STRAIN MEASUREMENT IN EPITAXIAL NiSi2/Si(lll) BY MeV ION CHANNELING

1985 ◽  
Vol 56 ◽  
Author(s):  
MASAKO OKAMOTO ◽  
SHIN HASHIMOTO ◽  
B.D. HUNT ◽  
L.J. SCHOWALTER ◽  
W.M. GIBSON
Keyword(s):  
Critical Thickness ◽  
Type A ◽  
Epitaxial Films ◽  
Misfit Dislocations ◽  
Type B ◽  
Ion Channeling ◽  
Partial Dislocations ◽  
Dislocation Densities ◽  
The Difference ◽  
Pseudomorphic Growth

AbstractStrains in both type-A and type-B NiSi2 epitaxial films grown on Si(lll) substrates were measured by means of MeV 4He+ ion channeling. The results show the critical thickness to maintain pseudomorphic growth strongly depends on theepitaxial orientation of the NiSi2 film. The difference in critical thicknesses between type-A and type-B NiSi2 can be explained by considering the different type of misfit dislocations introduced at the interface. Namely, at the type-B interface, 1/<112> partial dislocations associated with interface steps are allowed while they are prohibited at the type-A interface. Dislocation densities measured by TEM also support these results.

Tetragonal Strain in MBE GexSi1-x Films Grown on (100) Si Observed by Ion Channeling and X-Ray Diffraction

1983 ◽  
Vol 25 ◽  
Author(s):  
A. T. Fiory ◽  
L. C. Feldman ◽  
J. C. Bean ◽  
I. K. Robinson
Keyword(s):  
Molecular Beam ◽  
Critical Thickness ◽  
Ion Beam ◽  
Growth Surface ◽  
X Ray Diffraction ◽  
Strained Layers ◽  
X Ray ◽  
Ion Channeling ◽  
Pseudomorphic Growth ◽  
Beam Damage

ABSTRACTStructure of GexSi1-x alloy films grown on (100) Si by molecular beam epitaxy is analyzed by MeV He+ ion channeling and X-ray diffraction as functions of Ge concentration, film thickness and growth temperature. Critical thicknesses for pseudomorphic growth are determined for x ≤ 0.5, where coherent tetragonally-strained layers are observed. The average strain decreases approximately as the square-root of thickness when the critical thickness is exceeded. At temperatures near the threshold for islanding growth, surface roughness appears as a precursor to degradation of strained-layer epitaxy. No effect on the amount of the tetragonal strain was found in a study of ion-beam damage.

Elimination of Ammonium Ion from the a-Hydroxyalkyl Radicals of Serine and Threonine in Aqueous Solution and the Difference in the Reaction Mechanism

1985 ◽  
Vol 40 (11-12) ◽  
pp. 785-797 ◽  
Author(s):  
Günter Behrens ◽  
Günther Koltzenburg
Keyword(s):  
Kinetic Data ◽  
Type A ◽  
Ammonium Ion ◽  
Type B ◽  
Ketyl Radical ◽  
Time Resolved ◽  
Hydroxyalkyl Radical ◽  
The Difference ◽  
Hydroxyalkyl Radicals ◽  
Radical Attack

Abstract The zwitterionic radicals HO-ĊH-CH(COO-)NH3+ (4a) and HO-Ċ(CH3)-CH(COO-)NH3+ (4b) are the main species produced upon OH· radical attack in aqueous solutions at pH 3-7 at the amino acids serine, HO-CH2-CH(COO-)NH3+, or threonine, HO-CH(CH3)-CH(COO-)NH3+, respectively. Both radicals undergo elimination of NH4+ ion to form the radicals O=CH-ĊH-COO- (7) or CH3-CO-ĊH-COO- (9) respectively.The pKa of the serine-derived cationic radical HO-ĊH-CH(COOH)NH3+ (3a) (3a ⇄ 4a + H+), was determined by ESR spectroscopy to 2.2 ± 0.1 at 276 K. From kinetic data the pKa(OH) of radical 4a (4a ⇄ O-ĊH-CH(COO-)NH3+ (5a) + H+) was calculated to 7.0. The elimination of NH3 takes place from the ketyl radical 5a (type-B mechanism), the rate constant was calculated from kinetic data to 2.4 × 106 s-1 at 290 K.The half-lives of radicals 4a and 4b were measured by time-resolved conductivity changes upon pulse radiolysis, 170 ± 10 μs for 4a and 26 ± 2 μs for 4b, at 290 K and pH 5.8 .With the threonine derived radicals elimination of NH3 takes place at the stage of the α-hydroxyalkyl radical 4b (type-A mechanism). In this series the pKa of the product radical CH3-CO-ĊH-COOH (8) (8 ⇄ 9 + H+), was determined by ERS spectroscopy to 2.7 ± 0.1. The reasons for the observed mechanistic differences (type-A versus type-B decay) are discussed. As further examples for a type-B decay some preliminary data on the elimination of HF from the radicals CF3-Ċ(OH)-CF3 and CF3-ĊH-OH have been added.

Epitaxial Relations in Fluoride Films Grown on GaAs{lll} and Ge(lll) Substrates

1985 ◽  
Vol 47 ◽  
Author(s):  
K. Tsutsui ◽  
H. Ishiwarya ◽  
T. Asano ◽  
S. Fijrukawa
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Type A ◽  
Matching Condition ◽  
Type B ◽  
Substrate Type ◽  
Lattice Matching ◽  
Lattice Constants ◽  
Ion Channeling ◽  
Transmission Electron

ABSTRACTEpitaxial relations in Cax Sr1−xF2(0⫶×⫶l) and BaF2 films grown on GaAs(111), (111) and Ge(111) substrates were investigated by He ion channeling analysis and transmission electron microscopy. Though the lattice constants of GaAs and Ge are nearly the same, the relations were found to be completely different. That is, the fluoride films on GaAs prefered to have an orientation identical to that of the substrate (type A orientation), whereas the orientation of the films on Ge was mainly rotated by 180° about the surface normal 〈111〉 axis (type B orientation). A hypothesis is proposed that the epitaxial relations in these systems are affected by the ionicity of the substrate as well as the lattice matching condition.

The population of germ cells in immature male rats following irradiation at birth

1966 ◽  
Vol 165 (998) ◽  
pp. 103-135 ◽  
Keyword(s):  
Germ Cells ◽  
Total Population ◽  
Primordial Germ Cells ◽  
Type A ◽  
Male Rats ◽  
Type B ◽  
The Absolute ◽  
The Difference ◽  
Transitional Cells ◽  
Type A Spermatogonia

Male rats were irradiated with 19 r on the day of birth, and killed at intervals ranging from 5 to 18 days. Estimates were made of the absolute and relative numbers of germ cells at different stages of spermatogenesis in 64 irradiated and 61 untreated specimens. In the normal rat, the calculated population of germ cells increased from about 160000 at 5 days to 30 million at 18 days. Only negligible numbers of primordial germ cells (gonocytes and transitional cells) persisted beyond the age of 10 days. Small numbers of spermatogonia type A appeared at 5 days (15000) and their population rose to about 1 million at 12 days, and 2 million at 18 days (7 % of all germ cells). Intermediate spermatogonia first occurred in appreciable numbers (23000 to 55000) at 8 or 9 days, when the population of type-A spermatogonia was 360000. The subsequent rise in the population of intermediate spermatogonia was more rapid than that of type A (4 million at 18 days). Spermatogonia type B and primary spermatocytes appeared at 9 to 10 days, and their numbers rose more steeply still (6.5 and 16 million at 18 days, respectively). Irradiation at birth exerted no rapid effect on the cytological appearance of primordial germ cells. Transformation from gonocytes to transitional cells appeared to proceed normally and the estimated total population of germ cells at 5 days was no smaller than in the controls. Subsequently, however, many of the transitional cells failed to divide: they enlarged to form giant cells, acquired bizarre nuclear outlines, and persisted for unusually long periods. Some degenerated at mitotic prophase or metaphase, while a few seemed to die at interphase, without entering division. The calculated total population of germ cells in irradiated rats rose from 160000 at 5 days to 9.4 million at 18 days. Small numbers of spermatogonia type A, presumably derived from such primordial germ cells as were able to complete mitosis, appeared some 2 to 3 days later than in controls. The number of type-A spermatogonia in 7-day-old irradiated rats was 44000, cf. 215000 in controls; the difference became less pronounced with time, and by the age of 18 days, the population of 1.9 million was comparable to that estimated for the controls. Small numbers of intermediate spermatogonia appeared on the 9th (8000) and 10th day (35000), when the population of type-A spermatogonia was about 110000 and 260000 respectively. By the 18th day, intermediate spermatogonia numbered 2 million. The populations of type-B spermatogonia and primary spermatocytes rose from 11000 to 13000 at 10 days to 1.6 and 3.4 million, respectively, at 18 days. The difference in the absolute and relative numbers of germ cells between normal and irradiated testes widened progressively with advance in the developmental stage of the germ cells. Analysis of the results indicates that in the reduced population of spermatogonia type A after irradiation, the pattern of spermatogonial mitoses is modified so as to favour the formation of more type-A, in preference to intermediate, spermatogonia.

Derivation of correction terms for general quadrature formulae

1969 ◽  
Vol 66 (3) ◽  
pp. 571-586 ◽  
Author(s):  
J. A. Grant
Keyword(s):  
Finite Interval ◽  
Bernoulli Polynomials ◽  
Type A ◽  
Weighted Sum ◽  
Type B ◽  
Quadrature Formulae ◽  
The Difference ◽  
Correction Terms

AbstractIn this paper, it will be shown how it is possible, using Bernoulli polynomials of the first kind, to derive correction terms for any quadrature approximation in the form of a weighted sum over a finite interval. The terms derived will involve either the difference or the sum of derivatives taken at the ends of the range of integration, and they will be described as being of either Type A or Type B respectively. There will also be some discussion of the uses of such terms.

scholarly journals Voltage-Activated Potassium Outward Currents in Two Types of Spider Mechanoreceptor Neurons

1999 ◽  
Vol 81 (6) ◽  
pp. 2937-2944 ◽  
Author(s):  
Shin-Ichi Sekizawa ◽  
Andrew S. French ◽  
Ulli Höger ◽  
Päivi H. Torkkeli
Keyword(s):  
Outward Current ◽  
Type A ◽  
Transient Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Type B ◽  
Outward Currents ◽  
The Difference ◽  
Major Factors ◽  
Kinetics Of

Voltage-activated potassium outward currents in two types of spider mechanoreceptor neurons. We studied the properties of voltage-activated outward currents in two types of spider cuticular mechanoreceptor neurons to learn if these currents contribute to the differences in their adaptation properties. Both types of neurons adapt rapidly to sustained stimuli, but type A neurons usually only fire one or two action potentials, whereas type B neurons can fire bursts lasting several hundred milliseconds. We found that both neurons had two outward current components, 1) a transient current that activated rapidly when stimulated from resting potential and inactivated with maintained stimuli and 2) a noninactivating outward current. The transient outward current could be blocked by 5 mM tetraethylammonium chloride, 5 mM 4-aminopyridine, or 100 μM quinidine, but these blockers also reduced the amplitude of the noninactivating outward current. Charybdotoxin or apamin did not have any effect on the outward currents, indicating that Ca2+-activated K+ currents were not present or not inhibited by these toxins. The only significant differences between type A and type B neurons were found in the half-maximal activation ( V 50) values of both currents. The transient current had a V 50 value of 9.6 mV in type A neurons and −13.1 mV in type B neurons, whereas the V 50 values of noninactivating outward currents were −48.9 mV for type A neurons and −56.7 mV for type B neurons. We conclude that, although differences in the activation kinetics of the voltage-activated K+ currents could contribute to the difference in the adaptation behavior of type A and type B neurons, they are not major factors.

scholarly journals Repellent activities of dichloromethane extract of Allium sativum (garlic) (Liliaceae) against Hyalomma rufipes (Acari)

2016 ◽  
Vol 87 (1) ◽  
Author(s):  
Felix Nchu ◽  
Solomon R. Magano ◽  
Jacobus N. Eloff
Keyword(s):  
Avoidance Response ◽  
Allium Sativum ◽  
Type A ◽  
Test Solution ◽  
Hard Tick ◽  
Type B ◽  
Repellent Effect ◽  
The Mean ◽  
The Difference ◽  
Hyalomma Rufipes

Dichloromethane (DCM) extract of garlic (Allium sativum Linn.) bulbs was assessed for its repellent effect against the hard tick, Hyalomma rufipes (Acari: Ixodidae) using two tick behavioural bioassays; Type A and Type B repellency bioassays, under laboratory conditions. These bioassays exploit the questing behaviour of H. rufipes, a tick that in nature displays ambush strategy, seeking its host by climbing up on vegetation and attaching to a passing host. One hundred microlitres (100 µL) of the test solution containing DCM extract of garlic bulbs and DCM at concentrations of 0.35%, 0.7% or 1.4% w/v were evaluated. DCM only was used for control. Tick repellency increased significantly (R2 = 0.98) with increasing concentration (40.03% – 86.96%) yielding an EC50 of 0.45% w/v in Type B repellency bioassay. At concentration of 1.4% w/v, the DCM extract of garlic bulbs produced high repellency index of 87% (male ticks) and 87.5% (female ticks) in the Type A repellency bioassay. Only 4% avoidance of male ticks or female ticks was recorded in the Type B repellency bioassay. In the corresponding controls, the mean numbers of non-repelled male or female ticks were 80% and 41 males or 38 females of 50 ticks in the Type A and Type B repellency bioassays, respectively. The variations in the results could be attributed to the difference in tick repellent behaviours that were assessed by the two repellency bioassays; the Type A repellency bioassay assessed repellent effect of garlic extracts without discriminating between deterrence and avoidance whereas the Type B repellency bioassay only assessed avoidance response. Generally, DCM extract of garlic was repellent against H. rufipes, albeit weak tick repellency was obtained in the Type B repellency bioassay. Furthermore, this study established that the tick repellent activity of garlic extracts is predominantly by deterrence.

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