70 research outputs found
p-Type doping of II-VI heterostructures from surface states: application to ferromagnetic CdMnTe quantum wells
We present a study of p-type doping of CdTe and CdMnTe quantum
wells from surface states. We show that this method is as efficient as usual
modulation doping with nitrogen acceptors, and leads to hole densities
exceeding cm. Surface doping was successfully applied
to obtain carrier-induced ferromagnetism in a CdMnTe quantum well.
The observed temperature dependence of photoluminescence spectra, and the
critical temperature, correspond well to those previously reported for
ferromagnetic quantum wells doped with nitrogen.Comment: 4 figure
Carrier-induced ferromagnetism in p-Zn1-xMnxTe
We present a systematic study of the ferromagnetic transition induced by the
holes in nitrogen doped Zn1-xMnxTe epitaxial layers, with particular emphasis
on the values of the Curie-Weiss temperature as a function of the carrier and
spin concentrations. The data are obtained from thorough analyses of the
results of magnetization, magnetoresistance and spin-dependent Hall effect
measurements. The experimental findings compare favorably, without adjustable
parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY)
model or its continuous-medium limit, that is, the Zener model, provided that
the presence of the competing antiferromagnetic spin-spin superexchange
interaction is taken into account, and the complex structure of the valence
band is properly incorporated into the calculation of the spin susceptibility
of the hole liquid. In general terms, the findings demonstrate how the
interplay between the ferromagnetic RKKY interaction, carrier localization, and
intrinsic antiferromagnetic superexchange affects the ordering temperature and
the saturation value of magnetization in magnetically and electrostatically
disordered systems.Comment: 14 pages, 10 figure
Microphotoluminescence study of disorder in ferromagnetic (Cd,Mn)Te quantum well
Microphotoluminescence mapping experiments were performed on a modulation
doped (Cd,Mn)Te quantum well exhibiting carrier induced ferromagnetism. The
zero field splitting that reveals the presence of a spontaneous magnetization
in the low-temperature phase, is measured locally; its fluctuations are
compared to those of the spin content and of the carrier density, also measured
spectroscopically in the same run. We show that the fluctuations of the carrier
density are the main mechanism responsible for the fluctuations of the
spontaneous magnetization in the ferromagnetic phase, while those of the Mn
spin density have no detectable effect at this scale of observation.Comment: 4 pages, 3 figure
Light and electric field control of ferromagnetism in magnetic quantum structures
A strong influence of illumination and electric bias on the Curie temperature
and saturation value of the magnetization is demonstrated for semiconductor
structures containing a modulation-doped p-type Cd0.96Mn0.04Te quantum well
placed in various built-in electric fields. It is shown that both light beam
and bias voltage generate an isothermal and reversible cross-over between the
paramagnetic and ferromagnetic phases, in the way that is predetermined by the
structure design. The observed behavior is in quantitative agreement with the
expectations for systems, in which ferromagnetic interactions are mediated by
the weakly disordered two-dimensional hole liquid.Comment: 4 pages and 3 figure
A lattice gas model of II-VI(001) semiconductor surfaces
We introduce an anisotropic two-dimensional lattice gas model of metal
terminated II-IV(001) seminconductor surfaces. Important properties of this
class of materials are represented by effective NN and NNN interactions, which
result in the competition of two vacancy structures on the surface. We
demonstrate that the experimentally observed c(2x2)-(2x1) transition of the
CdTe(001) surface can be understood as a phase transition in thermal
equilbrium. The model is studied by means of transfer matrix and Monte Carlo
techniques. The analysis shows that the small energy difference of the
competing reconstructions determines to a large extent the nature of the
different phases. Possible implications for further experimental research are
discussed.Comment: 7 pages, 2 figure
Polarity determination in ZnSe nanowires by HAADF STEM
High angle annular dark field scanning transmission electron microscopy is
used to analyze the polarity of ZnSe nanowires grown, by molecular beam
epitaxy, on GaAs substrates. The experimental results are compared to simulated
images in order to verify possible experimental artefacts. In this work we show
that for this type of nano-objects, a residual tilt of the specimen below 15
mrad, away from the crystallographic zone axis does not impair the
interpretation of the experimental images
Stabilized Phase Variants of <I>Vibrio cholerae</I> El Tor P-18895
Produced have been stabilized phase variants of V. cholerae El Tor P-18895 (O- and rugose colonies). Frequency of reversion to initial ST-phenotype does not exceed 10 %. Identity of the origin is verified in VNTR. Evaluated has also been their activity by means of the following diagnostic tests: agglutination assay, sensitivity to diagnostic bacteriophages test, and studies of growth behavior in solid nutrient media. Stabilized variants of V. cholerae El Tor P-18895 can be deployed for further investigations of peculiarities of biofilm formation on various surfaces, bacterial resistance to environmental factors, and for the enhancement of methods for isolation of cholera vibrio variants from ambient environment
Технология педагогического управления конфликтами в среде иностранных студентов
The article reveals procedure of interaction between the subjects of pedagogical technology, efficiency of pedagogical technology applying and ways to arrange anticonflict activity. The authors studied reasons and types of conflicts and their influence on international students ’ life by means of applyingpredictive methods, observation methods, methods of theoretical analysis and statistic data processing. The paper considers principles of pedagogical management in details. The authors suppose the nature of pedagogical conflict management to lie in correction of contradictions and formation of structurak skills aimed at controlling and managing conflicts.В статье представлен алгоритм взаимодействия субъектов педагогической технологии, условия эффективности ее реализации и способы организации антиконфликтной деятельности. Используя прогностические и обсервационные методы, методы теоретического анализа и статистической обработки данных, авторы изучили причины возникновения и основные виды конфликтов, а также их влияние на жизнедеятельность иностранных студентов. Детально рассматриваются принципы педагогического управления конфликтами. Авторы считают, что сущность педагогического управления конфликтами заключается в коррекции имеющихся противоречий и формировании конструктивных умений координировать и регулировать развитие конфликтной ситуации
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