OH absorption spectroscopy in a flame using spatial heterodyne spectroscopy

We demonstrate measurements of OH absorption spectra in the post-flame zone of a McKenna burner using spatial heterodyne spectroscopy (SHS). SHS permits high-resolution, high-throughput measurements. In this case the spectra span approximately 308-310 nm with a resolution of 0.03 nm, even though an extended source (extent of approximately 2x10(-7) m(2) rad(2)) was used. The high spectral resolution is important for interpreting spectra when multiple absorbers are present for inferring accurate gas temperatures from measured spectra and for monitoring weak absorbers. The present measurement paves the way for absorption spectroscopy by SHS in practical combustion devices, such as reciprocating and gas-turbine engines.     

Zeptogram-scale nanomechanical mass sensing

Very high frequency (VHF) nanoelectromechanical systems (NEMS) provide unprecedented sensitivity for inertial mass sensing. We demonstrate in situ measurements in real time with mass noise floor approximately 20 zg. Our best mass resolution corresponds to approximately 7 zg, equivalent to approximately 30 xenon atoms or the mass of an individual 4 kDa molecule. Detailed analysis of the ultimate sensitivity of such devices based on these experimental results indicates that NEMS can ultimately provide inertial mass sensing of individual intact, electrically neutral macromolecules with single-Dalton (1 amu) resolution.     

Realization of a multichannel integrated Young interferometer chemical sensor

We report on the design, realization, and characterization of a four-channel integrated optical Young interferometer device that enables simultaneous and independent monitoring of three binding processes. The generated interference pattern is recorded by a CCD camera and analyzed with a fast-Fourier-transform algorithm. We present a thorough theoretical analysis of such a device. The realized device is tested by monitoring glucose solutions that induce well defined phase changes between output channels. The simultaneous measurement of three different glucose concentrations shows the multipurpose feature of such devices. The observed errors, caused by the mismatching of spatial frequencies of individual interference patterns with those determined from the CCD camera, are reduced with different reduction schemes. The phase resolution for different pairs of channels was approximately 1 x 10(-4) fringes, which corresponds to a refractive-index resolution of approximately 8.5 x 10(-8). The measured sensitivity coefficient of the phase change versus refractive-index change of approximately 1.22 x 10(3) x 2pi agrees well with the calculated coefficient of approximately 1.20 x 10(3) x 2pi.     

Improved critical current density of MgB2--carbon nanotubes composite

In the present study, we report a systematic study of doping/admixing of carbon nanotubes (CNTs) in different concentrations in MgB2. The composite material corresponding to MgB2-x at.% CNTs (35 at.% > or = x > or = 0 at.%) have been prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/microstructural characterization employing XRD, Scanning electron microscopic (SEM), and Transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by Physical property measurement system (PPMS) and electrical transport measurements have been done by the four-probe technique. The microstructural investigations reveal the formation of MgB2-carbon nanotube composites. A CNT connecting the MgB2 grains may enhance critical current density due to its size (approximately 5-20 nm diameter) compatible with coherence length of MgB2 (approximately 5-6 nm) and ballistic transport current carrying capability along the tube axis. The transport critical current density (Jct) of MgB2 samples with varying CNTs concentration have been found to vary significantly e.g., Jct of the MgB2 sample with 10 at.% CNT addition is approximately 2.3 x 10(3) A/cm2 and its value for MgB2 sample without CNT addition is approximately 7.2 x 102 A/cm2 at 20 K. In order to study the flux pinning effect of CNTs doping/ admixing in MgB2, the evaluation of intragrain critical current density (JJ) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on Jc is obtained for 10 at.% CNTs admixed MgB2 sample at 5 K, the Jc reaches approximately 5.2 x 10(6) A/cm2 in self field, -1.6 x 10(6) A/cm2 at 1 T, approximately 2.9 x 10(5) A/cm2 at 2.6 T, and approximately 3.9 x 10(4) A/cm2 at 4 T. The high value of intragrain Jc in 10 at.% CNTs admixed MgB2 superconductor has been attributed to the incorporation of CNTs into the crystal matrix of MgB2, which are capable of providing effective flux pinning centres. A feasible correlation between microstructural features and superconducting properties has been put forward.     

Cavity ringdown spectroscopy of thin films in the mid-infrared

To demonstrate the potential of the cavity ringdown technique in mid-infrared spectroscopy of thin film samples, we measured absorption losses in a C60 film on a BaF2 substrate using a tunable optical parametric amplifier source. With a Brewster angle sample geometry, we achieved a fractional loss sensitivity as small as 1.3 x 10(-7) with 1.5 cm(-1) resolution, an improvement in sensitivity of 2 orders of magnitude compared to standard Fourier transform infrared methods. At an absorption sensitivity of 5 x 10(-7), spectra of several C60 overtone lines were recorded.     

High-performance transparent conducting oxide nanowires

We report the growth and characterization of single-crystalline Sn-doped In2O3 (ITO) and Mo-doped In2O3 (IMO) nanowires. Epitaxial growth of vertically aligned ITO nanowire arrays was achieved on ITO/yttria-stabilized zirconia (YSZ) substrates. Optical transmittance and electrical transport measurements show that these nanowires are high-performance transparent metallic conductors with transmittance of approximately 85% in the visible range, resistivities as low as 6.29 x 10(-5) Omega x cm and failure-current densities as high as 3.1 x 10(7) A/cm2. Such nanowires will be suitable in a wide range of applications including organic light-emitting devices, solar cells, and field emitters. In addition, we demonstrate the growth of branched nanowire structures in which semiconducting In2O3 nanowire arrays with variable densities were grown epitaxially on metallic ITO nanowire backbones.     

Ultrasensitive hot-electron nanobolometers for terahertz astrophysics

The submillimetre or terahertz region of the electromagnetic spectrum contains approximately half of the total luminosity of the Universe and 98% of all the photons emitted since the Big Bang. This radiation is strongly absorbed in the Earth's atmosphere, so space-based terahertz telescopes are crucial for exploring the evolution of the Universe. Thermal emission from the primary mirrors in these telescopes can be reduced below the level of the cosmic background by active cooling, which expands the range of faint objects that can be observed. However, it will also be necessary to develop bolometers-devices for measuring the energy of electromagnetic radiation-with sensitivities that are at least two orders of magnitude better than the present state of the art. To achieve this sensitivity without sacrificing operating speed, two conditions are required. First, the bolometer should be exceptionally well thermally isolated from the environment; second, its heat capacity should be sufficiently small. Here we demonstrate that these goals can be achieved by building a superconducting hot-electron nanobolometer. Its design eliminates the energy exchange between hot electrons and the leads by blocking electron outdiffusion and photon emission. The thermal conductance between hot electrons and the thermal bath, controlled by electron-phonon interactions, becomes very small at low temperatures ( approximately 1 x 10-16 W K-1 at 40 mK). These devices, with a heat capacity of approximately 1 x 10-19 J K-1, are sufficiently sensitive to detect single terahertz photons in submillimetre astronomy and other applications based on quantum calorimetry and photon counting.     

Human serum albumin adsorption study on 62-MHz miniaturized quartz gravimetric sensors

We have designed and fabricated 25-microm-thick quartz resonators operating at a fundamental resonance frequency of approximately 62 MHz. The results show a substantial increase in the mass sensitivity compared to single monolithic commercial resonators operating at lower frequencies in the approximately 5-10-MHz range. The overall performance of the micromachined resonators is demonstrated for the example of human serum albumin protein adsorption from aqueous buffer solutions onto gold electrodes functionalized with self-assembled monolayers. The results show a saturation adsorption frequency change of 6.8 kHz as opposed to 40 Hz for a commercial approximately 5-MHz sensor under identical loading conditions. From the analysis of the adsorption isotherm, the equilibrium adsorption constant of the adsorption of the protein layer was found to be K = 8.03 x 10(6) M(-1), which is in agreement with the values reported in the literature. The high sensitivity of the miniaturized QCM devices can be a significant advantage in both vapor and solution adsorption analyses.     

A Novel Method for Heat Capacity Measurements near 2K

We have constructed a calorimeter of novel design for high resolution heat capacity measurements near 2K. This device resembles high resolution paramagnetic salt thermometers used in previous heat capacity measurements on the ⁴ He-Vycor system. ² However, we have modified this thermometer so that our signal is no longer directly proportional to the temperature of the sample, but rather to the change in temperature with respect to time. We demonstrate the technique by measuring the heat capacity of paramagnetic gadolinium trichloride (GdCl ₃ ) salt near its critical temperature of 2.21K.     

Nanometer scale polarimetry studies using a near-field scanning optical microscope

We describe a new technique that incorporates polarization modulation into near-field scanning optical microscopy (NSOM) for nanometer scale polarimetry studies. By using this technique, we can quantitatively measure the optical anisotropy of materials with both the high sensitivity of dynamic polarimetry and the high spatial resolution of NSOM. The magnitude and relative orientation of linear birefringence or linear dichroism are obtained simultaneously. To demonstrate the sensitivity and resolution of the microscope, we map out stress-induced birefringence associated with submicrometer defects at the fusion boundaries of SrTiO3 bicrystals. Features as small as 150 nm were imaged with a retardance sensitivity of approximately 3 x 10(-3) rad.     

Use of phosphine as an n-type dopant source for vapor-liquid-solid growth of silicon nanowires

Phosphine (PH3) was investigated as an n-type dopant source for Au-catalyzed vapor-liquid-solid (VLS) growth of phosphorus-doped silicon nanowires (SiNWs). Transmission electron microscopy characterization revealed that the as-grown SiNWs were predominately single crystal even at high phosphorus concentrations. Four-point resistance and gate-dependent conductance measurements confirmed that electrically active phosphorus was incorporated into the SiNWs during VLS growth. A transition was observed from p-type conduction for nominally undoped SiNWs to n-type conduction upon the introduction of PH3 to the inlet gas. The resistivity of the n-type SiNWs decreased by approximately 3 orders of magnitude as the inlet PH3 to silane (SiH4) gas ratio was increased from 2 x 10(-5) to 2 x 10(-3). These results demonstrate that PH3 can be used to produce n-type SiNWs with properties that are suitable for electronic and optoelectronic device applications.     

Phase-matched third-harmonic generation in mercury-(I)-chloride

Using phase-matched third-harmonic generation we determine the effective nonlinear susceptibilities in Hg2Cl2 (Calomel) to /chi(3)eff,I/ = 4.5 x 10(-22) m2V(-2) and /chi(3)eff,II/ = 9.7 x 10(-22) m2V(-2) for type I and type II phase matching, respectively. The type III phase matching uses the same tensor components as type I and is deduced to be /chi(3)eff,III/ approximately equal to 1.5 x 10(-22) m2V(-2). The effective third-order susceptibilities of Hg2Cl2 are two orders of magnitude higher than those of CaCO3, and the tensor components chi11 - 3chi18 exceed the components of ADP by a factor of 5. These measurements demonstrate that Calomel might be a promising material to be used for nonlinear optical devices.     

Magnetic properties of magnetically soft nanocomposite Co-SiO2 prepared via mechanical milling

Nanocomposite of Co-SiO2, a soft magnetic material, with Co weight fraction x = 0.3 and 0.7 was prepared via mechanical milling. The magnetic properties of these samples, both zero-field-cooled (ZFC) and field-cooled (FC), have been measured as a function of x, milling time, and temperature. The structural assessment of the composite indicates a presence of only ferromagnetic (FM) hcp-Co phase in the composite. However, reported magnetic properties of these composites appear to be dependent on the presence of antiferromagnetic (AFM) phases of cobalt oxide as well. The observed enhancement in ZFC coercivity and a reduction in saturation magnetization with the milling time are due to an increase in defect density upon milling. The ZFC coercivity for the x = 0.3 samples has been found to be much higher than the x = 0.7 samples for all milling times. The coercivity above 50 K depends on temperature according to the law corresponding to isotropic uniaxial superparamagnetic particles. Below 50 K the presence of an AFM phase Co3O4 (TN approximately 33 K) and increased interparticle interactions bring in a departure from that law. The saturation magnetization is found to be temperature dependent for the x = 0.3 samples and temperature independent for the x = 0.7 samples, which further provides evidence of the presence of higher AFM phase fraction in the composite with a low metal volume fraction. The FC magnetic measurements show a presence of an exchange bias field and an enhanced coercivity which are higher than the ZFC measurements. All magnetic measurements indicate that the overall magnetic properties of the composite are dictated by the presence of a trace amount of cobalt oxides.     

Spray pattern and droplet size analyses for high-shear viscosity determination of aqueous suspension corticosteroid nasal sprays

Aqueous suspension corticosteroid nasal sprays exhibit the rheological property of shear thinning, meaning they exhibit a decrease in viscosity upon application of shear. Most rheological methods are limited in the amount of shear that can be applied to samples (approximately 1,000 s(-1)) and thus can only approximate the viscosities at the high-shear conditions of nasal spray devices (approximately 10(5)-10(6) s(-1)). In the current work, spray area and droplet size were shown to demonstrate viscosity dependence. Three Newtonian fluids were used to determine equations to approximate viscosity at the spray nozzle from correlations to spray area and droplet size using a standard 100 microL Pfeiffer nasal spray pump. Several shear-thinning solutions, including four commercial aqueous suspension corticosteroid nasal sprays and three aqueous Avicel (1, 2, and 3%, wt/wt) samples, were analyzed to demonstrate the ability of spray area and droplet size analysis to estimate high-shear viscosities. The calculated viscosity values trend in accordance with the rheometer data along with the ability to distinguish differences between all samples analyzed.     

Rapid prototyping of thermoset polyester microfluidic devices

This paper presents a simple procedure for the fabrication of thermoset polyester (TPE) microfluidic systems and discusses the properties of the final devices. TPE chips are fabricated in less than 3 h by casting TPE resin directly on a lithographically patterned (SU-8) silicon master. Thorough curing of the devices is obtained through the combined use of ultraviolet light and heat, as both an ultraviolet and a thermal initiator are employed in the resin mixture. Features on the order of micrometers and greater are routinely reproduced using the presented procedure, including complex designs and multilayer features. The surface of TPE was characterized using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Following oxygen plasma treatment, the hydrophilicity of the surface of TPE increases (determined by contact angle measurements) and the proportion of oxygen-containing functional groups also increases (determined by XPS), which indicates a correlated increase in the charge density on the surface. Native TPE microchannels support electroosmotic flow (EOF) toward the cathode, with an average electroosmotic mobility of 1.3 x 10(-4) cm(2) V(-1) s(-1) for a 50-microm square channel (20 mM borate at pH 9); following plasma treatment (5 min at 30 W and 0.3 mbar), EOF is enhanced by a factor of 2. This enhancement of the EOF from plasma treatment is stable for days, with no significant decrease noted during the 5-day period that we monitored. Using plasma-treated TPE microchannels, we demonstrate the separation of a mixture of fluorescein-tagged amino acids (glycine, glutamic acid, aspartic acid). TPE devices are up to 90% transparent (for approximately 2-mm-thick sample) to visible light (400-800 nm). The compatibility of TPE with a wide range of solvents was tested over a 24-h period, and the material performed well with acids, bases, alcohols, cyclohexane, n-heptane, and toluene but not with chlorinated solvents (dichloromethane, chloroform).     

Nanocrystallization of ferroelectric strontium bismuth vanadium niobate in lithium tetraborate glasses

Transparent glass samples in (100-3x) (Li2O-2B2O3)-x(SrO-Bi2O3-0.7Nb2O5-0.3V2O5) (10 < or = x < or = 60, in molar ratio) system have been fabricated via conventional melt-quenching technique. The as-quenched samples, of all the compositions under study have been confirmed to be amorphous, by X-ray powder diffraction (XRD) studies. Differential thermal analysis (DTA) was employed to confirm the glassy nature of the as-quenched glasses. Glass composites comprising vanadium doped strontium bismuth niobate nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. Perovskite SrBi2(Nb0.7VO3)2O9-delta phase formation was found to be preceded by an intermediate fluorite phase which was established via XRD and transmission electron microscopy (TEM). The dielectric constants (epsilonr) of the as-quenched glasses as well as the glass nanocrystal composites decreased with increase in frequency (100 Hz-10 kHz) at 300 K. Interestingly, the dielectric constant of the glass nanocrystal composite (heat-treated at 783 K/6 h) undergoes a maximum in the vicinity of the crystallization temperature of the host glass (Li2B4O7) reaching an anomalously high value (approximately 10(6)) at 800 K. Different dielectric mixture formulae were employed to rationalize the dielectric properties of the glass nanocrystal composite. The optical transmission properties of these glass nanocrystal composites were found to have strong compositional dependence.     

In situ combustion measurements of CO with diode-laser absorption near 2.3 microm

In situ measurements of CO concentration were recorded with tunable diode-laser absorption spectroscopy techniques in both the exhaust and the immediate post-flame regions of an atmospheric-pressure flat-flame burner operating on ethylene air. Two room-temperature cw single-mode InGaAsSb/AlGaAsSb diode lasers operating near 2.3 microm were tuned over individual transitions in the CO first overtone band (v' = 2 <-- v" = 0) to record high-resolution absorption line shapes in the exhaust duct [79 cm above the burner, approximately 470 K; R(15) transition at 4311.96 cm(-1)] and the immediate postflame zone [1.5 cm above the burner, 1820-1975 K; R(30) transition at 4343.81 cm(-1)]. The CO concentration was determined from the measured absorption and the gas temperature, which was monitored with type-S thermocouples. For measurements in the exhaust duct, the noise-equivalent absorbance was approximately 3 x 10(-5) (50-kHz detection bandwidth, 50-sweep average, 0.1-s total measurement time), which corresponds to a CO detection limit of 1.5 ppm m at 470 K. Wavelength modulation spectroscopy techniques were used to improve the detection limit in the exhaust to approximately 0.1 ppm m (approximately 500-Hz detection bandwidth, 20-sweep average, 0.4-s total measurement time). For measurements in the immediate postflame zone, the measured CO concentrations in the fuel-rich flames were in good agreement with chemical equilibrium predictions. These experiments demonstrate the utility of diode-laser absorption sensors operating near 2.3 microm for in situ combustion emission monitoring and combustion diagnostics.     

Heat Capacity and Thermodynamic Properties of Poly(chlorotrifluoroethylene) from 2.5 to 620 K

Heat capacities and thermodynamic properties of a number of poly(chlorotrifluoToethylene) samples subjected to various thermal treatments, to achieve crystallinities ranging from approximately 10 to 90%, have been studied from 2.5 to 370 K by automated adiabatic calorimetiy and from 250 to 620 K by differential scanning calorimetry. Small heat capacity discontinuities in the temperature range from 320 to 350 K were observed in all samples with crystallinities greater than 40%. Spontaneous adiabatic temperature drifts associated with these anomalies were prasitive (exothermic) for quenched samples and negative (endothermic) for annealed samples. Therefore these anomalies were believed to be associated with a relaxation phenomenon similar to that of a glass transition. For highly quenched low crystallinity films, a much larger heat capacity discontinuity of greater than 15% was observed, amidst a crystallization exotherm. In addition to the above phenomena, annealing of the sample at any temperature between 240 to 400 K would produce a shift in the population distribution of crystallites from reorganization or melting and recrystallization. As a result, the apparent heat capacity became somewhat lowered at the annealing temperature and somewhat raised at about 20 K above the annealing temperature.     

Microspotting streptavidin and double-stranded DNA arrays on gold for high-throughput studies of protein-DNA interactions by surface plasmon resonance microscopy

We present two strategies for microspotting 10 x 12 arrays of double-stranded DNAs (dsDNAs) onto a gold-coated glass slide for high-throughput studies of protein-DNA interactions by surface plasmon resonance (SPR) microscopy. Both methods use streptavidin (SA) as a linker layer between a biotin-containing mixed self-assembled monolayer (SAM) and biotinylated dsDNAs to produce arrays with high packing density. The primary mixed SAM is produced from biotin- and oligo(ethylene glycol)-terminated thiols bonded as thiolates onto the gold surface. In the first method, a robotic microspotter is used to deliver nanoliter droplets of dsDNA solution onto a uniform layer of this SA ( approximately 2 x 10(12) SA/cm(2)). SPR microscopy shows a density of (5-6) x 10(11) dsDNA/cm(2) (0.2-0.3 dsDNA/SA) in the array elements. The second method uses instead a microspotted array of this SA linker layer, onto which the microspots of dsDNA are added with spatial registry. SPR microscopy before addition of the dsDNA shows a SA coverage of 2 x 10(12) SA/cm(2) within the spots and a dsDNA density of 8.5 +/- 3.5 x 10(11) dsDNA/cm(2) (0.3-0.7 dsDNA/SA, depending on the length of dsDNA) after dsDNA spotting. We demonstrate the ability to simultaneously monitor protein binding with the SPR microscope in many 200-microm spots with 1-s time resolution and sensitivity to <1 pg of protein.     

The microwave characterization of single crystal lithium and calcium fluoride at cryogenic temperatures

The whispering-gallery mode method is used for very accurate permittivity and dielectric loss measurements of single crystal lithium fluoride (LiF) and calcium fluoride (CaF2) over the temperature range of 4.5 K to 300 K. The absolute uncertainty in the real part of permittivity was estimated to be less than 0.1%, and it was limited principally by uncertainty in dimensions of the samples. Dielectric losses were measured with uncertainties of about 10% limited by the accuracy of Q-factor measurements. The measured materials exhibited dielectric losses between 2-4 x 10(-7) near 5 K. The relative permittivity was evaluated as 6.502 (4.9 K) to 6.844 (296 K) at 17.5 GHz for CaF2 and 8.534 (4.6 K) to 9.063 (300 K) at 13.5 GHz for LiF.