74 research outputs found
НАНОРАЗМЕРНЫЙ КРЕМНИЙ, ИЗГОТОВЛЕННЫЙ С ИСПОЛЬЗОВАНИЕМ ЭЛЕКТРОЛИТА HCl : HF : C2H5OH
Results of experimental work with nanosized silicon (NcSi) samples which are not degraded under the action of intense laser radiation have been obtained. We show that that a significant increase in the intensity of thephotoluminescence signal from NC may be caused by the structural features of their formation and by the presence of a thin SiO2 layer on the surface of the nanocrystals.Представлены результаты исследований образцов наноразмерного кремния (НК), не деградирующих под действием интенсивного лазерного излучения. Показано, что значительное увеличение интенсивности сигнала фотолюминесценции от НК может быть связано как с особенностями их структурного строения, так и с наличием тонкого слоя SiO2 на поверхности нанокристаллов
Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films
We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial
films prepared by the hot-wall technique on -BaF_2 substrates. Variation
of the substrate temperature allowed us to change the resistivity of the films
from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is
associated with a slight excess of Ga concentration, disturbing the Fermi level
pinning within the energy gap of n-PbTe(Ga). PC has been measured under
continuous and pulse illumination in the temperature range 4.2-300 K. For films
of low resistivity, the photoresponse is composed of negative and positive
parts. Recombination processes for both effects are characterized by
nonexponential kinetics depending on the illumination pulse duration and
intensity. Analysis of the PC transient proves that the negative
photoconductivity cannot be explained in terms of nonequilibrium charge
carriers spatial separation of due to band modulation. Experimental results are
interpreted assuming the mixed valence of Ga in lead telluride and the
formation of centers with a negative correlation energy. Specifics of the PC
process is determined by the energy levels attributed to donor Ga III, acceptor
Ga I, and neutral Ga II states with respect to the crystal surrounding. The
energy level corresponding to the metastable state Ga II is supposed to occur
above the conduction band bottom, providing fast recombination rates for the
negative PC. The superposition of negative and positive PC is considered to be
dependent on the ratio of the densities of states corresponding to the donor
and acceptor impurity centers.Comment: 7 pages, 4 figure
Spatially, Temporally and Polarization-Resolved Photoluminescence Exploration of Excitons in Crystalline Phthalocyanine Thin Films
The lack of long range order in organic semiconductor thin films prevents the
unveiling of the complete nature of excitons in optical experiments, because
the diffraction limited beam diameters in the bandgap region far exceed typical
crystalline grain sizes. Here we present spatially-, temporally- and
polarization-resolved dual photoluminescence/linear dichroism microscopy
experiments that investigate exciton states within a single crystalline grain
in solution-processed phthalocyanine thin films. These experiments reveal the
existence of a delocalized singlet exciton, polarized along the high mobility
axis in this quasi-1D electronic system. The strong delocalized {\pi} orbitals
overlap controlled by the molecular stacking along the high mobility axis is
responsible for breaking the radiative recombination selection rules. Using our
linear dichroism scanning microscopy setup we further established a rotation of
molecules (i.e. a structural phase transition) that occurs above 100 K prevents
the observation of this exciton at room temperature.Comment: submitted to Journal of Chem Phys letter
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