A Rotating-Tip-Based Mechanical Nano-Manufacturing Process: Nanomilling

Pulse-Atomic Force Lithography: A Powerful Nanofabrication Technique to Fabricate Constant and Varying-Depth Nanostructures

The widespread use of nanotechnology in different application fields, resulting in the integration of nanostructures in a plethora of devices, has addressed the research toward novel and easy-to-setup nanofabrication techniques to realize nanostructures with high spatial resolution and reproducibility. Owing to countless applications in molecular electronics, data storage, nanoelectromechanical, and systems for the Internet of Things, in recent decades, the scientific community has focused on developing methods suitable for nanopattern polymers. To this purpose, Atomic Force Microscopy-based nanolithographic techniques are effective methods that are relatively less complex and inexpensive than equally resolute and accurate techniques, such as Electron Beam lithography and Focused Ion Beam lithography. In this work, we propose an evolution of nanoindentation, named Pulse-Atomic Force Microscopy, to obtain continuous structures with a controlled depth profile, either constant or variable, on a polymer layer. Due to the modulation of the characteristics of voltage pulses fed to the AFM piezo-scanner and distance between nanoindentations, it was possible to indent sample surface with high spatial control and fabricate highly resolved 2.5D nanogrooves. That is the real strength of the proposed technique, as no other technique can achieve similar results in tailor-made graded nanogrooves without the need for additional manufacturing steps.

Molecular Dynamics Study on Tip-Based Nanomachining: A Review

Tip-based nanomachining (TBN) approaches has proven to be a powerful and feasible technique for fabrication of microstructures. The molecular dynamics (MD) simulation has been widely applied in TBN approach to explore the mechanism which could not be fully revealed by experiments. This paper reviews the recent scientific progress in MD simulation of TBN approach. The establishing methods of the simulation model for various materials are first presented. Then, the analysis of the machining mechanism for TBN approach is discussed, including cutting force analysis, the analysis of material removal, and the defects analysis in subsurface. Finally, current shortcomings and future prospects of the TBN method in MD simulations are given. It is hopeful that this review can provide certain reference for the follow-up research.

Shaping and Edge Engineering of Few-Layered Freestanding Graphene Sheets in a Transmission Electron Microscope

Full exploitation of graphene's superior properties requires the ability to precisely control its morphology and edge structures. We present such a structure-tailoring approach via controlled atom removal from graphene edges. With the use of a graphitic-carbon-capped tungsten nanoelectrode as a noncontact "milling" tool in a transmission electron microscope, graphene edge atoms approached by the tool tip are locally evaporated, thus allowing a freestanding graphene sheet to be tailored with high precision and flexibility. A threshold for the tip voltage of 3.6 ± 0.4 V, independent of polarity, is found to be the determining factor that triggers the controlled etching process. The dominant mechanisms involve weakening of carbon-carbon bonds through the interband excitation induced by tunneling electrons, assisted with a resistive-heating effect enhanced by high electric field, as elaborated by first-principles calculations. In addition to the precise shape and size control, this tip-based method enables fabrication of graphene edges with specific chiralities, such as "armchair" or "zigzag" types. The as-obtained edges can be further "polished" to become entirely atomically smooth via edge evaporation/reconstruction induced by in situ TEM Joule annealing. We finally demonstrate the potential of this technique for practical uses through creating a graphene-based point electron source, whose field emission characteristics can effectively be tuned via modifying its geometry.

Scratch on Polymer Materials Using AFM Tip-Based Approach: A Review

As a brand new nanomachining method, the tip-based nanomachining/nanoscratching (TBN) method has exhibited a powerful ability at machining on polymer materials and various structures have been achieved using this approach, ranging from the nanodot, nanogroove/channel, bundle to 2D/3D (three-dimensional) nanostructures. The TBN method is widely used due to its high precision, ease of use and low environmental requirements. First, the theoretical models of machining on polymer materials with a given tip using the TBN method are presented. Second, advances of nanostructures achieved by this method are given, including nanodots/nanodot arrays, a nanogroove/channel, 2D/3D nanostructures and bundles. In particular, a useful approach called the ultrasonic vibration-assisted method introduced to integrate with TBN method to reduce the wear of the tip is also reviewed, respectively. Third, the typical applications of the TBN method and the nanostructures achieved by it are summarized in detail. Finally, the existing shortcomings and future prospects of the TBN method are given. It is confirmed that this review will be helpful in learning about this method and push the technology toward industrialization.

Fabrication of polydimethylsiloxane nanofluidic chips under AFM tip-based nanomilling process

In current research realm, polydimethylsiloxane (PDMS)-based nanofluidic devices are widely used in medical, chemical, and biological applications. In the present paper, a novel nanomilling technique (consisting of an AFM system and a piezoelectric actuator) was proposed to fabricate nanochannels (with controllable sizes) on PDMS chips, and nanochannel size was controlled by the driving voltage and frequency inputted to the piezoelectric actuator. Moreover, microchannel and nanochannel molds were respectively fabricated by UV lithography and AFM tip-based nanomilling, and finally, PDMS slabs with micro/nanochannels were obtained by transfer process. The influences of PDMS weight ratio on nanochannel size were also investigated. The bonding process of microchannel and nanochannel slabs was conducted on a homemade alignment system consisted of an optical monocular microscope and precision stages. Furthermore, the effects of nanochannel size on electrical characteristics of KCl solution (concentration of 1 mM) were analyzed. Therefore, it can be concluded that PDMS nanofluidic devices with multiple nanochannels of sub-100-nm depth can be efficiently and economically fabricated by the proposed method.

Fabrication of nanochannels with ladder nanostructure at the bottom using AFM nanoscratching method

This letter presents a novel atomic force microscopy (AFM)-based nanomanufacturing method combining the tip scanning with the high-precision stage movement to fabricate nanochannels with ladder nanostructure at the bottom by continuous scanning with a fixed scan size. Different structures can be obtained according to the matching relation of the tip feeding velocity and the precision stage moving velocity. This relationship was first studied in detail to achieve nanochannels with different ladder nanostructures at the bottom. Machining experiments were then performed to fabricate nanochannels on an aluminum alloy surface to demonstrate the capability of this AFM-based fabrication method presented in this study. Results show that the feed value and the tip orientation in the removing action play important roles in this method which has a significant effect on the machined surfaces. Finally, the capacity of this method to fabricate a large-scale nanochannel was also demonstrated. This method has the potential to advance the existing AFM tip-based nanomanufacturing technique of the formation these complex structures by increasing the removal speed, simplifying the processing procedure and achieving the large-scale nanofabrication.

Investigating bioconjugation by atomic force microscopy

Nanotechnological applications increasingly exploit the selectivity and processivity of biological molecules. Integration of biomolecules such as proteins or DNA into nano-systems typically requires their conjugation to surfaces, for example of carbon-nanotubes or fluorescent quantum dots. The bioconjugated nanostructures exploit the unique strengths of both their biological and nanoparticle components and are used in diverse, future oriented research areas ranging from nanoelectronics to biosensing and nanomedicine. Atomic force microscopy imaging provides valuable, direct insight for the evaluation of different conjugation approaches at the level of the individual molecules. Recent technical advances have enabled high speed imaging by AFM supporting time resolutions sufficient to follow conformational changes of intricately assembled nanostructures in solution. In addition, integration of AFM with different spectroscopic and imaging approaches provides an enhanced level of information on the investigated sample. Furthermore, the AFM itself can serve as an active tool for the assembly of nanostructures based on bioconjugation. AFM is hence a major workhorse in nanotechnology; it is a powerful tool for the structural investigation of bioconjugation and bioconjugation-induced effects as well as the simultaneous active assembly and analysis of bioconjugation-based nanostructures.

SPM nanolithography of hydroxy-silicates

Bio-nanopatterning of surfaces is becoming a crucial technique with applications ranging from molecular and cell biology to medicine. Scanning probe microscopy (SPM) is one of the most useful tools for nanopatterning of flat surfaces. However, these patterns are usually built on homogeneous surfaces and require chemical functionalization to ensure specific affinity. Layered magnesium-aluminum hydroxide-silicates have already shown unique self-assembly properties on DNA molecules, due to their peculiar crystal chemistry based on alternating positive and negative crystal layers. However, patterns on these surfaces tend to be randomly organized. Here we show etching and oxidation at the nanometer scale of magnesium-aluminum hydroxide-silicates using the same SPM probe for the creation of organized nanopatterns. In particular, it is possible to produce three-dimensional structures in a reproducible way, with a depth resolution of 0.4 nm, lateral resolution of tens of nm, and a speed of about 10 μm s(-1). We report, as an example, the construction of an atomically flat charged pattern, designed to guide DNA deposition along predetermined directions without the need of any chemical functionalization of the surface.

Nanopatterning on silicon surface using atomic force microscopy with diamond-like carbon (DLC)-coated Si probe

Atomic force microscope (AFM) equipped with diamond-like carbon (DLC)-coated Si probe has been used for scratch nanolithography on Si surfaces. The effect of scratch direction, applied tip force, scratch speed, and number of scratches on the size of the scratched geometry has been investigated. The size of the groove differs with scratch direction, which increases with the applied tip force and number of scratches but decreases slightly with scratch speed. Complex nanostructures of arrays of parallel lines and square arrays are further fabricated uniformly and precisely on Si substrates at relatively high scratch speed. DLC-coated Si probe has the potential to be an alternative in AFM-based scratch nanofabrication on hard surfaces.