Scanning Probe Microscopy Group.
Laboratory of Surface
Optics.
Ioffe Physical-Technical Institute RAS.
Members of the group
Main directions of works
Source of
financings of work
Main work instrument
Main publications
Contact
person
Postal address
Members of the
group
| Alexander
N.Titkov |
the
leader of the group, Dr.Sc Alexander.Titkov@pop.ioffe.rssi.ru |
| Alexander V.Ankudinov | researcher. Dr. |
| Theodore A.Grishin | probationer-researcher, |
| Michael S.Dunaevsky | Ph.D. student, |
| Leonid N.Ivanzov | radio-engineer, |
| Alexander K.Kryzhanovskii | researcher, |
| Igor V.Makarenko | senior researcher, Dr., |
| Theodore M.Snegov | researcher, |
| Zafar Waqar | probationer from Islamabad University (Pakistan) |
Main directions of works
Atomic force microscopy and scanning tunnel microscopy and
spectroscopy of solid state nanostructures.
Source of financings of
work
Foundation
support: Researches are supported by Russian Foundation for Basic Research,
Russian Ministry of Science and in cooperation with foreign scientific
groups
Main work
instrument
Main
working instruments: atomic force microscope P4-SPM-MDT, and vacuum STM own
creation.
Main
publications
1.
M.Mynbaeva, A.Titkov, A.Kryganovskii, V.Ratnikov, K.Mynbaev et al., Structural
characterization and strain relaxation in porous GaN layers//
Applied Physics
Letters 76(8), (2000)
Surface and subsurface structures of porous GaN prepared by anodizing
epitaxial GaN layers grown on SiC substrates are investigated by atomic force
microscopy. Comparison of the images of the porous GaN surfaces with those taken
on planes cleft perpendicular to the surface shows that the pores are formed
along the boundaries of columnar structures of the original GaN films. X-ray
investigations show that the porous GaN has less residual stresses than the
initial GaN epitaxial layers. Use of porous GaN as a buffer layer for growth of
low-stress GaN is proposed.
2.
A.V.Ankudinov, A.N.Titkov, T.V.Shubina, S.V.Ivanov, P.S.Kop'ev et al.,
Cross-sectional atomic force microscopy of ZnMgSSe- and BeMgZnSe-based laser
diodes//
Applied Physics Letters 75(17), 2626-28
(1999).
Atomic force microscopy of cleaved facets of ZnSe-based lasers with
various active region designs is reported. Different AFM probe friction on the
materials forming the laser structures are exploited for imaging their basic
layers. Unlike ZnMgSSe-based lasers, the cleaved surface of cladding layers in
BeMgZnSe-based structures is atomically flat, which is attributed to hardening
of the II-VI materials by Be incorporation. Nanomiter-high steps and undulations
are observed at the laser heterointerfaces on cleaved facets. The shape and
height of such topographic singularities located in the vicinity of a (Zn,Cd)Se
quantum well active region depend on the strain distribution in the laser
waveguide.
3.
L.N.Bolotov, A.Nakamura, V.P.Evtikchiev, V.E.Tokranov, A.N.Titkov UHV STM
studies of the decapped InAs quantum dots on GaAs(001) surface after desorption
of a protective As layer//
Surface and Interface Analysis 27, 533-536
(1999).
The
morphology and electronic properties of InAs QDs on the GaAs(001) surface has
been studied by UHV STM/S after removal of a preliminary deposited protective As
layer. A thermal annealing procedure has been developed, which, applied to a
sample with an As cap layer, allows InAs QDs to be opened on the surface of InAs
wetting layer (WL) exhibiting a [2x4] reconstruction of As dimers. Scanning
tunneling spectroscopy measurements on the decapped surface show that I-V
characteristics taken with the tip positioned over single InAs QDs have a
smaller voltage width for zero conductivity (dI/dV=o) when compared with those
taken over the InAs WL, which are essentially the same as the I-V
characteristics for a clean GaAs surface. This observation seems to indicate a
weakening of the surface band bending in the area beneath InAs
QDs.
4.
I.Grechov, L.Delimova, I.Liniichuk, I.Veselovskii, A.Titkov, M.Dunaevskii et
al., Growth mode study of ultrathin HTSC YBCO films on YBaCuNbO
buffer//
Physica C 324, 39-46 (1999)
It is
known that the critical temperature Tc of ultrathin YBCO films is reduced to
values far less than 77K. To improve the superconducting properties of ultrathin
YBCO films, we developed a new buffer layer which allowed an increase in the
critical temperature of five-unit-cell-thick YBCO films to values above 77K.
Using atomic-force microscopy to study the growth modes of ultrathin YBCO films
deposited on a SrTiO3 substrate and on a YBaCuNbO buffer layer, we found that
ultrathin YBCO films deposited on a SrTiO3 substrate are formed due to 2D
nucleation. The growth of ultrathin YBCO films deposited on YBaCuNbO buffer is
governed by the step-flow mode. As a consequence of the different growth modes,
the ultrathin films deposited on a SrTiO3 substrate and a YBaCuNbO buffer layer
have different surface morphologies and superconductive properties. We believe
that the step-flow mode makes it possible to improve the ultrathin YBCO folms
structure and increase the critical temperature.
5.
V.P.Evtikhiev, V.E.Tokranov, A.K.Kryganovskii, A.M.Boiko, R.A.Suris, A.N.Titkov
Characterization of the InAs quantumdots MBE grown on the vicinal GaAs (001)
surfaces misoriented to the [010] direction//
Journal of Crystal Growth
201/202, 1154-57 (1999)
Atomic force microscopy is used to study InAs quantum dot arrays grown by
MBE on vicinal GaAs (001) surfaces misoriented to the [010] direction by 1, 2, 4
and 6 degrees. For a chosen misorientation direction , it is shown that the
vicinal GaAs (001) surface is covered with a net of steppe terraces. The
condensation of the network of terraces upon increasing of the misorientation
angle leads to the suppression of adatom surface diffusion and makes it possible
to achieve higher densities and better unifomity of quantum dots
arrays.
6.
N.M.Shmidt, V.V.Emtsev, A.K.Kryganovskii, R.N.Kyutt, W.V.Lundin, A.N.Titkov et
al., Mosaic structure and Si doping related peculiarities of charge carrier
transport in III-V nitrides//
Phys. Stat. Sol. (b) 216, 581-586
(1999).
Studies of the charge carrier transport in undoped moderatevily and
heavily Si doped GaN and AlGaN epilayers with different mosaic structure are
presented. The epilayer were grown by low-pressure MOCVD on (0001) sapphire
substrates. The mosaic (columnar) structure of the epilayer has been
characterized by X-ray diffraction and AFM surface topography studies.
Application of electrostatic force microscopy (EFM) permitted to reveal
irregular potential barriers at the mosaic domain boundaries in undoped layers
and their reduction in Si doped layers. For undoped GaN and AlGaN epilayers
unconventional transport of electrons and a low RT mobility have been found. We
relate the peculiarities in the electron transport in undoped samples with
additional carrier scatterring on the potential barriers at domain boundaries.
Si doping reduces the potential barriers. Moderate Si doping causes a
considerable increase of the electron RT mobility and restores normal mobility
dependence on the temperature.
Contact person: Alexander N.Titkov
Postal
address:
Ioffe Physical Technical Institute RAS,
26 Polytekchnicheskaya, 194021
St.-Petersburg,
Russia
Tel.: (812) - 247-93-17
Fax: (812) 247-10-17
E-mail: Alexander.Titkov@pop.ioffe.rssi.ru