Showing papers by "Xinxin Li published in 2012"
TL;DR: The results show that hexagonal lamelliform SBA-15 with a uniform particle size and short vertical channels plays two significant roles in uniformly dispersing amine-functionalizing groups and effectively adjusting the loadings of the functional groups within the mesopore channels.
Abstract: Amine-functionalized SBA-15 with uniform morphology and well-defined mesostructure was prepared using a postgrafting route. The morphology, mesostructure, and functionality of the materials were characterized by scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, nitrogen adsorption–desorption, Fourier transform infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy techniques. The results show that hexagonal lamelliform SBA-15 with a uniform particle size and short vertical channels plays two significant roles in uniformly dispersing amine-functionalizing groups and effectively adjusting the loadings of the functional groups within the mesopore channels. To confirm the potential application of the hybrids in gas sensors, using amine-functionalized SBA-15 as a sensing material and a quartz crystal microbalance as a transducer, a parts per billion level formaldehyde sensor with high sensitivity (response time about 11 s, recovery time about ...
105 citations
TL;DR: A strategy for the synthesis of 3D porous nanostructures by controlled aggregation of nanoparticles in oleylamine is presented in this article, where the atomic ratio between the two components (Pt and Rh) is tuned by varying the concentration of precursor salts.
Abstract: A strategy for the synthesis of PtRh alloy 3D porous nanostructures by controlled aggregation of nanoparticles in oleylamine is presented. The atomic ratio between the two components (Pt and Rh) is tuned by varying the concentration of precursor salts acc
100 citations
TL;DR: In this article, the authors focused on microcantilever-based sensing and probing functions that are realized by integrating a mechanically compliant cantilever with self-sensing and self-actuating elements, specific sensing materials as well as functionalized nano-tips.
Abstract: This topical review is focused on microcantilever-based sensing and probing functions that are realized by integrating a mechanically compliant cantilever with self-sensing and self-actuating elements, specific sensing materials as well as functionalized nano-tips Such integrated cantilever devices have shown great promise in ultra-sensitive applications such as on-the-spot portable bio/chemical detection and in situ micro/nanoscale surface analysis and manipulation The technical details of this review will be given in a sequence of cantilever sensors and, then, cantilever-tip probes For the integrated cantilever sensors, the frequency-output style dynamic cantilevers are described first, with the contents including optimized resonance modes, sensing-group-modified nanostructures for specific bio/chemical mass adsorption and nanoscale sensing effects, etc Thereafter, the static cantilever sensors for surface-stress detection are described in the sequence of the sensing mechanism, surface modification of the sensitive molecule layer and the model of specific reaction-induced surface-energy variation After technical description of the cantilever sensors, the emphasis of the review moves to functionalized nano-tip equipped cantilever-tip probing devices The probing functions are not only integrated on the cantilever but also integrated at the sharp apex of the tip After description of single integrated cantilever probes and their applications in surface scanning and imaging, arrayed cantilever-tip devices and their simultaneous parallel operation for high throughput imaging and nanomechanical data storage are also addressed With cantilever-tip probes as key elements, micro-analysis instruments are introduced that can be widely used for macro/nanoscale characterizations
91 citations
TL;DR: In this article, the design and fabrication of batch-processed cantilever probes with electrical shielding for scanning microwave impedance microscopy is presented, and the diameter of the tip apex, which defines the electrical resolution, is less than 50 nm.
Abstract: This paper presents the design and fabrication of batch-processed cantilever probes with electrical shielding for scanning microwave impedance microscopy. The diameter of the tip apex, which defines the electrical resolution, is less than 50 nm. The width
73 citations
TL;DR: With -NH2-group-functionalized MTF directly grown onto the surface of the cantilever free end, the micro-/nanocombined gravimetric sensor has experimentally exhibited quick response and highly sensitive detection of CO2 gas.
Abstract: This paper reports a novel top-down/bottom-up combined resonant microcantilever chemical sensor, where the nanosensing material of a functionalized mesoporous thin film (MTF) is directly self-assembled on the sensing region of the integrated microcantilever. By using the batch-producible nano-on-micro construction technique, a large number of such sensors can be batch fabricated with uniform performance and low cost. More importantly, the sensing molecule terminals can be simultaneously constructed at the pore inner surface when the MTF is directly grown on the cantilever. With -NH2-group-functionalized MTF directly grown onto the surface of the cantilever free end, the micro-/nanocombined gravimetric sensor has experimentally exhibited quick response and highly sensitive detection of CO2 gas.
55 citations
TL;DR: In this paper, a novel surface-micromachining technology is developed to monolithically integrate piezoresistive pressure sensor and accelerometer for tire-pressure monitor system (TPMS) applications.
51 citations
TL;DR: In this article, a single-side micromachined tire-pressure monitoring system (TPMS) sensor for automobiles, which is with a piezoresistive pressure sensor and a cantilever-mass PPS accelerometer monolithically integrated in a 1.6 mm × 1.5 mm sized (111)-silicon chip.
Abstract: This paper concerns the development of a single-side micromachined tire-pressure monitoring system (TPMS) sensor for automobiles, which is with a piezoresistive pressure sensor and a cantilever-mass piezoresistive accelerometer monolithically integrated in a 1.6 mm × 1.5 mm sized (111)-silicon chip. Single-wafer-based front-side silicon micromachining and metal electroplating technologies are employed to fabricate the device. Specially designed releasing trenches along (111) orientation are constructed to form the hexagonal pressure-sensitive diaphragm and the postsealed vacuum reference cavity. The fabrication of the accelerometer is also based on a hexagonal diaphragm that is latterly cut into suspended cantilevers and seismic mass. To achieve a high sensitivity, a high-density copper thick film is selectively electroplated to significantly increase the mass. The performance of the 115-g-ranged accelerometer is measured, exhibiting a sensitivity of 99.9 μV/g (under 3.3-V supply), nonlinearity of ±0.45% FS, and the noise floor of better than 0.2 g. The 750-kPa-ranged pressure-sensor sensitivity is measured as 0.108 mV/kPa (under 3.3-V supply), with the nonlinearity error smaller than ±0.1% FS and the temperature coefficient of sensitivity as -0.19%/°C FS before compensation. The noise floor of the pressure-sensor out- put signal is 0.15 kPa. The zero-point temperature coefficient is tested as -0.11%/°C FS and -0.024%/°C FS for the accelerometer and the pressure sensor, respectively. Fabricated with the low-cost front-side micromachining technique, the small-sized TPMS sensors are promising in practical applications and volume production.
47 citations
TL;DR: In this article, two mesoporous SBA-15/organic hybrids featuring fluoroalcohol and fluorinated-phenol derivatives were successfully synthesized via a co-condensation route.
Abstract: Two new mesoporous SBA-15/organic hybrids featuring fluoroalcohol and fluorinated-phenol derivatives were successfully synthesized via a co-condensation route. Hexafluorobisphenol and hexafluoroisopropanol were chosen to graft onto mesostructured silica, respectively. The as-synthesized hybrids preserve their mesoscopic structures with relative large surface areas and pore volume, as confirmed by SAXS, TEM and N2 adsorption–desorption porosimetry. Moreover, FT-IR and solid-state MAS NMR spectroscopy proved covalent anchoring of the organic functional groups onto the SBA-15. In order to confirm the potential application of the hybrids in gas sensing, investigations on the sensing properties toward the nerve agent simulant dimethyl methylphosphonate (DMMP) were carried out by QCM transducer. The QCM sensors based on hybrid materials exhibit excellent sensitivity toward trace DMMP vapour down to 26 ppb. In comparison with pristine SBA-15, the hybrids also show remarkably enhanced selectivity to DMMP due to suitable H-bonding interactions. Therefore, the well-defined mesoscopic porosity of the organic–inorganic hybrids together with the grafted fluoroalcohol and fluorinated-phenol derivatives lead to excellent sensing properties to DMMP vapour, and show great potential in the area of nerve agent detection.
42 citations
TL;DR: With specific sensing-groups modified, the porous-layered nanostructure can be constructed onto resonant microcantilevers for chemical sensing.
41 citations
TL;DR: In this paper, a hyper-branched polymer is self-assembled on a resonant micro-cantilever and functionalized with sensing-terminals for the specific detection of the trace chemical vapor of dimethyl methylphosphonate (DMMP), a typical simulant for nerve agents.
Abstract: A hyper-branched polymer is layer-by-layer self-assembled on a resonant micro-cantilever and, then, functionalized with sensing-terminals for the specific detection of the trace chemical vapor of dimethyl methylphosphonate (DMMP, a typical simulant for nerve agents). The hyper-branched polymer is directly constructed on the SiO2 surface of the cantilever via an A2 + B4 layer-by-layer route, where A2 and B4 are complementary interacting groups which undergo coupled linking. After modification with 4-(2-(4-(allyloxy)phenyl)-1,1,1,3,3,3-hexafluoropropan-2-yl)phenol (APHFPP) groups specific to DMMP, the high specific-surface-area hyper-branched polymer provides very dense sensing sites to adsorb a great number of DMMP molecules for micro-gravimetric detection. Moreover, the sensing polymer possesses a “more branches but fewer roots” configuration on the cantilever surface to depress the cross-talk effect caused by adsorption induced cantilever spring-stiffening. Experimental results indicate that, self-assembled with the hyper-branched sensing polymer, the resonant cantilevers exhibit rapid and reproducible detection of trace DMMP (with the detection limit lower than 7.2 ppb) and effectively depressed parasitic frequency-shift from the cantilever spring stiffening effect. In addition, the sensor features satisfactory selectivity in the presence of water and organic solvents. When an alternative sensing-group of 2-allylhexafluoroisopropanol (AHFIP) is modified on the hyper-branched architecture, the cantilever becomes specifically sensitive to trace explosive vapor. Therefore, the developed technique for the functionalization of hyper-branched polymer directly grown on a cantilever provides a widely usable micro/nano sensing-platform for the detection of trace chemical vapors.
32 citations
TL;DR: In this paper, thiol-functionalized SBA-15 mesoporous silica materials with various pore sizes and specific surface areas were prepared by using a post-grafting process.
Abstract: Thiol-functionalized SBA-15 mesoporous silica materials with various pore sizes and specific surface areas were prepared by using a post-grafting process. All the obtained materials were characterized by SAXS, FT-IR, TGA, TEM and N-2 adsorption isotherms.
TL;DR: In this paper, a scanning microwave impedance microscope (MIM) is employed to resolve the local conductivity distribution of a static random access memory (SRAM) sample, which can also be adjusted to the scanning capacitance microscopy (SCM) mode, allowing both measurements on the same region.
Abstract: Real-space mapping of doping concentration in semiconductor devices is of great importance for the microelectronic industry. In this work, a scanning microwave impedance microscope (MIM) is employed to resolve the local conductivity distribution of a static random access memory (SRAM) sample. The MIM electronics can also be adjusted to the scanning capacitance microscopy (SCM) mode, allowing both measurements on the same region. Interestingly, while the conventional SCM images match the nominal device structure, the MIM results display certain unexpected features, which originate from a thin layer of the dopant ions penetrating through the protective layers during the heavy implantation steps.
TL;DR: A pair of opposite sequence in sensing-signal amplitude has indeed been obtained that verifies the proposed joint-sensing method, and the two sensing signals both show a linear relationship with chemical concentration (at low-concentration range).
Abstract: The study presents a novel chemo-mechanical joint-sensing method to distinguish a certain molecule from its homologous chemicals, using both a resonant cantilever for gravimetric sensing and a static cantilever for surface-stress sensing. Homologous amines of trimethylamine (TMA, Me(3)N), dimethylamine (DMA, Me(2)NH), and monomethylamine (MMA, MeNH(2)) are herein used as model objects for investigation. The molecular identification is based on experimental characterizations on both molecule adsorbing capability (by the resonant cantilever) and intermolecular lateral interaction (by the static cantilever). The intensities of the two sets of sensing signals are expected to be in opposite sequence with each other, due to the complementary relationship among the interhomologue molecule structures, i.e., a molecule containing a greater number of methyl substituents must possess a fewer number of nonsubstituted hydrogens. On the basis of the proposed idea, ppm-level vapors of the three amines are sequentially detected by a resonant microcantilever to characterize the molecular adsorption speed and another static cantilever to characterize the intermolecular lateral attraction induced surface stress. From the experiment, a pair of opposite sequence in sensing-signal amplitude has indeed been obtained that verifies the proposed joint-sensing method. In addition, the two sensing signals both show a linear relationship with chemical concentration (at low-concentration range). Further comparison between the two sensing results can help to build a model to identify the molecule among a series of its homologous chemicals by eliminating the influence from concentration. Since a complementary relationship among homologous molecule structures widely exists, the dual-sensing method is promising in on-the-spot rapid molecular identification among homologous chemicals.
TL;DR: In this article, two structural types of piezoresistive micro flow sensors are designed and fabricated in (1 1 1/1/1) wafers, where sensor-bare chips directly packaged into micro-fluidic systems with low-cost surface mounting technology (SMT).
Abstract: This paper reports novel single-wafer-based piezoresistive micro flow sensors, which are bulk micromachined only from the front side of the silicon wafer to facilitate the sensor-bare chips directly packaged into micro-fluidic systems with low-cost surface mounting technology (SMT). With neither double-sided micromachining nor multiwafer bonding needed, two structural types of the piezoresistive flow sensors are designed and fabricated in (1 1 1) wafers, where ‘type A’ sensor has a smaller channel cross section area compared to ‘type B’ sensor. After the bare sensor chip directly attached on a printed circuit board (PCB), wire bonded between the pads and the PCB for electric interconnection and the inlet/outlet front side connected, deionized water is flowed into the both types of flow sensors to characterize piezoresistive output of the differential pressure sensing elements in terms of the flow rate. For ‘type A’ and ‘type B’ sensors that are both power supplied with DC 5 V, the sensitivities are sequentially measured as 766.80 mV (µL s−1)−1 and 19.12 mV (µL s−1)−1, with the nonlinearities as 0.4% FS and 0.9% FS, respectively. Compared with traditionally fabricated micro flow sensors, the single-chip fabricated differential-pressure flow sensors can be low-cost volume manufactured. Moreover, the bare sensor chips can be simply SMT packaged for low-cost micro-system applications.
15 Mar 2012
TL;DR: In this article, a nonlinear energy harvester that can be operated in a wide frequency range of tens of Hz, as a potential power supply for tire pressure monitoring systems (TPMS), is presented.
Abstract: This paper presents a nonlinear energy harvester that can be operated in a wide frequency range of tens of Hz, as a potential power supply for tire pressure monitoring systems (TPMS). Frequency up-conversion is achieved by a two-stage oscillator structure. The non-contact magnetic repulsive driving mechanism eliminates mechanical collision during operation, thereby improving efficiency and endurance. A miniature energy harvester has been designed, fabricated and characterized, resulting in a generation capability of over 10μW of average power within the frequency range of 10Hz to 22Hz (under 1g acceleration).
TL;DR: In this paper, a nonlinear equation-based closed-form solution for a springloading-enclosed electrothermal post-buckling microbeam was proposed to express the relation between the compressive loads and its corresponding lateral deflections and the threshold loads required to trigger the buckling phenomenon, under the condition of a variety of transverse loads.
Abstract: We report on a nonlinear equation-based closed-form solution for a spring-loading-enclosed electrothermal post-buckling microbeam that expresses (a) the relation between the compressive loads and its corresponding lateral deflections and (b) the threshold loads required to trigger the buckling phenomenon, under the condition of a variety of transverse loads. Our theoretical research reveals that the post-buckling behavior varies considerably under different transverse load ranges. Three types of double-clamped microbeams connected to microsprings with different dimensions and compliances representing transverse loads were fabricated and measured using microelectromechanical systems (MEMS) technology. Excellent agreement was found between our theoretical analysis and experimental results to confirm our exact solutions. It proves that the influences on thermal post-buckling behavior are dependent on different microbeam dimensions and microspring compliances (i.e., transverse loads). Therefore, an electrothermal buckling/post-buckling beam under external transverse loads can be accurately predicted using our theoretical model, which can be applied to either existing microdevices that are based on similar principles or other potential applications.
TL;DR: The proposed fast regeneration method is promising in repeatedly or multi-target detection applications of micro/nano immune-sensors, e.g. the resonant micro-cantilevers.
Abstract: With high sensitivity and specificity to antigen, immune micro-sensors can be used in rapid detection of pathogenic microbial. This study proposes and develops a method for rapidly regeneration of antibody on a resonant micro-cantilever sensor. A nitrilotriacetic acid (NTA) derivative is synthesized with cystine and bromoacetic acid, then added with 2-mercaptoethanol to prepare a mixed self-assembled monolayer (SAM) on Au (111) surface of the cantilever. Ni2+ ions are thereafter chelated on the mixed SAM to form a breakable and re-linkable chelating-bond layer. Repeatable cycles of antibody immobilization and erasing are experimentally validated with a detectable marker of synthesized biotinylated poly peptides harboring six histidine residues (named as His-Bio). Two distinguished pathogenic microbial, Escherichia. coli O157:H7 and Bacillus Anthracis, are detected with the rapidly regenerated sensor. The E. coli O157:H7 sensor exhibits a three-time repeated detection to the 103 CFU/ml concentration microbial. Then, an E. coli O157:H7 sensor is eluted with Tris–HCl (20 mM Tris, 150 mM NaCl, 0.1% Tween 20, pH = 3.0) and rapidly reconstructed into a B. Anthracis sensor by changing the re-immobilized antibody. The cantilever sensor no longer responses to E. coli O157:H7 even in a high concentration of 107 CFU/ml. In contrast, the sensor is experimentally confirmed being resoluble to low concentration B. Anthracis at 103 spores/ml level. The proposed fast regeneration method is promising in repeatedly or multi-target detection applications of micro/nano immune-sensors, e.g. the resonant micro-cantilevers.
01 Oct 2012
TL;DR: In this paper, a new micro-gravimetric organophosphate (OP) sensor is developed, which shows satisfactory detection limit of hundreds of ppb (parts per billion) to acephate vapor in air.
Abstract: Carboxylic acid-functionalized mesoporous silica nanoparticles (CF-MSNs) with ultra-high specific surface area are synthesized successfully as sensing material. With the CF-MSNs sensing material loaded onto our lab-made resonant micro-cantilever, which is with both resonance-exciting and self-sensing elements integrated, a new micro-gravimetric organophosphate (OP) sensor is developed. The sensor shows satisfactory detection limit of hundreds of ppb (parts-per-billion) to acephate vapor in air.
TL;DR: The first sentence of the acknowledgments was incorrect and the authors would like to acknowledge the following projects that support the research works related in this topical review: Chinese 973 Program, NSFC, and Korean WCU project.
Abstract: The first sentence of the acknowledgments was incorrect. It should read as follows: "The authors would like to acknowledge the following projects that support the research works related in this topical review: Chinese 973 Program (2011CB309503), NSFC projects (60725414, 91023046) and Korean WCU project (R32-2009-000-20087-0)."
17 Jun 2012
TL;DR: In this paper, a stacked-spiral inductor with VERTICAL closed-circuit nano-particle magnetic core in CMOS is reported, which shows a high inductance-density up to 920 nH/mm2 in multi-GHz.
Abstract: A new concept of stacked-spiral inductor fully-filled with VERTICAL closed-circuit nano-particle magnetic core in CMOS is reported. Prototypes, fabricated in a six Al metal layer CMOS backend process using ferrite nanoparticles, show a high inductance-density up to 920 nH/mm2 in multi-GHz, which is promising for making super compact inductors in RF system-on-a-chip (SoC).
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TL;DR: In this article, the authors used a unique cryogenic microwave impedance microscope to directly image QSH edges in a HgTe quantum well, with the spatial width of edge conduction increasing monotonically across the bulk gap from the p-type side through the Dirac point into n-type.
Abstract: To establish the central role of the helical edge states for the recently-discovered quantum spin Hall (QSH) system, direct imaging of those edge states is an important milestone Employing a unique cryogenic microwave impedance microscope, we directly image QSH edges in a HgTe quantum well The edge states emerge prominently when the Fermi level is tuned into the bulk gap, with the spatial width of edge conduction increasing monotonically across the bulk gap from the p-type side through the Dirac point into n-type This monotonic evolution of edge width is counterintuitive at first glance but is in good agreement with the underlying particle-hole asymmetry of HgTe band structure The observed dependence of edge state width on magnetic field is not expected from single-electron Landau level physics but may be understood by including band bending at the edge Detailed agreement between theory and the imaging experiment supports the notion of HgTe being a model system for the QSH effect
TL;DR: With additional advantages of elimination of single-sided adsorption induced bimetallic effect noise, tinier size, and easier fabrication, the ultrasensitive nanothick beam sensors show promise to replace the state-of-the-art piezoresistive cantilevers for bio/chemical nanomechanical detection.
Abstract: This study proposes nanothickness piezoresistive double-clamped beams that are used in a double-side adsorbing mode. The axially stressed clamped beam exhibits continually increasing sensitivity as it is thinned down to nanoscale, and the thinning is theoretically without limitation. Sensing experiments to part-per-million levels of trimethylamine vapor well verify the proposal. A 93 nm thick beam sensor exhibits higher than 1 order of magnitude sensitivity compared to typical piezoresistive cantilever sensors, and its chemomechanical sensing resolution is comparable with that obtained by the off-cantilever optical detection method. With the nanobeam, a surprisingly ultrahigh sensitivity to surface molecular self-assembly induced surface stress is also obtained that is about 150 times higher than that obtained from a conventional cantilever. With additional advantages of elimination of single-sided adsorption induced bimetallic effect noise, tinier size, and easier fabrication, the ultrasensitive nanothic...