Devices and Systems

2004;():1-6. doi:10.1115/NANO2004-46012.

Block copolymer-based membrane technology represents a versatile class of nanoscale materials in which biomolecules, such as membrane proteins, can be reconstituted. Among its many advantages over conventional lipid-based membrane systems, block copolymers can mimic natural cell biomembrane environments in a single chain, enabling large-area membrane fabrication using methods like Langmuir-Blodgett deposition, or spontaneous protein-functionalized nanovesicle formation. Based on this unique membrane property, a wide variety of membrane proteins possessing unique functionalities including pH/voltage gatable porosity, photon-activated proton pumping, and gradient-dependent production of electricity have been successfully inserted into these biomimetic systems.

Commentary by Dr. Valentin Fuster
2004;():7-12. doi:10.1115/NANO2004-46013.

We demonstrate the possibility of making conductive and dry adhesive interfaces between multiwalled carbon nano-tube (MWNT) and nanofiber (MWNF) arrays grown by chemical vapor deposition with transition-metal as catalyst on silicon substrates. The maximum observed adhesion force between MWNT and MWNF surfaces is 3.5 mN for an apparent contact area of 2 mm by 4 mm. The minimum contact resistance measured at the same time is ∼20 Ω. Contact resistances of MWNT-MWNT and MWNT-gold interfaces were also measured as pressure forces around several milli-Newton were applied at the interface. The resulting minimum contact resistances are on the same order but with considerable variation from sample to sample. For MWNT-MWNT contacts, a minimum contact resistance of ∼ 1 Ω is observed for a contact area of 2 mm by 1 mm. The relatively high contact resistances, considering the area density of the nanotubes, might be explained by the high cross-tube resistances at the contact interfaces and limited inter-penetration of the nanotube arrays.

Commentary by Dr. Valentin Fuster
2004;():13-18. doi:10.1115/NANO2004-46016.

We have successfully purified BR from purple membrane of Halobacterium Salinarium and Cox from the genetically engineered plasmid inserted in Rhodobacter Sphaeroides. The activities of the purified enzymes have shown in lipid vesicles as well as in polymer vesicles and planar membranes. Phosphatidylcholine derived lipid vesicles created the most nature like environment for the enzymes. Triblock copolymer membrane was the alternative choice for membrane protein reconstitution since polymers are more durable, ideal for industrial applications and support enzyme activities better. We also demonstrated the backward function of Cox in vitro by changing proton concentration in the surrounding medium. Langmuir-Blodgett method was used to reconstitute the enzymes into the planar lipid or polymer membranes. The enzyme activities of the enzymes in planar membrane system were tested by impedance spectroscopy.

Topics: Membranes , Proteins
Commentary by Dr. Valentin Fuster
2004;():19-23. doi:10.1115/NANO2004-46018.

Protein-functionalized biomimetic membranes, based upon a triblock copolymer simulating a natural lipid bilayer in a single chain, serves as a core technology for applications in bioenergetics. Monolayers of block copolymer, which simulates the hydrophilic-hydrophobic-hydrophilic chain of a natural cell membrane, can be formed by Langmuir-Blodgett (LB) deposition and provides a favorable environment for protein refolding. Large-scale membrane formation is achieved using LB deposition on a variety of substrates, such as gold, quartz, silicon, and Nafion®. We have successfully inserted membrane proteins, such as the light-activated proton pump, bacteriorhodopsin (BR) and the pH/voltage-gateable porin, Outermembrane Protein F (OmpF), into large-area LB monolayers. We have also established sustained protein functionality in films through the measurement of light-activated proton transport.

Commentary by Dr. Valentin Fuster
2004;():25-26. doi:10.1115/NANO2004-46033.

In recent years several surface stress sensors based on microcantilevers have been developed for biosensing [1–4]. Since these sensors are made using standard microfabrication processes, they can be easily made in an array format, making them suitable for high-throughput multiplexed analysis. Specific reactions occurring on one surface (enabled by selective modification of the surface a priori) of the sensor element change the surface stress, which in turn causes the sensor to deflect. The magnitude and the rate of deflection are then used to study the reaction. The microcantilevers in these sensors are usually fabricated using material like silicon and its oxides or nitrides. The high elasticity modulus of these materials places limitations on the sensitivity and sensor geometry. Alternately polymers, which have a much lower elastic modulus when compared to silicon or its derivatives, offers greater design flexibility, i.e. allow the exploration of innovative sensor configurations that can have higher sensitivity and at the same time are suitable for integration with microfluidics and electrical detection systems.

Commentary by Dr. Valentin Fuster
2004;():27-28. doi:10.1115/NANO2004-46034.

A label-free technique capable of rapidly screening human blood samples simultaneously for multiple serum tumor markers would enable accurate and cost-effective diagnosis of cancer before physiological symptoms appear. Recently, microfabricated, bimaterial cantilever sensors have been demonstrated to detect DNA hybridization and antigen-antibody binding at clinically relevant concentrations. Cantilever sensors deflect measurably under the surface stress resulting when biomolecules immobilized on one surface of the sensor interact with their binding partners [1]. We present an array of cantilever sensors (silicon nitride with a gold coated surface) capable of simultaneously interrogating 100 different biomolecular interactions.

Topics: Nanosensors , Tumors
Commentary by Dr. Valentin Fuster
2004;():29-30. doi:10.1115/NANO2004-46037.

Nanoelectromechanical systems (NEMS) are interesting for both probing nanoscale physical fundamentals and exploring new technological applications [1]. In particular, nanomechanical resonators possess superb attributes including surprisingly-high operating frequency, ultra-small mass, high quality factor (Q), and thus are promising candidates for components in novel signal processing systems and ultra-sensitive sensors [1,2]. NEMS resonators with fundamental resonant frequencies exceeding 1GHz have been realized [3] and unprecedented mass sensitivity has also been demonstrated with VHF high-Q NEMS resonant mass sensors [2,4]. Among many engineering challenges to boost NEMS to more practical applications, it is of great importance to develop the generic protocol of integrating NEMS resonators with feedback and control systems. This work presents the first implementation of the integration of a UHF NEMS resonator with a low-noise phase locked loop (PLL).

Commentary by Dr. Valentin Fuster
2004;():31. doi:10.1115/NANO2004-46047.

The magnetic data storage industry has followed a similar density (and data rate) improvement curve as the semiconductor technology (Moore’s Law) for the past decade. However, whether the storage densities will continue to increase at this rate and be able to keep up with the improvements in processor technology is under a near term threat resulting from the fundamental physics up on which the hard disk drives are based. It is expected that novel, more unconventional technological solutions become necessary to overcome limitations, however, many of these technologies rely heavily on heating and energy transport at extremely short time and length scales. It is widely believed that further advances in high-technology data storage systems will be difficult, if not impossible, without rigorous treatment of the nano-scale energy transport. The nano-scale heat transfer research effort at Data Storage System Center (DSSC) has been focused on three interwoven areas of thermal design, failure analysis, and metrology of micro/nano-devices and structures relevant to data storage technologies. In this presentation, underlying physics and fundamentals of heat transport at nanoscale will be discussed. In addition, applications of the nanoscale heat transfer to the thermal analyses of the magnetic and phase change optical data storage technologies will be presented.

Commentary by Dr. Valentin Fuster
2004;():33-36. doi:10.1115/NANO2004-46050.

There have been many attempts in the recent years to improve the device performance by enhancing carrier mobility by using the strained-induced changes in silicon electronic bands [1–4] or reducing the junction capacitance in silicon-on-insulator (SOI) technology. Strained silicon on insulator (SSOI) is another promising technology, which is expected to show even higher performance, in terms of speed and power consumption, comparing to the regular strained-Si transistors. In this technology, the strained silicon is incorporated in the silicon on insulator (SOI) technology such that the strained-Si introduces high mobility for electrons and holes and the insulator layer (usually SiO2 ) exhibits low junction capacitance due to its small dielectric constant [5, 6]. In these devices a layer of SiGe may exist between the strined-Si layer and insulator (strained Si-on-SiGe-on-insulator, SGOI) [6] or the strained-Si layer can be directly on top of the insulator [7]. Latter is advantageous for eliminating some of the key problems associated with the fabrication of SGOI.

Commentary by Dr. Valentin Fuster
2004;():37-38. doi:10.1115/NANO2004-46051.

We report the design, fabrication and testing of a microchip that exploits a capacitive detection scheme for multiplexed label-free biomolecular assays. The detection scheme is based on the nanoscale gap parallel-plate capacitor formed by the electrical double layer at the interface of a metal electrode and an ionic solution, which is sensitive to biological reactions at the electrode surface. Since the nanogap is obtained by electrical and chemical control, no nano-patterning techniques are needed and the simple device structure facilitates sensor readout, multiplexing, and packaging. Finally, this sensing technique is universal and can be applied to detection of diverse biological entities such as proteins and cells.

Commentary by Dr. Valentin Fuster
2004;():39-40. doi:10.1115/NANO2004-46052.

We have investigated the field emission behavior of lithographically patterned bundles of multiwalled carbon nanotubes arranged in a variety of array geometries. Such arrays of nanotube bundles are found to perform significantly better in field emission than arrays of isolated nanotubes or dense, continuous mats of nanotubes, with the field emission performance depending on the bundle diameter and inter-bundle spacing. Arrays of 2-μm diameter nanotube bundles spaced 5 μm apart (edge-to-edge spacing) produced the largest emission densities, routinely giving 1.5 to 1.8 A/cm2 at ∼ 4 V/μm electric field, and >6 A/cm2 at 20 V/μm.

Commentary by Dr. Valentin Fuster
2004;():41-44. doi:10.1115/NANO2004-46057.

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. The tip is made of Ir/Pt alloy. Pulse voltages of 3–7 V with a duration of 500 ns were applied to a CoNi/Pt multilayered film. Written by a blunt tip (radius 1000 nm), marks are formed with a nearly uniform mark size of 170 nm when the pulse voltage is above 4 V. While sharp tip (radius 50 nm) writing achieves no mark. The emission area of our tip-sample system derived from an analytic expression for field emission current is approximately equal to the mark size, and is largely independent of pulse voltage. For the blunt tip, the emission region is almost the same as the mark size. While for the sharp tip, the initially formed mark is too small, so that the domain wall surface tension shrinks the mark and it crashes finally.

Topics: Heat , Probes , Shapes
Commentary by Dr. Valentin Fuster
2004;():45-46. doi:10.1115/NANO2004-46073.

Layer-by-layer deposition of polyelectrolytes form multiple layers in the nanometer scale. Charged magnetic [1] and biomolecular [2] nano-colloids can be incorporated in to the layers. These multilayer assemblies are formed on the inner walls of a microchannel using laminar flow; alternatively polyanions and polycations are pumped through the channel. Water is also pumped through, between the deposition of each layer, in order to wash away the un-absorbed polyelectrolytes. The first charged layer is formed by silanation. The microfluidic device consists of a ‘T’ junction as shown in Fig. 1. Switching flow between polyelectrolytes and water is controlled by three syringe pumps, automated through a Labview virtual instrument.

Commentary by Dr. Valentin Fuster
2004;():47-48. doi:10.1115/NANO2004-46078.

We report nano-engineered surfaces (NanoTurf), designed to make various micro- and nano-fluidic devices and systems less frictional for liquid flows, and describe microchannels made with such a surface. While our group has reported a dramatic (> 95%) drag reduction of discrete droplets flowing in a space between two parallel-plates covered with “random” nano-posts created by the “black silicon method” [1], this paper describes various nanofabrication techniques, including those capable of “designing” nanostructures with not only a good control of pattern sizes and periods but also practical manufacturability to be embedded in various micro- and nano-fluidic devices and systems. Microchannels are developed using the designed nanostructure surfaces and used for continuous flow tests.

Commentary by Dr. Valentin Fuster
2004;():49-50. doi:10.1115/NANO2004-46081.

Based on the concept that the FH of a portion of the slider that carries the read/write element can be adjusted by a piezoelectric actuator and the FH can be measured according to the magnetic signal, a new 3-DOF analytic model and an observer-based nonlinear compensator are proposed to achieve ultra-low FH with minimum modulation under short range attractive forces. Numerical simulations show that the FHM due to disk waviness is effectively reduced with a control voltage of less than ±2V.

Topics: Bearings , Design , Disks
Commentary by Dr. Valentin Fuster
2004;():51-52. doi:10.1115/NANO2004-46086.

According to the recent Laboratory News’ Proteomics Special article Mass Spectroscopy (MS) has become the technology of choice to meet today’s unprecedented demand for accurate bioanalytical measurements, including protein identification. Although MS can be used to analyze any biological sample, it must be first converted to gas-phase ions before it can be introduced into a mass spectrometer for analysis. It is transfer of a very small liquid sample (proteins are very expensive and often very difficult to produce in sizable quantities) into a gas-phase ions that is currently considered to be a bottleneck to high throughput proteomics. Electrospray ionization (ESI) is a technique developed in early 1990th to generate a spray gas-phase ions by applying high voltage (from several hundreds volts and up to a few thousands kilovolts relative to the ground electrode of the MS interface) to a small capillary through which the liquid solution is pumped. The high electric field ionizes the fluid forming the converging Taylor cone of the exiting jet which eventually breaks into many small droplets when the repulsive Coulombic forces overcome the surface tension. Because of the focusing effect associated with the spraying the electrically charged fluid, the size of the electrospray cone and thus of the formed droplets is in a few tens of nanometers range although the inner diameter of the capillary is in the micrometer range.

Commentary by Dr. Valentin Fuster
2004;():53-54. doi:10.1115/NANO2004-46094.

The majority of biomolecular motors are powered by nucleoside triphosphate (NTP), especially adenosine triphosphate (ATP). These motors consist of a β-sheet with highly conserved motifs and the nucleotide binding domain around it. The highly conserved protein folds are the engines of these motors, which convert the energy of NTP hydrolysis cycle to mechanical work. Although functions of molecular motors are widely diverse, (including cargo movement, DNA unwinding, protein degradation, ion pumping, etc), the nucleotide binding domains are very similar. In the binding site, NTP undergoes a hydrolysis cycle

where E is the enzyme (motor protein), the small dot represents the docking of NTP, and the large dot represents the tightly-bound states. The hydrogen bond network formed in the NTP binding step, as shown in Figure 1 [1], deforms the β-sheet and adjacent structures. The local deformation propagates to conformational changes of functional residues to do mechanical work or to change the affinity to the substrate [2]. For multimeric motor proteins, we must also consider the stress paths among subunits which control the sequence and the activity of the protein. Stress trajectories emanating from a binding site either passes through a circumferential stress loop or a stress loop through the substrate.

Commentary by Dr. Valentin Fuster

Nanoscale Phenomena

2004;():55-56. doi:10.1115/NANO2004-46006.

Low thermal conductivity is essential for efficient operation of thermoelectric/thermionic power generation devices. There have been several attempts to design materials with low thermal conductivity without sacrificing electrical transport. These approaches utilized different mechanisms of phonon scattering, such as acoustic impedance mismatch of the adjacent layers in superlattices or defect scattering of phonons etc [1, 2]. However, each of these approaches scatter phonons only in a particular region of the phonon spectrum. In this paper we present experimental results of the thermal conductivity of epitaxially grown superlattices engineered to take advantage of the various scattering mechanisms to scatter phonons over the entire phonon spectrum.

Commentary by Dr. Valentin Fuster
2004;():57-60. doi:10.1115/NANO2004-46019.

A mechanics-based model is presented which predicts a “neutral annulus” for quasi-crystalline self-assembling nanostructure such as collagen fibrils, wherein transcript length, torsional and axial stiffness along with primary and quaternary protein structure limit the size to which these structures may aggregate. In the present treatment, a neutral annulus is predicted at 0.625 of the fibril radius, wherein portions of the fibril interior to the neutral annulus are in compression, balanced by portions exterior to the neutral annulus which are in tension.

Commentary by Dr. Valentin Fuster
2004;():61-62. doi:10.1115/NANO2004-46036.

Ion transport in nanoscale channels has recently received increasing attention. Much of that has resulted from experiments that report modulation of ion transport through the protein ion channel, α-hemolysin, due to passage of single biomolecules of DNA or proteins [1]. This has prompted research towards fabricating synthetic nanopores out of inorganic materials and studying biomolecular transport through them [2]. Recently, the synthesis of arrays of silica nanotubes with internal diameters in the range of 5–100 nm and with lengths 1–20 μm was reported [3]. These tubes could potentially allow new ways of detecting and manipulating single biomolecules and new types of devices to control ion transport. Theoretical modeling of ionic distribution and transport in silica nanotubes, 30 nm in diameter and 5 μm long, suggest that when the diameter is smaller than the Debye length, a unipolar solution of counterions is created within the nanotube and the coions are electrostatically repelled [4]. We proposed two different types of devices to use this unipolar nature of solution, i.e. ‘transistor’ and ‘battery’. When the electric potential bias is applied at two ends of a nanotube, ionic current is generated. By locally modifying the surface charge density through a gate electrode, the concentration of counterions can be depleted under the gate and the ionic current can be significantly suppressed. This could form the basis of a unipolar ionic field-effect transistor. By applying the pressure bias instead of electric potential bias, the fluid flow is generated. Because only the counterions are located inside the channel, the streaming current and streaming potential are generated. This could form the basis of an electro-chemo-mechanical battery. In the present study, transport phenomena in nanofluidic channels were investigated and the performance characteristics were evaluated using continuum dynamics.

Commentary by Dr. Valentin Fuster
2004;():63-64. doi:10.1115/NANO2004-46039.

Employing the fountain pen principle, a micropipette is used to write an Au nanoparticle ink on glass substrates. A continuous-wave laser (488–515 nm) is subsequently used as a controlled, localized energy source to evaporate the carrier liquid (toluene) in the ink and sinter the nanoparticles together thus fabricating continuous gold stripes 5 micrometers in width and a few hundred nanometers in height. The scanning speed, the laser intensity, and the degree of defocusing are identified as important parameters to the successful manufacturing of the gold microstructures. The electrical resistivity of the stripes, within the parametric domain of the present work, is measured to be the order of 10−6 ohm-m.

Topics: Lasers
Commentary by Dr. Valentin Fuster
2004;():65-66. doi:10.1115/NANO2004-46041.

In the late 19th century, Edison observed electrical current flowing between hot and cold electrodes [1]. Since this discovery of thermionic emission, research has occurred with varying intensity in order to harness the simplicity and utility of the thermionic effect in power generation devices. Hatsopoulos and Gyftopoulos [2,3] provide details of the development of thermionic theory and practice. In general, thermionic power generation has not found widespread use, despite many inherent advantages over alternative power generation methods, because of material limitations that have precluded an attractive combination of power generation efficiency and capacity. This paper presents semiclassical and quantum models for the thermionic behavior of a newly developed class of materials, quantum wires, that may offer some promise in alleviating historic materials limitations of thermionic devices.

Commentary by Dr. Valentin Fuster
2004;():67-68. doi:10.1115/NANO2004-46059.

Thermal transport in thin film transistors (TFTs) composed of nanowires embedded in plastic substrates is considered. Random ensembles of intersecting and contacting wires embedded in a substrate are analyzed using Fourier theory. Heat generation due to self-heating is included. A finite volume scheme is used to obtain the temperature solutions in the wires and substrate. Temperature profiles in the ensemble are investigated as a function of wire number density, wire-contact Biot number as well as the Biot number for heat transfer to the substrate.

Commentary by Dr. Valentin Fuster
2004;():69-70. doi:10.1115/NANO2004-46066.

Nanoinks show great potential for patterning of surfaces in small scales. Further reduction of pattern size, however, is limited in current inkjet and other related deposition technologies. We present a method to overcome this problem and reduce the size of deposited nanoparticle suspension films by water induced dewetting of the nanoink film.

Commentary by Dr. Valentin Fuster
2004;():71-72. doi:10.1115/NANO2004-46080.

Low-dimensional nanostructures such as nanotubes, nanowires, and quantum dots are promising building blocks for electronic, optical, sensing, and energy conversion applications. For effective device design it is important to understand how the basic thermal properties of nanostructures differ from those of bulk materials. For example, the measured thermal conductivity of silicon nanowires [1] can be understood with a 3-dimensional dispersion relation [2] for diameters down to about 40 nm, although at 22 nm diameter the experiment and modeling diverge sharply.

Commentary by Dr. Valentin Fuster
2004;():73-77. doi:10.1115/NANO2004-46083.

We present results of a droplet placed on a controlled super-hydrophobic surface cooled underneath by a thermal electrical cooler to demonstrate quick change in contact angles from the Cassie composite contact state to the Wenzel wetting contact state. The measured contact angles are compared with the theoretical predictions of Cassie’s and Wenzel’s equations and found to be consistent. The actual details of the transition phenomena are observed under a microscope through a specially designed one-dimensional micro-channel with concaved structures at the two sidewalls. It is found that the temperature gradient enhanced mass transfer can cause a rapid condensation in the air-filled cavities, which is believed to be the possible mechanism to trigger the energy state transition and explain instabilities of super-hydrophobic surfaces at the Cassie state. The phenomenon of mass transport into micro and nanocavities is important in understanding the nature of nano-structured super-hydrophobic surfaces.

Commentary by Dr. Valentin Fuster
2004;():79-82. doi:10.1115/NANO2004-46084.

Dynamics of atoms around the interface of tip and substrate has close relationship to adhesive forces. This paper investigates the interactive behaviors by utilizing molecular dynamic (MD) simulation with the consideration of external applied electrostatic (ES) field between the atomic force microscopy (AFM) tip and substrate, which are both coated with gold. Morse potential was employed herein for modeling the energy between the atoms on the tip and substrate. The simulation model is composed of the gold-coated parts of the AFM tip and substrate, which are connected to the rest parts of the AFM tip and substrate, respectively, by the use of boundary conditions. The gold atoms were arranged in order according to face centric cubic (FCC) structure. The tip with the pyramidal shape was formed from 664 gold atoms while the substrate with cuboid shape was constructed from 2400 gold atoms. Simulation results show that both jump-to-contact interactions and the atom transfer increase as a result of enhancing the bias voltage between the tip and the substrate. The results agree well with experimental observation and also have the same trend as the experiment.

Commentary by Dr. Valentin Fuster
2004;():83-84. doi:10.1115/NANO2004-46085.

Controlled heating of nano-particles is a key enabling technology for various nano-manufacturing and biomedical applications. They include controlled fabrication of nano-particles,1 and targeted heating of biological molecules and cells for research as well as therapeutic purposes.2 Recent studies also demonstrated improved heat transfer properties of colloids of nano-particles.3

Commentary by Dr. Valentin Fuster
2004;():85-87. doi:10.1115/NANO2004-46090.

Surface tension prediction of liquid-vapor interfaces of polyatomic fluids using traditional methods in molecular dynamics simulations has shown to be difficult due to the requirement of evaluating complex intermolecular potentials even though these methods provide accurate predictions. In addition, the traditional methods may only be performed during a simulation run. However, analytical techniques have recently been developed that determine surface tension by using the characteristics of the density profile of the interfacial region between the bulk liquid and vapor regions. Since these characteristics are a standard result of many liquid-vapor interfacial region simulations, these data may be used in a post-simulation analysis. One such method, excess free density integration (EFEDI), provides results from the post-simulation analysis, but the expansion from monatomic to polyatomic fluids is not straightforward [1]. A more general and powerful approach to surface tension involves the application of a Redlich-Kwong-based mean-field theory [2], which has resulted in a single equation linking the surface tension of a fluid, σlv , with the density gradient at the center of the interfacial region,

σlv = 0.1065(1 − T / Tc)−0.34 Li2dρ⁁dzz=0 aR0NA2bRNAT1/2
    ln1 + ρ⁁lbRNA1 + ρ⁁vbRNA    (1)
where z is the position normal to the interfacial region and is zero at its center, ρ⁁l and ρ⁁v are the liquid and vapor molar densities, respectively, TC is the critical temperature, NA is Avogadro’s number, Li is a characteristic length given by
Li = kBTCPC1/3    (2)
and aR0 and bR are the coefficients in the Redlich-Kwong equation of state,
P = NkBTV − bRN − aR0N2T1/2V(V + bRN)    (3)
Furthermore, PC is the critical pressure for the fluid. Reference [2] shows that the relation provided by Equation 1 provides a approximate prediction of surface tension for argon fluid using data from molecular dynamics simulations. The derivation of Equation 1 is based on the assumption that the density profile in the interfacial region follows
ρ⁁ − ρ⁁vρ⁁l − ρ⁁v = 1e4z/δzi + 1    (4)
where δzi is the interfacial region thickness,. Note that Equation 4 is more commonly expressed in the equivalent form
ρ⁁(z) = 12(ρ⁁l + ρ⁁v) − 12(ρ⁁l − ρ⁁v)tanh2zδzi    (5)
Wemhoff and Carey [1] have recommended the use the fit curve relation given by Equation 5 for the liquid-vapor interfacial region of a diatomic nitrogen system. Therefore, Equation 1 may be used to predict the surface tension for diatomic nitrogen at various temperatures.

Commentary by Dr. Valentin Fuster
2004;():89-90. doi:10.1115/NANO2004-46091.

A self assembly process is characterized by the spontaneous and ordered aggregation of similar components. At the nanoscale, these constituents can be colloids, or other nanoparticles that combine to form structures of meso- and macroscopic dimensions. Self assembly is most evident during the growth of biological structures. Due to its natural elegance, there is considerable interest in investigating similar methods in other fields of sciences. In principle, the process of dynamic self assembly is characterized by a competition between at least two forces — one attractive and the other repulsive — in thermodynimacally nonequilibrium systems. Several researchers have described self assembly in configurations where biological [1] or chemical [2] mediation, electrostatic [3], capillary [4] or fluid dynamic [5] forces have provided a motive potential.

Commentary by Dr. Valentin Fuster
2004;():91-92. doi:10.1115/NANO2004-46092.

Zeolites (nanoporous crystalline aluminosilicates) have important applications in catalysis and separations [1,2], and are also being considered for adsorption-based heating and cooling systems [3]. We are investigating the use of zeolite films in the fabrication of more efficient adsorption heat pumping and refrigeration systems that use water vapor as the working fluid. The thermal conductivity of the adsorbent is an important property affecting heat transfer in an adsorption heat pumping system. There are few reports (e.g. [4]) of the thermal conductivity of zeolites, which is measured by compacting the zeolite powder into a disk sample and using a model to extract the ‘intrinsic’ thermal properties. Another approach [5] relies on molecular dynamics simulation using parameterized force fields to predict the intrinsic thermal conductivity.

Commentary by Dr. Valentin Fuster
2004;():93-94. doi:10.1115/NANO2004-46097.

Nanoscale metal films and electrodes are extensively used in today’s micro and nano electronics as well as nano mechanical systems. These metal structures are usually polycrystalline in nature with nano scale grains connected to each other by grain boundaries. The small size offers large grain boundary to volume ratio that is likely to affect the metal properties significantly. Here, we discuss the role of grain size and boundaries in determining the mechanical behavior of metals, such as elasticity and yielding.

Topics: Metals , Brittleness
Commentary by Dr. Valentin Fuster


2004;():95-96. doi:10.1115/NANO2004-46008.

In this paper, we describe using high transmission nanoscale apertures of C and H shapes for nanolithography applications. We demonstrate that these ridge apertures provide a highly localized and intense light spot that can be used in lithography experiments.

Commentary by Dr. Valentin Fuster
2004;():97-98. doi:10.1115/NANO2004-46021.

The scale decomposition of a multi-scale system into small-scale order domains will reduce the complexity of the system and will subsequently ensure a success in nanomanufacturing. A novel method of assembling individual carbon nanotube has been developed based on the concept of scale decomposition. Current technologies for organized growth of carbon nanotubes are limited to very small-scale order. The nanopelleting concept is to overcome this limitation by embedding carbon nanotubes into micro-scale pellets that enable large-scale assembly as required. Manufacturing processes have been developed to produce nanopellets, which are then transplanted to locations where the functionalization of carbon nanotubes are required.

Commentary by Dr. Valentin Fuster
2004;():99-100. doi:10.1115/NANO2004-46023.

As the next-generation technology moves below 100 nm mark, the need arises for a capability of manipulation and positioning of light on the scale of tens of nanometers. Plasmonic optics opens the door to operate beyond the diffraction limit by placing a sub-wavelength aperture in an opaque metal sheet. Recent experimental works [1] demonstrated that a giant transmission efficiency (>15%) can be achieved by exciting the surface plasmons with artificially displaced arrays of sub-wavelength holes. Moreover the effectively short modal wavelength of surface plasmons opens up the possibility to overcome the diffraction limit in the near-field lithography. This shows promise in a revolutionary high throughput and high density optical lithography. In this paper, we demonstrate the feasibility of near-field nanolithography by exciting surface plasmon on nanostructures perforated on metal film. Plasmonic masks of hole arrays and “bull’s eye” structures (single hole surrounded by concentric ring grating) [2] are fabricated using Focused Ion Beam (FIB). A special index matching spacer layer is then deposited onto the masks to ensure high transmissivity. Consequently, an I-line negative photoresist is spun on the top of spacer layer in order to obtain the exposure results. A FDTD simulation study has been conducted to predict the near field profile [3] of the designed plasmonic masks. Our preliminary exposure test using these hole-array masks demonstrated 170 nm period dot array patterns, well beyond the resolution limit of conventional lithography using near-UV wavelength. Furthermore, the exposure result obtained from the bull’s eye structures indicated the characteristics of periodicity and polarization dependence, which confirmed the contribution of surface plasmons.

Commentary by Dr. Valentin Fuster
2004;():101-102. doi:10.1115/NANO2004-46029.

Nanostructured materials are attractive candidates for advanced friction and wear-resistant coatings due to their potentially enhanced mechanical properties. We have developed a one-step method called hypersonic plasma particle deposition [1] to produce and deposit nanoparticles using a thermal plasma reactor. Particle synthesis is achieved by dissociating vapor phase reactants in the plasma, and quenching the hot gas in a supersonic nozzle expansion. Particles are deposited on a substrate by hypersonic impaction to form a film, or are deposited as micropatterns using a process called focused particle beam deposition [2]. In-situ particle size distribution measurements are performed using a sampling probe interfaced to an extraction/dilution system for measurement by a scanning electrical mobility spectrometer.

Commentary by Dr. Valentin Fuster
2004;():103-112. doi:10.1115/NANO2004-46040.

Advances in micromachining (MEMS) applications such as optical components, inertial and pressure sensors, fluidic pumps and radio frequency (RF) devices are driving lithographic requirements for tighter registration, improved pattern resolution and improved process control on both sides of the substrate. Consequently, there is a similar increase in demand for advanced metrology tools capable of measuring the Dual Side Alignment (DSA) performance of the lithography systems. There are a number of requirements for an advanced DSA metrology tool. First, the system should be capable of measuring points over the entire area of the wafer rather than a narrow area near the lithography alignment targets. Secondly, the system should be capable of measuring a variety of different substrate types and thicknesses. Finally, it should be able to measure substrates containing opaque deposited films such as metals. In this paper, the operation and performance of a new DSA metrology tool is discussed. The UltraMet 100 offers DSA registration measurement at greater than 90% of a wafer’s surface area, providing a true picture of a lithography tool’s alignment performance and registration yield across the wafer. The system architecture is discussed including the use of top and bottom cameras and the pattern recognition system. Experimental data is shown for tool performance in terms of repeatability and reproducibility over time. The requirements for tool accuracy and methods to establish accuracy to a NIST traceable standard are also discussed.

Commentary by Dr. Valentin Fuster
2004;():113-114. doi:10.1115/NANO2004-46053.

Chemically synthesized nanostructures such as nanowires1 , carbon nanotubes2 and quantum dots3 possess extraordinary physical, electronic and optical properties that are not found in bulk matter. These characteristics make them attractive candidates for building subsequent generations of novel and superior devices that will find application in areas such as electronics, photonics, energy and biotechnology. In order to realize the full potential of these nanoscale materials, manufacturing techniques that combine the advantages of top-down lithography with bottom-up programmed assembly need to be developed, so that nanostructures can be organized into higher-level devices and systems in a rational manner. However, it is essential that nanostructure assembly occur only at specified locations of the substrate and nowhere else, since otherwise undesirable structures and devices will result. Towards this end, we have developed a hybrid micro/nanoscale-manufacturing paradigm that can be used to program the assembly of nanostructured building blocks at specific, pre-defined locations of a chip in a highly parallel fashion. As a prototype system we have used synthetic DNA molecules and gold nanoparticles modified with complementary DNA strands as the building blocks to demonstrate the highly selective and specific assembly of these nanomaterials on lithographically patterned substrates.

Commentary by Dr. Valentin Fuster
2004;():115-116. doi:10.1115/NANO2004-46056.

A near-field optical technique, using a new type of solid immersion lens (SIL), has been developed and applied to various areas, for example, high-density optical storage, near-field-scanning-optical-microscope probes, photolithography. Solid immersion microscopy offers a method for achieving resolution below the diffraction limit in air with significantly higher optical throughput by focusing light through a high refractive-index SIL held close to a sample [1]. The minimum resolution of a focusing system is inversely proportional to numerical aperture (NA), where NA = n sinθ, θ is the maximum angle of incidence, and n is the index of refraction at the focal point. Light with vacuum wavelength λ can be focused by an aberration-free lens to a spot whose full width at half maximum (FWHM) is λ/(2 NA) in the scalar diffraction limit, equivalent to Sparrow’s criterion for spatial resolution. In a medium of refractive index n, the effective wavelength is λeff = λ/n and corresponding effective numerical aperture is NAeff = n2 sinθ. When a SIL is used, improvements in NAeff and spatial resolution are proportional to the refractive index of the SIL material. Fletcher et al. demonstrated imaging in the infrared with a microfabricated SIL [1, 2]. Baba et al. analyzed the aberrations and allowances for an aspheric error, a thickness error, and an air gap when using a hemispherical SIL for photoluminescence microscopy with submicron resolution beyond the diffraction limit [3]. Terris et al. developed and applied a SIL-based near-field optical technique for the writing and reading domains in a magneto-optic material [4]. Song et al. proposed the new concept of a SIL for high density optical recording using the near-field recording technology [5]. In this paper, we propose a sub-micron scale laser processing technique with spatial resolution beyond the diffraction limit in air using near-field optics. Our goal is to eventually develop a massively parallel nano-optical direct-write nano-manufacturing technique.

Topics: Optics , Lasers , Machining
Commentary by Dr. Valentin Fuster
2004;():117-118. doi:10.1115/NANO2004-46060.

The development of DNA sensors has attracted substantial research efforts. Such devices could be used for the rapid identification of pathogens in humans, animals, and plant; in the detection of specific genes in animal and plant breeding; and in the diagnosis of human genetic disorders. The first step to fabricate the DNA sensors is the probe immobilization on the suitable substrate. Traditionally, the DNA probes are spotted on the substrate while the technique hardly controlled the small pattern and surface density of DNA probes. The main challenge here is to achieve probe layer uniformity and the nature of the probe layer itself in few micron and sub-micron feature range.

Topics: Printing , DNA
Commentary by Dr. Valentin Fuster
2004;():119-120. doi:10.1115/NANO2004-46067.

We present a hybrid nano-electromechanical system for study of the mechanics of nanostructures. The system has a testing platform based on a deep reactive ion-etched high aspect ratio MEMS device. A new approach has been developed with top-down manufacturing of the micro-device and bottom-up post-fabrication assembly of samples (nanostructures) to be tested. A process that minimizes chemical or physical damage of the sample is used to integrate suspended nanowires/nanotubes into the system. The system provides nanoscale resolution of displacement and force. The device is used in an SEM and is being tested for in situ experiments on various nanowires or nanotubes.

Commentary by Dr. Valentin Fuster
2004;():121-123. doi:10.1115/NANO2004-46072.

This paper reports the development of an apparatus, technique, and method for calibrating the field emission phenomena’s dependence on both the voltage applied between the anode and cathode and the electrodes gap. A precise knowledge of the electrodes gap is required for calibrating field emitters. The I-V characteristic of isolated carbon nanotube field emitter is a strong function of the electrodes gap distance. A consolidated IV curve is obtained by calculating the current density and the local electric field with the field enhancement factor taken into consideration. The field enhancement factor and emitting area are unique for each electrodes gap distance. We also found that the turn-on voltage decreases as the electrodes gap distance decreases.

Commentary by Dr. Valentin Fuster
2004;():125-126. doi:10.1115/NANO2004-46074.

The manufacture of nanoscale devices is at present constrained by the resolution limits of optical lithography and the high cost of electron beam lithography. Furthermore, traditional silicon fabrication techniques are quite limited in materials compatibility and are not well-suited for the manufacture of organic and biological devices. One nanomanufacturing technique that could overcome these drawbacks is dip pen nanolithography (DPN), in which a chemical-coated atomic force microscope (AFM) tip deposits molecular ‘inks’ onto a substrate [1]. DPN has shown resolution as good as 5 nm [2] and has been performed with a large number of molecules, but has limitations. For molecules to ink the surface they must be mobile at room temperature, limiting the inks that can be used, and since the inks must be mobile in ambient conditions, there is no way to stop the deposition while the tip is in contact with the substrate. In-situ imaging of deposited molecules therefore causes contamination of the deposited features.

Topics: Nanolithography
Commentary by Dr. Valentin Fuster
2004;():127-128. doi:10.1115/NANO2004-46075.

Over the last two decades, a variety of micro-robotic systems have been developed including electrothermal, electrostatic, electrochemical, piezoelectric, and electromagnetic actuators based on MEMS technology. The development of these micro-actuators promises a revolution in biological and medical research and applications analogous to that brought about by the miniaturization of electrical devices in information technology. For example, controllable manipulation of these tiny actuators may enable precise temporal and spatial delivery of chemicals, micro-optics or microelectronics to specific targeted sites.

Commentary by Dr. Valentin Fuster
2004;():129-130. doi:10.1115/NANO2004-46098.

Transition metal carbides are an interesting class of electronic materials owing to their high electrical conductivity at room temperature, which is only slightly lower than that of their constituent transition metal elements. For example, the room temperature electrical resistivity of bulk Mo2 C is ∼70 μΩ-cm compared to that of Mo (4.85 μΩ-cm), whereas that of NbC is ∼50 μΩ-cm as compared to 15.2 μΩ-cm for Nb. Indeed, the temperature dependent resistivity of many transition metal carbides suggests metallic-like conduction. Furthermore, certain transition metal carbides are known to become superconducting, with transition temperatures ranging from 1.15 °K for TiC1−x to 14 °K for NbC. [1] They are also able to withstand high temperatures and are chemically stable. Initial synthesis of metal carbide nanorods was demonstrated using the carbon nanotube (CNT) confined reaction mechanism by Lieber and co-workers [2] and subsequent superconducting behavior was shown by Fukunaga et al. [3]. Vapor-liquid-solid growth was employed by Johnson et al. [4] to synthesize micron-sized carbide whiskers. Here, we have successfully synthesized Mo2 C nanorods and ribbons on Si substrates using a novel two-step catalytic approach, which allows for synthesis of such high temperature nanostructures at manufacturable temperatures (≤ 1000 °C) and time scales (≤ 60 min). In the first step we utilize a catalytic vapor phase process to grow Mo and/or molybdenum oxide nanostructures, which are subsequently carburized in situ to form the desired Mo2 C nanostructures. Unlike true VLS growth of carbides, in which high temperature (≤ 1100–1200 °C) is required to adequately dissolve carbon into the catalyst particles, our strategy is to react the nanostructures along their entire length with a carbon vapor source after creating the oxide/metal nanostructures, which for Mo2 C can be achieved at relatively low temperatures. (≤ 1000 °C). The nanorods and ribbons are polycrystalline, with a mean grain size of 20–50 nm and 50–150 nm, respectively. We hypothesize that the growth mechanism is a complex mixture of VLS, VSS, and auto-catalytic growth, in which molten catalyst nanoparticles enter a three phase region once the metal precursor is supplied. The growth then presumably continues via a vapor-solid-solid process and is possible assisted by the presence of various molybdenum oxide species on the surface. Initial single nanowire electrical measurements yield a higher resistivity than in the bulk, which is attributed to the fine grain sizes and/or the presence of an oxide layer. A discussion of the growth mechanism will be presented along with issues relating to single nanowire device fabrication and control of nanowire orientation.

Topics: Vapors , Nanowires
Commentary by Dr. Valentin Fuster

General Topics in Nano Science and Engineering

2004;():131-132. doi:10.1115/NANO2004-46024.

This paper discusses the use and creation of virtual reality based models and information oriented process models related to the study of Nanomanufacturing. EML, (which is an evolving language), was originally proposed [1] to enable the capture of information rich contexts at various levels of the manufacturing levels. In this paper, the use of EML models as a basis for describing and analyzing nano manufacturing processes will be described; their subsequent use in the creation of simulation models is also discussed. A framework for analysis, reasoning and simulation is proposed which includes a virtual reality based simulation module. Our experience in using VRML 2.0 (Virtual Reality Modeling Language) for the creation of such virtual reality environments will also be addressed.

Commentary by Dr. Valentin Fuster
2004;():133-134. doi:10.1115/NANO2004-46043.

Carbon microelectromechanical systems (C-MEMS) and carbon nanoelectromechanical system (C-NEMS) have received much attention because of the many potential applications. Some important applications include: DNA arrays, glucose sensors, microbatteries and biofuel cells. Microfabrication of carbon structures using current processing technology, including focused ion beam (FIB)1 and reactive ion etching (RIE)2 , is time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as widely varying properties of the resulting devices limits the use of screen printing of commercial carbon inks for C-MEMS. Our newly developed C-MEMS microfabrication technique is based on the pyrolysis of photo patterned resists34 . Figure 1(a) shows a typical SEM image of C-MEMS/NEMS features with carbon posts connected by carbon fibers. Figure 1(b) shows a typical carbon post with carbon nanofibers on its side surfaces.

Commentary by Dr. Valentin Fuster
2004;():135-137. doi:10.1115/NANO2004-46062.

In this paper, we introduce a novel methodology to determine the size and structure of nano-particles on a surface. We present an analysis, dubbed Elliptically Polarized Surface-Wave Scattering (EPSWS) approach, to show that 5–10 nm size particles on or above an interface can be characterized by using the scattered surface plasmon (SP) or evanescent waves. We present an analysis to show that the scattering matrix elements of the evanescent waves scattered by the nano-particles on or near an interface can be used for characterization of nano-size particles.

Commentary by Dr. Valentin Fuster
2004;():139-146. doi:10.1115/NANO2004-46087.

Analytical analysis of fluid flow in cylindrical microchannels subjected to uniform wall injection at various Reynolds numbers is presented. The classical Navier-Stokes equations are used in the present study. Mathematically, using an appropriate change of variable, Navier-Stokes equations are transformed to a set of nonlinear ordinary differential equations. The governing equations are solved analytically using series solution method. The presented analytical results can be used for the prediction of velocity profiles and pressure drops in the cylindrical micro channels. The results are validated against available data in the literature and have shown good agreement.

Commentary by Dr. Valentin Fuster

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