Physics, Chemistry and Application of Nanostructures

The following sections are included:

• FOREWORD

• CONTENTS

A historical survey of main contributions made possible to understand phenomena in nanoworld, which is the world spreading from individual atoms to low-dimensional structures, is composed on the basis of the achievements awarded the Nobel Prizes.

Well-ordered high-density quantum dot arrays of InGaAs have been fabricated on high-index substrates by atomic-hydrogen assisted molecular beam epitaxy. The density and the dot size are controlled by growth temperature and substrate structure. The dot growth mechanism is explained not only by simple strain relaxation but also by phase separation. The surface coverage of the high density quantum dots is almost 100 %, which implies the lateral coupling between the dots. Photoluminescence and photoconductivity measurements show the existence of minibands formed by lateral coupling of dots.

We have investigated the multiexciton states confined in a single GaAs/AlGaAs quantum dot (QD) grown on a GaAs (411)A surface by means of micro-photoluminescence and excitation spectra. We observed three types of photoluminescence lines, originating from one exciton, biexciton, and multiple exciton states confined in the QD. We also observed sharp resonances in the excitation spectra, not only in Stokes side but also in anti-Stokes side. The unusual anti-Stokes resonance indicates the efficient energy transfer process probably driven by Auger excitation.

Photoreflectance spectroscopy on several low-dimensional structures has been presented. The optical transitions have been investigated in coupled In_xGa_1-xAs/GaAs quantum wells, double Al_xGa_1-xAs/GaAs quantum wells and vertically coupled In_xGa_1-xAs/GaAs double quantum dots as a function of the thickness and separating barrier layer. Transition and splitting energies versus barrier thickness have been obtained and compared with the results of the envelope function calculations.

Thermopower measurements can often provide the transport physicist with information that is complementary to results obtained from ordinary conductance measurements. Here, we present two examples of thermopower measurements on chaotic transport in a quantum dot in two different transport regimes, for the ballistic (G = 4e²/h) and the Coulomb blockade regime (lead conductance G ≤ 2e²/h). In both cases the experimental results show an excellent agreement with the theoretical prediction.

An approximate model to describe a multilayered heterostructure is proposed. The details of the heterostructure are taken into account by the confining potential V(z) generated by the layers. The multilayered GaAs/Al_xGa_1-xAs heterostructure is considered as an effective medium. Its mean parameters are defined by averaging the subsequent layer-dependent parameters over the ground-state wave function. Only the effective bulk phonon mode inhabits the effective medium with mean characteristics. As a result, properties of charge carries in the heterostructure can be described through the Pekar-Fröhlich polaron model. The polaron energy and its effective mass are calculated for different quantum wells. We obtained a rather monotonous behavior between the asymptotic values for the polaron energy as a function of the confining potential width. As to the effective polaron mass it exhibits a peak. The comparison is made with theoretical results by other authors.

This paper presents a comprehensive review on the fabrication and properties of germanium based nanostructures formed by self-assembling process. The 2D - 3D transition is described in detail. The influence of the Si substrate orientation on the Si_1-xGe_x, growth modes and relaxation mechanisms is also discussed. We show that while island formation can be described by the classic S-K growth scheme on Si(111), more complex mechanisms based on the competitive effects of kinetics and thermodynamics take place on (001). In the latter case, we define four main growth regimes that are driven either by kinetic growth instability or by stress relaxation and that correspond to four different steady state morphologies (obtained after long term annealing of the as grown samples). These steady state equilibrium morphologies consist of: rough 2D layer in regime I, strained "hut" (105) facetted islands in regime II, coexistence of "hut" and "dome" in regime III and bimodal size distribution of relaxed (elastic or plastic relaxation) "domes" in regime IV.

By applying molecular dynamics simulation with a three-body potential for SiGe we have studied the elastic interaction between realistic SiGe dots and Si(001) substrate. Stress and strain distributions were computed indicating a complex and deep deformation of the substrate and a slight relaxation in the Ge pyramid.

It has recently been shown that room temperature electroluminescence can be obtained from silicon containing nanostructures of β-FeSi₂. These structures have been prepared using either Ion Beam Synthesis (IBS) or Reaction Deposition Epitaxy (RDE). For the IBS structures a maximum in the EL intensity is found for doses ~ 1.5 × 10¹⁶ Fe/cm². The quenching of the EL is found to vary with both the doping of the p-type layer and hence the proximity of the precipitates to the depletion region of the p-n junction and the thickness of the silicon overlying the precipitates where radiative recombination can occur. The optimum results, in terms of EL quenching are found for the highest p-type doping (1 × 10¹⁸ cm^-3) and for the thickest p-type layer (1 µm). For the RDE sample where the β-FeSi₂ nanostructures are fabricated at the junction between the p- and n-type regions, the EL increased superlinearly with increasing injected current density, with a reasonable EL signal above 10 A/cm². These results indicate that by reducing the defect density in the silicon surrounding the β-FeSi₂ nanostructures and optimising the device structure, it should be possible to form practical silicon based light emitting devices incorporating β-FeSi₂ in the next few years.

We briefly review a couple of highlights in multiwalled carbon nanotube research. We will emphasize mechanical properties of nanotubes in general and then focus on electrical properties of multiwalled nanotubes in particular.

We comparatively analyze three distinct C₆₀-based superstructures grown on Ag(100), Si(111)-(7 × 7), and Ge(111)-c(2 × 8) as to their molecular arrangement and electronic structure. The basic elements characterizing covalent vs. ionic bond of the buckyballs with the substrate are discussed. In particular, the attention is focused onto STM images, photoemission spectra of the C 1s core level and valence band states.

The possibility of the dielectric-metal transition (Mott transition) as a result of increase of charge carriers concentration in the conductivity band of an ensemble of close-packed monodispersed nanocrystals is mathematically proved. The results of statistical analysis providing of occurrence of metal conductivity in a system of ordered and disordered semiconductor nanocrystals depending on their concentration, size and electron effective mass are reported.

Analytical description of Coulomb field screening generated by extra point charge, placed in the center of semiconductor ball (nanocluster) with a limited number of donors and acceptors is given in the continual approximation. The screening occurs due to hopping of electrons between donors. Our calculations of the electrostatic potential is compared with the results of the Monte-Carlo numerical modeling at zero temperature.

We study theoretically the electron spectrum and infrared transitions in a superlattice with a unit cell allowing resonant carrier states. The dispersion relation and the band structure of such a system is found. The dipole matrix element and optical absorption strength for inter-subband carrier infrared transitions are calculated for the first time.

We present results of theoretical investigation of the plasmon-polaritons formed due to the interaction of two-dimensional plasmons in a planar Bragg microresonator with guided modes of dielectric substrate slab. The guided plasmon-polaritons may be taken up for development of controllable guided wave frequency filters and modulators in the far-infrared.

Optical properties of fractal Cantor-like multilayer structures are investigated theoretically and experimentally. The structures are shown to exhibit distinct optical properties, such as existence of band gaps and sharp resonances (peaks) in transmission spectra. Connection between the stack geometry and optical properties is found, namely spectral scalability and sequential splitting.

Vertical electron transport in semiconductor superlattices with a disorder intentionally introduced into their parameters is studied theoretically. Short superlattices with low carrier concentration and in finite electric field are considered. Electron transmission spectra and current-voltage characteristics are calculated numerically for various types and degrees of the disorder. Virtual scattering by a quasi-localized level with a negative energy is observed for the first time.

Phonon-plasmon interaction in tunnelling thin GaAs_n/AlAs_m superlattices (SLs) was studied using Raman spectroscopy. It was observed that when GaAs layers was thinned from 6 to 0.6 monolayers the coupled phonon-plasmon modes became 3D-like, and the interaction of plasmons with LO-phonons of AlAs type takes place. The phonon-plasmon interaction in the case of SLs was numerically modelled on the basis of a microscopic approach. The qualitative agreement of the experiment and the calculations occurs.

Illumination of a double p-Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As heterostructure by a red light emitting diode results in a negative photoconductivity that, after the diode is switched off, slowly relaxes to a positive persistent photoconductivity, characterized by about 1.5 increase of a two-dimensional hole concentration. This metastable state may be explained in a framework of the model in which deep electron traps are supposed to be located above the Fermi level on the inverted heterointerface.

The GaAs/AlAs superlattices (SLs) grown on facet surfaces (311)A,B and (100) surface were studied using Raman and photoluminescence (PL) spectroscopy. Sharp differences in Raman and PL spectra of the ultrathin SLs grown on (311)A and (311)B surfaces were observed. These effects probably are result of differences in interface reconstructions. The observed phonon anisotropy of (311)A SLs can be indirect evidence of anisotropic structure of surface quantum objects formed on (311)A GaAs. The PL peaks of (311)A and (311)B SLs differ both the intensities and the positions. In the Raman spectra of the SL containing GaAs submonolayers grown on (2 × 4) reconstructed (100) surface, the triplet Raman peak corresponding to scattering on GaAs-like confined LO phonons was observed. The triplet structure appears due to additional lateral confinement of LO phonons in GaAs quantum islands. Calculations of Raman spectra were carried out using the models of rigid ions, bond charge and Wolkenstain bond polarisability. The theoretical Raman spectra of the islands grown (in the context of a known model) on the (001)-(2 × 4) reconstructed surface are in surprisingly good agreement with the experimental ones. The calculations show that 70 % of the islands contains less than 18 Ga atoms, what is in very good agreement with the known STM data.

The scanning probe microscopy methods have been applied to investigate morphology and local photocurrent spectra in InAs/GaAs structures with quantum dots grown near a sample surface. The influence of a strong electric field on the STM spectrum was investigated.

The availability of n-i-p-i crystal layers in periodic structures with a photonic band gap has been considered. It is shown that such photonic structures can be attractive as low-threshold optical switches. The dispersion and transmission characteristics of the structures are examined at high excitation levels where light amplification in the n-i-p-i superlattice layers occurs. Properties of optical resonators with the photonic band gap structures in these conditions are discussed.

The influence of high-energy electron irradiation on the time-resolved photoluminescence (PL) of quantum dot (QD) and quantum well (QW) InGaAs/GaAs structures are investigated. Both rise and decay kinetics is changed due to radiation-induced defects. The decay kinetics of as-grown QWs and QDs can be described by a single time constant. The irradiated QWs still exhibit the single exponential decay but with the less time constant, whereas the second faster component appears in the PL decay of QDs along with the component present prior to irradiation. Thus, we observed interaction of confined carriers with radiation-induced defects inside or near the QDs.

Highly monodisperse 1.8 nm CdSe quantum dots were synthesized capped with surface monolayer of 1-thioglycerol. The optical absorption of thin films of matrix free close-packed and isolated in PMMA matrix quantum dots was studied at various electric field biases. The broadening and red shift of optical transitions in close-packed ensemble against the isolated quantum dots are attributed to the formation of collective electronic submini-bands between interacting nanocrystals. The reversible collapse of collective electronic subminibands has been achieved by applying strong electric field to the thin film of close-packed quantum dots.

Ab initio plane-wave pseudopotential calculations of optical properties of Ge nanocrystals embedded in cubic SiC are reported. Optical matrix elements and band energies are obtained from the PAW method. States within the gap of the host material arise. The spectral properties are calculated using an extrapolative version of the linear analytic tetrahedron method. Due to the interaction between clusters in adjacent supercells the results for a given nanocrystal depend on the supercell size. Moreover, the type of the interface between nanocrystal and host material influences the results considerably. This means that simple two-component effective medium theories cannot fully explain the optical properties of such a composite material.

Formation of nanocrystallites and determination of their equilibrium shapes are discussed using Wulff construction and absolute surface energies depending on orientation. Energetics is studied considering the low-index surfaces (111), (110), and (100) of Ge and Si with different reconstructions such as (1 × 1), c(4 × 2), c(2 × 8), and (7 × 7) using an ab initio plane-wave-pseudopotential code. Examples of Ge nanocrystallites are.

The mechanism of rare-earth metal/Si(111) interface formation is found to be similar to the Stranski-Krastanov type within a wide range of temperatures. The properties of both 2D ordered nanostructures and 3D rare-earth silicide nanocrystallites are studied. Some results (thermal stability, work function, the binding energy of RE atoms in 2D domains and 3D silicide islands) are discussed for the first time.

The effect of rapid thermal annealing upon the properties of porous silicon+silicon carbide film structures is investigated. Significant transformation of the emission bands after rapid thermal annealing is discovered. Models of the observed processes are presented.

We investigated photoluminescence of nanocrystalline silicon in the visible range at room temperature within the framework of two effects: quantum size and dielectric amplification. The estimates of exciton binding energies E_exc showed that in the case of small quantum dots in vacuum these energies could be ~ 1 eV. It is a reason to consider an exciton recombination share to be large. The auger excitonic recombination was considered as well. It is shown that observed phenomena can be explained with excitonic recombination mechanism besides band-to-band recombination of free charge carriers.

Time-resolved visible photoluminescence (PL) of nanocrystalline silicon (nc-Si) films obtained by laser ablation is described and discussed. The PL has the emission spectrum ranging from ~ 1.4 to 3.2 eV with PL relaxation time in the range of 50 ns - 10 µs. The relation between time-resolved characteristics (intensity, emission spectra, relaxation times, their temperature dependencies) and structural, dielectric properties (size and shapes of Si nanocrystals (NC), oxide phase of NC coating, porosity) were studied. To explain experimental results we consider a PL model in which absorption and emission of photons take place in quantum-sized Si NC. It implies that dynamically coupled subsystems of free charge carries and excitons take part in recombination. Slow (S, τ > 50 ns) band of PL is connected with low-dimensional exciton localized in Si NC. High intensity of nc-Si PL as compared with bulk silicon (c-Si) is determined not only by amplification of a radiative recombination channel, but also by damping of the nonradiative one. It was shown that in the temperature range of 150-300 K, relaxation times of PL observed in the range 50 ns-1 ms were related to nonradiative processes. The mechanisms of nonradiative recombination are considered.

The coupling constant in electron-phonon interaction is a very important issue in nanoscale applications. We have measured this constant in heavily doped silicon. Electron-phonon interaction is proportional to T⁶ and the coupling constant is found to be 1.5 × 10⁸ W/K⁵m³, which is about one tenth of the value in normal metals.

A surface conductivity of the samples with silicon-adsorbate surface phases on Si(100) was measured in ultra-high vacuum by the four-point probe method at room temperature. It is shown that surface phases act as conductive channels. Surface phases Si(100)c(8 × 2)-Au, Si(100)5 × 1-Au, Si(100)√26 × 3-Au enhance conductivity of the silicon sample, surface phase Si(100)2 × 3-Na reduces conductivity, surface phase Si(100)4 × 3-In has no influence on conductivity. A possible mechanism of the surface conductance is suggested.

Growth conditions of CrSi₂ and Mg₂Si quantum dots, their sizes and density on Si(111) substrates and optical properties of new materials were investigated. Technologies of CrSi₂ and Mg₂Si island formation on Si(111) were proposed. Two direct interband transitions at 0.95 eV and 1.30 eV were observed in CrSi₂ quantum dot materials. It was shown that Mg₂Si quantum dots do not influence strongly optical properties of silicon substrate.

Localization of light in the vicinity of a microcavity layer incorporated in a photonic crystal of porous silicon leads to 150-fold enhancement of the second - harmonic intensity and 30-fold enhancement of Raman scattering around the microcavity mode.

The surface morphology and current-voltage characteristics of 3 nm thick CaF₂ layers are presented. The layers have been grown by molecular beam epitaxy on a 50 nm thick Si buffer at different substrate temperatures. Those deposited at low and high temperatures have very good insulating properties with electrical breakdown fields of about 10⁷ V/cm.

Electronic structure model of the lead phthalocyanine (PbPc) stacking-fault nanostructure is proposed. Semi-empirical molecular orbital calculations show 0.6e charge transfer from the lead atom to the macrocyclic ring of the PbPc molecule. Stack of PbPc molecules is considered as a metal-filled nanotube. This allows for the first time quantitative interpretation of the earlier observed switching effect in the PbPc films. 1D quantum transport in the nanostructure is discussed and charge carrier (polaron) effective mass is estimated.

The effect of nanometer dielectric films on the reflection of linearly polarized light from transparent or absorbing bulk substrate is investigated. Approximate formulas describing the contribution of such layers to Fresnel reflectivity for s- and p-polarized light are obtained. It is shown that approximate expressions describing the differential reflectivity can be used for unambiguous determination of the thickness and refractive index of nanometer-scale films.

Green phosphors for high-resolution displays were formed from sol-precursors onto porous layers of anodic alumina (Al₂O₃). High-resolution near-field cathodoluminescence study reveals these films treated at relatively low temperatures (< 200 °C) to show bright luminescence at 480 and 540 nm from 200-300 nm clusters consisting of xerogel globules of about 50 nm in diameter.

Sol-gel process is shown as a promising synthetic route to fabricate three-dimensional photonic crystals doped with luminescent lanthanides. Using silica and Tb-doped titania sol the colloidal crystals with photonic stop band ranging from 480 to 550 nm have been developed, thus fitting the ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. Pronounced inhibition of optical transitions of Tb³⁺ ions was observed.

Sol-gel derived TiO₂ films containing 40 wt. % Eu₂O₃, were fabricated onto porous anodic alumina by spin-on deposition. Strong room temperature europium photoluminescence, with a maximum at 617 nm, was observed. The dependence of photoluminescence intensity on xerogel amount and temperature has been revealed.

The growth of Cu on clean and hydrogen-terminated Si(111) surfaces is studied in situ by low energy electron microscopy (LEEM). After completion of the "5 × 5" layer not only regular-shaped three-dimensional islands reported before are observed but also irregular-shaped two-dimensional islands. On the hydrogen-terminated Si(111) surface the formation of the "5 × 5" structure is suppressed and nanoscale islands are formed preferentially at the step edges and domain boundaries. This is attributed to the enhancement of the surface migration of Cu atoms by the elimination of the surface dangling bonds. Many LEED spots from the nanoislands move with electron energy, which indicates that the islands are faceted. From the analysis of the LEED pattern it is concluded that the nanoislands are the (111)-oriented β-phase Cu-Si compound and are terminated by (111), {5 5 4} and {15 16 13} faces.

The method for calculation of layer-periodic metal nanoparticle structure transmission and reflection is proposed. Correlation effects in close-packed monolayers and size dependence of metal particle optical constants are taken into account. The dependence of spectral characteristics of silver nanosphere monolayers near the surface plasmon frequency has been investigated at various particle concentrations and sizes. The long-wave shift of the plasmon resonance with increasing fitting factor is shown. Formation of the photonic stopband accompanied by variation of a plasmon absorption band structure has been established.

We have built a measuring system for investigations on electrical conductance of nanowires. Our measurements concern nanowires formed in both magnetic and nonmagnetic metals. The statistical results (histograms) of the quantization are compared for magnetic and nonmagnetic nanowires. The results of conductance quantization in cobalt nanowires are presented before for the first time.

In situ Hall measurements at room and elevated temperatures of chromium (Si(111)√3 × √3/30°-Cr) and iron (Si(111)2 × 2-Fe) surface phases are presented. The ultrathin chromium surface phase displays the p-type semiconductor properties with the activation energy of 0.12 eV, while the ultrathin iron surface behaves as a metal with low hole concentration.

The effect of symmetry and boundary conditions on the critical parallel magnetic field H_c2|| in superconductor/normal metal (S/N) nanostructures has been examined both experimentally and theoretically. The H_c2|| versus temperature (T) dependence was strongly influenced by the sample symmetry plane position. Regard of the symmetry effect allows to determine more definitely parameters of any model describing the superconducting state of S/N superlattices.

Alkali metals deposited on suitable substrates are model systems to investigate the formation of self-assembled metallic nanowires. The aim of this review is to provide a comparative study of the atomic geometry and the mesoscopic properties of self-assembled alkali nanowires. The self-assembling is controlled at the atomic scale via the topography deduced from Scanning Tunnelling Microscopy. The long range ordering of the nanowires can be easily followed by grazing incidence x-ray diffraction proposing a model to study the probability distribution of the nanowires at the surface. Self-assembling of Cs adatoms on III-V(110) surfaces is the result of competing driving forces: a short range attractive force inducing the coupling of Cs adatoms within the chain and a long range dipole-like repulsive interaction keeping the chains apart from each other.

Our research focuses on the modeling of primary photoevents (electronic excitation energy transfer and photoinduced electron transfer) realized in natural structurally well-organized photosynthetic systems. Nanoscale self-assembling multiporphyrin arrays with well-defined geometry, controllable number and properties of interacting components were formed in solutions and polymeric films using the combination of covalent and non-covalent binding interactions. On the basis of steady-state, time-resolved picosecond fluorescence (Δ_1/2 ≈ 30 ps) and femtosecond pump-probe (Δ_1/2 ≈ 280 fs) spectral-kinetic data at 77-300 K it has been found that the non-radiative relaxation of excited states in these models is due to the competition between the singlet-singlet energy transfer (within < 10 ps) and electron transfer (within 600 fs – 700 ps). The interplay between the above processes depends on the structure, spectral and redox properties of interacting subunits and may be driven by temperature and solvent polarity. The mechanisms of relaxation processes are discussed.

A brief review of some approaches which can be used to govern the conduction as well as electron and light emission properties of island metal films on dielectric substrates is given. Two approaches are considered: (1) the control of the film structure by evaporation of metal onto grooved substrates, which allows preparation of chain island films, and (2) evaporation of organic molecules onto the island films that results in formation of planar metal-organic nanocomposites. Some peculiar properties of these systems such as voltage-controlled negative differential resistance and electroluminescence are described and discussed.

Zeolites with less-than-nanometer cavities within the regular crystal lattice incorporate silver and copper species produced by the hydrogen reduction of the ion-exchanged matrices. The metals were stabilized within the mordenite in the form of both few-atomic clusters and nanoparticles (< 50 nm). The clusters and nanoparticles were discovered by means of diffuse reflectance spectroscopy (DRS). Their contribution into optical absorption was calculated by the Mie theory for nanoparticles and with the quantum chemical ab initio MOLCAO method for small clusters.

Two preparation method of ultradispense Ag/Cu bimetallic nanoparticles are presented. They include the reduction of insoluble metal compounds or metal ions in aqueous solutions. the reduction process is monitored by optical absorption spectroscopy.

A novel approach to incorporate different polymers into micro- and nanocapsules fabricated by means of layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes on colloidal particles is proposed. This method comprises two stages. At first, the polymers, which are supposed to be incorporated, precipitate on the surface of colloidal particles. This can be done either by complexation of polyelectrolytes with multivalent ions or by adding miscible non-solvents. Then stable LbL assembled polyelectrolyte shells are formed. After the core decomposition the inner polymer molecules are released from the wall but captured by the outer shell and floating in the capsule interior. The possibilities to encapsulate a wide class of charged and non-charged polymers were demonstrated on the examples of sodium poly(styrene sulfonate) (PSS) like a polyanion, poly(allylamine hydrochloride) (PAH) like a polycation and dextrane like non-charged water soluble polymer.

The possibility of using the layer-by-layer (LbL) technique for the formation of latex-core TiO₂-shell particles and TiO₂ hollow spheres was established. The TiO₂ colloid was produced by the sol-gel technique. Composite organic-inorganic particles were formed by the controlled assembly of the preformed titania nanoparticles in alternation with oppositely charged polyelectrolytes onto latex microspheres. These hybrid core-shell particles were calcined to produce TiO₂ hollow spheres with predetermined diameters.

The diffusion of individual rhodamine 6G molecules in ethylene glycol close to a glass interface has been studied. Diffusion coefficients ate analyzed by photon burst analysis and real time wide field microscopy. It is shown by photon burst analysis that the diffusion of dye molecules becomes slower near the interface of the droplet and the glass as compared to the bulk value. We attribute this to anomalous diffusion of molecules close to the interface, due to attachment and detachment of molecules caused by molecule surface interaction. This has been studied by wide field microscopy.

We report on recent progress in the synthesis, surface modification and functionalizaton, and fabrication of polymer composites, and their use in light-emitting and photonic devices for a number of chemically grown quantum dots: CdSe, CdTe, Cd_xHg_1-xTe and HgTe.

Fast electrochemical impedance spectroscopy technique has been developed for in situ simultaneous investigation of the AC frequency and DC potential dependence of the nanostructures impedance and their electrochemical transformations monitoring. The technique based on the time domain analysis of the response to the digitally generated multi-frequency excitation provides the real-time three-dimensional data visualization in Windows and does not require any additional software.

It is shown that the tip induced oxidation process can be considered as an electrochemical anodic oxidation. The model of the oxidation kinetics is proposed. It is shown that film resistance, relative humidity, applied voltage and duration of oxidation influence the rate and spatial resolution of the process. The formation of 8 nm oxide patterns by tip induced oxidation is demonstrated.

Technological conditions for electrodeposition of luminescent CdS into porous anodic alumina are determined on the basis of calculation of thermodynamic equilibria in the CdS-H₂O electrochemical system. A potential-pH diagram of CdSO₄-Na₂S₂O₃-H₂O solution is used to determine the deposition mechanism. Possibility of CdSe and ZnSe nanowire fabrication into nanopores is demonstrated.

Thin films of copper phthalocyanine (CuPc) – polystyrene (PS) composites were prepared by laser evaporation in vacuum. The crystalline structure of CuPc nanoparticles and composite film morphology were investigated by TEM, AFM and optical absorption method in relation with DC electrical conduction and adsorption-resistive response to NO₂.

Micro- and nanostructures are of exponentially creasing importance in our information community. The realisation of those structures makes use of the very successful technology used already for microelectronics, i.e. corresponding material and microstructuring processes (lithography and etching). The combination of these technologies to quite new devices, complex systems, i.e. MEMS and MOEMS is the great challenge. The paper presents our results mainly obtained in realising complex sensors for scanning probe microscopy [1-9].

The atomic scale ordering and properties of cubic silicon carbide surfaces are investigated by room and high temperature scanning tunneling microscopy. In this review, I focus on the Si-terminated β-SiC(100) surfaces only. Self-formation of Si atomic lines and dimer vacancy chains on the β-SiC(100) surface is taking place at the phase transition between the 3 × 2 (Si rich) and c(4 × 2) surface reconstructions. Using a rigorous protocol in surface preparation, it is possible to build very long, very straight and defect free Si atomic lines, forming a very Large superlattice of massively parallel lines. These self-organized atomic lines are driven by stress. They have unprecedented characteristics with the highest thermal stability ever achieved for nanostructures on a surface (900 °C) and the longest atomic lines ever built on a surface (µm scale long). Investigating their dynamics, we learn that their dismantling at high temperature results from collective and individual mechanisms including one-by-one dimer removal. Overall, this is a model system especially suitable in nanophysics and nanotechnologies.

Using a scanning reflection electron microscopy (SREM) and a high-temperature scanning tunneling microscopy (STM), we study formation processes of Si and Ge nanostructures on Si substrates covered with ultrathin SiO₂ films. It is found that windows are formed in the SiO₂ films by focused electron beams used for SREM or field emission (FE) electron beams from STM tips during heating of the samples. Ge nanoislands are formed by Ge deposition into the windows in the ultrathin SiO₂ films and subsequent annealing of the samples. The islands are formed only at the window positions. Si or Ge nanocrystals are also formed in the windows produced with the FE electron beams by selective growth using Si₂H₆ or GeH₄ gases. It is further found that Ge nanoislands with about 7 nm size and ultrahigh density (>10¹² cm^-2) are grown on the ultrathin SiO₂ films. These nanoislands can be manipulated by STM when they are separated from Si substrates by the ultrathin SiO₂ films. These results imply new methods for forming Si and Ge quantum structures at given areas.

The realization and the study of artificially layered high temperature superconductivity systems is a field of growing interest for basic physics and practical applications. Here a non exhaustive review of some of the most interesting results in this area is given, with particular attention to three main classes of HTS artificial structures: YBa₂Cu₃O_x based multilayers, Bi₂Sr₂Ca_n-1Cu_nO_x based layered systems and infinite layer based superlattices. A brief overview of the present applications and of the potential perspectives is also proposed.

In this report new semi-spherical SiGe/Si nanostructures are presented. Epitaxial islands of 30 - 40 nm in base diameter and 11 nm in height, and with a number density about 6 × 10¹⁰ cm^-2 were produced on (001)-Si by MBE growth of Si/Si_0.5Ge_0.5 layers with in situ implantation of 1 keV As⁺ ions. It was found by XTEM that the islands have a complicated inner structure and consist of semi-spherical nano-layers of different SiGe composition. Their nature and possible applications are discussed.

We present experimental results on the growth of InAs self-organized quantum dots on patterned substrates via molecular beam epitaxy. Luminescence spectra of these quantum dots have been studied.

We have developed the AIX 2000 G3 HT MOVPE machine for large scale production of nitride semiconductors. Extensive numerical modeling of the reactor chamber has enabled us to establish process windows for the growth of nitride quantum wells. We report excellent wafer-to-wafer, on wafer and run to run uniformities across all wavelength regions accessible to the InGaN material system. Laser action in GaN epitaxial layers and InGaN/GaN quantum well heterostructures at optical excitation was achieved in the spectral range from 370 nm to 470 nm. The working temperature reached 580 K for the best multiple quantum well structures.

Different methods of nanostructure fabrication with scanning probes are reported. We show square holes and more complex patterns created on dithienylpyrrole Langmuir-Blodgett films. The shape of nanostructures is found to be strongly dependent on the film morphology and formation methods.

The work is focused on the most serious problems of MFM, connected with the development of new types of cantilevers, fabrication of calibration structures and evolution of the method itself. We present a construction of the silicon cantilever with the two-layer coating: magnetic and protective. The structures for calibration and the approach for measurements of objects with small magnetization are shown.

The paper summarises our recent results on synthesis and investigation of photoluminescence (PL) from Er and Tb doped microporous xerogel solids mesoscopically confined in porous anodic alumina. Possible mechanisms, driving the enhancement of lanthanides PL are discussed.

The technology of pillar microstructure formation based on anodic oxides of aluminum and tantalum by the multistep electrochemical method is developed. The method allowed to produce a nanometer size thin-film active elements of a three-electrode type. The main features of the developed technology and main geometrical sizes of structured layers are presented.

New stable electroluminescent nanosize materials on the basis of amorphous triazinstylbene and naphthalimide derivatives, luminescing polynaphthalimide, sol-gel prepared organic-inorganic porous polysilane doped with organic Eu(III) complex, and porous alumina with organic phosphor are presented.

A number of experimental data is presented which demonstrate the realization of the conception of quantum dot-in-photonic dot structure. Chemically sythesized CdSe nanocrystals are incorporated into both monolithic and hollow polymethylmethacrylate micron-sized microspheres. The emitting properties of nanocrystals are strongly modified inside microspheres resulting in a number of sharp discrete modes. The effective coupling of broad nanocrystal emission with quantized photon states in spherical microcavity brings the ability to create room temperature nearly thresholdless microlasers with optical pumping.

The influence of a porous layer on silicon tips upon the electron field emission has been investigated. The porous silicon layer obtained by electrochemical method and stain-etching was studied. The improvement of emission parameters in comparison with those for single-crystalline Si tips (without porous layer) was observed at some growth conditions. At lower emission current densities the non-monotonous current-voltage characteristics were revealed. The effect of the porous silicon layer upon the electron field emission was explained by the formation of asperities (fibres) on the silicon surface. The formation of porous silicon is simulated with the of single-pore approach.

A method of focusing of Bessel light beams of zero and first orders is proposed for the first time and studied theoretically and experimentally. This method allows to form axially-symmetric light fields with radii of its central bright or dark spots changing linearly with axial coordinate. The minimum possible spot dimensions are on the order of a wavelength. A new optical element for production of converging Bessel beams is proposed. It is suggested to use focused Bessel beams in nanotechnologies for guiding of cold atoms.

The comprehensive gas-phase model of silane (SiH₄) decomposition during plasma enhanced chemical vapor deposition (PECVD) of amorphous silicon including the formation of stable negative hydrogenated silicon ion clusters containing 30 silicon atoms is suggested. The kinetics of the silane decomposition and the reaction products accumulation are computed.

Methods for synthesis of nanostructured metallized fiber materials based on the polyacrylonitrile and cellulose modification and ion-exchange reaction are developed. Structure and element analysis of synthesized materials is carried out. It is shown that these materials contain atoms of deposited metals and have microdispersed or disordered cluster structure. Electrical properties of nickel and cobalt containing materials are investigated. Design of multilayers flexible electromagnetic shields and microwave absorbers are presented. Developed microwave absorber has non-resonance frequency characteristic in the frequency range from 1.5 to 118 GHz.

In this paper, different factors which influence carrier transport in Si/CaF₂ multi quantum wells and superlattices are reviewed. It is shown that when CaF₂ thickness in each period is above ≈ 1 nm Si/CaF₂ multilayers behave as an insulating structure. Charge exchange between the silicon substrate and Si/CaF₂ layers occurs, giving rise to impedance frequency dependent effects. Carriers injected into the multilayers are trapped and form a space charge region near the injecting interface. The conduction mechanism seems to be thermally activated above 200 K, involving a continuous distribution of trapping levels in the range of 0.3-0.8 eV. In the superlattices with CaF₂ below 1 nm, a Poole-Frenkel mechanism of carrier transport has been demonstrated at temperatures below 280 K. At higher temperatures, an important increase of current through the layers is observed above a threshold voltage of 4-5 V, which is accompanied by hysteresis effects and current instabilities probably involving structural changes of the material. Electroluminescence is observed under these conditions, with a spectrum similar to those of photoluminescence.

An overview of reverse biased porous silicon (PS) light emitting diodes (LEDs) is presented. Emphasis is given to LED designs and technological processes for PS fabrication. Basic parameters of PS LEDs are analyzed with particular attention to their application in optoelectronics. A silicon integrated optoelectronic unit including a reverse biased PS LED connected with a photodetector by an alumina waveguide is considered for intra-chip optical interconnects. The other use the reverse biased PS LEDs in microdisplay devices is also discussed. Advantages and disadvantages of PS LEDs for optoelectronics are exposed.

Energy transfer processes in the InGaN/GaN multiple quantum well (MQW) laser heterostructures are studied using photoluminescence (PL), photoluminescence excitation (PLE) and laser spectroscopy in a wide interval of temperatures (4.2-300 K) and excitation intensities (0.01–1 MW/cm²). It was shown that there are two efficient channels of the energy transfer to the states localized inside the InGaN active layers of both types of the MQWs lasing in the violet (400-440 nm) and in the blue (450-470 nm) spectral regions.

A novel design of cascaded resonant tunneling device is proposed and theoretically described. It consists of diodes with linearly increasing area connected in series. There are with separate contacts to interconnecting doped layers between the diodes. The device is shown to have a predictable successive diode quenching as well as an allowance for differential voltage measurements detecting this quenching. These features are useful to perform an analog-to-digital signal conversion.

Far infrared photoresponse of the QHE device operating at cyclotron resonance has been investigated. The possibility of the detector band tuning at the simultaneous increase of the magnetic field and the 2D electron concentration (due to the persistent photoconductivity after band-gap illumination) is demonstrated. Time characteristics of the response have been studied.

Effect of trap energy levels on carrier transport across nanosize structures Si/CaF₂ is considered. The charge accumulated by these traps and subsequent discharge of the traps are found to result in the shift of the current origin as well as in the appearance of negative differential resistance region on current-voltage characteristics. Deep and shallow traps are observed to control the transport phenomena at high and low temperatures, respectively.

Silicon single electron transistors with a side gate have been fabricated on a heavily doped silicon-on-insulator substrate. I-V characteristics of all devices have a Coulomb blockade region. Electrical conductivity of single electron transistors demonstrates long term relaxation after cooling to 4.2 K. At temperatures below 20 K long-term relaxation of the source-drain current after switching of the gate voltage has been observed.

The intersubband electron scattering rates in one-dimensional Si MOS-structure are calculated. The results obtained are in a good agreement with known theoretical insight.

β-FeSi₂ has been shown to have a minimum direct band gap of 0.87 eV [1], with a large absorption coefficient above the fundamental edge (10⁵ cm^-1) [2]. In this paper we report the formation of β-FeSi₂ by co-sputtering of Fe and Si, for the use in solar cell applications.

Quantum transport characteristics of an array of semiconductor quantum dots coupled to superconducting leads are studied under the effect of magnetic field. The conductance of this mesoscopic device was deduced by solving the Bogoliubov-de Gennes (BdG) equation. The energy dependence of the normalized conductance show a resonance behavior for different transparency of the superconductor (S) - semiconductor (Sm) interface. The magnetic field dependence of the conductance shows quantization in units of 2 e²/h with resonance.

Quantum conductance properties of a mesoscopic device are studied. The device is composed of a semiconductor between two superconducting electrodes. The results show the importance of the differential conductance measurements in order to get information about the subgap structure.

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