Fully engineered high performance UHF SQUID magnetometer

A miniaturised UHF (430 MHz) ac-biased SQUID magnetometer operating at 4.2 K has been designed in which the first stage amplification is provided by a liquid helium cooled GaAs FET amplifier. The magnetometer, which uses in situ varactor tuning for the SQUID tank circuit and FETAmp has a signal energy sensitivity (figure of merit) ? 1.3 × 10^?3JHz^?1 ($\text{ 1 × 10}{}^{\mathrm{?5}}\text{Φ}{}_0\text{Hz}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ flux sensitivity) in flux lock. The system operates in full flux lock over a frequency range from dc to 5 MHz.     

Growth and characterisation of epitaxial Gax In1−x Asy P1−y

Epitaxial layers of the quatternary semiconducting compounds Ga_x In_1?x As_y P_1?y have been grown on (111)B InP substrates by liquid phase epitaxy. Undoped compounds of this general formula with $\text{y}\text{?2}\text{x}$ are lattice matched to InP. Both cathodoluminescence (CL) and photoluminescence (PL) measurements on a range of nominally undoped and doped samples that (a) are lattice matched and (b) of varying degrees of lattice mismatch allow the selection of optimum material characteristics for subsequent fabrication into light emitting diodes. n-type material ($\text{ca}\text{2 × 10}{}^1{}^8\text{cm}{}^{\mathrm{?3}}\text{Sn}$) appears best suited for such devices.     

Carburization and decarburization kinetics of iron in CH4 — H2 mixtures between 1000 – 1100 °C

In this study the rate constants of the methane decomposition reaction on iron surfaces were determined in the 1000–1100°C temperature range, by grav? metric methods. Earlier works showed that the reaction velocity was given by The results indicate that the constant values vary from 2.72 × 10^?6 to $\text{16.74 × 10}{}^{\mathrm{?6}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for k and 2.61 × 10^?8 to $\text{8.62 × 10}{}^{\mathrm{?8}}\text{mol C/cm}{}^2\text{/sec/atm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ for k′ between 1000 and 1100°C.     

Properties of aluminum-based cermet thin film resistors

A family of novel aluminum-aluminum oxide cermet resistance thin films has been deposited by the controlled oxidation of thermally decomposing triethyl aluminum vapor. Film resistivity can be varied, controllably, from 10^?2 to 10⁴ Ωcm. Over the range $\text{10}{}^{\mathrm{?1}}\text{?10}{}^3\text{Ωcm}$, the temperature coefficient of resistivity decreases monotonically from zero to ?1200 ppm/°C. High value resistors having surface resistivities from $\text{1 kΩ/sq. to 1000 MΩ/sq}$. have been fabricated by conventional aluminum metallization patterning techniques and they are compatible with silicon wafer processing technology.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

Formation and properties of metallic organotin films

Semiconductive and conductive films of metallic appearance are formed by glow discharge of appropriate organometallic compounds. Tetramethyltin is used as a starting compound for the film-forming experiments. The resulting films contain carbon, tin and hydrogen with a carbon-to-tin atomic ratio of 2.5 or less. These films are semiconductors with conductivities between 2 × 10^-1 and $\text{1 × 10}{}^{-2}\text{Ω}{}^{-1}\text{cm}{}^{-1}$. Transmission electron microscopy shows the films to be amorphous. Films of a certain composition are transformed to β-Sn on exposure to an electron beam. Thermal treatment increases the conductivity gradually to values of about $\text{1 × 10}{}^2\text{Ω}{}^{-1}\text{cm}{}^{-1}$.     

Conductivite ionique dans les verres AgPO3-AgX (X = I.Br.Cl)

The glass-forming regions in the systems AgPO₃- AgX with X = I.Br.Cl were determined and the study of the electrical conductivity of glasses belonging to these systems was carried out. The glass-forming region and conductivity increase with increasing halogen ion size. The conductivity reaches maxima values of the order of 10^?2, 10^?3, $\text{10}{}^{\mathrm{?4}}\text{(Ω ·}\text{cm}\text{)}{}^{\mathrm{?1}}$ with AgI, AgBr, AgCl respectively. The study of the electrical conductivity shows that the conduction is essentially ionic in nature and due to silver ions movements only.     

Photoelectrochemical study of TiS3 in aqueous solution

TiS₃ single crystals have been grown by chemical vapor transport. They were characterized by X-ray diffraction and measurement of their electronic transport properties. A photoelectrochemical study shows both anodic and cathodic dark currents and anodic photocurrents. Flat band potentials and anodic corrosion p$\text{o}$te$\text{n}$tials in acidic and basic solutions and in the presence of an $\text{I}{}^{\mathrm{?}}{}_3\text{I}{}^{\mathrm{?}}$ redox couple have been determined from the onset of photocurrent and from the Schottky-Mott plot of capacitance. The flat band potential ex$\text{h}$ibits a pH dependence but is almost independent of the presenc$\text{e}$ o$\text{f}$ I^? in solution. The stability of this material in a 1N H₂SO₄+ 1N $\text{I}{}^{\mathrm{?}}{}_3\text{I}{}^{\mathrm{?}}$ solution has been observed for a period of fourteen days with a photocurrent of approximately $\text{1}\text{mA}\text{cm}{}^2$. A particular photocorrosion mechanism is reported. The reaction starts at the edges of the layer and proceeds toward the interior. These mechanisms are discussed in relation to the existence of two types of S atoms in the structure: sulfur dimers and S^2? ions.     

Ionic conductivity in low carnegieite compositions based on NaAlSiO4

Carnegieite compositions of the type Na_1+xAl_1+xSi_1?xO₄ with x = 0 to ～0.7 were prepared. Na ion conductivities, measured with Na and Au electrodes at ～10³ Hz, range from $\text{4×10}{}_{\mathrm{?5}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ for NaAlSiO₄ to $\text{5×10}{}^{\mathrm{?3}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300 C for Na_1.7Al_1.7Si_0.3O₄. Substitutions of Li, K, Ca, or Sr for Na lowered σ whereas substitution of Ti for Si raised σ. Na aluminum silicates with the nepheline structure had lower σ than carnegieite compositions.     

Development of the AASHTO fracture-toughness requirements for bridge steels

This paper describes the effects of temperature and strain rate on the fracture-toughness behavior of bridge steels. The test results showed the existence of a fracture-toughness transition that is an inherent material property rather than a behavior caused only by a change in the stress state. The effect of a slow loading rate, compared with impact loading rates, is to shift the fracture-toughness transition to lower temperatures. The magnitude of the temperature shift between stow loading ($\text{?≈ 10}{}^{\mathrm{?5}}\text{sec}{}^{\mathrm{?1}}$)and impact loading ($\text{/.? ≈ 10 sec}{}^{\mathrm{?1}}$) decreased with increased yield strength of the steel. The fracture-toughness behavior of bridge steels under strain rates that are encountered in actual bridge ($\text{/.? t~ 10}{}^{\mathrm{?3}}\text{sec}{}^{\mathrm{?1}}$) is closer to slow loading than to impact loading.Relationships are presented among fracture-toughness values determined by testing fracture-mechanics-type specimens, Charpy $\text{V-}\text{notch}$ (CVN) specimens, and nil-ductility-transition (NDT) specimens. Moreover, procedures are presented for using CVN impact-test results to predict $\text{K}{}_{\mathrm{IC}}$ values at slow or at moderate loading rates such as occur in actual bridges. The predicted $\text{K}{}_{\mathrm{IC}}$ values are shown to be close to those experimentally determined by testing $\text{K}{}_{\mathrm{IC}}$ specimens at various strain rates.The test results were used to develop fracture-toughness requirements for bridge steels. These toughness requirements have been approved by the Federal Highway Administration (FHWA) and by the American Association of State Highway and Transportation Officials (AASHTO) and are mandatory requirements on all Federal-aid highway programs in the United States.     

Dielectric constant and electrical conductivity of liquid D-T

The first dielectric constant and electrical condutivity measurements on liquid deuterium-tritium are reported. The samples, which contain 0.9, 8.8, and 98.3% tritium, are measured for complex capacitance at 1592 Hz with an effective electric field of 2830 Vm^?1 at temperatures of 20 to 26 K. The tritium radioactivity converts the samples dielectrics, with dielectric constant as large as 4.5 and electrical conductivities of $\text{200 × 10}{}^{\mathrm{?9}}\text{(Ωm)}{}^{\mathrm{?1}}$. Carrier densities are about 10¹⁰ per mol sample; both free electrons and ions are apparently present.     

Nouveaux conducteurs ioniques caracterises par une structure a tunnels entrecroises

The ionic conductivity of pyrochlores A_1+α(Ta_1+αW_1?α)O₆ was investigated for A = Na and T1. The thallium compounds are rather good conductors (0.34 ≤ ΔE ≤ 0.40 eV and $\text{5 10}{}^{\mathrm{?8}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 5.5 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$); the sodium oxides are poor conductors (0.76 eV ≤ ΔE ≤ 1.48 eV and $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{500}\text{K}\text{≤ 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The differences between these two classes of pyrochlores are explained in terms of structure. New non-stoechiometric oxides T1_12+x(M_30+xW_3?x)O₉₀, with M = Ta, Nb, and 0 ≤ x ≤ 3, were isolated. They are, like pyrochlores, characterized by an intersecting tunnel structure, which is an intergrowth of pyrochlore and A₂M₇O₁₈ structures. These oxides show ionic conduction properties which are very close to those of pyrochlores: the tantalum oxides are better conductors (0.30 eV ≤ ΔE ≤ 0.37 eV ; $\text{3.6 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 1.4 10}{}^{\mathrm{?6}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$) than the niobium oxides (0.36 eV ≤ ΔE ≤ 0.42 eV ; $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 3.8 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The evolution ofionic conduction properties of all these compounds is discussed.     

Oxygen stoichiometry in the system (CaxSr1−x)FeO3−y. Its effect on crystallographic and thermodynamic properties

Oxygen-deficient perovskites of the system (Ca_xSr_1?x)FeO_3?y were prepared at high oxygen pressures up to 1900 atm (196 MPa), and measurements were made of their crystallographic and thermodynamic behavior. The a-spacing of perovskites expanded linearly with increasing oxygen deficiency for x = 0–0.4 and y = 0.01–0.19, and an eventual tetragonal distortion took place at the composition AFeO_2.82 (64% Fe⁴⁺). Thermogravimetric analysis of SrFeO_2.81 in vacuo revealed that oxygen atoms began to release from the perovskite lattice at 350°C. Thermodynamic analysis showed that oxygen deficiency had a linear relationship with the square root of the fugacity of oxygen gas, and the slope was $\text{?1.96 × 10}{}^{\mathrm{?3}}\text{atm}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{mol}{}^{\mathrm{?1}}$.     

Thermal expansion of corundum structure Rh2O3

The directional thermal expansion coefficients of the corundum structure form of Rh₂O₃ were determined from room temperature to 850°C by x-ray diffraction methods. Rh₂O₃ has a lower thermal expansion and is less anisotropic in thermal expansion than alumina. The directional thermal expansion coefficients of Rh₂O₃ expressed in second degree polynominal form are: $\text{“α}{}_{\mathrm{<mtext>a</mtext>}}\text{” = 5.350 ×10}{}^{\mathrm{?6}}\text{+ 1.281 ×10}{}^{\mathrm{?9}}\text{T}\text{? 1.133 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$ and $\text{“α}{}_{\mathrm{<mtext>c</mtext>}}\text{” = 5.246 ×10}{}^{\mathrm{?6}}\text{+ 6.369 ×10}{}^{\mathrm{?9}}\text{T}\text{? 7.480 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$.     

Electrical properties of D-T gas from 20 to 26 K

The dielectric constants and electrical conductivities of D-T gas at 20, 23, and 25 K are measured at 1592 Hz from 3 to 200 Vm² mol^?1. Tritium concentrations are 0.9, 8.8, and 98.3%. Both electrical quantities increase with density ans saturate above 400 mol m^?3. The gas is a soft dielectric, with an electrical conductivity as high as $\text{300 × 10}{}^{\mathrm{?9}}\text{Ω}\text{m}{}^{\mathrm{?1}}$. The saturated vapour conducts as well as the liquid beneath it. The total charge desity in pure tritium gas is about 10¹² mol^?1. Most electrons may react to form tritide ions, but the remaining electrons still carry most of the current.     

Formation of thin SiO2 films by high dose oxygen ion implantation into silicon and their investigation by IR techniques

The ion dose dependence of the infrared transmission spectra of SiO₂ layers formed by high dose ion implantation into silicon was investigated for ion doses ranging from $\text{10}{}^{16}\text{to}\text{2 × 10}{}^{18}\text{(}{}^{16}\text{O}{}_2\text{)}{}^{\mathrm{+}}\text{30}\text{kV ions cm}{}^{-2}$. The annealing temperature dependence of these spectra is also reported.The passivation properties of the SiO₂ layers and their dependence on annealing were investigated and monitored by IR techniques. It was found that an SiO₂ layer that is formed by implantation with 1 × 10¹⁸ ions cm^-2 and annealed at temperatures higher than 550 °C but not more than 800 °C is similar in its IR and passivation properties to thermally grown SiO₂ films.     

Conductivite electrique et spectres de diffusion raman des verres mixtes AgPO3 − MI2 AVEC M = Cd,Hg, Pb. Correlation entre conductivite et structure

The glass-forming regions in the AgPO₃ ? MI₂ systems with M = Cd,Pb,Hg were determined. Electrical conductivity measurements and Raman spectra were carried out. A maximum conductivity value of $\text{10}{}^{\mathrm{?2}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is obtained for a mole fraction of 0,19 in PbI₂ or in CdI₂, whereas a value of $\text{3×10}{}^{\mathrm{?5}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is found for a mole fraction of 0,5 in HgI₂. The conductivity results and Raman spectra are examined and compared with those of AgPO₃ ? AgI. An exchange between Ag⁺ and M²⁺ ions is proposed leading to AgI species in AgPO₃ ? CdI₂ and AgPO₃ ? PbI₂ glasses. It could explain the high conductivity values obtained and the similarities observed in Raman spectra.     

Liquid phase epitaxial growth of gallium arsenide on an etched substrate

A method is described for etching the surface of GaAs substrates with a Ga solution $\text{in}$$\text{situ}$ immediately prior to epitaxial layer growth from the liquid phase. Layers grown by this procedure show excellent surface morphologies and electrical properties ($\text{μ～5100}\text{cm}{}^2\text{v-sec}$ at 300°K for $\text{n～ 7.8×10}{}^{16}\text{cm}{}^3$). Advantages of the method and its applicability to epitaxial growth of other III-V compounds are discussed.     

Preferential oxygen sputtering from Nb2O5

The bombardment of Nb₂O₅ with Kr⁺ or O⁺₂ ions leads to the development of a surface layer NbO. The layer begins to form at (2–4) × 10¹⁵ ions cm^-2 as random nuclei which can be resolved by transmission electron microscopy. It is half complete at (4–8) × 10¹⁶ ions cm^?2, a much higher dose than that required for sputter equilibrium to be half complete. The final thickness is roughly 31 nm. These features, together with the further result that the layer forms independently of the bombarding current provided beam heating is avoided, can be understood from a model which combines preferential oxygen sputtering at the surface, diffusion of the relevant point defects, and random nucleation of a phase with lower stoichiometry. The governing equation is an extended form of the diffusion equation

$\text{?C}\text{?t}\text{=}\text{D?}{}^2\text{C}\text{?x}{}^2\text{+}\text{υ?C}\text{?x}\text{?}\text{DC}\text{L}{}^2$

where υ is the velocity of the surface recession due to sputtering and L is the diffusion length for trapping. Appropriate solution of the equation suggests that the altered layer will have a mean thickness similar to L, will be formed with a half-dose given by $\text{0.693LN}\text{S}$ where S is the sputtering coefficient, and will involve a total amount given by $\text{DC}{}_0\text{υ}$ atoms cm^?2, where C₀ is the stoichiometry at the outer surface. Current independence follows if the diffusion is bombardment enhanced, so that D is approximately proportional to υ. The main difficulty with the model is that it is strictly valid only for low concentrations.     

Cryostats for SQUID magnetometers

A non-metallic and non-magnetic cryostat, with a very low thermal budget and a container type autonomy was developed, to condition SQUID magnetometers whose maximum sensitivity reaches 10^?14$\text{T Hz}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$. This instrumentation uses composite materials, thermal shock and vibration resistant, multilayer thermal radiative insulation, to detect vibrations with thermal equivalent emissivity lower than 10^?3.