Despite its interest for CMOS applications, Atomic Layer Deposition (ALD) of GeO$_{2}$ thin films, by itself or in combination with SiO$_{2}$, has not been widely investigated yet. Here we report the ALD growth of SiO$_{2}$/GeO$_{2}$ multilayers on Silicon substrates using a so far unreported Ge precursor. The characterization of multilayers with various periodicities reveals successful layer-by-layer growth with electron density contrast and absence of chemical intermixing, down to a periodicity of 2 atomic layers.
We report on the investigation of morphology, magnetic and conductive properties of the mutilayered nanostructures [(Co$_{40}$Fe$_{40}$B$_{20}$)$_{34}$(SiO$_2$)$_{66}$]/[C]$_{47}$ consisting of the contacting magnetic (Co$_{40}$Fe$_{40}$B$_{20}$)$_{34}$(SiO$_2$)$_{66}$ nanocomposite and amorphous semiconductor carbon C layers. It is shown by Grazing-Incidence Small-Angle X-ray Scattering method that the ordering and the size of nanoparticles in the magnetic layers do not change profoundly with increasing of carbon layer thickness. Meanwhile, the electrical conductance and the magnetic properti…
Large-area growth of continuous transition metal dichalcogenides (TMDCs) layers is a prerequisite to transfer their exceptional electronic and optical properties into practical devices. It still represents an open issue nowadays. Electric and magnetic doping of TMDC layers to develop basic devices such as p-n junctions or diluted magnetic semiconductors for spintronic applications are also an important field of investigation. Here, we have developed two different techniques to grow MoSe$_2$ mono- and multi-layers on SiO$_2$/Si substrates over large areas. First, we co-deposited Mo and Se atoms…
The nucleation, distribution, composition and structure of Pd nanocrystals in SiO$_2$ multilayers containing Ge, Si, and Pd are studied using High Resolution Transmission Electron Microscopy (HRTEM) and X-ray Photoelectron Spectroscopy (XPS), before and after heat treatment. The Pd nanocrystals in the as deposited sample seem to be capped by a layer of PdO$_x$. A 1-2 eV shift in binding energy was found for the Pd-3d XPS peak, due to initial state Pd to O charge transfer in this layer. The heat treatment results in a decomposition of PdO and Pd into pure Pd nanocrystals and SiO$_2$.
We synthesize large-area graphene via atmospheric-pressure (AP) chemical vapor deposition (CVD) on copper, and transfer to SiO2 wafers. In contrast to low-pressure (LP) CVD on copper, optical contrast and atomic force microscopy measurements show AP-CVD graphene contains significant multi-layer areas. Raman spectroscopy always shows a single Lorentzian 2D peak, however systematic differences are observed in the 2D peak energy, width, and intensity for single- and multi-layer regions. We conclude that graphene multi-layers grown by AP-CVD on Cu are rotationally disordered.
The deposition of atomically thin highly uniform chemically derived graphene (CDG) films on 300 mm SiO2/Si wafers is reported. We demonstrate that the very thin films can be lifted off to form uniform membranes than can be free-standing or transferred onto any substrate. Detailed maps of thickness using Raman spectroscopy and atomic force microscopy (AFM) height profiles reveal that the film thickness is very uniform and highly controllable, ranging from 1-2 layers up to 30 layers. After reduction using a variety of methods, the CDG films are transparent and electrically active with FET device…
Transition-metal dichalcogenide (TMD) semiconductors have been widely studied due to their distinctive electronic and optical properties. The property of TMD flakes is a function of its thickness, or layer number (N). How to determine N of ultrathin TMDs materials is of primary importance for fundamental study and practical applications. Raman mode intensity from substrates has been used to identify N of intrinsic and defective multilayer graphenes up to N=100. However, such analysis is not applicable for ultrathin TMD flakes due to the lack of a unified complex refractive index ($\tilde{n}$) …
The detailed analysis of the structural variations of three GeO$_2$ and SiO$_2$ polymorphs ($α$-quartz, $α$-cristobalite, and rutile) under compression and expansion pressure is reported. First-principles total-energy calculations reveal that the rutile structure is the most stable phase among the phases of GeO$_2$, while SiO$_2$ preferentially forms quartz. GeO$_4$ tetrahedras of quartz and cristobalite GeO$_2$ phases at the equilibrium volume are more significantly distorted than those of SiO$_2$. Moreover, in the case of quartz GeO$_2$ and cristobalite GeO$_2$, all O-Ge-O bond angles vary w…
Evidence of the absence of the clear electron spin-resonance signal from Ge dangling bonds (DBs) at Ge/GeO$_2$ interfaces is explored by means of first-principles electronic-structure calculations. Comparing the electronic structures of the DBs at Si/SiO$_2$ and Ge/GeO$_2$ interfaces, we found that the electronic structure of the Ge-DB is markedly different from that of the Si-DB; the Ge-DB states does not position in the energy band gap of the Ge/GeO$_2$ interface while the Si-DB states clearly appears. In addition, the charge density distribution of the Ge-DB state spreads more widely than t…
First-principle study of bismuth-related oxygen-deficient centers ($=$Bi$\cdots$Ge$\equiv$, $=$Bi$\cdots$Si$\equiv$, and $=$Bi$\cdots$Bi$=$ oxygen vacancies) in Bi$_2$O$_3$-GeO$_2$, Bi$_2$O$_3$-SiO$_2$, Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$, and Bi$_2$O$_3$-Al$_2$O$_3$-SiO$_2$ hosts is performed. A comparison of calculated spectral properties of the centers with the experimental data on luminescence emission and excitation spectra suggests that luminescence in the 1.2-1.3 $μ$m and 1.8-3.0 $μ$m ranges in Bi$_2$O$_3$-GeO$_2$ glasses and crystals is likely caused by $=$Bi$\cdots$Ge$\equiv$ and $=$Bi$\c…
An extensive theoretical study is performed for wide bandgap crystalline oxides and nitrides, namely, SiO_{2}, GeO_{2}, Al_{2}O_{3}, Si_{3}N_{4}, and Ge_{3}N_{4}. Their important polymorphs are considered which are for SiO_{2}: $α$-quartz, $α$- and $β$-cristobalite and stishovite, for GeO_{2}: $α$-quartz, and rutile, for Al_{2}O_{3}: $α$-phase, for Si_{3}N_{4} and Ge_{3}N_{4}: $α$- and $β$-phases. This work constitutes a comprehensive account of both electronic structure and the elastic properties of these important insulating oxides and nitrides obtained with high accuracy based on density fu…
High-dielectric constant and wide band gap oxides have important technological applications. The crystalline oxide polymorphs having lattice constant compatibility to silicon are particularly desirable. One recently reported candidate is the inverse silver oxide phase of SiO$_2$. First-principles study of this system together with its isovalent equivalents GeO$_{2}$, SnO$_{2}$ as well as their ternary alloys are performed. Within the framework of density functional theory both generalized gradient approximation and local density approximation (LDA) are employed to obtain their structural prope…
Germanium dioxide ($GeO_2$) is a chemical analogue of $SiO_2$. Furthermore, it is also to some extent a structural analogue, as the low and high-pressure short-range order (tetrahedral and octahedral) is the same. However, a number of differences exist. For example, the $GeO_2$ phase diagram exhibits a smaller number of polymorphs, and all three $GeO_2$ phases (crystalline, glass, liquid) have an increased sensitivity to pressure, undergoing pressure induced changes at much lower pressures than their equivalent $SiO_2$ analogues. In addition, differences exist in $GeO_2$ glass in the medium ra…
In the paper, the processes occurring during low-temperature growth of non-hydrogenated amorphous Si and polycrystalline Si films on multilayer Si$_3$N$_4$/SiO$_2$/c-Si substrates from molecular beams under conditions of ultrahigh vacuum are studied in detail. Diffusion of hydrogen atoms from a dielectric layer into the growing film is shown to accompany the growth of a silicon film on a Si$_3$N$_4$ layer deposited by CVD or on a SiO$_2$ layer obtained by thermal oxidation of a silicon wafer. The process of hydrogen migration from the dielectric substrates into the silicon film is studied usin…
We present the evidence of the low defect density at Ge/GeO$_2$ interfaces in terms of first-principles total energy calculations. The energy advantages of the atom emission from the Ge/GeO$_2$ interface to release the stress due to the lattice mismatch are compared with those from the Si/SiO$_2$ interface. The energy advantages of the Ge/GeO$_2$ are found to be smaller than those of the Si/SiO$_2$ because of the high flexibility of the bonding networks in GeO$_2$. Thus, the suppression of the Ge-atom emission during the oxidation process leads to the improved electrical properties of the Ge/G…
In this paper we compute and compare the surface energy of various Ga liquid droplets wetting a cylindrical cavity in various configurations. While for some of these configurations the surface energy can be computed explicitely for others numerical computation is needed. Motivated by the results obtained for the cylindrical cavities we explore the case of the more realistic situation, conical cavities. Our results provide a relation between the geometry of the conical cavity and the equilibirum wetting angles of the droplet on the bottom and on the sidewall of the cavity which insure the dewet…
Synchrotron-based x-ray reflectivity is increasingly employed as an \textit{in situ} probe of surface morphology during thin film growth, but complete interpretation of the results requires modeling the growth process. Many models have been developed and employed for this purpose, yet no detailed, comparative studies of their scope and accuracy exists in the literature. Using experimental data obtained from hyperthermal deposition of pentane and diindenoperylene (DIP) on SiO$_2$, we compare and contrast three such models, both with each other and with detailed characterization of the surface m…
We investigate the effect of spatial doping of the Mott insulator LaVO$_3$ by inserting a few layers of the correlated metal SrVO$_3$ in multilayer geometries. Using density functional theory in combination with dynamical mean-field theory, we demonstrate that this leads to a geometrically confined and robust metallic layer that stabilizes the metallicity in SrVO$_3$ even in the ultrathin layer limit, suppressing a potential dimensionality-induced metal-insulator transition. For a thicker SrVO$_3$ layer, we find a continuous transition of both structural and electronic properties across the in…
Transport properties of magnetic multilayers in current perpendicular to the plane of the layers geometry are defined by diffusive scattering in the bulk of the layers, and diffusive and ballistic scattering across the interfaces. Due to the short screening length in metals, layer by layer treatment of the multilayers is possible, when the macroscopic transport equation (Boltzmann equation or diffusion equation) is solved in each layer, while the details of the interface scattering are taken into account via the boundary conditions. Embedding the ballistic and diffusive interface scattering in…
The hysteresis curves of multilayer microwires consisting of a soft magnetic nucleus, intermediate non-magnetic layers, and an external hard magnetic layer are investigated. The magnetostatic interaction between magnetic layers is proved to give rise to an antiferromagnetic-like coupling resulting in a magnetostatic bias in the hysteresis curves of the soft nucleus. This magnetostatic biasing effect is investigated in terms of the microwire geometry. The experimental results are interpreted considering an analytical model taking into account the magnetostatic interaction between the magnetic l…
We report the synthesis of AB-stacked multilayer graphene via ambient pressure chemical vapor deposition on Cu foils, and demonstrate a method to construct suspended multilayer graphene devices. In four-terminal geometry, such devices were characterized by hot carrier transport at temperatures down to 240 mK and in magnetic fields up to 14 T. The differential conductance (dI/dV) shows a characteristic dip at longitudinal voltage bias V=0 at low temperatures, indicating the presence of hot electron effect due to a weak electron-phonon coupling. Under magnetic fields, the magnitude of the dI/dV …
