Papers by Author: Yong Da Yan

Abstract: As the dimensions of parts become smaller, understanding the mechanical properties of these small components was becoming more important. Till present day, the methods and technology used to investigate the deformation behavior in nanoscale were still lacking. In this paper, the specimens were single crystal copper wires with diameter in 50 microns. Atomic force microscope integrated with an in- situ tensile system were used to determine the mechanical behavior of copper wires and observe the surface topography deformation in nanoscale simultaneously. The results were as follows: the modulus of elasticity, tensile strength and failure strain of the sample were 167Gpa, 0.564GPa and 0.011, respectively. By using AFM, the separation process between the copper wire and impurities on it, such as oxide film, was observed. The nanoscale deformation process of the copper wire was also obtained.

Abstract: The equations correlated the normal load and the tip penetration depth were derived through the theoretical analysis of the penetration process of the diamond tip. Verified by experiments, the equations can reflect the penetration process of the scratching machining system and provide theoretical basis for the optimization of depth control algorithm. The control of scratching depth realized in AFM deflection mode can effectively restrain the system drift during scratching process.

Abstract: Ultrathin block copolymer films are promising candidates for bottom-up nanotemplates in hybrid organic-inorganic electronic, optical, and magnetic devices. Key to many future applications is the long range ordering and precise placement of the phase-separated nanoscale domains. In this paper, a combined top-down/bottom-up hierarchical approach is presented on how to fabricate massive arrays of aligned nanoscale domains by means of the self-assembly of asymmetric poly (styrene-block-ethylene/butylenes-block-styrene) (SEBS) tirblock copolymers in confinement. The periodic arrays of the poly domains were orientated via the introduction of AFM micromachining technique as a tool for locally controlling the self-assembly process of triblock copolymers by the topography of the silicon nitride substrate. Using the controlled movement of 2- dimensional precision stage and the micro pressure force between the tip and the surface by computer control system, an artificial topographic pattern on the substrate can be fabricated precisely. Coupled with solvent annealing technique to direct the assembly of block copolymer, this method provides new routes for fabricating ordered nanostructure. This graphoepitaxial methodology can be exploited in hybrid hard/soft condensed matter systems for a variety of applications. Moreover, Pairing top-down and bottom-up techniques is a promising, and perhaps necessary, bridge between the parallel self-assembly of molecules and the structural control of current technology.

Abstract: Nanomachining tests have been conducted on single-crystal Al using atomic force microscope to simulate single-blade machining process of single gain. The influences of nanomachining experimental parameters (lateral feed and velocity) on the properties of engineering surface, material removal and chip formation were studied. Results indicated that the cutting depth of nanomachined surface increased as the lateral feed decreased. Insensitivity of cutting depth to velocity at same normal load was revealed. The different chip behaviors of nanomachined surface were investigated through scanning electron microscope (SEM). Results indicated that different lateral feeds caused different chip behaviors. Three typical chip behaviors were characterized as the lateral feed increased. In addition, the chip behavior and the volume of material removed were observed having no evident linear transformation with the evolution of the velocity by SEM graphics. Furthermore, it was concluded from the chip behaviors in nanomachining process that the material at high loads was removed by plastic deformation with no fracture or crack happened.

Abstract: Molecular dynamics is a rapidly developing field of science and has become an established tool for studying the dynamic behavior of material machining. A three-dimensional molecular dynamics (MD) model about the atoms of the diamond cutting tools and the diamond grits is built by using the molecular dynamics. The Tersoff potential function is used to calculate the force and potential energy among the atoms of the diamond tools and the atoms of the diamond grits. The lapping processes at a special cutting depth are simulated. The variety of the specimen potential energy in the lapping process is observed. The mechanism of the diamond micro machining and the form of the surface formation are given by comparing the distribution maps of atoms in initial and cutting states. This study will give a strong support to the diamond cutting tools’ lapping.

Abstract: A three dimensional molecular dynamics model is employed to simulate AFM-based lithography process. To investigate effects of tip geometry, three kinds of tip models are proposed: a cone-shape tip with a hemisphere at the end, a round-edged three sided pyramid tip with a hemisphere at the end and a sharp-edged three sided pyramid tip. These models simulate scratching behaviors of AFM tip at different scratching depths. Results showed that materials removal behavior and scratching forces were significantly affected by tip geometry, depending on the scratching depth and scratching directions. The specific energy using a sharp-edged three sided pyramid tip displayed a different behavior comparing to that using a round-edged three sided pyramid. However, scratching orientations exhibited no effects on the specific energy.

Abstract: Effects of the scratching feed on machined surface and scratching forces are studied by using AFM-based nanomachining process scratching along the long axis of the cantilever. Results show: A deeper structure and rougher surface can be obtained at a smaller feed. An increase in the feed results in increases in scratching forces and the resultant force and a decrease in the normal force. Finally, all forces reach to a saturation value. The ratio of the cutting force to the thrust force in the plane perpendicular to the cutting edge can reveal effects of ploughing and cutting between the tip and the sample in the nanomachining process. Correspondingly, different states (cutting or ploughing) play a key role in formation of the machined surface at different feeds.

Abstract: With the development of science and technology, Atomic Force Microscope is widely applied to the field of machining process in nanometer scale. Due to the limitation of the inventive purpose of AFM, only height mode and deflection mode can be applied in AFM-tip micromachining. It can’t control the machining depth during the micromachining process at present. In this paper, a new micromachining system is set up, which composed of a high precision three-dimensional stage, an AFM, a diamond probe and a special control device. By utilizing variation parameters PID algorithm and controlling the machining depth directly, the micromachining system can resolve the problem mentioned above.

Abstract: The measuring system was developed based on a reconstructed atomic force microscope (AFM) combined with the precision rotating air-bearing and assistant transform shaft. By this system the experiment was carried out according to the principle of three orthogonal orientations towards a micro sphere about 0.46 mm in diameter, and nine one-dimensional traces around the sphere were obtained. Analyses on roundness and sphericity are carried out from the measured data.The results show that the maximal roundness is 0.3895 μm, and the sphericity error is 0.3880 μm.These evaluations are significant references to evaluate its fabrication accuracy or to reform its machining processes.

Abstract: Atom Force Microscopy (AFM) can be employed to create surfaces in Si substrate with recessed features. The resulting patterns can serve as masters to make the required elastomeric stamps for soft lithography. Morphology analysis of patterned features on Si substrate and polydimethylsiloxane (PDMS) stamp by AFM imaging confirms that pattern can be successfully transferred from Si substrates to PDMS stamps. It is shown that this method for creating masters can be performed with an AFM, making this method particularly straightforward, economical and accessible to a large technical community that are provided with AFM for measurement.