Ferroelectric Templates Research Articles

Novel piezoelectric xNF–(1−x)PZT materials for catalytic/photocatalytic removal of pollutants

This study explores the potential of using nanocomposite powders consisting of NiFe2O4 and Pb(Zr0.47Ti0.53)O3 in varying concentrations (30 %, 40 %, 50 %, and 70 wt.%) to remove pollutants from water-based solutions. XRD, FTIR, and XPS analyses showed the successful synthesis of the pure ferrite phase directly on the ferroelectric templates. The presence of all elements specific to parents NF and PZT can be observed by XPS and EDS analyses. The AFM and PFM observations suggest that the addition of NF can locally enhance and possibly improve the piezoelectric properties. The degradation efficiency was tested under different conditions (mechanical stirring, ultrasonic vibration, and UV irradiation). The results showed that the nanocomposites exhibited high efficiency in the degradation of the reactive yellow 84 dye and Bisphenol A, with an optimum composition of x = 40 % NiFe2O4 addition, in line with PL tests. Also, no leached Pb ions could be detected in the solution. Furthermore, a simple rotational stirring method was found to be a fast and effective way to degrade the micropollutants.

Flexible silver-nanoparticles/PMMA SERS substrate derived from nanotips-equipped chemically patterned ferroelectric crystals for detecting antibiotics on irregular surfaces

Development of flexible and transparent detection platforms using surface-enhanced Raman spectroscopy has emerged as an intense research field due to the demand for in-situ, real-time analysis. Herein, we present the fabrication of soft and ultra-thin substrates composed of silver nanoparticles that are photoreduced on nanotips-equipped ferroelectric templates and then transferred to the poly(methyl methacrylate) film for ultrasensitive detection of antibiotics, nitrofurantoin and nifuroxazide. Compared with the conventional ferroelectric templates, the utilization of nanotips-equipped ferroelectric template boosts the effective mass transfer of dense silver nanoparticles to the polymeric film, which can effectively enhance the Raman performance through the electromagnetic mechanism. The produced substrate shows excellent performance for the detection of antibiotics, including ultra-low limit of detection in the order of 10−12 M, high enhancement factor about 1010, excellent sensitivity, superior reproducibility and uniformity. Besides, the quantitative multiplex detection of nitrofurantoin and nifuroxazide is demonstrated to discriminate the five-order concentration difference. The practicality of the developed substrate is proved by the detection of nitrofurantoin and nifuroxazide on fish surfaces by utilizing the fiber-coupled Raman probe with the limit of detection of 2.08 × 10−10 M and 1.25 × 10−9 M The proposed detection strategy can be applied to perform the in-situ, real-time analysis for the identification of antibiotics in environmental samples.

One-step surfactant-free photoreduction synthesis of single-crystal silver triangular nanoprisms by surface modified chemically patterned ferroelectric crystals for SERS application

Anisotropic metal nanoparticles with plasmonic and photocatalytic action exhibit significant applications for SERS detection and green transformation. Current synthetic approaches using multiple chemicals cause substantial resource consumption and surface chemical residues that hinder analyte adsorption and thus prevent efficient action. Herein, we present a green production process using surface modified ferroelectric templates to grow triangular Ag nanoprisms for surface enhanced Raman spectroscopy (SERS). Surface modification of ferroelectric templates with positively charged ions suppresses the Ag nucleation on template surface and enables the reaction-controlled process to promote anisotropic photoreduction for the growth of Ag nanoprisms. Under optimal experimental conditions, numerous Ag nanoprisms with the (111) plane can be photoreduced with sharp tips and edges and greatly strengthen the excited electric field for Raman signal enhancement. The synthesized Ag nanoprism array presents superior SERS performance, including enhancement factor of 3.78 × 108, limit of detection as low as 4.95 × 10-9 M, and Raman signal enhancement by 8.63 times. The practical application of Ag nanoprisms is effectively demonstrated by the SERS detection of antibiotics. The reaction control by utilization of surface-modified ferroelectric templates provides a promising prospect for the green synthesis of anisotropic metal nanomaterials and the technical development of green applications.

Transparent, Flexible Plasmonic Ag NP/PMMA Substrates Using Chemically Patterned Ferroelectric Crystals for Detecting Pesticides on Curved Surfaces.

Transparent and flexible surface-enhanced Raman scattering (SERS) substrates have attracted much interest for the detection of probe molecules on the curved surfaces of real samples, but a facile route to fabricate such substrates is still lacking. Herein, we present a rationally designed, high-performance flexible SERS substrate fabricated using a simple drop and peel-off technique for the ultrasensitive detection of pesticides. The proposed SERS substrate consists of a polymethyl methacrylate (PMMA) film anchored with plasmonic silver nanoparticles (Ag NPs), which are photoreduced using chemically patterned ferroelectric templates. The photoreduced Ag NPs extracted onto the PMMA film offer strong electromagnetic enhancement and produce intensive hotspots for the effective enhancement of the Raman signal. They provide superior SERS performance for the detection of parathion (PT) and fenitrothion (FNT) at trace-level concentrations of 10-9 M and 10-10 M with excellent enhancement factors in the order of 108 and 109, respectively. Moreover, the Ag NP/PMMA SERS substrate has good spot-to-spot uniformity and batch-to-batch reproducibility with the reservation of high detection sensitivity even after the mechanical deformation of bending and torsion up to 50 cycles. The multiplex detection ability is also investigated for the simultaneous detection of PT and FNT. To ensure the practical feasibility, the in-situ, real-time detection of PT and FNT on the curved surfaces of tomato and lemon using a fiber-coupled Raman probe is performed with limits of detection of 4.24 × 10-8 M and 2.74 × 10-9 M. The proposed Ag NP/PMMA flexible SERS substrate possesses unique features, such as easy fabrication through a simple, economical, rapid process, and facilitates straightforward implementation of in-situ SERS detection on curved fruit/vegetable surfaces.

Anisotropic growth of photoreduced silver nanostructures using surfactant-assisted ferroelectric templates for surface enhanced Raman spectroscopy

Photoreduction using ferroelectric templates is an emerging green technique for the production of noble-metal nanostructures by a reductant-free process. In this work, anisotropic growth of silver nanostructures is stimulated by a surfactant-assisted photoreduction process on ferroelectric templates. The preferential adsorption of surfactant (polyvinylpyrrolidone) on the specific facets of silver creates the anisotropic growth of nanostructures and thus the formation of silver nanoplates. The surfactant adsorption effects on the nanoparticle morphology and the nanoparticle properties are studied. Their influence levels depend on the ratio of surfactant concentration to precursor concentration. The produced silver nanostructures have superior SERS features, such as the limit of detection of <10−8 M, the enhancement factor of 2.2 × 109 and Raman intensity enhancement by 8.71 times. The study of anisotropic growth of photoreduced nanoparticles using ferroelectric templates provides a promising prospect to develop green production techniques for versatile anisotropic nanoparticles.

Epitaxy and controlled oxidation of chromium ultrathin films on ferroelectric BaTiO3 templates

Interfaces play a crucial role in the study of novel phenomena emerging at heterostructures comprising metals and functional oxides. In this work, we consider Cr/BaTiO3 heterostructures grown on Nb:SrTiO3 (001) substrates. Chromium thin films with 2 nm nominal thickness are deposited by molecular beam epitaxy on the BaTiO3 layer, and subsequently annealed in vacuum at temperatures ranging from 800 K to 970 K, and finally exposed to 10−7 torr of molecular oxygen for 300 s. Highly ordered films are obtained for each of this condition, ranging from metallic Cr to insulating Cr2O3 with tetragonal structure. Quite unexpectedly, an intermediate – fully ordered – case exists, with the co-presence of Cr and Cr2O3 compounds, each one with its proper crystal orientation. These results show the opportunity of controlling the metal/oxide state of crystalline Cr films grown onto the ferroelectric template BaTiO3/Nb:SrTiO3.

Photochemical synthesis of ZnO/Ag heterogeneous nanostructure on chemically patterned ferroelectric crystals for high performance SERS detection

An attractive strategy for effective Raman signal enhancement is to employ the synergistic action of electromagnetic and chemical mechanisms by using semiconductor/noble-metal nanostructures in the SERS substrates. This work presents the utilization of ferroelectric templates to synthesize the ZnO/Ag heterogeneous nanostructures photochemically for the SERS application. Under UVC illumination, the ferroelectric templates with permanent electrostatic field provide the photoelectrons required for silver photoreduction. Various shapes of ZnO nanostructures are grown on the ferroelectric templates by controlling the growth time. The influences of ZnO nanostructures on the size, density, and morphology of photoreduced silver nanomaterials are studied by various analytical techniques. The produced SERS substrate with the optimal ZnO/Ag nanostructures possesses the superior SERS performance, such as the limit of detection< 10−8 M, the enhancement factor 6.99 × 108, the uniformity 9.5% ± 1.0%, and 16-fold Raman intensity enhancement. This study demonstrates a promising green technique to produce semiconductor/noble-metal nanostructures using ferroelectric templates.

Nanotip-assisted photoreduction of silver nanostructures on chemically patterned ferroelectric crystals for surface enhanced Raman scattering

Nanotips made of metal and semiconductor have been widely utilized in versatile applications to strengthen the electric field through lightning rod effect and localized surface plasmon resonance (LSPR) effect. Here, we present the utilization of ferroelectric nanotips to assist photoreduction of silver nanostructures for surface enhanced Raman scattering (SERS). Ferroelectric nanotips with spontaneous polarization posses the unique feature of producing the permanent electrostatic field without requiring external excitation, which differs from the present nanotips requiring electrical and optical excitation. The enhanced electrostatic field promotes the formation of silver nanoparticles by reducing the effect of Stern layer and accelerating the movement of photoelectrons and silver ions to the template surface. Experimental results show that sharp ferroelectric nanotips facilitate the formation of large-diameter nanoparticles with strong LSPR action. Compared to the conventional ferroelectric templates, the SERS substrates using nanotip-equipped ferroelectric templates produce 5.51 times larger Raman intensity, which can be further increased by >10.76 times by increasing the reaction time. The proposed SERS substrate owns the limit of detection <10−8 M and the enhancement factor of 2.3 × 109. The presented ferroelectric nanotips with permanent electrostatic field would open promising applications in the versatile areas, such as nanomaterial fabrication and optoelectronic devices.

Electrostatic-field-tunable ferroelectric template for photoreduction of silver nanostructures applied in Raman scattering enhancement

We present an electrostatic-field-tunable ferroelectric template to produce photoreduced silver nanostructures for Raman scattering enhancement. The intensity and distribution of the surface electrostatic field in the ferroelectric template determine the morphology of the photoreduced silver nanostructures and thus the degree of the Raman signal enhancement. The surface electrostatic field is produced by periodically proton-exchanged (PPE) regions in LiNbO3 and is tuned by thermal annealing to obtain the favorable photoreduced silver nanostructure. The variation of surface electrostatic properties by thermal annealing is simulated using the finite element method and measured by electrostatic force microscopy. The mechanism of silver nanostructure formation affected by the electrostatic field distribution is discussed. The formed silver nanostructures are functionalized by R6G dye to enable Raman signal measurement. The proposed method is demonstrated to be effective in tuning the surface electrostatic field distribution and produces a 4.13 times higher silver nanostructure and a 2.51 times larger Raman intensity in comparison with the conventional PPE sample.

2D Arrays of Hexagonal Plasmonic Necklaces for Enhanced Second Harmonic Generation.

Hexagonal plasmonic necklaces of silver nanoparticles organized in 2D superlattices on functional ferroelectric templates are fabricated in large-scale spatial regions by using a surfactant-free photo-deposition process. The plasmonic necklaces support broad radiative plasmonic resonances allowing the enhancement of second harmonic generation (SHG) at the ferroelectric domain boundaries. A 400-fold SHG enhancement is achieved at the near-UV spectral region with subsequent interest for technological applications.

Bottom-Up Assembly of Molecular Nanostructures by Means of Ferroelectric Lithography.

Here, we report on the photochemical deposition of Rhodamine 6G (Rh6G) and Alexa647 molecules from aqueous and methanolic solution along 180° ferroelectric (FE) domain walls (DWs) of z-cut lithium niobate (LNO) single crystals. Molecules and FE domains were investigated by means of dynamic-mode AFM, piezoresponse force microscopy (PFM), and confocal scanning fluorescence microscopy. A high deposition affinity for 180° DWs on the LNO surface is observed, leading to the formation of molecular nanowires. Additionally, a more complex deposition pattern for Rh6G adsorbed to the domain areas of freshly poled samples was equally observed, being associated with the DW dynamics. These results are explained by considering contributions from screening-charge-dependent photochemistry as confined to the DWs, UV-induced DW motion, and transient electrostatic fields arising from the metastable defect distribution shortly after poling. Hence, tuning these effects offers the possibility for accurately controlling the complex bottom-up assembly of functional molecular nanostructures through domain-structured ferroelectric templates.

Magnetic and structural characteristics of multiferroic Fe3O4/(Bi3.25Nd0.65Eu0.10)Ti3O12 composite thin films deposited by metalorganic chemical vapor deposition

Ferromagnetic magnetite (Fe3O4) thin films for magnetoelectric multiferroic applications were deposited on (200) (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT)/(101) Nb:TiO2 substrates by metalorganic chemical vapor deposition (MOCVD) using an iron(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) precursor as the iron source. The BNEuT film utilized as a ferroelectric template material was in the form of freestanding nanoplates with narrow spaces between them. The effects of deposition conditions such as the deposition time and substrate temperature on the magnetic and structural characteristics of the Fe3O4/BNEuT composite films were investigated. All the films consisted of mostly single-phase Fe3O4 with a cubic inverse-spinel structure. When deposition was carried out at temperatures of 400–420 °C, the filling rates of particles introduced into the narrow spaces between the BNEuT nanoplates exhibited high values of 76–89% including the amorphous phase. This suggested that the deposition in this temperature range made progress according to the growth mechanism of MOCVD in the surface reaction rate determining state. Room-temperature magnetic moment–magnetic field curves for Fe3O4 thin films deposited at 400–500 °C for 60 min exhibited narrow rectangular hysteresis loops, indicating typical soft magnetic characteristics.

Biocompatible Gold Nanoparticle Arrays Photodeposited on Periodically Proton Exchanged Lithium Niobate.

Photodeposition of silver nanoparticles onto chemically patterned lithium niobate having alternating lithium niobate and proton exchanged regions has been previously investigated. Here, the spatially defined photodeposition of gold nanoparticles onto periodically proton exchanged lithium niobate is demonstrated. It is shown that the location where the gold nanoparticles form can be tailored by altering the concentration of HAuCl4. This enables the possibility to sequentially deposit gold and silver in different locations to create bimetallic arrays. The cytocompatibility of photodeposited gold, silver, and bimetallic ferroelectric templates to osteoblast-like cells is also investigated. Gold samples provide significantly greater cell biocompatibility than silver samples. These results highlight a potential route for using photodeposited gold on lithium niobate as a template for applications in cellular biosensing.

Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates

Photoreduction on a periodically proton exchanged ferroelectric crystal leads to the formation of periodic metallic nanostructures on the surface. By varying the depth of the proton exchange (PE) from 0.59 to 3.10 μm in congruent lithium niobate crystals, the width of the lateral diffusion region formed by protons diffusing under the mask layer can be controlled. The resulting deposition occurs in the PE region with the shallowest PE depth and preferentially in the lateral diffusion region for greater PE depths. PE depth-control provides a route for the fabrication of complex metallic nanostructures with controlled dimensions on chemically patterned ferroelectric templates.

Preparation and magnetoelectric properties of NiFe2O4–PZT composites obtained in-situ by gel-combustion method

Magnetoelectric composites of xNiFe2O4–(1 − x)Pb(Zr,Ti)O3 with x = 2, 5, 10, 20, 30% were prepared by citrate–nitrate combustion using PZT-based template powders. In order to ensure a better connectivity of dissimilar phases, we have used chemical methods for preparation in situ composites, followed by adequate sintering procedure. The structural, microstructural and functional properties of di-phase magnetoelectric composites of NiFe2O4–PZT are reported. The XRD analysis is demonstrating the synthesis of pure ferrite phase directly on the ferroelectric templates. An excellent mixing was obtained in the composite powders, as proved by a detailed SEM analysis. The magnetic and dielectric behaviors of the ceramic composites vary with the ratio of the two phases. The dielectric behavior is greatly influenced by the magnetic phase. The magnetoelectric (ME) coefficient was measured as a function of applied DC magnetic field. The maximum ME coefficient (dE/dH) varies from 0.0011 mV/(cm Oe) to 0.5 mV/(cm Oe) with increasing of NF addition.