Synthesis and magnetic properties of the size-controlled Mn-Zn ferrite nanoparticles by oxidation method

Size-controlled Mn_0.67Zn_0.33Fe₂O₄ nanoparticles in the wide range from 80 to 20 nm have been synthesized, for the first time, using the oxidation method. It has been demonstrated that the particle size can be tailor-made by varying the concentration of the oxidant. The magnetization of the 80 nm particles was 49 A m² kg⁻¹ compared to 34 A m² kg⁻¹ for the 20 nm particles. The Curie temperatures for all the samples are found to be within 630±5 K suggesting that there is no size-dependent cation distribution. The critical particle size for the superparamagnetic limit is found to be about 25 nm. The effective magnetic anisotropy constant is experimentally determined to be 7.78 kJ m⁻³ for the 25 nm particles, which is about an order of magnitude higher than that of the bulk ferrite.     

A study on the biological detection chip through the use of PDMS lens for the reinforcement of fluorescence receiving signal

In this study, MEMS process technology is adopted to produce microfluidic chip and PDMS lens. SU-8 thick film photo resist is coated onto silicon wafer surface in two times of spin coating, then through lithography and mold transfer technology, PDMS chip of minimal line width 100 μm and thickness 200 μm is printed. In fluorescence detection aspect, we use objective lens to couple laser optical source to optical fiber, and then have it incident to excite fluorescence sample, the excited fluorescence then passes through filter and detected by optical detector of experiment group and spectrophotometer of reference group. From the experiment result, the Hex fluorescence detection limit of the system is verified to be 1 pmol/5 μl. In addition, we have integrated PDMS lens into microfluidic chip to make generalized detection experiment, it was found that the signal measured by optical embedded type is higher than that of non-embedded type. Meanwhile, the microfluidic chip with double concave lens (135°) and10 mm PDMS focusing lens can be utilized to obtain optimal fluorescence receiving effect. The fluorescence intensity is raised by 2–3 times, and the measurement limit is lowered to 100 fmol/5 μl.     

Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts

Pt, Ru and Pt/Ru nano-particles, synthesized in ethylene glycol solutions, are studied using infrared (IR) spectroscopy and high resolution transmission electron microscopy (HRTEM). The synthesis method allows the control of the mono- and bi-metallic catalyst particle sizes between 1 and 5.5 nm. The IR spectra of CO adsorbed (CO_ads) on the Pt, Ru and bi-metallic Pt/Ru colloids are recorded as a function of the particle size. The stretching frequency of CO_ads depends on the particle size and composition. Strong IR bands due to the stretching vibration of CO_ads are observed between 2010 and 2050 cm⁻¹ for the Pt nano-particles, while two IR bands between 2030 and 2060 cm⁻¹ for linear bonded CO_ads, and at lower wavenumbers between 1950 and 1980 cm⁻¹ for bridged bonded CO_ads, are found for the Ru particles. The IR spectra for the Pt/Ru nano-sized catalyst particles show complex behaviour. For the larger particles (>2 ± 0.5 nm), two IR bands representative of CO_ads on Ru and Pt-Ru alloy phases, are observed in the range of 1970-2050 cm⁻¹. A decrease in the particle size results in the appearance of a third band at ∼2020 cm⁻¹, indicative of CO_ads on Pt. The relative intensity of the band for CO_ads on the Pt-Ru alloy vs. the Pt phase decreases with decreasing particle size. These results suggest that Ru is partially dissolved in the Pt lattice for the larger Pt/Ru nano-particles and that a separate Ru phase is also present. A Pt-Ru alloy and Ru phase is observed for all Pt/Ru particles prepared in this work. However, a decrease in particle size results in a decrease of the number of Pt and Ru atoms in the Pt-Ru alloy phase, as they are increasingly present as single Pt and Ru phases.     

Fabrication of Al nanoparticles and their electrical properties studied by capacitance-voltage measurements

Nanometer-scale Al particles are fabricated and are embedded in a GaAs matrix using molecular beam epitaxial technique. The Al particle is self-assembled on GaAs by supplying an Al molecular beam. The average particle size is found to be 25 nm. The density is 7 × 10¹⁰ cm⁻² when Al of 6.2 × 10¹⁵ atoms/cm² is supplied on (1 0 0)GaAs at a substrate temperature of 300 °C. Clear hysteresis and plateaus in capacitance-voltage (C-V) curves are found in an Al-embedded sample, whereas monotonic increase of capacitance is obtained in a reference sample having an AlAs layer instead of Al. This difference results from trapping of electrons by the Al particles, suggesting that the particles have metallic character.     

Characterization of nanoparticles of organic carbon (NOC) produced in rich premixed flames by differential mobility analysis

Differential mobility analysis (DMA) is used to measure on-line the size distributions of inception particles in atmospheric pressure premixed ethylene air flames ranging from C/O = 0.61 to 0.69, just at the onset of soot formation. DMA is also used, in combination with electrospray, to measure the size distributions of suspended flame products captured in water samples. The DMA systems used for this work employ detectors sensitive to the full range of molecular clusters/nanoparticles in gas-to-particle conversion processes (as small as about 1 nm) and they have much larger sheath gas flow rates than is typically used to reduce losses and peak broadening by diffusion. The measured size distributions show that the first particles observed in flames have a size of 2 nm, consistent with previous in situ measurements by light scattering and extinction (LSE) and the off-line measurements of material captured in water samples from the same flames. For richer flames, the quantity of the 2 nm particles measured increases, and the width of its size distribution shifts asymmetrically toward larger sizes. A numerical coagulation model assuming size-dependent coagulation efficiency predicts well the experimentally measured size distributions in the flames examined. Similarly, the slightly larger size distributions measured by atomic force microscopy of inception particles deposited on surfaces can also be attributed to the size-dependent coagulation/adhesion efficiency. The results imply that the smaller nanoparticles formed in combustion processes have a longer lifetime than those larger than 6-7 nm and may play an important role in the formation of fine organic carbon particulate in the atmosphere.     

Size-dependant heating rates of iron oxide nanoparticles for magnetic fluid hyperthermia

Using the thermal decomposition of organometallics method we have synthesized high-quality, iron oxide nanoparticles of tailorable size up to ∼15 nm and transferred them to a water phase by coating with a biocompatible polymer. The magnetic behavior of these particles was measured and fit to a log-normal distribution using the Chantrell method and their polydispersity was confirmed to be very narrow. By performing calorimetry measurements with these monodisperse particles we have unambiguously demonstrated, for the first time, that at a given frequency, heating rates of superparamagnetic particles are dependent on particle size, in agreement with earlier theoretical predictions.     

Assessment of the consistency of H2O line intensities over the near-infrared using sun-pointing ground-based Fourier transform spectroscopy

We report on the consistency of water vapour line intensities in selected spectral regions between 800-12,000 cm⁻¹ under atmospheric conditions using sun-pointing Fourier transform infrared spectroscopy. Measurements were made across a number of days at both a low and high altitude field site, sampling a relatively moist and relatively dry atmosphere. Our data suggests that across most of the 800-12,000 cm⁻¹ spectral region water vapour line intensities in recent spectral line databases are generally consistent with what was observed. However, we find that HITRAN-2008 water vapour line intensities are systematically lower by up to 20% in the 8000-9200 cm⁻¹ spectral interval relative to other spectral regions. This discrepancy is essentially removed when two new linelists (UCL08, a compilation of linelists and ab-initio calculations, and one based on recent laboratory measurements by Oudot et al. (2010) [10] in the 8000-9200 cm⁻¹ spectral region) are used. This strongly suggests that the H₂O line strengths in the HITRAN-2008 database are indeed underestimated in this spectral region and in need of revision. The calculated global-mean clear-sky absorption of solar radiation is increased by about 0.3 W m⁻² when using either the UCL08 or Oudot line parameters in the 8000-9200 cm⁻¹ region, instead of HITRAN-2008. We also found that the effect of isotopic fractionation of HDO is evident in the 2500-2900 cm⁻¹ region in the observations.     

Evolution of surface morphology of NiO thin films under swift heavy ion irradiation

NiO nanoparticle thin films grown on Si substrates were irradiated by 107 MeV Ag⁸⁺ ions. The films were characterized by glancing angle X-ray diffraction and atomic force microscopy. Ag ion irradiation was found to influence the shape and size of the nanoparticles. The pristine NiO film consisted of uniform size (∼100 nm along major axis and ∼55 nm along minor axis) elliptical particles, which changed to also of uniform size (∼63 nm) circular shape particles on irradiation at a fluence of 3 × 10¹³ ions cm⁻². Comparison of XRD line width analysis and AFM data revealed that the particles in the pristine films are single crystalline, which turn to polycrystalline on irradiation with 107 MeV Ag ions.     

ZnO nanoparticles produced by novel reactive physical deposition process

This paper reports the deposition of ZnO nanoparticles with controlled sizes and different particle densities and their structural, composition and optical properties. They were deposited by means of a DC magnetron based vacuum nanoparticle source onto different substrates (GaAs, Si and Ti/SiO₂/Si). We believe that this is the first time that such nanoparticles have been produced using this unique technique. Zinc was used as sputtering target to produce zinc nanoparticles which were oxidized in-line using molecular oxygen. The structural properties and chemistry of the ZnO were studied by transmission electron microscopy. An average particle size of 6(±2) nm was produced with uniform size distribution. The particle density was controlled using a quartz crystal monitor. Surface densities of 2.3 × 10¹¹/cm², 1.1 × 10¹³/cm² and 3.9 × 10¹³/cm² were measured for three different deposition runs. The ZnO particles were found to be single crystalline having hexagonal structure. Photoluminescence measurements of all samples were performed at room temperature using a cw He-Cd laser at 325 nm excitation. The UV emission around 375 nm at room temperature is due to excitonic recombination and the broad emission centered at 520 nm may be attributed to intrinsic point defects such as oxygen interstitials.     

In situ oxidation study of MgO(1 0 0) supported Pd nanoparticles

We have investigated the oxidation behavior of Pd nanoparticles grown epitaxially on MgO(1 0 0) single crystal substrates. We find that the interaction of oxygen with octahedral Pd nanoparticles at 500 K can be subdivided in three stages: above 10⁻⁶ mbar O₂ pressure, the particles start to flatten; above 10⁻³ mbar, the particles begin to shrink laterally and to be less truncated at the corners. The formation of epitaxial bulk PdO sets in at oxygen pressures above 0.1 mbar, which is accompanied by a continuous shrinkage of the Pd particles. Our results point to a novel nanoparticle oxidation mechanism: the Pd particles act as dissociation centers for O₂ and serve at the same time as source for Pd atoms resulting in epitaxial PdO growth on MgO(1 0 0).     

Sonosynthesis of nanobiotics with antimicrobial and antioxidant properties

Transforming small-molecule antibiotics into carrier-free nanoantibiotics represents an opportunity for developing new multifunctional therapeutic agents. In this study, we demonstrate that acoustic cavitation produced by high-frequency ultrasound transforms the antibiotic doxycycline into carrier-free nanobiotics. Upon sonication for 1 h at 10–15 W cm⁻³, doxycycline molecules underwent hydroxylation and dimerization processes to ultimately self-assemble into nanoparticles of ∼100–200 nm in size. Micrometer sized particles can be also obtained by increasing the acoustic power to 20 W cm⁻³. The nanodrugs exhibited antioxidant properties, along with antimicrobial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial strains. Our results highlight the feasibility of the ultrasound-based approach for engineering drug molecules into a nanosized formulation with controlled and multiple bio-functionalities.     

Deposition and electrostatic removal of gaseous organic contaminants on substrate surfaces

The adhesion behavior of di-n-butyl phthalate (DBP) onto different substrates (quartz, glass, and silicon) used as wafer surfaces was studied by using an in situ UV spectrophotometric technique. The results from the closed cell experiments revealed that greatest extent of DBP adhesion occurred on the quartz chip (0.154 μg cm⁻²), followed in the order by the glass (0.054 μg cm⁻²) and silicon (0.039 μg cm⁻²). By means of the in situ spectrophotometric observation, application of an electrical field at 290 V cm⁻¹ in the cell proved to be effective in inducing charging of DBP aerosols, which were consequently attracted towards the electrodes. This method can be applied to wafer storage and transport equipments to prevent wafer contamination from material outgassing representative by DBP.     

Surface roughness analysis and improvement of PMMA-based microfluidic chip chambers by CO2 laser cutting

For the microfluidic chip, the surface roughness of the chamber sidewall is an important parameter in estimating its quality. In this work, the chambers of the polymethyl methacrylate (PMMA)-based microfluidic chip were fabricated by CO₂ laser cutting, and then the surface roughness of the sections cut using different laser parameters and ambient temperature was studied by a non-contact 3D surface profiler. Our observation shows that the surface roughness results primarily from the residues on the laser-cut edge, which are produced by the bubbles bursting. To reduce the surface roughness of the cut section, a new approach is proposed, that is preheating the PMMA sheet to a suitable ambient temperature during laser processing. The results indicate that at a preheat temperature of 70-90 °C, the surface roughness resulting from the cut would be reduced. In our experiment, the best result was that the arithmetical mean roughness is R_a = 100.86 nm when the PMMA sheet was heated to 85 °C.     

On-chip free-flow magnetophoresis: Separation and detection of mixtures of magnetic particles in continuous flow

The complete separation of mixtures of magnetic particles was achieved by on-chip free-flow magnetophoresis. In continuous flow, magnetic particles were deflected from the direction of laminar flow by a perpendicular magnetic field depending on their magnetic susceptibility and size and on the flow rate. 2.8 and 4.5 μm superparamagnetic particles with magnetic susceptibilities of 1.1×10⁻⁴ and 1.6×10⁻⁴ m³ kg⁻¹, respectively, could be completely separated from each other reproducibly. The separated particles were detected by video observation and also by on-chip laser light scattering. Potential applications of this separation method include sorting of magnetic micro- and nanoparticles as well as magnetically labelled cells.     

Electroless Nickel Plating under Continuous Ultrasonic Irradiation to Fabricate a Near-Field Probe Whose Metal Coat Decreases in Thickness toward the Tip

This paper describes a size-dependent electroless plating method to fabricate a new type of probe with a locally decreasing thickness of metal and a tiny tip size for a combined high resolution shear-force and near-field optical microscope. In this method, the tip size and decreasing thickness profile, which affect the resolution capabilities of the microscopes, are controlled by adding a continuous ultrasonic wave with a frequency of 1 MHz to a nickel plating bath. The probe with a tip radius of curvature of 25 nm was successfully fabricated at an ultrasonic power density of 1.6 W cm⁻², its metal thickness gradually decreased from 850 to 20 nm toward the distal tip.     

Optimization of spin-valve parameters for magnetic bead trapping and manipulation

Magneto-optic Kerr effect (MOKE) and magnetoresistance (MR) measurements were used to measure the switching characteristics of spin-valve (SV) arrays currently being developed to trap and release superparamagnetic beads within a fluid medium. The effect of SV size on switching observed by MOKE showed that a 1 μm×8 μm SV element was found to have optimal switching characteristics. MR measurements on a single 1 μm×8 μm SV switched with either an external applied magnetic field or a local magnetic field generated by an integrated write wire (current density ranging from 10⁶ to 10⁷ A/cm²) confirmed the MOKE findings. The 1 μm×8 μm SV low field switching was observed to be +8 and −2 mT with two stable states at zero field; the high field switching was observed to be −18 mT. The low switching fields and the large magnetic moment of the SV trap along with our observation of minimal magnetostatic effects for dense arrays are necessary design characteristics for high-force, “switchable-magnet,” microfluidic bead trap applications.     

Valence band and core level X-ray photoelectron spectroscopy of lead sulfide nanoparticle-polymer composites

Valence band and core level X-ray photoelectron spectroscopy (XPS) were used to probe lead sulfide (PbS) nanoparticle-polymer nanocomposites. Composite materials were prepared by trapping commercially available monodisperse 3 and 10 nm PbS nanoparticles in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (referred to below as MEH-PPV). The nanocomposites prepared from commercial nanoparticles underwent oxidation, mainly to form lead sulfate. However, the narrow size distributions of the commercial nanoparticles allowed observation of distinct changes in the valence band from the 3 to 10 nm nanoparticles. Nanocomposites of 2-5 and 4-7 nm PbS nanoparticles were synthesized by growing the particles in poly(vinyl alcohol) (referred to below as PVA) and MEH-PPV, respectively. These composites both indicated the formation of lead sulfide nanoparticles. Furthermore, the XP spectra for the PVA/PbS composite displayed bonding between the PbS nanoparticles and the polymer while MEH-PPV showed no PbS-polymer bonding. The nanoparticles synthesized in MEH-PPV did not undergo oxidation. The particle size distributions of the synthesized nanoparticles were too broad to display size-dependent changes in the valence band.     

Order-disorder transformation in FePt nanoparticles studied by ferromagnetic resonance

We have investigated the ferromagnetic resonance (FMR) response of as-made and temperature annealed FePt magnetic nanoparticles. The as-made nanoparticles, which have been fabricated by a chemical route, crystallize in the low magnetic anisotropy fcc phase and have a diameter in the range of 2-4 nm. The annealing of the particles at high temperatures (T_A=550, 650 and C) in an inert Ar atmosphere produces a partial transformation to the high magnetocrystalline anisotropy L1₀ phase, with a significant increase in particle size and size distribution. FMR measurements at X-band (9.5 GHz) and Q-band (34 GHz) show a single relatively narrow line for the as-synthesized particles and a structure of two superimposed lines for the three annealed samples. The origin of this line shape has been attributed to the presence of the disordered fcc phase. Assuming that the system consists of a collection of identical particles with a random distribution of easy axes, we have been able to estimate a mean value for the magnetic anisotropy constant of the particles in the fcc phase, K∼2×10⁶ erg/cm³. The measured line shape in the annealed samples can be explained if we consider that the magnetic anisotropy of the particles has a gaussian distribution with a relatively broad width.     

Fabrication and electromagnetic performance of micro-tubular nanocomposites composed of monodisperse iron nanoparticles and carbon

Low density and thin thickness are essential for electromagnetic (EM) wave absorbers. In this study, we fabricated a novel micro-tubular iron nanocomposite (MTIC) that composed of carbon microtubes and monodisperse iron nanoparticles (NPs). The bulk density of MTIC is only 0.35±0.04 g cm⁻³ due to its micro-tubular structure. The presence of iron NPs increased the magnetic loss significantly and therefore enhanced the reflection loss (RL) of MTIC/paraffin composite. The optimum thickness for the composite is 1.5-1.8 mm, with maximum bandwidth of 7.6 GHz for RL<−5 dB and 3.6 GHz for RL<−10 dB. The corresponding frequency at this thickness is 10-18 GHz. Because of low density and broad bandwidth at thin thickness, MTIC is a promising light-weight absorber for EM wave absorption or microwave shielding. This study will also provide new ideas for fabricating microwave absorbers with low density and thin thickness.     

Diffusion of ions in supercritical water: Dependence on ion size and solvent density and roles of voids and necks

We have performed molecular dynamics simulations of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and halide (F⁻, Cl⁻, Br⁻, I⁻) ions in supercritical water at 673 K. The calculations were done for water at three different densities of 1.0, 0.7 and 0.35 g cm⁻³ to investigate the effects of solute size on the diffusion of ions in supercritical water. On increase of ion size, we observe a maximum for diffusion of ions in supercritical water of higher densities (1.0 and 0.7 g cm⁻³). However, no such maximum is found for ion diffusion in the supercritical water of low density (0.35 g cm⁻³) or for diffusion of neutral solutes at all densities. These results are analyzed in terms of passage through voids and necks present in supercritical water. Correlations of the observed diffusion behavior with the sizes of ions and voids present in the systems are discussed.