Size Confinement Effect Research Articles

Interfacial and Defective Construction from Diverse CuxSy Quantum Dots toward Broadband Carbon-Based Microwave Absorber.

In this study, highly monodisperse copper sulfide (CuxSy) quantum dots (QDs) have been successfully obtained using a ligand-chemistry strategy, and then a variety of S-deficient CuxSy/nitrogen-doped carbon (NC) heterointerfaces are constructed by compositional fine-tuning (Cu9S5 → Cu1.96S → Cu). First-principles calculations show that the S-deficient domains of CuxSy QDs and N-doped domains of carbon synergistically enhance the electron transfer from CuxSy to NC. In addition, the finite element simulations demonstrate that the diverse CuxSy QDs exhibit their intrinsic size and dielectric confinement effects to precisely manipulate the electric field distortion and improve the relaxation polarization. Consequently, CuxSy@NC achieves excellent impedance matching and a strong loss mode dominated by dielectric polarization. Among them, CuxSy@NC-650 has a maximum effective absorption bandwidth of 7.7 GHz at 2.5 mm, while CuxSy@NC-700 features a minimum reflection loss of -66.7 dB at 13.7 GHz, respectively. Furthermore, the simulations of radar cross-sections have confirmed that the CuxSy@NC series is promising in the field of radar stealth.

Photocatalytic dye degradation, H2 evolution, electrical and mechanical performances of mechano-synthesized multifunctional Bi2Te3 nanoparticles: Effect of milling time and thermal treatment

Bi2Te3 nanoparticles are synthesized by mechanical alloying the Bi and Te powders under the Ar and pressed powdered samples are sintered at 573 K. Rietveld refined XRD patterns, FESEM images and EDX spectra reveal the microstructure, morphology and phase purity of the samples. Bandgaps are obtained from the FTIR spectra and a blue shift with size reduction indicates the size confinement effect. The non Debye type ac conductivity and dielectric constant variations with milling time and sintering are measured. The improved photocatalytic degradation efficiency of the sintered sample (83.59 %) using Rhodamine B dye under visible light elucidates reduced porosity effect. The photocatalytic hydrogen evolution efficiencies of these nanoparticles are measured and a probable mechanism is depicted. The highest H2 generation efficiency (1462.5 μmol g−1h−1) is observed with the sintered sample. Microhardness measurement reveals normal indentation size effect. Empirical correlations among electrical conductivity, microhardness and photodegradation are established for the first time.

Effect of aggregate sizes on dilation properties and stress−strain behavior of FRP-confined recycled aggregate concrete

Aggregate size plays a crucial role in determining the mesoscale uniformity and compactness of concrete, directly influencing its dilation characteristics. This dilation behavior, especially under axial load, has significant implications for the tri-axial stress conditions when the concrete undergoes passive confinement using Fiber-Reinforced Polymer (FRP). This study focuses on comprehensively investigating the stress−strain behavior and dilation properties of FRP-confined recycled aggregate concrete (RAC), with a specific emphasis on the effects of recycled aggregate (RA) sizes. A series of compression tests were conducted to examine the stress−strain response of FRP-confined RAC, shedding light on how the dilation properties are influenced by varying RA sizes. The results revealed notable differences in the physical properties (crushing index and water absorption ratio) of RA compared to natural aggregates, with these differences significantly impacting the unconfined concrete strength. Although, an increase in aggregate size demonstrated an improvement in FRP confinement efficiency, it did not bring about a change in the ultimate strength of FRP-confined concrete due to the interaction between the weakening of unconfined concrete strength and the increase in confinement efficiency. In addtion, the transition stress on the stress−strain curve proved highly dependent on both aggregate size and FRP confinement efficiency to RAC. Consequently, a new modified transition stress model, accounting for the effect of aggregate size and FRP confinement, was introduced. Incorporating this newly proposed transition stress model into the existing stress−strain expression yielded predicted stress−strain curves that closely matched the experimental results for FRP-confined RAC with varying RA sizes.

Spontaneous crystallization of strongly confined CsSnxPb1-xI3 perovskite colloidal quantum dots at room temperature.

The scalable and low-cost room temperature (RT) synthesis for pure-iodine all-inorganic perovskite colloidal quantum dots (QDs) is a challenge due to the phase transition induced by thermal unequilibrium. Here, we introduce a direct RT strongly confined spontaneous crystallization strategy in a Cs-deficient reaction system without polar solvents for synthesizing stable pure-iodine all-inorganic tin-lead (Sn-Pb) alloyed perovskite colloidal QDs, which exhibit bright yellow luminescence. By tuning the ratio of Cs/Pb precursors, the size confinement effect and optical band gap of the resultant CsSnxPb1-xI3 perovskite QDs can be well controlled. This strongly confined RT approach is universal for wider bandgap bromine- and chlorine-based all-inorganic and iodine-based hybrid perovskite QDs. The alloyed CsSn0.09Pb0.91I3 QDs show superior yellow emission properties with prolonged carrier lifetime and significantly increased colloidal stability compared to the pristine CsPbI3 QDs, which is enabled by strong size confinement, Sn2+ passivation and enhanced formation energy. These findings provide a RT size-stabilized synthesis pathway to achieve high-performance pure-iodine all-inorganic Sn-Pb mixed perovskite colloidal QDs for optoelectronic applications.

Colloidal one-pot synthesis and characterization of Glycine capped Al(x) doped ZnS QDs for efficient UV light assisted photo-degradation of Stilbene 420 dye

In thisstudy, successful synthesis and characterization of undoped and Al-doped ZnS quantum dots (QDs) capped with bio-friendly glycine (ZnSAl/Gly) are described. The synthesis is accomplished through a one-pot colloidal co-precipitation process, followed by the characterization of QDs using various analytical techniques.X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) showed the formation of cubic-faced ZnS QDs, with the crystal size decreasing as the amount of Al doping increased. A ZnS phase layer on the QDs surface was also demonstrated by Fourier-transform infrared spectroscopy (FTIR) measurements. Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS) analysis was employed to examine the stoichiometry and shape of the synthesized QDs. Thermogravimetric analysis (TGA) showed a remarkable stability of Al-doped ZnS QDs over an extended period, enhancing their potential for a variety of applications. Measurements of the absorption band edge in the UV–Visible range demonstrated that Al ions were successfully incorporated into the ZnS lattice, causing a substantial red shift. This change, which caused the energy band gap to rise from 3.2 eV (ZnS/Gly) to 4.42 eV (ZnSAl1%/Gly), was attributed to the size confinement effect. The degradation of the Stilbene-420 dye under UV irradiation served as a test for the photodegradation capability of the synthesized QDs. The photodegradation efficiency of Al doping ranged from 60 % to 92 %, showing the induction of a significant number of crystalline structures with rising Al concentration. The Al-doped ZnS/Gly QDs are highly catalytic and photoactive, and they show great promise in the field of photoluminescence, medical and biological areas. Their potential for use as effective catalysts in waste water treatment methods is also remarkable.

Numerical simulation of size effect in concrete-encased high-strength steel columns under axial compression

Concrete-encased steel (CES) columns are extensively utilized in practical engineering due to their outstanding performance. However, there have been limited studies on the size effect of CES columns. To investigate the influences of stirrup ratio, steel ratio, and steel strength grade on the axial capacity and the mechanism of the size effect of members under axial compression, a finite element (FE) analysis model that considers the interaction between the size effect and the confinement effect is established and verified. The study results demonstrate that the nominal stress of CES columns can be remarkably increased by employing high-strength steel and enhancing the steel ratio. However, the nominal stress decreases as the cross-sectional size of specimen increases, indicating the presence of the size effect. Moreover, increasing the steel strength grade, stirrup ratio, and steel ratio can decrease the degree of reduction of the nominal stress. Furthermore, comparison of the FE analysis findings and the calculation results of EN1994–1–1:2010(Europe), AISC360–16 (U.S.), and JGJ138–2016(China) revealed that the three codes fail to accurately assess the axial capacity of CES columns. The accuracy and safety reserve of the codes calculation results are even more inadequate for the larger cross-sectional specimens. Finally, a theoretical formula that considers the size effect and confinement effect is developed to calculate the bearing capacity of CES columns, and its applicability and reliability are verified.

Cation substitution and size confinement effects on structure, magnetism and magnetic hyperthermia of BiFeO3-based multiferroic nanoparticles and hydrogels

Highly crystalline BiFeO3 (BFO), Bi0.97Sm0.03FeO3 and BiFe0.97Co0.03O3 nanoparticles are synthesized via the chemical co-precipitation method after calcination at 600 °C in air for 2 h. The effect of cation substitution, Sm for Bi and Co for Fe, on the structural and magnetic properties of BFO nanoparticles is investigated, whereas their magnetically induced heating efficiency in radio frequency alternating magnetic fields is examined. X-ray diffraction indicates the formation of the R3c phase in all compounds, while the corresponding Rietveld refinement reveals a variation of the lattice parameters upon doping, suggesting structural distortion within the BFO lattice due to the ionic radii mismatch between doped and host elements. Transmission electron microscopy unveils smaller particle sizes for the doped nanoparticles, owing to the frustrated particle growth induced by the dopants, whose presence is verified by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. The combined effect of cation substitution and size confinement results in the suppression of the spiral spin structure of BFO, leading to the significantly enhanced magnetic features of the doped nanoparticles at room temperature. For possible applications in the biomedical sector, we tested them as heating agents in magnetic hyperthermia. The dispersion of BiFe0.97Co0.03O3 nanoparticles in water at a concentration of 4 mg/mL could reach the therapeutic window of 41–45 °C for cancer treatment in 50 mT at 375 kHz, whereas the remarkable temperature increase of the BFO-based multiferroic hydrogels, under the same conditions, is auspicious for an effective local treatment at reduced toxicity.

Sn-Induced Synthesis of Highly Crystalline and Size-Confined Si Nanorods at Moderately High Temperatures Using Hydrogen Silsesquioxane

Size-confined Si nanorods (NRs) have gained notable interest because of their tunable photophysical properties that make them attractive for optoelectronic, charge storage, and sensor technologies. However, established routes for fabrication of Si NRs use well-defined substrates and/or nanoscopic seeds as promoters that cannot be easily removed, hindering the investigation of their true potential and physical properties. Herein, we report a facile, one-step route for the fabrication of Si NRs via thermal disproportionation of hydrogen silsesquioxane (HSQ) in the presence of a molecular tin precursor (SnCl4) at a substantially lower temperature (450 °C) compared to those used in the synthesis of size-confined Si nanocrystals (>1000 °C). The use of these precursors allows the facile isolation of phase-pure Si NRs via HF etching and subsequent surface passivation with 1-dodecene via hydrosilylation. The diameters (7.7–16.5 nm) of the NRs can be controlled by varying the amount of SnCl4 (0.2–3.0%) introduced during the HSQ synthesis. Physical characterization of the NRs suggests that the diamond cubic structure is not affected by SnCl4, HF etching, and hydrosilylation. Surface analysis of NRs indicates the presence of Si0 and Sin+ species, which can be attributed to core Si and surface Si species bonded to dodecane ligands, respectively, and a systematic variation of the Si0:Si–C ratio with the NR diameter. The NRs show strong size confinement effects with solid-state absorption onsets (2.51–2.80 eV) and solution-state (Tauc) indirect energy gaps (2.54–2.70 eV) that can be tuned by varying the diameter (16.5–7.7 nm). Photoluminescence (PL) and time-resolved PL (TRPL) studies reveal size-dependent emission (1.95–2.20 eV) with short, nanosecond lifetimes across the visible spectrum, which trend closely with absorption trends seen in solid-state absorption data. The facile synthesis developed for size-confined Si NRs with high crystallinity and tunable optical properties will promote their application in optoelectronic, charge storage, and sensing studies.

Dislocation mechanisms of low-temperature plasticity of nanocrystalline titanium: The role of impurity and grain boundary strengthening

The temperature dependences of the yield strength, the strain rate sensitivity of the deforming stress and the activation volume of the process of plastic deformation of nanocrystalline titanium VT1-0 under quasi-static tension in the temperature range 4.2–395 K are found. The nanoscale grain size was obtained using the method of cryomechanical grain fragmentation. A detailed thermal activation analysis of the experimental results was carried out and it was shown that the process of plastic deformation under conditions of ambient and low temperatures is determined by the overcoming of local impurity barriers by dislocations, and grain boundaries are a source of internal stresses. Empirical estimates are obtained for the parameters of the dislocation-impurity interaction. The unambiguous relationship between internal stresses and grain size established for monomodal nanocrystalline titanium made it possible to separate the effects of impurity and grain boundary hardening. The result obtained is an indirect basis for the conclusion about the impossibility of accumulation of dislocations in nanograins during plastic deformation. The decrease in the activation volume for a nanoscale grain at a constant impurity concentration is considered because of the manifestation of the dependence of the diameter of the dislocation loop generated by a grain boundary source on the grain size (confinement effect).

Experimentally characterizing the origins of confinement effects in membranes.

Diffusion in membranes plays a vital role in biological processes, governing reaction rates and reconfiguring membranes. The effect of crowding and inhomogeneity on the dynamics of lipids and proteins is substantial, but the underlying physical principles are not well understood. We investigate the effect of confinement on the two-dimensional diffusion of model lipids in supported bilayers using a novel lithographically-defined platform. Specifically, we explore how changing the geometry of escape routes influences the diffusion of confined lipids. We compare lipid diffusion through narrow escape funnels formed by wide range of structures, enabling us to systematically explore the effect of confinement size and geometry. Our results demonstrate that the local geometry, not just the size of the escape funnel, determines the characteristic diffusion timescale. Our approach enables us to directly test several competing theoretical descriptions, and demonstrates the utility of our simple, highly-customizable diffusion characterization platform.

Analysis of synthesized doped vertical silicon nanowire arrays for effective sensing of nitrogen dioxide: As gas sensors

In the present study, the controllable fabrication of silicon nanowires (Si NWs) with vertical alignment was accomplished using metal assisted chemical etching (MACE). The different characteristics, such as structural, morphological, chemical, optical, and dielectric properties were analyzed using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), and LCR [inductance (L), capacitance (C), and resistance (R)] meter (volume of the gas-sensing chamber is 650 mm3). It was revealed from the morphological study i.e., from the FESEM that p-type Si NWs are smaller in size than n-type Si NWs which is attributable to the energy band gap. The optical band gap (Eg) is observed to increase from 1.64 to 1.89 eV with the decreasing of the crystallite size and the optical reflection spectra of the Si NWs show a shift toward a lower wavelength (blue shift). Moreover, Raman spectra verified the red-shifted, asymmetrically broadened Raman line-shapes, which provides information about the size confinement effect in Si NWs. The MACE approach is excellent for synthesizing nanowire structures for use in gas-sensing applications due to its flexibility. The sensitivity of synthesized Si NWs was tested for NO2 gas. The sensor method is unique based on the testing of the device in the presence of a test gas because the use of the gas-sensing setup has the potential to measure the change in resistance by varying frequency, temperature, and time.

PbS QDs/Al2O3/In0.53Ga0.47As infrared photodetector with fast response and high sensitivity

Due to the size effect, multi-exciton effect, confinement effect, and tunable bandgap, quantum dots (QDs) have gradually been used in near-infrared photodetectors. In this paper, PbS QDs were integrated with In0.53Ga0.47As materials, and a PbS QDs/In0.53Ga0.47As hybrid photodetector with Al2O3 was investigated. Passivation of PbS QDs by ligand replacement and insertion of Al2O3 reduced the dark current density from 9.24 × 10−6 to 4.67 × 10−6 A·cm−2, which enabled the detector to obtain a high responsivity of 0.97 A·W−1 under −1 V bias, and the detectivity reached 2.21 × 1010 Jones. In addition, we found that the PbS QDs/In0.53Ga0.47As near-infrared photodetector with Al2O3 obtained a fast rise and fall time, which could respond to high-frequency signals. The findings will have application in the PbS QDs/In0.53Ga0.47As hybrid near-infrared photodetectors.

Electronic materials with nanoscale curved geometries

As the dimensions of a material shrink from an extended bulk solid to a nanoscale structure, size and quantum confinement effects become dominant, altering the properties of the material. Materials with nanoscale curved geometries, such as rolled-up nanomembranes and zigzag-shaped nanowires, have recently been found to exhibit a number of intriguing electronic and magnetic properties due to shape-driven modifications of charge motion or confinement effects. Local strain generated by curvature can also lead to changes in material properties due to electromechanical coupling. Here we review the development of electronic materials with nanoscale curved geometries. We examine the origin of shape-, confinement- and strain-induced effects and explore how to exploit these in electronic, spintronic and superconducting devices. We also consider the methods required to synthesize and characterize curvilinear nanostructures, and highlight key areas for the future development of curved electronics.

Tunable Noninteger Flux Quantum of Vortices in Superconducting Strips.

Flux quantization has been widely regarded as the hallmark of the macroscopic quantum state of superconductivity. However, practical design of superconductor devices exploiting finite size confinement effects may induce exotic phenomena, including nonquantized vortices. In our research, the magnetic flux of vortices has been studied in a series of superconducting strips as a function of the strip width and the penetration depth. In both circumstances, the observation using scanning Hall probe microscope (SHPM) displays a controlled evolution from singly quantized vortices to nonquantized ones. It is also found that the magnetic flux is immune to the flowing supercurrent. The simulations based on Ginzburg-Landau theory agree well with experimental results. The observed behavior of the vortex flux may open new perspectives for fundamental research and applications based on vortex matter, such as vortex-memory devices and magnetic field traps for ultracold atoms.

Enhanced N2-to-NH3 conversion efficiency on Cu3P nanoribbon electrocatalyst

Ambient electroreduction of nitrogen (N2) is considered as a green and feasible approach for ammonia (NH3) synthesis, which urgently demands for efficient electrocatalyst. Morphology has close relationship with catalytic activity of heterogeneous catalysts. Nanoribbon is attractive nanostructure, which possesses the flexibility of one-dimensional nanomaterials, the large surface area of two-dimensional nanomaterials, and lateral size confinement effects. In this work, Cu3P nanoribbon is proposed as a highly efficient electrocatalyst for N2-to-NH3 conversion under benign conditions. When measured in N2-saturated 0.1 M HCl, such Cu3P nanoribbon achieves high performance with an excellent Faradaic efficiency as high as 37.8% and a large yield of 18.9 µg·h−1µmgcat.−1 at −0.2 V. It also demonstrates outstanding stability in long-term electrolysis test at least for 45 h.

Magnetic field and anisotropic parabolic potential effects on ground state binding energy of impurity magnetopolaron in asymmetrical semi-exponential quantum wells

We performed the ground state binding energy (GSBE) and vibrational frequency (VF) of strong-coupling impurity magnetopolaron (SCIM) in asymmetrical semi-exponential quantum wells (ASEQWs) containing a hydrogen-like impurity in the center exposed to a uniform magnetic field through Lee-Low-Pines unitary transformation and linear combination operation method based on effective mass approximation. The results were expressed as functions of GSBE and VF for different magnetic field cyclotron frequency (MFCF) and Coulombic impurity potential (CIP) strength, the positive criteria of ASEQWs along the growth direction of QW and effectual confinement lengths of APCP along the coordinates were analyzed. Our findings revealed that the VF and GSBE were enhanced by increasing magnetic field cyclotron frequency and the parameter of asymmetrical semi-exponential confinement potential (ASECP), which was increased by reducing APCP effectual confinement length along the directions of coordinates. The above observations could be because of quantum size confinement effects.

ZIF-8 derived carbon with confined sub-nanometer pores for electrochemically selective separation of chloride ions

Selective ion separation from aqueous solution is challenging and crucial for water purification. In this work, zeolitic imidazolate framework (ZIF-8) derived nano-porous carbon (NC-X-A) with confined sub-nanometer pores was synthesized by acid leaching and alkali activation after the carbonization of ZIF-8 precursor for the selective electrochemical separation of chloride ions (Cl−). Here, the uptake capacity and selectivity of Cl− were improved by changing the carbonization temperature to tune the specific surface area and pore size. Based on the size confinement effect and the difference in free energies of dehydration, the obtained optimum carbon film, i.e., NC-1000-A coated electrode, exhibited separation factors of 1.384, 1.952 and 2.970 for Cl−/Br−, Cl−/F− and Cl−/SO42−, respectively. It also showed fast uptake/release ability with an uptake equilibrium time less than 90 min. The Cl− uptake capacity reached to 64.06 mg g−1 and retained 99.7% of its initial value even after 1000 uptake/release cycles due to its porous structure with high specific surface area, good electrical conductivity and extra electric driving force during the ESIX process. Thus, it is expected that this kind of carbon film would be applied as a promising electroactive material for the selective separation of Cl− from wastewater.

Constructing 0D/1D Ag3PO4/TiO2 S-scheme heterojunction for efficient photodegradation and oxygen evolution

An S-scheme heterojunction photocatalyst is capable of boosting photogenerated carrier separation and transfer, thus maintaining high photooxidation and photoredox ability. Herein, a 0D Ag3PO4 nanoparticles (NPs)/1D TiO2 nanofibers (NFs) S-scheme heterojunction with intimate interfacial contact was designed via the the hydro-thermal method. Benefiting from the abundant hydroxyl groups and size confinement effect of TiO2 NFs, the average diameter of the Ag3PO4 nanoparticles decreased from 100 to 22 nm, which favored the construction of a 0D/1D geometry heterojunction. The multifunctional Ag3PO4/TiO2 sample exhibited excellent photocatalytic activity and stability in photocatalytic oxygen production (726 µmol/g/h) and photocatalytic degradation of various organic contaminants such as rhodamine B (100%), phenol (60%) and tetracycline hydrochloride (100%). The significant improvements in the photocatalytic performance and stability can be attributed to the intimate interfacial contacts and rich active sites of 0D/1D geometry, fast charge carrier migration, and outstanding photoredox properties induced by the S-scheme charge-transfer route. This work offers a promising strategy for constructing 0D/1D S-scheme heterojunction photocatalysts for improved photocatalytic performance.

High Color Purity and Efficient Green Light-Emitting Diode Using Perovskite Nanocrystals with the Size Overly Exceeding Bohr Exciton Diameter.

Lead halide perovskite nanocrystals (PNCs) are emerging as promising light emitters to be actively explored for high color purity and efficient light-emitting diodes. However, the most reported lead halide perovskite nanocrystal light-emitting diodes (PNCLEDs) encountered issues of emission line width broadening and operation voltage elevating caused by the quantum confinement effect. Here, we report a new type of PNCLED using large-size CsPbBr3 PNCs overly exceeding the Bohr exciton diameter, achieving ultranarrow emission line width and rapid brightness rise around the turn-on voltage. We adopt calcium-tributylphosphine oxide hybrid ligand passivation to produce highly dispersed large-size colloidal CsPbBr3 PNCs with a weak size confinement effect and also high photoluminescence quantum yield (∼85%). Utilizing these large-size PNCs as emitters, we manifest that the detrimental effects caused by the quantum confinement effect can be avoided in the device, thereby realizing the highest color purity in green PNCLED, with a narrow full width at half-maximum of 16.4 nm and a high corrected maximum external quantum efficiency of 17.85%. Moreover, the operation half-life time of the large-size PNCLED is 5-fold of that based on smaller-size PNCs. Our work provides a new avenue for improving the performance of PNCLEDs based on unconventional large-size effects.

Optimizing the Performance of Perovskite Nanocrystal LEDs Utilizing Cobalt Doping on a ZnO Electron Transport Layer.

Metal halide perovskite nanocrystal (PNC) light-emitting devices (LEDs) are promising in the future ultra-high-definition display applications due to their tunable bandgap and high color purity. Balanced carrier injection is indispensable for realizing highly efficient LEDs. Herein, cobalt (Co) was doped into ZnO to modulate the electron mobility of a pristine electron transport layer (ETL) and to inhibit exciton quenching at the ZnO/EML interface due to the passivation of oxygen vacancies and the reduction of electron concentration resulting from the trapping of electrons by the Co2+-induced deep impurity level. Also, the bandgap was widened due to the size confinement effect. All of those were beneficial to achieve a balanced charge injection during the operating process. Consequently, the maximum luminance increased from 867 cd m-2 for ZnO LEDs to 1858 cd m-2 for Co-doped ZnO LEDs, and there was a 70% increase of external quantum efficiency (EQE). By further inserting a polyethylenimine (PEI) layer in the Co-doped ZnO LEDs, the EQE reached 13.0%.