Structure Zone Model Research Articles

Homologous substrate-temperature dependence of structure and properties of TiO2, ZrO2, and HfO2 thin films deposited by reactive sputtering

Group 4 metal oxides TiO2, ZrO2, and HfO2 were deposited on glass substrates at substrate temperatures ranging from 100 to 800 °C by reactive direct current magnetron sputtering using an Ar and O2 mixture as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the homologous substrate-temperature dependence of the film structure and properties for the sputter-deposited metal oxide thin films are discussed. The x-ray diffraction measurements show the diffraction patterns characteristic of the anatase (tetragonal) structure at substrate temperatures below 400 °C and those of the rutile (tetragonal) structure at substrate temperatures above 600 °C for TiO2 thin films and the patterns attributable to the monoclinic structure with 〈−111〉 orientation for ZrO2 and HfO2 thin films. Scanning electron microscopy (SEM) observations show voided columnar structures with rough surfaces for TiO2 thin films and fine columnar structures with smooth surfaces for ZrO2 and HfO2 thin films, which is supported by the results obtained from atomic force microscopy (AFM) analysis. The quantitative data on the lattice strain, crystallite size, surface roughness, and refractive index are plotted against the homologous substrate temperature, Tsub/Tm (Tsub: substrate temperature and Tm: melting point of thin film materials). The lattice strain reaches approximately zero at Tsub/Tm = 0.3–0.35, suggesting that the residual stress is relaxed at this point, and the crystallite size reaches a plateau at the same range of Tsub/Tm. The surface roughness increases sharply after passing Tsub/Tm = 0.25–0.30, and the refractive index shows a rise at Tsub/Tm = 0.30–0.35. The images obtained by SEM and AFM are categorized based on the property transition observed in the quantitative property changes. The data obtained in this work are utilized to systematically study the effectiveness and appropriateness of the homologous (normalized) substrate temperature to explain the changes in structure, morphology, and properties of oxide thin films. Furthermore, it is suggested that the structure zone model, which is normally applied to sputtered metal films, is also applicable to sputtered oxide thin films.

On the microstructure of magnesium thin films deposited by magnetron sputtering

Direct current magnetron sputtering (DCMS), and high power impulse magnetron sputtering (HiPIMS) are used to deposit magnesium thin films. The latter technique is characterized by a higher degree of ionization and an ion energy distribution which is significantly altered towards a higher mean ion energy. These differences between both techniques are also reflected in the obtained microstructure of the deposited Mg thin films. DCMS grown films present a rough surface, a porous microstructure and tilted columns, while films deposited by HiPIMS are smooth, dense and have straight columns. Energy and time resolved mass spectrometry show a distinct difference regarding the ion bombardment at the substrate level. The observed film differences are connected to structure zone models with as main focus the role of ion bombardment in the microstructural evolution.

Structure and Morphology Study of Very Thin TiCrN Films Deposited by Unbalanced Magnetron Co-Sputtering

Very thin titanium chromium nitride (TiCrN) films with various Ti content were deposited by unbalanced magnetron co-sputtering of Ti and Cr metals. Deposition time was set to 15 min to achieve film thickness ranging from 142 to 190 nm. Silicon wafers and copper grids were used as substrates. The Ti current (ITi) was varied from 0.4 to 1.0 A to achieve the differnt Ti content whereas Cr current (ICr) was fixed to 0.6 A. Effects of the Ti content on structure and morphology of these TiCrN thin films were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS). The XRD revealed that the films showed crystalline structure with fcc phase and were formed as TixCr1-xN solid solution with a crystallite size of about 13 nm. The TEM result confirmed that the films were polycrystalline. The AFM images of the films showed dome top characteristic with root-mean-square roughness slightly decreasing from 1.643 to 1.273 nm. FE-SEM cross-sectional images exhibited development of film morphology from columnar structure corresponding to zone 1 of Thornton’s structure zone model to fine structure gradually with the increase of the Ti content.

Physical properties of nanostructured ZnO thin films deposited by DC magnetron sputtering method with different volume of O2 in carrier gas

High-quality ZnO thin films with polycrystalline hexagonal structure and (101) preferentially oriented were deposited on Si and corning glass substrates by reactive direct current magnetron sputtering. The effects of different oxygen concentration in carrier gas on structural, morphological and optical properties have been investigated. The increase of O2 concentration resulted in the decrease of preferred orientation intensity and peak shifting to lower 2? values. Scanning electron microscopic images showed a porous tapered columnar structure similar to the zone 1 of Thornton?s structure zone model at lower O2 content and a smooth microstructure similar to the zone T structure at highest O2 content. AFM images showed that film morphology and surface roughness were influenced by O2 concentration. UV-Vis-NIR measurements indicated that the UV absorption intensity of samples was increased and shifted to shorter wavelength (blue shift) at higher O2 concentration. Moreover, the optical band gap increased from 3.91 to 4.41 eV as a function of the oxygen concentration.

Material structure and piezoresistive properties of niobium containing diamond-like-carbon films

Niobium-containing diamond-like carbon (Nb-DLC) films were deposited in a reactive high power impulse magnetron sputtering (HIPIMS) process, using a niobium target in an argon/acetylene atmosphere. Investigations of the electrical properties revealed their good suitability to serve as sensor material in strain gauges, with an elevated gauge factor of 35.5 and the possibility to adapt the temperature coefficient of the electrical resistance (TCR) to values near zero. Structure analysis of the crystallinity, chemical composition, and morphology of this material give insights of the correlations between structure and piezoresistive properties. A structure zone model in relation to the Nb content was developed, combining the results of the different measurements.

Tuning the antimicrobial behaviour of Cu85Zr15 thin films in “wet” and “dry” conditions through structural modifications

The antimicrobial behaviour of Cu85Zr15 at.% thin films prepared by magnetron sputtering was studied in both wet and dry conditions. Small variations in key deposition processing parameters (pressure and substrate temperature) enabled the growth of thin films with similar nanostructures but different degrees of compactness, according to the Thornton's structural zone model. This model has proven its effectiveness in providing sensitive structural information to explain significant differences in antimicrobial behaviour of the CuZr thin films, even when processing conditions lie within the same structural zone. The antimicrobial behaviour has been studied for E. coli and S. aureus for up to 4 h of “dry” contact. Structures of lower compactness, grown at higher deposition pressure, are shown to provide higher antimicrobial activity for “dry” conditions than for “wet” conditions. For thin films of CuZr deposited at 0.5 Pa, the reduction percentage of bacteria is 99.47%, which is much higher than the results of 70–80% obtained for the films deposited at 0.1 and 0.3 Pa. Microscopy studies indicate that for 4 h of contact time, bacteria exhibit inner damage and even lysis, however, no morphological changes are detected because of the short timeframes used.

Influence of sputtering pressure on microstructure and layer properties of iridium thin films

Iridium layers with low stress, high density, and low surface roughness find widespread use in different high-technology applications. This paper presents a study of the influence of the sputtering pressure on the properties of iridium thin films and of its effect on the substrate surface microstructure. We analysed the dependence of the microstructure, crystalline structure, electrical resistivity, and deposition rate on the sputtering pressure and surface defects of the substrate. For the latter, plasma etching of the substrate was performed for different processing times and its effect on the surface roughness of substrates and, subsequently, on the grown iridium films, was examined. The sputtering pressure and the substrate plasma etching time both had a strong influence on the microstructure and surface roughness. These microstructural changes are in good agreement with the tendency described in the Thornton Structure-Zone Model for different sputtering pressures and the microstructure phase map of Alvarez. The electrical resistivity, deposition rate, and crystalline structure were highly dependent on the sputtering pressure.

Revisitation of the structure zone model based on the investigation of the structure and properties of Ti, Zr, and Hf thin films deposited at 70–600 °C using DC magnetron sputtering

The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantitative data on the lattice strain, crystallite size, surface roughness, and electrical resistivity reduced to that of the bulk material were plotted both against the unnormalized and normalized substrate temperatures. The latter data plots show a smaller dispersion than the former ones. The lattice strain and reduced resistivity of all Ti, Zr, and Hf thin films display a sharp bend at a normalized temperature of ∼0.30–0.35. The film surface, cross-sectional morphologies, and film property changes display a clear transition from zones 1 to 2 through zone T. The data obtained in this paper are utilized to systematically explain the effectiveness and appropriateness of the use of the normalized substrate temperature to categorize the film structure, morphologies, and properties of thin films.The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantit...

Scaling behavior of columnar structure during physical vapor deposition

The statistical effects of different conditions in physical vapor deposition, such as sputter deposition, have on thin film morphology has long been the subject of interest. One notable effect is that of column development due to differential chamber pressure in the well-known empirical model called the Thornton's Structure Zone Model. The model is qualitative in nature and theoretical understanding with quantitative predictions of the morphology is still lacking due, in part, to the absence of a quantitative description of the incident flux distribution on the growth front. In this work, we propose an incident Gaussian flux model developed from a series of binary hard-sphere collisions and simulate its effects using Monte Carlo methods and a solid-on-solid growth scheme. We also propose an approximate cosine-power distribution for faster Monte Carlo sampling. With this model, it is observed that higher chamber pressures widen the average deposition angle, and similarly increase the growth of column diameters (or lateral correlation length) and the column-to-column separation (film surface wavelength). We treat both the column diameter and the surface wavelength as power laws. It is seen that both the column diameter exponent and the wavelength exponent are very sensitive to changes in pressure for low pressures (0.13 Pa to 0.80 Pa); meanwhile, both exponents saturate for higher pressures (0.80 Pa to 6.7 Pa) around a value of 0.6. These predictions will serve as guides to future experiments for quantitative description of the film morphology under a wide range of vapor pressure.

Dependence of Nanostructure and the Optical Properties of Ni Thin Films with Different Thicknesses on the Substrate Temperature

Nickel films with the thicknesses of 30 and 120 nm were deposited on glass substrates, at different substrate temperatures (313 to 600 K) under uhv condition. The nano-structure of the films and mean diameter of grains was obtained for each films using atomic force microscopy (AFM). Their optical properties were measured by spectrophotometry in the spectral range of 190-2500 nm. Kramers-Kronig method was used for the analysis of the reflectivity curves. The Effective Medium Approximation (EMA) analysis was used to determine the values of volume fraction of voids (fv)and establish the relationship between the nanostructure of the film and EMA predictions. Qualitatively good agreements between structure Zone Model (SZM) as a function of substrate temperature and the values of (fv), is achieved. There is good agreement between these values and the results of mean diameter of grains for Ni films too. The absorption peaks of Ni thin films at ~ 1.4 eV and 5 eV are observed, with an additional bump at about 2 eV. The 1.4 eV peak is in particular much stronger than that obtained in earlier works on Ni thin films (Johnson and Christy (1974)) and on bulk Ni sample (Lynch et al (1971) and Ehrenrich et al (1963)). This is resulted from producing thin films under uhv condition. The conductivities σ1 and σ2 calculated from ɛ1 and ɛ2 for Ni films and were plotted vs energy.

The structural characterizations of Ti-17 alloy films prepared by magnetron sputtering

Abstract One of the most attractive structural features of titanium (Ti) alloys is its α + β dual-phase growth. Previous work focused on α- or β-Ti phase films, but dual-phase growth in films has not yet been studied. This paper investigates the magnetron-sputtered structures of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy as a function of substrate temperature from 125 °C to 530 °C. The film shows a phase transformation from single β to α + β growth as substrate temperature rises. We discuss the morphology and texture evolutions that arise in sputtering deposition in reference to the structure zone model. We use nanoindentation to assess the mechanical properties of the films. The phase evolution, zone 1–zone T transition, and texture growth with the increasing substrate temperature all contribute to mechanical property improvements of the films.

Tunable transport property of oxygen ion in metal oxide thin film: Impact of electrolyte orientation on conductivity

Quest for efficient ion conducting electrolyte thin film operating at intermediate temperature (~600 °C) holds promise for the real-world utilization of solid oxide fuel cells. Here, we report the correlation between mixed as well as preferentially oriented samarium doped cerium oxide electrolyte films fabricated by varying the substrate temperatures (100, 300 and 500 °C) over anode/ quartz by electron beam physical vapor deposition. Pole figure analysis of films deposited at 300 °C demonstrated a preferential (111) orientation in out-off plane direction, while a mixed orientation was observed at 100 and 500 °C. As per extended structural zone model, the growth mechanism of film differs with surface mobility of adatom. Preferential orientation resulted in higher ionic conductivity than the films with mixed orientation, demonstrating the role of growth on electrochemical properties. The superior ionic conductivity upon preferential orientation arises from the effective reduction of anisotropic nature and grain boundary density in highly oriented thin films in out-of-plane direction, which facilitates the hopping of oxygen ion at a lower activation energy. This unique feature of growing an oriented electrolyte over the anode material opens a new approach to solving the grain boundary limitation and makes it as a promising solution for efficient power generation.

Ag films deposited on Si and Ti: How the film-substrate interaction influences the nanoscale film morphology

Submicron-thick Ag films were sputter deposited, at room temperature, on Si, covered by the native SiO2 layer, and on Ti, covered by the native TiO2 layer, under normal and oblique deposition angle. The aim of this work was to study the morphological differences in the grown Ag films on the two substrates when fixed all the other deposition parameters. In fact, the surface diffusivity of the Ag adatoms is different on the two substrates (higher on the SiO2 surface) due to the different Ag-SiO2 and Ag-TiO2 atomic interactions. So, the effect of the adatoms surface diffusivity, as determined by the adatoms-substrate interaction, on the final film morphology was analyzed. To this end, microscopic analyses were used to study the morphology of the grown Ag films. Even if the homologous temperature prescribes that the Ag film grows on both substrates in the zone I described by the structure zone model some significant differences are observed on the basis of the supporting substrate. In the normal incidence condition, on the SiO2/Si surface a dense close-packed Ag film exhibiting a smooth surface is obtained, while on the TiO2/Ti surface a more columnar film morphology is formed. In the oblique incidence condition the columnar morphology for the Ag film occurs both on SiO2/Si and TiO2/Ti but a higher porous columnar film is obtained on TiO2/Ti due to the lower Ag diffusivity. These results indicate that the adatoms diffusivity on the substrate as determined by the adatom-surface interaction (in addition to the substrate temperature) strongly determines the final film nanostructure.

Improving the mechanical properties of titanium films by texture strengthening

This paper focused on the correlations between the texture and mechanical properties of hexagonal Ti6Al7Nb films prepared by magnetron sputtering. The texture evolution was controlled under a combination of substrate temperature and sputtering power. It was found that the substrate temperature was the key factor to dominate the texture evolution. At constant sputtering power 275W, the films show an increasing (0002) growth from 100 to 300°C, and then transforms into a random growth at 500°C. According to two kinds of structure zone models, the intrinsic image of structure evolution from zone T, zone 2, to finally zone 3 was discussed. Nanoindentation measurements indicated that the texture strengthening contributes to the improvement of mechanical properties.

Morphology and crystal texture in tilted columnar micro-structured titanium thin film coatings

Titanium thin films deposited at various polar incidence angles by electron-beam evaporation are investigated by electron microscopy and X-ray diffraction pole-figures. The resulting film morphology and texture are shown to be strongly affected by the vapor flux direction. At normal incidence deposition angle, a fiber texture forms, with the c-axis of Ti crystallites aligned parallel to the surface normal with random in-plane (azimuthal) orientation. At off-normal deposition angles, porous morphologies with inclined micro-columns form. The texture of these films is an inclined fiber texture, where the texture tilt angle increases with increasing deposition angle. Biaxial texture is observed for films grown at polar incidence angles larger than 60°. The micro-column tilt axis, and the c-axis of the crystallites, both lie in the deposition plane but at different polar angles; the mechanism behind micro-column tilt is due to the shadowing effect, whereas the fiber texture tilt angle and the biaxial texture orientations of the films result from evolutionary crystal growth, determined by the kinetic growth habits of crystallites.Changes in the morphology of Ti films deposited at a vapor incidence angle of 84° and nominal thickness of 3μm at substrate temperatures corresponding to homologous temperatures of 0.15, 0.4, and 0.5 are studied, and compared to the Mukherjee and Gall structure zone model, proposed for high temperature glancing angle deposition. The observed morphology changes are consistent with their model of competition between shadowing length and adatom diffusion length. All the films were grown with homologous temperature lower than 0.5, and formed porous and inclined micro-column morphology, resulting from the dominance of shadowing over adatom surface diffusion.

Nanoscale structure of submicron-thick sputter-deposited Pd films: Effect of the adatoms diffusivity by the film-substrate interaction

Pd films were deposited, at room temperature, on Ti and SiO2 substrates by normal (0°) and oblique (36° and 48°) incidence sputtering processes. Scanning electron microscopy was used to analyze the surface and cross morphology of the Pd films so to study the effect of the Pd adatoms surface diffusivity on the films nanostructure. In fact, even if the low homologous temperature (0.17) prescribes that the Pd film grows on both substrates in the Zone I of the structure zone model, some differences are observed: in normal incidence condition, the Pd film on the Ti substrate was found to be formed by tapered grains, while on the SiO2 substrate the Pd film exhibited a columnar morphology with the columns showing a cauliflower shape. Also in the oblique deposition configurations, notable differences in the nanoscale morphology of the Pd films grown in the same conditions are observed on the basis of the supporting substrate. These data suggest that, during depositions, the Pd adatoms diffusivity on the substrate, as determined by the film-substrate interaction both in normal and oblique deposition conditions, is crucial in determining the final film nanostructure. This aspect is semi-quantitatively discussed on the basis of the adsorption energy of the Pd atoms on Ti (0.69eV) and on SiO2 (0.27eV).

Evolution of microstructure and macrostress in sputtered hard Ti(Al,V)N films with increasing energy delivered during their growth by bombarding ions

This letter reports on the effect of the energy Ebi, delivered to the sputtered Ti(Al,V)N film by bombarding ions, on its microstructure, macrostress σ, mechanical properties, and resistance to cracking. The films were deposited by reactive magnetron sputtering. Interrelationships between these parameters were investigated in detail. It was shown that (1) the increase of the energy Ebi makes it possible to convert (1) the film microstructure from columnar to dense, noncolumnar, (2) the macrostress σ from tensile (σ > 0) to compressive (σ < 0), (3) the brittle hard film with low ratio H/E* < 0.1 and low elastic recovery We < 60% to the flexible hard film with high ratio H/E* ≥ 0.1 and high elastic recovery We ≥ 60%, (2) the flexible hard Ti(Al,V)N films with high ratio H/E* ≥ 0.1, high elastic recovery We ≥ 60%, and compressive macrostress can be formed not only in the transition zone (zone T in which the films exhibit a dense, voids-free microstructure) of the Thornton's structural zone model (SZM) but also in zone 1 in which the films exhibit a columnar microstructure and (3) the line corresponding to the films with zero macrostress (σ = 0) in the SZM lies in zone 1 corresponding to the columnar microstructure; here, H is the film hardness and E* = E(1 − ν2) is the effective Young's modulus, E is the Young's modulus, and ν is the Poisson's ratio.

Density modulated nanoporous tungsten thin films and their nanomechanical properties

Abstract

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3m and the diameter of drilling is 300mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Morphology and thermal conductivity of La2(Ce0.3Zr0.7)2O7-3wt.%Y2O3 coatings

Abstract The La 2 (Ce 0.3 Zr 0.7 ) 2 O 7 -3 wt%Y 2 O 3 coating was deposited by electron beam physical vapor deposition (EB-PVD). In order to reveal the structure evolution of the coating with the deposition parameter, the selected rotation rates of the substrate were 0 rpm, 5, 15 and 25 rpm, while the substrate temperature was fixed at 870 °C based on the structure zone model of 0.3 sub /T mp direction. The tips of the ‘roof top’ or the pyramids were covered by four {111} planes. During rotation deposition, the columnar crystal grew along the direction. If one assumes that the pore fraction has little effect on the thermal conductivity, the ‘C’ shaped Type I pores reduced the thermal conductivity, the straight Type I pores increased the thermal conductivity, the lamellar Type II pores significantly reduced the thermal conductivity. The minimum thermal conductivity was 0.761 W/(m K) at the rotation rate of 15 rpm. This gives an approach to optimize the structure of the La 2 (Ce 0.3 Zr 0.7 ) 2 O 7 -3 wt%Y 2 O 3 coatings.