Current Nanoscience - Volume 12, Issue 6, 2016

Background: Nanomachining techniques not only provide novel opportunities to fabricate three-dimensional nanostructures, but also induce great challenges in understanding their machining mechanisms at the nanometer scale. While nanomachining exhibits a strong dependence on chemical, physical and mechanical properties of workpiece materials, the molecular dynamics (MD) simulation has been demonstrated to be a powerful tool to explore the materialoriented nanomachining process. In this concise review we focus on the recent scientific progress in MD simulation of nanomachining of metals with different microstructures. Methods: The construction of atomic structures of single crystalline, bicrystal and nanocrystalline metals is first presented. Then MD models of nanomachining with different modes, i.e., load-controlled and displacement-controlled, are discussed. Since defect evolution plays an important role in plastic deformation of metals, finally advanced techniques of lattice defects for identifying types of dislocation and grain boundary (GB) are reviewed. Results: According to different microstructures of workpiece materials, MD simulations of nanomachining of metals are categorized into three parts, i.e., single crystalline, bicrystal and nanocrystalline. For single crystalline metals that plastic deformation is dominated by dislocation mechanisms, aspects of workpiece properties dependence, tool geometry dependence, tool/chip interface, thermal effect, machining direction, tool wear and mechanical properties of machined surface are reviewed. For bicrystals that containing GBs, dislocation-GB interactions and their correlation with machining results are emphasized. For more complex nanocrystalline metals with crystallites of varying size and orientation, the GB accommodation and deformation twinning found in nanomachining of metals are discussed, in addition to dislocation mechanisms and dislocation-GB interactions. Furthermore, grain size dependence of nanomachining is also addressed. Finally, current limitations and future prospections on MD simulations of nanomachining are also addressed in terms of empirical potential, length and time scale, tool wear and chemistry. Conclusion: This concise review of MD simulation of nanomachining demonstrates the strong dependence of nanomachining on the microstructure and properties of workpiece materials, which not only provides theoretical fundamentals for nanomachining experiments, but also is important for the rational synthesis or preparation of nanostructured materials with good machinability at the nanometer scale.

Background: Nowadays, atomic force microscopy (AFM) tip-based nanofabrication technique has been determined as an effective material removing tool for fabricating various nanostructures due to its low cost, easy operation, nanoscale accuracy and requirement of atmospheric experimental environment. Methods: We conducted a structured search of AFM tip-based machining databases for peer-reviewed research literature using a focused classification criterion. The advantages and deficiencies of the screened papers are analyzed in detail. Results: Fifty-one papers were included in this review and they were mainly divided into five parts. Thirteen papers outlined the influence of the normal load on the machined depth and both experimental and theoretical methods to obtain the relationship between the normal load and the machined depth are discussed based on these papers. Seven papers presented the effect of the scratching velocity on the machining results and the authors found the scratching velocity have a large influence on the tip wear and the shape accuracy of the machined nanostructures. The effects of the tip geometrical shape and the scratching direction are described in five papers to demonstrate the importance of the selection of the scratching direction. Ten papers defined the influences of the sample and probe materials on the machining outcomes. They estimated the nanoscale machinability of the sample materials by using AFM-based scratching method and the tip wear after machining. Moreover, some applications of AFM-based mechanical nanomachining method were outlined in six papers. Conclusion: Following an overview of the feasibility and effectiveness of using mechanical scratching with various machining parameters, specific directions for future research in AFM tip-based mechanical scratching method is presented.

Background: Femtosecond laser provides a versatile tool for microand nanofabrication, such as periodic surface structures with a periodicity much less than the wavelength, microfluidic channels for biological uses, photonic metamaterials and optical integrated circuits for quantum applications. These facts prove that fabrication methods based on femtosecond laser have provided convenience for novel applications in the fields of high precision fabrication, experimental quantum physics, functional materials, etc. Methods: We focus on the novel applications of the femtosecond laser high precision fabrication, such as quantum integrated circuits, biological and medical devices, multifunctional surfaces and functional periodic arrays. These applications are mostly undertook this 5 years, especially the quantum integrated circuits which were studied since 2013. Moreover, case studies were shown to illustrate the representative results and study methods. Results: We have reviewed 128 papers that are associated with the novel applications and case studies. Approximate 50% papers introduced the novel applications in the fields of quantum integrated circuits, biological and medical devices, multifunctional surfaces and functional periodic arrays. Other papers presented illustrated the case studies including femtosecond laser-induced forward transfer, characterization of femtosecond laser-induced periodic surface structures and results led by femtosecond vortex beam generated by a q-plate. Conclusion: The applications of the technology of the femtosecond laser direct writing waveguides in the fields of integrated quantum optics, photonic metamaterials, biological and medical circuits will surely pave a new way to fabricate full-size quantum computer and provide enormous kinds of biomimetic and medical finer devices. These state-of-the-art microdevices will provide much more convenience than before and even probably overturn the structure of the modern industry society. With the development of the relative technologies, femtosecond laser will prominently enhance the level of the fabrication in particular fields.

Background: Although various advanced FIB processing methods for the fabrication of 3D nanostructures have been successfully developed by many researchers, the FIB milling has an unavoidable result in terms of the implantation of ion source materials and the formation of damaged layer at the near surface. Understanding the ion-solid interactions physics provides a unique way to control the FIB produced defects in terms of their shape and location. Methods: We have carefully selected peer-reviewed papers which mainly focusing on the review questions of this paper. A deductive content analysis method was used to analyse the methods, findings and conclusions of these papers. Based on their research methods, we classify their works in different groups. The theory of ion-matter interaction and the previous investigation on ion-induced damage in diamond were reviewed and discussed. Results: The previous research work has provided a systematic analysis of ion-induced damage in diamond. Both experimental and simulation methods have been developed to understand the damage process. The damaged layers created in FIB processing process can significantly degrade/alter the device performance and limit the applications of FIB nanofabrication technique. There are still challenges involved in fabricating large, flat, and uniform TEM samples in undoped non-conductive diamond. Conclusions: The post-facto-observation leaves a gap in understanding the formation process of ioninduced damage, forcing the use of assumptions. In contrast, MD simulations of ion bombardment have shed much light on ion beam mixing for decades. These activities make it an interesting and important task to understand what the fundamental effects of energetic particles on matter are.

Background: Focused Ion Beam (FIB) nanofabrication technology has an important status in micro-nano manufacturing technology for its advantages of direct writing, nanoscale fabrication, SEM in-situ observation, high reproducibility, and 3D complex micro/nanofabriction, etc. This review aims to present some recent developments in Focused Ion Beam and its application in nanotechnology. Methods: The new developments of FIB equipment and their performance were introduced. The FIB fundamental research of ion-sample interaction, FIB application in material properties study at the micro/nanoscale and 3D nanostructures fabrication were presented and discussed. Results: Seventy papers were included in the review. The developments of new ion sources of Xe plasma FIB and helium ion (He+) microscopy and their performances were introduced, which can offer higher material removal rate of ~ 100 times faster than traditional Ga+ source FIB and fabrication of sub-10 nm scales structures, respectively. Then, the fundamental research of FIB induced modification on substrate material has studied by methods of microscopy characterization, molecular dynamics (MD) simulation and FIB induced material redistribution (Rayleigh- Plateau instability). Finally, FIB application in material properties study at the micro/nanoscale and 3D nanostructures fabrication were discussed. Conclusion: The findings of this review confirm the importance of FIB nanofabrication and its applications in delicate 3D nanostructures, functional devices and material fundamental research, etc. With the developments of FIB advanced equipment and ion-sample interaction mechanism research, FIB technique can give more and more contributions to nanotechnology.

Background: Nanoimprinting lithography technique uses a very simple concept of transferring pattern of nanoscale features from a mold to a target substrate. In the past two decades, this technique has successfully broken through the barrier of laboratory scale production and become an industrial scale production technique. The aim of this paper is to introduce to readers to the basic working principle, applications, analysis the technological limitations. It will also point out future research direction of this useful nanofabrication technique. Methods: We adopted a systematic approach to give a comprehensive review of the work principle, hardware and analysis of advantaged and disadvantages of major nanoimprint lithography techniques. Moreover, a technical comparison of these methods is carried out to provide future research direction. Results: 87 papers were reviewed. Four techniques including thermal NIL, ultraviolet light NIL, laser-assisted direct imprint and nanoelectrode lithography have been identified as main stream of NIL techniques. These techniques possess certain advantages and disadvantages in terms of cost, throughput, attainable resolution. Lack of flexibility is the common limitation of current NIL techniques. NIL has gained wide applications in the fabrication of optoelectronics devices, solar cells, memory devices, nanoscale cells, hydrophobic surfaces and bio-sensors. The potential applications of NIL in biochips, artificial organs, diagnostic system, and fundamental research in cell biology will demand large scale 3D fabrication capability with resolution towards 10nm or less. Conclusions: The findings of this review confirm that NIL is one of the most employed commercial platforms for nanofabrication which offers high throughput and cost-effectiveness. One of the disadvantages of NIL over other nanofabrication techniques is the flexibility of patterning. Integrating NIL with other existing nanofabrication techniques can be helpful to overcome such issue. The potential applications of NIL in biochips, artificial organs, diagnostic system, and fundamental research in cell biology will attract researchers to push nanoimprint lithography forward at a resolution of 10 nm or less in the future.

Background: In the past few decades, colloidal self-assembly method has been widely investigated and developed. This review will summarize several typical self-assembly routes, and introduce their recent progress, innovation and application. Methods: This review firstly presented the methodology and its developments for typical colloidal self-assembly methods. Then, typical applications of colloidal self-assembly methods in optics and biology fields were discussed. Results: 137 papers were included in the review. The colloidal particle size can range from tens of nanometers to a few microns to develop one-dimensional (1D) to three-dimensional (3D) superstructures. It can fabricate from simple single layer to multi-layer structures, and even more complex structures, like a variety of linear, circular and particles clusters with different shapes, etc. Secondary particles can also be realized through the self-assembly process with primary particles, such as polymer, inorganic or metal particles, even the inorganic and polymer composites. Meanwhile, due to the high accuracy and special properties of nanostructured materials or devices constructed with colloidal assembly, this review will also discuss their applications in fields of physics, chemistry, biology and so on. Conclusion: The findings of this review presented the importance of colloidal self-assembly methods and its applications for the fabrications of large area 3D micro/nanostructures, functional optical devices and biological devices, etc. With the research developments of colloidal self-assembly methods, this technique can give more and more contributions to nanotechnology, optics and biology.

Background: Silver is the most often studied and the most used substance in the form of nanoparticles. Currently, the production of silver nanoparticles (SNPs) reached the level of 320 tons per year. SNPs consisting of approximately 20–15000 silver atoms. SNPs are most commonly used as antimicrobial and antifungal agents in production of clothing, cosmetics, toys, paints, and in water filters. In the field of medicine, SNPs are used in dentistry, orthopedics, surgery, and in the production of medicines. Methods: During electric discharge between silver electrodes, plasma is produced under the effect of strong electric field with high temperature causing the removal of silver atoms from surface of the electrodes. In aqueous solutions, dissociation of water into oxygen and hydrogen atoms occurs. The interaction of active silver atoms with oxygen and hydrogen atoms and water particles causes the formation of stable nanoparticle colloid. Results: The arc discharge produces metallic silver nanoparticles and silver ions in water, tri-Sodium citrate dehydrate (TSC), and ethanol. The size distribution of obtained SNPs has maximum size between 7 and 20 nm. The properties of colloidal silver prepared with HVAD method are analyzed by UV-Vis spectroscopy, dynamic light scattering, and transmission electron microscopy. The stability of silver colloids is tested thermal treatment under high pressure. On the basis of AAS measurements of centrifuged colloids, silver ion to SNP ratio was estimated. Conclusions: Using HVAD method, one can produce SNPs quickly with silver concentration of approximately 15 ppm in various dispersant such as water, TSC solution, and ethanol. The aqueous solution contains 4.5% silver ions and the 3.3 μM TSC solution contains 0.5% silver ions.

Background: The presence of heavy metals in water is very harmful for the environment and the human’s health. Some heavy metals such as copper, at trace levels, are indispensable to preserve the metabolism of the human body. The application of the electrochemical methods (potentiometric and impedimetric) for Cu detection are simple and low cost with short detection times. One of the most important challenges in sensors development is how to increase sensibility and the obtained the best detection limit. The aim of this work is to investigate and compare two different types of electrochemical (potentiometric and impedimetric) methods for detection of Cu2+ ions in aqueous solution using chitosan-gold nanoparticles (CS-AuNPs) membrane. Methods: CS-AuNPs membrane has been prepared by adding of AuNPs obtained using Turkevich method to the CS dispersed in the acid acetic solution. Potentiometric and impedimetric measurements were performed using a graphite-epoxy electrode modified by CS-AuNPs membrane in aqueous solution in the concentration range of 10−9 to 10−1 M of Cu(NO3)2. Results: For the first time, the relation between percolation threshold and detection limit of copper ions has been established. The best detection limit in both methods has been observed when the concentration of AuNPs is near the percolation threshold. Obtained results show that potentiometric method has a detection limit of 2.36 × 10-5 and a linear response range between 2.36 × 10-5 and 4 × 10-2 M of Cu2+. However, impedimetric method shows superior properties: detection limit ca. 10-7 M, linear response range 10-7-10-3 M of Cu2+ ions. Conclusion: The obtained relationship between impedance measurements and critical percolation concentration of AuNPs are of primary importance in the design and optimization of nanocomposite for sensor application. Our results suggest that CS-AuNPs membranes can be used for the development of a low cost sensor for copper detection based upon potentiometric and impedimetric measurements.

Background: Nanotechnology has become an essential and important field tool to develop various kinds of nanoparticles with high surface area to volume ratios and unique properties. Therefore, nanoparticles have been utilized for several biomedical applications; including diagnostics, drug delivery, biomarkers, and distinct antibacterial, antifungal and anti-biofilm agents. Silver nanoparticles (AgNPs) are known to be effective antibacterial agents and exhibit strong cytotoxicity against a broad range of microorganisms compared to conventional usage of silver salt and silver metal. The aim of this study was to synthesize graphene oxide- silver nanoparticle nanocomposites using a novel biomolecule called pepsin. Methods: The synthesized graphene oxide (GO) silver nanoparticle nanocomposite (GO–AgNPs) was characterized by ultraviolet-visible absorption spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The antibacterial and anti-biofilm activity of synthesized nanocomposite was evaluated using various assays, such as cell growth, cell viability, and reactive oxygen species generation. Results: The graphene oxide (GO)-silver nanoparticle nanocomposite (GO–AgNPs) was synthesized in the presence of AgNO3 and pepsin. The synthesized GO–AgNPs were characterized by various analytical techniques. The AgNPs were distributed uniformly on the surface of graphene oxide with an average size of 20 nm. Antibacterial activities of GO–AgNPs were evaluated by cell viability and anti-biofilm assay. GO, AgNPs and GO-AgNPs nanocomposites showed significant antibacterial activity against Shigella flexneri and Streptococcus pneumoniae. The loss of viability was observed in S. flexneri and S. pneumonia decreased in a dose- and time-dependent manner. GO-AgNPs showed significantly higher production of reactive oxygen species (ROS) compared to GO, AgNPs and the control, which is a possible mechanism of cell death. N-acetyl cysteine (NAC) significantly prevented cell death induced by GO, AgNPs, GO-AgNPs from oxidative stress in Shigella flexneri and Streptococcus pneumoniae via decreasing ROS generation. It suggests that elevated ROS is responsible for the loss of cell viability. Conclusion: Pepsin mediated GO–AgNPs could facilitate the simple, easy approach for large-scale production of graphene-based nanocomposites; GO–AgNPs exhibited an efficient and significant inhibitor for cell viability compared to GO, and silver nanoparticles. The nanocomposites could be effective antibacterial agents for the treatment of various infectious diseases.

Background: Silver nanowires (Ag-NWs) are promising as a kind of novel conducting materials for the next generation nanodevice for space application either in the form of interconnecting conducting NWs to integrate nanodevices or for transparent electrodes for solar cell. In order to explore the possible application of Ag-NWs for upper space, radiation hardness testing is important. Methods: In this research work, total dose radiation tolerance of Ag-NWs under proton environment is investigated. Ag-NWs were irradiated with proton ions in MeV energy range. The dose of ions varies from 5x1015 to 1x1017 protons/cm2 and its effects on morphology and structure of the Ag-NWs are studied by scanning electron microscopy and X-ray diffraction respectively. Results: It is observed that Ag-NWs remained stable under proton beam irradiation at the dose of 1x1017 protons/cm2 and high proton flux (1013 p/cm²/sec). Moreover, for the first time whole Ag- NWs network are embedded into a glass and silicon substrates by proton beam irradiation and depth of embedding increases with increase proton dose. At the dose of 7x1016 protons/cm2 Ag-NWs networks are fully buried while morphology and structure of Ag-NWs remain stable. At a given energy the flux plays a major role in mass transport. Burying of Ag-NWs is explained on the basis of ioninduced viscous flow and thermal processes. Conclusion: It is concluded that morphology and structure of Ag-NWs remain stable after irradiation with MeV proton ions at different doses ranging from 5x1015 to 1x1017 protons/cm2. Whereas, at the dose of 1x1017 protons/cm2 the proton irradiation reveals that the structure deterioration in the Ag- NWs crystallinity from the nearly single to polycrystalline orientation. Moreover, Ag-NWs network is buried into the substrate materials via proton beam irradiation.

Background: Instead of traditional antibiotics, antimicrobial property of nanoparticle has been documented in various research reports. In such cases, nanoparticle mainly interacts with proteins and DNA like macromolecules. But still the mechanism of anti-microbial activity of CdS nanoparticles is partially known. Methods: We have synthesized CdS nanoparticles by using Aspergillus foetidus (MTCC8876). Our process for synthesis of nanoparticle is hazard free as well as economic. To investigate the mode of interaction between CdS nanoparticles and BSA, a number of photo- and fluorometric analyses were considered. Furthermore, DNA (calf thymus DNA) binding ability of CdS nanoparticles was also studied through photo- and fluorometric analyses and viscosity measurement. Results: About 10-15 nm of stable CdS nanoparticle has been synthesized by Aspergillus foetidus. Our results ascertained that CdS nanoparticles interact with BSA (binding constant, K=13.8 104M−1) and DNA (binding constant, K=10.47 102M−1) successively. Conclusion: Aspergillus foetidus mediated biosynthesized CdS nanoparticles effectively interact with BSA and calf thymus DNA.