298 research outputs found
The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios
The following scenarios of Re-embedding into SiO2-host by pulsed
Re-implantation were derived and discussed after XPS-and-DFT electronic
structure qualification: (i) low Re-impurity concentration mode -> the
formation of combined substitutional and interstitial impurities with
Re2O7-like atomic and electronic structures in the vicinity of oxygen
vacancies; (ii) high Re-impurity concentration mode -> the fabrication of
interstitial Re-metal clusters with the accompanied formation of ReO2-like
atomic structures and (iii) an intermediate transient mode with Re-impurity
concentration increase, when the precursors of interstitial defect clusters are
appeared and growing in the host-matrix structure occur. An amplification
regime of Re-metal contribution majority to the final Valence Band structure
was found as one of the sequences of intermediate transient mode. It was shown
that most of the qualified and discussed modes were accompanied by the MRO
(middle range ordering) distortions in the initial oxygen subnetwork of the
a-SiO2 host-matrix because of the appeared mixed defect configurations.Comment: 19 pages, 7 figures, accepted to J. Alloys and Compound
Finite size and intrinsic field effect on the polar-active properties of the ferroelectric-semiconductor heterostructures
Using Landau-Ginzburg-Devonshire approach we calculated the equilibrium
distributions of electric field, polarization and space charge in the
ferroelectric-semiconductor heterostructures containing proper or incipient
ferroelectric thin films. The role of the polarization gradient and intrinsic
surface energy, interface dipoles and free charges on polarization dynamics are
specifically explored. The intrinsic field effects, which originated at the
ferroelectric-semiconductor interface, lead to the surface band bending and
result into the formation of depletion space-charge layer near the
semiconductor surface. During the local polarization reversal (caused by the
inhomogeneous electric field induced by the nanosized tip of the Scanning Probe
Microscope (SPM) probe) the thickness and charge of the interface layer
drastically changes, it particular the sign of the screening carriers is
determined by the polarization direction. Obtained analytical solutions could
be extended to analyze polarization-mediated electronic transport.Comment: 35 pages, 12 figures, 1 table, 2 appendices, to be submitted to Phys.
Rev.
Polarization reversal induced by heating-cooling cycles in MgO doped lithium niobate crystals
Polarization reversal during heating-cooling cycles was investigated in MgO doped lithium niobate (MgO:LN) crystal using piezoresponse force microscopy. The essential dependence of the domain structure evolution scenario on the maximal temperature in the cycle has been revealed experimentally. It has been shown that the heating of the engineered domain matrix from room temperature to 85 °C leads to light size reduction of the isolated domains at the matrix edges, whereas the heating to 170 °C leads to essential reduction of the domain size. The opposite strong effect of the domain formation and growth during cooling after pulse heating have been revealed in single domain MgO:LN. The simulation of the time dependence of the pyroelectric field during heating-cooling cycle allowed to reveal the temperature hysteresis and to explain all observed effects taking into account the temperature dependence of the bulk conductivity. © 2013 AIP Publishing LLC
Low loss optical waveguides fabricated in LiTaO3 by swift heavy ion irradiation
© 2019 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reservedOptical waveguides are fabricated by irradiation of LiTaO 3 with a variety of swift heavy ions that provide increasing levels of both nuclear and electronic damage rates, including C, F and Si ions, in the energy range of 15-40 MeV. A systematic study of the role of the ion fluence has been carried out in the broad range of 1e13-2e15 at/cm 2 . The kinetics of damage is initially of nuclear origin for the lowest fluences and stopping powers and, then, is enhanced by the electronic excitation (for F and Si ions) in synergy with the nuclear damage. Applying suitable annealing treatments, optical propagation losses values as low as 0.1 dB have been achieved. The damage rates found in LiTaO 3 have been compared with those known for the reference LiNbO 3 and discussed in the context of the thermal spike modelV. Tormo-Márquez thanks the CMAM-UAM for their financial support. We thank the Technical staff of the CMAM-UAM center for support with the ion irradiation
Domain diversity and polarization switching in amino acid β-glycine
Piezoelectric materials based on lead zirconate titanate are widely used in sensors and actuators. However, their application is limited because of high processing temperature, brittleness, lack of conformal deposition and, more importantly, intrinsic incompatibility with biological environments. Recent studies on bioorganic piezoelectrics have demonstrated their potential in these applications, essentially due to using the same building blocks as those used by nature. In this work, we used piezoresponse force microscopy (PFM) to study the domain structures and polarization reversal in the smallest amino acid glycine, which recently attracted a lot of attention due to its strong shear piezoelectric activity. In this uniaxial ferroelectric, a diverse domain structure that includes both 180° and charged domain walls was observed, as well as domain wall kinks related to peculiar growth and crystallographic structure of this material. Local polarization switching was studied by applying a bias voltage to the PFM tip, and the possibility to control the resulting domain structure was demonstrated. This study has shown that the as-grown domain structure and changes in the electric field in glycine are qualitatively similar to those found in the uniaxial inorganic ferroelectrics. © 2019 by the authors
Plasmonic terahertz detection by a double-grating-gate field-effect transistor structure with an asymmetric unit cell
Plasmonic terahertz detection by a double-grating gate field-effect
transistor structure with an asymmetric unit cell is studied theoretically.
Detection responsivity exceeding 8 kV/W at room temperature in the photovoltaic
response mode is predicted for strong asymmetry of the structure unit cell.
This value of the responsivity is an order of magnitude greater than reported
previously for the other types of uncooled plasmonic terahertz detectors. Such
enormous responsivity can be obtained without using any supplementary antenna
elements because the double-grating gate acts as an aerial matched antenna that
effectively couples the incoming terahertz radiation to plasma oscillations in
the structure channel.Comment: Submitted to APL, 8 pages, 2 figure
Static conductivity of charged domain wall in uniaxial ferroelectric-semiconductors
Using Landau-Ginzburg-Devonshire theory we calculated numerically the static
conductivity of both inclined and counter domain walls in the uniaxial
ferroelectrics-semiconductors of n-type. We used the effective mass
approximation for the electron and holes density of states, which is valid at
arbitrary distance from the domain wall. Due to the electrons accumulation, the
static conductivity drastically increases at the inclined head-to-head wall by
1 order of magnitude for small incline angles theta pi/40 by up 3 orders of
magnitude for the counter domain wall (theta=pi/2). Two separate regions of the
space charge accumulation exist across an inclined tail-to-tail wall: the thin
region in the immediate vicinity of the wall with accumulated mobile holes and
the much wider region with ionized donors. The conductivity across the
tail-to-tail wall is at least an order of magnitude smaller than the one of the
head-to-head wall due to the low mobility of holes, which are improper carries.
The results are in qualitative agreement with recent experimental data for
LiNbO3 doped with MgO.Comment: 20 pages, 6 figures, 1 appendi
Morphological Criteria for Diagnosis of Pulmonary Lesions of Lungs in Tumors Based on Resection Material
Morphological criteria of diagnosis of dust lesions of lungs in tumors on resectionmaterial are considered in the article. It is shown that the complex application of various research methods allows the identification of dust particles in the lung and lymph node tissues, and contributes to the improvement of the diagnosis of dust lesions of the respiratory system. Morphological characteristics of bauxite pneumoconiosis in primary lung cancer on resection material are presented
Domain Shape Appeared in Stoichiometric Lithium Niobate as a Result of Ion Beam Irradiation
We have studied the formation of isolated domains induced by ion beam irradiation in the stoichiometric lithium niobate (SLN) single crystals covered by surface dielectric layer. The unusual domain shape was revealed at the irradiated polar surface at the doses above 20 pC. The nested domain shape with hexagonal outer part and circle inner one has been distinguished. The domains visualization in the bulk showed the hexagonal domain shape in the depth. The obtained effect was attributed to backswitching under the action of electric field produced by space charge dipped to LN plate at the doses above 20 pC due to essential ion beam sputtering effect
- …