Session P15: Instrumentation for Nanoscale Science

Triaxial AFM Contact-Free Tweezers

We present a triaxial atomic force microscope contact-free tweezer (TACT) capable of controlled assembly of nanoparticles suspended in a liquid[1]. The TACT uses negative dielectrophoresis to trap a single nanoparticle at the tip of an AFM so it can be positioned on a substrate. The ``sticky finger'' problem of irreversible adhesion to any surface is overcome by holding the nanoparticle away from the tip in the zero of an electric field created by the electrodes at the tip. The trap is size-matched to the nanoparticle to ensure that only one nanoparticle is held at a time. We present initial experiments and simulations that explore the potential of the TACT. Analysis of the model system of a silicon semiconductor nanoparticle suspended in water shows that single nanoparticle trapping and placement is possible. We propose methods to use the TACT for the controlled assembly of single semiconductor quantum dots, semiconductor nanowires, carbon nanotubes, and biological molecules. \\[4pt] [1] K.A. Brown and R.M. Westervelt, Nanotechnology \textbf{20}, 385302 (2009).   

Nanobits, Nembranes and Micro Four-Point Probes: Customizable Tools for insitu Manipulation and Characterisation of Nanostructures

We present a range of highly adaptable microtools for direct interaction with nanoscale structures; (i) semiautomatic pick-and-place assembly of multiwalled carbon nanotubes onto cantilevers for high-aspect ratio scanning probe microscopy, using electrothermal microgrippers inside a SEM. Topology optimisation was used to calculate the optimal gripper shape defined by the boundary conditions, resulting in 10-100 times better performance. By instead pre-defining detachable tips using electron beam lithography, free-form scanning probe tips (Nanobits) can be mounted in virtually any position on a cantilever; (ii) scanning micro four point probes allow fast, non- destructive mapping of local electrical properties (sheet resistance and Hall mobility) and hysteresis effects of graphene sheets; (iii) sub 100 nm freestanding devices with wires, heaters, actuators, sensors, resonators and probes were defined in a 100 nm thin membrane with focused ion beam milling. By patterning generic membrane templates (Nembranes) the fabrication time of a TEM compatible NEMS device is effectively reduced to less around 20 minutes.   

Atomic Force Controlled Capillary Electrophoresis

Lithography based on scanning probe microscopic techniques has considerable potential for accurate {\&} localized deposition of material on the nanometer scale. Controlled deposition of metallic features with high purity and spatial accuracy is of great interest for circuit edit applications in the semiconductor industry, for plasmonics {\&} nanophotonics and for basic research in surface enhanced Raman scattering {\&} nanobiophysics. Within the context of metal deposition we will review the development of fountain pen nanochemistry and its most recent emulation Atomic Force Controlled Capillary Electrophoresis (ACCE). Using this latter development we will demonstrate achievement of unprecedented control of nanoparticle deposition using a three-electrode geometry. Three electrodes are attached: one on the outside of a metal coated glass probe, one on the inside of a hollow probe in a solution containing Au nanoparticles in the capillary, and a third on the surface where the writing takes place. The three electrodes provide electrical pulses for accurate control of deposition and retraction of the liquid from the surface overcoming the lack of control seen in both dip pen lithography {\&} fountain pen nanochemistry when the tip contacts the surface. With this development, we demonstrate depositing a single 1.3 nm Au nanoparticle onto surfaces such as semiconductors.   

Electron Beam Crosslinked Au-nanoparticle Films for Sensor Array Patterning

We have fabricated chemiresistors, arranged in a 2x2 array with 4 $\mu $m spacing between the sensors, for use in a micro-gas chromatography ($\mu $-GC) system. To discriminate between analytes, each sensor should be coated with a different thiol coated Au-nanoparticle film. Due to their close spacing, it is not possible to pattern the sensors with different films with traditional film coating methods. Electron beam exposure crosslinks the nanoparticles and renders the film insoluble, and it possible to selectively expose a single sensor in an array. After crosslinking, the remaining film can be rinsed away leaving one coated sensor. This process can be repeated for different films until all sensors in the array have a distinct coating. Using this technique we have made the smallest chemiresistor array with four different films to date. The sensors were characterized by four volatile organic compounds and exhibit different response patterns making them suitable for $\mu $-GC applications.   

Greenhouse Gas Sensing Properties of ZnO Nanorods

We report on the sensing properties of electrochemically deposited zinc oxide (ZnO) nanorod films. The interaction between methane and the ZnO nanorods causes a drop in the resistivity depending on the methane concentration. We will present our first results for ZnO nanorods grown on different substrates and operated between 150 $^{\circ}$C and 300 $^{\circ}$C. Our first measurement indicate a sensitivity for methan of better than 0.1{\%}. The ZnO nanosensor characterization was carried out by using bulk X-ray diffraction (XRD) and by scanning electron microscopy (SEM).   

Novel solid-state nuclear detectors based on defect-free crystalline $\alpha $-HgI$_{2}$ nanowires synthesized at diffusion controlled conditions

Solid-state detectors are based on semiconductors materials that directly convert X-Ray or Gamma-Ray photons in hole-electron pair with sufficient mobility to produce electric current. HgI$_{2}$ is a very large band-gap semiconductor material able to operate at room-temperature (RT) under ideal conditions provide by perfect crystallinity. Crystals of $\alpha $-HgI$_{2}$ were proposed as the perfect detector material due to its large seminsulating band-gap and large stopping power. Although HgI$_{2}$ crystals of good quality and large size have been grown, their commercial use is reduced because the crystalline quality degrades during the processes for fabrication of devices. Trapping defects are created and no fabrication method has been found to circumvent the problem in a systematic and reproducible manner. Based on our capability to synthesized defect-free crystalline HgI$_{2}$ nanoneedles inside porous matrix we are proposing to fabricate detectors that will not require manipulation of the HgI$_{2}$ crystals and, therefore, will not suffer degradation and the associated lack of performance. Fundamental understanding, control and application for the fabrication of these detectors will be studied in the context of preparation and synthesis of HgI$_{2}$ nanostructures in the porous matrix.   

Probing the SERS Gap Dependence Through Controlled Nanoparticle Positioning

Since its first observation in 1970, surface enhanced Raman scattering (SERS) has been regarded as a promising new tool in the field of sensing technology. Unfortunately, reproducibility issues have made it difficult for scientists to devise experiments that accurately characterize the SERS enhancement factor. The key to this problem lies in the ability to elicit control over the small nanostructure spacings required to attain large enhancement factors. Previous theoretical studies have determined that the SERS enhancement is extremely sensitive to the spacing between features, decreasing at a rate of approximately one order of magnitude per nanometer of separation and disappearing almost entirely for spacings greater than 5 nm. In this research, we present a facile method to regulate this spacing on the sub-5 nm level that utilizes the stretching properties of an elastomeric substrate. By building our nanostructures on a flexible substrate and varying the amount of strain applied, nanostructures can be moved relative to one another with the precision necessary to study this effect.   

Automated Crystal Orientation and Phase Mapping of Nanocrystals in a Transmission Electron Microscope

An automated technique for the crystal phase and orientation mapping of polycrystalline materials in a transmission electron microscope has been developed [1]. This technique is based on template matching of experimental electron diffraction spot patterns to their pre-calculated theoretical counterparts. Precession of the primary electron beam around the optical axis of the microscope during the recording of the diffraction patterns improves the reliability of this technique significantly. Promising results have so far been obtained with this technique for precipitates in heavily deformed austenitic stainless steels [1] and ensembles of iron-oxide nanocrystals [2]. \\[4pt] [1] E. Rauch et al. \textit{Microscopy and Analysis}, Issue \textbf{93}, November 2008, S5-S8 \\[0pt] [2] P. Moeck et al., \textit{Mater. Res. Soc. Proc. Vol.} \textbf{1184}, paper 1184-GG03-07 (2009)   

Structural Fingerprinting of Nanocrystals in the Transmission Electron Microscope

Three novel strategies for the structurally identification of nanocrystals in a transmission electron microscope are presented. Either a single high-resolution transmission electron microscopy image [1] or a single precession electron diffractogram (PED) [2] may be employed. PEDs from fine-grained crystal powders may also be utilized. Automation of the former two strategies is in progress and shall lead to statistically significant results on ensembles of nanocrystals. Open-access databases such as the Crystallography Open Database which provides more than 81,500 crystal structure data sets [3] or its mainly inorganic and educational subsets [4] may be utilized. [1] http://www.scientificjournals.org/journals 2007/j{\_}of{\_}dissertation.htm [2] P. Moeck and S. Rouvimov, in: \textit{Drugs and the Pharmaceutical Sciences}, Vol. 191, 2009, 270-313 [3] http://cod.ibt.lt, http://www.crystallography.net, http://cod.ensicaen.fr, http://nanocrystallography.org, http://nanocrystallography.net, http://journals.iucr.org/j/issues/2009/04/00/kk5039/kk5039.pdf [4] http://nanocrystallography.research.pdx.edu/CIF-searchable   

Quality assessment of samples by in-air Ion-Tracked Transmission Ion Microscopy

The need for sample quality assessment exists in many fields. An ion-tracked transmission ion microscope (ITTIM) will fulfill one such need -- the nondestructive monitoring of changes in sample areal density. A simplified low-cost ITTIM technology demonstrator will be constructed. Known thickness variations in aluminum thin foil samples will be mapped with the ITTIM. The aluminum samples will then be stressed to impart changes in the areal density and remapped. Detected changes in areal density maps between the unstressed and stressed conditions for each foil will demonstrate the usefulness of and limits to the ITTIM. Applications in materials research, biology and other areas will be explored as time permits.   

A versatile membrane-based calorimeter for studies of sub-microgram samples

We present a differential nanocalorimeter for milligram to sub-microgram samples as well as deposited thin films. The device is based on two free-standing SiN membranes that, combined with thin film heaters and temperature sensors, give a background heat capacity $<$ 200 nJ/K at 300 K, decreasing to sub-nJ/K at 10 K. The device has several unique features. i) In differential mode, used for small samples, the background at room temperature is reduced to 2 nJ/K. ii) The thermometers made of AuGe have high sensitivity, $d\ln T/d\ln R\approx-1$, for the entire temperature range down to 1 K. iii) The sample is placed in direct contact with the thermometer which is allowed to self-heat, and can thus be operated at high DC current to increase the resolution. iv) Data are acquired with a set of 8 synchronized lock-in amplifiers measuring DC, $1^{st}$ and $2^{nd}$ harmonic signals of heater powers and temperature oscillations with combined good absolute accuracy and high resolution. The design allows concurrent use of AC state steady and relaxation methods for general studies of specific heat, latent heat and dynamic heat capacity.   

Operation of Nanoelectromechanical Sensors in Damping Fluid Environment

The quality factor of these devices is strongly influenced by environment that directly impacts their sensitivity and performance, which is particularly important for biosensing and medical applications. To shed a light on this problem, we present a comprehensive study of nanomechanical sensor resonators submerged in the damping environment of three gases (He, N2, CO2), and one liquid (CO2). Resonant dynamics, in multiple devices of varying size (0.15-3 $\mu$m) and frequency (10-350 MHz) over 10 decades of pressure (from 1 mPa to 20 MPa), is measured using a specially built gas pressurization optical chamber and real time-domain stroboscopic optical interferometry. The wide pressure range allows full exploration of the regions of validity of Newtonian and non- Newtonian flow damping models. Observing free molecular flow behavior extending above atmospheric pressure, we find a fluid relaxation time model to be valid throughout, but not beyond, the non-Newtonian regime, and a Newtonian flow vibrating spheres model to be valid in the viscous limit.   

Nano-Position Sensors with Superior Linear Response to Position and Dynamic Range from Sub-nm to Centimeters

Commercial nano-positioners have achieved direct position measurements at the scale of 0.01 nm with capacitive sensing metrology. However, the commercial sensors have small dynamic ranges (up to only a few hundred $\mu $m) and are relatively large in size (centimeters in the transverse directions), which is necessary for healthy signal detections but making it difficult to use on smaller devices. The small dynamic range also limits its applications in which large materials (on the scale of centimeters or greater) are handled with needs of sub-nm resolutions. What has been done in the past is to combine the fine and coarse position sensors with different dynamic ranges to cover the required dynamic range. In this paper, we present a novel capacitive position sensing metrology with ultra-wide dynamic range from sub-nm to literally any practically desired length for a translation stage. This sensor will greatly simplify the task and enhance the performance of direct metrology in a hybrid translational stage covering translation tasks from sub-nm to centimeters.   

Optimizing Bismuth Hall Probe Performance

Scanning Hall probe microscopy is a quantitative magnetic imaging technique that combines high spatial resolution with high flux sensitivity, occupying a unique niche in magnetic microscopy [S.J. Bending, Adv. Phys. \textbf{48}, 449 (1999)]. Hall sensors are useful in studying materials with microscopic or nanoscale magnetic structures, like high temperature superconductors and magnetic thin films. Development of conventional semiconductor Hall sensors has run into charge depletion and excess noise problems. Sandhu recently introduced bismuth Hall probes in an effort to avoid these effects [A. Sandhu \textit{et al}. Jpn. J. Appl. Phys. \textbf{40}, L524 (2001)]. The bismuth probes lack a good model to optimize their performance. I will propose a refinement of the current model with an increased emphasis on material parameters that can be more intuitively manipulated. I will compare the spatial and flux resolution predicted by the refined model with those of my nanoscale bismuth Hall sensors at different dopings.   

Crystallographic Image Processing Software for Scanning Probe Microscopists

Following the common practice of structural electron crystallography, scanning probe microscopy (SPM) images can be processed ``crystallographically'' [1,2]. An estimate of the point spread function of the SPM can be obtained and subsequently its influence removed from the images. Also a difference Fourier synthesis can be calculated in order to enhance the visibility of structural defects. We are currently in the process of developing dedicated PC-based software for the wider SPM community. \\[4pt] [1] P. Moeck, B. Moon Jr., M. Abdel-Hafiez, and M. Hietschold, Proc. NSTI 2009, Houston, May 3-7, 2009, Vol. I (2009) 314-317, (ISBN: 978-1-4398-1782-7). \\[0pt] [2] P. Moeck, M. Toader, M. Abdel-Hafiez, and M. Hietschold, Proc. 2009 International Conference on Frontiers of Characterization and Metrology for Nanoelectronics, May 11-14, 2009, Albany, New York, \textbf{\textit{Best Paper Award}}