Lanthanum Hexaboride Nanoparticles Research Articles

Evaluation of the optical properties of various-shaped and core-shell-structured lanthanum hexaboride nanoparticles based on discrete dipole approximation

The extinction behavior of various-shaped and core-shell-structured lanthanum hexaboride (LaB6) nanoparticles was theoretically studied based on the discrete dipole approximation method. It was found that different nanoparticle shapes yielded a great influence on extinction efficiency. In comparison to spherical and cubic particles, the near-infrared (NIR) extinction peak of rod-like nanoparticles appeared at a longer wavelength. For core-shell-structured LaB6 particles, all of LaB6@TiO2, LaB6@ZnO, and LaB6@SiO2 exhibited low extinction in the visible region and high extinction in the NIR region, indicating that these three structures are potential transparent heat-shielding materials. Moreover, LaB6@TiO2 manifested better NIR extinction behavior than LaB6@ZnO and LaB6@SiO2; however, its transmittance in the visible region was slightly reduced.

Hot electron emission from waveguide integrated lanthanum hexaboride nanoparticles

Recently, it has been shown that hot-electron photoemission in waveguide-integrated graphene can occur at peak optical power densities many orders of magnitude lower than multiphoton and strong field emission. In this work, we study how the deposition of low-work function lanthanum hexaboride nanoparticles can alter the behavior of hot-electron emission from graphene and thin gold waveguide-integrated hot electron emitters. This approach is promising, as the graphene enables an electrically conductive platform on which to deposit the nanoparticles, while still enabling interaction between the nanoparticles and incident photons. Despite nonideal coatings of LaB6 nanoparticles on the waveguide integrated graphene and gold, there is a nearly order of magnitude improvement over previous graphene-based hot-electron emitters. This hybrid approach demonstrates how a combination of integrated photonics and low-work function coatings can improve the performance of the emerging class of hot-electron emitters.

Effects of different milling conditions on the properties of lanthanum hexaboride nanoparticles and their sintered bodies

In this study, the preparation and consolidation of nanocrystalline LaB 6 powders originating from powder blends of La 2 O 3 , B 2 O 3 and Mg were reported. A consecutive route of mechanochemical synthesis (MCS) and purification was utilized for the achievement of nano-sized LaB 6 powders. As-synthesized powders were leached out from intermediate reaction products or impurities. Then, a sequential step of cold pressing (uniaxial pressure at 800 MPa) and pressureless sintering (at 1700 °C for 5 h under Ar gas flow) were utilized for the consolidation of the purified LaB 6 powders. The type of mill (vibratory and planetary high-energy ball mills) was employed as a MCS parameter to reveal its effect on the physical, microstructural and mechanical properties of the LaB 6 powders, and their bulk structures. Compositional, physical and microstructural properties of the products after powder processing were determined via X-ray diffractometer (XRD), particle size analyzer (PSA), differential scanning calorimeter (DSC), stereomicroscope (SM), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectrometer (EDS) coupled with both SEM and TEM, and vibrating sample magnetometer (VSM). The bulk properties of the LaB 6 consolidated from nanocrystalline powders with a minimum 99.99% purity, and ∼62 nm (for vibratory ball mill) or ∼74 nm (for planetary ball mill) average particle size were compared according to various properties. LaB 6 powders were synthesized in planetary mill at an approximately six times longer duration than that of in vibratory mill. According to the results, density, surface area and mean particle size values of the vibratory ball-milled samples (containing paramagnetic powders) are better than those of planetary ball-milled (containing diamagnetic powders) ones. However, mechanical properties such as hardness, surface roughness, wear rate, friction coefficient, and also electrical conductivity were improved in the planetary ball-milled LaB 6 bulks.

The influence of additives of lanthanum hexaboride nanoparticles on the cast structure of high-chromium steel of austenitic and martensitic classes

The paper presents the results of studying the influence of lanthanum hexaboride, modified with nanosized powder, on the cast structure of martensitic and austenitic steel, aluminium and silicon killed. A study was carried out on high-chromium steel 08H18N12 and 10H9MFB. As the addition, there were used compressed tablets containing different amounts of nanosized powder of lanthanum hexaboride and carbonyl iron. The conducted research allowed to conclude that the use of lanthanum hexaboride atomizes the dendritic structure of high-chromium steel of martensitic and austenitic classes. Furthermore, it is established that lanthanum hexaboride can be an effective means of introducing boron into high-chromium steel, including nitrogen-containing one. In addition to the above, lanthanum hexaboride actively interacts with sulfur and thus forms primary lanthanum sulphides which are the substrate for forming complex oxysulphides.

Melt-assisted synthesis to lanthanum hexaboride nanoparticles and cubes

Lanthanum hexaboride (\(\hbox {LaB}_{6}\)) nanocrystals and cubes were successfully synthesized at \(700{^{\circ }}\hbox {C}\) for 2 h under argon atmosphere by a melt-assisted method using \(\hbox {LaCl}_{3}\) and \(\hbox {NaBH}_{4}\) as reactants, NaCl–KCl or zinc or NaCl–KCl–zinc as reaction melt. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. XRD patterns and Raman spectra confirmed the formation of \(\hbox {LaB}_{6}\) with high purity. TEM and SEM results showed \(\hbox {LaB}_{6}\) powders prepared in mixed molten salts of NaCl–KCl were mainly composed of nanoparticles with sizes of ca. 8 nm. The morphology of \(\hbox {LaB}_{6}\) presented as regular cubes (100–300 nm) when metal zinc was used as reaction melt. Photothermal conversion test indicated that nanoparticles had a better photothermal conversion performance than cubes.

Size dependent optical properties of LaB6 nanoparticles enhanced by localized surface plasmon resonance

Lanthanum hexaboride nanoparticles, with high emission electrons in cathode materials and peculiar blocking near infrared wavelengths, were applied for many aspects. Based on the quasi-static approximation of Mie theory, the size dependent optical properties of LaB6 nanoparticles were researched, such as refractive index n(ω), extinction coefficient k(ω), reflectivity R(ω), absorption coefficient α(ω), and electron energy loss L(ω). Due to the localized surface plasmon resonance (LSPR), the extinction coefficient k(ω) and absorption coefficient α(ω) depended on the size, and the LSPR peaks red-shifted with sizes increased, which was different from that of bulk materials. In addition, electron energy-loss spectrum L(ω) showed electrons oscillation reinforced, since electrons absorbed the photon energy and generated resonance. Further, reflectivity R(ω) and refractive index n(ω) indicated that the light in near infrared region could not be propagated on the surface of LaB6 materials, which exhibited metallic behaviors. So the resonance peak of LaB6 nanoparticle was located in near-infrared region, making use of this property for solar control glazing and heat-shielding application.

Uniform Dispersion of Lanthanum Hexaboride Nanoparticles in a Silica Thin Film: Synthesis and Optical Properties

Silica thin films containing uniformly dispersed lanthanum hexaboride (LaB₆) nanoparticles have been prepared by spin-coating a sol-gel silica solution containing cetyltrimethyl ammonium bromide (CTAB)-stabilized LaB₆ nanoparticles onto a glass substrate followed by a standard heat treatment. The production of this thin film involved three steps: (i) a CTAB-stabilized LaB₆ nanoparticle dispersion was prepared in water and then dried, (ii) the dried nanoparticles were redispersed in a small amount of water and mixed with tetraethoxyorthosilane (TEOS), ethanol, and a little acid to initiate the sol-gel reaction, and (iii) this reaction mixture was spun to produce a thin film and then was annealed. A range of techniques such as zeta potential, laser sizing, energy-filtered transmission electron microscopy (EFTEM), scanning TEM (STEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrum (EDS) were employed to characterize the particle's size, elemental composition, and stability and the optical properties of silica thin films with LaB₆ nanoparticles. On the basis of the optical transmittance and reflectance spectra of an annealed silica thin film with LaB₆ nanoparticles, the annealed thin films clearly showed positive absorption of radiation in the near infrared (NIR) region meeting a main objective of this study. A potential optical micro-electromechanical sensing system in the NIR range can be realized on the basis of this silica thin film with LaB₆ nanoparticles.

Improving the field emission of carbon nanotubes by lanthanum-hexaboride nano-particles decoration

Field emission of carbon nanotubes (CNTs) was remarkably improved by lanthanum-hexaboride (LaB6) nano-particles (NPs) decoration. CNTs were grown on the silicon substrate by chemical vapor deposition. Field emission of bare CNTs and LaB6-NPs decorated CNTs was carried out under same conditions. Physical, morphological, elemental, and graphitic nature changes were ascertained by scanning electron microscope, transmission electron microscope, energy dispersive x-ray spectroscopy, and Raman analysis. LaB6-NPs decorated CNTs show significant reduction of turn-on electric-field from 3.0 to 2.1 V/μm. A remarkable improvement of more than six-fold from 2.05 to 13.19 mA/cm2 at a field of 4.6 V/μm was also observed in the current-density.

Absorption and scattering of near-infrared light by dispersed lanthanum hexaboride nanoparticles for solar control filters

Optical absorption and scattering behaviors of lanthanum hexaboride (LaB6) nanoparticulate dispersion coatings with various particle sizes have been investigated in the ultraviolet to near-infrared (NIR) wavelengths for application to solar control filters. Large characteristic near-infrared absorption is introduced as the decreased particle size falls into nanoscale, and its origin is discussed in terms of a localized surface plasmon resonance (LSPR) of conduction electrons. Optical constants of LaB6 have been measured and Mie scattering theory analysis was conducted. The theory was found to generally replicate the optical characteristics, and variations of absorbed and scattered wave fractions as well as the LSPR wavelength have been discussed with varying particle size. The absorption peaks are found as shaped narrower and located at shorter wavelength in theory than in experiment, which is suggested as ascribed mainly to the nonspherical distorted shape of LaB6 nanoparticles.