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The study was carried out by LEED, AES, EELS, and AFM methods. Films of Fe/Si(001)2 × 1 were obtained at substrate temperatures of 30°C and source temperatures of 1250°C. Wetting layer (WL) Fe on Si(001)2 × 1 was formed by two-stage annealing at temperatures and thicknesses of 500 and 250°C and 1 monolayer (ML) and 3 ML, respectively. Analysis and interpretation of the data obtained, taking into account possible reaction patterns, showed that after annealing at 1 ML thickness, the Fe composition corresponded to 2 ML Si/Fe. Further, at 2 ML, it changed to Fe/Si/Fe, at 3 ML, it changed to Fe–FeSi, and after annealing, to FeSi. At 4 ML, there was formation of FeSi/FeSi2 film. And, further, at 7 ML and 10 ML, the composition of the films became Fe3Si/FeSi2 and, respectively, Fe/Fe3Si/FeSi2. At the same time, the upper Fe3Si layers were coated with 0.6 ML and the Fe layers with 0.3 ML of segregated Si atoms, which number increased, after annealing at 250°C, to 0.6 ML in the latter case. In the obtained Fe film, the size and average grain height were 10−20 nm and, respectively, ∼0.4 nm. [ABSTRACT FROM AUTHOR]

Many body effects in the wetting layer (WL)-double quantum dot (DQD)-metal nanoparticle (MNP) structure have been studied by modeling the Coulomb scattering rates in this structure. The strong coupling between WL-DQD-MNPs was considered. An orthogonalized plane wave (OPW) is assumed between WL-QD transitions. The transition momenta are calculated accordingly to specify the normalized Rabi frequency on this structure, considering the strong coupling between the WL-DQD-MNP structures. This approach is important for realizing scattering rates, including in-and-out capture and relaxation rates, which are essential for specifying the type of structure used depending on the optimum value of the scattering time required to fit the application. The QD hole capture rate is the highest, and the hole capture times are the shortest. The relaxation times are less than the electron capture times by one order, while they are half of the hole capture times. The capture rates increase with increasing distance R between the DQDs and the MNP. High tunneling increases hole-capture rates and changes the relaxation rates, showing the importance of tunneling in controlling the scattering rates. [ABSTRACT FROM AUTHOR]

The quantum dots embedded in nanowires are of great interest for their applications in nanolasers and quantum emitters. In this regard, the electronic confined states and optical properties of an InAs conical quantum dot located on an InAs wetting layer and embedded in an infinite GaAs nanowire are investigated theoretically. This is accomplished by numerically solving the Schrodinger equation using the effective mass approximation. The results show the existence of an energy continuum for each cannel of angular momentum whose lower limit raises by the angular momentum. This causes discrete bound states of higher angular momentum to lie in the continuum of the lower ones. On the other hand, although the confined energy levels decrease smoothly by increasing the nanowire radius, their decline by dot radius and height represents some step-like features. This effect could be explained based on the relative concentration of the electron probability density in the dot and wetting layer. Finally the oscillation strength for intersubband transition between confined energy states of the system have been investigated. [ABSTRACT FROM AUTHOR]

During Stransky Kratsanov growth process, quantum dots with non-uniform shapes appear in a random way. Semi-prolate and oblate shapes are among the most likely nanostructures to be self-organized due to their dynamic stability on a substrate. It has been demonstrated that temperature and wetting layer play a very important role in this distribution. In these conditions, physical properties of the deposed semiconductor materials depend on the final structure obtained during the growth process. S i 0. 7 G e 0. 3 / S i is a semiconductor mainly intended for the manufacture of optoelectronic detectors or in quantum transport. Thus it is important to understand their thermal properties such as heat capacity, entropy and Helmholtz energy. Finite Element Method is used in our calculation to solve numerically the Schrödinger equation for a confined electron in semi-prolate and semi-oblate S i 0. 7 G e 0. 3 / S i quantum dots. We have taken into account the size of the wetting layer thickness, the strain potential induced by lattice mismatch as well as the temperature. The energy spectrum is then used to determine the thermal characteristics using the statistical Boltzmann–Gibbs distribution. The internal energy of system, entropy, heat capacity, and Helmholtz free energy are determined as a function of the sizes of the quantum dots and wetting layer. The analysis of the behavior of thermodynamic properties presented in this study is considered as complementary and even necessary information to master for a good performance of optoelectronic devices. • Investigated the growth process of quantum dots with non-uniform shapes during Stransky Kratsanov growth. • Explored the thermal properties (heat capacity, entropy, and Helmholtz energy) of Si0.7Ge0.3/Si Semi-prolate and oblate quantum dots. • Studied the dependence of thermodynamic properties on quantum dot dimensions and wetting layers sizes. • Highlighted the relevance of understanding thermodynamic behavior for optimizing optoelectronic devices. [ABSTRACT FROM AUTHOR]

Layered nanofilms based on Fe, Co, and Cu were grown on Si(001)2×1-Cu wetting layers with thicknesses of 1 and 2 ML and studied using the AES, EELS, and LEED methods in an ultrahigh vacuum chamber. After unloading into air, the samples were studied by AFM and MOKE methods. It was found that an increase in the thickness and annealing of the Si(001)2×1-Cu wetting layer increase the agglomeration of nanofilms and, as a consequence, their magnetization and coercive force. Although, annealing the Cu wetting layer reduces the degree of squareness of the magnetic hysteresis loop.

Abstract Oxide/metal/oxide (OMO) layer stacks are used to replace transparent conductive oxides as front contact of thin-film solar cells. These multilayer structures not only reduce the overall thickness of the contact, but can be used for colouring of the cells utilizing interference effects. However, sheet resistance and parasitic absorption, both of which depend heavily on the metal layer, should be further reduced to reach higher efficiencies in the solar cells. In this publication, AgO X wetting layers were applied to OMO electrodes to improve the performance of Cu(In,Ga)Se2 (CIGS) thin-film solar cells. We show that an AgO X wetting layer is an effective measure to increase transmission and conductivity of the multilayer electrode. With the presented approach, we were able to improve the short-circuit current density by 18% from 28.8 to 33.9 mA/cm2 with a metal (Ag) film thickness as low as 6 nm. Our results highlight that OMO electrodes can be an effective replacement for conventional transparent conductive oxides like aluminium-doped zinc oxide on thin-film solar cells.

The dewetting process is crucial for several applications in nanotechnology. Even though not all dewetting phenomena are fully understood yet, especially regarding metallic fluids, it is clear that the formation of nanometre-sized particles, droplets, and clusters as well as their movement are strongly linked to their wetting behaviour. For this reason, the thermodynamic stability of thin metal layers (0.1–100 nm) with respect to their free energy is examined here. The decisive factor for the theoretical considerations is the interfacial energy. In order to achieve a better understanding of the interfacial interactions, three different models for estimating the interfacial energy are presented here: (i) fully theoretical, (ii) empirical, and (iii) semi-empirical models. The formation of nanometre-sized gold particles on silicon and silicon oxide substrates is investigated in detail. In addition, the strengths and weaknesses of the three models are elucidated, the different substrates used are compared, and the possibility to further process the obtained particles as nanocatalysts is verified. The importance of a persistent thin communication wetting layer between the particles and its effects on particle size and number is also clarified here. In particular, the intrinsic reduction of the Laplace pressure of the system due to material re-evaporation and Ostwald ripening describes the theoretically predicted and experimentally obtained results. Thus, dewetting phenomena of thin metal layers can be used to manufacture nanostructured devices. From this point of view, the application of gold droplets as catalysts to grow germanium nanowires on different substrates is described.

Oxide/metal/oxide (OMO) layer stacks are used to replace transparent conductive oxides as front contact of thin-film solar cells. These multilayer structures not only reduce the overall thickness of the contact, but can be used for colouring of the cells utilizing interference effects. However, sheet resistance and parasitic absorption, both of which depend heavily on the metal layer, should be further reduced to reach higher efficiencies in the solar cells. In this publication, AgOX wetting layers were applied to OMO electrodes to improve the performance of Cu(In,Ga)Se2 (CIGS) thin-film solar cells. We show that an AgOX wetting layer is an effective measure to increase transmission and conductivity of the multilayer electrode. With the presented approach, we were able to improve the short-circuit current density by 18% from 28.8 to 33.9 mA/cm2 with a metal (Ag) film thickness as low as 6 nm. Our results highlight that OMO electrodes can be an effective replacement for conventional transparent conductive oxides like aluminium-doped zinc oxide on thin-film solar cells. [ABSTRACT FROM AUTHOR]

We exhibit both experimentally and theoretically a novel growth mode for the epitaxy of AlGaN quantum dots (QD), where they are eventually produced without their usual surrounding wetting layer (WL). If the generic evolution of QD is ruled by the elastic relaxation and capillary effects, evaporation occurs here on a time scale similar to that of growth. Using a dedicated surface diffusion model accounting for elasticity, wetting, and anisotropy, we evidence numerically different kinetic regimes as a function of the evaporation flux, which rationalizes the experimental outcome. The resulting QD are characterized by enhanced optical properties compared to the common QD with a WL. These nanostructures are promising candidates for deep-ultraviolet-light-emitting diodes. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical study of the second harmonic generation (SHG) in a coupled lens shaped InAs/GaAs quantum dots is presented within the framework of the compact density-matrix approach and the finite difference method. In literature, many theoretical studies have neglected the wetting layer (WL) effect. As well, other effects such as the pressure, the external electric field, the temperature and the structural dimensions are not introduced together. Furthermore, in many researches only a single quantum dot (SQD) with and without wetting layer is investigated. What is done in this work, a detailed and comprehensive study of a vertically coupled lens-shaped InAs/GaAs coupled to a WL is presented under the external proofs effects mentioned above. Also, the structural dimensions, the electric field, the relaxation rate, the hydrostatic pressure, and the temperature effects are explored in details and the SHG is optimized. We have found out that the wetting layer has been shown to be so influential on the SHG magnitude and on the corresponding resonant energy. So, calculated results show that a strong SHG coefficient can be obtained by choosing a group of the optimized structural dimensions and the external proofs previously mentioned above. With a good choice of these parameters, it's found that the SHG coefficient reaches the order of magnitude of 10−7 m/V, which is larger than the corresponding values obtained with a SQD. Besides, obtained results revealed that a red or a blue-shifted energy can be obtained. This behavior in the SHG gives a new degree of freedom in regions of interest for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

• The 3-dimensionally confined CQDNW energy states tend to energy continuum of the NW in sufficiently strong magnetic fields. • In the presence of a magnetic field, the m = −1 states are more bound to the CQDNW system. • The OS for E 01 → E ± 12 transitions first tends to 0, then grow by magnetic field, due to the dipole transition's phase change. In this paper, we have investigated theoretically the effect of the external magnetic fields on the electronic structuctures and optical properties of a nanosystem consisting of a conical InAs quantum dot embedded in an infinite GaAs nanowire. To this end the Schrodinger equation have been solved numerically utilizing the effective mass approximation to calculate the confined energy states and binding energies of the system. The findings demonstrate that under the effect of the magnetic fields, the energies of confined states in the Quantum Dot of +|m| and −|m| angular momentum have been separated and increased toward the energy continuum of the nanowire. It has been shown that the lower limit of energy continuum of ± m states are split which results in different binding energy for states of +|m| and −|m| angular momentum. Finally, the oscillator strength for intersubband transitions between the system's confined energy states has been explored in order to discuss the optical properties of the described system. [ABSTRACT FROM AUTHOR]

Using the finite element method, we have performed a systematic study on the ground-state binding energy (Eb) of a donor impurity confined in a InAs/GaAs conical quantum dot (CQD) with wetting layer (WL) and a realistic finite confining potential. The simultaneous effect of the applied electric and magnetic fields as well as the influence of an intense laser field have been performed on the Eb within the effective mass approximation. The band non-parabolicity effect is also considered using the energy dependent effective mass approximation. It has been shown that the Eb is highly dependent on the internal and external CQD structure parameters such as radial thickness, height and WL thickness, external electric, magnetic fields and intense laser field. The results we have obtained show that a quite significant contribution of the WL effects on the ground state energy and the (Eb) has found at small values of the cone radius. In the low confinement regime, the effect of the conduction band non-parabolicity becomes gradually smaller as the value of the cone radius increases and the influence of high-frequency laser increases with the non-parabolicity effect in the regime of small QD radius. Our results are in good agreement with those obtained in the literature. [ABSTRACT FROM AUTHOR]

Copyright of Albahir Journal is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract In this paper, we theoretically report competition behaviour of size and strain effects on the InAs/GaAs quantum dots (QDs) eigenenergies, the envelop functions and also transition energies of the z-polarized WL-to-S states with varying the QD height and WL thickness. The obtained result for the bounded ground state of S implies that although the size-dependence behaviour with the inclusive of the strain effects generally resembles that of unstrained case, the energy values have changed appreciably for the short dots with value of 200 meV and for tall dots with nearly 300 meV. The competition behaviour of strain and size effects on the electronic properties of the structure revealed that the WL state is more sensitive to the size and WL thickness in presence of strain. For the weakly bounded WL state, the envelop function was localized in the wetting layer or bulk regions as a continuum state for the thick WL within the strain-modified structure. The calculated optical wavelength from z-polarized transition of WL-to-S in the strain-modified structure agrees well with previous experimental photoluminescence data from other studies. Highlights • Truncated pyramidal-shaped QDs have been investigated with considering strain and size effects. • The strain distribution was calculated using the continuum elastic theory. • The energy of the bounded ground state of S shifted due to the strain effect. • The WL-state is more sensitive to the size and WL thickness variation in presence of strain. • The envelop function act as a continuum state for the thick WL within the strain-modified structure. [ABSTRACT FROM AUTHOR]

Copyright of Albahir Journal is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The practical realization of epitaxial quantum dot (QD) nanocrystals led before long to impressive experimental advances in optoelectronic devices, as well as to the emergence of new technological fields. However, the necessary capping process is well-known to hinder a precise control of the QD morphology and therefore of the possible electronic structure required for certain applications. A straightforward approach is shown to tune the structural and optical properties of InAs/GaAs QDs without the need for any capping material different from GaAs or annealing process. The mere adjust of the capping rate allows controlling kinetically the QD dissolution process induced by the surface In-Ga intermixing taking place during overgrowth, determining the final metastable structure. While low capping rates make QDs evolve into more thermodynamically favorable quantum ring structures, increasing capping rates help preserve the QD height and shape, simultaneously improving the luminescence properties. Indeed, a linear relationship between capping rate and QD height is found, resulting in a complete preservation of the original QD geometry for rates above ∼2.0 ML s −1 . In addition, the inhibition of In diffusion from the QDs top to the areas in between them yields thinner WLs, what could improve the performance of several QD-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the electronic properties of (In,Ga)N/GaN coupled wetting layer-quantum dot system using the numerical approach. The finite element method code is used to solve the Schrödinger equation, in the presence of the impurity. In our model, parallelepiped-shape, circular and square based-pyramidal and their wetting layers embedded in GaN matrix were considered. Based on the single band parabolic and the effective mass approximations, the envelop function and its corresponding energy eigenvalue are obtained assuming a finite potential barrier. Our results reveal that: (1) the wetting layer has a great influence on the electronic properties especially for a small quantum dot and acts in the opposite sense of the geometrical confinement, (2) a wetting layer-dependent critical QD-size is obtained limiting two different behaviors and (3) its effect is strongly-dependent on the quantum dot-shape. [ABSTRACT FROM AUTHOR]

Morphological evolution of Ge layers on SiO 2 substrates grown by photo-excited chemical vapor deposition from GeH 4 was monitored in real time by recording (Ψ, Δ ) angles of spectroscopic ellipsometry and ex-situ analyzed by atomic force microscopy (AFM). Distinct Ψ - Δ trajectory shapes were demonstrated to discriminate the two-dimensional (2D) and three-dimensional (3D) growth modes. While the trajectory of 2D growth is characterized by a one-turn spiral, that of 3D growth consisted of three sections corresponding to initial wetting of the SiO 2 surface, creation of nucleation centers, and dot growth. The critical point where the system turns into 2D or 3D growth can be in situ identified in terms of the directions of the Ψ- Δ trajectories. AFM images revealed characteristic changes in the microstructure, including self-assembling dots and dots merging with one another. While the root-mean-square surface roughness increased linearly against film thickness, the maximum peak-to-valley height deviated once from linear dependence and later returned back to it, which reflected coarsening of dots and embedding of valleys between dots. [ABSTRACT FROM AUTHOR]

In view of the pore defect of vacuum glazing sealing layer, the research on side edge sealing of laser was made. The phase analysis of microstructure on sealing layer was investigated using scanning electron microscope (SEM) and energy spectrum analysis (EDS) to study the formation mechanism of sealing pores. The influence of laser power and welding rate on sealing edge porosity was researched. The results show that the sealing layer has evenly distributed bilayer structure of wetting layer with few pores caused by the residual gases between the solder particles (external) –melting layer with a large number of mutually disconnected isolated pores (inside). As the increase of laser power, the interface layer is compact and smooth and the pores decline in numbers. When the power exceeds a certain value, the interface becomes unsmooth with the increasing number of pores. The phenomenon of surface defects and blocky structures is generated with lower welding speed and greater energy output. On the other hand, the blocky structures, unmelted solders, pores and cracks are formed by the higher welding speed and smaller energy output. Therefore, the pore defect can be effectively avoided and reduced by the reasonable control of laser power and welding rate. [ABSTRACT FROM AUTHOR]