Session Y1: Measurement Science from Optics through Thermodynamics

Robustness of holographic particle tracking and characterization against defects in illumination

Images obtained with holographic video microscopy can be interpreted with predictions of the Lorenz-Mie theory of light scattering to track individual colloidal particle's motions with nanometer resolution in three dimensions over ranges extending to hundreds of micrometers, to measure their radii with nanometer resolution, and to characterize their complex refractive indexes with part-per-thousand precision. In this work we numerically and experimentally investigate how defects in the illumination system, such as divergence and tilt of the illuminating laser beam, and spherical aberrations in the optical train affect the measured properties of the particles. We show that for the usual conditions where the experiments are performed divergence and tilt of the laser beam do not affect the measured parameters significantly, while spherical aberration can introduce significant errors.   

Quantification of metallic nanoparticle morphology with tilt series imaging by transmission electron microscopy

We report on the quantitative analysis of electrolessly deposited Au and Ag nanoparticles (NPs) on SU8 polymer with the help of High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) in tilt series. Au NPs act as nucleating agents for the electroless deposition of silver. Au NPs were prepared by attachingAu$^{3+}$cations to amine functionalized SU8 polymeric surfaces and then reducing it with aqueous NaBH$_{4}$. The nanoscale morphology of the deposited NPs on the surface of polymer has been studied from the dark field TEM cross sectional images. Ag NPs were deposited on the cross-linked polymeric surface from a silver citrate solution reduced by hydroquinone. HAADF-STEM enables us to determine the distances between the NPs and their exact locations at and near the surface. The particle distribution, sizes and densities provide us with the data necessary to control the parameters for the development of the electroless deposition technique for emerging nanoscale technologies.   

Novel Imaging and Nano Fabrication with a Focused Beam of Helium Ions

A newly introduced commercial instrument can produce a focused beam of helium ions with a focused probe size of 0.35 nm, and an energy range from 5 to 35 keV. While using only small beam currents (0.1 to 10 pA), it provides a means of generating images with high lateral resolution and surface specific information. The imaging is based up the generation of detectable particles (such as secondary electrons) as the beam interacts with the sample. Although similar to the scanning electron microscope, this instrument offers several unique imaging advantages. In addition to imaging, the focused helium beam has also been used for fabrication at the nanometer scale. Recent result have shown that this beam can be very effective for sputtering away materials to produce fine patterns for applications in biosensors, graphene, and plasmonic devices. The helium beam has also been used for lithographic purposes, producing 7 nm features with no apparent proximity effects. In another application, when the beam interacts with adsorbed molecules, the molecules are fixed -- permitting the fabrication of three dimensional nano-structures. A review of the recent work, and future plans will be presented.   

Neutral Atom Microscopy: A New Surface Imaging Probe

Recent advances have made microscopy using scanned neutral atom beams a practical reality. This technique is also called Atomic DeBroglie Microscopy, Neutral Beam Microscopy, and Scanning Helium Microscopy. Using thermal energy (under 70 meV) gas particles with neutral charge results in a probe beam that scatters from the first atomic layer of samples, with little chance of beam damage. The technique presented eliminates any need to focus the beam by using an aperture in close proximity to the sample, and has produced the first published images from gas scattering. Resolution has reached 0.6 $\mu $m and much higher resolution is possible$^{1}$. Now that NAM is a reality, a great deal of research can be done to show what it is uniquely useful for, and to explain the image contrast mechanisms. Molecular beam experiments show a wide range of surface properties that may be possible to image with such a microscope, some that are difficult to see otherwise. For example, thermal helium has a strong scattering interaction with surface hydrogens. Imaging un-coated surfaces with high electric fields is possible and imaging through high magnetic fields has been demonstrated. Recent image results and the basic instrument design will be presented. $^{1 }$A simple approach to neutral atom microscopy, Rev. Sci. Instrum. 82, 103705 (2011)   

Imaging the solar cell p-n junction and depletion region using secondary electron contrast

We report on secondary electron (SE) images of cross-sectioned multicrystalline Si and GaAs/GaInP solar cell devices, focusing on quantifying the relationship between the apparent n$^{+}$-p contrast and characteristic electronic features of the device. These samples allow us to compare the SE signal from devices which have very different physical characteristics: differing materials, diffused junction versus abrupt junction, heterojunction versus homojunction. Despite these differences, we find that the SE image contrast for both types of sample, and as a function of reverse bias across the diode, closely agrees with PC1D simulations of the bulk electrostatic potential in the device, accurately yielding the depletion edge and width. A spatial derivative of the SE data shows a local maximum at the metallurgical junction. Such data are valuable, for example, in studying the conformity of a diffused junction to the textured surface topography. These data also extend our understanding of the origin of the SE contrast.   

Resonant excitation of Rayleigh waves in a narrow fluid channel clad between two metal plates

We study extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two unidentical metal plates with Brass plate on one side of the channel and Aluminium plate on the other. The extraordinary absorption is observed at discrete resonant frequencies. From the elastic properties of the metal plates we derive a dispersion equation for coupled Rayleigh waves. Two different types of resonances, corresponding to different polarizations of the coupled waves, are studied for different channel widths and are experimentally confirmed. We also present the experimental confirmation of coupling through measurements of change in transmission minima with channel aperture. Experimental, theoretical, and numerical results are in a good agreement.   

Probing Heat Transfer in the Nanoscale Using Optomechanical Sensors.

The transition from heat conduction to radiation at extremely small gaps cannot be captured by current theories. Experimentally researchers are only slowly starting to learn how to approach this domain. To this end, the development of a measurement platform based on the picowatt sensitivity of optomechanical sensors will be presented. The bending of a custom designed bimorph cantilever accurately allows the absolute amount of transferred heat to be extracted and temperature to be determined based on the response from thermal inputs. The versatility of the platform permits thermal radiation and conduction measurements, as well as the characterization of material thermal conductivities and absorptivities in nearly identical configurations. Results of this measurement platform for fundamental heat transfer measurements will considerably improve the current understanding of nanoscale energy transport and conversion, as well as lead to advanced design guidelines for energy capture and conversion devices, in particular thermophotovoltaic cells, (solar) thermoelectric generators and waste heat recovery heat exchangers.   

Heat Capacity Measurements by Simultaneous Relaxation and AC-Calorimetry

A high-resolution method for measuring the heat capacity $C_p$ using simultaneously AC and Relaxation Calorimetry techniques has been developed. This technique is useful for both first and second-order phase transitions of liquids and complex fluids. The difference of the $C_p$'s measured by the Relaxation and AC calorimetry is a direct measurement of a phase transitions' latent heat. As a test, the $C_p$ of two cyanobiphenyl liquid crystals, 5CB and 8CB, were measured using a square wave modulation pulse train over a base temperature range from $300$ to $320$~K in which 5CB exhibits a first-order phase transition and 8CB exhibits a first and second-order phase transition. Fourier transform analysis allows for the direct $C_p$ measurement at the fundamental frequency of the square wave pulse train (as well as higher frequency orders) as function of temperature (i.e., AC-mode). The heating and cooling relaxations at the beginning and end of the square pulse heating allows for a relaxation analysis of $C_p$ by applying the dual slope-method that includes all enthalpic conversions.   

The State of the Unit: A documentary film about the kilogram

The definition of the SI unit of mass is based on the international prototype of the kilogram, created in 1879 [1]. In the next years, metrologists will redefine the kilogram in relation to fundamental physical constants [2]. Intended for a general audience, the forthcoming documentary, \textit{The State of the Unit: The Kilogram}, presents the history of the kilogram, interviews with researchers at national metrology institutes in the U.S., France, and Germany, and everyday mass measurement activities at varying scales. Excerpts of the film will be shown, and followed by a discussion with the filmmaker about the project to date. This film is supported in part by the Materials Computation Center at the University of Illinois at Urbana-Champaign, the California Institute of the Arts, Valencia, California, and La F\'{e}mis, Paris, France.\\[4pt] [1] The Kilogram and Measurements of Mass and Force, Z. J. Jabbour and S. L. Yaniv. J. Res. Natl. Inst. Stand. Technol. 106, 25--46 (2001).\\[0pt] [2] Redefining the SI Base Units, Peter Mohr. National Institute of Standards and Technology website. November 1, 2011. http://www.nist.gov/pml/newsletter/siredef.cfm. Accessed November 3, 2011.   

Wall friction measurement in the absence of mean shear

The dimensionless frictional force $f$ between a pipe wall and a flowing turbulent fluid is $f=\nu \overline {s} /U^2$, where $U$ is mean flow speed in the $x$-direction, $\nu$ is kinematic viscosity, and $\overline s=\frac{\partial u }{\partial y }$, where the $y$ axis is perpendicular to the flow direction. The derivative is evaluated at the wall, $y$ = 0. Described here a scheme for measuring $f$ in a turbulent fluid where $\overline{s}$ is close to zero. Hence the source of frictional dissipation is from $fluctuations$ in the shear about its mean, namely $\overline {s^2}$. This type of shear is encountered in turbulence in a closed container such as a food mixer. The scheme, which involves photon correlation spectroscopy, averages the shear rate over a laser spot size $w$ $\simeq$ 100 $\mu$m or smaller. The scheme yields the probability density function (PDF) of components of the shear rate tensor and the moments of of the PDF. The theory will be described briefly and measurements will be presented where $\overline{s} \simeq$ 0. In that limit $f$ is redefined to be $f =u' \overline{s_{ij}}/\nu$, where $\overline{s_{ij}}$ is the dominant component being measured, and $u'$ is the rms fluctuations of the velocity.   

Mid-Infrared Photothermal Response in a Liquid Crystal Using a Quantum Cascade Laser

We report on a new technique to measure the mid-infrared photothermal response induced by a tunable Quantum Cascade Laser (QCL) in the neat liquid crystal 4-Octyl-4'-Cyanobiphenyl (8CB), without using any intercalated dye. The modulated pump QCL range spanned a weak combination absorption band centered at $1912 cm^{-1}$. The thermally induced modulation of a Ti:Sapphire probe laser operating at 800 nm was measured by lockin detection. Heterodyne measurement of the response in the solid, smectic, nematic(N) and isotropic(I) liquid crystal phases allows direct detection of a weak mid-infrared normal combination mode absorption using an inexpensive room temperature silicon photodetector. The sensitivity of the response exceeds that of a conventional FTIR spectrometer equipped with a liquid nitrogen cooled detector. At high pump power in the nematic phase close to the N-I phase transition, we observe an interesting peak splitting in the photothermal response. The advent of tunable lasers that can access still stronger modes suggests that the photothermal mid-infrared response has the potential to detect ultralow concentration of absorbers.   

Optical detection of thermal noise modes in torsional microelectromechanical oscillators

We present the optical detection of the thermal noise spectrum for different torsional MEMS that will be implemented in a study of magnetomechanical coupling at the nanoscale. The interferometric measurement yields the differential dynamic displacement between two diffraction-limited spots on the surface to sub-pm precision, allowing us to identify the thermal modes in the low MHz frequency range. Flexion and torsional modes from thermal noise at room temperature can be distinguished by different amplitudes at different positions of the probe beam. The different mechanical eigenmodes are identified with the help of finite element simulations. This study of the thermal oscillation serves to identify the torsional mode frequencies that can be matched to low frequency magnetization dynamics of magnetic domain wall oscillators. At this point we have fabricated torsional oscillators with a resonance frequency of 6.53 MHz and a Q-factor of 1030, which are at the same time compatible with magnetic domain wall oscillators.   

Advances in Surface Plasmon Resonance Imaging allowing for quantitative measurement of laterally heterogeneous samples

The Surface Plasmon Resonance (SPR) phenomenon is routinely exploited to qualitatively probe changes to materials on metallic surfaces for use in probes and sensors. Unfortunately, extracting truly quantitative information is usually limited to a select few cases -- uniform absorption/desorption of small biomolecules and films, in which a continuous ``slab'' model is a good approximation. We present advancements in the SPR technique that expand the number of cases for which the technique can provide meaningful results. Use of a custom, angle-scanning SPR imaging system, together with a refined data analysis method, allow for quantitative kinetic measurements of laterally heterogeneous systems. The degradation of cellulose microfibrils and bundles of microfibrils due to the action of cellulolytic enzymes will be presented as an excellent example of the capabilities of the SPR imaging system.   

Use of Cavity Ring Down Spectroscopy to Characterize Organic Acids and Aerosols Emitted in Biomass Burning

One poorly understood, but significant class of volatile organic compounds (VOC) present in biomass burning is gas-phase organic acids and inorganic acids. These acids are extremely difficult to measure because of their adsorptive nature. Particulates and aerosols are also produced during biomass burning and impact the radiation budget of the Earth and, hence, impact global climate. Use cavity ring down spectroscopy (CRD) to measure absorption cross sections for OH overtone induced photochemistry in some organic acids (acetic acid and peracetic acid) will be presented and planed measurements of optical properties of aerosols composed of mixtures of different absorbing and non-absorbing species using CRD will be discussed.   

Modeling large screening length effects in Electrostatic Force Microscopy

Electrostatic Force Microscopy (EFM) and its variants such as Kelvin Probe Microscopy (KPM) are ordinarily used to image charged states or electrochemical surface potentials. However, EFM can also be used to measure the local capacitance between the tip and the substrate. For perfectly metallic substrates, this capacitance is purely geometrical, i.e. it is set by the tip shape and substrate geometry. In semi-metals with long screening length, the measured capacitance contains a ``quantum'' component, which is set by the electronic compressibility. Using finite element calculations, we demonstrate that this quantum capacitance component can be measured by EFM. We apply these calculations to the analysis of EFM data on magnetite nanoparticles presented by A. Mottaghizadeh during this meeting.