Alloying and Strain Relaxation in SiGe Islands Grown on Pit-Patterned Si(001) Substrates Probed by Nanotomography

The three-dimensional composition profiles of individual SiGe/Si(001) islands grown on planar and pit-patterned substrates are determined by atomic force microscopy (AFM)-based nanotomography. The observed differences in lateral and vertical composition gradients are correlated with the island morphology. This approach allowed us to employ AFM to simultaneously gather information on the composition and strain of SiGe islands. Our quantitative analysis demonstrates that for islands with a fixed aspect ratio, a modified geometry of the substrate provides an enhancement of the relaxation, finally leading to a reduced intermixing.     

Ordered Arrays of SiGe Islands from Low-Energy PECVD

SiGe islands have been proposed for applications in the fields of microelectronics, optoelectronics and thermoelectrics. Although most of the works in literature are based on MBE, one of the possible advantages of low-energy plasma-enhanced chemical vapor deposition (LEPECVD) is a wider range of deposition rates, which in turn results in the possibility of growing islands with a high Ge concentration. We will show that LEPECVD can be effectively used for the controlled growth of ordered arrays of SiGe islands. In order to control the nucleation of the islands, patterned Si (001) substrates were obtained by e-beam lithography (EBL) and dry etching. We realized periodic circular pits with diameters ranging from 80 to 300 nm and depths from 65 to 75 nm. Subsequently, thin films (0.8–3.2 nm) of pure Ge were deposited by LEPECVD, resulting in regular and uniform arrays of Ge-rich islands. LEPECVD allowed the use of a wide range of growth rates (0.01–0.1 nm s⁻¹) and substrates temperatures (600–750°C), so that the Ge content of the islands could be varied. Island morphology was characterized by AFM, while μ-Raman was used to analyze the Ge content inside the islands and the composition differences between islands on patterned and unpatterned areas of the substrate.     

Optimal Growth Conditions for Selective Ge Islands Positioning on Pit-Patterned Si(001)

We investigate ordered nucleation of Ge islands on pit-patterned Si(001) using an original hybrid Kinetic Monte Carlo model. The method allows us to explore long time-scale evolution while using large simulation cells. We analyze the possibility to achieve selective nucleation and island homogeneity as a function of the various parameters (flux, temperature, pit period) able to influence the growth process. The presence of an optimal condition where the atomic diffusivity is sufficient to guarantee nucleation only within pits, but not so large to induce significant Ostwald ripening, is clearly demonstrated.     

Excitation Intensity Driven PL Shifts of SiGe Islands on Patterned and Planar Si(001) Substrates: Evidence for Ge-rich Dots in Islands

For randomly nucleated SiGe/Si(001) islands, a significantly stronger blue-shift of the PL spectra as a function of the excitation intensity is observed when compared to islands grown on patterned substrates side by side within the same run in a solid source molecular beam epitaxy chamber. We ascribe this different PL behavior to the much larger inhomogeneity of the Ge distribution in islands on planar substrates when compared to islands grown on pit-patterned ones, as observed previously. 3D band-structure calculations show that Ge-rich inclusions of approximately 5 nm diameter at the apex of the islands can account for the observed differences in the PL spectra. The existence of such inclusions can be regarded as a quantum dot in an island and is in agreement with recent nano-tomography experiments.     

Anodic oxidation of chemically hydrogenated Si(100)

The first oxidation stages of HF-etched Si surfaces were studied at potentials lower than 10 V by using conventional electrochemical techniques. The use of the droplet cell allows defining areas of less than 10⁻³ cm² and a great number of measurements can be carried out in a relative short period of time. In this way, the first layer transformation may be studied before the surface becomes oxidised by the air humidity, assuring a better reproducibility. Potentiodynamic measurements of surface capacity give evidence of the formation of surface states generated by an adsorption process at the beginning of oxidation. As a consequence of an increasing OH⁻ coverage, the potential drop is gradually displaced from the semiconductor space charge layer to the Helmholtz layer with increasing pH. A model for the oxidation of the H-terminal bonds based on a charge transfer via the conduction band was proposed.     

Surface characterization of a semiconductor SiGe/Si heterostructure by contact angle measurements

For the integration of strained Si_1-xGe_x epilayers in future silicon technologies it is necessary to obtain flat planar interfaces. Thus, a good understanding of the growth mechanism and a good knowledge of the properties of this strained material are required. Many articles have dealt with these problems in the literature. In a previous study, atomic force microscopy (AFM) was used to analyze the morphological modifications in SiGe epilayers grown on Si. The different stages of surface evolution have been determined, particularly the onset of undulations. In this study, we have investigated these surface modifications using the contact angle measurement technique. We observed a correlation between the root mean square (RMS) values of the roughness obtained with AFM and the water contact angle values. We demonstrate that the contact angle measurement technique, taking certain precautions, allows the critical thickness, i.e. the thickness beyond which the undulation pseudo-period increases, to be determined accurately.     

Microwave plasma chemical vapor deposition of cone-like structure of diamond/SiC/Si on Si (100)

Diamond deposition on 1 × 1 cm² Si (100) substrates with bias was carried out by microwave plasma chemical vapor deposition (MPCVD). Distribution of deposited diamonds has been significantly improved in uniformity over all the Si substrate surface area by using a novel designed dome-shaped Mo anode. The deposits were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman analysis. SEM observations show that there is a high density of cone-like particles uniformly deposited on the surface of the substrate in short bias nucleation period. The average diameter, height and density of cone-like structure were increased with methane concentration in the bias stage. TEM reveals that the cone-like structure is actually composed of Si conic crystal covered with diamond. Between Si and diamond, a thin layer of cubic SiC is found in epitaxy with Si. Furthermore, for 3% CH₄ concentration, the range of diameter of cone-like structure was about 20–90 nm and the size of diamond was about 10–60 nm.     

H、He离子联合注入单晶Si引起的表面损伤研究进展

H和He离子联合注入单晶Si可以促使其表面产生发泡、剥落和层离等表面损伤,由此引发了一种有效地制备SOI材料的新方法,即智能剥离技术.文章简述了H和He离子注入单晶Si在随后的热处理过程中引起表面损伤的机理,探讨了注入条件变化对表面损伤的影响,提出了该领域存在的关键问题并介绍了智能剥离技术在现代半导体技术中潜在的应用前景.     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Formation and Organization of Amino Terminated Self-assembled Layers on Si(001) Surface

We have investigated the effects of dipping time, solution concentration and solvent type on the formation of self-assembled monolayers with aminosiloxane molecules (i.e., N-(3 trimethoxysilylpropyl)diethylenetriamine (TPDA)) on the Si(001) surface. Studies performed with an ellipsometer showed that monolayers with a thickness of about 1.2 nm were formed when the dipping time is about 2 h, while multilayer were observed for longer time periods. The effect of the TPDA concentration on the thickness of the deposited layer was not very profound, however, the contact angle data exhibit importance of concentration on the surface coverage. The type of the solvent used in the formation of the monolayers was found an important parameter. Monolayers were formed with solvent having larger dielectric constants. Relatively thick multilayer was observed when benzene was used as the solvent, due to its quite low dielectric constant (hydrophobicity).     

Surface interaction of different Cu precursors on oxidised Si(100)

The liquid phase chlorination of naphthalene with gaseous chlorine to monochloronaphthalenes in high yields using K-L zeolite as catalyst is reported. The zeolite, K-L, catalyzed chlorination of naphthalene is found to be more selective than the conventional catalyst, FeCl₃, catalyzed chlorination.     

From the nucleation of wiggling Au nanostructures to the dome-shaped Au droplets on GaAs (111)A, (110), (100), and (111)B

In this paper, the systematic evolution process of self-assembled Au droplets is successfully demonstrated on GaAs (111)A, (110), (100), and (111)B. On various GaAs substrates, self-assembled Au clusters begin to nucleate at around 300°C, and then, they develop into wiggly Au nanostructures at 350°C. Between 400°C and 550°C, the self-assembled dome-shaped Au droplets with fine uniformity are fabricated with various sizes and densities based on the Volmer-Weber growth mode. Depending on the annealing temperature, the size including the average height and lateral diameter and the density of Au droplets show the opposite trend of increased size with correspondingly decreased density as a function of the annealing temperature due to the difference in the diffusion length of adatoms at varied activation energy. Under an identical growth condition, depending on the surface index, the size and density of Au droplets show a clear distinction, observed throughout the temperature range. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM) images, cross-sectional line profiles, and Fourier filter transform (FFT) power spectra as well as the summary plots of the size and density.     

Surface Chemistry Involved in Epitaxy of Graphene on 3C-SiC(111)/Si(111)

Surface chemistry involved in the epitaxy of graphene by sublimating Si atoms from the surface of epitaxial 3C-SiC(111) thin films on Si(111) has been studied. The change in the surface composition during graphene epitaxy is monitored by in situ temperature-programmed desorption spectroscopy using deuterium as a probe (D₂-TPD) and complementarily by ex situ Raman and C1s core-level spectroscopies. The surface of the 3C-SiC(111)/Si(111) is Si-terminated before the graphitization, and it becomes C-terminated via the formation of C-rich (6√3 × 6√3)R30° reconstruction as the graphitization proceeds, in a similar manner as the epitaxy of graphene on Si-terminated 6H-SiC(0001) proceeds.     

Thermal imidization of poly(amic acid) on Si(100) surface modified by plasma polymerization of glycidyl methacrylate

The plasma polymerization of glycidyl methacrylate (GMA) on pristine and Ar plasma-pretreated Si(100) surfaces was carried out. The epoxide functional groups of the plasma-polymerized GMA (pp-GMA) could be preserved, to a large extent, through the control of the glow discharge parameters, such as the radio-frequency (RF) power, carrier gas flow rate, system pressure, and monomer temperature. The pp-GMA film was used as an adhesion promotion layer for the Si substrate. The polyimide (PI)/pp-GMA-Si laminates, formed by thermal imidization of the poly(amic acid) (PAA) precursor poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PMDA-ODA) on the pp-GMA-deposited Si surface (the pp-GMA-Si surface), exhibited a 180°-peel adhesion strength as high as 9.0 N/cm. This value was much higher than the negligible adhesion strength for the PI/Si laminates obtained from thermal imidization of the PAA precursor on both the pristine and the argon plasma-pretreated Si(100) surfaces. The high adhesion strength of the PI/pp-GMA-Si laminates was attributed to the synergistic effect of coupling the curing of epoxide functional groups in the pp-GMA layer with the imidization process of the PAA, and the fact that the plasma-deposited GMA chains were covalently tethered onto the Si(100) surface. The chemical composition and structure of the deposited films were characterized, respectively, by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy, while the surface morphology of the deposited films was characterized by atomic force microscopy (AFM).     

Diffusion behavior of benzene/cyclohexane molecules in poly(vinyl alcohol)-graphite hybrid membranes by molecular dynamics simulation

Understanding the effects of incorporated inorganic particles in organic-inorganic hybrid membranes at molecular level is crucial to design hybrid membranes with tailored structure and desired properties. In this study, molecular dynamics simulation has been employed to investigate the effects of graphite particle on the diffusion behavior of benzene and cyclohexane in poly(vinyl alcohol)-graphite hybrid membranes. Firstly, the non-bonding interaction energies between PVA polymer and graphite particle with different amount of hydroxyl and carboxyl groups were calculated by DREIDING force field. Next, polymer chain mobility was analyzed by mean-square displacement (MSD) and glass transition temperature (T_g), and found that incorporation of graphite particle into PVA increased the polymer chain mobility. Free volume characteristics of membranes were investigated by Connolly surface, and found that free volumes in PVA-graphite hybrid membranes were larger than those in PVA control membranes. This simulation result showed the same tendency with the PALS measurement. Finally, the diffusion coefficients of benzene and cyclohexane in the membranes were calculated by Einstein relation, and found that the diffusion coefficients in hybrid membranes were larger than those in the control membrane. Furthermore, it was found that the diffusion coefficients of benzene and cyclohexane in the membranes exhibited exponential relation with the inverse fractional free volumes and agreed well with the free volume theory.     

Thermal stability of MgO film on Si grown by atomic layer deposition using Mg(EtCp)2 and H2O

MgO films were deposited on Si via atomic layer deposition (ALD) using Mg(EtCp)₂ and H₂O precursors and their thermal stability was examined as a function of the post-deposition annealing (PDA) temperature. The characteristic self-limiting behavior of the ALD process was confirmed by changing several parameters, such as precursor pulsing times, deposition temperature, and number of cycles. The exceptional resulting step coverage was verified on a patterned wafer with a high aspect ratio. The band gap and dielectric constant of the as-deposited ALD-MgO film were extracted to be approximately 7.5 eV and 8.4, respectively, and were stable up to the PDA temperature of 700 °C. However, considerable outward diffusion of the underlying Si atoms toward MgO started to occur above 700 °C, and most of the MgO film was converted to an amorphous Mg-silicate phase at 900 °C with a thin layer of remaining MgO on top.     

Growth of GeSi nanoislands on nanotip-patterned Si (100) substrates with a stress-induced self-limiting interdiffusion

ABSTRACT: GeSi nanoislands grown on nanotip pre-patterned Si substrates at various temperatures are investigated. Nanoislands with a high density and narrow size distribution can be obtained within an intermediate temperature range, and the Ge atom diffusion length is comparable to half of the average distance of the Si nanotips. The Ge concentration distributions at the center and edge of the GeSi nanoislands are measured by scanning transmission electron microscopy. The results reveal that there is a Si core at the center of the GeSi nanoisland, but the Ge concentration presents a layered distribution above the Si nanotips. The radial component of the stress field in Ge layer near the Ge/Si interface on the planar, and the nanotip regions is qualitatively discussed. The difference of the stress field reveals that the experimentally observed concentration profile can be ascribed to the stress-induced interdiffusion self-limiting effect of the Si nanotips.     

Synthesis of cobalt nanoparticles on Si (100) by swift heavy ion irradiation

We report the growth and characterization of uniform-sized nanoparticles of cobalt on n-type silicon (100) substrates by swift heavy ion (SHI) irradiation. The Co thin films of 25-nm thicknesses were grown by e-beam evaporation and irradiated with two different types of ions, 45-MeV Li³⁺ and 100-MeV O⁷⁺ ions with fluences ranging from 1 × 10¹¹ to 1 × 10¹³ ions/cm². SHI irradiation, with the beam rastered over the area of the film, resulted in the restructuring of the film into a dense array of Co nanostructures. Surface topography studied by atomic force microscopy revealed narrowed size distributions, with particle sizes ranging from 20 to 50 nm, formed through a self-organized process. Ion fluence-dependent changes in crystallinity of the Co nanostructures were determined by glancing angle X-ray diffraction. Rutherford backscattering spectroscopy analysis showed the absence of beam-induced mixing in this system. Surface restructuring and beam-induced crystallization are the dominant effects, with the nanoparticle size and density being dependent on the ion fluence. Results are analyzed in the context of molecular dynamics calculations of electron-lattice energy transfer.     

Crystalline structure of YSZ thin films deposited on Si(111) substrate by chemical vapor deposition

Yttria-stabilized zirconia (YSZ) thin films were formed on Si(111) substrate by chemical vapor deposition (CVD) in a temperature range of 650–800 °C using β-diketone metal chelates. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) data evidenced that YSZ thin films have a smooth surface with fine grains and crystalline structure, respectively. The crystalline structure of YSZ films was affected by the deposition temperature. The X-ray photoelectron spectroscopy (XPS) data indicated that the YSZ film grows thick enough to prevent the diffusion of Si.