Volume 76, Issue 6, June 2005
- review article
- special topic: combinatorial instruments and techniques
- optics; atoms and molecules; spectroscopy; photon detectors
- particle sources, optics and acceleration; particle detectors
- nuclear physics, fusion and plasmas
- microscopy and imaging
- condensed matter; materials
- biology and medicine
- gravity; geophysics; astronomy and astrophysics
- electronics; electromagnetic technology; microwaves
- thermometry; thermal diffusivity; acoustic; photothermal and photoacoustic
- general instruments
Index of content:
- REVIEW ARTICLE
76(2005); http://dx.doi.org/10.1063/1.1927327View Description Hide Description
Nanoelectromechanical systems(NEMS) are drawing interest from both technical and scientific communities. These are electromechanical systems, much like microelectromechanical systems, mostly operated in their resonant modes with dimensions in the deep submicron. In this size regime, they come with extremely high fundamental resonance frequencies, diminished active masses,and tolerable force constants; the quality factors of resonance are in the range —significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultrafast sensors, actuators, and signal processing components. Experimentally, NEMS are expected to open up investigations of phonon mediated mechanical processes and of the quantum behavior of mesoscopic mechanical systems. However, there still exist fundamental and technological challenges to NEMS optimization. In this review we shall provide a balanced introduction to NEMS by discussing the prospects and challenges in this rapidly developing field and outline an exciting emerging application, nanoelectromechanical mass detection.
- SPECIAL TOPIC: COMBINATORIAL INSTRUMENTS AND TECHNIQUES
76(2005); http://dx.doi.org/10.1063/1.1921587View Description Hide Description
76(2005); http://dx.doi.org/10.1063/1.1906063View Description Hide Description
Micro-x-ray fluorescence (MXRF) is a useful characterization tool for high-throughput screening of combinatorial libraries. Due to the increasing threat of use of chemical warfare (CW) agents both in military actions and against civilians by terrorist extremists, there is a strong push to improve existing methods and develop means for the detection of a broad spectrum of CW agents in a minimal amount of time to increase national security. This paper describes a combinatorial high-throughput screening technique for CW receptor discovery to aid in sensor development. MXRF can screen materials for elemental composition at the mesoscale level (tens to hundreds of micrometers). The key aspect of this work is the use of commercial MXRF instrumentation coupled with the inherent heteroatom elements within the target molecules of the combinatorial reaction to provide rapid and specific identification of lead species. The method is demonstrated by screening an 11-mer oligopeptide library for selective binding of the degradation products of the nerve agent VX. The identified oligopeptides can be used as selective molecular receptors for sensor development. The MXRF screening method is nondestructive, requires minimal sample preparation or special tags for analysis, and the screening time depends on the desired sensitivity.
76(2005); http://dx.doi.org/10.1063/1.1906090View Description Hide Description
To speed up synthetic polymer research, a workflow dedicated to automated polymer synthesis and characterization was developed. The workflow consists of several synthesis robots with online and offline analytical equipment. For screening of reaction parameters and for library synthesis, robots equipped with glass reactors and vortex agitation are applied that match very well the classical (small-scale) laboratory experiments. For the screening and library preparation also a microwavesynthesizer can be used. For upscaling purposes and process development, a robot containing tank reactors with mechanical stirring is utilized. This robot also offers the possibility to continuously feed reagents to the reactor and to operate in batch, semibatch or continuous mode.
Using open-source software technologies and standardized data structures to build advanced applications for high-throughput experimentation environments76(2005); http://dx.doi.org/10.1063/1.1906104View Description Hide Description
Herein we present a modular approach to a high-throughput experimentation software environment. Instead of a monolithic master system, small tools with a limited set of tasks are interconnected using standardized, self-descriptive data structures. This approach is highly flexible with respect to the rapidly changing needs of the scientists: Since the modules are isolated and intermodule communication is standardized, new components can be integrated without side effects. The developed software environment follows to a large extent the UNIX design philosophy and is heavily based on open-source software technologies that are used to solve specific tasks within the overall system to achieve high productivity in using the software for ambitious high-throughput experimentation programs. It is shown that the orchestration of the system significantly benefits from clear and standardized interfacedesign based on hteML, the high-throughput experimentation markup language, an XML language for the description of high-throughput experimentation data and processes.
Combinatorial microelectrochemistry: Development and evaluation of an electrochemical robotic system76(2005); http://dx.doi.org/10.1063/1.1906106View Description Hide Description
An electrochemicalrobotic system using standard microtiter plates as reaction wells for potentiostatic and galvanostatic electrosynthesis and high-throughput electroanalysis was conceived and realized using stepmotor driven positioning stages in combination with a flexible software.Electrode bundles specifically adapted to the experimental needs are accurately positioned in the wells of a microtiter plate followed by the automatic performance of sequences of electrosynthetic or electroanalytical techniques. The system allows us to work under inert-gas atmosphere, in aqueous and organic solvents, and to add or remove solutions by means of integrated syringe pumps. A specifically developed script language permits the user to perform very complex experimental sequences in the different wells of the microtiter plate. The hardware and software features of the developed electrochemicalrobotic system, the design of suitable electrode arrangements for electrosynthesis and electroanalytical techniques, as well as the reproducibility in aqueous and organic electrolytes are described. The performance of the system is demonstrated by redox screening of a Ru-complex library and by electrosynthesis with in situ analysis of a compound library.
76(2005); http://dx.doi.org/10.1063/1.1924651View Description Hide Description
The diffusionvelocity of an inhomogeneous unmagnetized plasma is measured by means of the phase velocities of ion-acoustic waves propagating along and against the direction of the plasma flow. Combined with the measurement of the plasma density distributions by usual Langmuir probes, the method is applied to measure the ambipolar diffusion coefficient and effective ion collision frequency in inhomogeneous plasmas formed in an asymmetrically discharged double-plasma device. Experimental results show that the measuredflowvelocities,diffusion coefficients, and effective collision frequencies are in agreement with ion-neutral collision dominated diffusion theory.
76(2005); http://dx.doi.org/10.1063/1.1905967View Description Hide Description
Basic considerations for implementing combinatorial approach to molecular beam epitaxy(MBE) are discussed, focusing on the key issues relevant to conventional MBE synthesis using solid sources and characterization. The primary objective for implementing combinatorial approach is to make MBE do more, more able to carry out controlled and systematic work in large parameter space, without sacrificing any existing capabilities of conventional MBE. Methods for accomplishing this by integrating current instrumentation technology are described.
76(2005); http://dx.doi.org/10.1063/1.1906085View Description Hide Description
We describe the design and refinement of a high-throughput buckling-based metrology for ascertaining the mechanical properties (e.g., modulus) of combinatorial thin polymer film libraries. We provide critical details for the construction of a suitable strain stage, describe sample preparation, and highlight methods for high-throughput data acquisition and data analysis. To illustrate the combinatorial and high-throughput capability of this metrology, we prepare and evaluate films possessing a gradient in the elastic modulus and compare the results with an analytical expression derived from composite beam theory. Application of this metrology is very simple and practically any laboratory, academic or industrial, can perform such measurements with only modest investment in equipment. Although developed as a platform for investigating combinatorial libraries, researchers can take advantage of the high-throughput nature of this metrology to measure noncombinatorial film specimens as well.
76(2005); http://dx.doi.org/10.1063/1.1906086View Description Hide Description
This study reports a detailed investigation of catalyst library design by genetic algorithm (GA). A methodology for assessing GA configurations is described. Operators, which promote the optimization speed while being robust to noise and outliers, are revealed through statistical studies. The genetic algorithms were implemented in GA platform software called OptiCat, which enables the construction of custom-made workflows using a tool box of operators. Two separate studies were carried out (i) on a virtual benchmark and (ii) on real surface response which is derived from HT screening. Additionally, we report a methodology to model a complex surface response by binning the search space in small zones that are then independently modeled by linear regression. In contrast to artificial neural networks, this approach allows one to obtain an explicit model in an analogical form that can be further used in Excel or entered in OptiCat to perform simulations. While speeding the implementation of a hybrid algorithm combining a GA with a knowledge-based extraction engine is described, while speeding up the optimization process by means of virtual prescreening the hybrid GA enables one to open the “black-box” by providing knowledge as a set of association rules.
Investigation of machine compliance uniformity for nanoindentation screening of wafer-supported libraries76(2005); http://dx.doi.org/10.1063/1.1906089View Description Hide Description
The reliability of nanoindentation results can depend critically on an accurate assessment of the machine compliance term. The common practice is to determine the machine compliance from a small reference specimen, then apply its value to a much larger wafer-supported library. The present study investigates the validity of this approach by thoroughly testing bare 76.2 mm diameter, thick Si(100) wafers mounted on two vacuum chucks of different design. We find that the small-sample value of the machine compliance is adequate for the majority of the wafer, including areas directly over vacuum rings and a circular center port of ordinary dimensions. However, vacuum chucks with a tweezer slot should be avoided in combinatorial materials science applications. But even in the absence of a tweezer slot, it may be necessary to generate an accurate machine compliance map for the wafer perimeter if the thin-film library extends beyond the outermost vacuum ring to the wafer edge. The Young’s modulus and the hardness of silicon are found to be and , respectively, over well-mounted regions of the wafer; both values are in good agreement with the literature.
76(2005); http://dx.doi.org/10.1063/1.1906105View Description Hide Description
We describe the design and application of a temperature gradient probe tack apparatus for investigating the adhesive performance of model pressure-sensitive adhesives (PSAs). In particular, we illustrate a probe tack apparatus for studying the effect of temperature on three critical adhesion identifiers: adhesion energy, elongation at break, and debonding mechanisms. The measurementtemperature is varied across the PSA film using a gradient temperature stage constructed from a transparent sapphire plate with a heating and cooling source positioned at opposite ends. The transparent substrate allows visualization of the contact area and debonding mechanisms during the test. The gradient temperature stage is integrated onto a motorized stage, enabling a matrix of probe tack tests to be conducted across the PSA film at different sample temperatures. We use a spherical probe to evaluate the adhesive performance of a thick model poly(styrene-b-isoprene-b-styrene) PSA film between a temperature range of 10 °C to 100 °C. We demonstrate that this apparatus is a viable combinatorial design for tack measurements and may be extended to more complicated two-dimensional gradient films.
Integration of MALDI-TOFMS as high-throughput screening tool into the workflow of combinatorial polymer research76(2005); http://dx.doi.org/10.1063/1.1906123View Description Hide Description
The possibilities of an integration of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) as an high-throughput screening tool into the workflow of combinatorial materials research are discussed. A multiple layer sample preparation technique for MALDI is described in detail and its possibilities of automation and miniaturization are discussed. Automated MALDIsample preparation could be performed within an automated synthesizerrobot as well as with an ink-jet printer. The first approach offers the possibility of online reaction monitoring, whereas the second approach gives the opportunity of applications in ultra-high-throughput environments. Moreover, an example of high-throughput screening of a polymerization reaction by MALDI-TOFMS is discussed.
Use of fluorescence for the high-throughput evaluation of synergistic thermal and photo stabilizer interactions in poly (vinyl chloride)76(2005); http://dx.doi.org/10.1063/1.1906124View Description Hide Description
The selection of thermal and photo stabilizers for poly (vinyl chloride) (PVC) using conventional methods is a time-consuming process. The high-throughput screening method developed in this research demonstrates rapid and efficient ways to quantify the effectiveness of PVC stabilizers with respect to raw plastic materials, stabilizers, levels of use, and testing conditions. An experimental protocol using liquid sampling and fluorescence measurement was developed to determine the effectiveness of formulations. This was used to evaluate the performance of stabilizers based on the change of fluorescence emission at after thermal aging or ultraviolet (UV)radiation. The performance of PVC formulations using six different types of stabilizers was successfully mapped for both PVC resin and flexible PVC.
76(2005); http://dx.doi.org/10.1063/1.1904272View Description Hide Description
A pen-shaped electrode probe is designed for high-throughput screening of electrochemical libraries. The electrode probe consists of a large-area electrode and a cylindrical electrolyte sponge with a short cone tip for screening. This type of design can easily minimize the probe resistance contributed by the electrolyte. A zincelectrode library is generated using a nonautomated method to deposit metal zinc on a graphite plate. The zincelectrode library and the -electrode probe form an electrochemical library containing 128 micro zinc/air batteries. High-throughput screening of the zinc/air batteries are carried out by moving the tip of the electrode probe under constant potential and measuring the current. A Gaussian distribution is used for statistical analysis of the experimental data. These data obtained with the combinatorial method have a relative standard deviation of 8.9% based on a nonautomated coating procedure. The electrode probe is used to study the effect of addition of Cu in the anode on the performance of the zinc/air battery.
76(2005); http://dx.doi.org/10.1063/1.1926967View Description Hide Description
In this article we review the design, construction, and operation of an instrument for high-throughput mechanical characterization (HTMECH) of polymer films. In particular, the HTMECH is applied here to free-standing polymer libraries with gradients in properties such as temperature and composition. Here, the goal is discovery of mechanical property relationships with polymer formulation and processing. However, HTMECH can also measure strain-rate libraries for uniform samples from near-static to meters-per-second (impact velocities). HTMECH measures force and deformation of film regions that undergo transverse biaxial loading by an instrumented thin contact tip. We demonstrate the salient features of mechanical models of the HTMECH assay and how they are employed to extract meaningful parameters from the raw data. The HTMECH instrument is compared and contrasted with conventional implementations of the dart impact and blister techniques.
Design, fabrication, and application of a massively parallel single-bead microreactor system for high-throughput experimentation in heterogeneous catalysis76(2005); http://dx.doi.org/10.1063/1.1906088View Description Hide Description
We present a unique approach to high-throughput catalyst testing that is based on using individual beads in a massively parallel arrangement of microreaction chambers on a chip and describe its excellent scalability to very high numbers of parallel reaction chambers that have not been realized before in continuous flow applications. The reactor design benefits to a large extent from the principle of using individual, independent flow restrictors for equi-distribution of the fluid flow to the parallel reaction chambers. As a model reaction for the comparison of results obtained with a 384-parallel and a 625-parallel single-bead reactor, the selective CO oxidation in hydrogen is used. The same relative catalyst performances and catalytic trends can be measured in both reactor systems.
76(2005); http://dx.doi.org/10.1063/1.1906125View Description Hide Description
A technique has been developed for the high-throughput (HT) parallel screening of liquid crystal(LC)phase transitions, using optical anisotropic effects observed only in the LC state to allow the determination of melting and clearing points. A camera was used to monitor optical changes observed in arrays of LC samples upon heating, when illuminated with plane polarized light and viewed through a second polarizer aligned perpendicular to the plane of polarized light. Data was processed using Image Pro Plus, extracting values for the melting point and clearing point of each sample in the array. When compared with literature and conventional differential scanning calorimetry the new technique was found to be in excellent agreement, establishing the technique as a viable HT alternative. The method was used to analyze a 75 formulation library prepared using liquid handling for HT clearing point determination, showing the scope and power of the technique in the analysis of larger libraries.
Development of a spatially controllable chemical vapor deposition reactor with combinatorial processing capabilities76(2005); http://dx.doi.org/10.1063/1.1906183View Description Hide Description
Most conventional chemical vapor deposition(CVD) systems do not have the spatial actuation and sensing capabilities necessary to control deposition uniformity or to intentionally induce nonuniform deposition patterns for single-wafer combinatorial CVD experiments. In an effort to address these limitations, a novel CVD reactor system has been developed that can explicitly control the spatial profile of gas-phase chemical composition across the wafer surface. This paper discusses the construction of a prototype reactor system featuring a three-zone, segmented showerhead design. Experiments are performed to assess the ability of this reactor system to deposit tungsten films by the hydrogen reduction process; segment-to-segment process recipes are controlled to deposit spatially nonuniform W films. The capabilities of this reactor system for materials discovery research are discussed.
High throughput oxide lattice engineering by parallel laser molecular-beam epitaxy and concurrent x-ray diffraction76(2005); http://dx.doi.org/10.1063/1.1926927View Description Hide Description
A laser molecular-beam epitaxy (LMBE) system for the fabrication of atomically controlled oxides superlattices and an x-ray diffractometer that measures spatially resolved x-ray diffraction spectra have been developed based on the concept of combinatorial methodology. The LMBE chamber has two moving masks, an automated target stage, a substrate heating laser, and an in situ scanning reflection high-energy electron diffraction system. The x-ray diffractometer with a curved monochromator and two-dimensional detector is used for rapid concurrent x-ray diffraction intensity mapping with the two axes of the detector corresponding to the diffraction angle and a position in the sample.