bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement problem and local hidden variables with entangled photons
Authors: Muchowski Eugen
Published: January 2018

It is shown that there is no remote action with polarization measurements of photons in singlet state. A model is presented introducing a hidden parameter which determines the polarizer output. This model is able to explain the polarization measurement results with entangled photons. It is not ruled out by Bell’s Theorem.
Field analysis & eddy current losses calculation in five-phase tubular actuator
Authors: Waindok Andrzej , Tomczuk Bronislaw
Published: January 2018

Field analysis including eddy currents in the magnetic core of five-phase permanent magnet tubular linear actuator (TLA) has been carried out. The eddy currents induced in the magnetic core cause the losses which have been calculated. The results from 2D finite element (FE) analysis have been compared with those from 3D calculations. The losses in the mover of the five-phase actuator are much lower than the losses in its stator. That is why the former ones can be neglected in the computer aided designing. The calculation results have been verified experimentally
Electromagnetic phenomena analysis in brushless DC motor with speed control using PWM method
Authors: Ciurys Marek Pawel
Published: January 2018

Field-circuit model of a brushless DC motor with speed control using PWM method was developed. Waveforms of electrical and mechanical quantities of the designed motor with a high pressure vane pump built in a rotor of the motor were computed. Analysis of electromagnetic phenomena in the system: single phase AC network – converter - BLDC motor was carried out.
The lactation process in primiparas in early postpartum period depending on the mode of delivery. The mode of delivery and the lactation process
Authors: Humaj-Grysztar Magdalena , Bobek Monika , Matuszyk Dorota , Put Marzena
Published: January 2018

Aim. The aim of the study was to determine the relationship between the mode of delivery and the course of lactation in primiparas in early postpartum period. Material and methods. The research was conducted amongst 200 primiparas including 100 after vaginal delivery and 100 after cesarean section. The study was conducted with the method of diagnostic survey with the author’s original questionnaire as a research tool. Results. The women after vaginal delivery initiate breastfeeding earlier and more often find it successful (p < 0.001). Almost all the primiparas after cesarean delivery formula-fed their newborns (p < 0.001) and they started supplementary formula feeding earlier in comparison to women who had vaginal delivery (p < 0.001). Problem-free breastfeeding was declared by 15% of the respondents after vaginal delivery and 4% of those who had a cesarean section. Conclusions. The mode of delivery influences the lactation process. The primiparas after cesarean delivery had problems with breastfeeding more often than those after vaginal birth.
Independence and domination on shogiboard graphs
Authors: Chatham Doug
Published: January 2018

Given a (symmetrically-moving) piece from a chesslike game, such as shogi, and an n×n board, we can form a graph with a vertex for each square and an edge between two vertices if the piece can move from one vertex to the other. We consider two pieces from shogi: the dragon king, which moves like a rook and king from chess, and the dragon horse, which moves like a bishop and rook from chess. We show that the independence number for the dragon kings graph equals the independence number for the queens graph. We show that the (independent) domination number of the dragon kings graph is n − 2 for 4 ≤ n ≤ 6 and n − 3 for n ≥ 7. For the dragon horses graph, we show that the independence number is 2n − 3 for n ≥ 5, the domination number is at most n−1 for n ≥ 4, and the independent domination number is at most n for n ≥ 5.
An Attempt to Design a Naturally Ventilated Tower in Subtropical Climate of the Developing Country; Pakistan
Authors: Sohail Maha
Published: January 2018

A large proportion of the world’s population resides in developing countries where there is a lack of rigorous studies in designing energy efficient buildings. This study is a step in designing a naturally ventilated high rise residential building in a tropical climatic context of the developing country, Pakistan. Karachi, the largest city of Pakistan, lies in the subtropical hot desert region with constant high temperature of average 32 °C throughout the summer and no particular winter season. The Design Builder software package is used to design a 25 storey high rise residential building relying primarily on natural ventilation. A final conceptual design is proposed after optimization of massing, geometry, orientation, and improved building envelope design including extensive shading devices in the form of trees. It has been observed that a reduction of 8 °C in indoor ambient temperature is possible to achieve with passive measures and use of night time ventilation. A fully naturally ventilated building can reduce the energy consumption for cooling and heating by 96 % compared to a building using air conditioning systems.
Antiproliferative Activity of Gold(III) Complexes with Esters of Cyclohexyl-Functionalized Ethylenediamine-N,N’-Diacetate
Authors: Pantelić Nebojša , Stanojković Tatjana P. , Zmejkovski Bojana B. , Kaluđerović Goran N. , Sabo Tibor J.
Published: January 2018

Six gold(III) complexes with esters of cyclohexyl-functionalized ethylenediamine-N,N’-diacetate, general formula [AuCl2{(S,S)-R2eddch}]PF6, [(S,S)-eddch = (S,S)-ethylenediamine-N,N’-di-2-(3-cyclohexyl)propanoate, R = Me, Et, n-Pr, n-Bu, i-Bu, i-Am, 1–6, respectively], were tested against cancer cell lines such as human melanoma Fem-x, human colon carcinoma LS174T and non-small cell lung carcinoma A549 as well as a non-cancerous human embryonic lung fibroblasts MRC-5 using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay with the aim of assessing in vitro antitumoral activity and selectivity. All investigated complexes showed lower cytotoxicity and better or similar selectivity in comparison to cisplatin, used as reference compound. Complex [AuCl2{(S,S)-(i-Am)2eddch}]PF6 (6) demonstrated the highest activity against Fem-x (IC50 = 14.98 ± 0.34 μM). Additionally, the same complex expressed 4.5 times higher selectivity than cisplatin.
The potential of bioash for utilization in road construction in eastern Croatia
Authors: Zagvozda Martina , Dimter Sanja , Rukavina Tatjana
Published: January 2018

In recent years usage of biomass as energy source has intensified in eastern Croatia. Newly built biomass power plants generate great amounts of bioash that is being disposed at landfills. Due to its favorable properties bioashes could be reused as alternative materials in road construction or road fundation. Therefore, research on application of bioashes in construction industry is being conducted at Faculty of Civil Engineering in Osijek. The main motivation behind this research, in a form of biomass and bioash production in eastern Croatia as well as international research on potential application of this types of bioashes, is show in this paper.
Investigation of Flow Field Around the Pointed Cowl Air Intake at Mach 2.0
Authors: Urbahs Aleksandrs , Das Sudip , Vutukuru Shravan Koundinya , Carjova Kristīne
Published: January 2018

Experiments and computational studies were carried out to get an understanding of the flow field around a rectangular supersonic intake with pointed cowl shape. Experiments include quantitative pressure measurements and flow visualization studies by using schlieren techniques. The effects of the presence of various cowl shapes on ramp surface have been obtained computationally at Mach 2.0. The experiments were carried out only for the pointed cowl. Schlieren Photographs were taken. Three-Dimensional simulations were made by using FLUENT at supersonic speed. The details of the experiments and computations are discussed.
Depression is associated with CRP SNPs in patients with family history
Authors: Yibulaiyin Hasiyeti- , Sun Haixia , Yang Yue
Published: January 2018

Objective

The pathogenesis of depression is not fully understood, but studies have suggested that higher circulating levels of C reactive protein (CRP) might relate to depression occurrence. However, due to the highly variability of individual patients’ conditions, the results to date are inconsistent. Considering Single nucleotide polymorphisms (SNPs) of CRP gene have also been suggested to predict plasma CRP levels. In the present study, we hypothesize that inherited CRP allelic variations may co-vary with depressive symptomatology.

Methods

We recruited patients with a diagnosis of depression, with or without family depression history. We then detected serum CRP levels, as well as genome CRP SNPs from participants of this project.

Results

We found a significantly higher circulating CRP levels in patients with a positive family history. Furthermore, we also identified certain inherited CRP SNPs (A allele in rs1417938 and C allele in rs1205) which could up-regulate serum CRP levels and thus be associated with depression occurrence.

Conclusion

Our findings raise new evidence for the relationship between circulating CRP level and depression occurrence.
Investigating the Relationship of the Functional Gait Assessment to Spatiotemporal Parameters of Gait and Quality of Life in Individuals With Stroke
Authors: Price Richard , Choy Nancy Low
Published: January 2018

Background and Purpose:

Walking in the community is an important aspect of independence and quality of life (QOL) that poses challenges for individuals with stroke. This study investigated whether performance on the Functional Gait Assessment (FGA) differentiated spatiotemporal gait parameters, QOL, and fall history of community-ambulating individuals with stroke. We hypothesized that those scoring higher on the FGA would present with better gait speed and cadence, stride width and length, and improved load time on the paretic limb, report a higher QOL, and be less likely to have a fall history than those who scored lower on the FGA.

Methods:

Participants were screened for cognitive impairment and the ability to walk independently. Participant demographics and stroke characteristics were recorded. The Falls Risk for Older People in the Community (FROP-Com) screening tool determined whether the participant had incurred 1 or more falls within the preceding 12 months. The FGA provided a composite measure of gait with varied walking tasks challenging different aspects of walking. The total score was recorded. The GAITRite instrumented-walkway was used to acquire high-resolution footfall data during performance of the first 9 FGA walking tasks. The Assessment of Quality of Life-6D (AQoL-6D) was used to measure health-related QOL across the domains of independent living, mental health, coping, relationships, pain, and senses. Pearson and Spearman correlations were used to check for correlations between FGA score and the demographic characteristics, AQoL-6D scores, and 12-month fall history. Pearson correlations were used to check for correlations between FGA score and multiple spatiotemporal gait parameters for each FGA item.

Results and Discussion:

A sample of 29 volunteers who were community-ambulating individuals with stroke was recruited. Participants had a mean age of 62.31 (10.89) years, mean time since stroke of 3.78 (4.10) years, and included both males and females (52% male). Individuals presented with both left- and right-sided strokes. FGA score correlated positively with velocity, cadence, and step length, and negatively with stride width, double-support percent, and single-support variability (P = .001 to P = .031). FGA score correlated positively with the AQoL-6D dimension of independent living. FGA score correlated significantly with the FROP-Com screening tool predicted fall risk, but not with fall history.

Conclusions:

The FGA is a clinical measure of functional gait performance that reflected spatiotemporal gait parameters and ability of individuals with chronic stroke to live independently. The FGA could be used to target interventions to improve functional gait performance of individuals with chronic stroke.
Muscle Nicotinic Acetylcholine Receptors May Mediate Trans-Synaptic Signaling at the Mouse Neuromuscular Junction
Authors: Wang Xueyong , McIntosh J. Michael , Rich Mark M.
Published: January 2018

Block of neurotransmitter receptors at the neuromuscular junction (NMJ) has been shown to trigger upregulation of the number of synaptic vesicles released (quantal content, QC), a response termed homeostatic synaptic plasticity. The mechanism underlying this plasticity is not known. Here, we used selective toxins to demonstrate that block of α1-containing nicotinic acetylcholine receptors (nAChRs) at the NMJ of male and female mice triggers the upregulation of QC. Reduction of current flow through nAChRs, induced by drugs with antagonist activity, demonstrated that reduction in synaptic currentper sedoes not trigger upregulation of QC. These data led to the remarkable conclusion that disruption of synaptic transmission is not sensed to trigger upregulation of QC. During studies of the effect of partial block of nAChRs on QC, we observed a small but reproducible increase in the decay kinetics of miniature synaptic currents. The change in kinetics was correlated with the increase in QC and raises the possibility that a change in postsynaptic nAChR conformation may be associated with the presynaptic increase in QC. We propose that, in addition to functioning in synaptic transmission, ionotropic muscle nicotonic nAChRs may serve as signaling molecules that participate in synaptic plasticity. Because nAChRs have been implicated in a number of disease states, the finding that nAChRs may be involved in triggering synaptic plasticity could have wide-reaching implications.

SIGNIFICANCE STATEMENTThe signals that initiate synaptic plasticity of the nervous system are still incompletely understood. Using the mouse neuromuscular junction as a model synapse, we studied how block of neurotransmitter receptors is sensed to trigger synaptic plasticity. Our studies led to the surprising conclusion that neither changes in synaptic current nor spiking of the presynaptic or postsynaptic cell are sensed to initiate synaptic plasticity. Instead, postsynaptic nicotinic acetylcholine receptors (nAChRs), in addition to functioning in synaptic transmission, may serve as signaling molecules that trigger synaptic plasticity. Because nAChRs have been implicated in a number of disease states, the finding that they may mediate synaptic plasticity has broad implications.
Upregulation of GH, but not IGF1, in the hippocampus of the lactating dam after kainic acid injury
Authors: Arellanes-Licea Elvira C , Ávila-Mendoza José , Ramírez-Martínez Elizabeth C , Ramos Eugenia , Uribe-González Nancy , Arámburo Carlos , Morales Teresa , Luna Maricela
Published: January 2018

Lactation embodies a natural model of morphological, neurochemical, and functional brain plasticity. In this reproductive stage, the hippocampus of the female is less sensitive to excitotoxins in contrast to nulliparity. Growth hormone (GH) and insulin-like growth factor 1 (IGF1) are known to be neuroprotective in several experimental models of brain lesion. Here, activation of the GH–IGF1 pituitary–brain axis following kainic acid (7.5 mg/kg i.p. KA) lesion was studied in lactating and nulliparous rats. Serum concentrations of GH and IGF1 were uncoupled in lactation. Compared to virgin rats, the basal concentration of GH increased up to 40% but IGF1 decreased 58% in dams, and only GH increased further after KA treatment. In the hippocampus, basal expression of GH mRNA was higher (2.8-fold) in lactating rats than in virgin rats. GH mRNA expression in lactating rats increased further after KA administration in the hippocampus and in the hypothalamus, in parallel to GH protein concentration in the hippocampus of KA-treated lactating rats (43% vs lactating control), as detected by Western blot and immunofluorescence. Except for the significantly lower mRNA concentration in the liver of lactating rats, IGF1 expression was not altered by the reproductive condition or by KA treatment in the hippocampus and hypothalamus. Present results indicate upregulation of GH expression in the hippocampus after an excitotoxic lesion, suggesting paracrine/autocrine actions of GH as a factor underlying neuroprotection in the brain of the lactating dam. Since no induction of IGF1 was detected, present data suggest a direct action of GH.
Acid-Suppressive Drug Use During Pregnancy and the Risk of Childhood Asthma: A Meta-analysis
Authors: Lai Tianwen , Wu Mindan , Liu Juan , Luo Man , He Lulu , Wang Xiaohui , Wu Bin , Ying Songmin , Chen Zhihua , Li Wen , Shen Huahao
Published: January 2018

CONTEXT:

The association between acid-suppressive drug exposure during pregnancy and childhood asthma has not been well established.

OBJECTIVE:

To conduct a systematic review and meta-analysis on this association to provide further justification for the current studies.

DATA SOURCES:

We searched PubMed, Medline, Embase, the Cochrane Database of Systematic Reviews, EBSCO Information Services, Web of Science, and Google Scholar from inception until June 2017.

STUDY SELECTION:

Observational studies in which researchers assessed acid-suppressive drug use during pregnancy and the risk of childhood asthma were included.

DATA EXTRACTION:

Of 556 screened articles, 8 population-based studies were included in the final analyses.

RESULTS:

When all the studies were pooled, acid-suppressive drug use in pregnancy was associated with an increased risk of asthma in childhood (relative risk [RR] = 1.45; 95% confidence interval [CI] 1.35–1.56; I2 = 0%; P < .00001). The overall risk of asthma in childhood increased among proton pump inhibitor users (RR = 1.34; 95% CI 1.18–1.52; I2 = 46%; P < .00001) and histamine-2 receptor antagonist users (RR = 1.57; 95% CI 1.46–1.69; I2 = 0%; P < .00001).

LIMITATIONS:

None of the researchers in the studies in this meta-analysis adjusted for the full panel of known confounders in these associations.

CONCLUSIONS:

The evidence suggests that prenatal, maternal, acid-suppressive drug use is associated with an increased risk of childhood asthma. This information may help clinicians and parents to use caution when deciding whether to take acid-suppressing drugs during pregnancy because of the risk of asthma in offspring.
InGaN/GaN/AlGaN-Based Leds and Laser Diodes
Authors: Nakamura S. , Senoh M. , Nagahama S. , Iwasa N. , Matushita T. , Mukai T.
Published: January 2018

InGaN quantum-well-structure blue LEDs were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. The output power of both LEDs was as high as 6 mW at a current of 20 mA. The LED on sapphire had a considerable amount of leakage current in comparison with that on ELOG. These results indicate that In composition fluctuation is not caused by threading dislocations (TDs), free carriers are captured by radiative recombination centers before they are captured by nonradiative recombination centers in InGaN, and that the dislocations form the leakage current pathway in InGaN. Red LED with an emission peak wavelength of 650 nm was fabricated by increasing the In composition and thickness of InGaN well layer. When the laser diodes (LD) was formed on the GaN layer above the SiO2 mask region, the threshold current density was as low as 3 kAcm−2. When the LD was formed on the window region, the threshold current density was as high as 6 to 9 kAcm−2. There is a possibility that a leakage current due to a large number of TDs caused the high threshold current density on the window region. InGaN multi-quantum-well (MQW) structure LDs grown on the ELOG substrate showed an output power as high as 420 mW under RT-CW operation. The longest lifetime of 9,800 hours at a constant output power of 2 mW was achieved. The InGaN MQW LDs were fabricated on a GaN substrate. The fundamental transverse mode was observed up to an output power of 80 mW.
Characterization of InGaN/GaN-Based Multi-Quantum Well Distributed Feedback Lasers
Authors: Hofstetter Daniel , Thornton Robert L. , Romano Linda T. , Bour David P. , Kneissl Michael , Donaldson Rose M. , Dunnrowicz Clarence
Published: January 2018

We present a device fabrication technology and measurement results of both optically pumped and electrically injected InGaN/GaN-based distributed feedback (DFB) lasers operated at room temperature. For the optically pumped DFB laser, we demonstrate a complex coupling scheme for the first time, whereas the electrically injected device is based on normal index coupling. Threshold currents as low as 1.1 A were observed in 500 μm long and 10 μm wide devices. The 3rd order grating providing feedback was defined holographically and dry-etched into the upper waveguiding layer by chemically-assisted ion beam etching. Even when operating these lasers considerably above threshold, a spectrally narrow emission (3.5 Å) at wavelengths around 400 nm was seen.
Carrier Dynamics of Abnormal Temperature-Dependent Emission Shift in MOCVD-Grown
Authors: Cho Yong-Hoon , Little B. D. , Gainer G. H. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: January 2018

Temperature-dependent photoluminescence (PL) studies have been performed on InGaN epilayers and InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous temperature dependent emission behavior (specifically an S-shaped decrease-increase-decrease) of the peak energy (EPL) of the InGaN-related PL emission with increasing temperature. In the case of the InGaN epilayer, EPL decreases in the temperature range of 10 – 50 K, increases for 50 – 110 K, and decreases again for 110 – 300 K with increasing temperature. For the InGaN/GaN MQWs, EPL decreases from 10 – 70 K, increases from 70 – 150 K, then decreases again for 150 – 300 K. The actual temperature dependence of the PL emission was estimated with respect to the bandgap energy determined by photoreflectance spectra. We observed that the PL peak emission shift has an excellent correlation with a change in carrier lifetime with temperature. We demonstrate that the temperature-induced S-shaped PL shift is caused by the change in carrier recombination dynamics with increasing temperature due to inhomogeneities in the InGaN structures.
Composition Dependence of the Band Gap Energy of InxGa1−xN Layers on GaN (x≤0.15) Grown by Metal-Organic Chemical Vapor Deposition
Authors: Wagner J. , Ramakrishnan A. , Behr D. , Maier M. , Herres N. , Kunzer M. , Obloh H. , Bachem K.-H.
Published: January 2018

We report on the composition dependence of the band gap energy of strained hexagonal InxGa1−xN layers on GaN with x≤0.15, grown by metal-organic chemical vapor deposition on sapphire substrates. The composition of the (InGa)N was determined by secondary ion mass spectroscopy. High-resolution X-ray diffraction measurements confirmed that the (InGa)N layers with typical thicknesses of 30 nm are pseudomorphically strained to the in-plane lattice parameter of the underlying GaN. Room-temperature photoreflection spectroscopy and spectroscopic ellipsometry were used to determine the (InGa)N band gap energy. The composition dependence of the band gap energy of the strained (InGa)N layers was found to be given by EG(x)=3.43−3.28 × (eV) for x≤0.15. When correcting for the strain induced shift of the fundamental energy gap, a bowing parameter of 3.2 eV was obtained for the composition dependence of the gap energy of unstrained (InGa)N.
Electrical and Photoelectrical Characterization of Deep Defects In Cubic GaN on GaAs
Authors: Lisker M. , Krtschil A. , Witte H. , Christen J. , AS D.J. , Schöttker B. , Lischka K.
Published: January 2018

Nominally undoped cubic GaN epilayers deposited by rf-plasma assisted molecular beam epitaxy on semi-insulating GaAs substrates were investigated by electric and photoelectric spectroscopical methods. As a consequence of the existence of deep levels in the GaAs-substrate itself, special care has to be taken to separate the contributions of the substrate from that of the cubic GaN epilayer in the various spectra. Two different contact configurations (coplanar and sandwich structures) were successfully used to perform this separation. In the cubic GaN epilayer a trap with a thermal activation energy of (85±20)meV was found by thermal admittance spectroscopy and thermal stimulated currents. Optical admittance spectroscopy and photocurrent measurements furthermore revealed defects at EG-(0.04-0.13) eV, EG-(0.21-0.82) eV and two additional deeper defects at 1.91 Ev and 2.1 eV, respectively. These defect related transitions are very similar to those observed in hexagonal GaN.
Domain Structure of Thick GaN Layers Grown by Hydride Vapor Phase Epitaxy
Authors: Paskova T. , Svedberg E.B. , Madsen L.D. , Yakimova R. , Ivanov I.G. , Henry A. , Monemar B.
Published: January 2018

The crystal structure and surface morphology of hydride vapour phase epitaxy grown thick (12-105 μm) GaN layers have been investigated as a function of growth rate using several structure sensitive techniques like atomic force microscopy (AFM), x-ray diffraction (XRD) in ω-2θ and ω-rocking curve measurements as well as low temperature photoluminescence (PL). PL and XRD measurements reveal rather narrow lines: full width at half maximum (FWHM) values of the strongest donor-bound exciton line are in the range from 6.0 to1.8 meV and ω-2θ FWHM values are between 80 and 23 arcsec indicating good structural quality of the films. The ω-rocking curves show a single peak for the thinnest films with a FWHM of 250 arcsec and multiple peaks with FWHM of about 250-350 arcsec in thicker films indicating the formation of several high-quality domains when increasing either thickness or growth rate. Optical microscopy and AFM images reveal a domain type of morphology and also show an appearance of spiral hillocks in layers grown at growth rates exceeding a critical value. We interpret these results as dominating 2D multilayer growth at low growth rates, and competing 2D multilayer and spiral growth mechanisms at high growth rates.
Optical Absorption, Raman, and Photoluminescence Excitation Spectroscopy of Inhomogeneous InGaN Films
Authors: Robins L.H. , Paul A.J. , Parker C.A. , Roberts J.C. , Bedair S.M. , Piner E.L. , El-Masry N.A.
Published: January 2018

InxGa1−xN films with x=0.06 to x=0.49 were characterized by optical transmittance, Raman, and photoluminescence excitation spectroscopies. Previous microstructural characterizations detected phase separation only in films with x>0.2. The transmittance data suggest that compositional inhomogeneity is also present in the lower-x films (x<0.2). Both Raman and photoluminescence excitation spectra show features that correlate with compositional inhomogeneity and phase separation in the films with x>0.2. The composition dependence of the Raman spectra, from x=0.28 to x=0.49, is consistent with an increase in the size of the phase-separated regions with increasing x.
Influence of Doping on the Lattice Dynamics of Gallium Nitride
Authors: Kaschner A. , Siegle H. , Hoffmann A. , Thomsen C. , Birkle U. , Einfeldt S. , Hommel D.
Published: January 2018

We present results of Raman-scattering experiments on GaN doped with Si, C, and Mg, respectively, grown by molecular beam epitaxy (MBE). The influence of the different dopants on strain and free-carrier concentration was investigated. Furthermore, we report on several local vibrational modes (LVM) around 2200 cm−1 in Raman spectra of highly Mg-doped GaN. A possible explanation of these high-energy modes in terms of hydrogen-related vibrations is given. We also found a variety of new structures in the range of the GaN host lattice phonons. Secondary ion mass spectroscopy (SIMS) was applied to determine the concentration of magnesium and unintentionally incorporated hydrogen.
Photoluminescence Excitation Spectroscopy of Carbon-Doped Gallium Nitride
Authors: Reuter E. E. , Zhang R. , Kuech T. F. , Bishop S. G.
Published: January 2018

We have done a comparative study of carbon-doped GaN and undoped GaN utilizing photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies in order to investigate deep levels involved in yellow luminescence (YL) and red luminescence (RL). When the GaN was excited by above-bandgap light, red luminescence (RL) centered at 1.82 eV was the dominant below-gap PL from undoped GaN, but carbon-doped GaN below-gap PL was dominated by yellow luminescence (YL) centered at 2.2 eV. When exciting PL below the band-gap with 2.4 eV light, undoped GaN had a RL peak centered at 1.5 eV and carbon-doped GaN had a RL peak centered at 1.65 eV. PLE spectra of carbon-doped GaN, detecting at 1.56 eV, exhibited a strong, broad excitation band extending from about 2.1 to 2.8 eV with an unusual shape that may be due to two or more overlapping excitation bands. This RL PLE band was not observed in undoped GaN. We also demonstrate that PL spectra excited by below gap light in GaN films on sapphire substrates are readily contaminated by 1.6−1.8 eV and 2.1−2.5 eV chromium-related emission from the substrate. A complete characterization of the Cr emission and excitation bands for sapphire substrates enables the determination of the excitation and detection wavelengths required to obtain GaN PL and PLE spectra that are free of contributions from substrate emission.
Optical Properties of Si-DOPED AlxGa1−xN/AlyGa1−yN (x=0.24−0.53, y=0.11) Multi-Quantum-Well Structures
Authors: Hirayama H. , Aoyagi Y.
Published: January 2018

We demonstrate strong ultraviolet (UV) (280-330nm) photoluminescence (PL) emission from multi-quantum-well (MQW) structures consisting of AlGaN active layers fabricated by metal-organic chemical-vapor-deposition (MOCVD). Si-doping is shown to be very effective in order to enhance the PL emission of AlGaN QWs. We found that the optimum values of well thickness and Si-doping concentration of AlxGa1−xN/AlyGa1−yN (x=0.24−0.53, y=0.11) MQW structure for efficient emission were approximately 3nm and 2×1019cm−3, respectively. In addition, the PL intensities of AlGaN, GaN and InGaN quantum well structures are compared. We have found that the PL emission at 77K from a Al0.53Ga0.47N/Al0.11Ga0.89N MQW is as strong as that of InGaN QWs.
Epitaxial Growth of III-Nitride Layers on Aluminum Nitride Substrates
Authors: Schowalter L.J. , Shusterman Y. , Wang R. , Bhat I. , Arunmozhi G. , Slack G.A.
Published: January 2018

High quality, epitaxial growth of AlN and AlxGa1−xN by OMVPE has been demonstrated on single-crystal AlN substrates. Here we report characterization of epitaxial layers on an a-face AlN substrate using Rutherford Backscattering/ion channeling, atomic force microscopy (AFM), x-ray rocking curves, and preliminary electrical characterization. Ion channeling along the [100] axis gives a channeling minimum yield of 1.5% indicating a very high quality epitaxial layer.
GaN: From Selective Area to Epitaxial Lateral Overgrowth
Authors: Li X. , Bishop S. G. , Coleman J. J.
Published: January 2018

The evolution of the topography of GaN stripes as a function of stripe width (2 – 120 μm), fill factor and substrate smoothness has been explored. The spatially resolved optical properties of these structures have been characterized by cathodoluminescence imaging and line scans. Implications from the optical study have been discussed.
Process Routes for Low Defect-Density GaN on Various Substrates Employing Pendeo-Epitaxial Growth Techniques
Authors: Linthicum K.J. , Gehrke T. , Thomson D.B. , Tracy K.M. , Carlson E.P. , Smith T. P. , Zheleva T.S. , Zorman C.A. , Mehregany M. , Davis R.F.
Published: January 2018

GaN films have been grown on 6H-SiC substrates employing a new form of selective lateral epitaxy, namely pendeo-epitaxy. This technique forces regrowth to start exclusively on sidewalls of GaN seed structures. Both discrete pendeo-epitaxial microstructures and coalesced single crystal layers of GaN have been achieved. SEM and TEM analysis are used to evaluate the morphology of the resulting GaN films. Process routes leading to GaN pendeo-epitaxial growth using silicon substrates have also been achieved and the preliminary results are discussed.
Absorption Coefficient and Refractive Index of GaN, AlN and AlGaN Alloys
Authors: Muth J. F. , Brown J. D. , Johnson M. A. L. , Yu Zhonghai , Kolbas R. M. , Cook J. W. , Schetzina J. F.
Published: January 2018

The design of optoelectronic devices fabricated from III-nitride materials is aided by knowledge of the refractive index and absorption coefficient of these materials. The optical properties of GaN, AlN and AlGaN grown by MOVPE on sapphire substrates were investigated by means of transmittance and reflectance measurements. Thin (less than 0.5 μm) single crystal films were employed to insure that transmission measurements could be obtained well above the optical band gap. The influence of alloy broadening on the absorption edge was investigated by using a series of AlGaN alloy samples with a range of Al compositions. The optical absorption coefficient above the band gap was obtained for AlGaN having up to 38% Al composition. The refractive index below the band gap was determined for the same series of samples. These properties provide information critical to the optimal design of solar blind detectors or other optoelectronic devices.
Monte Carlo Simulation of Hall Effect in n-Type GaN
Authors: Albrecht J.D. , Ruden P.P. , Bellotti E. , Brennan K.F.
Published: January 2018

Results of Monte Carlo simulations of electron transport for wurtzite phase GaN in crossed, weak electric and magnetic fields are presented. It is found that the Hall factor, rH = μHall/μdrift, decreases monotonically as the temperature increases from 77K to 400K.The low temperature value of the Hall factor increases significantly with increasing doping concentration. The Monte Carlo simulations take into account the electron-lattice interaction through polar optical phonon scattering, deformation potential acoustic phonon scattering (treated as an inelastic process), and piezoelectric acoustic phonon scattering. Impurity scattering due to ionized and neutral donors is also included, with the latter found to be important at low temperature due to the relatively large donor binding energy which implies considerable carrier freeze-out already at liquid nitrogen temperature. The temperature dependences of the electron concentration, drift mobility, and Hall factor are calculated for donor concentrations equal to 5 × 1016 cm−3, 1017 cm−3, and 5 × 1017 cm−3. The Monte Carlo simulations are compared to classical analytical results obtained using the relaxation-time approximation, which is found to be adequate at low temperatures and sufficiently low carrier concentrations so that inelastic scattering effects due to optical phonons and degeneracy effects are negligible. The influence of dislocations on the Hall factor is discussed briefly.
Rapid Thermal Processing of Implanted GaN up to 1500°C
Authors: Cao X. A , Pearton S. J. , Singh R. K. , Abernathy C. R. , Han J. , Shul R. J. , Rieger D. J. , Zolper J. C. , Wilson R. G. , Fu M. , Sekhar J. A. , Guo H. J. , Pennycook S. J.
Published: January 2018

GaN implanted with donor(Si, S, Se, Te) or acceptor (Be, Mg, C) species was annealed at 900-1500 °C using AlN encapsulation. No redistribution was measured by SIMS for any of the dopants and effective diffusion coefficients are ≤2 × 10−13 cm2. s−1 at 1400 °C, except Be, which displays damage-enhanced diffusion at 900 °C and is immobile once the point defect concentration is removed. Activation efficiency of ∼90% is obtained for Si at 1400 °C. TEM of the implanted material shows a strong reduction in lattice disorder at 1400-1500 °C compared to previous results at 1100 °C. There is minimal interaction of the sputtered AlN with GaN under our conditions, and it is readily removed selectively with KOH.
Extrinsic Performance Limitations of AlGaN/GaN Heterostructure Field Effect Transistors
Authors: Ruden P.P. , Albrecht J.D. , Sutandi A. , Binari S.C. , Ikossi-Anastasiou K. , Ancona M.G. , Henry R.L. , Koleske D.D. , Wickenden A.E.
Published: January 2018

Extrinsic effects on the DC output characteristics of AlGaN/GaN HFETs with 1 m gate lengths are examined. The devices investigated were fabricated on MOCVD-grown AlGaN/ GaN heterostructures on sapphire substrates. An analytical model that takes into account parasitic resistances and thermal effects is constructed, and its results are compared with experimental data. With parameters determined from characterization experiments on the same wafer and from independent theoretical results, the agreement between the data and the model predictions is found to be very good. The model is then applied to performance predictions for devices with improved series resistances and heat sinking.
Photoelectrochemical Etching of InxGa1−xN
Authors: Cho Hyun , Donovan S.M. , Abernathy C.R. , Pearton S.J. , Ren F. , Han J. , Shul R.J.
Published: January 2018

A comparison of KOH, NaOH and AZ400K solutions for UV photo-assisted etching of undoped and n+ GaN is discussed. The etching is diffusion-limited (Ea < 6kCal·mol−1) under all conditions and is significantly faster with bias applied to the sample during light exposure. No etching of InN was observed, due to the very high n-type background doping (> 1020cm−3) in the material.
Focused Ion Beam Etching of GaN
Authors: Flierl C. , White I.H. , Kuball M. , Heard P.J. , Allen G.C. , Marinelli C. , Rorison J.M. , Penty R.V. , Chen Y. , Wang S.Y.
Published: January 2018

We have investigated the use of focused ion beam (FIB) etching for the fabrication of GaN-based devices. Although work has shown that conventional reactive ion etching (RIE) is in most cases appropriate for the GaN device fabrication, the direct write facility of FIB etching – a well-established technique for optical mask repair and for IC failure analysis and repair – without the requirement for depositing an etch mask is invaluable. A gallium ion beam of about 20nm diameter was used to sputter GaN material. The etching rate depends linearly on the ion dose per area with a slope of 3.5 × 10−4 μm3/pC. At a current of 3nA, for example, this corresponds to an each rate of 1.05 μm3/s. Good etching qualities have been achieved with a side wall roughness significantly below 0.1 μm. Change in the roughness of the etched surface plane stay below 8nm.
Generation Recombination Noise in GaN Photoconducting Detectors
Authors: Misra M. , Doppalapudi D. , Sampath A.V. , Moustakas T.D. , McDonald P.H.
Published: January 2018

Low frequency noise measurements are a powerful tool for detecting deep traps in semiconductor devices and investigating trapping-recombination mechanisms. We have performed low frequency noise measurements on a number of photoconducting detectors fabricated on autodoped n-GaN films grown by ECR-MBE. At room temperature, the noise spectrum is dominated by 1/f noise and thermal noise for low resistivity material and by generationrecombination (G-R) noise for high resistivity material. Noise characteristics were measured as a function of temperature in the 80K to 300K range. At temperatures below 150K, 1/f noise is dominant and at temperatures above 150K, G-R noise is dominant. Optical excitation revealed the presence of traps not observed in the dark, at room temperature.
Fabrication of Self-Assembling AlGaN Quantum Dot on AlGaN Surfaces Using Anti-Surfactant
Authors: Hirayama H. , Aoyagi Y. , Tanaka S.
Published: January 2018

We report on the first artificial fabrication of self-assembling AlGaN quantum dots (QDs) on AlGaN surfaces using metal organic chemical vapor deposition (MOCVD). The AlGaN QDs are fabricated using a growth mode change from 2-dimensional step-flow growth to 3-dimensional island formation by modifying the AlGaN surface energy with Si anti-surfactant. The average lateral size and the thickness of fabricated AlGaN QDs, as determined by AFM, are approximately 20 nm and 6nm, respectively. The dot density was found to be controlled from 5×1010 cm−2 down to 2×109 cm−2 by increasing the dose of Si anti-surfactant. We obtained the photoluminescence (PL) from AlGaN QDs embedded with Al0.38Ga0.62N capping layers. The Al incorporation in AlGaN QDs was controllable within the range of 1-5 %.
Scanning Tunneling Microscopy Studies of InGaN Growth by Molecular Beam Epitaxy
Authors: Chen Huajie , Smith A. R. , Feenstra R. M. , Greve D. W. , Northrup J. E.
Published: January 2018

InGaN alloys with indium compositions ranging from 0–40% have been grown by molecular beam epitaxy. The dependence of the indium incorporation on growth temperature and group III/group V ratio has been studied. Scanning tunneling microscopy images, interpreted using first-principles theoretical computations, show that there is strong indium surface segregation on InGaN. Based on this surface segregation, a qualitative model is proposed to explain the observed indium incorporation dependence on the growth parameters.
Etch Processing of III-V Nitrides
Authors: Eddy Charles R.
Published: January 2018

As III-V nitride devices advance in technological importance, a fundamental understanding of device processing techniques becomes essential. Recent works have exposed various aspects of etch processes. The most recent advances and the greatest remaining challenges in the etching of GaN, AlN, and InN are reviewed. A more detailed presentation is given with respect to GaN high density plasma etching. In particular, the results of parametric and fundamental studies of GaN etching in a high density plasma are described. The effect of ion energy and mass on surface electronic properties is reported. Experimental results identify preferential sputtering as the leading cause of observed surface non-stoichiometry. This mechanism provides excellent surfaces for ohmic contacts to n-type GaN, but presents a major obstacle for Schottky contacts or ohmic contacts to p-type GaN. Chlorine-based discharges minimize this stoichiometry problem by improving the rate of gallium removal from the surface. In an effort to better understand the high density plasma etching process for GaN, in-situ mass spectrometry is employed to study the chlorine-based high density plasma etching process. Gallium chloride mass peaks were monitored in a highly surface sensitive geometry as a function of microwave power (ion flux), total pressure (neutral flux), and ion energy. Microwave power and pressure dependencies clearly demonstrate the importance of reactive ions in the etching of wide band gap materials. The ion energy dependence demonstrates the importance of adequate ion energy to promote a reasonable etch rate (≥100-150 eV). The benefits of ion-assisted chemical etching are diminished for ion energies in excess of 350 V, placing an upper limit to the useful ion energy range for etching GaN. The impact of these results on device processing will be discussed and future needs identified.
Damage-Free Photo-Assisted Cryogenic Etching of GaN as Evidenced by Reduction of Yellow Luminescence
Authors: Hsieh J. T. , Hwang J. M. , Hwang H. L. , Hung W. H.
Published: January 2018

Damage-free etching of GaN by Cl2, assisted by an ArF (193 nm) excimer laser, is demonstrated. At low temperatures, photo-assisted etching can provide a better etch rate and largely improve the surface morphology and quality. AFM results show that the etched GaN surface is obtained with a root-mean-square roughness of 1.7 nm. As compared with the photoluminescence spectra of photoelectrochemical wet etched GaN, the photo-assisted cryogenic etching is proved to be a damage-free dry etching technique.
Optical and Structural Properties of AlGaN/GaN Quantum Wells Grown by Molecular Beam Epitaxy
Authors: Grandjean Nicolas , Massies Jean , Leroux Mathieu , Laügt Marguerite , Lefebvre Pierre , Gil Bernard , Allègre Jacques , Pierre Bigenwald
Published: January 2018

AlGaN/GaN quantum well (QWs) were grown on (0001) sapphire substrates by molecular beam epitaxy (MBE) using ammonia as nitrogen precursor. The Al composition in the barriers was varied between 8 and 27 % and the well thickness from 4 to 17 monolayers (MLs, 1ML = 2.59Å). X-ray diffraction (XRD) experiments are used to investigate the strain state of both the well and the barriers. The QW transition energy are measured by low temperature photoluminescence (PL). A large quantum confined Stark effect is observed leading to QW luminescence much lower than the emission line of the GaN buffer layer for well width above a certain critical thickness. The built-in electric field responsible for such a phenomenon is deduced from fit of the PL data. Its magnitude is of several hundred kV/cm and increases linearly with the Al composition.
EFEKTIVITAS KOMBINASI PROBIOTIK MIKROENKAPSULASI MELALUI PAKAN UNTUK PENGENDALIAN PENYAKIT MOTILE AEROMONADS SEPTICEMIA PADA IKAN LELE, Clarias gariepinus
Authors: Lusiastuti Angela Mariana , Andriyanto Septyan , Samsudin Reza
Published: January 2018

Penelitian ini bertujuan untuk mengetahui efektivitas kombinasi probiotik mikroenkapsulasi melalui pakan dalam pengendalian penyakit pada ikan lele, Clarias gariepinus. Penelitian dilakukan mulai dari penyiapan kombinasi probiotik Bacillus cereus ND2 dan Staphylococcus lentus L1K, mikroenkapsulasi probiotik, uji probiotik mikroenkapsulasi, serta uji dosis secara in vivo. Proses mikroenkapsulasi menggunakan BUCHI mini spray dryer dengan suhu inlet 131°C-133°C dan suhu outlet 65°C-70°C. Pakan yang digunakan adalah pakan buatan dengan kadar protein 38% yang dicampur dengan probiotik mikroenkapsulasi sesuai dengan dosis perlakuan dan diberi putih telur 2% sebagai binder. Perlakuan yang dilakukan adalah membandingkan secara in vivo probiotik mikroenkapsulasi (PM) dan probiotik non-mikroenkapsulasi (PNM), dan dilanjutkan pengujian dosis melalui pakan untuk memperoleh dosis terbaik dari aplikasi probiotik mikroenkapsulasi. Parameter pengamatan berupa tingkat sintasan, biomassa, kadar hematokrit, hemoglobin, respiratory burst activity, dan total bacterial count. Hasil penelitian menunjukkan bahwa suplementasi kombinasi probiotik mikroenkapsulasi Bacillus cereus ND2 dan Staphylococcus lentus L1K pada pakan lebih efektif, dan dengan dosis 2% menunjukkan hasil yang lebih baik dalam meningkatkan sintasan hingga 97,33%, biomassa dan respons imun (NBT assay, hematocrit, hemoglobin) ikan lele terhadap A. hydrophila.This study was aimed to know the effectivity of microencapsulated probiotic combinations administered through diet to control motile aeromonads septicemia disease in catfish (Clarias gariepinus). The research stages consisted of preparation probiotics, microencapsulation of probiotics and probiotic microencapsulation testing in vivo. BUCHI mini spray dryer was used in the microencapsulation process with inlet temperature ranged between 131°C-133°C and outlet temperature ranged between 65°C-70°C. The diets used in the research were pelleted feeds with a protein content of 38% and mixed with different dosages of microencapsulated probiotics. Egg albumen (2%) was used to bind the mixture. The effectivity of microencapsulated and non-microencapsulated feeds was compared in order to find an optimum microencapsulation dosage. The observed parameters were survival rate, biomass, hematocrit, hemoglobin, respiratory burst activity, and total bacterial count. The results showed that the supplementation of microencapsulated probiotic Bacillus cereus ND2 and Staphylococcus lentus L1K in the diets was more effective at a dose of 2%, showing better survival rate (97.33%), biomass gain, and immune responses (NBT assay, hematocrit, hemoglobin) against A. hydrophila in catfish Clarias gariepinus.