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Jul 2007

Volume 78, Issue 7, Articles (07xxxx)

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Preface to Special Topic: Instruments and methods for combinatorial science and high-throughput screening

Christopher M. Stafford and Jaime C. Grunlan

Rev. Sci. Instrum. 78, 072101 (2007); http://dx.doi.org/10.1063/1.2754653 (1 page) | Cited 1 time

Online Publication Date: 12 July 2007

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01.30.Kj Handbooks, dictionaries, tables, and data compilations
07.05.Kf Data analysis: algorithms and implementation; data management

Miniaturized dynamic light scattering instrumentation for use in microfluidic applications

Thomas Q. Chastek, Kathryn L. Beers, and Eric J. Amis

Rev. Sci. Instrum. 78, 072201 (2007); http://dx.doi.org/10.1063/1.2755569 (8 pages) | Cited 7 times

Online Publication Date: 10 July 2007

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Five designs for a miniaturized dynamic light scattering (DLS) instrument are described that incorporate microfluidic flow of the sample volume and fiber optic probes directly embedded into the sample. These instruments were demonstrated to accurately determine the size of 10–100 nm particles dispersed in organic and aqueous solvents with most sample sizes less than 150 μl. Small stir bars were incorporated directly into the instruments, and enabled blending of different solutions immediately prior to DLS measurements. Demonstration of the instruments’ capabilities include high throughput measurements of the micelle to unimer transition for poly(styrene-b-isoprene) in mixed toluene/hexadecane solvent, obtained by systematically blending toluene-rich and hexadecane-rich polymer solutions. The critical solvent composition was quickly identified with less than 20 mg of polymer. Further capabilities include temperature control, demonstrated by identification of a critical micelle temperature of poly(ethylene oxide-b-propylene oxide-b-ethylene oxide), as well as multiangle DLS measurements.
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47.85.Np Fluidics
42.81.Pa Sensors, gyros
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Versatile platform for creating gradient combinatorial libraries via modulated light exposure

Brian C. Berry, Christopher M. Stafford, Mayur Pandya, Leah A. Lucas, Alamgir Karim, and Michael J. Fasolka

Rev. Sci. Instrum. 78, 072202 (2007); http://dx.doi.org/10.1063/1.2755729 (6 pages) | Cited 12 times

Online Publication Date: 10 July 2007

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This article details the design, construction, and operation of flexible system that modulates light exposure for the purpose of fabricating continuous and discrete gradient combinatorial libraries. Designed for versatility, the device combines “off the shelf” components, modular accessories, and flexible computer control, so that it can be used for a variety of combinatorial research applications. Salient aspects and capabilities of the instrument are illustrated through two practical examples. The first case demonstrates how user defined exposure functions can be used to create continuous surface energy gradient libraries with a linear profile. The second example illustrates the creation of continuous and discrete libraries for mapping exposure-property functions in a photocurable polymer system.
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42.79.Hp Optical processors, correlators, and modulators
68.35.Md Surface thermodynamics, surface energies
42.70.Jk Polymers and organics

Model, prediction, and experimental verification of composition and thickness in continuous spread thin film combinatorial libraries grown by pulsed laser deposition

N. D. Bassim, P. K. Schenck, M. Otani, and H. Oguchi

Rev. Sci. Instrum. 78, 072203 (2007); http://dx.doi.org/10.1063/1.2755783 (7 pages) | Cited 3 times

Online Publication Date: 11 July 2007

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Pulsed laser deposition was used to grow continuous spread thin film libraries of continuously varying composition as a function of position on a substrate. The thickness of each component that contributes to a library can be empirically modeled to a bimodal cosine power distribution. We deposited ternary continuous spread thin film libraries from Al2O3, HfO2, and Y2O3 targets, at two different background pressures of O2: 1.3 and 13.3 Pa. Prior to library deposition, we deposited single component calibration films at both pressures in order to measure and fit the thickness distribution. Following the deposition and fitting of the single component films, we predict both the compositional coverage and the thickness of the libraries. Then, we map the thickness of the continuous spread libraries using spectroscopic reflectometry and measure the composition of the libraries as a function of position using mapping wavelength-dispersive spectrometry (WDS). We then compare the compositional coverage of the libraries and observe that compositional coverage is enhanced in the case of 13.3 Pa library. Our models demonstrate linear correlation coefficients of 0.98 for 1.3 Pa and 0.98 for 13.3 Pa with the WDS.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
82.80.-d Chemical analysis and related physical methods of analysis

Combinatorial materials research applied to the development of new surface coatings VI: An automated spinning water jet apparatus for the high-throughput characterization of fouling-release marine coatings

Shane J. Stafslien, James A. Bahr, Justin W. Daniels, Lyndsi Vander Wal, Jonathan Nevins, Jeremy Smith, Kris Schiele, and Bret Chisholm

Rev. Sci. Instrum. 78, 072204 (2007); http://dx.doi.org/10.1063/1.2755965 (6 pages) | Cited 10 times

Online Publication Date: 11 July 2007

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Large numbers of coatings can be generated very quickly using a combinatorial high-throughput approach. Rapid screening assays are typically required to adequately evaluate and down select coating candidates to identify promising compositions. An automated, spinning water jet apparatus was developed to rapidly characterize the adhesion strength of marine organisms to coating surfaces. Coating arrays are cast in multiwell plates and subjected to a jet of water of controlled pressure and duration. Array plates are manipulated by a robotic arm to facilitate accurate and repeatable water jet treatments. Jet pressures of 40–688 kPa can be generated and precisely maintained by computer control. A five axis robotic arm selects plates from three plate stacking hotels yielding a total of 39 plates or 936 individual coating samples for each experimental run. All robotic instructions, process parameters, and data are stored and controlled by the computer. The large plate handling capacity offered by the robotic system enables the analysis of a wide variety of coatings for “fouling-release” properties. A brief example demonstrating the capability of the automated water jet apparatus to evaluate marine bacterial adhesion to coating surfaces is provided.
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89.40.Cc Water transportation
81.65.-b Surface treatments
07.07.Tw Servo and control equipment; robots

Combined micro-Raman/UV-visible/fluorescence spectrometer for high-throughput analysis of microsamples

Jermim Noh, Yung Doug Suh, Yong Ki Park, Seung Min Jin, Soo Ho Kim, and Seong Ihl Woo

Rev. Sci. Instrum. 78, 072205 (2007); http://dx.doi.org/10.1063/1.2755745 (6 pages) | Cited 4 times

Online Publication Date: 11 July 2007

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Combined micro-Raman/UV-visible (vis)/fluorescence spectroscopy system, which can evaluate an integrated array of more than 10 000 microsamples with a minimuma size of 5 μm within a few hours, has been developed for the first time. The array of microsamples is positioned on a computer-controlled XY translation microstage with a spatial resolution of 1 μm so that the spectra can be mapped with micron precision. Micro-Raman spectrometers have a high spectral resolution of about 2 cm−1 over the wave number range of 150–3900 cm−1, while UV-vis and fluorescence spectrometers have high spectral resolutions of 0.4 and 0.1 nm over the wavelength range of 190–900 nm, respectively. In particular, the signal-to-noise ratio of the micro-Raman spectroscopy has been improved by using a holographic Raman grating and a liquid-nitrogen-cooled charge-coupled device detector. The performance of the combined spectroscopy system has been demonstrated by the high-throughput screening of a combinatorial ferroelectric (i.e., BaTixZr1−xO3) library. This system makes possible the structure analysis of various materials including ferroelectrics, catalysts, phosphors, polymers, alloys, and so on for the development of novel materials and the ultrasensitive detection of trace amounts of pharmaceuticals and diagnostic agents.
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07.60.Rd Visible and ultraviolet spectrometers
78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.55.Hx Other solid inorganic materials
77.80.-e Ferroelectricity and antiferroelectricity

Linear combinatorial approach to thin film research

Vladimir Matias and Brady J. Gibbons

Rev. Sci. Instrum. 78, 072206 (2007); http://dx.doi.org/10.1063/1.2755776 (7 pages) | Cited 2 times

Online Publication Date: 11 July 2007

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We describe high-throughput experimentation of film synthesis by use of a linear tape transport system (similar to a web-coating system). Metal tape is fed continuously in a reel-to-reel transport system inside the vacuum deposition chamber. Ion-beam assisted deposition (IBAD) texturing is used to enable the growth of epitaxial films on flexible, polycrystalline metal tapes which further enhances the capability of this research. The tape that is continuously fed can be used as a sample itself, via the use of IBAD-textured templates on the tape, or can be a carrier of other smaller substrates (even nonflexible ones). Characterization of samples is done by means of in situ monitoring as well as ex situ sequential analysis. We utilize in situ reflection high-energy electron diffraction for high-throughput analysis of samples. Epitaxial films are deposited on heated samples by evaporation and by pulsed laser deposition. Here, we explain the techniques and the methodologies developed for this type of combinatorial experimentation and show some examples of the material research completed.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Fabrication of combinatorial polymer scaffold libraries

Carl G. Simon, Jr., Jean S. Stephens, Shauna M. Dorsey, and Matthew L. Becker

Rev. Sci. Instrum. 78, 072207 (2007); http://dx.doi.org/10.1063/1.2755761 (7 pages) | Cited 13 times

Online Publication Date: 12 July 2007

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We have designed a novel combinatorial research platform to help accelerate tissue engineering research. Combinatorial methods combine many samples into a single specimen to enable accelerated experimentation and discovery. The platform for fabricating combinatorial polymer scaffold libraries can be used to rapidly identify scaffold formulations that maximize tissue formation. Many approaches for screening cell-biomaterial interactions utilize a two-dimensional format such as a film or surface to present test substrates to cells. However, cells in vivo exist in a three-dimensional milieu of extracellular matrix and cells in vitro behave more naturally when cultured in a three-dimensional environment than when cultured on a two-dimensional surface. Thus, we have designed a method for fabricating combinatorial biomaterial libraries where the materials are presented to cells in the form of three-dimensional, porous, salt-leached, polymer scaffolds. Many scaffold variations and compositions can be screened in a single experiment so that optimal scaffold formulations for tissue formation can be rapidly identified. In summary, we have developed a platform technology for fabricating combinatorial polymer scaffold libraries that can be used to screen cell response to materials in a three-dimensional, scaffold format.
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87.85.J- Biomaterials
87.17.-d Cell processes

High-throughput combinatorial study of local stress in thin film composition spreads

Noble C. Woo, Bryan G. Ng, and R. Bruce van Dover

Rev. Sci. Instrum. 78, 072208 (2007); http://dx.doi.org/10.1063/1.2755779 (5 pages) | Cited 7 times

Online Publication Date: 12 July 2007

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We investigate the stresses in thin films with sub-millimeter lateral spatial resolution using a dense array of prefabricated cantilever beams prepared by microelectromechanical-system techniques. Stress induced deflection of the cantilever is interrogated by an optical (laser/position sensitive detector) measurement system. Composition spread films are deposited on the cantilever array using a three gun on-axis magnetron cosputtering system. The position dependent composition is inferred using rate calibrations and verified by electron microprobe/energy dispersive spectroscopy. We demonstrate the function of this system using an Fe–Ni–Al composition spread with ∼ 1 at. % resolution. This approach allows for measurement of the composition dependence of other electromechanical properties such as the martensitic phase transition temperature of traditional and ferromagnetic shape-memory alloys, as well as the properties of hydrogen storage materials and the magnetic response of magnetostrictive materials.
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07.10.Cm Micromechanical devices and systems
68.60.Bs Mechanical and acoustical properties
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Combinatorial electrochemical cell array for high throughput screening of micro-fuel-cells and metal/air batteries

Rongzhong Jiang

Rev. Sci. Instrum. 78, 072209 (2007); http://dx.doi.org/10.1063/1.2755439 (7 pages) | Cited 7 times

Online Publication Date: 13 July 2007

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An electrochemical cell array was designed that contains a common air electrode and 16 microanodes for high throughput screening of both fuel cells (based on polymer electrolyte membrane) and metal/air batteries (based on liquid electrolyte). Electrode materials can easily be coated on the anodes of the electrochemical cell array and screened by switching a graphite probe from one cell to the others. The electrochemical cell array was used to study direct methanol fuel cells (DMFCs), including high throughput screening of electrode catalysts and determination of optimum operating conditions. For screening of DMFCs, there is about 6% relative standard deviation (percentage of standard deviation versus mean value) for discharge current from 10 to 20 mA/cm2. The electrochemical cell array was also used to study tin/air batteries. The effect of Cu content in the anode electrode on the discharge performance of the tin/air battery was investigated. The relative standard deviations for screening of metal/air battery (based on zinc/air) are 2.4%, 3.6%, and 5.1% for discharge current at 50, 100, and 150 mA/cm2, respectively.
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82.47.Pm Phosphoric-acid fuel cells (PAFC); other fuel cells
82.47.Gh Proton exchange membrane (PEM) fuel cells
82.47.Nj Polymer-electrolyte fuel cells (PEFC)
82.47.Cb Lead-acid, nickel-metal hydride and other batteries
82.45.Fk Electrodes

Protocols for printing thick film ceramic libraries using the London University Search Instrument (LUSI)

L. Chen, Y. Zhang, S. Yang, and J. R. G. Evans

Rev. Sci. Instrum. 78, 072210 (2007); http://dx.doi.org/10.1063/1.2755469 (6 pages) | Cited 4 times

Online Publication Date: 13 July 2007

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Thick film combinatorial libraries can be prepared by mixing ceramic suspensions using stepper-driven syringes to control ink-jet-printing nozzles, but a more tolerant and efficient method has been devised using a simplification of the same equipment. By simplifying the printing sequence and using direct deposition from the stepper syringes, the time committed to a repetitive sequence of priming and cleaning the ink-jet printer nozzles is reduced. Polytetrafluoroethylene (PTFE) open ended tubes and commercial pipette tips are used as the printing nozzles. Calibration and corrections for the method are described. This method opens up the possibility for making ceramic libraries more rapidly with much simpler and less expensive equipment.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
82.70.Kj Emulsions and suspensions
64.75.-g Phase equilibria

High-throughput reactor system with individual temperature control for the investigation of monolith catalysts

Joseph C. Dellamorte, Rohit Vijay, Christopher M. Snively, Mark A. Barteau, and Jochen Lauterbach

Rev. Sci. Instrum. 78, 072211 (2007); http://dx.doi.org/10.1063/1.2755781 (7 pages) | Cited 3 times

Online Publication Date: 13 July 2007

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A high-throughput parallel reactor system has been designed and constructed to improve the reliability of results from large diameter catalysts such as monoliths. The system, which is expandable, consists of eight quartz reactors, 23.5 mm in diameter. The eight reactors were designed with separate K type thermocouples and radiant heaters, allowing for the independent measurement and control of each reactor temperature. This design gives steady state temperature distributions over the eight reactors within 0.5 °C of a common setpoint from 50 to 700 °C. Analysis of the effluent from these reactors is performed using rapid-scan Fourier transform infrared (FTIR) spectroscopic imaging. The integration of this technique to the reactor system allows a chemically specific, truly parallel analysis of the reactor effluents with a time resolution of approximately 8 s. The capabilities of this system were demonstrated via investigation of catalyst preparation conditions on the direct epoxidation of ethylene, i.e., on the ethylene conversion and the ethylene oxide selectivity. The ethylene, ethylene oxide, and carbon dioxide concentrations were calibrated based on spectra from FTIR imaging using univariate and multivariate chemometric techniques. The results from this analysis showed that the calcination conditions significantly affect the ethylene conversion, with a threefold increase in the conversion when the catalyst was calcined for 3 h versus 12 h at 400 °C.
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82.80.-d Chemical analysis and related physical methods of analysis
07.20.Dt Thermometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Getter sputtering system for high-throughput fabrication of composition spreads

John M. Gregoire, R. B. van Dover, Jing Jin, Francis J. DiSalvo, and Héctor D. Abruña

Rev. Sci. Instrum. 78, 072212 (2007); http://dx.doi.org/10.1063/1.2755967 (6 pages) | Cited 6 times

Online Publication Date: 13 July 2007

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We describe a sputtering system that can deposit composition spreads in an effectively UHV environment but which does not require the high-throughput paradigm to be compromised by a long pump down each time a target is changed. The system deploys four magnetron sputter guns in a cryoshroud (getter sputtering) which allows elements such as Ti and Zr to be deposited with minimal contamination by oxygen or other reactive background gases. The system also relies on custom substrate heaters to give rapid heating and cool down. The effectiveness of the gettering technique is evaluated, and example results obtained for catalytic activity of a pseudoternary composition spread are presented.
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07.30.Cy Vacuum pumps
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Cd Deposition by sputtering
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Combinatorial materials research applied to the development of new surface coatings VII: An automated system for adhesion testing

Bret J. Chisholm, Dean C. Webster, James C. Bennett, Missy Berry, David Christianson, Jongsoo Kim, Bret Mayo, and Nathan Gubbins

Rev. Sci. Instrum. 78, 072213 (2007); http://dx.doi.org/10.1063/1.2755505 (9 pages) | Cited 6 times

Online Publication Date: 17 July 2007

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An automated, high-throughput adhesion workflow that enables pseudobarnacle adhesion and coating/substrate adhesion to be measured on coating patches arranged in an array format on 4×8 in.2 panels was developed. The adhesion workflow consists of the following process steps: (1) application of an adhesive to the coating array; (2) insertion of panels into a clamping device; (3) insertion of aluminum studs into the clamping device and onto coating surfaces, aligned with the adhesive; (4) curing of the adhesive; and (5) automated removal of the aluminum studs. Validation experiments comparing data generated using the automated, high-throughput workflow to data obtained using conventional, manual methods showed that the automated system allows for accurate ranking of relative coating adhesion performance.
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89.20.Kk Engineering

Wireless resonant sensor array for high-throughput screening of materials

Radislav A. Potyrailo and William G. Morris

Rev. Sci. Instrum. 78, 072214 (2007); http://dx.doi.org/10.1063/1.2755657 (6 pages) | Cited 4 times

Online Publication Date: 23 July 2007

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Screening of materials arrays for their viscoelastic, gas-sorbing, and dielectric properties is important in a wide variety of combinatorial materials science applications. Impedance analysis is an attractive approach to analyze these materials properties and to generate the required new knowledge. Often, these measurements are performed by applying a material onto a suitable sensor and monitoring the changes in materials properties. However, when such a sensor is positioned into a test cell, a direct-wired connection to the analyzer becomes complicated. These complications further increase dramatically when a whole array of sensors is being tested in the test cell. To eliminate these complications, we developed a wireless proximity resonant sensor array system. In the developed system, tested materials are applied onto an array of thickness-shear mode (TSM) resonators operating at 10 MHz and arranged for performance testing in a test chamber. Each TSM resonator is coupled to a receiver coil (antenna). An array of these coils is read with a single scanning transmitter coil or an array of transmitter coils. This high-throughput screening approach of sensing materials permits their evaluation in complex environments where additional wiring is not desirable or adds a prohibitively complex design. We demonstrated the applicability of the wireless sensor materials screening approach for the rapid evaluation of the effects of conditioning of polymeric sensing films at different temperatures on the vapor-response patterns to several vapors of industrial, health, law enforcement, and security interest (ethanol, acetonitrile, and water vapors).
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Time of flight secondary ion mass spectrometry: A powerful high throughput screening tool

Vincent S. Smentkowski and Sara G. Ostrowski

Rev. Sci. Instrum. 78, 072215 (2007); http://dx.doi.org/10.1063/1.2755693 (6 pages) | Cited 3 times

Online Publication Date: 24 July 2007

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Combinatorial materials libraries are becoming more complicated; successful screening of these libraries requires the development of new high throughput screening methodologies. Time of flight secondary ion mass spectrometry (ToF-SIMS) is a surface analytical technique that is able to detect and image all elements (including hydrogen which is problematic for many other analysis instruments) and molecular fragments, with high mass resolution, during a single measurement. Commercial ToF-SIMS instruments can image 500 μm areas by rastering the primary ion beam over the region of interest. In this work, we will show that large area analysis can be performed, in one single measurement, by rastering the sample under the ion beam. We show that an entire 70 mm diameter wafer can be imaged in less than 90 min using ToF-SIMS stage (macro)rastering techniques. ToF-SIMS data sets contain a wealth of information since an entire high mass resolution mass spectrum is saved at each pixel in an ion image. Multivariate statistical analysis (MVSA) tools are being used in the ToF-SIMS community to assist with data interpretation; we will demonstrate that MVSA tools provide details that were not obtained using manual (univariate) analysis.
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07.75.+h Mass spectrometers

Combinatorial preparation and characterization of thin-film multilayer electro-optical devices

Christian Neuber, Markus Bäte, Mukundan Thelakkat, Hans-Werner Schmidt, Helmut Hänsel, Heiko Zettl, and Georg Krausch

Rev. Sci. Instrum. 78, 072216 (2007); http://dx.doi.org/10.1063/1.2756993 (11 pages) | Cited 5 times

Online Publication Date: 26 July 2007

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In this article we present a setup for the combinatorial vapor deposition of thin-film multilayer devices as well as methods for the fast and efficient analytic screening of the libraries obtained. The preparation setup is based on a commercially available evaporation chamber equipped with various evaporation sources for both organic and metallic materials. The combinatorial approach is realized by the combination of a rotation stage for the substrate, a five-mask sampler, and an additional mask whose position can be deliberately varied along one axis during the evaporation process. The latter is used to evaporate linear as well as step gradients by continuous or stepwise movement of a shutter mask. The mask sampler allows to define the sectors of the library and to evaporate more complex structures, e.g., an electrode layout. Finally, the simultaneous evaporation of two or more materials enables us to produce layers of varying composition ratio in general and doped materials, in particular. For the control of the evaporation process we have developed an automation software, which is particularly helpful for complex library designs and which grants excellent repeatability of experiments. Efficient and fast characterization of the obtained libraries is realized by (i) a purely optical setup and (ii) an electro-optical setup. (i) The UV/vis reader FLASHScan® 530 permits to map out the UV/vis absorbance or fluorescence of the whole library. The UV/vis absorbance is primarily used to determine layer thicknesses and to confirm thickness uniformity across larger regions. The fluorescence measurements are used to determine the composition of layers containing fluorescent dyes. (ii) For a detailed short- and long-term electro-optical analysis we have developed an automated measurement system, which allows the characterization of 8×8 optoelectronic devices and to study their degradation behavior. Both solar cells and organic light-emitting diodes can be tested. Finally, we have developed a data analysis software to extract characteristic values from the huge amount of data and with this facilitate the finding of systematic dependencies.
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42.79.-e Optical elements, devices, and systems
84.60.Jt Photoelectric conversion

Rapid structural mapping of ternary metallic alloy systems using the combinatorial approach and cluster analysis

C. J. Long, J. Hattrick-Simpers, M. Murakami, R. C. Srivastava, I. Takeuchi, V. L. Karen, and X. Li

Rev. Sci. Instrum. 78, 072217 (2007); http://dx.doi.org/10.1063/1.2755487 (6 pages) | Cited 8 times

Online Publication Date: 31 July 2007

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We are developing a procedure for the quick identification of structural phases in thin film composition spread experiments which map large fractions of compositional phase diagrams of ternary metallic alloy systems. An in-house scanning x-ray microdiffractometer is used to obtain x-ray spectra from 273 different compositions on a single composition spread library. A cluster analysis software is then used to sort the spectra into groups in order to rapidly discover the distribution of phases on the ternary diagram. The most representative pattern of each group is then compared to a database of known structures to identify known phases. Using this method, the arduous analysis and classification of hundreds of spectra is reduced to a much shorter analysis of only a few spectra.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
81.30.Bx Phase diagrams of metals, alloys, and oxides
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Noise analysis and noise reduction methods in kilohertz pump-probe experiments

Kevin E. H. Anderson, Samuel L. Sewall, Ryan R. Cooney, and Patanjali Kambhampati

Rev. Sci. Instrum. 78, 073101 (2007); http://dx.doi.org/10.1063/1.2755391 (6 pages) | Cited 8 times

Online Publication Date: 6 July 2007

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We analyze sources of noise in kilohertz frequency pump/probe experiments and present a method for reducing experimental noise by identifying and filtering noisy shots. The power spectrum of instrumental noise shows high frequency, small amplitude modulations which cannot be averaged out. A histogram analysis shows that low frequency, large amplitude signals pose a serious obstacle to signal averaging for improved signal to noise. In kilohertz frequency pump/probe experiments, this low frequency noise typically arises from laser scatter due to bubbles, dust, and defects. We quantify the effectiveness in analyzing and rejecting these large amplitude signals which can produce a hindrance to the effectiveness of signal averaging.
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07.60.Rd Visible and ultraviolet spectrometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Absolute metastable atom-atom collision cross section measurements using a magneto-optical trap

K. J. Matherson, R. D. Glover, D. E. Laban, and R. T. Sang

Rev. Sci. Instrum. 78, 073102 (2007); http://dx.doi.org/10.1063/1.2754444 (6 pages) | Cited 6 times

Online Publication Date: 9 July 2007

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We present a new technique to measure absolute total collision cross sections from metastable neon atoms. The technique is based on the observation of the decay rate of trapped atoms as they collide with room temperature atoms. We present the first measurement of this kind using trapped neon atoms in the 3P2 metastable state colliding with thermal ground state argon. The measured cross section has a value of 556±26 Å2.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides

Laser beam quality and pointing measurement with an optical resonator

Patrick Kwee, Frank Seifert, Benno Willke, and Karsten Danzmann

Rev. Sci. Instrum. 78, 073103 (2007); http://dx.doi.org/10.1063/1.2754400 (10 pages) | Cited 20 times

Online Publication Date: 12 July 2007

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We present a compact diagnostic breadboard that is based on an optical ring resonator for measuring beam quality and pointing of single-frequency continuous wave lasers at a wavelength of 1064 nm. To determine the beam quality of the coherent test beam, this optical resonator is used to perform a mode decomposition into Hermite-Gaussian modes. For our laser system, a power fraction in the fundamental Gaussian mode of 97.2%±0.2% was measured. Residual misalignment and mis-mode-matching to the resonator as well as the astigmatism and/or ellipticity of the test beam have been determined. Numerical simulations showed that measurements of the M2 factor and transversal intensity distribution are not suitable for determining this power fraction. To measure the beam pointing, the fundamental mode of the optical resonator was used as a stable reference. The pointing of the test beam was measured with the differential wave front sensing technique up to Fourier frequencies of 1 kHz with a sensitivity to relative pointing of ∣ϵ∣ = 1×10−6/math. Pointing measurements with an alternative method were performed and showed good agreement.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Rz Doped-insulator lasers and other solid state lasers
07.60.Ly Interferometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Influence of the cavity parameters on the output intensity in incoherent broadband cavity-enhanced absorption spectroscopy

Sven E. Fiedler, Achim Hese, and Uwe Heitmann

Rev. Sci. Instrum. 78, 073104 (2007); http://dx.doi.org/10.1063/1.2752608 (7 pages) | Cited 4 times

Online Publication Date: 17 July 2007

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The incoherent broadband cavity-enhanced absorption spectroscopy is a technique in measuring small absorptions over a broad wavelength range. The setup consists of a conventional absorption spectrometer using an incoherent lamp and a charge coupled device detector, as well as a linear optical cavity placed around the absorbing sample, which enhances the effective path length through the sample. In this work the consequences of cavity length, mirror curvature, reflectivity, different light injection geometries, and spot size of the light source on the output intensity are studied and the implications to the signal-to-noise ratio of the absorption measurement are discussed. The symmetric confocal resonator configuration is identified as a special case with optimum imaging characteristics but with higher requirements for mechanical stability. Larger spot sizes of the light source were found to be favorable in order to reduce the negative effects of aberrations on the intensity.
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07.60.Rd Visible and ultraviolet spectrometers

Development of a high-efficiency high-resolution particle-induced x-ray emission system for chemical state analysis of environmental samples

J. Hasegawa, T. Tada, Y. Oguri, M. Hayashi, T. Toriyama, T. Kawabata, and K. Masai

Rev. Sci. Instrum. 78, 073105 (2007); http://dx.doi.org/10.1063/1.2756623 (6 pages) | Cited 7 times

Online Publication Date: 18 July 2007

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We have developed a high-efficiency high-resolution particle-induced x-ray emission (PIXE) system employing a von Hamos–type crystal spectrometer for a chemical state identification of trace elements in environmental samples. The energy resolution of the system was determined to be about 0.05% through the observation of Si Kα1,2 x rays (1.74 keV) from elemental silicon. The throughput efficiency of the system was also evaluated quasitheoretically to be 1.6×10−7 counts/incident proton for Si Kα1,2 emission. To demonstrate a chemical state analysis using the high-resolution PIXE system, Si Kα1,2 and Kβ x-ray spectra for SiC, Si3N4, and SiO2 were measured and compared. The observed chemical shifts of the Si Kα1,2 peaks for SiC, Si3N4, and SiO2 relative to elemental silicon were 0.20, 0.40, and 0.55 eV, respectively. The tendency of these shifts were well explained by the effective charges of the silicon atoms calculated by a molecular orbital method.
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82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
07.85.Nc X-ray and γ-ray spectrometers
76.60.Cq Chemical and Knight shifts

Precise thermodynamic control of high pressure jet expansions

Wolfgang Christen, Tim Krause, and Klaus Rademann

Rev. Sci. Instrum. 78, 073106 (2007); http://dx.doi.org/10.1063/1.2756630 (3 pages) | Cited 3 times

Online Publication Date: 24 July 2007

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We describe an experimental setup for supersonic jet expansions of supercritical fluids. It is characterized by well-defined thermodynamic values to allow systematic investigations of pressure and temperature effects on molecular beam parameters. The design permits stagnation temperatures T0 = 225–425 K with a thermal stability ΔT0<30 mK and stagnation pressures p0 = 0.2–12 MPa that are measured with 0.05% precision. For optimum stability, gas reservoir, pressure transducer, and gauge amplifier are temperature-controlled, and a feedback loop permits active pressure stabilization using a pulseless syringe pump. With this approach stagnation pressures can be reproduced and kept constant to Δp0<2.9 kPa. As a result, flow velocity and kinetic energy of molecular beams can be controlled with maximum accuracy.
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47.27.wg Turbulent jets
47.40.Ki Supersonic and hypersonic flows
47.45.Dt Free molecular flows

Ground-based prototype quantum cascade laser heterodyne radiometer for atmospheric studies

D. Weidmann, W. J. Reburn, and K. M. Smith

Rev. Sci. Instrum. 78, 073107 (2007); http://dx.doi.org/10.1063/1.2753141 (10 pages) | Cited 6 times

Online Publication Date: 27 July 2007

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The advent of quantum cascade lasers has provided matured continuously tunable solid state laser sources emitting from mid-infrared to terahertz wavelengths. Such sources, used as local oscillators, offer the practical prospect of aircraft, high altitude platform, and satellite deployment of compact and shot noise limited heterodyne radiometers for Earth observation and astronomy. A ground-based prototype of a quantum cascade laser heterodyne radiometer operating in the mid-infrared has been developed and is presented. The instrument design and concepts are described, together with evaluation of the instrument in the laboratory and during field measurements of atmospheric ozone. In this study the best performance achieved by the prototype quantum cascade laser heterodyne radiometer was a signal-to-noise ratio of three times the theoretical shot-noise limit. The prototype has allowed the main sources of excess noise to be identified as residual optical feedback in the local oscillator optical path and a lack of mechanical and thermal stability in the local oscillator collimation system. Instrument improvements are currently being implemented and enhanced performance is expected in the near future.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
07.60.Dq Photometers, radiometers, and colorimeters
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
85.60.Gz Photodetectors (including infrared and CCD detectors)
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