共查询到20条相似文献,搜索用时 680 毫秒
1.
C. Vadla V. Horvatic K. Niemax 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):23-25
The “forbidden” Pb 6p2
3P
0
↦6
p
2
3P1 line at 1278.9 nm is measured by diode laser absorption in a resistively heated hot-pipe filled with a lead vapour and argon
as buffer gas. The measurements performed at a temperature of 1170 K and a lead number density of 2.4×10
15
cm-3 yield the oscillator strength f
F
= (4.5±1.1)×10
-7
which corresponds to a radiative transition probability A
F
= (6.1±1.5) s-1. Within the error bars, the result is in agreement with theoretical data published by different authors.
Received 11 October 2000 and Received in final form 5 January 2001 相似文献
2.
B. Gorshunov P. Haas M. Dressel V.I. Torgashev V.B. Shirokov A.V. Prokofiev W. Assmus 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):427-435
The infrared spectra of the one-dimensional antiferromagnet LiCuVO4 are measured in the frequency range from 10 cm-1 to 10 000 cm-1 and at temperatures from 2 K to 300 K, for the electric field vector E of the radiation polarized either along the a- or along the b-crystallographic directions. For each polarization six infrared active phonon modes are observed in accordance with factor
group analysis of the crystal structure of LiCuVO4. The theoretical group analysis of the possible spinel low-symmetry phases is performed within the framework of Landau's
theory of phase transitions. The parameters of several phonon lines show noticeable anomalies around 150 K where the magnetic
correlations appear in the copper chains, which may indicate a finite interaction between the phonon and the magnon subsystems
in LiCuVO4.
Received 19 February 2001 and Received in final form 26 June 2001 相似文献
3.
D. Jacquemart J.-Y. Mandin V. Dana N. Picqué G. Guelachvili 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):55-69
To deduce accurate infrared molecular line parameters (positions at zero pressure, pressure-shifting and pressure-broadening
coefficients, collisional narrowing coefficients, and intensities) from rovibrational spectra, an automatic method based upon
a multispectrum fitting procedure has been set up, able to treat simultaneously several laboratory Fourier transform spectra.
A validation of this method, using absorption spectra of the 3-0 vibrational band of CO around 6 350 cm-1, already used to measure line intensities and self-broadening coefficients, is presented, and the advantages of the method
are pointed out. The self-collisional narrowing of CO was observed and determined for the first time in Fourier transform
spectra: β
= 0.028±0.004 cm-1 atm-1 at about 296 K.
Received 21 September 2000 and Received in final form 15 January 2001 相似文献
4.
M. Putti E. Galleani d'Agliano D. Marrè F. Napoli M. Tassisto P. Manfrinetti A. Palenzona C. Rizzuto S. Massidda 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):439-443
We report measurements of the resistivity, ρ, and the Seebeck coefficient, S
, of a MgB2 sintered sample, and compare S with theoretical calculations based on precise electronic structure calculations. ρ is fitted well by a generalized Bloch-Grüneisen equation with a Debye temperature Θ
R
of 1050 K. S is given by the sum of a diffusive and a phonon drag term and the behavior in the temperature region T
c
<
T
< 0.1Θ
R
follows the relationship AT+BT3. The phonon drag term indicates a strong electron-phonon interaction. The diffusive term, compared with calculations, suggests
that σ bands give the main contribution to the Seebeck effect.
Received 16 November 2001 and Received in final form 21 December 2001 相似文献
5.
X. Hao J. Ma D. Zhang X. Xu Y. Yang H. Ma S. Ai 《Applied Physics A: Materials Science & Processing》2002,75(3):397-399
Transparent conducting antimony-doped tin oxide (SnO2:Sb) films were deposited on organic substrates by r.f. magnetron-sputtering. Polycrystalline films with a resistivity of
≈ 6.5×10-3 Ω cm, a carrier concentration of≈ 1.2×1020 cm-3 and a Hall mobility of ≈ 9.7 cm2 v-1 s-1 were obtained. The average transmittance of these films reached 85% in the wavelength range of the visible spectrum.
Received: 20 April 2001 / Accepted: 23 July 2001 / Published online: 17 October 2001 相似文献
6.
Ch. Lisdat O. Dulieu H. Knöckel E. Tiemann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):319-328
We present a new determination of the potential curves and interactions of the coupled electronic states A
1
Σ
+
u
and b
3
Π
u
of the potassium dimer, based on new laser spectroscopy measurements within a molecular beam, combined with data available
in the literature. We used a new global deperturbation approach, involving the Fourier Grid Hamiltonian method for energy
level calculation. A standard deviation of 1.2 is obtained corresponding to a variance of 7.5×10
-3
cm-1, representing a significant improvement compared to the standard deviation of 4 yielded by the traditional local deperturbation
approach.
Received 12 June 2001 and Received in final form 3 September 2001 相似文献
7.
R. Ramakumar K. Yamaji 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):71-75
A simple model is developed to understand superconductivity in α
′
-TTF[Pd(dmit)2]2. We include electron-intra molecular and intermolecular phonon interactions as the mechanism of superconductivity. Intramolecular vibrations included are the eight symmetric Ag modes of the Pd(dmit)2 molecule. Intermolecular vibrations included are the longitudinal acoustic and transverse acoustic (LA and TA) modes of the Pd(dmit)2 column. All the electron-phonon coupling constants are calculated from first principles. We find that largest el-intramolecular vibration coupling is to the Ag mode with the highest frequency (1449 cm-1). The el-intermolecular coupling to the LA mode is found to be larger than the total el-intramolecular couplings. We also find el-(TA)phonon coupling to be at least an order of magnitude smaller than el-(LA)phonon coupling.
Estimate of superconducting transition temperature is comparable to experimental result. We also provide a detailed discussion,
employing the results of recent numerical calculations on two-chain Hubbard model and the specific material parameters, on
the relative importance of el-ph and Coulomb-origin mechanisms of superconductivity in α
′
-TTF[Pd(dmit)2]2 and TTF[Ni(dmit)
2
]
2
.
Received 29 March 2001 and Received in final form 7 August 2001 相似文献
8.
A. Boschetti D. Bassi E. Iacob S. Iannotta L. Ricci M. Scotoni 《Applied physics. B, Lasers and optics》2002,74(3):273-278
A compact multi-component trace-gas detector based on the resonant photoacoustic technique and a NIR external cavity diode
laser has been developed. It has been characterized using a mixture of ethylene and methane diluted in ambient air. A spectroscopic
investigation of combination bands and overtones between 5900 and 6250 cm-1, obtained with an IR pulsed laser photoacoustic spectrometer, allowed us to find a wavelength region where the 2ν3 overtone of CH4 and the ν5+ν9 combination band of C2H4 show uncongested rotational lines. Using a single-mode scan of the diode laser in this region, around 6150 cm-1, the sensitivity for the simultaneous detection of ethylene and methane is 8 ppm/mW and 40 ppm/mW respectively. Factors affecting
the sensitivity and selectivity of the detection system and possible improvements suitable to reach the sub-ppm detection
limit are discussed.
Received: 1 August 2001 / Revised version: 28 November 2001 / Published online: 7 February 2002
An erratum to this article is available at . 相似文献
9.
V. P.S. Awana A. Vajpayee M. Mudgel V. Ganesan A. M. Awasthi G. L. Bhalla H. Kishan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(3):281-294
We report synthesis, structure/micro-structure, resistivity under magnetic
field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity
κ(T), and magnetization of ambient pressure argon annealed
polycrystalline bulk samples of MgB2, processed under identical
conditions. The compound crystallizes in hexagonal structure with space
group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs
showing various types of defect features along with the presence of 3–4 nm
thick amorphous layers forming the grain boundaries of otherwise crystalline
MgB2. Raman spectra of the compound at room temperature exhibited
characteristic phonon peak at 600 cm-1. Superconductivity is observed
at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power
S(T), and thermal conductivity κ(T) measurements. The power law fitting
of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is
found consistent with the theoretical fitting of S(T), exhibiting Θ
D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal
conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was
missing in some earlier reports. Critical current density (Jc) of up to
105 A/cm2 in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K
is seen from magnetization measurements. The irreversibility field, defined
as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe
at 4, 10 and 20 K respectively. The superconducting performance parameters
viz. irreversibility field (Hirr) and critical current density
Jc(H) of the studied MgB2 are improved profoundly with addition of
nano-SiC and nano-diamond. The physical property parameters measured for
polycrystalline MgB2 are compared with earlier reports and a
consolidated insight of various physical properties is presented. 相似文献
10.
V.L. Kasyutich C.E. Canosa-Mas C. Pfrang S. Vaughan R.P. Wayne 《Applied physics. B, Lasers and optics》2002,75(6-7):755-761
We present an application of continuous-wave (cw) cavity-enhanced absorption spectroscopy (CEAS) with off-axis alignment geometry
of the cavity and with time integration of the cavity output intensity for detection of narrow-band and broadband absorbers
using single-mode red diode lasers at λ=687.1 nm and λ=662 nm, respectively. Off-axis cw CEAS was applied to kinetic studies
of the nitrate radical using a broadband absorption line at λ=662 nm. A rate constant for the reaction between the nitrate
radical and E-but-2-eneof (3.78±0.17)×10-13 cm3 molecule-1 s-1 was measured using a discharge-flow system. A nitrate-radical noise-equivalent (1σ≡ root-mean-square variation of the signal)
detection sensitivity of 5.5×109 molecule cm-3 was achieved in a flow tube with a diameter of 4 cm and for a mirror reflectivity of ∼99.9% and a lock-in amplifier time
constant of 3 s. In this case, a noise-equivalent fractional absorption per one optical pass of 1.6×10-6 was demonstrated at a detection bandwidth of 1 Hz. A wavelength-modulation technique (modulation frequency of 10 kHz) in
conjunction with off-axis cw CEAS has also been used for recording 1f- and 2f-harmonic spectra of the RR(15) absorption of the b1Σg
+-X3Σg
- (1,0) band of molecular oxygen at =14553.947 cm-1. Noise-equivalent fractional absorptions per one optical pass of 1.35×10-5, 6.9×10-7 and 1.9×10-6 were obtained for direct detection of the time-integrated cavity output intensity, 1f- and 2f-harmonic detection, respectively,
with a mirror reflectivity of ∼99.8%, a cavity length of 0.22 m and a detection bandwidth of 1 Hz.
Received: 24 June 2002 / Revised version: 12 August 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +44-1865/275410, E-mail: vlk@physchem.ox.ac.uk 相似文献
11.
Thep-Si/HF-electrolyte interface was characterized by capacitance–voltage (C–V) and current–voltage (I–V) studies. At low frequency, the measured capacitance exhibits two maxima: one in the weak accumulation regime (around 0.8 V
[SCE]) and the other in the strong accumulation regime (around 2.6 V [SCE]), both of which disappear at high frequency. The
disappearance of the two capacitance maxima is attributed to the slow response of interface traps to high frequencies. The
flat-band potential, VFB, is found to be frequency dependent. The surface state densities corresponding to the two capacitance maxima are estimated
to be 3.2×1011 cm-2 and 2.4×1011 cm-2, respectively. The in situ I–V characteristics distinguish pore formation, transition and electropolishing regions. Porous Si synthesized at 50 mA cm-2 gives a broad photoluminescence peak around 2.04 eV at 300 K.
Received: 4 September 2000 / Accepted: 9 February 2001 / Published online: 26 April 2001 相似文献
12.
Ch. Kegler N. Büttgen H.-A. Krug von Nidda A. Krimmel L. Svistov B.I. Kochelaev A. Loidl A. Prokofiev W. Aßmus 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):321-326
EPR and 7Li NMR measurements were performed in the distorted inverse spinel V(LiCu)O4 down to 1.5 K. Anisotropy effects on magnetic resonance spectra due to the Jahn-Teller distortion of the oxygen octahedra
surrounding the copper ions are discussed. The estimation of the spin-spin interactions deduced from the EPR-relaxation rate
Δ
H reveals a situation comparable to the prototypical one-dimensional S
= 1/2 Heisenberg antiferromagnet CuGeO3. Approaching three-dimensional antiferromagnetic order ( T
N
≈ 2 K) from above, both magnetic relaxation rates, Δ
H
EPR
and
7
(1/
T
1
), respectively, exhibit nearly the same critical divergence reminding to the onset of three-dimensional order in two-dimensional
layered systems.
Received 22 January 2001 and Received in final form 6 May 2001 相似文献
13.
J. Luque J.B. Jeffries G.P. Smith D.R. Crosley 《Applied physics. B, Lasers and optics》2001,73(7):731-738
The combination of two-dimensional, planar laser-induced fluorescence (PLIF) and cavity ring-down (CRD) absorption spectroscopy
is applied to map quantitatively the spatial distributions of CH2O and CH in a methane/air flame at 25 Torr. Both species are detected in the same spectral region using the overlapping CH2O A 1
A
2
-X
1
A
1
41
0 and CH B-X(1,0 )bands. The combination of diagnostic techniques exploits the spatial resolution of LIF and the quantitative
CRD absorption measure of column density. The spatially resolved PLIF provides the distribution of absorbers and line-of-sight
CRD absorption the absolute number density needed for quantitative concentration images. The peak CH2O concentration is (3.5±1.4 )×1014 cm-3, or 1450±550 ppm at 1000 K. The lack of precise absorption cross-section data produces these large error limits. Although
a flame model predicts lower amounts, these large uncertainties limit this measurement’susefulness as a test of the flame
chemistry.
Received: 24 April 2001 / Revised version: 10 July 2001 / Published online: 10 October 2001 相似文献
14.
A. Urbina C. Díaz-Paniagua A.F. Braña F. Batallán 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):463-468
We present measurements of the diagonal Rxx and off-diagonal Rxy magnetoresistance under quantum Hall conditions on several high electron mobility transistors (HEMT) based on InxGa1-xAs quantum wells. From the magnetoresistance tensor we obtain the longitudinal conductivity σ
xx
. We study the transport mechanisms near the σ
xx
minima at temperatures ranging between 2 K and 35 K; activated transport is the dominant mechanism for temperatures above
7 K while variable range hopping conductivity is significant for lower temperatures. We show that electron-electron correlations
should be taken into account to explain the conductivity vs temperature behaviour below 5 K. Finally, we study the behaviour of the localization length as a function of Landau level
filling and obtain a critical exponent γ = 3.45±0.15.
Received 6 June 2001 and Received in final form 16 October 2001 相似文献
15.
I. Kirschner R. Laiho A.C. Bódi A.D. Caplin E. Lähderanta G. Zsolt 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):389-399
Using a new starting material of Ba2Cu3O5 and a three step heat treatment, single phase Tl2Ca1Ba2Cu2O8 high- superconducting samples have been prepared, possessing the onset- and critical temperatures K and K. The morphology dependent value of is 17 Oe, 8 Oe and 5 Oe at 77 K in the case of bulk, crushed and powdered materials, respectively. The a.c. susceptibility,
r.f. susceptibility and microwave absorption properties show a significant dependence on the particle size with a sharp change
in the interval between 750 μm and 1200 μm. These experiments provide characteristic parameters for intergrain material (treated
as 3D Josephson network) as mm, Oe and A/cm2 at 77 K. The data are controlled by modulated microwave absorption measurements. The results obtained can be explained well
both by the finite size junction model and cavity mode absorption model. The Josephson network is determined unambiguously
by metallic S-N-S weak links.
Received 10 October 1998 相似文献
16.
M. Celasco R. Eggenhöffner 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):415-419
A dynamical percolative model explaining the universality of 1/
f
γ
noise is reported. Exponents γ ranging from 0 to 2 are obtained under the hypothesis that noise originates from random switching events between two ON-OFF
states in elemental parts (switchers) of a physical system. The usual noise behaviour with γ very close to 1 in an arbitrarily wide frequency range is obtained assuming a statistical distribution of switcher relaxation
time τ proportional to τ
-1
, as in McWhorter's model. The impact of these results with respect to recent self-organised criticality models is discussed.
Received 6 November 2000 and Received in final form 22 May 2001 相似文献
17.
Zirconium oxide layers have been successfully deposited by photo-CVD at low temperatures. ZrO2 growth was observed at temperatures as low as 100 °C. When deposited at 250 °C and above, these films exhibited a polycrystalline
structure with a mixture of different crystal phases. Deposition at 300 °C was found to form moisture-free ZrO2 films with a high refractive index of 2.1, a very low effective density of trapped electrons of ∼8.8×108 cm-2 and an interface trap density of 6.6×109 cm-2 eV-1 being readily obtained.
Received: 17 December 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002 相似文献
18.
H. Hess K.R. Asmis T. Leisner L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):145-149
We present results on the ultrafast dynamics of mass-selected neutral Ag4 clusters using NeNePo (negative ion - neutral - positive ion) femtosecond pump-probe spectroscopy. One-color pump-probe spectra
of the Ag4
-/Ag4/Ag4
+ system measured at 385 nm and an internal cluster temperature of 20 K display a complex beat structure over more than 60
ps. The oscillatory structure is attributed to vibrational wave packet dynamics in an excited “dark" state of neutral Ag4. A dominant 740 fs wave packet period as well as wave packet dephasing and rephasing are observed in the spectra. Fourier
analysis of the spectra yields a group of frequencies centered around 45 cm-1 and an anharmonicity χ
e2νχ
eχ
e of 2.65 cm-1 for the active vibrational mode.
Received 30 November 2000 相似文献
19.
M.P. Lissitski A. Naddeo C. Nappi A. Tagliacozzo V.N. Gubankov R. Monaco M. Russo 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):309-314
Measurements of differential resistance in a superconductor-degenerate semiconductor junction Nb
-
n
+ +
GaAs at T
= 1.6 K show close similarity to those for a conventional superconductor-insulator- normal metal junction, except for the position
of the minimum which is located at 3.6 meV. Using a simple model for the charge screening at the Schottky barrier, we give
an argument why this minimum is by far displaced with respect to the superconducting gap energy ( Δ
g
= 1.5 meV for bulk Nb). We argue that a rebuilding of the density of states takes place at the barrier, due to the imperfect metal
screening in the degenerate semiconductor. Energy states close to the degenerate semiconductor Fermi energy are depleted at
the barrier and are not available for tunneling, up to an energy Eg which adds to the superconducting gap Δ
g
.
Received 11 November 2002 / Received in final form 21 February 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: c.nappi@cib.na.cnr.it 相似文献
20.
《International Journal of Infrared and Millimeter Waves》1997,18(9):1663-1679
The optical constants of crystal quartz in the far infrared (10 – 600 cm−1) are reported at room temperature and at 10 K, for both polarizations parallel and perpendicular to the c-axis, respectively
extraordinary and ordinary ray. These constants are obtained from the analysis of the transmissivity channeled spectra below
300 cm−1, and from the analysis of the reflectivity spectra between 300 – 600 cm−1, measured by using a grating infrared spectrometer. The extrapolated zero frequency refractive indices of quartz obtained
in the present work are: no(0) = 2.106 and ne(0) = 2.153 at 300 K; no(0) = 2.072 and ne(0) = 2.130 at 10 K. 相似文献