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ABSTRACT: The movement of the magnetic domain wall could result in the changing of the contact resistance. Such a resistance change is named as the domain wall Magnetoresistance (DWMR), which can be used as a basic signal of nanodevices. For application, a large DWMR is necessary to improve the device performance. An approach to improve the DWMR value is to fabricate magnetic structures with narrow contact width. However, due to the proximity effect during the process of electron beam lithography (EBL), it is not easy to fabricate sub-20 nm width structures by EBL technique directly. In this paper, we investigated the fabrication of sub-20 nm width nanocontact structures by combined techniques of EBL and shadow evaporation. Upon optimizing the resist thickness, opening width, and the evaporation angle, the contact width was tuned and the corresponding variation trends with these parameters were explored. Using the optimized fabrication conditions, 14 nm wide ferromagnetic contact structures were successfully fabricated.
Journal of Nanoscience and Nanotechnology 02/2013; 13(2):1199-202. · 1.56 Impact Factor
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ABSTRACT: Specific biorecognition is essential for many biological processes, for which highly sensitive and label-free biosensors are strongly demanded. The recently developed metamaterials are a potential choice for biosensing due to their exotic properties. In the current work, a label-free and specific sensor for streptavidin-agarose (SA) was fabricated based on terahertz metamaterial functionlized by octadecanthiols and biotins. Both low and high frequency resonant modes from the metamaterials are found applicable for the detection of SA, and a redshift up to 6.76GHz for the high frequency mode was measured in the undiluted commercial solution. The low frequency mode is attributed to inductor-capacitor (LC) oscillation, while the high frequency mode originates from the plasmonic dipole oscillator, both of which are highly sensitive to the micro-environment change. Adsorption of SA of different concentrations causes different redshifts, and the replacement of high refractive-index substrate with low refractive-index substrate can efficiently promote the sensitivity, well agreeing with the numerical simulation. Moreover, for a particular biomolecule, the sensitivity can be further improved by optimizing the metamaterial design. This method might be very helpful for desirable biorecognition in biology, medicine, and drug industry.
Biosensors & bioelectronics 11/2012; 42C:626-631. · 5.43 Impact Factor
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ABSTRACT: Graphene sheet is expected to be a highly efficient field emitter due to its unique electrical properties and open surface with sharp edges. However, it is still a tremendous technical challenge to grow and align a graphene sheet in one particular direction to protrude its sharp edges for good field emission. Here, we report an ideal graphene field emitter of flower-like graphene nanosheets grown on a silicon nanocone array, wherein nanocone array guides the alignment of vertical nanosheets and produces high-density sharp edge protrusions on the conical tip. We observe high performance and stable field emission with low turn-on fields from floral-clustered graphene nanosheets. Protrusive sharp edges on the nanocone tip and optimized spacing between clusters both appear to locally enhance the electric field and dramatically increase field emission. Our new graphene emitter design provides a robust approach to the prospect for development of practical electron sources and advanced devices based on graphene field emitters.
Nanoscale 09/2012; 4(20):6383-8. · 5.91 Impact Factor
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ABSTRACT: Metamaterials (MMs) have shown huge potential in sensing applications by detecting their optical properties, which can be designed to operate at frequencies from visible to mid-IR. Here we constructed complementary split ring resonator (CSRR) based metamaterials in nanoscale with unit length of 100 nm and slit width of 30 nm, and observed obvious responses in the visible waveband from 600 to 900 nm. These visible responses show a good tunability with the structure's geometry, and are well suited for dielectric detection. We demonstrated good refractive index sensing of CSRR based metamaterials in the visible region under both 0° and 90° polarized incidence. Our results extend the study of CSRR based metamaterials to the visible region, which is expected to deepen the understanding of the response mechanism of CSRRs and benefit their sensing applications in the visible region.
Nanotechnology 06/2012; 23(27):275503. · 3.98 Impact Factor
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Jia Wang,
Qiang Zhang,
Bin Cui,
Jin Guo,
YongBo Bian,
XiaoFeng He,
ChunGuang Li,
XueQiang Zhang,
Hong Li,
WuXia Li, ChangZhi Gu,
JiBao Meng,
YuSheng He
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ABSTRACT: An L-band HTS duplexer with improved performance for communication applications has been developed. This is an improved version
of the duplexer previously developed by our group. The duplexer was composed of a T-junction and two channels. Each channel
has a 10-pole quasi-elliptic function bandpass HTS filter with a bandwidth of 27 MHz, and center frequencies at 1200 MHz and
1260 MHz. To achieve higher performance, especially a good balance between selectivity and flat group delay, the two pairs
of transmission zeros from the two filters were reassigned so that one pair is used for high selectivity and the other for
flat group delay. To reduce the influence of parasitical coupling, new coupling structures were developed in the simulation
process. The duplexer was fabricated on a 2 inch diameter, 0.5 mm thick LaAlO3 wafer with a double-sided YBCO film. The measured results showed a very high performance: a mid-band insertion loss of 0.2
dB, a return loss better than −14 dB, a shape factor better than 1.4:1, an out-of-band rejection of better than 70 dB in a
wide frequency range up to 3 GHz and excellent isolation (higher than 80 dB) between the two channels. In addition, the frequency
band 5 ns group delay variation is over 10.5 MHz (38.7% of 1 dB bandwidth).
KeywordsHTS duplexer-bandpass filter-coupling-group delay-selectivity
Chinese Science Bulletin 04/2012; 55(31):3527-3532. · 1.32 Impact Factor
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Lu Gao,
Jin Guo,
YueHui Wang,
Tao Yu,
Qiang Zhang,
ChunGuang Li,
XueQiang Zhang,
Hong Li,
JunJie Li,
WuXia Li, ChangZhi Gu,
JiBao Meng,
Ji Feng,
YuSheng He
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ABSTRACT: This paper reports a 6-pole high-temperature superconducting (HTS) microstrip bandpass filter for radio astronomy applications.
The filter has a center frequency of 23 GHz and a bandwidth the 2 GHz. We have made many efforts, such as adopting 0.25-mm-thick
substrate, carefully designing the housing box and filter layout, to solve the problems in realizing a K-band planar filter.
A special straight-line half-wavelength resonator (center-widen resonator) was also designed to reduce the insertion loss
of the filter. The measured results showed a midband insertion loss of 0.11 dB with a ripple of 0.4 dB, and a return loss
better than 11.5 dB. Good agreement was obtained between simulated and measured results.
Chinese Science Bulletin 04/2012; 54(19):3485-3488. · 1.32 Impact Factor
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ABSTRACT: We report that, to enable studies of their compositional, structural and electrical properties, freestanding individual nanoobjects can be selectively felled in a controllable way by the technique of low-current focused-ion-beam (FIB) milling with the ion beam at a chosen angle of incidence to the nanoobject. To demonstrate the suitability of the technique, we report results for zigzag/straight tungsten nanowires grown vertically on support substrates and then felled for characterization. We also describe a systematic investigation of the effect of the experimental geometry and parameters on the felling process and on the induced wire-bending phenomenon. The method of felling freestanding nanoobjects using FIB is an advantageous new technique enabling investigations of the properties of selected individual nanoobjects.
Nanotechnology 03/2012; 23(10):105301. · 3.98 Impact Factor
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ABSTRACT: Nanostructured surface possessing ultrahigh adhesion like "gecko foot" or "rose petal" can offer more opportunities for bionic application. We grow flower-like few-layer graphene on silicon nanocone arrays to form graphene nanoclusters, showing robust adhesion. Their contact angle (CA) is 164° with a hysteresis CA of 155° and adhesive force for a 5 μL water droplet is about 254 μN that is far larger than present reported results. We bring experimental evidences that this great adhesion depends on large-area plentiful edges of graphene nanosheets tuned by conical nanostructure and intrinsic wetting features of graphene. Such new hierarchical few-layer graphene nanostructure provides a feasible strategy to understand the ultra-adhesive mechanism of the "gecko effect" or "rose effect" and enhance the wettability of graphene for many practical applications.
Scientific Reports 01/2012; 2:511.
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ABSTRACT: Excellent field electron emission properties of a diamond/CoSi(2)/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi(2) conducting interlayer. The results show that the main emission properties were modified by varying the CoSi(2) thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi(2 )interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi(2) layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays.
Scientific Reports 01/2012; 2:746.
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ABSTRACT: Vertically aligned single-crystal SnO(2) nanoshuttle arrays with uniform morphology and a relatively high aspect ratio were synthesized by a simple hot-wall chemical vapor deposition (CVD) method. It was found that regulating the growth temperature gradient could change the shape of the SnO(2) nanostructure from nanoshuttles to nanochisels and nanoneedles, and a self-catalyzing growth process was responsible for tunable morphologies of SnO(2) nanostructures. The as-synthesized SnO(2) nanoshuttles showed ultrahigh flexibility and strong toughness with a large elastic strain of ∼ 6.2, which is much higher than reported for Si and ZnO nanowire as well as most crystalline metallic materials. The field emitter fabricated using SnO(2) nanoshuttle arrays has a low turn-on electric field of around 0.6 V µm(-1), and a high field emission current density of above 10 mA cm(-2), which is comparable with the highest emission current density of carbon nanotube and nanowire field emitters.
Nanotechnology 11/2011; 22(50):505601. · 3.98 Impact Factor
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ABSTRACT: A novel approach based on the Poisson spot effect in a conventional optical lithography system is presented for fabricating large-scale ordered ring patterns at low cost, in which the pattern geometries are tuned by controlling the exposure dose and deliberate design of the mask patterns. Following this by cryogenic deep etching, the ring patterns are transferred into Si substrates, resulting in various vertical tubular Si array structures. Microscopic analysis indicates that the as-fabricated Si microtubes have smooth interior and exterior surfaces that are uniform in size, shape and wall-thickness, which exhibit potential applications as electronic, biological and medical devices.
Nanotechnology 09/2011; 22(39):395301. · 3.98 Impact Factor
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ABSTRACT: We report thickness-dependent morphologies of a Pd film on n-layer graphenes. Via Raman spectroscopy-based technique, obvious charge transfer has been observed among Pd and graphenes, which is also dependent on the layer number. With the increase of the layer number, the Pd film becomes coarser, and the electron transfer becomes lower.
Chemical Communications 09/2011; 47(33):9408-10. · 6.17 Impact Factor
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ABSTRACT: The electrical properties of lateral ultra-fine tungsten nanowires, which were grown by focused-ion-beam-induced deposition with 1 pA ion-beam current, were investigated. Temperature-dependent electrical measurements show that the wires are conducting and have a superconducting transition with a transition temperature (Tc) about 5.1 K. Resistance vs. temperature measurements reveal that, with decreasing cross-sectional area, the wires display an increasingly broad superconducting transition. A residual resistive tail extending down to the low-temperature region is found only for the thinnest tungsten nanowire, which is 10 nm thick and 19 nm wide. The logarithm of the residual resistance of this wire appears as two linear sections as a function of temperature, one within 300 mK below Tc and the other extending down to the lowest measuring temperature of 4.26 K. Such features have previously been identified with phase slip processes. Our results are suggestive that the focused-ion-beam technique might be a potential approach to fabricate ultra-thin and ultra-narrow nanowires for the study of superconducting suppression in nanoscale materials and for maskless superconducting device fabrication.
Microelectronic Engineering 08/2011; 88:2636. · 1.56 Impact Factor
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Haiqing Zhou,
Huaichao Yang,
Caiyu Qiu,
Zheng Liu,
Fang Yu,
Minjiang Chen,
Lijun Hu,
Xiaoxiang Xia,
Haifang Yang, Changzhi Gu,
Lianfeng Sun
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ABSTRACT: Ferromagnetism in graphite/graphenes is attractive for fundamental science and potential applications in carbon-based magnetism and spintronics. In this work, we show that magnetic particle inspection can be miniaturized to detect local magnetic moments with a high spatial resolution of 1.0 nm using scanning electron microscopy. A metal nanowire and adjacent nanogap can be found at the edges of graphenes and graphite for atoms with magnetic moments (Fe, Co, Ni, Mn, Pd, Al), whereas no similar characteristics are found for diamagnetic metals (Au, Ag). By investigating these features under an external magnetic field and at different temperatures, we discuss possible mechanisms and propose that intrinsic ferromagnets exist and form a one-dimensional array at the edges of graphenes and graphite. Meanwhile, the size of individual magnets (<4.8 Å), orientation, magnitude (0.45 μB per carbon edge atom) of magnetic moments, and their Curie temperature (>95 °C) are obtained, which are novel and interesting.
07/2011;
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ABSTRACT: In this Letter, the nanoporous anodic alumina membranes (nanoPAAM) were first fabricated by the two-step anodic oxidisation method, and then based on these nanoPAAM master molds, polymer polymethylmethacrylate nanopillars with controllable heights and diameters were achieved by the direct casting method. Subsequently, combined with the ultraviolet lithography or electron beam lithography, a kind of useful platform of microfluidic channel that was embedded with nanopillar arrays was achieved. Finally, the transferring processes of DNA molecules around the entrance of the hybrid channel were monitored with an epi-fluorescence microscopy and electron multiplying charge coupled device camera in real time. The hybrid structure of microchannel with nanopillar arrays provides critical advantages when using the fluorescent microscopy to detect the dynamics of single DNA molecules.
Micro & Nano Letters 06/2011; · 0.94 Impact Factor
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Advanced Materials 03/2011; 23(10):1246-51. · 13.88 Impact Factor
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ABSTRACT: In this paper, we report the fabrication of permalloy nanocontact structures with greatly improved surface and edge smoothness. Magnetic sputtering and thermal evaporation were used for metal film deposition, and lift-off and dry etching techniques were employed for nanocontact structure patterning. The compositional properties of the resulting nanocontacts were investigated using energy dispersive analysis of X-ray (EDAX). Atom force microscope and scanning electron microscope were used for morphological characterisation. We found that high quality permalloy nanocontact structures can be obtained by using the combination of thermal evaporation and lift-off with optimised processing parameters; meanwhile, in the case of depositing metal films using magnetic sputtering, dry etching technique rather than lift-off was used for improved surface morphology of the nanostructures.
Journal of Nanoscience and Nanotechnology 11/2010; 10(11):7138-41. · 1.56 Impact Factor
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ABSTRACT: The anodic aluminum oxide (AAO) template with ordered pores was firstly fabricated in oxalic acid solutions using two-step anodization method. Then, a layer of polymethylmethacrylate (PMMA) was uniformly laid on one surface of the AAO template by a Spin-Coater, then baked and cooled them, after that, the H3PO4 solution was utilized to dissolve the residual aluminum and barrier layer, as the result, the functional nanopillar arrays were achieved. Finally, the morphology of the functional PMMA nanopillars was examined with the Scanning Electron Microscope (SEM) and the properties were discussed. The functional nanopillar arrays could be applied to the micro and nano-scale devices as the sensors for the biological, chemical and single molecular detection.
Journal of Nanoscience and Nanotechnology 11/2010; 10(11):7447-50. · 1.56 Impact Factor
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ABSTRACT: Freestanding tungsten composite nanofeatures were grown by focused-ion-beam-induced deposition with 1 pA ion beam current. The temperature dependent electrical measurements show that the flying nanoscale tungsten is conducting with a room temperature resistivity of 550 micro omega cm. It is also superconducting with a Tc, above 5.1 K and can be repeatedly thermally cycled. Our results suggest that FIB direct-writing of three-dimensional tungsten composites might be a potential approach to fabricate vertical nanodevices and mask-free superconducting devices.
Journal of Nanoscience and Nanotechnology 11/2010; 10(11):7436-8. · 1.56 Impact Factor
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Zheng Liu,
Kaihong Zheng,
Lijun Hu,
Ji Liu,
Caiyu Qiu,
Haiqing Zhou,
Haibo Huang,
Haifang Yang,
Meng Li, Changzhi Gu,
Sishen Xie,
Lijie Qiao,
Lianfeng Sun
Advanced Materials 03/2010; 22(9):999-1003. · 13.88 Impact Factor
