Sol-gel processed highly (100)-textured (K,Na)NbO3-based lead-free thin films: Effect of pyrolysis temperature

Recently, lead-free piezoelectric thin films have received increasing attention due to the growing demands for mircoelectromechanical systems and the significant progress in lead-free piezoelectric research. Here, potassium sodium niobate [(K, Na)NbO₃ (KNN)]-based thin films were fabricated via a sol-gel method. The effects of pyrolysis temperature on the resulting microstructure and electrical properties of KNN-based films were investigated. The KNN-based film pyrolyzed at 550°C and annealed at 700°C shows a dominant (100) orientation with a high texturing degree of 91.7%. The microstructures, morphologies, piezo- and ferroelectric properties of the KNN-based films were discussed in association with different pyrolysis temperatures. The crystallization mechanism of the (100) textured KNN-based thin films was elaborated in detail.     

Annealing effect upon chain orientation, crystalline morphology, and polarizability of ultra-thin P(VDF-TrFE) film for nonvolatile polymer memory device

The ferroelectric behavior of spin-cast ultra-thin P(VDF-TrFE) (72-28) film is highly influenced by sample preparation methods including thermal annealing. The effect of sample preparation methods on the surface morphology, chain and dipole orientation, ferroelectric properties, and nonvolatile memory characteristics were studied using FTIR-grazing incident reflection absorption spectroscopy (GIRAS), grazing incident wide angle X-ray diffraction (GIWAXD), atomic force microscope (AFM), dynamic contact electrostatic force microscope (DC-EFM), and polarization-electric field (P-E) hysteresis measurements to find the feasibility of applying the ultra-thin P(VDF-TrFE) film to scanning probe microscopy (SPM)-based storage device or low-cost nonvolatile ferroelectric polymer random access memory (NvFePoRAM) device. From the collective analysis of GIRAS, GIWAXD, and AFM data, annealing the as-cast sample at temperature (ca. 120 °C) above Curie transition, but below its melting transition temperature was found to be the most suitable condition to fabricate the NvFePoRAM and/or SPM-based storage device with a memory density of about 30 GB/in². DC-EFM technique was successfully used to characterize the nonvolatile memory properties by ‘writing and erasing’ the data bit through applying a dc bias voltage much larger than coercive voltage with different polarities and then reading the data bit by applying a high frequency ac voltage of only 2 V to the ‘written or erased’ area.     

Microstructure Evolution during Crystallization of Vapor‐Deposited Hexanitroazobenzene Films

Vapor‐deposited hexanitroazobenzene (HNAB) films were observed to form a dense amorphous structure that crystallizes to a mixture of the HNAB‐II polymorph and an unidentified structure over a period ranging from hours to weeks depending on the ambient temperature. Films crystallized at various temperatures were characterized using scanning electron microscopy, atomic force microscopy, X‐ray diffraction, and Raman spectroscopy to measure the impact of crystallization temperature on resultant microstructure. Crystallization temperature was observed to have different effects on film microstructure over two temperature regimes. At temperatures below approximately 65 °C, increases in temperature led to a greater fraction of the film forming the HNAB‐II polymorph and caused subtle changes in morphology. However, at higher temperatures, a thin surface layer was observed to form prior to crystallization, which led to films composed primarily of the unknown crystal structure with conspicuous differences in morphology.     

The influence of the crystallization temperature on the reliability of PbTiO3 thin films prepared by chemical solution deposition

The preparation of quality ferroelectric PbTiO₃ (PT) thin films at the lowest possible temperature preserving its functional properties is necessary for their integration in microdevices. The crystallization below, close or above the para-ferrolectric transition temperature of the PbTiO₃ must produce an important effect on the microstructure, texture and residual stress state of the films and on functional properties. In this paper, the Chemical Solution Deposition method has been used to prepare PbTiO₃ films at different temperatures around that of the ferroelectric to paraelectric phase transition. The films were analyzed by X-ray diffraction, Optical and Scanning Electron Microscopy, and their microstructure, texture and residual stress correlated with their functional properties. The results show that these PT films prepared with crystallization temperatures close or below the phase transition develop a favorable microstructure and texture that lead to high remnant and saturation polarization values, making them good candidates for their integration in microdevices.     

掺锶对钛酸铅薄膜结晶性能的影响

钛酸锶铅(PST)薄膜是一类重要的铁电薄膜材料.采用溶胶-凝胶法在硅(100)衬底上制备了钛酸锶铅薄膜.利用X射线衍射(XRD)、原子力显微镜(AFM)等表征手段,表征了不同锶掺杂量及不同退火温度对薄膜结晶性能的影响.通过实验发现:锶掺杂对薄膜的微观结构和表面形貌有重要的影响.由XRD谱图发现,随着锶掺入量的增加,Pb 1-xSrxTiO3薄膜中的晶轴比、晶胞体积都逐渐减小,晶化温度降低.通过AFM发现,相同掺锶量的薄膜随着退火温度的升高,结晶性能增强,颗粒增大,粗糙度增加.     

Confined intra-molecular clustering in orientated polyethylene after annealing

Deuterated polyethylene tracer molecules with small amount of branches (12 C₂H₅- branches per 1000 backbone carbon atoms) were blended with a hydrogenated polyethylene matrix to form a homogenous mixture. The conformational evolution of the deuterated chains in a stretched semi-crystalline film was observed via online small angle neutron scattering measurements during annealing at high temperatures close to the melting point. Because the sample was annealed at a temperature closely below its melting point, the crystalline lamellae were only partially molten and the system could not fully relax. The global chain dimensions were preserved during annealing. Recrystallization of released polymeric chain segments allows for local phase separation thus driving the deuterated chain segments into the confining inter-lamellar amorphous layers giving rise to an interesting intra-molecular clustering effect of the long deuterated chain. This clustering is deduced from characteristic small angle neutron scattering patterns. The confined phase separation has its origin in primarily the small amount of the branches on the deuterated polymers which impede the crystallization of the deuterated chain segments.     

Annealing Effect on the Properties of Cu(In0.7Ga0.3)Se2 Thin Films Grown by Femtosecond Pulsed Laser Deposition

This work reports the crystallization, microstructure, and surface composition of CuIn_0.7Ga_0.3Se₂ (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X‐ray diffraction, Raman scattering, UV‐visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuSe initially formed on the as‐deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as‐deposited and annealed films as demonstrated by preliminary tests.     

Nanoscale localization of poly(vinylidene fluoride) in the lamellae of thin films of symmetric polystyrene-poly(methyl methacrylate) diblock copolymers

We employed thin film blends of diblock copolymers with functional homopolymers as a simple strategy to incorporate organic functional materials into nanodomains of diblock copolymers without serious synthesis. A blend pair of polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers and poly(vinylidene fluoride) (PVDF) was selected as a model demonstration because PVDF is a well-known ferroelectric polymer and completely miscible with amorphous PMMA. Thin films of symmetric PS-PMMA copolymers provided the nanometer-sized PMMA lamellae, macroscopically parallel to the substrate, in which PVDF chains were dissolved. Thus, amorphous PVDF chains were effectively confined in the PMMA lamellae of thin film blends. The location of PVDF chains in the PMMA lamellae was investigated by the dependence of the lamellar period on the volume fraction of PVDF, from which we found that PVDF chains were localized in the middle of the PMMA lamellae. After the crystallization of PVDF, however, some of PVDF migrated to the surface of the film and formed small crystallites.     

Microstructure and ferroelectric properties of Ta-doped Bi3.25La0.75Ti3O12/ZnO thin film capacitors

Ta-doped Bi_3.25La_0.75Ti₃O₁₂(BLTT)/ZnO films were fabricated on Pt(111)/Ti/SiO₂/Si substrates by a magnetron sputtering method. Firstly, ZnO crystal thin films were grown on the substrates by a reactive sputtering method. Then, BLTT thin films were deposited on the ZnO layers at room temperature and post-annealed at 600 °C. The micromorphology, ferroelectric and dielectric properties of BLTT/ZnO films were analyzed. The XRD analysis shows that ZnO buffer layer significantly reduces the crystallization temperature of BLTT thin film. The TEM results show that lamellar BLTT grains are grown on ZnO layer at a certain angle with few elements diffusion at the interface of ZnO phase and Bi₄Ti₃O₁₂ phase. The ferroelectric properties indicate that BLTT/ZnO films exhibit different remanent polarization and coercive fields under electric field with different directions. The novel mechanism of tailoring ferroelectric properties may open new possibilities for designing special ferroelectric devices.     

脉冲准分子激光扫描沉积(PLD)高c轴取向V2O5/Si薄膜及结构分析

采用脉冲准分子激光大面积扫描沉积技术,在Si(111)单晶衬底上沉积了多晶V2O5薄膜,经300℃以上退火处理得到了具有高c-轴取向生长的V2O5膜。300℃以上热退火处理的薄膜表面具有正常的化学计量比（无氧缺位）,晶粒间界明显,晶粒呈针棒状,晶粒尺寸在100－200nm之间。采用X射线衍射（XRD）、Raman光谱（RS）、Fourier红外光谱（FT－IR）及透射电镜扫描附件（STEM）对沉积及不同温度下退火处理的样品进行了结构分析。研究结果表明：V2O5/Si薄膜经400℃热处理后表面部分处于低价态的钒离子已被氧化为V2O5。     

Thermodynamical characteristics of thin ferroelectric films

Thermodynamic characteristics of the KDP type ferroelectrics are analysed in the paper. Dispersion laws of the ferroelectric excitations in the thin ferroelectric films are considered. The ordering parameter was investigated at the low temperatures and at the temperatures near the phase transition temperature. The analysis shows that the spontaneous polarization in the film decreases more slowly with increase of the temperature than in the bulk structure. This conclusion is important for practical application because the thin films keep the ferroelectric properties at significantly higher temperatures than the bulk structures.     

Thermal treatment effect on nanostructured TiO2 films deposited using diethanolamine stabilized precursor sol

A clear ethanol based precursor sol obtained using diethanolamine has been utilized for the deposition of TiO₂ films annealed at different temperatures. The influence of annealing temperature on the structural, optical and electrochemical properties of TiO₂ thin films has been examined. Diethanolamine stabilizes the precursor sol due to its chelate forming ability with the alkoxides. It reacts as a tridentate ligand with the titanium isopropoxide. The threshold for the onset of crystallization in the films is identified at a temperature of 300 °C. The SEM study on the films elucidates segregation of irregularly shaped features into finer round clusters as a function of annealing temperature. As determined from the AFM study, the roughness parameter in the films has shown an increase with the annealing temperature. Photoluminescence measurements have given an indirect evidence for the presence of stoichiometric titanium oxide in the films. An optimum crystallite size and high ion storage capacity in the 300 °C annealed film has led to its superior electrochromic activity with the transmission modulation and coloration efficiency of the same film being 42% and 8.1 cm² C⁻¹, respectively at 550 nm. The highest degree of porosity in the 300 °C annealed film as established from the SEM study is also the reason behind its best electrochromic performance. In addition, the 300 °C annealed film also exhibits the fastest coloration switching kinetics.     

Confined crystallization of polymeric materials

The interest in confined crystallization has greatly increased with the development and progress of nanotechnology applications. Polymeric confined crystallization has been studied in droplets, ultrathin films, nanolayers, nanostructures from solutions, blends, copolymers, polymers infiltrated within AAO templates and nanocomposites. As confinement increases, the crystallization temperature first decreases, then splits into several fractions (i.e., fractionated crystallization) and finally occurs in one step at the maximum possible supercooling, near the glass transition temperature. Two factors are responsible for these effects: (a) a change in nucleation mechanism, from heterogeneous nucleation to surface nucleation (or in extreme cases, homogeneous nucleation), (b) the dependence of the crystallization temperature on the volume or the surface (or interphase) of the crystallizable micro or nanodomains. The melting point also decreases with confinement but to a lesser degree. A preferential orientation of polymeric crystals is generally induced by one or two dimensional confinement. Avrami indexes decrease with confinement until values of 1 (or even lower) are achieved in the limit of isolated domains, as the material approaches a first order crystallization kinetics. This type of kinetics reflects that nucleation is the rate determining step in the overall crystallization of ideally confined polymers.     

Crystallization Behavior of Sol–Gel-Derived Strontium Barium Niobate Thin Films

The crystallization of sol–gel-derived strontium barium niobate (SBN) thin films on various substrates is enhanced by a two-step heating process. Also, SBN films with c -axis preferred orientation are obtained on MgO (100) substrates. The crystallized phase and the degree of orientation are dependent on crystallization temperature and film composition. The crystallization temperature required to form a single tetragonal tungsten bronze (TTB) SBN phase increases with an increase of Sr content due to the distorted SBN structure. However, in the case of the film on MgO substrate, the oriented crystallization which forms the single tetragonal phase occurs at a lower crystallization temperature than those of polycrystalline films because of lattice matching between the film and the substrate. Its optical and ferroelectric properties were also investigated. They vary depending on film composition, due to the effect of the distorted SBN structure.     

Blocked crystallization in capped ultrathin polymer films studied by molecular simulations

The crystallization of capped ultrathin polymer films is closely dependent on film thickness and interfacial interaction. Using dynamic Monte Carlo simulations, the crystallization behaviors of polymer films confined between two substrates were investigated. The crystallization rate of confined polymers is reduced with high interfacial interactions. Above a critical strength of interfacial interaction, polymer crystallization in the thin film is inhibited within the simulation time scales. An increase in film thickness leads to a rise in critical interfacial interaction. In thicker films, the chains have more space to change conformation to form crystal stems. In addition, there are fewer absorbed segments in confined chains for the thicker films, and thus the chains have stronger ability to adjust their conformation. Therefore an increase in film thickness can cause a reduction in the entropic barrier required for the formation of crystals and thus an increase in the critical interfacial interaction. © 2018 Society of Chemical Industry     

Poly(caprolactone) thin film preparation,morphology, and surface texture

The properties and surface uniformity of poly‐ (caprolactone) (PCL) thin films were measured. Thin films were prepared using a spin‐coating technique. Film thickness and roughness were correlated with variation in solution concentration, spinning speed and spinning time. Differential scanning calorimetry (DSC) was used to investigate the crystallization and melting processes. The enthalpy of melting variation correlated with the film thickness, while melting temperature was independent of film thickness. In addition, surface roughness was found to be a function of PCL thickness. Film thickness and roughness showed a progressive decrease when spinning speed was increased, while spinning time provided no significant influence on film thickness. PCL thickness and roughness significantly increased when PCL solution concentration increased. Hot stage optical microscopy showed that larger spherulitic crystals were present in thin films, and the smaller crystals present in thicker films had a coarser texture consistent with increased surface roughness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1287–1294, 2007     

Annealing temperature influence on sol-gel processed zirconium oxide thin films for electronic applications

A study of zirconium oxide (ZrO₂) thin films obtained by the non-alkoxide sol-gel method at different annealing temperatures, up to 450?°C, is presented. Morphological, compositional, and optical characterizations of zirconia thin films show high transparency and high bandgap, besides homogeneous and non-porous surface. Metal-insulating-metal (MIM) devices were assembled from this zirconia material for electrical characterizations and have shown high electric resistivity and high specific capacitance. A study of the thin film composition shows residues of S and Cl elements from the precursor solution that contributes for reduction of the dielectric constant of the zirconia thin films, even though they still present higher values when compared to SiO₂, which is a positive alternative to replace this oxide in electronic devices. A parallel study of MIM assembled on polymeric substrate and annealed at 100?°C also leads to positive results concerning high electrical insulating and capacitance. This study aims the understanding of the relations between annealing temperature and impurities found in sol-gel based thin films, as well as their relations to dielectric characteristics of zirconia thin films that impact the final properties of electronic devices, such as in field effect transistors.     

Does isothermal crystallization ever occur?

Much of what we think we know about crystallization in polymers is obtained from studies carried out under isothermal conditions. From extrapolations of equilibrium melting temperature to crystallization regimes, interpretations in the literature all assume that the measured temperature of a polymer film is the temperature at which the crystallization occurred.Recently it has been possible to study crystallization at very high supercoolings, even in rapidly crystallizing polymers, through the use of a rapid cooling technique in which a thin film contains a microthermocouple to measure actual temperature. In adequately thin films an isothermal temperature is set up through a balance between the heat of fusion released and the cooling rate applied. This technique has been applied successfully to polypropylenes, and to polyethylene homopolymers and copolymers. The results have told us much about crystallization at very high supercoolings. Recently, a study of the effect of nucleating agents on quench-crystallization in PET and in nylon 6 was conducted, in which it was discovered that films containing nucleating agents generated the expected temperature plateau when crystallization occurred.In this paper, we wish to report the results of studies of thin films of nylon 66 and PET which did not contain nucleating agents. The results are totally unexpected and indicate that a steady state condition exists at the growth face of the polymer, which is not reflected in the macroscopic temperature of the thin film, as measured using a microthermocouple. In other words the measured temperature of a film is not the temperature at which crystallization occurs. The consequences of this finding to our general understanding of crystallization in polymers will be discussed.     

Fabrication and characterization of planar and channel polymer waveguides. III. Compositional distribution and solute loss in polymer thin films

For many microelectronic and optoelectronic applications, polymer thin films require the addition of small molecules. However, the thin‐film geometry and associated processing techniques will influence the final morphology and compositional distribution of the constituents. It is therefore important that these be examined directly rather than inferred from bulk measurements. As an example system, the concentration and distribution of Disperse Red 1 (DR1) molecules in poly(methyl methacrylate) thin films were examined. Ultraviolet visibility spectroscopy and dynamic secondary ion mass spectrometry indicate that the composition of the molecules decreased dramatically with thermal treatment of the film. The sublimation of the chromophore was observed to occur at temperatures well below the melting point of the small molecule and the glass transition of the pure polymer; this solute loss manifested itself in changes in the glass transition temperature of the film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2021–2024, 2002     

Crystallization of linear low density polyethylene under two-dimensional confinement in high barrier blend systems

Blends of linear low density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with different weight fractions are extruded to fabricate thin films. The extruded blend film morphology is investigated by atomic force microscopy (AFM). The extruded blend films have shown extended morphology along the extrusion direction (ED) and dispersed morphology along the transverse direction (TD). We report that due to this morphology, a two-dimensional (2-D) confined crystallization occurs. The EVOH has successfully confined the LLDPE from both film normal direction (ND) and transverse direction (TD) in this study. The confinement from ND results in an on-edge orientation of LLDPE, while the confinement from TD forces the on-edge oriented LLDPE crystals to further elongate and extend along the extrusion direction (ED). This specific crystal orientation is different from one-dimensional (1-D) confined crystallization observed in multilayered films. Both wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) are utilized to investigate the crystal orientations of LLDPE in the extruded blend films. Moreover, due to the morphology, the extruded blend films have shown high oxygen barrier properties, which make this material valuable in packaging applications.