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At least 865 records · Page 48

Effect of Group-III precursors on unintentional gallium incorporation during epitaxial growth of InAlN layers by metalorganic chemical vapor deposition

Unintentional incorporation of gallium (Ga) in InAlN layers grown with different molar flow rates of Group-III precursors by metalorganic chemical vapor deposition has been experimentally investigated. The Ga mole fraction in the InAl(Ga)N layer was increased significantly with the trimethylindium (TMIn) flow rate, while the trimethylaluminum flow rate controls the Al mole fraction. The evaporation of metallic Ga from the liquid phase eutectic system between the pyrolized In from injected TMIn and pre-deposited metallic Ga was responsible for the Ga auto-incorporation into the InAl(Ga)N layer. The theoretical calculation on the equilibrium vapor pressure of liquid phase Ga and the effective partial pressure of Group-III precursors based on growth parameters used in this study confirms the influence of Group-III precursors on Ga auto-incorporation. More Ga atoms can be evaporated from the liquid phase Ga on the surrounding surfaces in the growth chamber and then significant Ga auto-incorporation can occur due to the high equilibrium vapor pressure of Ga comparable to effective partial pressure of input Group-III precursors during the growth of InAl(Ga)N layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Ion Mobility Measurements of Multianionic Metalloporphyrin Dimers: Structural Changes Induced by Countercation Exchange

We present gas-phase structures of dimers of Mn{sup III} and Fe{sup III} meso-tetra(4-sulfonatophenyl)porphyrin multianions with various amounts of sodium and hydrogen counterions. The structural assignments are achieved by combining mass spectrometry, ion mobility measurements, quantum chemical calculations, and trajectory method collision cross section calculations. For a common charge state, we observe significant topological variations in the dimer structures of [(MTPPS){sub 2}+nX]{sup (6-n)-} (M=Mn{sup III}, Fe{sup III}; X=H, Na; n = 1–3) induced by replacing hydrogen counterions by sodium. For sodium, the dimer structures are much more compact, a finding that can be rationalized by the stronger interactions of the sodium cations with the anionic sulfonic acid groups of the porphyrins as compared to hydrogen. .

74 ATOMIC AND MOLECULAR PHYSICS↗

New Synthesis Strategies to Improve Co-Free LiNi0.5Mn0.5O2 Cathodes: Early Transition Metal d0 Dopants and Manganese Pyrophosphate Coating

In this work, we report solution-based doping and coating strategies to improve the electrochemical performance of the Co-free layered oxide cathode LiNi0.5Mn0.5O2 (LNMO). Small amounts of d0 dopants (e.g., Mo6+and Ti4+, 0.5-1 at. %) increase the cathode’s specific capacity, cycling stability, and rate capability. More specifically, a Mo-doped cathode with the nominal composition LiNi0.495Mn0.495Mo0.01O2 achieves a high reversible capacity of 180 mAh/g at 20 mA/g with good retention at higher rates (e.g., 120 mAh/g at 100 mA/g). Effects of 1 at.% Mo dopant on the cathode structure were studied using a suite of characterization tools including X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). These measurements demonstrate that Mo6+ reduces Li+/Ni2+cation mixing and mitigates undesirable phase transformations near the cathode surface during cycling. This work also reports the use of an inorganic Mn2P2O7 coating which enhances cycling stability, presumably through formation of a stable cathode electrolyte interphase (CEI) layer. Overall, the synthesis approaches reported herein are quite general and can potentially be expanded to other high voltage LIB cathodes.

Co-free cathodes, d0 cation, pyrophosphate coating↗

Potentiometric and electrokinetic signatures of iron(II) interactions with (a,y)-Fe2O3

The role of surface electrostatics on the reductive dissolution of iron (III) oxides is poorly understood, despite its importance in controlling the amount of mobilized iron. We report the potentiometric titration of the a; y -Fe2O3 oxides exposed to reductants and complexing ligands (Fe(II), ascorbate, oxalate, malonate). We monitored in situ surface and potentials, the ratio of mobilized ferric to ferrous ions, and periodically analyzed nanoparticle crystal structure using X-ray diffraction. We found that addition of Fe2+ ions produces a response consistent with the iron solubilityactivity curve, whereas the presence of ascorbate significantly decreases the amount of mobilized Fe(III) due to reduction to Fe(II). In addition, XRD analysis proved that y-Fe2O3 particles remain structurally unchanged along the titration pathway despite iron cycling between aqueous and solid reservoirs. Our studies, suggest that the surface redoxactivity of iron oxides is primarily governed by the balance between Fe(III) and Fe(II) ions in aqueous phase, which may be easily altered by complexing and reducing agents.

Toczydlowska, Diana↗

Boron phosphide under pressure: In situ study by Raman scattering and X-ray diffraction

Cubic boron phosphide, BP, has been studied in situ by X-ray diffraction and Raman scattering up to 55 GPa at 300 K in a diamond anvil cell. The bulk modulus of B{sub 0} = 174(2) GPa has been established, which is in excellent agreement with our ab initio calculations. The data on Raman shift as a function of pressure, combined with equation-of-state (EOS) data, allowed us to estimate the Grüneisen parameters of the TO and LO modes of zinc-blende structure, γ{sub G}{sup TO }= 1.26 and γ{sub G}{sup LO }= 1.13, just like in the case of other A{sup III}B{sup V} diamond-like phases, for which γ{sub G}{sup TO }> γ{sub G}{sup LO }≅ 1. We also established that the pressure dependence of the effective electro-optical constant α is responsible for a strong change in relative intensities of the TO and LO modes from I{sub TO}/I{sub LO} ∼ 0.25 at 0.1 MPa to I{sub TO}/I{sub LO} ∼ 2.5 at 45 GPa, for which we also find excellent agreement between experiment and theory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Effect of heterostructure design on carrier injection and emission characteristics of 295 nm light emitting diodes

The effects of the heterostructure design on the injection efficiency and external quantum efficiency of ultraviolet (UV)-B light emitting diodes (LEDs) have been investigated. It was found that the functionality of the Al{sub x}Ga{sub 1−x}N:Mg electron blocking layer is strongly influenced by its aluminum mole fraction x and its magnesium doping profile. By comparing LED electroluminescence, quantum well photoluminescence, and simulations of LED heterostructure, we were able to differentiate the contributions of injection efficiency and internal quantum efficiency to the external quantum efficiency of UV LEDs. For the optimized heterostructure using an Al{sub 0.7}Ga{sub 0.3}N:Mg electron blocking layer with a Mg to group III ratio of 4% in the gas phase the electron leakage currents are suppressed without blocking the injection of holes into the multiple quantum well active region. Flip chip mounted LED chips have been processed achieving a maximum output power of 3.5 mW at 290 mA and a peak external quantum efficiency of 0.54% at 30 mA.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

MBE Growth and Structural Properties of GaP and InP Nanowires on a SiC Substrate with a Graphene Layer

The possibility in principle of the MBE (molecular-beam epitaxy) growth of GaP and InP nanowires on a SiC substrate with a graphene layer is demonstrated for the first time. InP nanowires on such a substrate have no stacking faults and possess an ideal crystallographic quality. At the same time, GaP nanowires have structural defects of the type of twins and the reversal of crystallographic phases at the top and at the base. The results of structural measurements demonstrate that the nanowires are formed in the wurtzite phase, which is not typical of bulk III–V materials.

36 MATERIALS SCIENCE↗

Technical Note CRYOFRABR#002/2021: Activated-copper-coated alumina granules synthesis

Detailed experimental studies of oxygen capture in the argon purification process using activated-copper on alumina and layered double hydroxide (LDH) were carried out, and the results were compared to the BASF commercial copper material Cu-0226 S performance. Here, we report the following main findings: i) the desired crystal structures for the studied materials were obtained after the synthesis process, ii) the use of the LDH structure promoted greater dispersion of the CuO phase when compared to BASF commercial catalyst, iii) alumina impregnated with copper demonstrated a similar result as the BASF sample for O 2 capture, and iv) among the three samples evaluated, the LHD sample demonstrated the best results regarding oxygen capturing performance becoming a promising structure for further studies.

36 MATERIALS SCIENCE↗

On Jupiter's rate of rotation

It is suggested that the apparent lag of Jupiter's mean rotation rate in extratropical latitudes (System II) behind the rotation rate of Jupiter's radio emissions (System III) is caused by the difference between phase speeds and true speeds in extratropical latitudes. An estimate of the difference based on the formula for the phase speed of Rossby waves agrees with the difference calculated from the two rotation rates.

Stone, P. H.↗

Adsorption and chemical reaction of gaseous mixtures of hydrogen chloride and water on aluminum oxide and application to solid-propellant rocket exhaust clouds

Hydrogen chloride (HCl) and aluminum oxide (Al2O3) are major exhaust products of solid rocket motors (SRM). Samples of calcination-produced alumina were exposed to continuously flowing mixtures of gaseous HCl/H2O in nitrogen. Transient sorption rates, as well as maximum sorptive capacities, were found to be largely controlled by specific surface area for samples of alpha, theta, and gamma alumina. Sorption rates for small samples were characterized linearly with an empirical relationship that accounted for specific area and logarithmic time. Chemisorption occurred on all aluminas studied and appeared to form from the sorption of about a 2/5 HCl-to-H2O mole ratio. The chemisorbed phase was predominantly water soluble, yielding chloride/aluminum III ion mole ratios of about 3.3/1 suggestive of dissolved surface chlorides and/or oxychlorides. Isopiestic experiments in hydrochloric acid indicated that dissolution of alumina led to an increase in water-vapor pressure. Dissolution in aqueous SRM acid aerosol droplets, therefore, might be expected to promote evaporation.

Cofer, W. R., III↗

The nova-like variable KQ Mon and the nature of the UX Ursa Majoris stars

The KQ Mon is a UX UMa type nova-like variable discovered by Howard Bond. Optical spectra taken by Bond in 1978 reveal very shallow Balmer absorption lines and He I absorption. Bond also did UBV and high speed photometry in 1978 and early 1981. There has been no evidence of orbital variations but the appearance of the optical spectrum and the presence of low amplitude flickering suggested a strong similarity to CD-42-14462 (=V3885 Sgr) and other members of the UX UMa class. Low dispersion observations of KQ Mon were made with the International Ultraviolet Explorer satellite. Six spectra taken with the shot wavelength prime camera are dominated by strong broad absorption lines due to N V, O I, Si III, Si IV, C IV, He II, N IV, and Al III. There is little evidence of orbital phase modulation over the time baseline of the observations. Unlike UV observations of other UX UMa type objects, KQ Mon exhibits no emission lines or P Cygni type profiles and the velocity displacements appear to be smaller, suggesting the absence of a hot, high velocity wind characterizing other UX UMa stars. The relationship of KQ Mon to other UX UMa disk stars is discussed and a model is suggested to explain their observed properties and the lack of major outbursts.

Sion, E. M.↗

Use of column V alkyls in organometallic vapor phase epitaxy (OMVPE)

The use of the column V-trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs(1-y)Sb(y), Al(x)Ga(1-x)Sb, and Ga(1-x)In(x)As as examples.

Ludowise, M. J.↗

Ultraviolet studies of nova-like variables with the IUE

KQ Mon is a new UX UMa-type nova-like variable. Optical spectra taken in 1978 reveal very shallow Balmer absorption lines and He I (wavelength 4471) absorption. There was no evidence of orbital variations but the appearance of the optical spectrum and the presence of low amplitude flickering suggested a strong similarity to CD-42 degrees 14462 (=V3885 Sgr) and other members of the UX UMa class. KQ Mon was observed at low dispersion with the IUE satellite. Six spectra taken with the short wavelength prime (SWP) camera are dominated by strong broad absorption lines due to N V, O I, Si III, Si IV, C IV, He II, N IV, and A1 III. There is little evidence of orbital phase modulation over the time baseline of the observations. Unlike UV observations of other UX UMa-type objects, KQ Mon exhibits no emission lines or P Cygni-type profiles and the velocity displacements appear to be smaller, suggesting the absence of a hot, high velocity wind characterizing other UX UMa stars. The relationship of KQ Mon to other UX UMa disk stars is discussed and a model is suggested to explain their observed properties and the lack of major outbursts.

Guinan, E. F.↗

Acquisition times of carrier tracking sampled data phase-locked loops

Phase acquisition times of type II and III loops typical of the Advanced Receiver are studied by computer simulations when the loops are disturbed by gaussian noise. Reliable estimates are obtained by running 5000 trials for each combination of loop signal-to-noise ratio (SNR) and frequency offset. The probabilities of acquisition are shown versus time from start of acquisition for various loop SNRs and frequency offsets. For frequency offsets smaller than one-fourth of the loop bandwidth and for loop SNRs of 10 dB and higher, the loops acquire with probability 0.99 within 2.5 B sub L for type II loops and within 7/B sub L for type III loops.

Aguirre, S.↗

The ammonia-water phase diagram and its implications for icy satellites

A Holzapfel-type diamond anvil cell is used to determine the NH3 - H2O phase diagram in the region from 0 to 33 mole percent NH3, 240 to 370 K, and 0 to 5 GPa. The following phases were identified: liquid; water ices Ih, III, V, VI, VII, and VIII; ammonia monohydrate, NH3.H2O; and ammonia dihydrate NH3.2H2O. Ammonia dihydrate becomes prominent at moderate pressures (less than 1 GPa), with planetologically significant implications, including the possibility of layering in Titan's magma ocean.

Johnson, M. L.↗

The ammonia-water phase diagram and its implications for icy satellites

A Holzapfel-type diamond anvil cell is used to determine the NH3 - H2O phase diagram in the region from 0 to 33 mole percent NH3, 240 to 370 K, and 0 to 5 GPa. The following phases were identified: liquid; water ices Ih, III, V, VI, VII, and VIII; ammonia monohydrate, NH3.H2O; and ammonia dihydrate NH3.2H2O. Ammonia dihydrate becomes prominent at moderate pressures (less than 1 GPa), with planetologically significant implications, including the possibility of layering in Titan's magma ocean.

Johnson, Mary L.↗

System III variations in apparent distance of Io plasma torus from Jupiter

System III variations in apparent distance of the Io plasma torus from Jupiter are examined on the basis of data obtained from UVS scans across Jupiter's satellite system. The displacement of the dawn and dusk ansae are found to be unexpectedly complex. The displacements are unequal and both ansae are in motion with the motion of the approaching ansa being the lesser of the two. The radial motions, as measured from either the center of Jupiter or the offset-tilted dipole, are of unequal magnitude and have the System III periodicity. It is concluded that the cross-tail electric field that causes these torus motions is concentrated on the dusk ansa, varied with the System III period, and shows magnetic-anomaly phase control. It is found that the dawn-dust asymmetry in brightness is not explained simply by the cross-tail electric field. It is concluded that there is a heating mechanism that causes the dusk side of the Io plasma torus to be brighter than the dawn side.

Dessler, A. J.↗

Various Ambiguities in Re-constructing Laser Pulse Parameters

We think that mode lock laser pulses are generated by the summation process that take place between the monochromatic EM filed frequencies as if they interact with each other as shown in equation 1. In reality, the pulse generation is a collaborative interaction process between EM fields and various material medium. When we carry out the actual mode lock analysis, we do take into account of interpaly between all the temporal dynamics of the cavity gain medium, cavity round trip time and the response time of the intra cavity element (saturable absorber, Kerr medium, etc.). that really enforces the locking of the phase of the cavity spontaneous emissions. On a conceptual level, this simplistic representation of the mode locking by Eq.1 ignores all these critical physical processes. When we try to analyze a pulsed field, again we start by representing it very much like this equation, even though we can only detect the square modulus of this complex field and loose a lot of phase related information to the detectors quantum whims and their time constants. The key parameters for a light pulse are as follows. Foremost is the (i) carrier frequency, which cannot be described or imagined without its state of undulation expressed as its (ii) phase. Next is our imagined time finite (iii) carrier envelope that provides the temporal boundary of the field amplitude strength of the undulating E-field. The final parameter is the (iv) state of polarization or the unique plane along which the strength of the E-field gradient undulates. None of these filed characteristics are made self-evident to us by the fields themselves. We do not see light. Light does not see light. Light beams pass through each other without altering each others energy distribution unless there are interacting material molecules (dipoles) within the physical volume of superposition of the beams. In contrast, we can sense the material particles. Material particles sense each other and they cannot pass through each other without interacting with (scattering from) each other. Thus the interpretation of the superposition phenomenon of multiple fields on detectors should not be lumped under the mysterious "wave-particle duality" philosophy. The phenomenon of superposition can be understood better when we focus on the actual process experienced by the detecting dipoles when allowed by QM rules, they respond to and sum all the induced stimulations due to all the superposed fields followed by the proportionate energy absorption giving rise to the fringes we observe. We will present various experimental results to illustrate our arguments. Our position is that such detector behavior driven interpretations rather than the generally implied field-field interaction driven explanations, will help us better understand the ultimate nature of light and hence invent better and newer devices and instruments.

Roychoudhuri, Chandrasekhar↗