Current noise in (111) n-channel Si-MOSFET's at T = 4.2 K

We have investigated the drain current-drain voltage characteristics and the spectral noise intensity of the drain current of (111) n-channel MOSFET's at T = 4.2 K. At T = 4.2 K the drain current-drain voltage characteristics showed a hysteresis which was not observed at T =77 K and at room temperature. A qualitative explanation of this hysteresis is given in terms of electron transfer from high mobility valleys to low mobility valleys due to hot electrons. In the spectra of the current noise three contributions could be distinguished: 1/ƒ-noise, white noise and generation-recombination noise. The 1/ƒ-noise is interpreted as number fluctuations noise. The effective trap density was found to be 2.3 × 10²² m^-3. At low drain voltages the white noise can be interpreted as diffusion noise. At higher drain voltages extra noise is observed over and above diffusion noise. This extra noise may be inter-valley noise. The generation-recombination noise was very sensitive to the gate voltage. A tentative explanation can be given if it is assumed that the traps which cause this noise have a non-uniform energy distribution.     

Effect of series resistance on the performance of silicon Schottky diode in the presence of tin oxide layer

The current–voltage (I–V) characteristics of Al/SnO₂/p-Si (MIS) Schottky diodes prepared by means of spray deposition method have been measured at 80, 295 and 350 K. In order to interpret the experimentally observed non-ideal Al/SnO₂/p-Si Schottky diode parameters such as, the series resistance R_s, barrier height Φ_B and ideality factor n, a novel calculation method has been reported by taking into account the applied voltage drop across interfacial oxide layer V_i and ideality factor n in the current transport mechanism. The values obtained for V_i were subtracted from the applied voltage values V and then the values of R_s were recalculated. The parameters obtained by accounting for the voltage drop V_i have been compared with those obtained without considering the above voltage drop. It is shown that the values of R_s estimated from Cheung’s method were strongly temperature-dependent and decreased with increasing temperature. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I–V characteristics. The interface state density N_ss of the diodes has an exponential growth with bias towards the top of the valance band for each temperature; for example, from 2.37 × 10¹³ eV⁻¹ cm⁻² in 0.70−E_v eV to 7.47 × 10¹³ eV⁻¹ cm⁻² in 0.62−E_v eV for 295 K. The mean N_ss estimated from the I–V measurements decreased with increasing the temperature from 8.29 × 10¹³ to 2.20 × 10¹³ eV⁻¹ cm⁻².     

The high-resolution spectrum of the ν1 (A1) band of 12CD3F

The spectrum of the ν₁ (A₁) band of ¹²CD₃F has been recorded with a resolution of 0.010 cm⁻¹ and deconvolved to 0.005 cm⁻¹. Over 1050 transitions have been assigned with K ≤ 16 and J ≤ 42. The spectrum is highly perturbed, exhibiting avoided crossings in most of the observed sub-bands. The origin of most of the local and global resonances has been determined and the coupling constants estimated. Due to the complexity of the spectrum resulting from the 24 potential interacting states in the region, the assigned frequencies were fitted in a restricted manner (K ≤ 3, J ≤ 15), to obtain the following effective constants for the band: ν₀ = 2090.8118(20) cm⁻¹, α^A = 1.19743 × 10⁻² cm⁻¹, and α^B = −1.8489 × 10⁻³ cm⁻¹. From an unrestricted least-squares analysis, fixing the above parameters the β's (D_v^x = D₀^x − β_v^x) were calculated to be β^J = 1.7776 × 10⁻⁷ cm⁻¹, β^JK = 8.3406 × 10⁻⁷ cm⁻¹, and β^K = −6.3829 × 10⁻⁷ cm⁻¹. These constants serve as good starting parameters for the global analysis necessary to fully analyze the 5-μm region of the ¹²CD₃F spectrum.     

Superconducting transitions from states with low normal conductivity in ceramic SrTi0.97Zr0.03O3

Broad superconducting transitions or commencements of transitions have been observed by electrical resistance and magnetic inductance measurements on polycrystalline speciments of SrTi_0.97Zr_0.03O₃ with resistivities above T_c between 3.7 × 10⁻³ Ωm and 1.7 × 10⁻¹ Ωm. Room temperature Hall measurements have been made on some samples and the current dependence of the resistivity and has been determined for one other sample.     

Ion exchange properties of lithium iron oxides

The αLiFeO₂ rock salt material has been prepared from lithium carbonate and ferric oxide. It was found that the lithium can be exchanged for silver in silver nitrate and, initially, a substituted rock salt is produced, Ag_xLi_1−xFeO₂. The ultimate phase in the ion-exchange process is αAgFeO₂. The diffusion coefficient of Ag in Ag_xLiFeO₂, determined by transient electrochemical measurements, was found to be around 5 × 10⁻⁸ cm⁻² s⁻¹.     

Simultaneous Analysis of Rovibrational and Rotational Spectra of thev5= 1 andv8= 1 Vibrational Levels of Propyne

The microwave and submillimeter wave spectra of propyne between 17 and 358 GHz were measured and the rotational transitions in thev₈= 1 excited vibrational state of the CH₃rocking vibration were assigned. About 1050 wavenumbers of the ν₈vibration–rotation fundamental band and about 600 wavenumbers of the ν₅fundamental band of the[formula]stretching vibration were assigned from the infrared spectrum between 910 and 1130 cm⁻¹which was used previously (G. Graneret al., J. Mol. Spectrosc.161,80–101 (1993)) in the analysis of the combinationv₉=v₁₀= 1 and thev₁₀= 3 overtone levels (ν₉being the[formula]bending and ν₁₀the[formula]bending vibrations). The rovibrational and rotational data corresponding to the two fundamental levels were analyzed simultaneously in least-squares fits using a model which treats together all the vibrational levels in the region around 1000 cm⁻¹with their strong anharmonic and vibration–rotation resonances. The refined parameters reproduce the infrared and submillimeter wave data of thev₅= 1 level with standard deviations of 0.32 × 10⁻³cm⁻¹and 59 kHz, respectively, while for thev₈= 1 level the standard deviations were 0.41 × 10⁻³cm and 290 kHz. The refined parameters of the combination and overtone levels provide reliable predictions for future submillimeter wave studies.     

Absorption of 12CH3D at 6–10 μm: Triad ν3, ν5, ν6

The absorption of ¹²CH₃D at 6–10 μm was recorded under vacuum with a resolution of 0.0054 cm⁻¹. For the first time the ν₅ band was assigned extensively, allowing the analysis of ν₃, ν₅, and ν₆ together within a “triad model,” including a rigorous treatment of all the Coriolis couplings involved. The assignments in the spectral range were anlarged from the original 1000 to the present 3500. The newly assigned lines essentially concerned the ν₅ band and a great number of perturbation-allowed transitions (about 30% of all observations). Ground state energy parameters were refined from 2641 combination differences involving J up to 19 and |ΔK| up to 6; the standard deviation of the fit was 0.0003 cm⁻¹. A set of 35 triad upper state energy parameters was derived, reproducing all observations with a standard deviation of 0.0076 cm⁻¹. The three dipole moment derivatives involved in the intensity calculations were estimated theoretically, by taking advantage of the recent accurate determination of the band strengths S₃ and S₄ of ¹²CH₄. Finally, about 6000 triad transitions predicted with linestrengths at least equal to 4 × 10⁻²⁵ cm·molecule⁻¹ were tabulated with assignments, wavenumbers, linestrengths, and lower and upper energy levels.     

Conductivity of lithium gallium silicates

Lithium gallium silicates, Li_1−xGa_1−xSi_2+xO₆: 0.03 < x < 0.37, with a beta-spodumene structure, have a low Li⁺ ion conductivity, ca. 10⁻⁹ ω⁻¹ cm⁻¹ at 400 K rising to ca. 10⁻³ ω⁻¹ cm⁻¹ by 1000 K, that changes little with composition. The phase, LiGaSiO₄, with an alpha-eucryptite structure, exhibits mainly electronic conductivity, but at a low level, ca. 10⁻⁸ ω⁻¹ cm⁻¹ at 600 K, rising to ca. 10⁻⁵ ω⁻¹ cm⁻¹ at 1000 K.     

Diode laser measurements of line strengths and widths in the 4.5-μm bands of N2O

We have made line-strength measurements in the N₂O ν₃-fundamental region using a tunable diode-laser spectrometer. From these measurements and the Herman-Wallis factor determined by Boissy et al., we find the ν₃-fundamental band strength to be S_v = 1203 ± 22 cm⁻² atm⁻¹ at 297 K. Line-broadening parameters for two ν₃-fundamental lines were determined using nitrogen (N₂) as the broadening gas. Measured strengths and N₂ line-broadening parameters for several (ν¹₂ + ν₃ − ν¹₂) hot-band lines are also presented.     

Determination of the kinetic parameters of the isomerization reaction of ethyl isocyanide using HeI photoelectron spectroscopy

The use of HeI photoelectron spectroscopy (PES) for the kinetic study of chemical reactions was introduced previously by us. As another example of the determination of the kinetic parameters of a chemical reaction using the PES method, the isomerization reaction of ethyl isocyanide CH₃CH₂NC → CH₃CH₂CN is investigated. It is found to be first order and the kinetic equations at 193.6, 200.0 and 210.3°C can be expressed as ln R_{466.6 K} = − (7.600 ± 0.026) × 10⁻⁵t − 0.4350; ln R_{473.0 K} = − (1.329 ± 0.032) × 10⁻⁴ − 0.4375 and ln R_{483.3 K} = − (3.170 ± 0.052) × 10⁻⁴ − 0.4354, respectively. The rate constants of the reactions at 193.6, 200.0 reactions at 193.6, 200.0 and 210.3°C are respectively (7.600 ± 0.026) × 10⁻⁵, (1.329 ± 0.032) × 10⁻⁴ and (3.170 ± 0.052) × 10⁻⁴ s⁻¹. The calculated activation energy (E_a) of this isomerization reaction is 38.36 ± 0.32 kcal mol⁻¹. These results are also in excellent agreement with the results obtained by a traditional method. This means that PES is a valuable method for determining the kinetic parameters of chemical reactions. The value of the intercept in the kinetic equations is related to the logarithm of the ratio of the photoionization cross-section of the bands used. This also means that the relative photoionization cross-sections of the bands used for the sample studied are obtained in the kinetic study of a chemical reaction using the PES method.     

Tunable diode-laser spectra of the very weak ν10 absorption band of C2H3D

The C₂H₃D spectra from 730 to 780 cm⁻¹ have been investigated with a tunable diode laser spectrometer at Doppler-limited resolution and a wavenumber accuracy of better than 10⁻³ cm⁻¹. This resolution, combined with a long absorption path, has allowed the identification of K_a series lines belonging to the ν₁₀ level. A five-level combined analysis was performed, including previous data available for the energy states involved in the region around 1000 cm⁻¹.     

Fourier transform spectroscopy of methanol: Taylor coefficients for the region between 8 and 80 cm−1

In our systematic investigation of the FTS of CH₃OH we have assigned about 3000 lines connecting levels of the vibrational ground state with frequencies between 8 and 80 cm⁻¹. Here we present the parameters for Taylor expansions of the energy levels in J(J + 1) which allow us to reconstruct the spectral lines with a precision usually of the order of 10⁻⁴cm⁻¹.     

Double magnetic entropy change peaks and high refrigerant capacity in Gd1-xHoxNi compounds in the melt-spun form

Gd_1-xHo_xNi melt-spun ribbons were fabricated by a single-roller melt spinning method. All the compounds crystallize in an orthorhombic CrB-type structure. The Curie temperature (T_C) was tuned between 46 and 99 K by varying the concentration of Gd and Ho. A spin reorientation (SRO) transition is observed around 13 K. Different from T_C, the SRO transition temperature is almost invariable for all compounds. Two peaks of magnetic entropy change (ΔS_M) were found. One at the higher temperature range was originated from the paramagnet-ferromagnet phase transition and the other at the lower temperature range was caused by the SRO transition. The maximum of ΔS_M around T_C is almost same. The other maximum of ΔS_M around SRO transition, however, had significantly positive relationship with x. It reached a maximum about 8.2 J kg⁻¹ K⁻¹ for x = 0.8. Thus double large ΔS_M peaks were obtained in Gd_1-xHo_xNi melt-spun ribbons with the high Ho concentration. And the refrigerant capacity power reached a maximum of 622 J kg⁻¹ for x = 0.6. Gd_1-xHo_xNi ribbons could be good candidate for magnetic refrigerant working in the low temperature especially near the liquid nitrogen temperature range.     

Ammonia: Experimental absolute linestrengths and self-broadening parameters in the 1800- to 2100-cm−1 range

Absolute linestrengths were obtained for over 750 vibration-rotation transitions of ammonia in the 1800- to 2100-cm⁻¹ range, at various temperatures (293-170 K), using a high-resolution (0.0054 cm⁻¹) Fourier transform spectrometer. The precision of the measurements is about 10%. Lower state energy levels of the transitions were determined and used to extend the assignments in the 2ν₂(s → a) and ν₄ bands on the basis of the predictions by S. Urban, V. Spirko, D. Papousek, R. S. McDowell, A. F. Krupnov, J. Curtis, and K. Narahari Rao (J. Mol. Spectrosc. 79, 455–495 (1980)). In addition, self-broadening parameters (including temperature dependence) were determined for more than 350 lines.     

On the precision of calculations of initial state radiation in the LEP Z line-shape fits

Calculation of initial state radiation (ISR) in the fitting program MIZA and in the Standard Model program BHM is improved within the analysis of the Z line-shape measurements at LEP. The uncertainty on the determination of the Z line-shape parameters coming from the precision of ISR calculations is 2×10⁻⁴ on σ₀ and 0.1 MeV on m_Z and Γ_Z.     

Quasi-solid state polymer electrolytes for dye-sensitized solar cells: Effect of the electrolyte components variation on the triiodide ion diffusion properties and charge-transfer resistance at platinum electrode

Quasi-solid state polymer electrolytes have been prepared from poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) as gelator for 1-ethyl-3-methylimidazolium based ionic liquids (with anions like trifluoromethanesulfonate [EMIM][TfO], bis(trifluoromethanesulfonyl)imide [EMIM][Tf₂N]) and polyacrylonitrile (PAN) for gelation of 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA] as well as I⁻/I₃⁻ as the redox couple. All electrolytes exhibit high ionic conductivity in the range of 10^− 3 S/cm. The effect of gelation, redox couple concentration, I⁻/I₃⁻ ratio, choice of cations and additives on the triiodide diffusion and charge-transfer resistance of the platinum/electrolyte interface (R_ct) were studied. The apparent diffusion coefficient of triiodide ion (D(I₃⁻)) at various iodide/triiodide ratios in liquid and gelified electrolytes has been calculated from measurements of the diffusion limited current (I_lim) in electrochemical cell resembling the set-up of a dye-sensitized solar cell. The charge-transfer resistance of the platinum/electrolyte interface as well as the capacitance of the electrical double layer (C_dl) have been calculated from impedance measurements. Electrolytes with reduced content of polymer (2.5 wt.%) were doped with Al₂O₃ particles of different sizes (50 nm, 300 nm, 1 μm). The dispersion of the particles proceeds by speedy stirring of the hot electrolyte and the addition of PAN provides a homogeneous suspension. The addition of Al₂O₃ particles causes a slight increase of the triiodide diffusion constants. Furthermore the suggested enhancement of the charge transfer rate shows a dependence on the size of the particles.     

Low noise field-effect transistor for integrated strain sensing in microelectromechanical systems at 77 K

We have fabricated a strain-sensing field-effect transistor (FET) from a GaAs/AlGaAs heterostructure containint a near surface two-dimensional electron gas. At 77 K the FET shows a typical transconductance of 30 μS and small signal drain-source resistance of 30 MO. The charge noise has a flat spectrum at high frequencies with magnitude 0.7eHz^−1/2and a 1/fnoise corner of approximately 1 kHz. The strain response, due to the piezoelectric effect, shows a noise limited strain sensitivity <4×10⁻⁹Hz^−1/2. Integrated strain sensing FETs offer advantages in small GaAs/AlGaAs microelectromechanical systems.     

Reactions of hydrazine with the amidogen radical and atomic hydrogen

The rate coefficient k₁ for NH₂ + N₂H₄ was measured to be (5.4 ± 0.4) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ at 296 K. NH₂ was generated by pulsed laser photolysis of NH₃ at 193 nm, and monitored as a function of time by pulsed laser-induced fluorescence excited at 570.3 nm under pseudo-first order conditions in the presence of excess N₂H₄ in an Ar bath gas. This reaction was also investigated computationally, with geometries and scaled frequencies obtained with M06-2X/6-311+G(2df,2p) theory, and single-point energies from CCSD(T)-F12b/cc-pVTZ-F12 theory, plus a term to correct approximately for electron correlation through CCSDT(Q). Three connected transition states are involved and rate constants were obtained via Multistructural Improved Canonical Variational Transition State Theory with Small Curvature Tunneling. Combination of experiment and theory leads to a recommended rate coefficient for hydrogen abstraction of k₁ = 6.3 × 10⁻²³ T^3.44 exp(+289 K/T) cm³ molecule⁻¹ s⁻¹. The minor channel for H + N₂H₄ forming NH₂ + NH₃ was characterized computationally as well, to yield 5.0 × 10⁻¹⁹ T^2.07 exp(-4032 K/T) cm³ molecule⁻¹ s⁻¹. These results are compared to several discordant prior estimates, and are employed in an overall mechanism to compare with measurements of half-lives of hydrazine in a shock tube.