Layer Growth Mode Research Articles

Diffraction spot profile analysis for heteroepitaxial surfaces applied to the initial growth stages of CaF 2 adlayers on Si(111)

We have studied the heteroepitaxial growth of CaF 2 on Si(111) by high resolution low energy electron diffraction. Analysing spot profiles recorded during CaF 2 deposition (SPA-LEED) we obtained information about the film morphology. The spots show a central spike and diffuse shoulder caused by atomic steps of the CaF 2 film. In order to evaluate quantitatively the layer distribution from the intensity oscillations of the central spike at the out-of-phase condition we included the interference between substrate and adlayer in our analysis. Depositing CaF 2 at 300°C we conclude from the central spike intensity that the nucleation of the second CaF 2 layer starts immediately. We attribute this behaviour to the poor binding of the CaF 2 molecules to the 7 × 7 substrate so that obviously the nucleation at surface defects (atomic steps, anti-phase boundaries) is favoured. The analysis of the central spike oscillations also reveals that the film grows in the multi layer growth mode at higher coverages.

Heteroepitaxy of KCl on KBr substrate

The heteroepitaxy of KCl on a KBr(001) substrate, with a lattice mismatch of −4.7%, was studied, and the relaxation mechanism of the lateral lattice constant was clarified. The stable atomic configuration were calculated by minimizing the total interaction energy between the ions. At submonolayer coverages, two-dimensional island configurations are more stable than three-dimensional structures, indicating a layer growth mode. At integer monolayer thicknesses, both the strained layer structure with the lateral lattice constant of KBr and the pecudomorphic commensurate layer structure with KBr(001) were investigated. The strained layer structure is more stable than the pseudomorphic structure below the critical thickness of three monolayers. The commensurate layer separates into two regions: a strained layer region and a dislocation region with one extra cation and anion row relative to the KBr substrate. The width of the dislocation region increases es the layer thickness increases, corresponding to the observed gradual relaxation of the lateral lattice constant above the critical thickness.

The role of neutral oxygen radicals in the oxidation of Ag films

Silver films with thickness between 2 and 500 nm were exposed to an excited gas mixture of argon and oxygen from a microwave ECR ion source. Oxidation was observed, even with the extraction optics grounded, with a positive or negative bias voltage on the film, and without direct sight between the film and the source. Thus, the reaction must be caused by neutral oxygen species, probably atoms. The oxygen uptake was monitored with a quartz microbalance, and yielded, after a delay of ambiguous origin, a linear increase with time until all Ag had reacted to nominally Ag 2O. The rate strongly depended on the gas pressure. Simultaneous measurements of the optical transmittance, reflectance, and of the electrical resistivity suggested a layer growth mode of the oxide. Comparison of the experimental dependence of the transmittance on film thickness with computer simulations yielded a bes fit with n=2.5 ± 0.1 and k=0,11 ± 0.02 for the oxide. Further oxygen absorption was slower, and approached an equilibrium of the production and decay of AgO.

Preparation of large area and investigation of initial film growth of YBa2Cu3O7 by scanning pulsed laser deposition

A pulsed laser deposition system with a rotating reflector, which can generate an extended plume with a diameter of about 40 mm, has been proven to be viable in producing large area YBa2Cu3O7 (YBCO) thin films. Films with uniformity of thickness and electrical properties to within a few percents were obtained. By making a further modification on this laser scanning system, YBCO films with various thicknesses can be deposited in situ on several pieces of substrates under essentially identical deposition conditions, and particularly, in a continuous fashion. The atomic force microscopy (AFM) images reveal that films grown on NdGaO3 follow the Stranski–Krastanov (layer then island growth) mode, while films grown on as-polished MgO and on annealed MgO follow the Volmer–Weber (islands without layer growth) mode and step-flow mode, respectively.

Scanning tunneling microscopy study of the epitaxial growth of strained In 0.82Ga 0.18As layers on InP

The 2D–3D growth mode transition of compressively strained In x Ga 1− x As layers ( x = 0.82 or 2% lattice mismatch) grown on an In 0.53Ga 0.47As buffer layer lattice matched to InP was studied using scanning tunneling microscopy. Up to 4 deposited monolayers, a layer by layer growth mode is maintained. The surface layer appears to be more compact for the strained layers than for the lattice matched buffer layer. After 5 monolayers were deposited the surface topography undergoes very significant change and threedimensional patterns, highly anisotropic in the growing plane, appear. These remarkable evolutions are attributed to the competition between surface energy necessary to form new island facets and elastic energy relaxation allowed with small sized islands.

Growth and structure of Pt on Co(112̄0) versus Pt on Co(101̄0) and Pt on Co(0001)

Abstract In this paper we consider the growth and structure at room temperature of the Pt Co (11 2 0) interface as compared to previous studies on Pt Co (0001) and Pt Co (10 1 0) . We evidence a layer by layer growth mode lacking of long range order. discuss the inelastic mean free path values compared to the ones obtained in the previous studies. We also describe the coverage dependent LEED patterns and their evolution while annealing interfaces grown at room temperature.

Growth of Te thin films deposited at room temperature on the Si(100)2 × 1 surface

The electronic properties and the growth mode of very thin films of tellurium deposited in ultra-high vacuum, at room temperature, on the Si(100)2 × 1 surface have been studied by means of XPS, AES and LEED spectroscopy. Additionally the measured AES weighted peak to peak intensity ratio between Te and Si was compared with calculated layer by layer and Stransky-Krastanov growth mode curves. Our results indicate that the interaction between tellurium and silicon is very weak like the characteristic behaviour of simple metals near Si in the Periodic Table. Tellurium grows on large 1 × 1 domains reconstructed on Si(100)2 × 1 until a layer is completed, at ≈ 2 Å of nominal coverage. Once the substrate is completely covered by the first Te layer, and up to ≈ 10 Å, the deposited tellurium grows, forming islands which have a 1 × 1 order on Si(100), and covers ≈ 40% of the underlying continuous layer. With increasing thickness the islands begin to coalesce and the Te atoms do not follow the lattice order of the Si(100) substrate any more. The behaviour of Te on Si(100) is found to be very similar to that of antimony because of the similar electronic core level structure and atomic radius. However, the higher mobility of Te atoms with respect to Sb atoms allows the formation of a continuous layer of Te on Si(100)2 × 1 also at room temperature, whereas Sb needs higher temperatures. The observed weak absorbate-substrate interaction, together with a strong adsorbate-adsorbate interaction, leads to the saturation of the dangling bonds of the silicon substrate, which shows a bulk-like behaviour, and are responsible for the growth mode of the tellurium deposited on Si(100)2 × 1.

GROWTH OF Ge ON In-ADSORBED Si(111) SURFACES STUDIED BY UHV-REM

Growth of Ge on In-adsorbed Si (111)[Formula: see text] and 4×1 surfaces was studied by REM-RHEED. Indium atoms were segregated to the topmost surface during Ge deposition. The formation of the 1×1 structure, which is one of the In-adsorbed structures on the Ge (111) surface, was observed on both the [Formula: see text] structure and the 4×1 surface structures. Suppression of two- and three-dimensional island nucleation of Ge by In predeposition was noticed below 430°C on both surface structures. The critical thickness at which the layer growth mode changed to the island growth mode on the 4×1 surface structure was larger than that on the [Formula: see text] surface structure. Apparent surface diffusion lengths of Ge changed after 2 ML deposition of Ge on the [Formula: see text] surface structure.

Theory of strained-layer epitaxial growth near step flow.

A reaction-diffusion theory of homoepitaxial growth on a stepped surface introduced by Myers-Beaghton and Vvedensky [Phys. Rev. A 44, 2457 (1991)] and Fuenzalida [Phys. Rev. B 44, 10 835 (1991)] is generalized to the case of heteroepitaxy by taking account of misfit strain relief in the growing epilayer. For deposition conditions where two-dimensional (2D) islands nucleate on the terraces before individual adatoms can migrate to vicinal step edges, analysis of the distribution of island sizes resolved in both space and time reveals a strain-driven transition from the familiar layer growth mode dominated by 2D island coalescence to a form of step flow where moving steps engulf very many very small 2D islands. The latter mode of growth is predicted to persist until three-dimensional island formation disrupts layer growth altogether. Both with and without strain, it is found that the island size distribution averaged over a terrace very rapidly approaches a steady-state form, even when kinematic theory predicts oscillations in the signal from diffraction measurements.

An experimental study of the growth of Co/Pt(111) by core level photoemission spectroscopy, low-energy electron diffraction and Auger electron spectroscopy

We have analysed by use of synchrotron radiation induced angle resolved photoemission spectroscopy (PES), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) the growth of ultrathin Co layers deposited at room temperature on Pt(111) surfaces. The LEED patterns indicate an incoherent epitaxy and AES data can be explained by a near layer by layer growth mode. Decomposition of the Pt 4f7/2 photoemission line shows characteristic core level shifts for the different environments of Pt atoms, giving insight concerning a relatively sharp interface structure. On the other hand, the Pt/Co interface in the Pt/Co/Pt(111) sandwich is less sharp, giving rise to two Pt surface sites. Annealing of the Co/Pt(111) system at 400 degrees C gives a surface alloy structure with the same symmetry and orientation as the Pt substrate.

Observation of the early stages of growth and the formation of growth spirals in epitaxial YBa2Cu3O7-? thin films by AFM

Ultrathin epitaxial films of YBa2Cu3O7−δ on SrTiO3 prepared by Direct Current (DC) sputtering and pulsed laser deposition were imaged by Atomic Force Microscopy (AFM) to follow the different stages of growth of the thin films. Series of films with thicknesses between 1.2 nm and 12 nm (1–10 monolayers of YBa2Cu3O7−δ) were prepared under identical conditions, optimized with respect to electrical and structural properties, to obtain information on the mechanisms responsible for the formation of growth spirals which are commonly observed in films having a thickness of several 10 nm or more. It could be shown that few layers are formed by a layered growth mode where material is attached laterally to 2D islands which are only one c-axis unit cell in height. In a later stage of growth when about 8–10 layers have been formed, the growth process changes to a mode which is mediated by growth spirals. This could be directly monitored in the AFM images where different defect structures like vertically sheared growth fronts and dendrite-like terraces of stacked islands as well as the resulting growth spirals could be identified.

Conditions for successful low-temperature growth of hydrogenated amorphous silicon film from silyl radicals conformed to layer-growth mode

By utilizing the reaction between H-radicals and disilanes, we have constructed a silyl-radical-driven deposition system, suitable for illuminating the conditions for successful low-temperature growth of hydrogenated amorphous silicon film. The system could be operated with typically a 15 ms gas residence time to minimize the secondary radical reactions in the gas phase. Most of the bulk properties of films grown in this condition proved not only comparable with those generally associated with device-quality films, but independent of the substrate temperature at least in the 20–200°C range, except for the electric conductivity characteristics. The corresponding initial stages of film deposition on cleaved and sputter-roughened graphite surfaces, studied by the XPS method, exhibited good conformity to the layer-growth mode.

Layered heteroepitaxial growth of germanium on Si(015) observed by scanning tunneling microscopy

Germanium growth on a Si(015) substrate was examined by scanning tunneling microscopy (STM) on an atomic scale. The Ge deposition on a Si(001) substrate showed the Stranski-Krastanov growth mode, where the deposited films grew layer-by-layer up to a few ML followed by three-dimensional island growth with {015} facets. Thus the Ge films were deposited on the Si(015) substrate in this study. As expected, the deposited Ge layers exhibited the layered growth mode up to thicker than 10 ML at a growth temperature of 400°C. The surface and the step structures, which seemed deeply related to the layered growth mechanism, were observed with STM and discussed in detail.

Step-flow growth on strained surfaces

A theoretical study is presented of the effect of misfit strain on the transition from step flow to island nucleation dominated epitaxial layer growth on a vicinal surface. The analysis generalizes a set of reaction-diffusion equations used for homoepitaxy to include the fact that heteroepitaxial strain changes the Arrhenius barrier for diffusion and promotes the detachment of atoms from the edge of strained terraces and islands. The first effect is equivalent to changing the deposition flux; the latter can drive the system into a new layer growth mode characterized by moving steps that engulf very many very small islands. Experiments to test these predictions are suggested.

Initial Stage of Heteroepitaxial Growth of SiC on Si by Gas Source MBE Using Hydrocarbon Radicals

ABSTRACTHeteroepitaxial growth of 3C-SiC on Si in gas source molecular beam epitaxy ( GSMBE ) was carried out by a combination of carbonization of a Si surface and subsequent crystal growth on it using hydrocarbon radicals and Si2H6. The carbonization process and the initial stage of the subsequent growth during the intermittent supply of Si2H6 have been studied by a reflection high-energy electron diffraction (RHEED) observation. A Si surface was chemically converted to 3C-SiC at 750°C, and homoepitaxial growth on the carbonized layer could be obtained at 1000°C. Si atoms generated by thermal decomposition on a surface would react with hydrocarbon radicals, forming SiC through a layer by layer growth mode.

TUNABLE-SAMPLING-DEPTH ELECTRON ENERGY LOSS SPECTROSCOPY AND AUGER ELECTRON SPECTROSC-OPY STUDIES OF Pb/Ni(001) INTERFACE

We have studied the interface formation process of Pb/Ni (001) system by means of tunable-sampling-depth electron energy loss spectroscopy (TELS) and Auger electron spectroscopy (AES). During the deposition of Pb, the AES peak height ratio of Pb to Ni versus time of deposition consists of three segments with the two turning points corresponding to 1 mono-layer (ML) and 2 ML respectively, indicating the Franck-Van der Merwe, i.e. layer by layer growth mode. Also during the Pb deposition, the Pb 6s band ELS peak appears as the Pb coverage is beyond 1 ML, while the Pb bulk plasmon peak appears at about 2 ML of Pb coverage. During the whole process of deposition and annealing, the ELS peak position and width of the Pb bulk plasmon peak, the 6s band peak as well as the Ni 3p band peak maintain their own pure metal values, and there was no new bulk plasmon peak. In view of all these facts, we have reached the conclusion that there is no intermixing of Pb with Ni and the interface of this system is abrupt.

Thermodynamic study of ethane thin films adsorbed on MgO(100) powder

Stepped adsorption isotherms of C 2H 6 adsorbed on a MgO(100) surface have been measured in the temperature range 102–154 K. A layer by layer growth mode is observed at least up to a 5 layer thick film. Presumably ethane wets the MgO(100) surface of square symmetry. We have deduced from our adsorption isotherm network the thermodynamic properties of the first and the second ethane layers. The adsorption heat Q 1 adsof the C 2H 6 condensed 2D phasee on the MgO(100) surface is significantly lower (=20%) than that measured on the hexagonal graphite basal plane surface, on the other hand the 2D critical temperatures T (1) 2c of the C 2H 6 monolayers adsorbed on both substrates are quite similar, T (1) 2c = 133 ± 3K. Such results indicate that the surface electric field influence of the ionic (100) MgO surface is weak. Preliminary neutron diffraction experiments point out that in the monolayer range the ethane film absorbed on Mg(100) is characterized by a short range order. This result is in agreement with the large differential entropy of the C 2H 6 2D film, which is likely in a 2D liquid phase.

Effects of film growth mode on magnetic exchange coupling in trilayer structures (abstract)

In situ temperature-dependent spin-polarized cascade electron spectroscopy is used to study exchange coupling processes between a magnetic substrate and a magnetic overlayer separated by a nonferromagnetic spacer layer. Relative Auger intensities of the overlayer/substrate configurations as a function of overlayer coverage together with a model by Ossicini are used to evaluate the degree to which these trilayer structures grow by a continuous layer growth mode. Measurement of the spin polarization and Auger spectroscopy are used during film growth as criteria of chemical film purity. Evidence will be given to show that the oscillatory magnetic coupling behavior as a function of Cr thickness of a NiFe/Cr/NiFe trilayer changes significantly depending on the deposition temperature, which may be associated with microstructural changes. Competing coupling mechanisms are thought to account for this behavior. Data will also be presented to suggest how trace quantities of residual gas sorbates, presumably acting as surfactants, can dramatically alter the magnetization behavior of ultrathin films. Significant increases in magnetization of a 5-Å Fe overlayer film in a Fe/Ta/Fe trilayer structure were observed and are attributed to changes in wetting characteristics at the Fe/Ta interface which cause morphological changes in the film structure. Conversion of weakly interacting magnetic islands to a long-range ferromagnetic continuous film medium exhibiting remanence and a steady-state Brillouin functional M(T ) behavior is thought consistent with these observations. The possible significance of these kinds of observations to some conflicting data in the literature will be mentioned.

Characteristic features of laser-produced plasmas for thin film deposition

Peculiarities of the pulsed laser plasma method for the deposition of thin films are demonstrated. The interaction between the laser beam and the solid target results in the generation of a plasma. The features of the laser plasma depend on the laser power density and the kind of incident laser light. The model investigations considered contain low and high temperature plasmas, which permit the evaporation threshold as well as the electron temperature and density of an absorbing laser plasma to be estimated. The change in crater depth on the target with variation of the laser flux gives information on the plasma generation and its characteristics, particle flow and energy. A set of Saha equations defines the average charge of the ions and the degree of ionization. The freezing length of particles in the laser plasma depends on their energy and can be larger than the radius of the laser spot. Deposition and growth rates on the substrate during the laser pulse are calculated and turn out to be very high in comparison with those of other deposition methods. Both the high deposition rate and the particle energy, which is transformed into lateral mobility of particles and local heating on the substrate, are the relevant parameters for a two-dimensional layer growth mode of homogeneous dense films.

Nucleation and growth mechanisms in ion-plated TiN films on steel substrates

Cross-sectional transmission electron microscopy was used to investigate the nucleation and growth characteristics of TiN films, ion plated on tool steel substrates with an α-Ti underlayer (about 100 nm thick). It was found that (1) at 100 °C, the underlayer α-Ti remains unchanged and exhibits a layer and island growth mode; (2) at 300 and 500 °C, the underlayer may tranform into a TiC phase on M50 steel, and (3) the growth behavior of TiN films was controlled primarily by the reaction thermodynamics and diffusion rates of titanium and nitrogen adatoms. Model relationships based on microscopic evidence together with kinetic and thermodynamic considerations were established to describe the nucleation and growth mechanisms of ion-plated TiN films under the deposition conditions explored in this study.