In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

In situ observation of oscillatory growth of bismuth nanoparticles

We study the growth of Bi nanoparticles in an engineered precursor-scarce environment in a liquid cell at an elevated temperature (180 °C) using transmission electron microscopy. Observation reveals dynamics of oscillatory growth of individual nanoparticles, pairwise Ostwald ripening and anti-Ostwald ripening and a global collective oscillation. The experimental results suggest a mass-transport zone is present around each particle, which couples to the observed growth kinetics. This study shed light on a new route for system engineering to reverse particle coursing by Ostwald ripening.     

Small angle X-ray scattering and photoluminescence study of ZnO nanoparticles synthesized by hydrothermal process

Polydisperse ZnO nanoparticles have been synthesized by a hydrothermal process. Small-angle X-ray Scattering (SAXS) was performed for particle size distribution analysis of ZnO nanoparticles. Room-temperature photoluminescence measurements revealed that the ZnO nanoparticles have a single visible emission peak ～600?nm, although polydispersity of the sample shows no presence on PL spectrum. It seems the orange emission ～600?nm is due to the presence of Zn(OH)₂ on the surface of ZnO nanoparticles, instead of the commonly assumed interstitial oxygen defect.     

Probing in situ the nucleation and growth of gold nanoparticles by small-angle X-ray scattering

We probe in situ by synchrotron SAXS/WAXS and UV-visible spectroscopy the nucleation and growth of gold nanoparticles. The use of a fast-mixing stopped-flow device enables the assessment of the whole particle formation process with a 200 ms time resolution. The number of particles, their size distribution, and the yield of the reaction is determined in real time through the quantitative analysis of the SAXS data on an absolute scale. Two ligands exhibit drastically different behaviors: when an alkanoic acid is used, a nucleation phase of 1 s is followed by a growth step whose rate is limited by the reaction of the monomers at the interface; on the other hand, when an alkylamine is used, the nucleation rate is increased by an order of magnitude, thus annealing growth by a lack of monomer and yielding R=1 nm particles in 2 s, as compared with R=3.7 nm in 12 s for the acid case.     

In situ growth of silver nanoparticles in porous membranes for surface-enhanced raman scattering

We demonstrate the in situ growth of silver nanoparticles in porous alumina membranes (PAMs) for use as a surface-enhanced Raman scattering (SERS) detection substrate. This fabrication method is simple, cost-effective, and fast, while providing control over the size of silver nanoparticles through the entire length of the cylindrical nanopores with uniform particle density inside the pores unachievable by the traditional infiltration technique. The in situ growth of silver nanoparticles was conducted from electroless-deposited nanoscale seeds on the interior of the PAM and resulted in the formation of numerous hot spots, which facilitated significantly higher SERS enhancement for these substrates compared with previously reported porous substrates.     

In situ observation of temperature-dependent atomistic and mesoscale oxidation mechanisms of aluminum nanoparticles

Oxidation is a universal process causing metals’ corrosion and degradation. While intensive researches have been conducted for decades, the detailed atomistic and mesoscale mechanisms of metal oxidation are still not well understood. Here using in situ environmental transmission electron microscopy (E-TEM) with atomic resolution, we revealed systematically the oxidation mechanisms of aluminum from ambient temperature to ~ 600 °C. It was found that an amorphous oxide layer formed readily once Al was exposed to air at room temperature. At ~ 150 °C, triangle-shaped Al2O3 lamellas grew selectively on gas/solid (oxygen/amorphous oxide layer) interface, however, the thickness of the oxide layer slowly increased mainly due to the inward diffusion of oxygen. As the temperature further increased, partial amorphous-to-crystallization transition was observed on the amorphous oxide film, resulting in the formation of highly dense nano-cracks in the oxide layer. At ~ 600 °C, fast oxidation process was observed. Lamellas grew into terraces on the oxide/gas interface, indicating that the high temperature oxidation is controlled by the outward diffusion of Al. Single or double/multi-layers of oxide nucleated at the corners of the terraces, forming dense γ’-Al₂O₃, which is a metastable oxide structure but may be stabilized at nanoscale.

     

In situ X-ray scattering evaluation of heat-induced ultrastructural changes in dental tissues and synthetic hydroxyapatite

Human dental tissues consist of inorganic constituents (mainly crystallites of hydroxyapatite, HAp) and organic matrix. In addition, synthetic HAp powders are frequently used in medical and chemical applications. Insights into the ultrastructural alterations of skeletal hard tissues exposed to thermal treatment are crucial for the estimation of temperature of exposure in forensic and archaeological studies. However, at present, only limited data exist on the heat-induced structural alterations of human dental tissues. In this paper, advanced non-destructive small- and wide angle X-ray scattering (SAXS/WAXS) synchrotron techniques were used to investigate the in situ ultrastructural alterations in thermally treated human dental tissues and synthetic HAp powders. The crystallographic properties were probed by WAXS, whereas HAp grain size distribution changes were evaluated by SAXS. The results demonstrate the important role of the organic matrix that binds together the HAp crystallites in responding to heat exposure. This is highlighted by the difference in the thermal behaviour between human dental tissues and synthetic HAp powders. The X-ray analysis results are supported by thermogravimetric analysis. The results concerning the HAp crystalline architecture in natural and synthetic HAp powders provide a reliable basis for deducing the heating history for dental tissues in the forensic and archaeological context, and the foundation for further development and optimization of biomimetic material design.     

In situ high temperature X-ray diffraction study of UO2 nanoparticles

Nanocrystallites of UO₂ with a size of 3–5 nm were studied in situ with high temperature X-ray diffraction (HT-XRD), thermogravimetry (TGA), and differential thermal analysis. The evolution of the crystallite size, the lattice parameter, and the strain were determined from ambient temperature up to 1200 °C. Below 700 °C, a weak effect on the crystallite size occurs and it remains below 10 nm, while a strong expansion of the lattice parameter is measured. The strain decreases with temperature and is completely released at 700 °C. Above this temperature, begins the sintering of the nanocrystallites reaching a size of about 80 nm at 1200 °C. The weight loss curve observed in TGA is assigned to the desorption of water molecules and is correlated with the strain evolution observed by HT-XRD. The linear thermal expansion and the thermal expansion coefficient at 800 °C are 1.3% and 16.9 × 10⁻⁶ °C⁻¹, respectively.     

Parallel patterning of nanoparticles via electrodynamic focusing of charged aerosols

The development of nanodevices that exploit the unique properties of nanoparticles will require high-speed methods for patterning surfaces with nanoparticles over large areas and with high resolution. Moreover, the technique will need to work with both conducting and non-conducting surfaces. Here we report an ion-induced parallel-focusing approach that satisfies all requirements. Charged monodisperse aerosol nanoparticles are deposited onto a surface patterned with a photoresist while ions of the same polarity are introduced into the deposition chamber in the presence of an applied electric field. The ions accumulate on the photoresist, modifying the applied field to produce nanoscopic electrostatic lenses that focus the nanoparticles onto the exposed parts of the surface. We have demonstrated that the technique could produce high-resolution patterns at high speed on both conducting (p-type silicon) and non-conducting (silica) surfaces. Moreover, the feature sizes in the nanoparticle patterns were significantly smaller than those in the original photoresist pattern.     

In situ gamma-radiation: one-step environmentally benign method to produce gold-palladium bimetallic nanoparticles

Synthesis of gold-palladium bimetallic nanoparticles using in situ radioactivity from (198)Au isotope is reported in this paper. Gold solution spiked with (198)Au(III) has been mixed with PdCl2 solution in measured proportions in 50% polyethylene glycol solution. Au(III) and Pd(II) are reduced, and nanoparticles are formed due to radiolysis of the polymer solution. The solution has been characterized by UV-visible spectra, and the actual size has been determined using transmission electron microscopy in conjugation with energy dispersive X-ray measurements.     

In situ surface-enhanced Raman scattering analysis of biofilm

Biofilms represent the predominant form of microbial life on Earth. They are aggregates of microorganisms embedded in a matrix formed by extracellular polymeric substances (EPS). Detailed information about chemical composition and structure of the EPS matrix is relevant e.g. for the optimization of biocides, of antifouling strategies and for biological wastewater treatment. Raman microscopy (RM) is a capable tool that can provide detailed chemical information about biofilm constituents with spatial resolution of optical microscope. However, the sensitivity of RM is limited. Surface-enhanced Raman scattering (SERS), which enables investigations of biomolecules at very low concentration levels, allows overcoming this drawback. To our knowledge, this paper is the first report on reproducible SERS spectra from different constituents of a multispecies biofilm. We believe that the reproducibility is partly owed to the in situ measurement of the biofilm, while up to now SERS measurements of microbiological samples by RM were carried out after sample drying. We employed colloidal silver nanoparticles for in situ SERS measurements by RM. The achieved enhancement factor of up to 2 orders of magnitude illustrates a high potential of SERS for ultrasensitive chemical analysis of biofilms, including the detection of different components and the determination of their relative abundance in the complex biofilm matrix.     

In situ TEM observation of long range ordering via short range order in Cu3Pt

The thermoequilibrium state of short range order (SRO) and the ordering process to the long range order (LRO) phase in Cu₃Pt have been studied by thein situ transmission electron microscope (TEM) observation method. It is confirmed that the alloy has the SRO state in thermoequilibrium within the temperature region for the disordered fcc phase (designated as A1). The SRO state can be interpreted in the ‘microdomain model’. The degree of order fluctuates temporally as well as spatially at higher temperature, but freezes at a lower temperature in the A1 region. In the temperature region of (A1+LRO), some of the microdomains in the SRO grow up to large domains of LRO. This indicates that the transformation process to LRO via SRO proceeds without a process of nucleation even though the transformation is of a first order. Division of A1 into subregions and physical meaning of the phase boundary between (A1+LRO) and A1 are discussed.     

Oxidation study of polycrystalline InN film using in situ X-ray scattering and X-ray photoemission spectroscopy

Oxidation process of polycrystalline InN films were investigated using in situ X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). The films were grown by dc sputter on sapphire (0001) substrates and were oxidized in air at elevated temperatures. The XRD data showed that the structure of the films changed to the bixbyite In₂O₃ (a = 10.11 Å) above 450 °C. Chemical configurations of the sample surfaces were investigated using high-resolution XPS. For the non-intentionally oxidized InN film, XPS analysis on the In 3d peak and the N 1s main peak at 396.4 eV suggests that indium and nitrogen are bound dominantly in the form of InN. An additional peak observed at 397.4 eV in the N 1s photoelectrons and the O 1s peaks indicate that the InN film surface is partly oxidized to have InO_xN_y configuration. After oxidation of the InN film at elevated temperature, the O 1s spectrum is dominated by In₂O₃ peak, which indicates that the structure is stable chemically with In₂O₃ configuration at least within the XPS probing depth of a few nm.     

In situ observation of kink-band formation in a unidirectional carbon fiber reinforced plastic by X-ray computed tomography imaging

A compression test of a unidirectional carbon fiber reinforced plastic (CFRP) rectangular coupon was performed in an X-ray computed tomography (CT) system. Internal compressive failure of the CFRP was observed under loading. Two-dimensional fiber microbuckling developed non-uniformly in the specimen, and enlarged locally at one side. Fiber failure then initiated at the side edge and propagated through the whole cross section. A two-dimensional kink-band developed as a result of two-dimensional fiber microbuckling. The out-of-plane and in-plane band widths and band angles were almost the same. The coupon specimen twisted slightly owing to the two-dimensional kink-band, which resulted, macroscopically, in a transverse and through-thickness shear failure mode. The scenario of kink-band failure in a unidirectional CFRP coupon was revealed by X-ray CT imaging.     

In situ measurements of Raman scattering in clear ocean water

We have further developed and improved the prototype oceanic Fraunhofer line discriminator by using a well-protected fiber-optic-wire cable and in-water electronic housing. We conducted a series of in situ measurements in clear ocean water in the Florida Straits. By comparing the reduced data with the Monte Carlo simulation results, we verify the Raman scattering coefficient B(r) with an excitation wavelength at 488 nm to be 2.6 x 10(-4)m(-1) [Appl. Opt. 29, 71-84 (1990)], as opposed to 14.4 x 10(-4) m(-1) [Appl. Opt.14, 2116-2120 (1975)]. The wavelength dependence of the Raman scattering coefficient is found to have an insignificant effect on the in-water light field. We also discuss factors that lead to errors. This study can be used as a basis for inelastic light scattering in the radiative transfer theory and will allow other inelastic light, e.g., fluorescence, to be detected with in situ measurements.     

Rapid generation of protein aerosols and nanoparticles via surface acoustic wave atomization

We describe the fabrication of a surface acoustic wave (SAW) atomizer and show its ability to generate monodisperse aerosols and particles for drug delivery applications. In particular, we demonstrate the generation of insulin liquid aerosols for pulmonary delivery and solid protein nanoparticles for transdermal and gastrointestinal delivery routes using 20?MHz SAW devices. Insulin droplets around 3?μm were obtained, matching the optimum range for maximizing absorption in the alveolar region. A new approach is provided to explain these atomized droplet diameters by returning to fundamental physical analysis and considering viscous-capillary and inertial-capillary force balance rather than employing modifications to the Kelvin equation under the assumption of parametric forcing that has been extended to these frequencies in past investigations. In addition, we consider possible mechanisms by which the droplet ejections take place with the aid of high-speed flow visualization. Finally, we show that nanoscale protein particles (50-100?nm in diameter) were obtained through an evaporative process of the initial aerosol, the final size of which could be controlled merely by modifying the initial protein concentration. These results illustrate the feasibility of using SAW as a novel method for rapidly producing particles and droplets with a controlled and narrow size distribution.     

In situ growth of CoPt nanoparticles in porous germania nanospheres

Mesoporous nanospheres of germania were used as matrix to grow CoPt nanoparticles. The host germania nanospheres were prepared by biomineralization via the recognition of the peptide sequence T-G-H-Q-S-P-G-A-Y-A-A-H. The size of the cobalt/platinum nanoparticles embedded in germania is in the 8-9 nm range, as determined by TEM analysis. The porosity of the nanocomposites was confirmed by nitrogen isotherm analysis. MFM analysis confirmed the magnetic properties of the germania nanocomposites. This simple method of preparation of germania nanospheres via biomineralization, followed by growth of CoPt nanoparticles has an attractive potential for preparing new optomagnetic materials. Such nanocomposites for various device fabrications can be produced and potentially be used to target specific applications.     

In situ observation of electrode melting in multilayer ceramic capacitors

In the usage of multilayer ceramic capacitors, we are concerned with the intrinsic dielectric properties of the ceramic and its long-term stability/reliability under external stresses in service conditions. Of equal importance to long-term reliability is the short-term survivability under current (power)-surge conditions. It differs from the ability to withstand voltage surge, which is determined by the dielectric strength of the ceramic. In this paper, we present some observations on sectioned and polished multilayer ceramic capacitors, which were subjected to controlled current-surge test conditions. Capacitors from several vendors were examined. The samples were examinedin situ under an optical microscope while current pulses of varying magnitude were applied at a constant voltage. Subsequently some samples were further examined by scanning electron microscopy. The failure mechanism appeared to be the heat-induced local melting of internal electrodes, which might then lead to a blow-out or charring of the capacitor. In less severe cases, we observed local melting and crack formation in the surrounding ceramic as well. The primary change in capacitor properties was in the degradation of the insulation resistance. In severe cases, this also led to an increase in the dissipation factor.