Scanning Probe Instruments Research Articles

Advances in dry low-temperature scanning probe microscopy system development

Since the beginning of the 21st century, Scanning Probe Microscopy (SPM) has played an increasingly important role in the fields of micro- and nanoscale surface characterization, physical property measurement, and micro/nano fabrication. To provide a more stable operating environment and higher energy resolution for SPM, researchers have developed Low-Temperature Scanning Probe Microscopy (LT-SPM) systems that operate under ultra-high vacuum and low temperature conditions. Currently, most LT-SPM systems achieve temperatures around 4.2 K by supplying liquid helium-4 (<sup>4</sup>He) to continuous flow cryostats or low-temperature Dewars. However, due to the low natural abundance of <sup>4</sup>He and its rising demand, the price of liquid helium has surged dramatically, severely impacting the normal operation of <sup>4</sup>He-based low temperature equipment. To address this issue, dry (cryogen-free) refrigeration technology has emerged as a promising alternative for next-generation low-temperature systems. In this context, the integration of dry refrigeration technology with SPM to construct DRY-LT-SPM systems has become a key research focus in the field of scanning probe instruments.<br>This paper mainly discusses several reported closed-cycle DRY -LT-SPM systems, focusing on aspects such as system design, refrigeration schemes, vibration reduction methods, and overall performance. Finally, the paper summarizes the current challenges and issues faced by DRY -LT-SPM systems and explores potential future developments in this field.

Electronic effects and fundamental physics studied in molecular interfaces.

Scanning probe instruments in conjunction with a very low temperature environment have revolutionized the ability of building, functionalizing, and analysing two dimensional interfaces in the last twenty years. In addition, the availability of fast, reliable, and increasingly sophisticated methods to simulate the structure and dynamics of these interfaces allow us to capture even very small effects at the atomic and molecular level. In this review we shall focus largely on metal surfaces and organic molecular compounds and show that building systems from the bottom up and controlling the physical properties of such systems is no longer within the realm of the desirable, but has become day to day reality in our best laboratories.

Synthesis and Characterization of Cobalt Doped Lysine Carbon Nanotubes

Carbon nanotubes are fascinating electronic material with unique physical properties and many important potential applications. Due to various applications of CNTs it is necessary to develop new methods for the synthesis of CNTS. In this chemical method, complexes of transition metal Co (II) with amino acid present in egg albumin have been synthesized. The complex so formed, is analyzed on the basis of spectroscopic method using, IR and NMR spectra confirms the lysine cobalt metal ion complex. The lysine cobalt metal ion complex is decomposed at higher temperature using muffle furnace to get metal carbon nanotubes. These metal carbon nanotubes are characterized using scanning probe instruments like AFM and DLS and X- RD.

Multifunctional cantilever-free scanning probe arrays coated with multilayer graphene

Scanning probe instruments have expanded beyond their traditional role as imaging or "reading" tools and are now routinely used for "writing." Although a variety of scanning probe lithography techniques are available, each one imposes different requirements on the types of probes that must be used. Additionally, throughput is a major concern for serial writing techniques, so for a scanning probe lithography technique to become widely applied, there needs to be a reasonable path toward a scalable architecture. Here, we use a multilayer graphene coating method to create multifunctional massively parallel probe arrays that have wear-resistant tips of uncompromised sharpness and high electrical and thermal conductivities. The optical transparency and mechanical flexibility of graphene allow this procedure to be used for coating exceptionally large, cantilever-free arrays that can pattern with electrochemical desorption and thermal, in addition to conventional, dip-pen nanolithography.

Automated Scanning Probe Lithography with n-Alkanethiol Self-Assembled Monolayers on Au(111): Application for Teaching Undergraduate Laboratories

Controllers for scanning probe instruments can be programmed for automated lithography to generate desired surface arrangements of nanopatterns of organic thin films, such as n-alkanethiol self-assembled monolayers (SAMs). In this report, atomic force microscopy (AFM) methods of lithography known as nanoshaving and nano-grafting are used to write nanopatterns within organic thin films. Commercial instruments provide software to control the length, direction, speed, and applied force of the scanning motion of the tip. For nanoshaving, higher forces are applied to an AFM tip to selectively remove regions of the matrix monolayer, exposing bare areas of the gold substrate. Nanografting is accomplished by force-induced displacement of molecules of a matrix SAM, followed immediately by the surface self-assembly of n-alkanethiol molecules from solution. Advancements in AFM automation enable rapid protocols for nanolithography, which can be accomplished within the tight time restraints of undergraduate laboratories. Example experiments with scanning probe lithography will be described in this report that were accomplished by undergraduate students during laboratory course activities and research internships in the chemistry department of Louisiana State University. Students were introduced to principles of surface analysis and gained “hands-on” experience with nanoscale chemistry.

Atomic force acoustic microscopy for quantitative nanomechanical characterization

Abstract Atomic force acoustic microscopy is an interesting measurement technique for characterization and mapping of local elastic properties of different materials, taking advantage of high lateral resolutions typical of scanning probe instruments. The present work discusses applicability of the technique and the main factors to be considered for exploitation of quantitative measurements. Particular attention is given to the influence of tips and to the role of calibration. Investigations and comparison with nanoindentation technique are eventually reported on different samples produced by means of plasma enhanced chemical vapour deposition technique (PECVD).

Scanning Probe Evolution in Biology

Twenty years ago the first scanning probe instrument, the scanning tunneling microscope, opened up new realms for our perception of the world. Atoms that had been abstract entities were now real objects, clearly seen as distinguishable individuals at particular positions in space. A whole family of scanning probe instruments has been developed, extending our sense of touching to the scale of atoms and molecules. Such instruments are especially useful for imaging of biomolecular structures because they can produce topographic images with submolecular resolution in aqueous environments. Instruments with increased imaging rates, lower probe-specimen force interactions, and probe configurations not constrained to planar surfaces are being developed, with the goal of imaging processes at the single-molecule level-not only at surfaces but also within three-dimensional volumes-in real time.

Coated pipe interior surface roughness as measured by three scanning probe instruments

The objectives of this study were to determine: the type of coating that minimized pipe surface roughness and how the choice of metrological instrument could influence pipe surface roughness data. The internal surface of pipe was coated with either phenolic, modified novalac, epoxy, or nylon material. Roughness of coated pipe was assessed with two linear surface profilers, a Dektak3ST® and a Hommel T1000, and a Dimension 3000® atomic force microscope (AFM). Arithmetic roughness (Ra), root mean square roughness (Rq), and mean peak‐to‐valley height (RZD), were statistically analyzed. The ability of RZD to focus on the extremes of height and depth on the surface made it a significant parameter for detecting features that would affect fluid flow in pipes.

Efficient Replication of Nanostructured Surfaces

The defined fabrication of nanostructures on surfaces for the nanosciences today largely relies on tools such as scanning probe instruments or electron- and ion beam systems that are serial writing processes. For future production of components and devices, in particular if large nanostructured areas are needed, parallel processes, which are fast and cost-effective, have to be developed. In this paper we review the possibilities for the replication of nanostructures on surfaces using moulding of thermoplastic polymer materials. Using hot embossing, it has been shown that structures below 10 nm can be reproduced reliably and with a high fidelity using laboratory equipment. Mass fabrication of nanostructured components can be achieved using thermal injection moulding with cycle times in the order of 10 sec.

Surface modification with self-assembled monolayers for nanoscale replication of photoplastic MEMS

A release technique that enables to lift microfabricated structures mechanically off the surface without using wet chemistry is presented. A self-assembled monolayer of dodecyl-trichlorosilane forms a very uniform /spl sim/1.5-nm-thick anti-adhesion coating on the silicon dioxide surface, on full wafer scale. The structural layers are formed directly onto the organic layer. They consist here of a 100-nm-thick aluminum film and a high-aspect ratio photoplastic SU-8 structure. After the microfabrication the structure can be lifted off the surface together with the aluminum layer. This generic technique was used to make a variety of novel structures. First, aluminum electrodes that are embedded in plastic are made using lithography, etching and surface transfer techniques. Second, using a patterned monolayer as defined by microcontact printing, resulted in a spatial variation of the surface adhesion forces. This was used to directly transfer the stamped pattern into a metal structure without using additional transfer etching steps. Third, the monolayer's ability to cover surface features down to nanometer scale was exploited to replicate sharp surface molds into metal coated photoplastic tips with /spl sim/30-nm radii for use in scanning probe instruments such as near-field optical techniques. The advantage compared to standard sacrificial layer techniques is the ability of replication at the nanoscale and the absence of etchants or solvents in the final process steps.

Status and future aspects in nanoscale surface inspection of ferroics by scanning probe microscopy

The unbroken need of nanoscale characterisation methods for ferroelectric and ferroelastic materials unambiguously points towards the use and implementation of scanning probe instruments (SPM). This article clearly summarises the actual possibilities of addressing scanning force microscopy (SFM) in order to measure distinct surface properties like the surface chemical constitution, the surface polarisation making up the internal and external electric field, the 3-dimensional polarisation distribution, the switching properties, etc. We point out which method is best suited in order to unambiguously record the desired property. Then future trends in nanoscale surface and bulk inspection with SPM are formulated.

Inspection and Manipulation of Ferroelectrics on the Nanometer Scale

AbstractThe increasing interest in scanning probe instruments (SPM) stems from the outstanding possibilities in measuring electric, magnetic, optical, and structural properties of surfaces and surface layers down to the molecular and atomic scale. For the inspection of ferroelectric materials both the scanning force microscope (SFM) and the scanning near-field optical microscope (SNOM) are promising techniques revealing information on the polarization vector and the electric field induced stress within a crystal. Polarization sensitive modes are discussed as is friction force microscopy, dynamic force microscopy (DFM) and voltage modulated SFM. From these measurements, 180° domain walls (c-domains) are resolved down to 4 nm, while 3-dimensional polarization mapping in ferroelectric BaTiO3 ceramics reveals a 25 nm resolution. On the other hand, non-contact DFM measurements in ultra-high vacuum are able to resolve ferroelectric surfaces down to the atomic scale. Then also the chemical heterogeneity at the sample surface is differentiated from ferroelectric domains down to a 5 nm lateral resolution, taking advantage of the short range chemical forces. SNOM in contrast probes the optical properties of ferroelectric crystals both in transmission and reflection. Here image contrast arises from changes in the refractive index between different domains as well as at domain walls. In addition, SPM instruments are used for the local modification of ferroic samples by applying a relatively high voltage pulse to the SPM tip. Domains with diameters down to 30 nm are thus created with the size depending on both the switching and material parameters.

Scanning-probe-based science and technology.

Scanning-probe-based science and technology.

Active vibration control and actuation of a small cantilever for applications in scanning probe instruments

Abstract The deflection control of a small cantilever is described, which operates using a single active piezoelectric element and optical vibration sensing, so that unwanted vibrations in the cantilever are removed, and yet it remains possible to deflect the cantilever statically or dynamically as required. Such a control system is directly applicable to the very small cantilevers found in scanning probe microscopes, such as atomic force and magnetic force microscopes, the resolution of which is limited by unwanted vibration.

Prospects for scanned-probe microscopy

In the last 50+ years the electron microscope and allied instruments have led the way as means to acquire spatially resolved information about very small objects. For the material scientist and the biologist both, imaging using the information derived from the interaction of electrons with the objects of their concern, has had limitations. Material scientists have been handicapped by the fact that their samples are often too thick for penetration without using million volt instruments. Biologists have been handicapped both by the problem of contrast since most biological objects are composed of elements of low Z, and also by the requirement that sample be placed in high vacuum. Cells consist of 90% water, so elaborate precautions have to be taken to remove the water without losing the structure altogether. We are now poised to make another leap forwards because of the development of scanned probe microscopies, particularly the Atomic Force Microscope (AFM). The scanning probe instruments permit resolutions that electron microscopists still work very hard to achieve, if they have reached it yet. Probably the most interesting feature of the AFM technology, for the biologist in any case, is that it has opened the dream of high resolution in an aqueous environment. There are few restrictions on where the instrument can be used. AFMs can be made to work in high vacuum, allowing the material scientist to avoid contamination. The biologist can be made happy as well. The tips used for detection are made of silicon nitride,(Si3N4), and are essentially unaffected by exposure to physiological saline (about which more below). So here is an instrument which can look at living whole cells and at atoms as well.

Stm at High Temperature: What you see is what you see … usually

Abstract There remains two basic axioms of all microscopists: the first….if you look, you're bound to see something, and the second….not everything you will see is artifact. These axioms apply particularly well to scanning probe microscopy at the molecular and atomic level. Fortunately, coarser resolution images share comforting similarities with images from other established scanning methods. Holes in optical discs look like holes when probed with AFM tips, and these holes look very much like SEM images, a subject with which we have some familiarity. At the molecular and atomic level, however, the scanning probe instruments may or may not be “seeing” the sample, though they are clearly seeing something. Comparison of surface structure observed with indirect surface structural measurements, for example by LEED (Low Energy Electron Diffraction) or RHEED (Reflection High Energy Electron Diffraction) usually under ultra-high vacuum conditions can lead, by inference, to an understanding of the real bulk or average surface structure.