Jianlei Cui

Nanospot soldering polystyrene nanoparticles with an optical fiber probe laser irradiating a metallic AFM probe based on the near-field enhancement effect.

With the development of nanoscience and nanotechnology for the bottom-up nanofabrication of nanostructures formed from polystyrene nanoparticles, joining technology is an essential step in the manufacturing and assembly of nanodevices and nanostructures in order to provide mechanical integration and connection. To study the nanospot welding of polystyrene nanoparticles, we propose a new nanospot-soldering method using the near-field enhancement effect of a metallic atomic force microscope (AFM) probe tip that is irradiated by an optical fiber probe laser. On the basis of our theoretical analysis of the near-field enhancement effect, we set up an experimental system for nanospot soldering; this approach is carried out by using an optical fiber probe laser to irradiate the AFM probe tip to sinter the nanoparticles, providing a promising technical approach for the application of nanosoldering in nanoscience and nanotechnology.

Nanoscale soldering of axially positioned single-walled carbon nanotubes: a molecular dynamics simulation study.

The miniaturization of electronics devices into the nanometer scale is indispensable for next-generation semi-conductor technology. Carbon nanotubes (CNTs) are considered to be the promising candidates for future interconnection wires. To study the carbon nanotubes interconnection during nanosoldering, the melting process of nanosolder and nanosoldering process between single-walled carbon nanotubes are simulated with molecular dynamics method. As the simulation results, the melting point of 2 nm silver solder is about 605 K because of high surface energy, which is below the melting temperature of Ag bulk material. In the nanosoldering process simulations, Ag atoms may be dragged into the nanotubes to form different connection configuration, which has no apparent relationship with chirality of SWNTs. The length of core filling nanowires structure has the relationship with the diameter, and it does not become longer with the increasing diameter of SWNT. Subsequently, the dominant mechanism of was analyzed. In addition, as the heating temperature and time, respectively, increases, more Ag atoms can enter the SWNTs with longer length of Ag nanowires. And because of the strong metal bonds, less Ag atoms can remain with the tight atomic structures in the gap between SWNT and SWNT. The preferred interconnection configurations can be achieved between SWNT and SWNT in this paper.

Simulation study of near-field enhancement on a laser-irradiated AFM metal probe

A systematic study of near-field enhancement on a laser-irradiated atomic force microscope (AFM) metal probe is reported. The dependence of the electric field distribution on various parameters, like laser wavelength, tip curvature radius, half taper angle and tip–substrate distance, is numerically studied using the finite element method in this paper. The simulation results show that high field enhancement appears around the tip and is mainly concentrated under the apex of the tip when the incident laser interacts with the AFM metal tip. The results indicate that electric field enhancement easily appears when the AFM metal tip is irradiated by a higher frequency incident laser, with a similar phenomenon using a relatively sharp tip. In addition, as the tip–substrate distance increases, the peak electric field enhancement underneath the apex of the tip decreases. Based on the distribution of electric field enhancement, a new scheme combining an optical fiber probe and an AFM metal probe is proposed for nanolithography.

Nanospot welding of carbon nanotubes using near-field enhancement effect of AFM probe irradiated by optical fiber probe laser

The miniaturization of electronic devices into the nanometer scale is indispensable for next-generation semiconductor technology, and carbon nanotubes are considered to be the promising candidates for the future interconnection wires. To study carbon nanotube interconnection during nanowelding, we propose a new nanospot welding method with the near-field enhancement effect of the metallic AFM probe tip irradiated by an optical fiber probe laser. Based on theoretically analyzing the near-field enhancement effect, we set up the experimental system for nanospot welding with good interconnection results of silver nanoparticles and carbon nanotubes, not only proving that the interconnection operation of CNTs can be effectively achieved through the melting process of nanoparticles by the thermal AFM probe tip irradiated by an optical fiber probe laser, but also providing a promising technical approach for nanospot welding.

Molecular Dynamics Simulation Study of the Melting of Silver Nanoparticles

In the application process of nanoparticles, the melting process plays an important role. Holding the melting characteristics of nanoparticles can essentially improve the correlative technical level. To study the melting characteristics of silver nanoparticles, melting processes of silver nanoparticles are investigated using molecular dynamics simulation. Simulation results show that the microscopic melting process of nanoparticles is the uneven transition process of atomic structures from order to disorder. Also, the melting point of 3 nm particle with 856 atoms is about 815 K and the heat capacity of nanoparticles is negative near the melting temperature. The dominant mechanisms of melting process are analyzed from potential energy temperature relationship, radial distribution function, mean square displacement and atomic evolution configuration. We also found that nanoparticles bunch up due to high surface energy for multi-nanoparticles when the temperature is lower than the melting point. And, when nanoparticles melt into droplet, the liquid nanoparticles have stronger liquidity and automatically reduce to spherical structures due to the role of surface tension.

Application of positron annihilation spectroscopy to the study of zeolites

Positron annihilation lifetime measurements were carried out for various types of zeolites. The lifetime spectra were resolved into four components. The two longer lifetime components are attributed to the annihilation of o-Ps (Ps = positronium atoms) on the surface and in the cages of the zeolites. The o-Ps lifetimes on the surface and in the cages are shortened in the presence of Bronsted acidity due to oxidation reaction between o-Ps and the Bronsted acid sites. The o-Ps annihilation rates of NaHY and NaHM zeolites increase linearly with increasing Bronsted acid site concentration. For faujasites with different cations and Si/Al ratios, the lifetimes of o-Ps decrease with increasing electrostatic-field gradient in the zeolite. Experimental results show that positron annihilation spectroscopy is a useful tool for the characterization of zeolites.

Atomistic simulations on the axial nanowelding configuration and contact behavior between Ag nanowire and single-walled carbon nanotubes

As for the interesting new building blocks, the Ag nanowires (AgNWs) and single-walled carbon nanotubes (SWNTs) as the interesting new building blocks are viewed as the promising candidates for the next-generation interconnects due to their most remarkable electrical, thermal, optical, mechanical, and other properties. The axial nanowelding of head-to-head style and side-to-side style is relatively simulated with the molecular dynamics method. As for the head-to-head structural style, SWNTs will move toward the AgNWs and contact with the head of AgNWs. And, the part of the Ag nanowire may be subsequently encapsulated in SWNT with the core-filling Ag atom chain as the final atomic contact configuration during nanowelding, which is related to the nanowelding temperature. When the SWNTs and AgNWs are arranged by the side-to-side contact style, the SWNTs will move along the SWNT surface and may eventually catch up with the AgNW being neck and neck. Aiming at the final axial atomic configurations and the contact behavior during nanowelding process, the related dominant mechanism is revealed in this paper.

New optical near-field nanolithography with optical fiber probe laser irradiating atomic force microscopy probe tip

ABSTRACT A new optical near-field nanolithography scheme with optical fiber probe laser irradiating atomic force microscopy (AFM) probe tip is proposed. Through optical theoretical analysis, if the metallic AFM probe tip is in the evanescent field of optical fiber probe tip, the secondary near-field enhancement effect can appear underneath the metallic AFM probe tip. Based on the independently developed AFM system and optical system, the nanolithography platform is built and nanocraters structures can be successfully created, which demonstrates that the new scheme is an effective and promising nanolithography approach for the future nanoelectronics, nanobiotechnology, nanowelding, etc.

Local Field Enhancement Characteristics in a Tapered Metal-Coated Optical Fiber Probe for Nanolithography

In the nanolithography, some exciting developments have been motivated by the tapered metal-coated optical fiber probe irradiated by ultra-fast pulse laser. To explore the related mechanism, the local field is studied using the finite element method in this paper. The simulation results show the reflection at the cut-off plane, edge enhancement effect and surface plasmon resonance become the major factors affecting the near-field. In addition, Based on the near-field distribution and characteristics, the new promising scheme is proposed for near-field nanolithography.

Experimental Study on the Creation of Nanodots with Combined-Dynamic Mode “Dip-Pen” Nanolithography

The combined-dynamic mode DPN (CDDPN), rather than mostly used contact mode DPN or tapping mode DPN, becomes the important tool for the creation of nanodots with the direct-writing method of depositing the ink onto the substrate surface at the predetermined position. However, successful examples of using CDDPN to fabricate nanodots are relatively few, and the formation process and the size of nanodots are affected by various factors, such as humidity, substrate material, contact time and surface roughness. So the influences of various factors on nanodots are explored through the experimental method. The results are that the nanodots become larger with the increase of the relative humidity and the roughness of the surface, respectively; similarly, the nanodot is created easily on the soft surface with hydrophilicity in the longer contact time; in addition, for the better nanolithography quality of the nanodot, the nanolithography process, under the optimized influence parameters, is accomplished once without the intermediate scan imaging process as much as possible.