Zongwei Xu

Experimental investigation of superfocusing of plasmonic lens with chirped circular nanoslits

A plasmonic lens with metallic chirped circular nanoslits corrugated on Au film supported on quartz substrate for the purpose of superfocusing was put forth and fabricated by means of focused ion beam direct milling technique. Topography of the lens was imaged using an atomic force microscope. After that a near-field scanning optical microscope was employed for optical characterization of focusing performance of the lens. Our experimental results verify the focusing performance and further demonstrate that they are in agreement with the theoretical calculation results. Focusing performance is significantly improved in comparison to that of the non-chirped lens. The lenses are possible to be used for the applications of bioimaging, detection, and inspection in submicron scale resolution.

Fabrication of micro DOE using micro tools shaped with focused ion beam

A novel method is proposed to fabricate micro Diffractive Optical Elements (DOE) using micro cutting tools shaped with focused ion beam (FIB) milling. Micro tools with nanometric cutting edges and complicated shapes are fabricated by controlling the tool facets orientation relative to the FIB. The tool edge radius of less than 30 nm is achieved for the nano removal of the work materials. Semi-circular micro tools and DOE-shaped micro tools are developed to fabricate micro-DOE and sinusoidal modulation templates. Experiments show that the proposed method can be a high efficient way in fabricating micro-DOE with nanoscale surface finishes.

High performance surface-enhanced Raman scattering substrates of Si-based Au film developed by focused ion beam nanofabrication

A novel method with high flexibility and efficiency for developing SERS substrates is proposed by patterning nanostructures on Si substrates using focused ion beam direct writing (FIBDW) technology following with precise thermal evaporation of gold film on the substrate. The effect of SERS on the substrate was systematically investigated by optimizing the processing parameters and the gold film thickness. The results proved that small dwell time could improve the machining accuracy and obtain smaller nanogap. The Raman-enhanced performance of the substrate was investigated with 10−6mol/L Rhodamine 6 G solution. It was indicated that the elliptic nanostructures with 15-nm spacing on Si substrates, coated with approximately 15-nm thick gold film, have exhibited a high-enhanced performance, but dramatic performance degradation was found as the gold film thickness further increased, which most probably resulted from changes of the nanostructures’ morphology such as elliptical tip and spacing. To avoid the morphological changes effectively after depositing gold film, optimization design of the nanostructures for FIBDW on Si substrates was proposed. Besides, a similar phenomenon was found when the gold film was less than 15nm because there was little gold remaining on the substrate. The method proposed in this paper shows a great potential for the higher performance SERS substrates development, which can further reduce the spacing between hot spots.

Study on phase images of a carbon nanotube probe in atomic force microscopy

The attractive and repulsive interaction forces between a probe and a sample in atomic force microscopy (AFM) can be distinguished from the probes phase angle images. By changing the AFM scan parameters, the probes phase angle is found to be very sensitive to the properties of adhesion and viscoelasticity of the materials to be analyzed. The tapping probe is found to suffer great repulsive forces at the right edge of gratings, which is mainly due to the probe having a cantilever tilt angle of 11°. A single carbon nanotube (CNT) made by the chemical vapor method is found to be hydrophobic from the phase angle image of a carbon nanotube probe. The CNT probe shows better phase image resolution over the Si probe in AFM scanning immunoglobulin G proteins. The study of probe phase angles reveals that the image artifacts captured by CNT probes at grating edges result from the repeated CNT bending–adhesion–separation process.

Germanium nanopyramid arrays showing near-100% absorption in the visible regime

Solar energy is regarded as one of the most plentiful sources of renewable energy. An extraordinary light-harvesting property of a germanium periodic nanopyramid array is reported in this Letter. Both our theoretical and experimental results demonstrate that the nanopyramid array can achieve perfect broadband absorption from 500- to 800-nm wavelength. Especially in the visible regime, the experimentally measured absorption can even reach 100%. Further analyses reveal that the intrinsic antireflection effect and slow-light waveguide mode play an important role in the ultra-high absorption, which is helpful for the research and development of photovoltaic devices.

Controlled morphology of microtools shaped using focused ion beam milling technique

Advantages of focused ion beam (FIB) technology in micromachining are high feature resolution, capable of maskless processing, rapid prototyping, and adaptive for various materials and geometries. FIB was extensively used to fabricate a variety of microtools for ultraprecision machining and micromachining with typical dimensions ranging from 10 to 40 μm and a curvature radius of 25 nm or even smaller. The microtools with controlled geometries, such as arc and sawtooth shapes, were shaped using FIB milling technique corresponding to different cutting requirements. The FIB milling is able to shape desired tool geometries with microscale features by means of controlling suitable ion beam parameters and precise orientation of the tools with respect to projection direction of ion beam. The cutting microtools used here are made from hard alloy. Testing experiments were carried out using a microtool with arc-shaped cross section to machine concentric rings and an annular plane in planar metal workpiece. Another ...

Carbon Nanotube AFM Probe Technology

The invention of atomic force microscopy (AFM) is having a great impact on various areas, such as nano metrology, materials science, surface science and biology (Binnig et al., 1986). The lateral resolution of AFM is mainly determined by the probe’s shape and physical property, especially the geometry and dimension of the probe end. Conventional AFM probe is pyramidal shape by micro-fabrication. The pyramidal probe would result in image resolution degradation by severe probe broaden effect, especially for the structures with higher aspect ratio, such as gratings and structures in MEMS. To broaden the AFM applications, researchers pursue new kind probes that have longer lifetime, higher resolution, and better mechanical property. Carbon nanotubes (CNT) show many excellent properties, such as, high aspect ratio, high Youngs modulus, excellent elastic buckling property, and electrical and thermal conductivity (Iijima, 1991). The above characteristics make carbon nanotube be ideal as probes in AFM. Carbon nanotubes have demonstrated considerable potential as AFM probes after the first CNT AFM probe was invented in 1996 (Dai et al., 1996). This chapter would introduce the history of carbon nanotube AFM probes, including the CNT probes’ farbication and configuration optimization, the CNT probes’ image artefact and its elimination study, the applications of these new kind probes and researches to improve their performance.

Nanofabrication and Characterization of Plasmonic Structures

The nanofabrication processes can be divided into two well defined approaches: 1) ‘topdown’ and 2) ‘bottom-up’. The ‘top-down’ approach uses traditional methods to guide the synthesis of nanoscale materials. The paradigm proper of its definition generally dictates that in the ‘top-down’ approach it all begins from a bulk piece of material, which is then gradually or step-by-step removed to form objects in the regime of nanometer-size scale. Well known techniques such as photo lithography, electron beam lithography, anodization, and ionand plasma-etching, that will be later described, all belong to this type of approach. The top-down approach for nanofabrication is the method firstly suggested by Feynman in his famous American Physical Society lecture in 1959. Top down fabrication can be likened to sculpting from a block of stone. A piece of the base material is gradually eroded until the desired shape is achieved. That is, you start at the top of the blank piece and work your way down removing material from where it is not required. Nanotechnology techniques for top down fabrication vary but can be split into mechanical and chemical fabrication techniques. The most top down fabrication technique is nanolithography. In this process, required material is protected by a mask and the exposed material is etched away. Depending upon the level of resolution required for features in the final product, etching of the base material can be done chemically using acids or mechanically using ultraviolet light, and x-rays or electron beams. This is the technique applied to the manufacture of computer chips. Bottom up fabrication can be described as building a brick house. Instead of placing bricks one-by-one at a time to produce a house from bottom, bottom up fabrication technology places atoms or molecules one-by-on at a time to build the desired nanostructure. Such processes are time consuming and so self assembly techniques appeared where the atoms arrange themselves as required. Self assembling nanomachines are regularly mentioned by science fiction writers but significant obstacles including the laws of physics will need to be overcome or circumvented before this becomes a reality. Other areas involving bottom up fabrication are already quite successful. Manufacturing quantum dots by self-assembly

High power femtosecond Bessel-X pulses directly from a compact fiber laser system

We report on high power ultrashort Bessel-X pulses directly from a compact fiber laser system. For spatial profiles, non-diffracting Bessel-like wavepackets were generated with the combination of a collimating lens and a silica-based inverse micro-axicon, which is specially designed and fabricated on the facet of an amplifying fiber doped by ytterbium. For temporal profiles, the seed pulses from a mode-locked dissipative soliton fiber laser at a repetition rate of 56.9 MHz were pre-shaped by a grating pair and a spectral filter. Amplified 18.7 W average power chirped ps pulses were obtained and then dechirped to a duration of 38 fs.

Configuration control of carbon nanotube probe in atomic force microscopy

To precisely control the nanotube probe’s length and orientation, focused ion beam (FIB) milling and irradiation processes are utilized in the study. The carbon nanotube (CNT) probes’ length is optimized by FIB milling and the end of the CNT probe after FIB processing is found to be a round end with a fullerenelike cap. Using ion beam irradiations method, the carbon nanotube probes are bended and aligned to the desired orientation due to the strain introduced by the ion beam and CNT’s excellent plastic ability as well. The evaluation of carbon nanotube probe’s metrology performance is also made by correlating CNT probe structures with the probe’s atomic force microscopy (AFM) images resolution. It is found that the CNT probe can well overcome the bending response effect on the image resolution if its lateral force constant is larger than 0.086 N/m and CNT probe’s angle is less than 30°. The nanotube probe after FIB alignment shows high image resolution, and it can detect an edge with vertical angle of 88....