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  • 1.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Electronic Sensors Based on Nanostructured Field-Effect Devices2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Point-of-care (POC) diagnostics presents a giant market opportunity with profound societal impact. In particular, specific detection of DNA and protein markers can be essential for early diagnosis of e.g. cancer, cardiovascular disease, infections or allergies. Today, identification of these markers often requires extensive laboratory work and hence is expensive and time consuming. Current methods for recognition and detection of specific biomolecules are mostly optics based and thus impose severe limitations as to convenience, specificity, sensitivity, parallel processing and cost reduction.

    Electronic sensors based on silicon nanowire field-effect transistors have been reported to be able to detect biomolecules with concentrations down to femtomolar (fM) level with high specificity. Although the reported capability needs further confirmation, the CMOS-compatible fabrication process of such sensors allows for low cost production and high density integration, which are favorable for POC applications. This thesis mainly focuses on the development of a multiplex detection platform based on silicon nanowire field-effect sensors integrated with a microfluidic system for liquid sample delivery. Extensive work was dedicated to developing a top-down fabrication process of the sensors as well as an effective passivation scheme. The operation mechanism and coupling efficiencies of different gate configurations were studied experimentally with the assistance of numerical simulation and equivalent circuits. Using pH sensing as a model system, large effort was devoted to identifying sources for false responses resulting from the instability of the inert-metal gate electrode. In addition, the drift mechanism of the sensor operating in electrolyte was addressed and a calibration model was proposed. Furthermore, protein detection experiments were performed using small-sized Affibody molecules as receptors on the gate insulator to tackle the Debye screening issue. Preliminary results showed that the directionality of the current changes in the sensors was in good agreement with the charge polarities of the proteins. Finally, a graphene-based capacitor was examined as an alternative to the nanowire device for field-effect ion sensing. Our initial attempts showed some attractive features of the capacitor sensor.

  • 2.
    Chen, Si
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Niemi, Antti J
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Univ Tours, Lab Math & Phys Theor, Federat Denis Poisson, CNRS UMR 6083, Parc Grandmont, F-37200 Tours, France.;Beijing Inst Technol, Dept Phys, Beijing 100081, Peoples R China..
    On Ramachandran angles, closed strings and knots in protein structure2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 31, article id 315401Article in journal (Refereed)
    Abstract [en]

    The Ramachandran angles (phi, psi) of a protein backbone form the vertices of a piecewise geodesic curve on the surface of a torus. When the ends of the curve are connected to each other similarly, by a geodesic, the result is a closed string that in general wraps around the torus a number of times both in the meridional and the longitudinal directions. The two wrapping numbers are global characteristics of the protein structure. A statistical analysis of the wrapping numbers in terms of crystallographic x-ray structures in the protein data bank (PDB) reveals that proteins have no net chirality in the phi direction but in the psi direction, proteins prefer to display chirality. A comparison between the wrapping numbers and the concept of folding index discloses a non-linearity in their relationship. Thus these three integer valued invariants can be used in tandem, to scrutinize and classify the global loop structure of individual PDB proteins, in terms of the overall fold topology.

  • 3.
    Chen, Si
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Jokilaakso, Nima
    School of Biotechnology, KTH, Stockholm.
    Karlström, Amelie Eriksson
    School of Biotechnology, KTH, Stockholm.
    Linnros, Jan
    School of Information and Communication Technology, KTH, Stockholm.
    Smith, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Current Instability for Silicon Nanowire Field-Effect Sensors Operating in Electrolyte with Platinum Gate Electrodes2011In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 14, no 7, p. J34-J37Article in journal (Refereed)
    Abstract [en]

    Current instability is observed for silicon nanowire field-effect transistors operating in electrolytes with Pt gate electrodes. A comparative study involving an Ag/AgCl-reference gate electrode reveals that the effect results from a drift in the potential at the Pt-electrode/electrolyte interface. In a phosphate buffer saline of pH 7.4, the stabilization of the potential of the Pt electrode was found to require approximately 1000 s. A concurrent potential drift, with a comparable time constant, occurring at the electrolyte/oxidized-nanowire interface rendered a complex device current response which complicated the interpretation of the results.

  • 4.
    Chen, Si
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Contacting versus Insulated Gate Electrode for Si Nanoribbon Field-Effect Sensors Operating in Electrolyte2011In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 83, no 24, p. 9546-9551Article in journal (Refereed)
    Abstract [en]

    Electric response to pH variations is employed to investigate Si nanoribbon field-effect transistors (SiNRFETs) operating in electrolyte with different gate configurations. For devices with a concluding gate electrode for direct metal electrolyte contact, a well-defined electrode reaction leading to a stable electrode potential is essential for retaining a stable electrical potential of the electrolyte. However, noble metals such as Pt do not meet the stability requirement and consequently bring severe distortions to the electronic response. For devices with an insulated gate electrode relying on the principle of capacitive gate coupling, the capacitance between the gate electrode and the electrolyte should be made much larger than the gate capacitance established between the SiNR and the electrolyte. In this case, an efficient gate control as well as a high stability against external disturbances can be ensured. Further studies show that surface charging of the gate insulator is the main cause responsible for the pH response of the SiNRFETs. Hence, devices with different gate configurations give rise to a comparable pH sensitivity.

  • 5.
    Chen, Si
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gate coupling and carrier distribution in silicon nanowire/nanoribbon transistors operated in electrolyte2011In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 29, no 1, p. 011022-Article in journal (Refereed)
    Abstract [en]

    The transfer characteristics of back-gate silicon nanowire/nanoribbon (NW/NR) transistors measured in electrolyte exhibit a significantly higher on-current and a steeper subthreshold behavior than measured in air. Simulation results show that the gate capacitance for a NW/NR of a trapezoidal cross-section immersed in water is significantly higher than that exposed to air. Electrostatics simulations further show that for NWs/NRs with small widths, carriers are mainly accumulated at the two side-edges when they are immersed in water. Even the top surface of the NWs/NRs sees more accumulated carriers than the bottom one does; the latter is in fact located closest to the back-gate. These observations suggest that the interface properties at the side-edges and the top surface are crucial for NW/NR transistors to achieve high sensitivity when performing real-time sensing experiments in electrolyte. Finally, the sensitivity of back-gate NW/NR field-effect transistors to charge changes in electrolyte is found to have a weak dependence on the NW/NR width when the doping concentration is below 10(17) cm(-3). For higher NW/NR doping concentrations, narrower NWs/NRs are more sensitive.

  • 6.
    Chen, Si
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhi-Bin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ma, Laipeng
    Shenyang National Laboratory, Kina.
    Ahlberg, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gao, Xindong
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Qiu, Zhijun
    Fudan University, Kina.
    Wu, Dongping
    Fudan University, Kina.
    Ren, Wencai
    Institute of Metal Research, CAS, China.
    Cheng, Hui-Ming
    Institute of Metal Research, CAS, China.
    Zhang, Shili
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    A graphene field-effect capacitor sensor in electrolyte2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 15, p. 154106-Article in journal (Refereed)
    Abstract [en]

    The unique electronic properties of graphene are exploited for field-effect sensing in both capacitor and transistor modes when operating the sensor device in electrolyte. The device is fabricated using large-area graphene thin films prepared by means of layer-by-layer stacking. Although essentially the same device, its operation in the capacitor mode is found to yield more information than in the transistor mode. The capacitor sensor can simultaneously detect the variations of surface potential and electrical-double-layer capacitance at the graphene/electrolyte interface when altering the ion concentration. The capacitor-mode operation further facilitates studies of the molecular binding-adsorption kinetics by monitoring the capacitance transient

  • 7.
    Chen, Xi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hu, Qitao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Solomon, Paul
    IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, USA.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Device noise reduction for Silicon nanowire field-effect-transistor based sensors by using a Schottky junction gate2019In: ACS sensors, ISSN 2379-3694, Vol. 4, no 2, p. 427-433Article in journal (Refereed)
    Abstract [en]

    The sensitivity of metal-oxide-semiconductor field-effect transistor (MOSFET) based nanoscale sensors is ultimately limited by noise induced by carrier trapping/detrapping processes at the gate oxide/semiconductor interfaces. We have designed a Schottky junction gated silicon nanowire field-effect transistor (SiNW-SJGFET) sensor, where the Schottky junction replaces the noisy oxide/semiconductor interface. Our sensor exhibits significantly reduced noise, 2.1×10-9 V2µm2/Hz at 1 Hz, compared to reference devices with the oxide/semiconductor interface operated at both inversion and depletion modes. Further improvement can be anticipated by wrapping the nanowire by such a Schottky junction thereby eliminating all oxide/semiconductor interfaces. Hence, a combination of the low-noise SiNW-SJGFET sensor device with a sensing surface of the Nernstian response limit holds promises for future high signal-to-noise ratio sensor applications.

  • 8.
    Chen, Xi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Solomon, Paul
    IBM Corp, Div Res, TJ Watson Res Ctr, Yorktown Hts, NY 10598 USA.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Top-bottom gate coupling effect on low frequency noise in a Schottky junction gated silicon nanowire field-effect transistor2019In: IEEE Journal of the Electron Devices Society, ISSN 2168-6734, Vol. 7, p. 696-700Article in journal (Refereed)
    Abstract [en]

    In this letter, strong low frequency noise (LFN) reduction is observed when the buried oxide (BOX)/silicon interface of a Schottky junction gated silicon nanowire field-effect transistor (SJGFET) is depleted by a substrate bias. Such LFN reduction is mainly attributed to the dramatic reduction in Coulomb scattering when carriers are pushed away from the interface. The BOX/silicon interface depletion can also be achieved by sidewall Schottky junction gates in a narrow channel SJGFET, leading to an optimal LFN performance without the need of any substrate bias.

  • 9.
    Chen, Xi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Solomon, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. IBM Thomas J. Watson Research Center.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Low-Noise Schottky Junction Trigate Silicon Nanowire Field-effect Transistor for Charge Sensing2019In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 66, no 9, p. 3994-4000Article in journal (Refereed)
    Abstract [en]

    Silicon nanowire (SiNW) field-effect transistors (SiNWFETs) are of great potential as a high-sensitivity charge sensor. The signal-to-noise ratio (SNR) of an SiNWFET sensor is ultimately limited by the intrinsic device noise generated by carrier trapping/detrapping processes at the gate oxide/silicon interface. This carrier trapping/detrapping-induced noise can be significantly reduced by replacing the noisy oxide/silicon interface with a Schottky junction gate (SJG) on the top of the SiNW. In this paper, we present a tri-SJG SiNWFET (Tri-SJGFET) with the SJG formed on both the top surface and the two sidewalls of the SiNW so as to enhance the gate control over the SiNW channel. Both experiment and simulation confirm that the additional sidewall gates in a narrow Tri-SJGFET indeed can confine the conduction path within the bulk of the SiNW channel away from the interfaces and significantly improve the immunity to the traps at the bottom buried oxide/silicon interface. Therefore, the optimal low-frequency noise performance can be achieved without the need for any substrate bias. This new gating structure holds promises for further development of robust SiNWFET-based charge sensors with low noise and low operation voltage.

  • 10.
    Chen, Xi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hu, Qitao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Netzer, Nathan L.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wang, Zhenqiang
    Univ South Dakota, Dept Chem, Churchill Haines Labs, Room 115,414 East Clark St, Vermillion, SD 57069 USA.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Multiplexed analysis of molecular and elemental ions using nanowire transistor sensors2018In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 270, p. 89-96Article in journal (Refereed)
    Abstract [en]

    An integrated sensor chip with silicon nanowire ion-sensitive field-effect transistors for simultaneous and selective detection of both molecular and elemental ions in a single sample solution is demonstrated. The sensing selectivity is realized by functionalizing the sensor surface with tailor-made mixed-matrix membranes (MMM) incorporated with specific ionophores for the target ions. A biomimetic container molecule, named metal-organic supercontainer (MOSC), is selected as the ionophore for detection of methylene blue (MB+), a molecular ion, while a commercially available Na-ionophore is used for Na+, an elemental ion. The sensors show a near-Nernstian response with 56.4 ± 1.8 mV/dec down to a concentration limit of ∌1 ΌM for MB+ and 57.9 ± 0.7 mV/dec down to ∌60 ΌM for Na+, both with excellent reproducibility. Extensive control experiments on the MB+ sensor lead to identification of the critical role of the MOSC molecules in achieving a stable and reproducible potentiometric response. Moreover, the MB+-specific sensor shows remarkable selectivity against common interfering elemental ions in physiological samples, e.g., H+, Na+, and K+. Although the Na+-specific sensor is currently characterized by insufficient immunity to the interference by MB+, the root cause is identified and remedies generally applicable for hydrophobic molecular ions are discussed. River water experiments are also conducted to prove the efficacy of our sensors.

  • 11.
    Hu, Qitao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Solomon, Paul
    IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, USA.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Effects of Substrate Bias on Low-Frequency Noise in Lateral Bipolar Transistors Fabricated on Silicon-on-Insulator Substrate2019In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563Article in journal (Refereed)
  • 12.
    Hu, Qitao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Xi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Norström, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zeng, Shuangshuang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Yifei, Liu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Fredrik, Gustavsson
    Swerea KIMAB, Stockholm, Sweden.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Current gain and low-frequency noise of symmetriclateral bipolar junction transistors on SOI2018Conference paper (Refereed)
    Abstract [en]

    This paper presents a comprehensive study ofsymmetric lateral bipolar junction transistors (LBJTs) fabricatedon SOI substrate using a CMOS-compatible process; LBJTs findmany applications including being a local signal amplifier forsilicon-nanowire sensors. Our LBJTs are characterized by a peakgain (β) over 50 and low-frequency noise two orders ofmagnitude lower than what typically is of the SiO2/Si interfacefor a MOSFET. β is found to decrease at low base current due torecombination in the space charge region at the emitter-basejunction and at the surrounding SiO2/Si interfaces. This decreasecan be mitigated by properly biasing the substrate.

  • 13.
    Hu, Qitao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Symmetric Lateral Bipolar Transistors as Low Noise Signal Amplifier2019Conference paper (Other academic)
  • 14.
    Tseng, Chiao-Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wen, Chenyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Huang, Ding-Chi
    Institute of Chemistry, Academia Sinica, Taiwan.
    Lai, Chin-Hung
    Department of Medical Applied Chemistry, Chung Shan Medical University, Taiwan.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hu, Qitao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Xi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Xu, Xingxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Tao, Yu-Tai
    Institute of Chemistry, Academia Sinica, Taiwan.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Synergy of Ionic and Dipolar Effects by Molecular Designfor pH Sensing beyond the Nernstian Limit2019In: Advanced Science, ISSN 2198-3844Article in journal (Refereed)
  • 15.
    Zeng, Shuangshuang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wen, Chenyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shiyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Xi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Controlled size reduction and its underlying mechanism to form solid-state nanopores via electron beam induced carbon deposition2019In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 45, article id 455303Article in journal (Refereed)
    Abstract [en]

    Solid-state nanopores have drawn considerable attention for their potential applications in DNA sequencing and nanoparticle analysis. However, fabrication of nanopores, especially those of diameter below 30 nm, requires sophisticated techniques. Here, a versatile method to controllably reduce the diameter of prefabricated large-size pores down to sub-30 nm without greatly increasing the effective pore depth from the original membrane thickness is shown. This method exploits carbon deposition achieved via hydrocarbon evaporation, induced by an incident beam of electrons, and subsequent dissociation of hydrocarbon to solid carbon deposits. The carbon deposition employs a conventional scanning electron microscope equipped with direct visual feedback, along with a stable hydrocarbon source nearby the sample. This work systematically studies how electron beam accelerating voltage, imaging magnification, initial pore size and membrane composition affect the process of pore size reduction. Secondary electrons generated in the membrane material are confirmed to be the main cause of the dissociation of hydrocarbon. Thicker carbon deposited on one side than on the other of the membrane results in an asymmetric nanopore shape and a rectifying ionic transport. A physico-phenomenological model combined with Monte Carlo simulations is proposed to account for the observed carbon deposition behaviors.

1 - 15 of 15
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