Size-dependent Properties Research Articles

Finite element analysis of transverse size effect on the pyroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3 –PbTiO3 thin film for infrared array applications

Exploring and revealing the influence of the pyroelectric thin film array element size on its structure and pyroelectric performance is crucial for designing integrated pyroelectric infrared detectors. In this work, the transverse size effect on the piezoelectric, dielectric, and especially the pyroelectric properties for a new-generation relaxor ferroelectric material Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) was studied by a finite element method. The lateral size-dependent piezoelectric and dielectric properties of the PIMNT thin film indicated that with the decrease in the transverse size, the piezoelectric constant d33 and relative dielectric constant εr increased substantially. The piezoelectric constant d33 and relative dielectric constant εr along ⟨001⟩ and ⟨011⟩ orientation increased faster than those along ⟨111⟩. A critical aspect ratio (in this paper, it was defined as radius/thickness) was found around 1:1 for three directions. We further discovered that the pyroelectric coefficient for PIMNT thin film along the ⟨111⟩ direction (the best crystallographic orientation for pyroelectric performance) decreased from 8.5 × 10−4 to 8.0 × 10−4 C/(m2·K) with the aspect ratio down to 0.01. The variation of the piezoelectric, dielectric, and pyroelectric properties originated from the declamping of the PIMNT thin film from the substrate. This finding gives insight into the transverse size effect on the electrical properties of new-generation relaxor PIMNT thin film and provides a guidance for designing high-performance infrared array detectors.

Size tunable and controllable synthesis of PbS quantum dots for broadband photoelectric response

PbS quantum dots (QDs) with size-dependent photoelectric characteristics and wide spectral absorption show a great potential material for preparing near-infrared photodetectors, attracting numerous studies. This paper prepared size-tunable PbS QDs with a mean size varying from 3 nm to 9 nm via a modified hot injection method. And the effects of different factors on the size of PbS QDs in the synthesis were systematically summarized. Moreover, size-dependent optoelectronic properties of PbS QDs were studied. With the increase in size, the dark current, photocurrent, and responsivity of devices show an increase, while the 3 dB bandwidth decreases. In addition, the larger the size, the wider the detection spectrum coverage, the detectivity of the corresponding absorption peak in PbS QDs is better than another size PbS QDs, but the maximum detectivity of the large size PbS QDs is lower than that of the small size PbS QDs in the near-infrared. Therefore, selecting different PbS QDs to prepare photodetector is of great significance for practical applications with different detection requirements. Significantly, these size-tunable PbS QDs photodetectors show fast response and excellent responsivity, and detectivity.

Understanding the unique optical and vibrational signatures of sequential infiltration synthesis derived indium oxyhydroxide clusters for CO2 absorption

Sequential infiltration synthesis (SIS) is a vapor phase synthesis technique with potential to exert precise control over metal oxyhydroxide incorporation into polymer scaffolds. We observe strong size-dependent properties of InOx(OH)y few-atom clusters deposited with variable SIS cycle numbers within a polymethylmethacrylate (PMMA) matrix. Infrared spectroscopy and ultraviolet-visible absorption spectroscopy reveal that the metal atom coordination and optical properties of the clusters depend on the number of SIS cycles performed as well as the choice of processing parameters. The incorporation of indium oxyhydroxide in PMMA via SIS presents an opportunity to improve the CO2 absorption capacity and gas selectivity of inexpensive polymers.

Revisiting the initial reaction rates for TMS combustion and a new evidence for metastable silica nanoparticles in the gas-phase synthesis

Nanomaterials from gas-phase synthesis are tapping into new fields of application in research and industry due to their unique size-dependent properties. To produce tailored nanoparticles, the synthesis starting from the precursor decomposition to the particle formation must be fully understood. Tetramethylsilane is used as a precursor for the synthesis of silica nanomaterials in flames. The precursor starts to decompose by H-abstraction. Reaction rates for H-abstraction of tetramethylsilane (TMS) by +O/+H/+OH radicals are determined by means of quantum chemical calculations. The rate expressions are obtained in the temperature range from 300 to 1400 K: kH = 6,025,735 (T/K)2.1731exp(-(+2613.840 K)/T) cm3mol−1s−1 for the total bimolecular reaction coefficient of TMS with hydrogen atoms, kOH = 10,179,818 (T/K)1.7790 exp(-(+152.739 K)/T) cm3mol−1s−1 for TMS with OH radicals, and kO = 93,100 (T/K)2.4797 exp(-(+889.166 K)/T) cm3mol−1s−1 for TMS with O(3P) radicals, respectively. The reaction rates are implemented into the TMS reaction mechanism of Janbazi et al. [1], and a better agreement of the TMS reactivity in the flame is achieved. Experiments are conducted to obtain the mass deposition rates with a Quartz-Crystal-Microbalance (QCM) in a wide range of different equivalence ratios. The equivalence ratio is varied between ϕ = 0.6–1.2, and precursor amounts of 400, 600 and 800 ppm are used. These QCM-experiments are complementary to the MBMS-studies from Karakaya et al. [1–3] but use the same flame conditions to extend the data set. The results reveal that metastable particles exist in the reaction zone of the flame. Depending on flame conditions, their concentration decreases towards the end of the reaction zone, but particles subsequently grow again in the recombination zone of the flame. The mechanisms, which describe the reactivity of the metastable nanoparticles, are tentatively proposed. The understanding of the mechanisms can open up the way for tailored nanoparticles with different structures and stoichiometries.

Solid lipid nanoparticles; as a promising drug delivery method to get greater bioavailability: A review

Solid lipid nanoparticles (SLN) are the heart of nanotechnology's tremendous development, with multiple practical benefits in drug delivery and research. Because of their size-dependent properties, solid Lipid nanoparticles can be used to create innovative medicines. Drug conversion into nanoparticles provides a new drug delivery concept that could be used for drug targeting. As a result, solid lipid nanoparticles have great promise reaching the goal of targeted and site-specific drug delivery. The goals, production techniques, advantages, limits are all discussed in this review. Scanning electron microscopy and measurement of particle size and zeta potential, dynamic light scattering are examples of appropriate analytical techniques for SLN characterization. By using novel drug formulation technologies, the drug delivery system focuses on the regulation of in vivo dynamics in order to enhance the efficacy and safety of the included pharmaceuticals. Lipids used in the development of Nano particulate dosage forms, such as fatty acids, triglycerides, vegetable oils, and their derivatives. Solid lipid nanoparticles (SLNs) are a type of lipid drug delivery method that is relatively new. They were created to solve some of the limitations with traditional drug delivery systems, such as low drug encapsulation efficiency and limited bioavailability of Biopharmaceutical Classification Systems (BCS) class II and IV medications. SLNs are made up of physiologically well tolerated substances and melt-emulsified lipids that are solid at room temperature that helps to enhance drug bioavailability ultimately results in better desired therapeutic effect.

Size-Dependent Structures and Catalytic Properties of Supported Bimetallic PtSn Catalysts for Propane Dehydrogenation Reaction

Heterogeneous bimetallic catalysts are widely used in industrial processes, and the structural features of the bimetallic catalysts have profound impacts on their properties in numerous catalytic processes. Bimetallic nanoclusters with particle sizes ≤1 nm have shown better performances in various catalytic reactions in comparison to conventional bimetallic nanoparticles with sizes above 1 nm. Despite the progress made in recent years in the synthesis and catalytic studies of bimetallic nanoclusters, achieving a fundamental understanding of the structure–reactivity relationships at the molecular and atomic levels remains challenging because of the complexity of the bimetallic catalysts with particle sizes ≤1 nm. In this work, we have studied the structural features of supported bimetallic PtSn species with different sizes (∼0.6 to ∼1.6 nm), which is shown to be associated with the size-dependent formation process of bimetallic PtSn species according to theoretical modeling and experimental studies. Furthermore, the catalytic consequences of their size-dependent structural features are reflected in the dehydrogenation of propane to propylene, in which the subnanometer PtSn clusters are more active than the PtSn alloy nanoparticles.

Electrochemical and electrocatalytic performance of single Au@Pt/Au bimetallic nanoparticles

Bimetallic nanoparticles (NPs) are widely used in energy catalysis, chemical synthesis, and chemical/biosensing, but their performance at single NPs level is still needed to investigate. In this work, bimetallic Au@Pt/Au NPs with triple-layered core-shell structure was successfully prepared and characterized. The single bimetallic Au@Pt/Au NPs were immobilized on the surface of Au nanoelectrode through electrostatic adsorption. The results have showed that the single Au@Pt/Au NPs have size-dependent properties for voltametric response and electron-transfer rate, and exhibit excellent electrocatalytic activity, long-term tolerance and anti-toxicity compared with the traditional Pt catalyst. This work provides new insight into conventional electrocatalysis and will likely give a good platform for designing entirely new catalysts at single NPs level.

Sonication-assisted liquid exfoliation and size-dependent properties of magnetic two-dimensional α-RuCl3

Originating from the hexagonal arrangement of magnetic ions in the presence of strong spin orbit coupling, α-RuCl3 is considered as model system for the Kitaev-Heisenberg model. While the magnetic properties of α-RuCl3 have been studied in bulk single crystals or micromechanically-exfoliated nanosheets, little is known about the nanosheets’ properties after exfoliation by techniques suitable for mass production such as liquid phase exfoliation (LPE). Here, we demonstrate sonication-assisted LPE on α-RuCl3 single crystals in an inert atmosphere. Coupled with centrifugation-based size selection techniques, the accessible size- and thickness range is quantified by statistical atomic force microscopy. Individual nanosheets obtained after centrifugation-based size selection are subjected to transmission electron microscopy to confirm their structural integrity after the exfoliation. The results are combined with bulk characterisation methods, including Raman and x-ray photoelectron spectroscopy, and powder diffraction experiments to evaluate the structural integrity of the nanosheets. We report changes of the magnetic properties of the nanomaterial with nanosheet size, as well as photospectroscopic metrics for the material concentration and average layer number. Finally, a quantitative analysis on environmental effects on the nanomaterial integrity is performed based on time and temperature dependent absorbance spectroscopy revealing a relatively slow decay (half-life of ∼2000 h at 20 °C), albeit with low activation energies of 6–20 kJ mol−1.

Controllable Fabrication of Highly Uniform Sub-10nm Nanoparticles from Spontaneous Confined Nanoemulsification.

Sub-10nm nanoparticles are known to exhibit extraordinary size-dependent properties for wide applications. Many approaches have been developed for synthesizing sub-10nm inorganic nanoparticles, but the fabrication of sub-10nm polymeric nanoparticles is still challenging. Here, a scalable, spontaneous confined nanoemulsification strategy that produces uniform sub-10nm nanodroplets for template synthesis of sub-10nm polymeric nanoparticles is proposed. This strategy introduces a high-concentration interfacial reaction to create overpopulated surfactants that are insoluble at the droplet surface. These overpopulated surfactants act as barriers, resulting in highly accumulated surfactants inside the droplet via a confined reaction. These surfactants exhibit significantly changed packing geometry, solubility, and interfacial activity to enhance the molecular-level impact on interfacial instability for creating sub-10nm nanoemulsions via self-burst nanoemulsification. Using the nanodroplets as templates, the fabrication of uniform sub-10nm polymeric nanoparticles, as small as 3.5nm, made from biocompatible polymers and capable of efficient drug encapsulation is demonstrated. This work opens up brand-new opportunities to easily create sub-10nm nanoemulsions and advanced ultrasmall functional nanoparticles.

Methylene-Bridged [6]-, [8]-, and [10]Cycloparaphenylenes: Size-Dependent Properties and Paratropic Belt Currents

Cycloparaphenylenes (CPPs) and carbon nanobelts (CNBs) represent some of the most iconic cyclic molecular nanocarbons in recent chemistry owing to their unique properties derived from rigid, strained, and cyclic π-conjugated systems. In the last decade, the synthesis of various sizes of CPPs and CNBs has been achieved that allowed not only for investigating their size-dependent properties and strategically using such properties in various applications but also understanding the fundamental features of cyclic π-conjugated systems and molecular nanocarbons in general. Herein, we report on the synthesis, size-dependent properties, and paratropic belt currents of methylene-bridged [n]cycloparaphenylenes ([n]MCPP, n = 6, 8, 10). [8]MCPP and [10]MCPP were synthesized by the same strategy we developed for [6]MCPP synthesis. With readily available ethoxy-substituted pillar[8]arene and pillar[10]arene as precursors, [8]MCPP and [10]MCPP were successfully synthesized in three steps consisting of de-ethylation, triflation, and nickel-mediated aryl-aryl coupling. The structural and electronic properties of MCPPs were investigated by nuclear magnetic resonance analyses, absorption/fluorescence measurements, X-ray crystallographic analyses, and computational studies, revealing their interesting size-dependent properties. The differences in the size dependency between MCPPs and CPPs reflect the belt-form features of MCPPs, namely, methylene-bridging effects on MCPPs. Moreover, an interesting paratropic belt current along the MCPP backbone has been uncovered both experimentally and theoretically. The 1H NMR chemical shifts of MCPPs confirmed the presence of a paratropic belt current, whose strength rapidly decreases with increasing nanobelt size.

Size-dependence of AM Ti–6Al–4V: Experimental characterization and applications in thin-walled structures simulations

Previous studies show that the properties of parts manufactured via additive manufacturing, such as selective laser melting, depend on local feature sizes like lattice wall thickness and strut diameter. Although size dependence has been studied extensively, it was not included in constitutive models for numerical simulations. In this work, flat dog-bone tensile specimens of different thicknesses were manufactured and tested under quasi-static conditions to characterize the size-dependent properties experimentally. It was observed that key mechanical properties decrease with specimen thickness. Through curve-fitting to experimental data, this work provides approximate analytical expressions for the material properties values as a function of specimen thickness, furnishing a phenomenological size-dependent constitutive model. The interpolating capability of the model is cross-validated with existing experimental data. Two numerical examples demonstrate the application of the size-dependent material model. The axial crushing of thin-walled lattices at varying wall thicknesses was simulated by the size-dependent material model and one that ignores size effects. Results show that ignoring size effects leads to overestimated peak crushing force and specific energy absorption. The two material models were also compared in the topology optimization of thin-walled structures. Results show that the size-dependent model leads to a more robust optimized design: having higher energy absorption and sustaining less material fracture.

An Experimental Introduction to Colloidal Nanocrystals through InP and InP/ZnS Quantum Dots

Quantum dots are colloidal semiconductor nanocrystals that display size-dependent electronic and optical properties. These materials are a visual demonstration of a quantum-mechanical effect. Here we present a laboratory exercise for undergraduate/Bachelor students as an introduction to colloidal nanocrystals and quantum dots. The students synthesize three sizes of indium phosphide (InP) nanocrystals and perform one core/shell synthesis of indium phosphide cores shelled with zinc sulfide (InP/ZnS). The obtained quantum dots are characterized by quantitative UV–vis, photoluminescence, and 1H NMR spectroscopy. Students are acquainted with several concepts: nanocrystal synthesis, colloids, Beer–Lambert law, quantum confinement, photoluminescence, and surface chemistry. For each concept, background information is provided, rendering this report a comprehensive introduction for students and teachers. Indium phosphide is a safer material to handle in the undergraduate lab compared to cadmium selenide (CdSe), cesium lead bromide (CsPbBr3), or lead sulfide (PbS) nanocrystals.

Comparisons in molecular weight distributions and size-dependent optical properties among model and reference natural dissolved organic matter.

Humic acid (HA) and reference natural organic matter (NOM) have been widely used in environmental assessment, biogeochemistry, and ecotoxicity studies. Nevertheless, similarities and differences among the commonly used model/reference NOMs and bulk dissolved organic matter (DOM) have rarely been systematically evaluated. In this study, HA, SNOM (Suwannee River NOM) and MNOM (Mississippi River NOM), both from International Humic Substances Society, and freshly collected unfractionated NOM (FNOM) were concurrently characterized to evaluate their heterogeneous nature and size-dependent chemical properties. We found that molecular weight distributions, PARAFAC-derived fluorescent components, and size-dependent optical properties are NOM-specific and highly variable with pH. The < 1kDa DOM abundance followed the order of HA < SNOM < MNOM < FNOM. In addition, FNOM was more hydrophilic and contained more protein-like and autochthonous components with a higher UV-absorbance ratio index (URI) and biological fluorescenceindex, whereas HA and SNOM contained more allochthonous, humic-like components with a higher aromaticity and lower URI. Significant differences in molecular composition and size spectra between FNOM and model/reference NOMs suggest that environmental role of NOMs should be evaluated at the levels of molecular weight and functionalities under the same experimental conditions and that HA and SNOM may not represent bulkNOM in the environment. This study provides new information about similarities and differences in DOM size-spectra and chemical properties between reference NOMs and in-situ NOM and highlights the need to better understand the heterogenous roles of NOMs in regulating the toxicity/bioavailability and environmental fate of pollutants in aquatic environments.

How to Characterize 4–90 nm Size Gold Nanospheres with Experimental and Simulated UV–Vis and a Single SEM Image

It is crucial nowadays to predict in a fast and simple manner physical-chemical behaviors like, the size-dependent optical properties of gold nanospheres (Au NSs). The idea behind this experiment is trying to replace (as much as possible) robust and expensive microscopy techniques with UV–vis spectrophotometry and friendly simulations. Students chemically synthesized ∼4 and ∼15 nm diameter NSs and grew larger ones to ∼32, ∼50, and ∼70 nm diameter using the previously obtained ∼15 nm as seeds. They characterized them via UV–vis spectroscopy to ultimately compare the spectra with user-friendly software including MiePlot, nanoHUB.org, and the Amendola algorithm (Wolfram Mathematica). For Au NSs ≤25 nm diam., the experimental UV–vis spectra fitted very well with the Amendola algorithm to determine the size. For Au NSs >25 nm diam., the experiment exhibited larger Au NSs than expected as noticed by the systematic red shift of the plasmon band with respect to the simulated one. A SEM image confirmed larger Au NSs; therefore, students were challenged to determine the source of discrepancy between experimental and simulated UV–vis spectra, which was later attributed to the aging of the Au NSs seeds. This experiment demonstrates an easy way to accurately determine the nanoparticle size while exploring and solving potential issues that students may face during the chemical synthesis and simulations.

Size-dependent electrochemical properties of copper oxide microchip on sensing of neurochemicals

Since a high impact of nanostructured materials on the electrochemical performance of (bio)sensors has been demonstrated, novel nanostructure engineering strategies in recent years have been developed for the highly efficient catalytic nanomaterials through regulating their morphologies, sizes, and compositions. In this work, non-precious copper oxide (CuO) with a series of controlled sizes were synthesized onto a gold microchip via an electrodeposition method, which was further developed as an electrochemical interface for sensing neurochemicals. The dependence of the sizes of CuO ranging from 2.0 µm to 20 µm on its electrochemical behaviors was systematically investigated, and various kinds of neurochemicals were analyzed to present a reasonable result. It was found that much higher sensitivity can be achieved at CuO microchips with smaller size (2.0 µm) towards the neurochemicals, indicating a high impact of size on the electrochemical performance of (bio)sensors. The size-controlled CuO microchip presented a promising reference for the investigation of the size effect on the electrochemical behaviors of (bio)sensors.

Reversible Facet Reconstruction of CdSe/CdS Core/Shell Nanocrystals by Facet–Ligand Pairing

Synthesis of colloidal semiconductor nanocrystals with defined facet structures is challenging, though such nanocrystals are essential for fully realizing their size-dependent optical and optoelectronic properties. Here, for the mostly developed colloidal wurtzite CdSe/CdS core/shell nanocrystals, facet reconstruction is investigated under typical synthetic conditions, excluding nucleation, growth, and interparticle ripening. Within the reaction time window, two reproducible sets of facets─each with a specific group of low-index facets─can be reversibly reconstructed by switching the ligand system, indicating thermodynamic stability of each set. With a unique <0001> axis, atomic structures of the low-index facets of wurtzite nanocrystals are diverse. Experimental and theoretical studies reveal that each facet in a given set is paired with a common ligand in the solution, namely, either fatty amine and/or cadmium alkanoate. The robust bonding modes of ligands are found to be strongly facet-dependent and often unconventional, instead of following Green's classification. Results suggest that facet-controlled nanocrystals can be synthesized by optimal facet-ligand pairing either in synthesis or after-synthesis reconstruction, implying semiconductor nanocrystal formation with size-dependent properties down to an atomic level.

First-principles study of size effects on electrical properties of AlN/GaN heterostructured nanofilms

GaN-based heterostructures and their electrical properties play a crucial role in micro- and nanoelectronic device applications. In this work, the size-dependent electrical properties of wurtzite AlN/GaN heterostructured nanofilms are investigated by using the first-principles simulations. The electronic structures of 1.4 nm/1.4 nm, 1.8 nm/1.8 nm, 2.2 nm/2.2 nm, 2.6 nm/2.6 nm AlN/GaN heterostructured nanofilms are systemically analyzed. The simulations demonstrated that the surface and interface enable to affect the electron density of states of AlN/GaN nanofilms, and the potential well at the valence band of the AlN intermediate layer increases with increasing nanofilm thickness. The electrical conductivity of AlN/GaN nanofilms increases significantly with increasing the thickness from 2.8 nm to 4.4 nm, and the conductivity values stabilize from 4.4 nm to 5.2 nm. Therefore, it can be concluded that the size dependence of the conductivity becomes weaker with increasing the nanofilm thickness. The results of this work could be useful for realizing the tuning of electrical properties of AlN/GaN heterostructured nanofilms through the size effects and surface/interface engineering.

Zigzag-Edged Polycyclic Aromatic Hydrocarbons from Benzo[m]tetraphene Precursors.

A series of zigzag-edged polycyclic aromatic hydrocarbons (PAHs) (Z1-Z3) were synthesized from 2,12-dibromo-7,14-diphenyl-benzo[m]tetraphene (9) as a versatile building block. Their structures were unambiguously confirmed by laser desorption/ionization time-of-flight mass spectrometry, 1 H NMR, Raman, and Fourier-transformed infrared (FTIR) spectroscopies as well as scanning tunneling microscopy. The fingerprint vibrational modes were elucidated with theoretical support. The edge- and size-dependent optical properties were characterized by UV-Vis absorption and fluorescence spectroscopy and DFT calculations. Moreover, ultrafast transient absorption spectroscopy revealed distinct modulation of the photophysical properties upon π-extension from Z1 to Z2, the latter having a gulf edge.

Size-Controlled Synthesis of Luminescent Few-Atom Silver Clusters via Electron Transfer in Isostructural Redox-Active Porous Ionic Crystals.

Ag clusters with a controlled number of atoms have received significant interest because they show size-dependent catalytic, optical, electronic, or magnetic properties. However, the synthesis of size-controlled, ligand-free, and air-stable Ag clusters with high yields has not been well-established. Herein, it is shown that isostructural porous ionic crystals (PICs) with redox-active polyoxometalates (POMs) can be used to synthesize Ag clusters via electron transfer from POMs to Ag+ . Ag clusters with average numbers of three, four, or six atoms emitting blue, green, or red colors, respectively, are formed and stabilized in the PICs under ambient conditions without any protecting ligands. The cluster size solely correlates with the degree of electron transfer, which is controlled by the reduction time and types of ions or elements of the PICs. Thus, advantages have been taken of POMs as electron sources and PICs as scaffolds to demonstrate a convenient method to obtain few-atom Ag clusters.

Exfoliablity, magnetism, energy storage and stability of metal thiophosphate nanosheets made in liquid medium

The family of antiferromagnetic layered metal hexathiohypo diphosphates, M2P2S6 represents a versatile class of materials, particularly interesting for fundamental studies on magnetic properties in low dimensional structures, and yet exhibiting great potential for a broad variety of applications including catalysis, energy storage and conversion, and spintronics. In this work, three representatives of this family of 2D materials (M = Fe, Ni, and Mn) are exfoliated in the liquid phase under inert conditions and the nanosheet’s properties are studied in detail for different sizes of all three compounds. Centrifugation-based size selection is performed for this purpose. The exfoliability and structural integrity of the nanosheets is studied by statistical atomic force microscopy and transmission electron microscopy measurements. Further, we report size and thickness dependent optical properties and spectroscopic metrics for the average material dimensions in dispersion, as well as the nanomaterials’ magnetic response using a combination of cryo-Raman and superconducting quantum interference device measurements. Finally, the material stability is studied semi-quantitatively, using time and temperature dependent extinction and absorbance spectroscopy, enabling the determination of the materials’ half-life, portion of reacted substance and the macroscopic activation energy for the degradation.