Growth Of Thin Layers Research Articles

Chemically mediated diffusion of d-metals and B through Si and agglomeration at Si-on-Mo interfaces

Chemical diffusion and interlayer formation in thin layers and at interfaces is of increasing influence in nanoscopic devices, such as nanoelectronics and reflective multilayer optics. Chemical diffusion and agglomeration at interfaces of thin Ru, Mo, Si, and B4C layers have been studied with x-ray photoelectron spectroscopy, cross section electron energy loss spectroscopy, high-angle annular dark field scanning transmission electron microscopy, and energy dispersive x-ray in relation to observations in Ru-on-B4C capped Mo/Si multilayers. Rather than in the midst of the Si layer, silicides and borides are formed at the Si-on-Mo interface front, notably RuSix and MoBx. The interface apparently acts as a precursor for further chemical diffusion and agglomeration of B, Ru, and also other investigated d-metals. Reversed “substrate-on-adlayer” interfaces can yield entirely suppressed reactivity and diffusion, stressing the influence of surface free energy and the supply of atoms to the interface via segregation during thin layer growth.

Analysis of ambient gas influence on silicon layers crystallized by means of LPE

Epitaxial growth of thin layers from the liquid phase can occur with the use of solutions saturated under different ambient gases. Most often this process takes place in a vacuum or gaseous atmosphere of hydrogen or argon. As the experimental data show, the morphology of crystallized layers is determined by the ambient type in which the process occurs.The cohesion energy responsible for epitaxial lateral deposition processes on the substrate surface depends on the surface free energy which is a measure of attraction of the solution atoms by substrate atoms. In the case of crystallization of an epitaxial lateral layer of Si on a substrate partially masked with dielectric, the chemical potentials of atoms in the neighboring phases (determining the interface evolution) are not without influence on the relaxation velocity of the saturated liquid phase, and on the horizontal and vertical growth rate.The aim of the investigation was to analyze experimentally the influence of the ambient gases used during the LPE growth on the cohesion of the Sn–Si solution with substrates applied for the lateral epitaxial growth of Si layers. This work presents comparative temperature analysis of the wetting angle of such surfaces as Si, SiO2 and SiNx by the Sn–Si solution.

Quantitative analysis of ultra thin layer growth by time-of-flight low energy ion scattering

Time of flight low energy ion scattering is used to quantitatively characterize the growth mode of Au deposited on B. Information on the filling factor (surface area coverage) is deduced from the yield of backscattered ions and the spectrum height of scattered neutrals. From the variation of the filling factor with the nominal Au thickness, cluster growth is deduced. Information on the average cluster height is obtained from the energy distribution of scattered neutrals and the comparison with computer simulation. Finally, an estimate of the aspect ratios is obtained for the clusters from the filling factor and the cluster height.

Quantitative synchrotron micro-XRF study of CoTSPc and CuTSPc thin-films deposited on gold by cyclic voltammetry

Synchrotron radiation X-ray fluorescence (SR-XRF) spectroscopy has been applied for the microscopic characterization of cobalt(II) tetrasulfonated phthalocyanine (CoTSPc) and copper(II) 3,4′,4″,4‴-tetrasulfonated phthalocyanine (CuTSPc) thin films electrochemically deposited on gold electrodes. The deposited thin-film properties have been studied as a function of phthalocyanine concentration in solution during the modification process. The Co and Cu surface concentrations on the modified gold electrodes have been determined on the 20 and 600 μm levels. The SR-XRF quantification procedure and micro-heterogeneity determination of the CoTSPc and CuTSPc thin-films on the gold electrodes have been described in detail. The detailed comparison of scanning SR-XRF results with electrochemical data makes it possible to gain further insight in the mechanism of thin layer growth during the modification procedure.

A 3D moving grid algorithm for process simulation

A moving grid algorithm is presented for simulation of 3D oxidation processes. The algorithm combines local displacement of mesh points according to material velocity and local mesh cleanup. Several examples are shown that demonstrate the capabolity to simulate both the growth of thin layers of oxide during polysilicon gate reoxidation, as well at stress dependent growth of 3D locos oxides.

Scanning tunnelling microscope studies of growth of RuO 2 (110) thin layer on Ru(0001)

This paper reports that the growth of RuO2(110) thin layer growth on Ru(0001) has been investigated by means of scanning tunnelling microscope (STM). The STM images showed a domain structure with three rotational domains of RuO2(110) rotated by an angle of 120°. The as-grown RuO2(110) thin layer is expanded from the bulk-truncated RuO2(110) due to the large mismatch between RuO2(110) and the Ru(0001) substrate. The results also indicate that growth of RuO2(110) thin layer on the Ru(0001) substrate by oxidation tends first to formation of the Ru-O (oxygen) chains in the [001] direction of RuO2(110).

Growth Kinetics of Heterostructured GaP−GaAs Nanowires

We have studied the vapor-liquid-solid (VLS) growth dynamics of GaP and GaAs in heterostructured GaP-GaAs nanowires. The wires containing multiple GaP-GaAs junctions were grown by the use of metal-organic vapor phase-epitaxy (MOVPE) on SiO(2), and the lengths of the individual sections were obtained from transmission electron microscopy. The growth kinetics has been studied as a function of temperature and the partial pressures of the precursors. We found that the growth of the GaAs sections is limited by the arsine (AsH(3)) as well as the trimethylgallium (Ga(CH(3))(3)) partial pressures, whereas the growth of GaP is a temperature-activated, phosphine(PH(3))-limited process with an activation energy of 115 +/- 6 kJ/mol. The PH(3) kinetics obeys the Hinshelwood-Langmuir mechanism, indicating that the dissociation reaction of adsorbed PH(3) into PH(2) and H on the catalytic gold surface is the rate-limiting step for the growth of GaP. In addition, we have studied the competitive thin layer growth on the sidewalls of the nanowires. Although the rate of this process is 2 orders of magnitude lower than the growth rate of the VLS mechanism, it competes with VLS growth and results in tapered nanowires at elevated temperatures.

Amelogenin control over apatite crystal growth is affected by the pH and degree of ionic saturation

To study the mechanisms which promote the interactions of amelogenin proteins with the forming mineral to establish suitable conditions for the biomimetic synthesis of enamel in vitro. Saturated calcium phosphate solutions were used in conjunction with recombinant amelogenin proteins to induce mineral formation on glass-ceramics substrates containing oriented fluoroapatite crystals (FAP). The height of mineral layers formed on these substrates within 24 h was measured by atomic force microscopy (AFM). The effect of protein concentration, pH and degree of saturation (DS) on the growth of apatite mineral was evaluated. Mineralization experiments were performed at 0, 0.4 and 1.6 mg/ml amelogenin concentrations. Mineralization solutions were used at pH values of 6.5, 7.4, 8.0 and 8.8 and DS of calcium and phosphate between 9 and 13. Height and morphology of mineralized layer formed on glass-ceramic substrates as determined from AFM measurements. Homogeneous nucleation and crystal growth of thin layers on the FAP were observed, when calcium and phosphate ions were added. The height of these layers grown on (001) planes of FAP was strongly dependent on the protein concentration and pH. At concentrations of 0 and 0.4 mg/ml crystal grew 5-15 nm on the FAP, while they grew approximately to 200 nm at 1.6 mg/ml. The enhanced crystal growth was observed only at pH 6.5, 7.4 and 8.0, while layers only 20 nm thick were obtained at pH 8.8. An increase in DS resulted in uncontrolled growth of calcium phosphate mineral covering large areas of the substrate. Protein concentration, pH and the saturation of the mineralizing solution need to be considered carefully to provide suitable conditions for amelogenin-guided growth of apatite crystals.

A nanometer scale surface morphology study of W thin films

Microstructure of tungsten thin films deposited by RF-sputtering is studied as a function of their thicknesses. These films have been deposited on (100) oriented single crystal Si substrate and Si substrate covered by a 100-nm-thick Ti layer. The crystalline structure is studied by X-ray Diffraction (XRD) and Grazing Incidence XRD (GIXRD). The surface and the cross-section morphology are observed by high resolution Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). XRD patterns exhibit peaks corresponding to pure W phase. GIXRD analysis shows that the more the thickness increases, the more the film is oriented along the [110] direction. AFM observations show that films exhibit a particular morphology constituted of “piles of platelets” oriented perpendicularly to the wafer surface. These “piles of platelets” are in plane randomly oriented and are sometime observed upon all the thicknesses of the layer. This particular morphology is observed whatever the substrate is, and is explained by thin layer growth theories.

Pulsed laser deposition growth of Fe3O4 on III–V semiconductors for spin injection

We report on the growth of thin layers of Fe3O4 on GaAs and InAs by pulsed laser deposition. It is found that Fe3O4 grows epitaxially on InAs at a temperature of 350 °C. X-ray photoelecton spectroscopy (XPS) studies of the interface show little if any interface reaction resulting in a clean epitaxial interface. In contrast, Fe3O4 grows in columnar fashion on GaAs, oriented with respect to the growth direction but with random orientation in the plane of the substrate. In this case XPS analysis showed much more evidence of interface reactions, which may contribute to the random-in-plane growth.

Carbon dioxide activation and alkali compound formation. I. Vibrational characterization of oxalate intermediates

The activation of CO 2 in thin potassium layers adsorbed on Cu(1 1 1) has been studied with time-evolved Fourier transform-infrared reflection absorption spectroscopy. The growth of thin layers by reactive evaporation of potassium in a CO 2 atmosphere permits control of the K:CO 2 stoichiometry, which strongly affects the selectivity in the formation of intermediates and the decomposition pathways of the layer. Layers grown in a CO 2 rich atmosphere exhibit the preferential growth of stoichiometric potassium oxalate K 2C 2O 4 (D 2h). The molecular identity of oxalate with D 2h symmetry is confirmed by vibrational spectra utilizing isotopic substitution methods ( 13CO 2 and C 18O 2) and by the use of isotopic mixtures of CO 2/C 18O 2 and CO 2/ 13CO 2. A comparison of the isotope data with theoretical calculations gives an estimated OCO bond angle in oxalate of 132°. Far-IR spectra obtained with synchrotron radiation indicate the equivalent interaction of all oxygen atoms with the potassium. A comparison of the vibrational data with theoretical ab initio calculations confirms the structural model of an oxalate species that is bulk coordinated with no strong directional bonding and all oxygen atoms equally interacting with potassium. At medium and low CO 2:K ratios, very complex vibrational spectra are observed, indicating the formation of an oxalate surface species with C 2v symmetry in addition to D 2h − oxalate, CO 2 − and CO 2 2− species.

The effect of V:III ratio on the growth of InN nanostructures by molecular beam epitaxy

We have investigated the growth of thin layers of indium nitride (InN) on gallium nitride (GaN) by molecular beam epitaxy (MBE) using two different nitrogen sources. Using thermally cracked ammonia as the nitrogen source, we explored the effect of the V:III ratio by varying the ammonia pressure. With a low V:III ratio, we did not detect InN growth, and instead observed the formation of irregularly shaped indium islands on the GaN surface. With higher V:III ratios, nanostructure growth was observed for thin (≈2 ML) layers. Further deposition resulted in the growth of polycrystalline material. The differences between the two pressure regimes may be explained in terms of the interplay between equilibrium thermodynamics and growth kinetics. We performed similar experiments at higher V:III ratios using a modified nitrogen plasma source. Stranski–Krastanov growth occurred, and we were able to obtain high-temperature in vacuo STM images of the as-grown nanostructures.

Modelling of InAs thin layer growth from the liquid phase

InAs quantum wells have been grown using the rapid slider liquid phase epitaxial growth technique. Analysis of the layer thickness data as a function of supercooling and contact time revealed the presence of two different growth mechanisms. A mathematical model of the epitaxial growth based around simple assumptions relating to melt rolling has been shown to give a good explanation of the experimental findings and also provides an integrated mathematical description of the growth phenomena.

Growth of thin layers of metal sulfides by chemical vapour deposition using dual source and single source precursors: routes to Cr2S3, α-MnS and FeS

The growth of thin layers of the transition metal sulfides Cr2S3, α-MnS and FeS by Chemical Vapour Deposition (CVD) is reported. Layers of Cr2S3 in the rhombohedral or trigonal form have been grown onto Pyrex, molybdenum or aluminium substrates using the single-source precursor Cr(S2CN(C2H5)2)3 in a low-pressure flow reactor. The temperature of the precursor was held at 255 °C and the substrate was heated to 450 °C for these experiments. The nature of the layer formed was determined by a combination of EDX analysis and glancing angle XRD. Growth rates up to 10 µm h−1 were achieved. In a separate series of experiments thin layers of α-MnS and FeS have been grown onto Pyrex substrates using propylene sulfide (C3H6S) as the sulfur source and CpMn(CO)3 (Cp = η-C5H5) or Cp2Fe as the metal source using a CVD reactor under a flow of nitrogen gas. An approximately 1∶1 molar ratio of C3H6S and CpMn(CO)3 and a substrate temperature of 410 °C gave a growth rate of α-MnS of some 4 µm h−1 and a crystalline layer as shown by EDX analysis and powder XRD. However, increasing the flow rate of the sulfur source or decreasing that of the metal source gave rise to sulfur-rich layers. Layers of FeS were grown on Pyrex substrates from C3H6S and Cp2Fe with a molar ratio of reactants of 1∶3 or higher and a substrate temperature of 410 °C. A growth rate of around 2.5 µm h−1 was achieved.

Growth morphology and structure of bismuth thin films on GaSb(110)

Photoelectron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy and surface X-ray diffraction were used to investigate the growth of thin layers of bismuth on GaSb(110). At submonolayer coverages, growth of two-dimensional islands occurs. A uniform (1×1)-reconstruction is formed at a coverage of one monolayer. A structural model derived from X-ray diffraction data is presented for this phase. The (1×1)-phase consists of zigzag chains of bismuth atoms bonded alternately to the surface cations and anions of the bulk-terminated unrelaxed (110) surface. We propose that the (1×1)-phases formed by antimony and bismuth adsorbates on (110) surfaces of other III–V compound semiconductors are also described by the epitaxial continued layer model.

Phosphorus Passivation of GaAs

AbstractWe have performed a systematic study of the effect of various phosphorus passivation techniques on the room temperature photoluminescence (PL) intensity of undoped GaAs. The effects of passivation by two methods are compared: (1) the P-exchange reaction on exposure to tertiarybutylphosphine (TBP) vapour between 500-620°C, and (2) the growth of thin layers of GaP directly on GaAs. An x-ray diffraction technique was used to estimate the thickness of the passivating layers. Reflectance difference spectroscopy indicated a similar chemical origin for the two passivation methods. Both passivation techniques resulted in strong enhancements in the room temperature PL. PL intensity was observed to increase very rapidly with adsorbed P for both cases saturating at approximately 2 monolayers equivalent GaP coverage.

Carbonyl sulfide (OCS) as a sulfur-containing precursor in MOCVD: a study of mixtures of Me2Cd and OCS in the gas and solid phases and their use in MOCVD

Mixtures of dimethylcadmium (Me2Cd) and carbonyl sulfide (OCS) have been examined in the gas and solid phases over a wide range of temperatures. No interaction is observed between Me2Cd and OCS in a 1:1 molar ratio at room temperature in the gas phase, nor is any interaction detected in the solid phase at liquid-nitrogen temperature. On heating the 1:1 mixtures of Me2Cd and OCS to 250 °C in a sealed vessel, gaseous products are formed. These consist of methane, carbon monoxide and ethane in an approximately 12:2:1 molar ratio, although a large excess of unreacted OCS is also present showing that this compound does not react fully with Me2Cd at 250 °C. In a flow system at 300 °C only methane and carbon monoxide are formed, in the molar ratio 6:1, although the amount of reaction of the OCS is much less (as evidenced by a higher proportion of unreacted OCS). When the flow reaction is repeated at 450 °C more of the OCS reacts and the proportion of carbon monoxide in the gaseous reaction products is much higher. Using a commercial MOCVD apparatus, high-quality layers of cadmium sulfide are obtained from Me2Cd–OCS mixtures. Temperatures in the range 350–450 °C lead to somewhat slow growth rates which only reach 1 µm h–1 when a 200-fold molar excess of OCS over Me2Cd is used. A small amount of prereaction is observed, but only when H2 is used as the carrier gas. This is attributed to the formation of very small concentrations of H2S by reaction of OCS with H2. The resulting epitaxial layers have good thickness and electrical uniformity. These experiments confirm that OCS may be used as a precursor for the growth of thin layers of CdS by MOCVD. However, the large excess of OCS required here suggests that the compound might be more useful for doping than for the growth of pure layers of CdS.

Composition changes in Ga xIn 1− xAs/InP superlattice growth by chemical beam epitaxy

The variation of compositions in ultra-thin Ga x In 1− x As/InP layers grown by chemical beam epitaxy (CBE) was investigated. The Ga atomic content of the grown Ga x In 1− x As was evaluated by an X-ray diffraction method. By comparing with theoretical simulation, we found a lack of Ga content in very thin layer growth. The reduction of Ga content ranged from 0.47 to 0.33 for 4-monolayer superlattice. Our result implies that there are some transition layers at the beginning of Ga x In 1− x As growth which should be eliminated.

An experimental study of hydroxyapatite prosthesis in ossicular reconstructive surgery: long-term follow-up observation in the middle ear of cat

The author have conducted a series of experimental studies, using cats, to clarify the biocompatibility of Hydroxyapatite (HA) with the middle ear tissue in the cat. Partial ossicular replacement prosthesis of 99.5% of density was designed for the experiment. After removing the incus, the prosthesis was placed between the stapes and the malleus to reconstruct the ossicular chain.Postoperative hearing was assessed by measurment of the threshold of auditory brainstem response. Histological specimens of the middle ear after the operation were made using a cutting band saw at various postoperative periods. The maximum duration was 450 days. The specimens served for light microscopic observation. In addition, the HA prosthesis with surrounding tissue was observed by a scanning electron microscope and by a microradiography.The hearing threshold returned to certain level and remained stable within a month after the surgery, in all cats except for one, when the postoperative inflammation was well controlled. Fifteen days after the surgery, a fibrous tissue grew in layers around the ossicle in contact with HA. The HA prosthesis and the ossicles in the middle ear cavity were wholly covered with a connective tissue, 30 days after the surgery. Furthermore, the scanning electron microscopy revealed that the surface of the HA was quite promptly covered with the fibrous tissue mainly consisting of collagen fibers. This indicated the high affinity of the HA to middle ear tissue. On the face of junction between the HA and the ossicles the growth of thin layer of the connective tissue was evident and no osseous ankylosis which disturbed the mobility of the ossicular chain was recognized.Throughout the postoperative course, neither absorption, resolution nor disfigurement of the HA was found. The foreign body giant cells were hardly found under the microscopic observation. From the assessment of both hearing tests and histological findings, it can be said that the HA prosthesis is stabilized in the middle ear cavity within a month. The present experimental study confirmed the high grade of biocompatibility of HA and presented an important information for the clinical application of HA as the ossicular replacement prosthesis.

Scaling procedure for aes investigations of thin layer growth

Expressions for the substrate and adsorbate Auger signals have been derived, taking into consideration the differences in the values of backscattering factors for consecutive monolayers of the adsorbate. It has been shown that the analysis of changes of the layer Auger line width enables one to obtain additional information concerning the details of the layer growth process. The possibility of application of such an analysis has been proved by the use of results of numerical calculations. The approximate relation for the relative backscattering factors of the consecutive monolayers of the layer has been also derived. A method has been proposed for obtaining values of electron attenuation factors for the substrate and layer materials, as well as for obtaining values of relative backscattering factors.