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1.
A disclination line populated with point defects that break the translational symmetry forms near a free nematic (N) interface
in a confined geometry. The disclination line is, however, absent in the smectic-A phase (SmA). We use this fact to control
the formation of point defect distributions on a disclination line by directional melting of the SmA phase in a temperature
gradient. A threshold velocity ( v
th) exists below which a defect-free disclination line is formed. The frequency of nucleation of point defects increases steadily
for v > v
th and exhibits a remarkable regularity. We derive an empirical scaling for v
th in terms of the experimental tuning parameters. We propose a simple model that allows to understand the formation of the
point defects.
Received 1 October 2002 / Published online: 15 April 2003
RID="a"
ID="a"Permanent address: Departament de Quımica Fısica, Universitat de Barcelona, Martı i Franquès 1, Barcelona 08028, Spain; e-mail: jignes@qf.ub.es 相似文献
2.
Sh. Makhkamov N. A. Tursunov M. Ashurov R. P. Saidov S. V. Martynchenko 《Technical Physics》1999,44(1):110-112
The method of deep-level transient spectroscopy is used to investigate aspects of the formation of radiation defects in silicon
p
+-n diffusion structures when bombarded by accelerated electrons. It is shown that for base thicknesses of the p
+-n structures in the range 0.2–0.6mm a substantial change in the concentration of the radiation defects formed in this way is
observed, having a maximum at 0.25 mm. Below 0.2 mm and above 0.6 mm the concentration of radiation defects exhibits a weak
dependence on base thickness. The observed effect is explained by variation of the relative concentrations of vacancies and
interstitial silicon atoms in the base during formation of p
+-n pairs.
Zh. Tekh. Fiz. 69, 121–123 (January 1999) 相似文献
3.
Abstract Radiation defects created by γ-irradiation of Co60 and fast neutrons in high purity p-Si (p = 5×103 to 4 × 104 Ω.cm) and n-Si (p = 4 × 102 to 5 × 103 Ω.cm) are investigated by measurements of Hall effect, resistivity and minority carrier lifetime. The oxygen concentration in the crystals is in the range of 5 × 1014 to 5 × 1015 cm?3. It is shown that stable γ-defects at 300 °K are divacancies and complexes of vacancies with donor or acceptor impurities. Divacancies introduced by γ-irradiation are the secondary defects. They become predominant after ‘exhaustion’ of the dopant. When divacancies become the predominant defects the Fermi level occupies its boundary position Ev +0.39 eV in the gap. At low doses (Φ<1016 photons/cm2) vacancy-impurity complexes and at heavy doses (Φ>1017 photons/cm2) divacancies play the main role in the recombination process. In neutron irradiation disordered regions are introduced and the level at Ev +0.35 eV is observed. The Fermi level in both n- and p-Si shifts to the middle of the gap. At the annealing of disordered regions in the interval 200 to 250 °C the level at Ev +0.27 eV appears and Fermi level occupies its boundary position at Ev +0.39 eV. This indicates that divacancies become the predominant defects which can be formed as secondary defects at the destruction of the disordered regions. 相似文献
4.
P. Brovetto V. Maxia M. Salis G. Spano M. Lucco-Borlera D. Mazza 《Il Nuovo Cimento D》1993,15(7):1017-1022
Summary The thermoluminescent emissions of β-eucryptite and β-spodumene have been recordedvs. temperature and wavelength. Arguments are advanced which allow the observed emission to be ascribed to point defects originated
by the exchange of Si+4 and Al+3 ions in (Si, Al)O4 tetrahedra. 相似文献
5.
Quanli Hu Satoru Tanaka Toshiaki Yoneoka Viktors Grismanovs Tetsuji Noda 《辐射效应与固体损伤》2013,168(3):247-253
Abstract The aggregation of F-type defects in AIN has been observed for the first time under He+ ion irradiation by using in-situ luminescence measurement. The concentration of aggregation of F-type defects shows a strong dependence on irradiation temperature (300–773 K) under He+ ion irradiation. The mechanism of growth and annihilation of the aggregation of F-type defects was discussed. 相似文献
6.
P. de Mierry R. Madelon F. Cruège R. Rizk 《Applied Physics A: Materials Science & Processing》1995,61(2):135-140
PhotoLuminescence (PL) measurements are used to investigate the effects of a H2 plasma treatment in heavily doped p-type InP: Zn. Beside the large decrease in free hole concentration in the hydrogenated samples, a new Broad Luminescence Band (BLB) centered at about 1.32 eV appears upon laser irradiation during PL experiments above 50 K, and saturates for large values of the fight intensities. It is inferred that the plasma treatment produces some kind of non-radiative defects which can then rearrange into new BLB centers under illumination provided it is applied above a threshold temperature (50K). This mechanism is interpreted in terms of Recombination-Enhanced Defect Reaction (REDR) involving the two kinds of photogenerated carriers and appears to be low thermally assisted. The BLB is associated with the radiative emission at a phosphorus vacancy (Vp) close to a Zn acceptor (V
p
+
Zn
In
–
). It is believed that the formation of BLB centers originates from Vp-related defects initially present in the freshly plasma-treated InP sample. The mechanisms involved in the Light-Induced Creation (LIC) of BLB centers are discussed. 相似文献
7.
V. V. Evstifeev N. V. Kostina E. S. Zagornyakova 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(6):876-880
Computer simulation of Ga+ ion (E
0 = 40–100 eV) scattering on a GaAs film with defects in the form of vacancies and K+ ions (E
0 = 40–300 eV) on a V-target containing cerium has been carried out in the framework of the multiparticle interaction model.
The simulation results show that low-energy scattering can be used as a tool for detection of surface defects. 相似文献
8.
Following our experimental observations of disclination lines in freely suspended droplets and free-standing films (Yu.A.
Nastishin et al., Eur. Phys. J. E 5 353 (2001)), topological defects of the twist grain boundary (TGBA) phase are considered according to two aspects: topological
and energetical. There are two classes of line defects, disclinations (as in the cholesteric (N*) phase and the liquid vortices phase (NL*), relating to the directors tripod symmetries) and dispirations (relating to the translation-rotation symmetries); there are no topological point defects. Differences between N*, NL* and
TGBA disclinations are physical, not topological. The absence of focal conic domains in the TGBA phase is an immediate consequence of the materialization of the helical axis
(along the χ-director); the same feature, coupled to the trend to parallelism of the smectic layers, accounts for the predominance
of λ-lines. Finally, the presence of defects akin to developable domains is explained in the frame of the leastcurvaturemodel, that requires the introduction of a third type of defects: the densitiesofedgedislocations of the smectic layers.
Received 20 February 2002 相似文献
9.
It is pointed out that in the partial oxidation of porous silicon (PS) formed on heavily doped crystals, the topology of the
pores can result in the formation of an anisotropic material with strings of nanometersized silicon granules embedded in insulating
silicon dioxide SiO2. In this range of granule sizes the correlation effects in the tunneling of electrons (holes) are strong on account of their
Coulomb interaction. This should be manifested as discrete electron and hole tunneling at temperatures comparable to room
temperature. The room-temperature current-voltage characteristics of n
+-PSp
+-p
+ diode structures with a PS interlayer on p
+-Si, which exhibit current steps on the forward and reverse branches, are presented. The current steps are attributed to discrete
hole tunneling along the silicon strings in SiO2.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 794–797 (25 May 1998) 相似文献
10.
Yu.A. Nastishin M. Kléman J. Malthête H.T. Nguyen 《The European physical journal. E, Soft matter》2001,5(3):353-357
We have shown that cholesteryl nonanoate, a thermotropic compound which is well known to exhibit pretransitional effects at
the smectic A (SmA) cholesteric (N*) transition (W.L. McMillan, Phys. Rev. A 4, 1238 (1971); 6, 936 (1972)), has in fact a TGBA phase in between. Our arguments rely on the observation of new TGBA defects, either in Robinson
spherulites cooled from the N* phase or in free-standing films. The same new defects can be obtained in a well-documented
TGBA phase of a tolane compound. We analyze qualitatively the TGBA defects in both geometries, in particular their relation
to the disclination radius of the N* Robinson spherulites.
Received 12 February 2001 相似文献
11.
E. Gmeljn R. Stapf P. Klemt G. Landwehr W. Lichtenberg A. Przybylski 《辐射效应与固体损伤》2013,168(3-4):255-260
Abstract Tellurium single crystal samples with a hole concentration of 3 × 1014/cm2 were irradiated at 10 K with electrons with an energy of 0.6 and 1 MeV. In the range investigated resistivity and Hall-coeficient RH both decreased linearly with the integrated electron flux. The hole generation rate was 0.09 cm?1 and 0.47 cm?1 for 0.6 and 1 MeV electrons, respectively. The Hall-mobility RH/P increased with irradiation. Annealing of the radiation damage by raising the temperature clearly revealed three recovery stages in the resistivity- and Hall-data. At 180K p and RH returned to their pre-irradiation values. The original Hall-mobility was already restored close to 90 K. A more detailed study of the first recovery stage, which occurs at about 50 K, revealed an activation energy of 170±40meV. It is most likely, that the observed lattice defects are Frenkel-defects. There are indications, that the point defects interact with dislocations. 相似文献
12.
An improved adiabatic approach (IAA) previously proposed in atomic physics is extended to the case of collisions of mesic
atoms in excited states n⩾2. The computed rates λ
nn′
C
(E) of the Coulomb de-excitation processes (pπ)n+p→(pπ)
n′+p are substantially different from the IAA results. It is shown that the Coulomb de-excitation rates λ
nn′
C
are high enough to explain the appearance of pπ mesic atoms with kinetic energy ∼70 eV, which were observed in [J. E. Crawford, M. Daum, R. Frosch, et al., Phys. Lett. B 213, 391 (1988) and Phys. Rev. D 43, 46 (1991)].
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 129–133 (10 August 1996) 相似文献
13.
The excitation of the components of the 4p
2
P
1
2,3/2/0
resonance doublet of the Zn+ ion by monoenergetic electrons in the interval 4–10 eV is investigated by a spectroscopic method in crossed beams. Resonances
are found in the energy dependences below and above the excitation thresholds of resonance lines. The subthreshold resonances
are satellite of the lines investigated and are excited in the process of dielectronic recombination. The main competing process
here is the electronic decay of autoionizing states, which is manifested in a resonance excitation of the ions starting at
the thresholds for the excitation of the levels. Autoionizing states lying between the levels of the doublet splitting of
the 4p
2
P
1
2,3/2/0
state decay to the 4p
2
P
1
2/0
level in a Koster-Kronig process. Above the excitation energy of the 4p
2
P
3
2/0
level the the dominant contribution to resonance excitation is from autoionizing states with configurations 3d
9(2
D
5/2,3/2)4s
2
np,(n−1)f.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 614–617 (25 October 1998) 相似文献
14.
We revisit the problem of a two-dimensional polymer ring subject to an inflating pressure differential. The ring is modeled
as a freely jointed closed chain of N monomers. Using a Flory argument, mean-field calculation and Monte Carlo simulations, we show that at a critical pressure,
pc ∼ N-1, the ring undergoes a second-order phase transition from a crumpled, random-walk state, where its mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N2. The transition belongs to the mean-field universality class. At the critical point a new state of polymer statistics is
found, in which 〈A〉 ∼ N3/2. For p ≫ pc we use a transfer-matrix calculation to derive exact expressions for the properties of the smooth state. 相似文献
15.
Solcà N. Dopfer O. 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):469-480
Infrared (IR) photodissociation spectra of the aniline+-Arn cations, An
+
-
Ar
n
(n
= 1, 2), are analyzed in the vicinity of the N-H stretch fundamentals. The complexes are produced in an electron impact (EI) ion
source which produces predominantly the most stable cluster isomers. Two isomers of An+-Ar are identified by their characteristic N-H stretch frequencies: the planar proton-bound global minimum, in which the Ar
ligand forms a nearly linear H-bond to the amino group, and the less stable π-bound local minimum, in which the Ar atom is attached to the π-electron system of the aromatic ring. This result is the first unambiguous detection of the most stable H-bound An+-Ar dimer. All previous spectroscopic studies of An+-Ar employed resonance enhanced multiphoton ionization (REMPI) of neutral An-Ar and identified only the less stable π-bound cation due to restrictions arising from the Franck-Condon principle. The EI-IR spectrum of An+-Ar2 shows that the most stable structure of this trimer features two equivalent H-bonds (C2v symmetry). The interpretation of the experimental data is supported by quantum chemical calculations. The ab initio potential of An+-Ar calculated at the UMP2/6-311G(2df, 2pd) level features H-bound global minima ( D
e
= 513 cm-1) and π-bound local minima ( D
e
= 454 cm-1), with a barrier of V
b
≈ 140 cm-1 for isomerization from the π-bound toward the H-bound minimum.
Received 4 February 2002 Published online 13 September 2002 相似文献
16.
A theoretical study is carried out of quantum beats (QB) in the time-dependent intensities of absorption of a test pulse and
of spontaneous luminescence in a Cu2O crystal under conditions of double optical resonance. It is assumed that pumping is effected by a CO2-laser pulse which dynamically couples the exciton levels 1s(Γ
5
+
) and 2p(Γ
4
−
,Γ
5
−
,Γ
3
−
Γ
2
−
) and splits them into two or three pairs of quasi-energy levels. The frequency of the test pulse is in resonance with the
frequency Γ
5
+
of the exciton. The corresponding intensities for various directions of the electric vector of the pump field E
L, the polarization vector ξ, and the wave vector q of the test pulse are obtained. The frequency of the quantum beats is twice the Rabi frequency, which for different values
of E
L, ξ and q contains different sets of matrix elements of the dipole transitions between the levels 1s(Γ
5
+
) and 2p(Γ
4
−
,Γ
5
−
,Γ
3
−
Γ
2
−
). Thus, by measuring the period of the quantum beats it is possible to determine the unknown matrix elements of the indicated
transitions.
Fiz. Tverd. Tela (St. Petersburg) 39, 844–847 (May 1997) 相似文献
17.
A. N. Artemov 《Journal of Experimental and Theoretical Physics》1999,89(3):577-582
The effect of radiation defects on the thermodynamics of a system of Pearl vortices in a thin superconducting film is examined.
The scenario for a Kosterlitz-Thouless transition in this system is shown to depend on the defect concentration n
d
. At low concentrations, the transition takes place continuously, while at high concentrations, a range of temperatures exists
in which there are two metastable states. The concentrations of free vortices and of vortices captured by defects are calculated
as functions of temperature for different defect concentrations n
d
. A phase diagram is constructed for the vortex system in the n
d
−T plane.
Zh. éksp. Teor. Fiz. 116, 1081–1090 (September 1999) 相似文献
18.
The thermoluminescence of single crystals of corundum containing anion defects following x-ray and laser excitation is investigated.
Its features in the luminescence bands of F, F+, and Cr3+ centers are studied. Synchronous measurements of the thermoluminescence and thermally stimulated exoelectron emission are
performed by the fractional glow technique following x-ray and laser excitation of the samples. It follows from the results
obtained that several traps are active in the temperature range of the principal dosimetric peak (400–500 K). The spectral
sensitivity curve contains maxima corresponding to absorption bands of F, F+, and Al
i
+
centers. A possible mechanism for the recombination luminescence of F centers is discussed. It is found that the material
exhibits high sensitivity to small doses of ultraviolet laser radiation.
Zh. Tekh. Fiz. 67, 72–76 (July 1997) 相似文献
19.
G. Brauer C. Döring A. Andreeff G. Dlubek O. Brümmer M. Jurisch G. Behr 《Applied Physics A: Materials Science & Processing》1981,25(1):65-70
The sensitivity of positrons to point defects created by the irradiation of V3Si with neutrons is demonstrated. We found no indication of thermal vacancies by thermal equilibrium measurement up to 1273
K which indicates that the monovacancy formation enthalpy for V3Si isH
1V
F
≧(1.84±0.14) eV. Investigations within the range of homogeneity for excess vanadium suppot the idea that substitutional defects
are the dominating defect type, whereas for excess silicon a direct confirmation of existing structural vacancies as the dominating
defect type is given. 相似文献
20.
《Journal of Physics and Chemistry of Solids》2003,64(9-10):1657-1663
Preliminary ab initio calculation of different point defects energy and electronic density of states have been performed on the prototype chalcopyrite semiconductor CuInSe2. The simulation method used is based on the density functional theory within the framework of pseudo-potentials and plane waves basis. The isolated neutral defects considered are: VCu, VIn, VSe, Cui, Ini, InCu, CuIn and the complex defects are 2Cui+CuIn, InCu+CuIn and 2VCu+InCu, some of which being computed for the first time by advanced ab initio techniques. In agreement with previous results, we show that some point defects (such as VCu) and pair defects (2VCu+InCu) have very low formation energies. Some energies of formation were found significantly lower than previous estimations. The comparison of the formation energies with the exchange correlation (LDA or GGA) is discussed. The perturbation induced by the presence of some of these ideal defects on the density of states is also presented. 相似文献