Contribution of dynamic charging effects into dopant contrast mechanisms in silicon

In this work, SEM capability for imaging of both p- and n-doped regions in Si was demonstrated. The best dopant contrast was found when the primary electron range (R) is comparable or larger than the maximum escape depth of secondary electrons (∼5λ) (λ stands for mean free path). Beyond this scale (R < 5λ, R > > 5λ) the contrast between p-, n-doped and intrinsic regions gradually disappears. The dopant profiles obtained by SEM were judged using scanning capacitance microscopy (SCM), dopant selective etch (DSE) and secondary ion mass spectrometry (SIMS) measurements, and excellent matching was demonstrated. A novel dopant contrast mechanism incorporating dynamic charging effects that take place during e-beam/specimen interaction is suggested. Under threshold steady-state imaging conditions, an E _bi field in Si near the surface region is formed. This field, governed by secondary electron (SE) emission and trapping of some incident and generated SE, accelerates electrons towards the surface in p-type regions and decelerates them in n-type regions, compared with the intrinsic material. This results in the observed dopant contrast: C(n) < C(i) < C(p). Use of the SEM for 2D-dopant imaging provides many advantages; giving fast results, covering a wide range of dopant concentrations, applicable to real devices, and does not require sample preparation needed by SCM and DSE. In addition, SEM-dopant contrast data quantification is possible using SIMS standards which needs to be defined with more details.     

Thermal conductivity of amorphous Teflon (AF 1600) at high pressure

The thermal conductivity, λ of amorphous Teflon AF 1600 [poly(1,3-dioxole-4,5-difluoro-2,2-bis(trifluoromethyl)-co-tetrafluoroethylene)] has been measured at pressures up to 2 GPa in the temperature range 93–392 K. At 295 K and atmospheric pressure, we obtained λ=0.116, W·m⁻¹·K⁻¹. The bulk modulus was measured up to 1.0 GPa in the temperature range 150–296 K and the combined data yielded the following values ofg=(∂ln λ ∂lnp) _r :2.8±0.2 at 296 K, 3.0±0.2 at 258 K, 3.0±0.2 at 236 K. 3.4±0.2 at 200 K. and 3.4±0.2 at 150 K.     

Thermal Conductivity of Standard Sands. Part I. Dry-State Conditions

A comprehensive thermal conductivity (λ) database of three dry standard sands (Ottawa C-109, Ottawa C-190, and Toyoura) was developed using a transient line heat source technique. The database contains λ data representing a variety of soil compactions and temperatures (T) ranging from 25 °C to 70 °C. The tested standard sands, due to their repeatable physical characteristics, can be used as reference materials for validation of thermal probes applied to similar dry granular materials. The measured data show an increasing trend of thermal conductivity at dryness (λ_dry) against T in spite of declining quartz λ with T. The air content (porosity) controls the λ of dry sands by acting as a very effective thermal insulator around solid soil particles. As a result, a diminutive increase of λ_dry with T is driven by increasing λ of air. The experimental λ data of dry sands were exceptionally well predicted by de Vries and Woodside–Messmer models, and also by a thermal conductance model, a product of λ of solids and the thermal conductance factor.     

Eigenvalues of damped structures: Vectoriteration in the original space of DOF

The equations of motion in structural dynamics as well as the corresponding eigenvalue problem are governed by 3 matrices for mass, damping and stiffness of order n which equals the number of degrees of freedom. High-performance eigenvalue-solvers are developed for only pairs A, B of matrices. Nevertheless, to benefit from these solvers, the original eigenvalue problem (λ² M+λD+K)x=0 is transformed into a linear eigenvalue representation with only two hypermatrices of double order 2n. Consequently the total numerical effort depends on this order 2n. This paper presents a vectoriteration process which actually works in the original space of order n and which needs no special actions like simultaneous iteration if complex conjugate eigenvalues λ, λˉ with identical norm have to be calculated. The theoretical foundation of this process still goes back to the pair of hypermatrices.     

Effect of oxygen deficiency (δ) on normal state resistivity of YBa2Cu3O7-δ superconductors

We have investigated theoretically the effect of oxygen deficiency (δ) on normal state resistivity (ρ) as well as its temperature dependence in YBa₂Cu₃O_7-δ superconductors. This has been based on a potential which incorporates the structure factors and various interactions for double two-dimensional (2-D) conducting CuO₂ plane. Using the Coulomb and electron-phonon terms of the interaction potential, we have then worked out the coupling strength (γ) for neighbouring electrons linked via 2-D acoustic phonons (hω_). Furthermore, the scattering time (τ _e-ph) due to electron-phonon interaction is deduced. The variations inτ _e-ph andρ _e-ph are studied with oxygen deficiency (δ) which is in the range of 0·0≤δ≤1·0, and the results thus obtained are found to be consistent with the earlier reported data. The residual resistivityρ ₀ obtained by extrapolation from experimental data together withρ _e-ph will predict the nearly-linear behaviour of normal state resistivity at temperatures (T) [90≤T≤300 K] in YBa₂Cu₃O_7-δ superconductors.     

Thermal conductivity, heat capacity, and compressibility of atactic poly(propylene) under high pressure

The thermal conductivity λ and the heat capacity per unit volume of atactic poly(propylene) have been measured in the temperature range 90–420 K at pressures up to 1.5 GPa using the transient hot-wire method. The bulk modulus has been measured in the range 200–295 K and up to 0.7 GPa. These data were used to calculate the volume dependence of λ,g=−[∂λ/λ)/(∂V/V)] _T , which yielded the following values for the glassy state (T<256 K at atmospheric pressure): 3.80±0.19 at 200 K, 3.74±0.19 at 225 K, 3.90±0.20 at 250 K, 3.77±0.19 at 271 K, and 3.73±0.19 at 297 K. The resultant value forg of the liquid state was 3.61±0.15 at 297 K. Values forg which are calculated at 295 K, using theoretical models of λ(T), agree to within 12% with the experimental value for the glassy state.     

Emissive characteristics of mesa-stripe lasers (λ=3.0–3.6 μm) made from InGaAsSb/InAsSbP double heterostructures

The directional patterns, current-voltage characteristics, and spectral characteristics of mesastripe lasers with InGaAsSb active layers, emitting at λ=3.0–3.6 μm (77 K) and having threshold currents ≥15 mA (j _th≥200 A/cm²), are investigated. The maximum output power is 1.4 mW (λ∼3.3 μm), the differential quantum efficiency ∼3%(τ=5–30 μs, f=500 Hz) for lasing in a longitudinal mode with beam divergences ΔΘ∥∼15° and ΔΘ ⊥ ∼30°. The relationship of the differential quantum efficiency to the order of the spatial mode of the lasing is demonstrated. A single-mode, current-tunable (−30 cm⁻¹/A) laser is used to measure the transmission of methane in the region of the ν ₃ absorption band. Pis’ma Zh. Tekh. Fiz. 24, 40–45 (June 26, 1998)     

Studies on ionic transport properties of a new Ag+ ion conducting composite electrolyte system (1−x)[0·75 AgI: 0·25 AgCl]:xSnO2

A new Ag⁺ ion conducting composite electrolyte system (1−x)[0·75 AgI: 0·25 AgCl]:xSnO₂ using a quenched/annealed [0·75 AgI: 0·25 AgCl] as host compound in place of conventional host AgI, has been investigated. The effects of various preparation methods and soaking time are reported. The composition 0·8[0·75 Agl: 0·25 AgCl]:0·2SnO₂ exhibited optimum conductivity (σ = 8·4 × 10⁻⁴S/cm) with conductivity enhancement of ∼ 10¹ from the annealed host at room temperature. Transport property studies such as electrical conductivity (σ) as a function of temperature using impedance spectroscopy technique, ionic transference number (t _ion) using Wagner’s d.c. polarization method and ionic mobility (μ) by transient ionic current technique were carried out on the optimum conducting composition. The mobile ion concentration (n) was calculated from ‘σ’ and ‘μ’ data.     

Growth of strontium oxalate crystals in agar–agar gel

Single crystals of strontium oxalate have been grown by using strontium chloride and oxalic acid in agar–agar gel media at ambient temperature. Different methods for growing crystals were adopted. The optimum conditions were employed in each method by varying concentration of gel and reactants, and gel setting time etc. Transparent prismatic bi-pyramidal platy-shaped and spherulite crystals were obtained in various methods. The grown crystals were characterized with the help of FT–IR studies and monoclinic system of crystals were supported with lattice parameters a = 9·67628 ?, b = 6·7175 ?, c = 8·6812 ?, b\boldsymbol{\beta} = 113·566^°^{\boldsymbol\circ}, and V = 521·84 ?³ calculated from X-ray diffractogram.     

Topological birefringence and combined Rytov-Magnus effect

It is shown that the symmetry properties of the locally isotropic inhomogeneous medium of an optical fiber cause circular and linear topological birefringence. The circular birefringence δn _C in graded-index fibers is ∼(λ/ρ)² (where λ is the wavelength and ρ is the core radius), while the linear birefringence is δn _L ∼(λ/ρ)³. This topological birefringence is characterized not only by the polarization basis (as in crystals for example) but also by the magnitude and sign of the topological charge of the guided vortex. This topological birefringence forms the basis of the instability of the fiber IV vortex and is observed experimentally as the combined Rytov-Magnus effect. Pis’ma Zh. Tekh. Fiz. 25, 41–46 (March 12, 1999)     

Studies on thick films of photoconducting cadmium sulphide

Highly photosensitive films of CdS have been prepared using the thick film technique. The films obtained from the composition containing CdS-100, CdCl₂−10 and CuCl₂−0·05 parts by weight (reacted at 500° C) are found to give the best photosensitivity on firing at 600° C. The ratio of light to dark current ∼10⁸–10⁹ which is considerably higher than what is reported for thin films, single crystals and sintered layers. A strong chemisorption of oxygen is found to be responsible for high photosensitivity. The spectral response for doped CdS film is similar to that obtained for thin films, single crystals and sintered layers and also shows a red shift with increasing Cu concentration. However, the undoped CdS has a broad spectral response at room temperature ranging fromλ=550 to 690 nm; unlike the thin films and single crystals which give a sharp peak atλ=510 to 520 nm. A probable explanation has been suggested for this type of behaviour. NCL Communication No. 2502.     

Superheating of YBa2Cu3O7−x thin-film microbridges

It is found that the hysteresis that develops with decreasing temperature in the current-voltage characteristics of thin-film YBa₂Cu₃O_7−x microbridges is due to superheating of the bridges by the transport current. The heat transport coefficient is determined to be α=5500–7500 V/(cm²·K) and the thermal resistance of the YBa₂Cu₃O_7−x /MgO film-substrate interface is R _if=(1.3–1.8)×10₋₄ (cm²·K)/W. Pis’ma Zh. Tekh. Fiz. 23, 56–62 (June 26, 1997)     

Sealed efficient excilamps excited by a capacitive discharge

The development of sealed XeCl (λ∼308 nm), KrCl (λ∼222 nm), and XeI (λ∼253 nm) excilamps excited by a capacitive rf discharge is reported. It is shown that highly efficient emission of exciplex molecules is achieved under capacitive discharge excitation and the emitter has a simple design. An average emission power of 3W was obtained with a ∼12% efficiency and the lifetime of the sealed excilamps was longer than 1000 h. Pis’ma Zh. Tekh. Fiz. 25, 27–32 (November 12, 1999)     

Influence of acoustic treatment on the photoconductivity of zinc selenide crystals

It is shown that acoustic treatment of piezoelectric zinc selenide crystals by exciting strong natural elastic vibrations can specifically alter their photoelectric and other properties. Irreversible changes in the stressed-strained state of the crystals under this treatment are responsible for characteristic features in the spectral dependences of the permittivity ε′(λ) and the dielectric loss coefficient ε′’(λ). These dependences plotted in the form of ε*(λ) diagrams on the complex plane and also the spectrum of natural elastic vibrations can be used to monitor the treatment process. Pis’ma Zh. Tekh. Fiz. 25, 24–29 (December 26, 1999)     

Hydrogen-Bonded Structure of 2:1 TCNQ Salt of 2-Methyl-5-Phenyl-7,9-Dichloro-1,6-Diazaphenalene

The crystal structure of 2:1 TCNQ salt of 2-methyl-5-phenyl-7,9-dichloro-1,6-diazaphenalene (1) was investigated for the construction of new hydrogen-bonded charge-transfer complexes. This salt was composed of neutral 1, protonated 1 (1·H ⁺) and ionic TCNQ (TCNQ^{· −}), and constructed a segregated structure with uniform π-stackings. The N–H···N≡C hydrogenbonding between 1/1·H⁺ and TCNQ^{· −} formed the D-A-D triad, and connected the columnar structures.     

Dielectric, elastic, anelastic and conductivity behaviour of ferroelectromagnetic composites, Ni0·5Zn0·5Fe1·95O4?δ + Ba0·8Pb0·2TiO3

Ferroelectromagnetic composites with compositions, X Ni_0·5Zn_0·5Fe_1·95O_4−δ + (1 − X) Ba_0·8Pb_0·2TiO₃, in which X varies as 0, 0·005, 0·010, 0·015, 0·020, 0·040, 0·060, 0·080 and 1 in mole %, were prepared by conventional ceramic double sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric constant, ɛ′, dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in the temperature range 30–350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data were discussed in the light of phase transitions.     

Thermal Conductivity of Standard Sands II. Saturated Conditions

A non-stationary thermal probe technique was used to measure the thermal conductivity of three saturated standard sands (Ottawa sand C-109, Ottawa sand C-190, and Toyoura sand) in a range of soil porosities (n) from 0.32 to 0.42, and temperatures (T) from 25 °C to 70 °C. The sand thermal conductivities at full saturation (λ _sat) increased with decreasing n (increasing compaction, 1 − n). In addition, a declining λ _sat(T) _n=const trend was observed. The peak λ _sat values and highest decreasing rate of λ _sat with T were observed at the heaviest compaction and lowest tested T. This trend gradually diminished with increasing T and expanding volume of water (larger n) due to the markedly lower ability of water to conduct heat than quartz. A series-parallel model, containing three parallel paths of heat flow (through continuous solids, continuous fluid, and solids plus fluid in series), was successfully applied to predicted λ _dry and λ _sat data. The model by de Vries, with new fitted grain shape values, also closely followed measured λ _sat data. The corresponding square root of the relative mean squared errors varied from 2.9 % to 3.4 % for C-109, from 1.9 % to 3.0 % for C-190, and from 2.3 % to 2.4 % for Toyoura sand. The use of a weighted geometric mean model also provided good λ _sat estimates with errors ranging from 3.1 % to 3.5 % for C-109 and C-190 and 8.3 % for Toyoura sand. This paper also discusses a successful attempt to model λ _sat as a product of thermal conductivity of the solid fraction (quartz plus other minerals) and a thermal conductance factor of water.     

Effect of paramagnetic manganese ions doping on frequency and high temperature dependence dielectric response of layered Na<Subscript>1·9</Subscript>Li<Subscript>0·1</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript> ceramics

The manganese doped layered ceramic samples (Na_1·9Li_0·1)Ti₃O₇ : XMn(0·01 ≤ X ≤ 0·1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance (EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn³⁺ at Ti⁴⁺ sites, whereas for higher percentage of doping Mn²⁺ ions occupy the two different interlayer sodium/lithium sites. In both cases, the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice. The manganese doped derivatives of layered Na_1·9Li_0·1Ti₃O₇ (SLT) ceramics have been investigated through frequency dependence dielectric spectroscopy in this work. The results indicate that the dielectric losses in these ceramics are the collective contribution of electric conduction, dipole orientation and space charge polarization. Smeared peaks in temperature dependence of permittivity plots suggest diffuse nature of high temperature ferroelectric phase transition. The light manganese doping in SLT enhances the dielectric constant. However, manganese doping decreases dielectric loss due to inhibition of domain wall motion, enhances electron-hopping conduction, and impedes the interlayer ionic conduction as well. Manganese doping also gives rise to contraction of interlayer space.     

Experimental study on the vertical motion of grains in a vibrated U-tube

We investigate experimentally the behavior of the exponential growth rate of a column of grains, in a partially filled vertically shaken U-tube. For the set of frequencies used we identify three qualitatively different behaviors for the exponential growth rate γ as a function of the dimensionless acceleration Γ: (1) an interval of zero growth for low Γ with a smooth change to nonzero growth, analogous to a continuous phase transition; (2) a sigmoidal region for γ at intermediate values of the dimensionless acceleration Γ; and (3) an abrupt change from high values of γ to zero growth at high values of Γ, similar to a first order phase transition. We obtain that our experimental data is well described by a Boltzmann Sigmoidal funtion, for the change of the exponential growth rate with the dimensionless acceleration of the vertical vibrations.     

Structural investigation of bismuth borate glass ceramics containing gadolinium ions by X-ray diffraction and FTIR spectroscopy

X-ray diffraction and FTIR spectroscopy measurements have been employed to investigate the xGd₂O₃ · (100 − x)[2Bi₂O₃ · B₂O₃] glass ceramics system, with 0  ≤ x ≤ 20 mol%. Heat treatment of glass samples at 625 °C for 24 h led to the formation of two crystalline phases. One crystalline phase is for the sample without gadolinium ions which belongs to the cubic system and another one is for the sample containing 20 mol% Gd₂O₃ which is orthorhombic with two unit cell parameters very close to each other. Between x = 0 mol% and x = 20 mol% there is a mixture of these crystalline phases. FTIR spectroscopy data suggest that the gadolinium ions play the network modifier role in the studied glasses. These data show that the glass structure consists of the BiO₃, BiO₆, BO₃, and BO₄ structural units, and the conversion among these units mainly depends on the Gd₂O₃ content.