RAFT polymerization of temperature- and salt-responsive block copolymers as reversible hydrogels

Reversible-addition fragmentation chain transfer (RAFT) polymerization enabled the synthesis of novel, stimuli-responsive, AB and ABA block copolymers. The B block contained oligo(ethylene glycol) methyl ether methacrylate (OEG) and was permanently hydrophilic in the conditions examined. The A block consisted of diethylene glycol methyl ether methacrylate (DEG) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (TMA). The A block displayed both salt- and temperature-response with lower critical solution temperatures (LCSTs) dependent on the molar content of TMA and the presence of salt. Higher TMA content in the AB diblock copolymers increased the critical micelle temperatures (CMT) in HPLC-grade water due to an increased hydrophilicity of the A block. Upon addition of 0.9 wt% NaCl, the CMTs of poly(OEG-b-DEG₉₅TMA₅) decreased from 50 °C to 36 °C due to screening of electrostatic repulsion between the TMA units. ABA triblock copolymers displayed excellent hydrogel properties with salt- and temperature-dependent gel points. TMA incorporation in the A block increased the gel points for all triblock copolymers, and salt-response increased with higher TMA composition in the A block. For example, poly(DEG₉₈TMA₂-b-OEG-b-DEG₉₈TMA₂) formed a hydrogel at 40 °C in HPLC-grade water and 26 °C in 0.9 wt% NaCl aqueous solution. These salt- and temperature-responsive AB diblock and ABA triblock copolymers find applications as drug delivery vehicles, adhesives, and hydrogels.     

Thermo-responsive behavior of hybrid core cross-linked polymer micelles with biocompatible shells

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(N-isopropylacrylamide-co-2-(N,N-dimethylamino)ethyl methacrylate) (pMPC-b-p(NIPAM/DMA)) was synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. Below the critical aggregation temperature (CAT), i.e., about 40 °C, the diblock copolymer dissolved in water as a unimer with a hydrodynamic radius (R_h) of ca. 10 nm. Above CAT the diblock copolymers formed polymer micelles with an R_h of ca. 40 nm, composed of a p(NIPAM/DMA) core and biocompatible pMPC shell due to hydrophobic self-aggregation of the thermo-responsive p(NIPAM/DMA) block. The pendent 2-(N,N-dimethylamino)ethyl group of DMA in pMPC-b-p(NIPAM/DMA) reduced HAuCl₄ to form gold nanoparticles (AuNPs) and could attach to their surfaces. The cores of these polymer micelles could be cross-linked above CAT by HAuCl₄, which upon being reduced generated AuNPs as cross-linking points to form core cross-linked (CCL) polymer micelles, as confirmed by UV-vis absorption and dynamic light scattering measurements. The CCL polymer micelles absorbed visible light at 532 nm because of surface plasmon resonances of the AuNPs. The R_h of the CCL polymer micelles remained at ca. 40 nm regardless of temperature.     

Catalytic chain transfer polymerisation of CO2-expanded methyl methacrylate

The catalytic chain transfer polymerisation of methyl methacrylate expanded with dense CO₂ is reported. Experimental values of the chain transfer constant (C_s) are presented at 50 °C and in the range of pressure from 0.1 to 6 MPa, using a cobaloxime complex as the chain transfer catalyst. The effect of small quantities of poly(methyl methacrylate) on the volumetric expansion of the monomer with CO₂ is considered. Experimental data are presented on the pressure limit for homogeneous expansion as a function of the molecular weight of the polymer. It is shown that the values of C_s in CO₂-expanded methyl methacrylate are significantly higher than that in bulk monomer. This effect is mainly attributed to the enhancement of the chain transfer rate coefficient, arising from the reduction in the viscosity of the medium, and is consistent with a diffusion-controlled rate-determining step in the chain transfer process.     

Aqueous chemical solution deposition of ultra high-k LuFeO3 thin films

Thin orthorhombic ultra high-k LuFeO₃ (LFO) films on Si₃N₄/SiO₂/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Prior to thin film deposition, the precursor synthesis, thermal decomposition and crystallization behavior of the bulk material were studied. It was shown that phase-pure hexagonal LFO powder could be formed at 650 °C while a higher temperature of 900 °C was required to obtain the orthorhombic phase. Deposition on SiO₂/Si resulted in the development of silicates in this temperature range, thus preventing the formation of the orthorhombic LuFeO₃ phase. The use of Si₃N₄/SiO₂/Si as the substrate shifted the silicate formation to higher temperature, allowing the synthesis of phase-pure orthorhombic LuFeO₃ as a thin film at 1000 °C. Impedance spectroscopy analyses confirmed its associated ultra high dielectric constant (>10,000) at room temperature for frequencies lower than or equal to 1 kHz.     

Novel carbazole phenoxy-based methacrylates to produce high-refractive index polymers

A novel, high-refractive index homopolymer was produced by incorporating carbazole and phenol into the methacrylate monomer structure. The reaction of phenol with 9-(2,3-epoxypropyl)-carbazole, followed by the reaction of the carbazole phenoxy-based intermediate with methacryloyl chloride or methacrylic anhydride, and recrystallization from methanol, produced a good yield of highly pure carbazole phenoxy functionalized methacrylate monomer. Subsequent free radical polymerization or UV photopolymerization of the functionalized methacrylate monomer, in addition to copolymerizations with methyl methacrylate, provided for high-refractive index materials well suited for lightweight optical applications. Unlike N-vinyl carbazole, the novel carbazole phenoxy-based methacrylate readily copolymerized with methyl methacrylate. Statistical copolymers of carbazole based methacrylates with methyl methacrylate were produced by free radical solution polymerization in DMAC or by photopolymerization in DMF. The carbazole phenoxy-based methacrylate monomer was characterized for molecular weight using gel permeation chromatography (GPC), for melting point and glass transition temperature using differential scanning calorimetry (DSC), for decomposition using thermal gravimetric analysis (TGA), and for chemical composition by one- and two-dimensional ¹H nuclear magnetic resonance (NMR) spectroscopy and by elemental analysis. The AIBN initiated carbazole phenoxy-based methacrylate polymerization was followed using in situ FTIR, which showed the reaction to be complete within 40 min in DMAC at 90 °C. Refractive indices of the carbazole based methacrylate homopolymers and copolymers ranged from 1.52 to 1.63. PhotoDSC was used to determine the heat of polymerization (ΔH_p) for the carbazole phenoxy-based methacrylate (ΔH_p=−39.4 kJ/mol). The carbazole phenoxy-based methacrylate homopolymer had a surprisingly high onset of decomposition temperature (T_onset=316 °C). ¹³C NMR spectroscopy experiments and molecular modeling were used to explore the configuration of the polymerized carbazole phenoxy-based methacrylate. The lack of head-to-head linkages due to steric considerations reasonably explains the high thermal stability observed for the carbazole phenoxy-based methacrylate polymer.     

Preparation of asymmetric perovskite-type membranes by a settlement method

Asymmetric SrCe_0.95Yb_0.05O_3?α (SCYb) membranes were prepared by using a settlement method to deposit a thin dense SCYb layer on the green porous SCYb support, followed by conventional dry pressing and co-sintering. SCYb powder was mixed in a liquid media (isopropanol) and directly poured onto the pre-pressed green porous SCYb support placed in a beaker. After the powder fully settled onto the support, the green asymmetric sample was dried and co-sintered. The cross-sectional images of the asymmetric systems indicate that thin dense SCYb films in the asymmetric membranes had uniform thicknesses at this level of analysis and show excellent adhesion to the porous support without any undesirable defects, delamination or cracking. Further, different dense layer thicknesses (80–20 μm) were readily obtained by altering the amount of the SCYb powders in the liquid media. The minimum dense layer thickness obtained by the settlement method, with the synthesis conditions utilised in this study, was around 20 μm.     

Effect of the pyrolysis atmosphere on the mechanical properties of polymer-derived SiOC and SiCN

Mechanical properties of polymer-derived ceramics are usually measured on samples pyrolyzed in inert atmosphere. Here, we report the hardness and elastic modulus of SiOC and SiCN pyrolyzed in both inert (Ar) and reactive (CO₂) atmosphere. The external surface of the specimens exposed to the pyrolysis gas was characterized by Vickers microhardness measurements and infrared spectroscopy. The elastic modulus was evaluated by three-point bending tests on thin (150-200 µm) and dense specimens. Polished sections of the SiOC samples were prepared to study, by energy-dispersive X-ray spectroscopy (EDXS) and nanoindentation, how the elemental composition, hardness, and elastic modulus vary from the surface toward the bulk. For both compositions, pyrolysis in CO₂ leads to a strong decrease in the hardness and elastic modulus. The hardness of both the samples pyrolyzed in CO₂ approaches the typical value for fused silica, suggesting that CO₂ selectively breaks the Si–C and Si–N bonds and leads to the formation of a silica-like network. EDXS and nanoindentation reveal that the modification induced by the CO₂ flow extends below the surface at least for a thickness of about 30 µm.     

Impedance spectroscopic studies of sol–gel derived barium strontium titanate thin films

In the present work electroceramic thin films of barium strontium titanate (Ba_1?xSr_xTiO₃ – BST) were deposited on stainless steel substrates by sol–gel technique. Homogeneous Ba_0.6Sr_0.4TiO₃ thin films as well as spatially inhomogeneous BST thin films exhibiting artificial gradients in composition normal to the growth surface were deposited. Both up- and down-graded BST films were fabricated by depositing successive layers with Sr mole fraction x ranging from x = 0.5 to x = 0.3. In the present study the tool of impedance spectroscopy has been used to study the dielectric properties of BST thin films at room temperature. To analyze the impedance spectroscopy data the Nyquist (Z″ vs. Z′) plots as well as the simultaneous representation of the imaginary part of impedance and electrical modulus (Z″, M″) vs. frequency were used. Experimental data were fitted using the CNLS fitting method. Agreement between experimental and simulated data was established. The data indicated that the thin film samples fabricated can be represented by an equivalent circuit with two relaxation frequencies.     

Fabrication of BSCF-based mixed oxide ionic-electronic conducting multi-layered membrane by sequential electrophoretic deposition process

The Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF)-based multi-layered oxygen separation membrane was fabricated by the sequential electrophoretic deposition (EPD) process. A thin porous/dense bi-layer of BSCF was formed on a thick porous support of BSCF. The porous support prepared by a sacrificial template method using BSCF powder mixed with wheat starch (30 wt%) as a pore-forming agent, followed by uniaxial pressing and low-temperature sintering, was directly used as an EPD electrode. A thin BSCF layer was first formed on the porous support, and then a thin BSCF + PMMA (polymethyl methacrylate) layer was sequentially formed on the thin BSCF layer using a bimodal suspension of BSCF and PMMA. A 30-μm thin porous/dense bi-layer of BSCF of which the total thickness was obtained by optimizing the processes of EPD and subsequent co-sintering. The oxygen separation performance of 3.7 ml (STP) min^?1 cm^?2 at 860 °C was achieved for the BSCF-based multi-layered oxygen separation membrane.     

Impact of acidic monomer type and concentration on the adhesive performance of dental zirconia primers

This study evaluated the influence of acidic monomer type (phosphate–PAM or carboxylic–CAM) and concentration on the adhesive performance of single-solution model dental zirconia primers to yttria-stabilized polycrystalline dental zirconia ceramic. The acidic monomers 1,3-glycerol dimethacrylate phosphate (PAM) or mono-2-(methacryloyloxy)ethyl maleate (CAM) were added to a photocurable (di)methacrylate co-monomer at mass fractions of 10%, 20%, 40% or 60%, with constant 40% mass of ethanol. The degree of CC conversion (DC) of the primers was measured using mid-infrared spectroscopy. Zirconia bonds were assessed by shear bond strength test after two aging conditions: water storage for 24 h or thermal cycling (3,000 cycles in water at 5 °C and 55 °C). DC data were submitted to one-way ANOVA for each monomer type. Bond strength data were submitted to two-way ANOVA for each aging condition. Bond strengths at 24 h and after thermal cycling were compared using t-tests (α=0.05 for all analyses). Lower DC was observed for increased acidic monomer concentrations. The bond strengths of PAM-based primers were generally higher than CAM-based materials, irrespective of acidic monomer concentration or aging condition. After thermal cycling, the bond strengths for PAM-based primers were still higher compared with CAM-based primers, although CAM-based materials generally had more stable zirconia bonds. In conclusion, both the acidic monomer type and concentration had a significant impact on the adhesive performance of the primers. The primer with 40% of phosphate methacrylate showed the best overall bonding performance to dental zirconia.     

Fine-grained relaxor ferroelectric PMN-PT ceramics prepared using hot-press sintering method

Relaxor ferroelectric PbMg_1/3Nb_2/3O₃-PbTiO₃ (PMN-PT) ceramics are high-performance piezoelectric materials that are widely used in many electronic devices. However, it is extremely difficult to manufacture thin piezoelectric components dozens of micrometers in size using commercial coarse-grained PMN-PT ceramics. This limits the application of PMN-PT ceramics to high-frequency ultrasonic devices. In this work, we prepared a dense, fine-grained PMN-PT ceramic at low temperature using a hot-press sintering (HPS) method. The HPS ceramic had small grains with an average size of 1 μm and maintained high performance with a large permittivity (ε_r = 4500), piezoelectricity (d₃₃ = 650 pC/N), and electrostrain (S_E = 0.14% at 20 kV/cm). The large volume fraction of grain boundaries led to stronger relaxor behavior of the fine-grained PMN-PT ceramic than of the normal coarse-grained one. Owing to its small grains and high piezoelectric performance, this fine-grained PMN-PT ceramic meets the strict requirements of manufacturing thin piezoelectric components. Our results demonstrate that PMN-PT ceramics have great potential for developing low-cost, high-frequency ultrasonic devices by replacing expensive piezoelectric single crystals.     

High-quality c-axis oriented non-vacuum Er doped ZnO thin films

Preparation, growth, structure and optical properties of high-quality c-axis oriented non-vacuum Er doped ZnO thin films were studied. Zn_1−xEr_xO (x=0.0, 0.01, 0.02, 0.04, and 0.05) precursor solutions were prepared by sol–gel synthesis using Zn, and Er based alkoxide which were dissolved into solvent and chelating agent. Zn_1−xEr_xO thin films with different Er doping concentration were grown on glass substrate using sol–gel dip coating. Thin films were annealed at 600 °C for 30 min, and tried to observe the effect of doping ratio on structural and optical properties. The particle size, crystal structure, surface morphologies and microstructure of all samples were characterized by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The UV–vis spectrometer measurements were carried out for the optical characterizations. The surface morphology of the Zn_1−xEr_xO films depend on substrate nature and sol–gel parameters such as withdrawal speed, drying, heat treatment, deep number (film thickness) and annealing condition. Surface morphologies of Er doped ZnO thin films were dense, without porosity, uniform, crack and pinhole free. XRD results showed that, all Er doped ZnO thin films have a hexagonal structure and (002) orientation. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>85) in the visible region (400–700 nm).     

A novel well-defined amphiphilic diblock copolymer containing perfluorocyclobutyl aryl ether-based hydrophobic segment

A series of well-defined binary hydrophilic-fluorophilic diblock copolymers were synthesized by successive atom transfer radical polymerization (ATRP) of methoxylmethyl acrylate (MOMA) and 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate (TPFCBBMA) followed by the acidic selective hydrolysis of the hydrophobic poly(methoxymethyl acrylate) (PMOMA) segment into the hydrophilic poly(acrylic acid) (PAA) segment. ATRP of MOMA was initiated by 2-MBP at 50 °C in bulk to give two different PMOMA homopolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.15). PMOMA-b-PTPFCBBMA well-defined diblock copolymers were synthesized by ATRP of TPFCBBMA at 90 °C in anisole using Br-end-functionalized PMOMA homopolymer as macroinitiator and CuBr/PMDETA as catalytic system. The final PAA-b-PTPFCBBMA amphiphilic diblock copolymers were obtained via the selective hydrolysis of PMOMA block in dilute HCl without affecting PTPFCBBMA block. The critical micelle concentrations (cmc) of PAA-b-PTPFCBBMA amphiphilic copolymers in aqueous media were determined by fluorescence spectroscopy using pyrene as probe and these diblock copolymers showed different micellar morphologies with the changing of the composition.     

Role of vanadium oxide on the lithium silicate glass structure and properties

The structural role of V in 28Li₂O–72SiO₂ (in mol%) lithium silicate glass doped with 0.5 mol% V₂O₅ was assessed using ²⁹Si and ⁵¹V Nuclear Magnetic Resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopy techniques. Despite the low amount of V₂O₅ used, the structural information obtained or deduced from the statistical analysis of the NMR data could explain the evolution of glass properties after V₂O₅ addition. The XPS results indicated that all vanadium exists in 5+ oxidation state. Both the ²⁹Si NMR and FTIR data point toward an increase in the polymerization of the silicate network, caused by the V₂O₅ acting as network former, capable to form various tetrahedral units (for n = 0, 1, and 2) in the glasses. These units, which are similar to phosphate units, scavenge the Li⁺ ions and cause the silicate network to polymerize. However, in an overall balance, the entire glass network is depolymerized due to the additional nonbridging oxygens contributed by the vanadium polyhedra. The addition of vanadium causes the network to expand and increases the ionic conductivity.     

Viscosity-structure relationship of alkaline earth silicate melts containing manganese oxide and calcium fluoride

The effect of CaF₂ on the viscosities of the MO-SiO₂-xMnO-yCaF₂ melts (M[=Ca or Ba]O/SiO₂ = 0.4-0.5, x = 10[±1] or 40[±2] mol%, y = 0-15 mol%) have been studied at high temperatures. At MnO = 40[±2] mol%, the viscosity of Ba-Mn-silicate melts is lower than that of Ca-Mn-silicate melts because Mn²⁺ is a strong network modifier in the former system. However, the viscosities of both alkaline earth silicate melts with MnO = 10[±1] mol% are not affected by cation type because MnO activity is too low to affect the viscosity of the melts. The CaF₂ addition decreases the viscosities of the Ba-Mn-silicate melts with low-MnO contents, while it has less impact on the viscosities of the melts with high-MnO contents. The effect of CaF₂ on the relationship between viscosity and the structure of the silicate melts is quantitatively analyzed using the micro-Raman spectra of quenched glass samples. The NBO/Si ratio of alkaline earth silicate melts, which indicates the degree of polymerization of the silicate networks, has a linear relationship with the activation energy for the viscous flow of the melts.     

Synthesis and responsive behavior of poly(N,N-dimethylaminoethyl methacrylate) brushes grafted on silica nanoparticles and their quaternized derivatives

Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) was grafted onto the surface of silica nanoparticles via surface-initiated atom transfer radical polymerization to form temperature- and pH-responsive PDMAEMA brushes (silica-g-PDMAEMA). The resultant samples were characterized via ¹H NMR, transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Their molecular weights and molecular weight distributions were determined by gel permeation chromatography analysis after silica content etching. The control of brush thickness and the responsive behavior were systematically investigated. Dynamic light scattering (DLS) results indicate that the brush thickness can be controlled by changing the polymerization time and the DMAEMA, initiator, and THF concentrations. According to DLS and zeta potential results, the lower critical solution temperature (LCST) of the PDMAEMA brushes shifts to a higher temperature with decreasing solution pH, which is attributed to the weak charge of the polyelectrolyte brushes. When the temperature is kept above the transition temperature, the silica-g-PDMAEMA nanoparticles aggregate into clusters and disaggregate during the cooling process. Moreover, with the heating/cooling step increasing, the aggregation and disaggregation temperatures are decreased. Meanwhile, when the molecular weight is increased from 13.6 × 10⁴ to 23.1 × 10⁴ g/mol, a decrease in the LCSTs at constant pH is observed. The related properties of the corresponding quaternized analog, poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI) brushes, were also discussed. The hydrodynamic radius of the silica-g-PMETAI nanoparticles decreases with increasing ionic strength, and a salting-out/salting-in effect is observed when the ionic strength is adjusted using NaI instead of NaCl.     

Methacrylate-based polymer films useful in lithographic applications exhibit different glass transition temperature-confinement effects at high and low molecular weight

The effects of confinement on polymer films are important in applications related to photoresists. To optimize resolution, methacrylate polymers used in photoresists are often low molecular weight (MW). We use ellipsometry and fluorescence to study how the glass transition temperature (T_g) is affected by confinement in silica-supported films of low and high MW poly(1-ethylcyclopentyl methacrylate) (PECPMA) and poly(methyl methacrylate) (PMMA). With decreasing nanoscale thickness, T_g is nearly invariant for high MW (M_n = 22.5, 188 and 297 kg/mol) PECPMA but decreases for low MW PECPMA, with T_g – T_g,bulk = −7 to 8 °C in a 27-nm-thick film (M_n = 4.1 kg/mol) via ellipsometry and −15 °C in a 17-nm-thick film (M_n = 4.9 kg/mol) via fluorescence. Fluorescence studies using a 20-nm-thick dye-labeled layer in multilayer, bulk PECPMA films reveal a much greater perturbation to T_g in the free-surface layer for low MW PECPMA, which propagates tens of nanometers into the film. The effect of MW in single-layer monodisperse PMMA films is even more striking; T_g increases with confinement for high MW but decreases for low MW, with T_g – T_g,bulk = 9 °C in a 12-nm-thick film (nominal MW = 509 kg/mol) and −16 °C in a 17-nm-thick film (nominal MW = 3.3 kg/mol). The strong influence of MW on confinement effects in PECPMA and PMMA is in contrast to the previously reported invariance of the effect with MW in supported polystyrene films, reconfirmed here.     

Synthesis of poly[2-(α-d-mannopyranosyloxy)ethyl-co-2-dimethylaminoethyl methacrylates] and its lectin-binding and DNA-condensing properties

Radical copolymerizations of 2-(α-d-mannopyranosyloxy)ethyl methacrylate (ManEMA) with 2-dimethylaminoethyl methacrylate (DMAEMA) were carried out in N,N-dimethylformamide (DMF) containing 10 vol% water at 60 °C to yield cationic glycopolymers. The number-average molecular weights (M_ns, standard Pullulan calibration) and polydispersities (M_w/M_ns) of the resulting copolymers were ranged from 17,400 to 41,700 and from 1.7 to 3.2, respectively. The compositions of the resulting copolymers were very close to those in the feed. The monomer reactivity ratios r_ManEMA and r_DMAEMA were 0.98 and 1.22, respectively. The lectin-binding properties of poly(ManEMA-co-DMAEMA) to concanavalin A (ConA) was examined using a turbidimetric assay. The clustering rate increased with increasing mole fractions of the ManEMA units in the copolymer (F_ManEMA), even under a constant concentration of the ManEMA units (50 μM), indicating the typical cluster glycoside effect. The DNA-condensing ability of the resulting copolymers was examined by a gel retardation assay using pEGFP-N1 plasmid (4.7 kbp). Though the ManEMA units interfered with the complexation of the copolymer with the plasmid DNA, complete retardation was observed under the condition of lower contents of ManEMA units (F_ManEMA < 0.2) in pure water. These findings indicate that poly(ManEMA-co-DMAEMA) is a cationic glycopolymer exerting lectin-binding and DNA-condensing abilities.     

Deposition of polymethyl methacrylate on polypropylene substrates using an atmospheric pressure dielectric barrier discharge

In this work, an atmospheric pressure glow-like dielectric barrier discharge in helium with small admixtures of methyl methacrylate (MMA) is used for the deposition of thin polymethyl methacrylate (PMMA) films. The effect of discharge power and feed composition (monomer concentration) on film properties has been investigated by means of Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results are described by defining a W/FM value, where W is the discharge power, F the monomer flow rate and M is the molecular weight of the monomer. It is shown in this paper, that the deposition rate and the chemical composition of the deposited film change with varying W/FM values. At low W/FM values, high deposition rates of up to 2 nm/s are observed and the plasma-polymerized MMA chemically resembles the conventionally synthesized PMMA. In contrast, using high W/FM values (≥102 MJ/kg) leads to lower deposition rates (as low as 0.9 nm/s), while the plasma-polymerized MMA films contain less ester groups and a larger amount of ether and/or alcohol groups. One should therefore carefully choose the deposition parameters in order to obtain a high deposition rate and a high retention of ester groups in the plasma-polymerized MMA films.     

Ferroelectric and dielectric properties of manganese-doped Na0.5Bi0.5TiO3 nanocrystalline thin films prepared by metal organic decomposition: A single-layer thickness-dependent study

2 at% Manganese-doped Na_0.5Bi_0.5TiO₃ (NBTMn) thin films with single-layer thicknesses ranging from 15 to 45 nm/l were deposited on the indium tin oxide/glass substrates by a metal organic decomposition process and spin coating technique. The influence of single-layer thickness on the crystal structure, surface morphology, insulating ability, ferroelectric and dielectric properties was mainly investigated. Compared with the other films, NBTMn film with a single-layer thickness of 30 nm/l exhibits the (110)-preferred orientation and dense structure. Also, it shows the enhanced ferroelectricity with a large remanent polarization (P_r) of 38 μC/cm² due to the preferred orientation and low leakage current density. Meanwhile, a high dielectric tunability of 39% for NBTMn with 30 nm/l can be observed by varying the measuring applied voltage and frequency. These results indicate that the suitable layer thickness is beneficial to improve the electrical performances of NBTMn thin film.