isolate Acinetobacter baumannii. Ciprofloxacin was used as standard and DMSO at 1 % was the negative control. To understand the inhibitory action on ATP synthase, docking analysis was done by using Autodock ver. 4.2.6. The study found out that essential oils had potent antibacterial activity against both E. coli and A. baumannii as all the essential oils recorded zones above 15 mm against E. coli and above 20 mm against A. baumannii. Tea tree oil had the highest activity among the three essentials against E. coli with 21.000±0.00 mm and against A. baumannii 28.500±0.500 mm respectively. These results support the antibacterial activity of essential oils. Docking analysis confirmed the ability of active constituents of selected essential oils to inhibit ATP synthase enzyme which is a crucial drug target in antimicrobial activity. Natural products have been at the center stage in the research for alternative agents with antibacterial agents.
Assignment of the backbone 1H,15N, 13C NMR resonances and secondary structure of a double‐stranded RNA binding domain from the Drosophila protein staufen
Authors: Bycroft Mark , Proctor Mark , Freund Stefan M.V. , Johnston Daniel St.
Published: July 2002

NMR spectroscopy has been used to determine the secondary structure of one of the double‐stranded RNA binding domains from the Drosophila protein staufen. The domain has an αβββα arrangement of secondary structure, with the β strands forming an antiparallel β sheet. The secondary structure differs from that found in the RNP RNA binding domain.
Repeated immunolesions display diminished stress response signal
Authors: Gu Zezong , Yu Juan , Werrbach‐Perez Karin , Perez‐Polo J. Regino
Published: July 2002

Cholinergic basal forebrain neurons (CBFNs) retrogradely transport neurotrophins released in the hippocampus and cortex as part of a general response to injury in a process that is impaired in the aged rodent and can be spared by the exogenous addition of pharmacological doses of nerve growth factor (NGF). This observation suggests that components of stress response signal transduction pathways in the aged CNS can be exogenously activated. The extent and mechanism of the endogenous stimulation of NGF in response to injury can be mimicked via treatment with 192 IgG‐saporin of rat CNS, an immunolesion model. Here we report on the use of a conditioning lesion paradigm to determine if repeated partial immunolesions have a conditioning effect on the immunolesion‐induced increases in NGF protein or decreases in choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity.

We report that chronic repeated immunolesions, as used here, were not as effective as a one time equivalent immunolesion in terms of induced NGF protein increases or decreasing ChAT and AChE activity in the hippocampus and cortex. Thus, chronic lesions resulting in cholinergic impairment typical of the aged CNS may differ from acute toxic models as a result of desensitization due to a conditioning effect of chronic subthreshold lesioning events in the CNS.
Factors Important in the Extraction, Stability and in Vitro Assembly of the Hepatitis B Surface Antigen Derived from Recombinant Plant Systems
Authors: Smith Mark L. , Keegan Mark E. , Mason Hugh S. , Shuler Michael L.
Published: July 2002

The expression of vaccine antigens in edible plant material together with their delivery by the oral route constitutes a powerful paradigm, with the potential to dramatically reduce the cost of vaccine production and administration, in addition to improving distribution and patient compliance. These products will be subject to many of the same regulations applied to current injectable vaccines, so reliable methods to quantify antigen and ensure stability in crude plant extracts are required. As a model system the hepatitis B surface antigen (HBsAg) was expressed in soybean and tobacco cell cultures. This complex antigen consists of membrane‐associated small surface antigen proteins (p24s), disulfide cross‐linked to yield dimers and higher multimers. Although the total p24s extracted from plant cells was relatively unaffected by detergent concentration, the quantification of antigenically reactive product depended strongly on the ratio of detergent to cell concentration. Furthermore, 1–20% w/v sodium ascorbate improved the measured levels of monoclonal‐reactive antigen 4‐ to 12‐fold. Detergent also influenced antigen stability in cell lysates stored at 4 °C; under optimum conditions stability was maintained for at least 1 month, whereas excess detergent rendered the antigen susceptible to proteolytic degradation. This proteolysis could be counteracted by the addition of skim milk or its protein component, which stabilized antigenically reactive p24s for up to 2 months. The immunologically relevant epitopes of HBsAg are critically dependent on disulfide bonding. By altering the sodium ascorbate concentration or buffer pH the proportion of HBsAg displaying the monoclonal reactive epitopes was increased between 8‐ and 20‐fold. In addition, under certain conditions the dimerized p24s could be converted to oligomeric aggregates, resembling the form of the serum‐derived antigen. These simple in vitro manipulations, compatible with the goal of a minimally processed oral vaccine, may prove valuable in increasing the immunogenicity of the plant‐derived antigen.
Modeling Heat Transfer during High‐Pressure Freezing and Thawing
Authors: Denys Siegfried , Van Loey Ann M. , Hendrickx Marc E. , Tobback Paul P.
Published: July 2002

An existing theoretical model for predicting product temperature profiles during freezing and thawing processes was extended for simulating high‐pressure freezing and thawing processes. To take into account the influence of elevated pressure a simplifying approach is suggested, consisting of shifting the known thermophysical properties at atmospheric pressure on the temperature scale depending on the prevalent pressure. The applicability of the method to simulate high‐pressure freezing and thawing profiles was tested for a food simulant (Tylose) . Good agreement between experimental and predicted temperature profiles was observed for both high pressure freezing and thawing.
Assignment of the disulfide bonds of Ole e 1, a major allergen of olive tree pollen involved in fertilization
Authors: González E. , Monsalve R.I. , Villalba M. , Rodríguez R. , Puente X. S.
Published: July 2002

Abstract: The most prevalent allergen from olive tree pollen, Ole e 1, consists of a single polymorphic polypeptide chain of 145 amino acids which includes six cysteine residues at positions 19, 22, 43, 78, 90 and 131. By using an homogeneous form of the allergen expressed in Pichia pastoris, the array of the disulfide bridges has been elucidated. Specific proteolysis with thermolysin and reverse‐phase HPLC separation of the peptides allowed the determination of the disulfide bond between Cys43 and Cys78. Another thermolytic product, which contained three peptides linked by the remaining four cysteines, was digested with Glu‐specific staphylococcal V8 protease and the products isolated by reverse‐phase HPLC. Amino acid compositions and Edman degradation of the peptide products indicated the presence of the disulfide bonds at Cys19–Cys90 and Cys22–Cys131. These data can help in the analysis of the three‐dimensional structure of the protein as well as in studies of its allergenic determinants.
Study of the alkylation propensity of cations generated by acidolytic cleavage of protecting groups in Boc chemistry
Authors: Karlström A. , Rosenthal K. , Undén A.
Published: July 2002

Abstract: The alkylation of cysteine residue by different classes of carbonium ions, derived from the cleavage of side chain protective groups in anhydrous HF, was investigated. It was found that side chain protection as β‐2,4‐dimethylpent‐3‐yl ester (Dmp) or 2,4‐dimethylpent‐3‐yloxycarbonyl (Doc) groups resulted in more than seven‐fold lower level of alkylated byproducts. This makes Dmp and Doc protection of amino acid side chain during solid phase synthesis particularly valuable in the synthesis of peptides containing cysteine residues or other functional groups prone to alkylation by carbonium ions.
Solution stability of salmon calcitonin at high concentration for delivery in an implantable system
Authors: Stevenson C.L. , Tan M.M.
Published: July 2002

Abstract: Salmon calcitonin solutions (50 mg/mL and 100 mg/mL) were placed on stability at 37°C for 1 year in a variety of solvent systems including water, ethanol, glycerol, propylene glycol (PG) and dimethyl sulfoxide (DMSO). Calcitonin degradation was monitored by RP‐HPLC and size‐exclusion chromatography. DMSO and pH 3.3 solutions provided optimum stability. Conformational stability was also monitored by FTIR over the 1 year time course and compared with chemical and physical stability. After 12 months at 37°C, four major conformations were observed: a β‐sheet conformation (pH 3.3, pH 5.0, 70% DMSO and 70% glycerol), an aggregate conformation (pH 7.0 water), a strong α‐helical conformation (70% EtOH, 70% PG) and a weak α‐helical conformation (100% DMSO). No correlation between structure and chemical stability was observed in which both the β‐sheet structure (pH 3.3, water) and a loose α‐helical structure (100% DMSO) demonstrated good stability. However, some correlation was observed between structure and physical stability, where co‐solvents inducing an α‐helical structure resulted in a decrease in gelation. These two structural states associated with improved stability and minimal gelation, indicated that gelation can be reduced or eliminated by the use of pharmaceutically acceptable co‐solvents. Finally, salmon calcitonin (50 mg/mL) was formulated in 100% DMSO and delivered from a DUROS® implant over 4 months. Delivery at a target dose of 18 µg/day calcitonin at 37°C was confirmed.
A solid‐phase synthetic strategy for the preparation of peptide‐based affinity labels: synthesis of dynorphin A analogs
Authors: Leelasvatanakij L. , Aldrich J.V.
Published: July 2002

Abstract: Solid‐phase synthetic methodology was developed for the preparation of peptide‐based affinity labels. The initial peptides synthesized were dynorphin A (Dyn A) analogs [Phe(p‐X)4,d‐Pro10]Dyn A(1–11)NH2 containing isothiocyanate (X = –N=C=S) and bromoacetamide (X = –NHCOCH2Br) groups. The peptides were assembled on solid supports using Fmoc‐protected amino acids, and the side chain amine to be functionalized, Phe(p‐NH2), was protected by the Alloc (allyloxycarbonyl) group. Following removal of the Alloc group by palladium(0), the reactive isothiocyanate and bromoacetamide functionalities were successfully introduced while the peptides were still attached to the resin. Synthesis of these peptides was carried out on polystyrene (PS) and polyethylene glycol–polystyrene (PEG–PS) resins containing the PAL [peptide amide linker, 5‐(4‐Fmoc‐aminomethyl‐3,5‐dimethoxyphenoxy)valeric acid] linker. Both the rate of Alloc deprotection and the purity of the crude affinity‐labeled peptides obtained were found to be dependent on the resin used for peptide assembly.
Recent advances in the aetiology of cryptogenic fibrosing alveolitis
Authors: Britton J , Hubbard R
Published: July 2002

Crytogenic fibrosing alveolitis is the commonest intersititial lung disease but, until recently, very little has been known about its aetiology. The histopathologist usually sees this disease at transbronchial biopsy or at autopsy. This article reviews the current knowledge of the aetiology of cryptogenic fibrosing alveolitis looking at possible infective, occupational, drug‐related, smoking‐associated, genetic and dietary factors. Knowledge of the possible roles of these factors in the disease process informs histopathologists when they are reporting these biopsies and enables them to make a larger contribution to defining the pathogenetic mechanisms.
Sonographic diagnosis of diastematomyelia in utero: A case report and literature review
Authors: Dabra A , Gupta R , Sidhu R , Kochhar S , Kaur L , Singh J
Published: July 2002

Fetal diastematomyelia is a rare form of spinal dysraphism that is characterized by a complete or incomplete division of the spinal cord by an osseous or fibrocartilaginous septum. A case of diastematomyelia, which was detected on the routine third trimester detailed ultrasound scan, is presented. The diagnosis was based on the detection of an echogenic focus in the posterior aspect of the spine in association with widening of the interpedicular vertebral space. The case illustrates that diastematomyelia can occur in the absence of overt spina bifida and that prenatal detection will allow timely postnatal investigation and treatment. Prenatal literature is further reviewed to assess the clinical significance of this finding.
Local immune response after intravesical interferon gamma in superficial bladder cancer
Authors: Stavropoulos  , Ioachim  , Pavlidis  , Pappa  , Kalomiris  , Agnantis
Published: July 2002

Objective

 To investigate the lymphocyte subpopulations (T4, T8 and macrophages) and major histocompatibility (MHC) II antigens in patients with superficial bladder cancer before and after intravesical instillations of recombinant interferon‐γ (IFN‐γ).

Patients and methods

 Four intravesical weekly instillations of either 1.3 mg (20 patients, group A) or 0.7 mg (11 patients, group B) IFN‐γ were administered in 31 evaluable patients (28 men and three women, mean age 68.5 years). The CD4+, CD8+, CD68+and HLA‐DR antigens were detected immunohistochemically in tumours and a marker tumour before and after intravesical instillations.

Results

 The median number of T4 lymphocytes increased from 15 per high‐power field (HPF) to 27.5 in group A (P=0.0029) and to 45 in group B (P=0.0117). Macrophages increased from 6 cells/HPF to 15 cells/HPF in group A (P=0.0029) and from 2 to 8.75 cells/HPF in group B (P=0.0117). The T8 lymphocyte subpopulation decreased from 4 to 3 cells/HPF (P=0.0231) in group A and from 5 to 2 cells/HPF (P=0.0759) in group B. The median percentage of HLA‐DR antigens increased from 1.5% to 18% in general, (P<0.001), from 2.5% to 15% in group A (P=0.0064) and from 0% to 20% in group B (P=0.0077). The induction of HLA‐DR antigens was statistically significant in those receiving the lower dose (from 0% before instillation to 20% afterward, P=0.0277), while it was not with the higher dose (from 0% to 5%, P=0.068). Irrespective of the dose of IFN used, T4 lymphocytes and macrophages increased significantly after treatment in patients in whom the tumour HLA‐DR antigens were either upregulated or remained stable. The median net increase in T4 cells was 17.5 and 30 cells/HPF for groups A and B, respectively (P=0.0429).

Conclusion

 T4 lymphocytes, macrophages and HLA‐DR antigens increased after intravesical IFN‐γ in patients with superficial bladder cancer, but T8 lymphocytes decreased. Irrespective of the drug dose used, patients with either upregulated or stable HLA‐DR antigens after treatment showed the same pattern of changes in the lymphocyte subpopulations. The two doses generally had the same effect on the immunological variables assessed but the lower dose was more effective in inducing HLA‐DR antigens and in increasing the number of T4 lymphocytes in the tumours.
Analytical Investigation of Leakage Flow in Disk Clearance of a Magnetically Suspended Centrifugal Impeller
Authors: Chan W.K. , Akamatsu T. , Li H.D.
Published: July 2002

Abstract: Leakage flow through the disk clearance of a magnetically suspended centrifugal blood pump is essential for a good washout. An analytical approach, based on the theory of lubrication, is used to predict the leakage volume flow rate, nondimensional radial velocity, nondimensional mean pressure distribution, and comparative shear stress distribution for different disk clearance geometry under varying rotational speeds. The results showed that nondimensional mean pressure distribution and nondimensional radial velocity distribution along the clearance are independent of rotational speed. The flow through the gap depends on a nondimensional parameter S that denotes the ratio of centrifugal forces to the head generating capability of the impeller. It was found that an impeller having a lower S has less possibility of flow reversals in the gap, and gap with maximum height at the outside radius also is more susceptible to flow reversals at the impeller surface. The comparative shear stress within the gap reveals that, in general, the scalar stress is below 500 N/m2.
Regulatory, Developmental and Tissue Aspects of Mitochondrial Biogenesis in Plants
Authors: McCabe T. C. , Daley D. , Whelan J.
Published: July 2002

Abstract: Although mitochondria play a central role in energy production in all plant tissues, the amount and activity of mitochondria differs among tissues and with development. These differences are due to the changing demands of various tissues for energy during development and the presence of different metabolic pathways in mitochondria from a variety of tissues. As mitochondria contain proteins encoded in both the nuclear and mitochondrial genomes the expression of these genomes must be coordinated. Progress has been achieved in understanding transcription of genes in both genomes. It appears from investigations to date that: i) transcriptional regulation is not a major feature of control of mitochondrial‐encoded genes, and ii) the transcription of nuclear‐ and mitochondrial‐encoded genes for proteins of a multi‐subunit complex are not coordinated. Rather several post‐transcriptional and/or post‐translational mechanisms exist to achieve the desired coordination between the two genomes. Specific examples of the regulation of expression of mitochondrial proteins with development and among tissues are outlined which indicate the complexity of factors that interplay to achieve regulation of mitochondrial biogenesis.
Supermode control in diffraction-coupled semiconductor laser arrays
Authors: Mehuys D. , Mitsunaga K. , Eng L. , Marshall W. K. , Yariv A.
Published: July 2002

Supermode control is demonstrated theoretically and experimentally in diffraction-coupled semiconductor laser arrays. A linear theory is presented to determine the supermode threshold gain as a function of the coupling cavity length. By fabricating devices with different coupling cavity lengths, array operation in both the fundamental and highest order supermodes is achieved.
Pressure dependence of Schottky barrier height at the Pt/GaAs interface
Authors: Shan W. , Li M. F. , Yu P. Y. , Hansen W. L. , Walukiewicz W.
Published: July 2002

The Schottky barrier height at the Pt/GaAs interface has been measured as a function of pressure using a diamond anvil cell. The Schottky barrier height was found to shift to higher energy with a linear pressure coefficient of 11 meV/kbar, which is equal to the pressure coefficient of the fundamental gap of GaAs and with a nonlinear coefficient of −0.26 meV/kbar2. These results are discussed in terms of defect models which have been proposed to explain the Fermi level pinning in Schottky barriers.
Structural characterization of embedded gallium arsenide on silicon by molecular beam epitaxy
Authors: De Boeck J. , Liang J. B. , Deneffe K. , Vanhellemont J. , Arent D. J. , Van Hoof C. , Mertens R. , Borghs G.
Published: July 2002

A gallium arsenide film is grown embedded in masked pre-etched wells in silicon vicinal (001) substrates by molecular beam epitaxy. The morphology and crystallinity of the embedded GaAs on Si layers are identical to those of large area GaAs on Si grown on the same wafer, as indicated by the comparison of Nomarski contrast photomicrographs and electron channeling patterns. High-resolution electron microscope images reveal the epitaxial relation of the GaAs/Si interface on the bottom and the sidewall of the wells. On the slope most of the dislocations are restricted to a narrow region near the interface. The same photoluminescent behavior is found for the GaAs deposit in the different silicon environments. This embedded growth technique is suitable for realization of a coplanar GaAs on Si surface.
Spectral and dynamic characteristics of buried-heterostructure single quantum well (Al,Ga)As lasers
Authors: Derry P. L. , Chen T. R. , Zhuang Y. H. , Paslaski J. , Mittelstein M. , Vahala K. , Yariv A.
Published: July 2002

We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3×) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers.
Lateral solid phase epitaxy of amorphous Si films by selective surface doping method of P atoms
Authors: Dan Toru , Ishiwara Hiroshi , Furukawa Seijiro
Published: July 2002

Lateral solid phase epitaxy (L-SPE) of amorphous Si (a-Si) films by a selective surface doping method of P atoms was investigated, in which P atoms were doped only in the surface layers of a-Si films. It was found that the L-SPE growth rate and the growth length from the seed region were changed by thickness of the P-doped layer, but they weakly depended on the thickness of the a-Si film. It was also found from cross-sectional transmission electron microscopy that the growth front of L-SPE in the surface P-doped sample was composed of a single facet. In order to explain these experimental results, a L-SPE growth model in the surface P-doped sample is proposed.
Transverse magnetic field dependence of the current-voltage characteristics of double-barrier quantum well tunneling structures
Authors: Ben Amor S. , Martin K. P. , Rascol J. J. L. , Higgins R. J. , Torabi A. , Harris H. M. , Summers C. J.
Published: July 2002

We report the effects of a transverse magnetic field (J⊥B) on the conductivity of quantum well tunneling structures based on AlGaAs/GaAs/AlGaAs quantum wells. The current-voltage characteristics in the positive differential resistance regime show negative magnetoconductance for all values of B. The peak bias voltage increases monotonically with increasing B. For B<6 T there is a decrease in the peak tunneling current, but then it increases for B>6 T. The data also show dramatic magnetic field induced changes in the negative differential resistance (NDR) features. The behavior of the NDR changes from sharp hysteretic bistable-like transitions to astable NDR transitions. Both the valley current and its bias voltage position increase with increasing magnetic field. This behavior is described by a simple model that includes magnetic field effects across the barriers.
Multiple pulse laser excitation of capillary discharge
Authors: Lee R. W. , Zigler A.
Published: July 2002

The results of a proof of principle experiment is presented to illustrate the utility of the capillary discharge as a medium for the efficient production of soft x-ray lasing. The duration of the capillary discharge plasma, 8 μs, is long enough to allow multiple pulses from a Q-switched mode-locked Nd glass laser to be used as a heating source to create a hot, relatively dense plasma several times per discharge.
GaAs device passivation using sputtered silicon nitride
Authors: Chang Edward Y. , Cibuzar Gregory T. , Vanhove James M. , Nagarajan Rao M. , Pande Krishna P.
Published: July 2002

This letter describes the passivation of GaAs field-effect transistors (FET’s) using sputtered silicon nitride films. A low-power reactive sputtering process for silicon nitride film deposition was developed and applied to both metal-semiconductor FET (MESFET) and high electron mobility transistor (HEMT) passivation. It is shown that the shifts in the FET parameters such as threshold voltage, breakdown voltage, and transconductance, after nitride deposition, depend not only on the stress states of the nitride films but also on the surface composition and recess geometry of the passivated surfaces. With proper deposition parameters, the sputtered silicon nitride film can be successfully used for both MESFET and HEMT passivation with only minor degradation (less than 10%) of the device performance.
Tunnel junctions using oxide superconducting thin films epitaxially grown on SrTiO3
Authors: Takada J. , Terashima T. , Bando Y. , Mazaki H. , Iijima K. , Yamamoto K. , Hirata K.
Published: July 2002

Normal-metal/insulator/superconductor (NIS) junctions were fabricated using thin films of YBa2Cu3O7−x (YBCO) or ErBa2Cu3O7−x. These were epitaxially grown on single-crystal SrTiO3 by the activated reactive evaporation method. For some NIS junctions prepared on SrTiO3 (110) substrates, we observed multipeaks in the differential conductance versus voltage curve. NIS junctions using single-crystal YBCO films on SrTiO3 (100) showed a set of peaks, from which we obtained a gap parameter of 11.5±1.5 meV at 4.4 K and a coupling constant of 3.2±0.4.
Ion beam patterning of spin-on metalorganic precursors and formation of high T
c superconductors
Authors: Gross M. E. , Brown W. L. , DiCenzo S. B. , Hartford E. H. , Yeh J. J. , Hong M.
Published: July 2002

A new technique using ion beams to produce patterned thin films of the high-temperature perovskite superconductor YBa2Cu3O7−x from spin-on metalorganic precursors is described. Spin-coated precursor films are irradiated through a stencil mask with 2.5 MeV He+ ions, developed in solvent to remove unexposed material, and the remaining patterns are pyrolyzed. Black films of YBa2Cu3O7−x with pattern dimensions on the millimeter scale exhibit orientation with the c axis perpendicular to the film after heat treatments of 990 °C for 3 min. The conductivity of a highly oriented, ∼0.4-μm-thick patterned film is characterized by onset of the superconducting transition at 84 K and zero resistivity at 68 K, similar to those of an unirradiated film given the same thermal treatment. Studies on the nature of the ion beam exposed material are discussed.
Broadband tunability of gain-flattened quantum well semiconductor lasers with an external grating
Authors: Mittelstein Michael , Mehuys David , Yariv Amnon , Ungar Jeffrey E. , Sarfaty Rona
Published: July 2002

Quantum well lasers are shown to exhibit flattened broadband gain spectra at a particular pumping condition. The gain requirement for a grating-tuned external cavity configuration is examined and applied to a semiconductor quantum well laser with an optimized length of gain region. The predicted very broadband tunability of quantum well lasers is confirmed experimentally by grating-tuning of uncoated lasers over 85 nm, with single longitudinal mode output power exceeding 200 mW.
Resonant cavity for the stimulated emission of x rays
Authors: Caticha Ariel , Caticha Nestor , Caticha-Ellis S.
Published: July 2002

Rate equations are proposed which describe the operation of a crystal as a resonant cavity for x rays. The formalism, which applies equally well to two-beam or multibeam diffraction cases, is not restricted to any particular mechanism of x-ray emission. It automatically takes into account dynamical diffraction effects on energy flow (group velocity) and absorption (the Borrmann effect) which are shown to be instrumental in increasing gain and lowering the lasing threshold. The resonant x-ray modes are those for which the group velocity vanishes (the resonant diffraction condition).
Spin-polarized secondary electrons from a scanning tunneling microscope in field emission mode
Authors: Allenspach R. , Bischof A.
Published: July 2002

A new technique has been developed which opens the way to magnetic imaging with nm resolution. A narrow electron beam produced with a scanning tunneling microscope operating in field emission mode impinges on the magnetic surface, and the spin polarization of the emitted secondary electrons is monitored. As a first result, a hysteresis loop from an Fe-based metallic glass shows that the low-energy secondary electrons excited with this technique are spin polarized.
Electromigration in Al/SiO2 films prepared by a partially ionized beam deposition technique
Authors: Li P. , Yapsir A. S. , Rajan K. , Lu T.-M.
Published: July 2002

It has been found that the electromigration resistance of pure Al/SiO2 thin films prepared by the partially ionized beam (PIB) deposition technique can be improved significantly as compared to those deposited by the conventional means. The PIB contained 0.8–1.2% of Al self-ions and a bias potential of 2–5 kV was applied to the substrate during deposition. The enhancement of the electromigration resistance of the Al films is believed to be associated with the strong preferred orientation (in the [111] direction) that these films have. Surprisingly the preferred orientation effect is not accompanied by an enlargement of the Al grain size. This combination of preferred orientation and small grain size may find important applications in future very large scale integrated metallization.
Improvements of electrical and optical properties of GaAs by substrate bias application during electron-cyclotron-resonance plasma-excited molecular beam epitaxy
Authors: Kondo Naoto , Nanishi Yasushi
Published: July 2002

Electrical and optical properties of GaAs layers are improved by applying substrate bias during electron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE). The highest mobility obtained without substrate bias is 4500 cm2 V−1 s−1. By applying positive bias, the mobility of the grown layer is increased to as high as 6800 cm2 V−1 s−1. Intense photoluminescence spectra comparable to that of a high quality MBE-grown layer are also observed. The suppression of high-energy ion impingement on the growing surface plays an important role in obtaining high quality crystal.
Synthesis of composite thin films by simultaneous use of pulsed laser and conventional thermal evaporation
Authors: Dikshit S. J. , Godbole V. P. , Chaudhari S. M. , Kanetkar S. M. , Ogale S. B.
Published: July 2002

The concept of simultaneous use of pulsed laser evaporation and conventional thermal evaporation has been used for the first time to synthesize composite thin-film structures. It is shown that the use of pulsed laser evaporation of α-Fe2O3 concurrently with thermal evaporation of aluminum leads to a composite state defined by the presence of clusters of iron-related material in the aluminum matrix. The microstructural aspects of the physical state of the composite are studied by using conversion electron Mössbauer spectroscopy, glancing angle x-ray diffraction, and scanning electron microscopy.
Conduction-band structure dependence of persistent photoconductivity in Si-doped AlxGa1−xAs studied by Hall measurements under hydrostatic pressure
Authors: Goutiers B. , Gregoris G. , Lavielle D. , Portal J. C. , Chand Naresh
Published: July 2002

Low-temperature Hall measurements under hydrostatic pressure in Si-doped Alx Ga1−x As with x=0.165 and 0.32 confirm the earlier observation of Chand and co-workers that persistent photoconductivity has a strong band structure dependence. The band structure can be changed by changing either x or pressure. Each kilobar of pressure on Alx Ga1−x As has the same effect on the band structure as increasing x by 1%. The density of photoexcited carriers goes through a maximum value at about 15 kbar applied pressure for the Al0.165 Ga0.835 As sample and at 1 bar for the Al0.32 Ga0.68 As sample. It drops dramatically on further increasing the pressure. After photoexcitation, the electron mobility was found to increase in all cases. Shubnikov–de Haas measurements on these samples at 4.2 K indicated that for x ≤ 0.4 all of the free electrons after photoexcitation were in the Γ valley. The Hall curves were linear against magnetic fields up to 20 T which also indicated that after photoexcitation one type of carriers alone contributed to the conduction process with no involvement of holes or electrons in the L or X valleys.
Temperature dependence of spontaneous emission in GaAs-AlGaAs quantum well lasers
Authors: Blood P. , Kucharska A. I. , Foxon C. T. , Griffiths K.
Published: July 2002

Using quantum well laser devices with a window in the p-type contact, we have measured the relative change of spontaneous emission intensity at threshold with temperature for 58-Å-wide GaAs wells. Over the range 250–340 K the data are in good agreement with the linear relation obtained from a gain-current calculation which includes transition broadening. This linear behavior contrasts with the stronger temperature dependence of the total measured threshold current of the same devices which includes nonradiative barrier recombination processes.
Analysis of transients in pulse modulated semiconductor lasers biased near threshold
Authors: Mecozzi A. , Spano P. , D’Ottavi A. , Piazzolla S.
Published: July 2002

A theory of time jitter in semiconductor lasers initially biased just below threshold is developed. Simulations of the buildup of emitted optical pulses in lasers starting from below or above threshold are also presented which, for initial biasing up to threshold, are in good agreement with the theory. In particular, we show that time jitter does not vary for biasing currents up to about 0.95 of the threshold value, while it suffers a small increase at threshold and a steep decrease for higher biasing currents.
Compact directional coupler switches using quantum well electrorefraction
Authors: Zucker J. E. , Jones K. L. , Young M. G. , Miller B. I. , Koren U.
Published: July 2002

We have utilized excitonic electrorefraction in reverse-biased InGaAsP/InP quantum well heterostructures to produce directional coupler switches with active lengths under 600 μm operating at 1.3 and 1.55 μm wavelengths.
Single-crystal growth of CoSi2 (110) on Si (110)
Authors: Yalisove S. M. , Eaglesham D. J. , Tung R. T.
Published: July 2002

High quality epitaxial thin films of CoSi2(110) are grown for the first time on Si(110) surfaces using UHV template methods. Utilization of thin (10–15 Å) room-temperature deposits, followed by annealing, eliminates the role of long-range diffusion during the reaction to CoSi2 and produces epitaxial thin films with a single, coherent orientation. These thin epitaxial films can then be used as templates for further homoepitaxial growth of silicide. The thicker films are also of a single epitaxial orientation and exhibit χmin’s as low as 5% in Rutherford backscattering. Misfit in two orthogonal directions is taken up by two distinct sets of interfacial defects which appear to have different critical thicknesses.
Effect of ultraviolet irradiation on the white light degraded electronic properties of hydrogenated amorphous silicon films
Authors: Ganguly Gautam , Dutta Joydeep , Ray Swati , Barua A. K.
Published: July 2002

The electronic properties of hydrogenated amorphous silicon (a-Si:H) thin films are known to undergo metastable light-induced changes that can be reversed by annealing at elevated temperatures. We have observed for the first time that annealing of the light-induced changes in the dark conductivity and photoconductivity of a-Si:H thin films can also be achieved by ultraviolet (UV) irradiation (wavelength ∼254 nm) of the films at room temperature. It has been shown that the bulk photoconductivity changes in spite of the fact that UV radiation is mostly absorbed near the top surface of the films. A simple explanation of the observed phenomena has been proposed involving a nonequilibrium distribution of phonons generated by absorption of high-energy photons in the material.
Abrupt phase reversal in frequency-modulated external-cavity semiconductor lasers
Authors: Schremer A. , Tang C. L.
Published: July 2002

The carrier-induced optical frequency deviation undergoes an unusual phase reversal in external-cavity semiconductor lasers when the modulation frequency is equal to that of the external-cavity mode spacing. A model based on the coherent nature of the external optical feedback is used to explain this phenomenon.
Coherent, monolithic two-dimensional strained InGaAs/AlGaAs quantum well laser arrays using grating surface emission
Authors: Evans G. A. , Bour D. P. , Carlson N. W. , Hammer J. M. , Lurie M. , Butler J. K. , Palfrey S. L. , Amantea R. , Carr L. A. , Hawrylo F. Z. , James E. A. , Kirk J. B. , Liew S. K. , Reichert W. F.
Published: July 2002

Two-dimensional coherent strained-layer InGaAs/AlGaAs quantum well laser arrays consisting of 100 (10×10) active elements have been fabricated and characterized. The central lobe of the far field has a full width at half power of 0.04°×1°. Observation of about 2 W peak power from either the substrate or the junction surface, with differential quantum efficiencies from each side of about 40%, is reported. The mode spectrum of the emitted power is contained in a ∼2 Å wavelength interval at ∼2 W.
Thermogravimetric study of the recovery of oxygen-deficient superconducting YBa2Cu3O7−δ oxides in ambient oxygen
Authors: Shi L. T. , Tu K. N.
Published: July 2002

The oxides of oxygen-deficient YBa2Cu3O7−δ with δ≂0.32 in both powder and chunk form were annealed in ambient oxygen to investigate the behavior of oxygen indiffusion. Thermogravimetric measurements were used to monitor in situ weight gain during the annealing at constant heating rates between room temperature and 580 °C. The temperature for achieving a definite oxygen stoichiometry changes with the heating rates, which were varied from 0.1 to 15 °C/min. By measuring the rate dependence, the activation energy of oxygen diffusion in the powder oxide was determined to be 1.25±0.05 eV, in good agreement with the value obtained by previous resistivity measurements. However, the activation energy obtained from the chunk oxide is higher, i.e., 1.52±0.06 eV. A longer diffusion distance in the chunk oxide which requires diffusion across grains might be responsible for this discrepancy.
Selective dry etching of silicon with respect to germanium
Authors: Oehrlein G. S. , Bestwick T. D. , Jones P. L. , Corbett J. W.
Published: July 2002

We describe a plasma-based dry etching procedure which permits selective etching of Si over Ge with a Si/Ge etch rate ratio of over 70 and negligible etching of the Ge underlayer. This is achieved in a SF6/H2/CF4 gas mixture by the formation of a thin (≂3 nm) involatile etch stop layer on the Ge surface which consists of Ge-sulfide and carbonaceous material.
SiGe resonant tunneling hot-carrier transistor
Authors: Rhee S. S. , Chang G. K. , Carns T. K. , Wang K. L.
Published: July 2002

A SiGe three-terminal hot-hole transistor using a double-barrier resonant tunneling structure as an emitter is fabricated. Injected carriers from the emitter are transferred near-ballistically into the collector through a thin base. The demonstrated main feature of the device is a controllable negative differential resistance in the collector current. Utilizing the high-speed characteristics of the tunneling process and negative differential resistance, integration of the device into Si technology could find applications in the areas of high-speed digital circuits, frequency multipliers, and tunable oscillators/amplifiers.
Operation of an X-band dielectric Cherenkov maser amplifier
Authors: Garate E. , Kosai H. , Evans K. , Fisher A. , Cherry R. , Main W.
Published: July 2002

A dielectric Cherenkov maser has operated as an amplifier at a frequency of 9.8 GHz. The amplifier consisted of an electron beam interacting with the TM01 mode of a cylindrical, dielectric lined waveguide with the rf input provided by a tunable (9–10 GHz), 10 kW magnetron. The dielectric constant of the liner was 10 with inner and outer radii of 1.0 and 1.27 cm, respectively. At electron beam voltage and current of 190 kV and 90 A, respectively, the measured power gain of the amplifier was 11 dB over a 21 cm interaction length with a pulse length of approximately 1 μs.
Low-temperature growth of ZnSe by molecular beam epitaxy using cracked selenium
Authors: Cheng H. , DePuydt J. M. , Haase M. , Potts J. E.
Published: July 2002

Growth of high quality ZnSe films has been achieved at growth temperatures as low as 150 °C by using elemental zinc and thermally cracked selenium as source materials. Crystallinity of the films was determined by the Zn/Se flux ratio rather than by the growth rate; it was possible to grow good crystalline films at growth rates from 0.5 to 1 μm/h. Photoluminescence and x-ray measurements indicated that there is little degradation in the film quality as the growth temperature is lowered from 350 to 150 °C.