Binary Thin Films Research Articles

Atomic scale analysis of phase formation and diffusion kinetics in Ag/Al multilayer thin films

Thin films generally exhibit unusual kinetics leading to chemical reactions far from equilibrium conditions. Binary metallic multilayer thin films with miscible elements show some similar behaviors with respect to interdiffusion and phase formation mechanisms. Interfacial density, lattice defects, internal stresses, layer morphologies and deposition conditions strongly control the mass transport between the individual layers. In the present work, Ag/Al multilayer thin films are used as a simple model system, in which the effects of the sputtering power and the bilayer period thickness on the interdiffusion and film reactions are investigated. Multilayers deposited by DC magnetron sputtering undergo calorimetric and microstructural analyses. In particular, atom probe tomography is extensively used to provide quantitative information on concentration gradients, grain boundary segregations, and reaction mechanisms. The magnitude of interdiffusion was found to be inversely proportional to the period thickness for the films deposited under the same conditions, and was reduced using low sputtering power. Both the local segregation at grain boundaries as well as pronounced non-equilibrium supersaturation effects play crucial roles during the early stages of the film reactions. For multilayers with small periods of 10 nm supersaturation of the Al layers with Ag precedes the polymorphic nucleation and growth of the hcp γ-Ag2Al phase. In larger periods the γ phase formation is triggered at junctions between grain boundaries and layers interfaces, where the pathway to heterogeneous nucleation is local supersaturation. Other Ag-rich phases also form as intermediate phases due to asymmetric diffusion rates of parent phases in the γ phase during annealing.

Electrochemical synthesis of polyaniline/inorganic salt binary nanofiber thin films for electrochromic applications

Polyaniline conductive polymer thin films without or with LiClO4 inorganic salt were coated by electrochemical deposition method on ITO surface. Electrochromic stability test, electrochemical behavior, coloring performance, optical properties and surface formations of the produced films were studied in detail. The deposited films were found to have a good stability. Electrochemical analysis showed that the conductivity of LiClO4 doped PANI film was higher than that of the PANI. Oxidation and reduction peaks, and potentials differed significantly depending on the content of the electrolytes. SEM studies demonstrated that the surface of each film consisted of completely nanofibers. Addition of LiClO4 to the deposition electrolyte decreased substantially the diameter of these nanofibers. PANI film with LiClO4 exhibited four colors, while pure PANI film had three different colors. The EDX results obtained from the surface of LiClO4 doped PANI material indicated that PANI and LiClO4 could be successfully linked to form PANI/LiClO4 binary thin film.

Irradiation-induced intermixing effects at the interfaces of titanium and titanium-dioxide thin films and Fe-12%Cr substrate

Irradiation-induced compositional and structural changes at the interfaces between Fe-12%Cr binary alloy substrate and thin films of titanium and titanium-dioxide have been investigated. Irradiations were performed with 5MeV Ni2+ ions at 300°C and 500°C, up to damage levels of 35dpa (displacements per atom). For the 300°C irradiation case, irradiation enhanced the interdiffusion coefficient by a factor over twenty for the titanium film samples, but by a factor of only 1.2 for the titanium dioxide film samples. At 500°C, significant intermixing was observed in the titanium film samples and resulted in the formation of a wide Fe2Ti reaction zone. For the titanium dioxide film samples, chromium was observed to diffuse into sub-stoichiometric regions of the film. Irradiation caused the formation of chromium-rich nanoprecipitates within the oxide film and promoted a phase transformation in the film from anatase TiO2 to the Ti2O3 phase.

Development of Some Alternative Chalcogenide Materials, Thin Films and Diodes for Fabrication of Low Cost Solar Cells

There has been an immense interest in the development of alternatives materials and fabricate electronic devices which provide affordable solar energy generation as well as opto electronic energy transformation applications. Lot of efforts has, therefore, been put in to explore cost- effective, non-toxic and abundant materials. Chalcogenide materials quite recently have attracted attention particularly in the thin film technology due to their applications as non-linear optical materials, infrared sensors and solar energy convertors. Tin chalcogenide Sn(S,Se,Te) binary and ternary materials offer a wide range of optical band gaps suitable for various optical and optoelectronic applications. These materials have exhibited flexibility to possess variable band gaps which are suitable to tap different regions of solar spectrum which have made these materials as potential candidates for applications in photovoltaic solar cell devices. Besides, these materials have also been used as sensor and laser applications, thin film polarizer and thermo electric materials.The work to be presented in the meeting has been focused at the analysis of some Sn(S,Se,Te) binary and ternary thin films for their use as absorber layer in solar cell fabrications. The emphasis shall be made to analyze the change in the band gap, resistivity, absorption coefficient of the undertaken materials and thin films with variation in their elemental compositions and crystal structures. The undertaken materials and thin films were analyzed on the basis of structural, morphological, electrical and optical properties. SnSe and SnS demonstrated orthorhombic crystal structure while SnSe2 possessed hexagonal structure. SnTeSe, however, showed transition from hexagonal to orthorhombic crystal structures with increase in the substrate temperature from 300K to 550K. The electrical and optical analysis of the undertaken films showed change in the optical band gap, resistivity and absorption coefficient values. The films exhibited band gap energies spanning from the visible to near infrared regions. The Schottky barrier diodes of the deposited films were formed and their characteristics analyzed for the temperature dependent current voltage (I-V) and capacitance voltage (C-V) behavior. The current-voltage and capacitance-voltage characteristics of the diodes confirmed that the diodes formed on the deposited films are of good quality. The ideality factors decreased and barrier heights increased with increase in the substrate temperatures in all diodes. The temperature dependence of the barrier heights and ideality factors has been explained on the basis of “barrier inhomogenities” existing over the interface. Further, the variations between the experimentally observed values to the theoretically generated values have been explained on the basis of Gaussian distribution function which indicated the possibility of the presence of the tunneling current component in the electrical transport mechanism existing over the interface. The breakdown voltage phenomenon in the undertaken diodes provided negative temperature coefficient and depicted soft breakdown due to “defect assisted tunneling” over the interface.

Unipolar resistive switching effect and mechanism of solution-processed spinel Co3O4 thin films

Binary spinel Co3O4 thin films with smooth surface were fabricated by using chemical solution deposition method and unipolar resistive switching characteristics including set and reset switching voltages, low and high resistance ratio, cycling endurance, and retention time were investigated in the Pt/Co3O4/Pt sandwich structures. Through the analysis of conductive mechanism and temperature dependence of resistance states, it was suggested that Ohmic conduction behavior governed the carriers transport in low resistance state and Schottky emission dominated the conduction mechanism in high resistance state, respectively. Moreover, the switching mechanism was explained by the formation and rupture of conductive filament during the set and reset processes. This study suggests that the solution-processed spinel Co3O4 thin films could find potential application in nonvolatile resistive switching memory.

Binary Lithium Titanate–Titania Nanocomposite Thin‐Film Electrodes for Electrochemical Energy Storage

AbstractThis work introduces a facile approach for preparation of binary nanocomposite thin film electrodes for lithium‐ion batteries with excellent storage capability, high rate performance, and good electrochemical stability. The Li4Ti5O12‐TiO2 film electrodes are prepared by radio frequency (RF) magnetron sputtering deposition using a Li4Ti5O12 and TiO2 powder mixture target as sputtering source in an argon atmosphere. The Li4Ti5O12–TiO2 electrode yields good electrochemical performance in terms of high capacity (295 mAh g−1) at a current density of 0.1 C, good cycling stability (≈5 % capacity loss after 100 cycles at 0.1 C), and excellent rate capability (158 mAh g−1 at a current density of 5 C). The factors contributing to the excellent electrochemical performance are related to the binary nanocomposite structure. The results suggest that the Li4Ti5O12–TiO2 nanocomposite thin film can be used as an anode material for high‐performance lithium‐ion batteries.

Ambipolar Carrier Mobility in Binary Blend Thin Film of Non-Peripheral Alkylphthalocyanines

Charge carrier mobility in blend films of two types of soluble phthalocyanine derivatives with different substituent length, 1, 4, 8, 11, 15, 18, 22, 25-octapentyl-phthalocyanine (C5PcH2) and 1, 4, 8, 11, 15, 18, 22, 25-octahexyl-phthalocyanine (C6PcH2) has been investigated. The charge carrier mobility was measured by the time-of-flight technique. In the case of C5PcH2 blend ratio below 25 mol%, the high mobility, such as 0.8-1.1 cm2V-1s-1 for hole and 0.6 cm2V-1s-1 for electron, were obtained at room temperature. In the thin films with C5PcH2 above 30 mol%, the charge carrier mobility decreased by one order of magnitude and had the different temperature dependence from that below 25 mol%. The marked change of the charge carrier mobility depending on the blend ratio of phthalocyanine derivatives has been discussed by taking the miscibility and the molecular packing structure into consideration.

Theoretical and experimental study of metastable solid solutions and phase stability within the immiscible Ag-Mo binary system

Metastable solid solutions are phases that are synthesized far from thermodynamic equilibrium and offer a versatile route to design materials with tailor-made functionalities. One of the most investigated classes of metastable solid solutions with widespread technological implications is vapor deposited ternary transition metal ceramic thin films (i.e., nitrides, carbides, and borides). The vapor-based synthesis of these ceramic phases involves complex and difficult to control chemical interactions of the vapor species with the growing film surface, which often makes the fundamental understanding of the composition-properties relations a challenging task. Hence, in the present study, we investigate the phase stability within an immiscible binary thin film system that offers a simpler synthesis chemistry, i.e., the Ag-Mo system. We employ magnetron co-sputtering to grow Ag1−xMox thin films over the entire composition range along with x-ray probes to investigate the films structure and bonding properties. Concurrently, we use density functional theory calculations to predict phase stability and determine the effect of chemical composition on the lattice volume and the electronic properties of Ag-Mo solid solutions. Our combined theoretical and experimental data show that Mo-rich films (x ≥ ∼0.54) form bcc Mo-Ag metastable solid solutions. Furthermore, for Ag-rich compositions (x ≤ ∼0.21), our data can be interpreted as Mo not being dissolved in the Ag fcc lattice. All in all, our data show an asymmetry with regards to the mutual solubility of Ag and Mo in the two crystal structures, i.e., Ag has a larger propensity for dissolving in the bcc-Mo lattice as compared to Mo in the fcc-Ag lattice. We explain these findings in light of isostructural short-range clustering that induces energy difference between the two (fcc and bcc) metastable phases. We also suggest that the phase stability can be explained by the larger atomic mobility of Ag atoms as compared to that of Mo. The mechanisms suggested herein may be of relevance for explaining phase stability data in a number of metastable alloys, such as ternary transition metal-aluminum-nitride systems.

Fabrication and characterization of nanostructural WS2/WO3 binary compound semiconductors prepared by the sulfurization of sprayed thin films

We have investigated the impact of sulfurization and changing the metal salt ratio ([s]/[w] = 6–24 at.%) in the precursor solution on the structural, morphological, optical, electrical and photoconductivity properties of WS2/WO3 binary thin films grown on glass substrate by the spray pyrolysis technique. X–ray diffraction analysis showed that while the as-deposited samples present an amorphous nature, annealing these films in sulfur atmosphere generate a mix phase of WS2/WO3. FESEM study revealed the changes in surface morphology with increase in sulfur concentration in the spray solution. UV–Vis optical measurements analysis showed that these binary films have a relatively high absorption coefficient ~2 × 104–8 × 104 cm−1 in the visible spectrum with two distinct inflexions indicative of two transitions correspond to WS2/WO3 phases in agreement with the XRD analysis. The electrical studies showed that all these samples have a p-type conductivity; and the resistivity and photoconductivity decreases with increasing the sulfur to tungsten molar ratio.

Optical properties of pseudo binary oxides (TiO2)1-x-(Al2O3)x thin films prepared by spray pyrolysis technique

Pseudo binary oxide thin films,(TiO2)1-x-(Al2O3)x, were prepared by spray pyrolysis technique on cleaned quartz and silicon substrates. The prepared precursor solutions of Al2O3 and TiO2 were mixed thoroughly in appropriate volume, calculated from the molar fraction. The XRD pattern of Al2O3-TiO2 film shows anatase phase and mixed phase of Al2TiO5 (Aluminum Titanium oxide). The SEM micrograph shows spherical grains with nano porous surface and some clusters, it is also composed of crumb like nano particles and average grain sizes are estimated. In the EDAX spectrum, the signals corresponding to oxygen (O2), titanium (Ti), aluminum (Al) and substrate silicon (Si) are seen, elemental analysis shows that weight percentage are in stoichiometric ratio. Transmittance and Reflectance spectra were recorded in normal incidence by UV-Visible Spectrophotometer in wavelength range 350nm to 1200nm. Using these optical data the thickness, refractive index, extinction coefficient, real and imaginary part of dielectric constants, energy band gap, Urbach energy and Packing density are estimated. It is observed that, with the increase in molar fraction there is a variation of the energy band gap, which may be attributed to the mixed phase formation in the films as well as formation of defects. The obtained pseudo binary oxide thin films have wide band gap and porous surface structure; hence these films are further used for sensing application.

Effect of annealing parameters on structural and morphological properties of sprayed ZnS thin films

Abstract We have investigated the effect of annealing and substrate temperature on structural and morphological properties of ZnS binary thin films grown on glass substrates by the spray pyrolysis technique. The crystal structure and grain size of the particles were determined, using X-ray diffraction (XRD). The morphological properties were studied by the Atomic Force Microscopy (AFM) and the Scanning Electron Microscopy (SEM). The films were then annealed under nitrogen at 300 °C, 400 °C and 500 °C, under Vacuum and nitrogen at 500 °C and sulphur atmosphere for one hour at 500 °C. This process allows us to obtain peaks crystallized under mixture of hexagonal (H) and cubic (C) phase. The crystallites exhibit preferential orientation along the (2 0 0) C direction. The variation of grain size and roughness were studied. Thus the grain size of the ZnS film increases when the annealing temperature is increased.

Chalcogenide Thin Films Prepared using Chemical Bath Deposition Method: Review

The aim of this study is to discuss the synthesis of thin films using chemical bath deposition method. In recent years, studies of thin films of different groups have attracted great attention due to their applications are possible in many areas of modern technology. Researchers have deposited binary, ternary and quaternary thin films from aqueous solutions using chemical bath deposition method. Here, the growth of metal sulfide, selenide and telluride thin films has been reported. The influence of deposition parameters on the physical properties of films was investigated. The research findings indicate that an increase in deposition time allows more materials to be deposited onto the substrate. Morphological studies of films show that the films thicknesses were increased as the bath temperature was increased.

Solid-state dewetting of magnetic binary multilayer thin films

We examined solid-state dewetting behavior of magnetic multilayer thin film in both miscible (CoPd) and immiscible (CoAu) systems and found that CoPd and CoAu dewetting stages follow that of elemental materials. We established that CoPd alloy morphology and dewetting rate lie in between that of the elemental materials. Johnson-Mehl-Avrami analysis was utilized to extract the dewetting activation energy of CoPd. For CoAu, Au-rich particles and Co-rich particles are distinguishable and we are able to predict the interparticle spacings and particle densities for the particles that agree well with the experimental results. We also characterized the magnetic properties of CoPd and CoAu nanoparticles.

Physical vapor deposition of mixed-metal oxides based on Fe, Co and Ni as water oxidation catalysts

Physical vapor deposition (PVD) techniques are proposed as high performing and easily tunable methods to synthesize mixed-metal oxides thin films as water oxidation catalysts (WOC). These techniques allow us to have a good control on the catalyst film surface morphology and crystallinity, with good adhesion of the catalysts on electrodes. Pure and binary metal oxides thin films based on Fe, Co and Ni were synthesized using electron beam deposition (EBD). WOC films are systematically studied through SEM microscopy, Raman spectroscopy and XPS analysis. Electrochemical characterization has been carried out to investigate the relevance of synergistic effects towards the water oxidation reaction. Among all the mixed oxides Ni–Fe oxide showed the best catalytic results.

Binary iron-chromium oxide as negative electrode for lithium-ion micro-batteries – spectroscopic and microscopic characterization

(Fe,Cr)-binary oxide thin film electrodes were prepared as negative electrode material for lithium-ion micro-batteries by thermal growth on a stainless steel (AISI 410, FeCr12.5) current collector. The mechanisms of lithiation/delithiation were investigated by means of electrochemical (CV, galvanostatic cycling), spectroscopic (XPS, ToF-SIMS) and microscopic (SEM, AFM) analytical techniques. The as-prepared (Fe, Cr)-binary oxide electrodes exhibit a good cycling performance except the first discharge/charge cycle where a high irreversible capacity is observed due to formation of a solid electrolyte interphase (SEI) layer. The influence of substituting an oxidized iron by an oxidized chromium (CrxFe2−xO3 phase) was evaluated. The data show that the inferior electrochemical conversion activity of substituted oxidized chromium results in hindering lithium transport in the bulk thin film electrode. It was observed that the irreversible morphology modifications together with SEI evolution are critical to capacity degradation while retaining good coulombic efficiency.

(Invited) Ru-Based Binary or Ternary Thin Films By Atomic Layer Deposition for a Seedless Cu Interconnects

Ru has been suggested as a diffusion barrier that is compatible with the direct plating of Cu. However, previous studies showed that Ru itself is not a suitable diffusion barrier for Cu metallization due mainly to its poor microstructure with polycrystalline columnar grains. This study developed several Ru-based multi-component thin films, RuMn, RuSiN, and RuAlO using atomic layer deposition (ALD) process, which are compatible with the direct plating of Cu as well as show better diffusion barrier performance against Cu than Ru. Mn, SiNx, AlOx were incorporated into the Ru by combining the Ru and corresponding ALD cycles, and Ru-based binary alloy, RuMn, ternary thin films, RuSiN and RuAlO, were fabricated at 225 oC. As a typical example, the results on ALD-RuAlO were shortly described. The step coverage of ALD-RuAlO was perfect at contact holes with an aspect ratio of ~ 25 (top-opening diameter: ~ 85 nm). XRD and TEM results indicate that ALD-Ru film prepared without AlOx ALD cycle forms a polycrystalline structure with columnar grains. But, with incorporating the AlOx cycles, RuAlO films were formed with non-columnar grains and nano-crystalline microstructure consisting of Ru nano-crystals separated by amorphous AlOx matrix. XRD analysis showed that the structure of Cu/ALD-RuAlO (8 nm)/Si was stable after annealing at 600 oC for 30 minute while Cu/Ru (15 nm)/Si structure was failed after annealing at 450 oC. It was also shown that the electroplating of Cu was directly achieved on a very thin (~8-nm-thick) RuAlO film at blanket and pattern wafer. In the case of binary ALD-RuMn film, it should be noted that after annealing ALD-RuMn film at 500 oC, the self-formation of Mn silicate barrier between Ru(Mn) film and SiO2 was confirmed based on XRD and TEM analysis, which was due to the diffusion of Mn into underlying SiO2, resulting in better diffusion barrier performance than Ru counterpart. Acknowledgements This work was supported by the Technology Innovation Program (Industrial Strategic technology development program, 10035430, Development of reliable fine-pitch metallization technologies) funded by the Ministry of Knowledge Economy (MKE, Korea) and also partially supported by Tanaka Precious Metals, Japan.

Thin Films: Tuning Local Molecular Orientation–Composition Correlations in Binary Organic Thin Films by Solution Shearing (Adv. Funct. Mater. 21/2015)

Thin Films: Tuning Local Molecular Orientation–Composition Correlations in Binary Organic Thin Films by Solution Shearing (Adv. Funct. Mater. 21/2015)

Multifunctional Ti–Me (Me = Al, Cu) thin film systems for biomedical sensing devices

Ti–Me binary intermetallic thin films based on a titanium matrix doped with increasing amounts of Me (Me = Al, Cu) were prepared by magnetron sputtering (under similar conditions), aiming their application in biomedical sensing devices. The differences observed on the composition and on the micro(structural) features of the films, attributed to changes in the discharge characteristics, were correlated with the electrical properties of the intermetallic systems (Ti–Al and Ti–Cu). For the same Me exposed areas placed on the Ti target (ranging from 0.25 cm2 to 20 cm2) the Cu content increased from 3.5 at.% to 71.7 at.% in the Ti–Cu system and the Al content, in Ti–Al films, ranged from 11 to 45 at.%. The structural characterization indicated the formation of metastable Ti–Me intermetallic phases for Al/Ti atomic ratios above 0.20 and for Cu/Ti ratios above 0.25. For lower Me concentrations, the effect of the α-Ti(Me) structure dominates the overall structure. With the increase in the amount of the Me into the Ti structure a clear trend for amorphization was observed. For both systems a significant decrease of the electrical resistivity with increasing Me/Ti atomic ratios (higher than 0.5 for Al/Ti atomic ratio and higher than 1.3 for Cu/Ti atomic ratio) was observed. Although similar trends were observed in the resistivity evolution for both systems, the Ti–Cu films presented lower resistivity values in comparison to the Ti–Al system.

Combinatorial Study of Ag-Te Thin Films and Their Application as Cation Supply Layer in CBRAM Cells.

In this work, we investigate binary Ag-Te thin films and their functionality as a cation supply layer in conductive bridge random access memory devices. A combinatorial sputter deposition technique is used to deposit a graded Ag(x)Te(1-x) (0 < x < 1) layer with varying composition as a function of the position on the substrate. The crystallinity, surface morphology, and material stability under thermal treatment as a function of the composition of the material are investigated. From this screening, a narrow composition range between 33 and 38 at% Te is selected which shows a good morphology and a high melting temperature. Functionality of a single Ag(2-δ)Te composition as cation supply layer in CBRAM with dedicated Al2O3 switching layer is then investigated by implementing it in 580 μm diameter dot Pt/Ag(2-δ)Te/Al2O3/Si cells. Switching properties are investigated and compared to cells with a pure Ag cation supply layer. An improved cycling behavior is observed when Te is added compared to pure Ag, which we relate to the ionic conducting properties of Ag2Te and the preferred formation of Ag-Te phases.

Tuning Local Molecular Orientation–Composition Correlations in Binary Organic Thin Films by Solution Shearing

A general impact of solution shearing on molecular orientation correlation is observed in polymer:fullerene organic solar cells in which one of the components forms fibrils or aggregates. Further investigation with polarized soft X‐ray scattering reveals that solution shearing induces more face‐to‐face orientation relative to the interface of two components compared to spin‐coating. This impact is shearing speed dependent, that is, slow shearing speed can induce more face‐to‐face orientation than a fast shearing speed. These results demonstrate that solution shearing is an effective method to control the relative molecular orientation. Solution shearing can also modify the domain size and average composition variations.