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  • 1.
    Cheng, Dan-Chen
    et al.
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Hao, Hong-Chen
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Zhang, Miao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Royal Inst Technol KTH, S-16440 Kista, Sweden..
    Shi, Wei
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Lu, Ming
    Fudan Univ, Dept Opt Sci & Engn, Shanghai 200433, Peoples R China.;Fudan Univ, Shanghai Ultra Precis Opt Mfg Engn Ctr, Shanghai 200433, Peoples R China..
    Improving Si solar cell performance using Mn:ZnSe quantum dot-doped PLMA thin film2013In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 8, article id 291Article in journal (Refereed)
    Abstract [en]

    Poly(lauryl methacrylate) (PLMA) thin film doped with Mn:ZnSe quantum dots (QDs) was spin-deposited on the front surface of Si solar cell for enhancing the solar cell efficiency via photoluminescence (PL) conversion. Significant solar cell efficiency enhancements (approximately 5% to 10%) under all-solar-spectrum (AM0) condition were observed after QD-doped PLMA coatings. Furthermore, the real contribution of the PL conversion was precisely assessed by investigating the photovoltaic responses of the QD-doped PLMA to monochromatic and AM0 light sources as functions of QD concentration, combined with reflectance and external quantum efficiency measurements. At a QD concentration of 1.6 mg/ml for example, among the efficiency enhancement of 5.96%, about 1.04% was due to the PL conversion, and the rest came from antireflection. Our work indicates that for the practical use of PL conversion in solar cell performance improvement, cautions are to be taken, as the achieved efficiency enhancement might not be wholly due to the PL conversion.

  • 2.
    Schmidt, Torsten
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Zhang, Miao
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Roxhed, Niclas
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication2015In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, no 31, article id 314001Article in journal (Refereed)
    Abstract [en]

    Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

  • 3.
    Schmidt, Torsten
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Zhang, Miao
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Yu, Shun
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Fabrication of ultra-high aspect ratio silicon nanopores by electrochemical etching2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 12, p. 123111-Article in journal (Refereed)
    Abstract [en]

    We report on the formation of ultra-high aspect ratio nanopores in silicon bulk material using photo-assisted electrochemical etching. Here, n-type silicon is used as anode in contact with hydrofluoric acid. Based on the local dissolution of surface atoms in pre-defined etching pits, pore growth and pore diameter are, respectively, driven and controlled by the supply of minority charge carriers generated by backside illumination. Thus, arrays with sub-100 nm wide pores were fabricated. Similar to macropore etching, it was found that the pore diameter is proportional to the etching current, i.e., smaller etching currents result in smaller pore diameters. To find the limits under which nanopores with controllable diameter still can be obtained, etching was performed at very low current densities (several mu A cm(-2)). By local etching, straight nanopores with aspect ratios above 1000 (similar to 19 mu m deep and similar to 15 nm pore tip diameter) were achieved. However, inherent to the formation of such narrow pores is a radius of curvature of a few nanometers at the pore tip, which favors electrical breakdown resulting in rough pore wall morphologies. Lowering the applied bias is adequate to reduce spiking pores but in most cases also causes etch stop. Our findings on bulk silicon provide a realistic chance towards sub-10 nm pore arrays on silicon membranes, which are of great interest for molecular filtering and possibly DNA sequencing.

  • 4.
    Sychugov, Ilya
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zhang, Miao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Non-stationary analysis of molecule capture and translocation in nanopore arrays2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 8, article id 084904Article in journal (Refereed)
    Abstract [en]

    Analytical formulas for the ON- and OFF-time distributions as well as for the autocorrelation function were derived for the case of single molecule translocation through nanopore arrays. The obtained time-dependent expressions describe very well experimentally recorded statistics of DNA translocations through an array of solid state nanopores, which allows us to extract molecule and system related physical parameters from the experimental traces. The necessity of non-stationary analysis as opposite to the steady-state approximation has been vindicated for the molecule capture process, where different time-dependent regimes were identified. A long tail in the distribution of translocation times has been rationalized invoking Markov jumps, where a possible sequential ordering of events was elucidated through autocorrelation function analysis. Published under license by AIP Publishing.

  • 5.
    Zhang, Miao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Silicon Nanopore Arrays: Fabrication and Applications for DNA Sensing2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanopore biomolecule sensing and sequencing has emerged as a simple but powerful tool for single molecule studies over the past two decades. By elec- trophoretically driving single molecules through a nanometer-sized pore, often sitting in an insulating membrane that separates two buffer solutions, ionic current blockades can be detected to reveal rich information of the molecules, such as DNA length, protein size and conformation, even nucleic acid se- quence. Biological protein pores, as well as solid-state nanopores have been used, but both suffer from relatively low throughput due to the lack of abil- ity to scale up to a large array. In this thesis, we tackled the throughput issue from the fabrication aspect as well as from the detection aspect, aim- ing at a parallel optical single molecule sensing on an array of well-separated nanopores.

    From the fabrication aspect, several lithography-based self-regulating meth- ods were tested to obtain nanopore arrays in silicon membranes, including anisotropic KOH etching, thermal oxidation-induced pore shrinkage, metal- assisted etching and electrochemical etching. Among those, the most success- ful method was the electrochemical etching of silicon. By electron-beam or photo lithography, the positions of the pores were defined on a silicon mem- brane. Followed by anisotropic KOH etching, inverted pyramids were formed as etching pits. The nanopores were then formed by anodic etching of silicon in HF. Using this concept, the size of the pores does not depend on the lithog- raphy step; only the positions of pores were defined by lithography. In this way, an array of ∼ 900 pores with an average entrance diameter of 18 ± 4 nm was fabricated on a 120 μm × 120 μm membrane.

    From the detection aspect, parallel readout of fluorescence signals from the labelled DNA molecules while translocating through an array of nanopores was performed using a wide-field microscope with a relatively fast CMOS camera recording at 1 KHz frame rate. Statistics of duration and frequency of the translocation events were extracted and studied. It was found that the event duration decreases with rising excitation laser power. This can be attributed to a laser-induced heating effect. Simulation suggested that a sig- nificant thermal gradient was generated at the pore vicinity by the excitation laser due to photon absorption by the silicon membrane. Such temperature rise affects all mass transport in a solution via a viscosity change. The ther- mal effect has also been proven by that conductance of an array of nanopores scales with the laser power. The thermal effect on the translocation frequency has been studied systematically as well. Due to thermophoresis of DNA in a thermal gradient, the thermophoretic force serves as a repulsion force, op- posing the electrophoretic force at the pore vicinity, depleting molecules away from the pore. Because of the molecule-size-dependent thermal depletion, a size-dependent translocation frequency was observed. This can be potentially used for a high throughput molecule sorting by adjusting the balance between the thermophoretic force and the electrophoretic force.

  • 6.
    Zhang, Miao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH.
    Ngampeerapong, Chonmanart
    Redin, David
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Ahmadian, Afshin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Thermophoresis-Controlled Size-Dependent DNA Translocation through an Array of Nanopores2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 5, p. 4574-4582Article in journal (Refereed)
    Abstract [en]

    Large arrays of nanopores can be used for high-throughput biomolecule translocation with applications toward size discrimination and sorting at the single-molecule level. In this paper, we propose to discriminate DNA length by the capture rate of the molecules to an array of relatively large nanopores (50–130 nm) by introducing a thermal gradient by laser illumination in front of the pores balancing the force from an external electric field. Nanopore arrays defined by photolithography were batch processed using standard silicon technology in combination with electrochemical etching. Parallel translocation of single, fluorophore-labeled dsDNA strands is recorded by imaging the array with a fast CMOS camera. The experimental data show that the capture rates of DNA molecules decrease with increasing DNA length due to the thermophoretic effect of the molecules. It is shown that the translocation can be completely turned off for the longer molecule using an appropriate bias, thus allowing a size discrimination of the DNA translocation through the nanopores. A derived analytical model correctly predicts the observed capture rate. Our results demonstrate that by combining a thermal and a potential gradient at the nanopores, such large nanopore arrays can potentially be used as a low-cost, high-throughput platform for molecule sensing and sorting.

  • 7.
    Zhang, Miao
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Schmidt, Torsten
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Jemt, Anders
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Sahlén, Pelin
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Lundeberg, Joakim
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Nanopore arrays in a silicon membrane for parallel single-molecule detection: DNA translocation2015In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, no 31, article id 314002Article in journal (Refereed)
    Abstract [en]

    Optical nanopore sensing offers great potential in single-molecule detection, genotyping, or DNA sequencing for high-throughput applications. However, one of the bottle-necks for fluorophore-based biomolecule sensing is the lack of an optically optimized membrane with a large array of nanopores, which has large pore-to-pore distance, small variation in pore size and low background photoluminescence (PL). Here, we demonstrate parallel detection of single-fluorophore-labeled DNA strands (450 bps) translocating through an array of silicon nanopores that fulfills the above-mentioned requirements for optical sensing. The nanopore array was fabricated using electron beam lithography and anisotropic etching followed by electrochemical etching resulting in pore diameters down to similar to 7 nm. The DNA translocation measurements were performed in a conventional wide-field microscope tailored for effective background PL control. The individual nanopore diameter was found to have a substantial effect on the translocation velocity, where smaller openings slow the translocation enough for the event to be clearly detectable in the fluorescence. Our results demonstrate that a uniform silicon nanopore array combined with wide-field optical detection is a promising alternative with which to realize massively-parallel single-molecule detection.

  • 8.
    Zhang, Miao
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Schmidt, Torsten
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Roxhed, Niclas
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Oxidation of nanopores in a silicon membrane: self-limiting formation of sub-10nm circular openings2014In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, no 35, p. 355302-Article in journal (Refereed)
    Abstract [en]

    We describe a simple but reliable approach to shrink silicon nanopores with nanometer precision for potential high throughput biomolecular sensing and parallel DNA sequencing. Here, nanopore arrays on silicon membranes were fabricated by a self-limiting shrinkage of inverted pyramidal pores using dry thermal oxidation at 850 degrees C. The shrinkage rate of the pores with various initial sizes saturated after 4 h of oxidation. In the saturation regime, the shrinkage rate is within +/- 2 nm h(-1). Oxidized pores with an average diameter of 32 nm were obtained with perfect circular shape. By careful design of the initial pore size, nanopores with diameters as small as 8 nm have been observed. Statistics of the pore width show that the shrinkage process did not broaden the pore size distribution; in most cases the distribution even decreased slightly. The progression of the oxidation and the deformation of the oxide around the pores were characterized by focused ion beam and electron microscopy. Cross-sectional imaging of the pores suggests that the initial inverted pyramidal geometry is most likely the determining factor for the self-limiting shrinkage.

  • 9.
    Zhang, Miao
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Schmidt, Thorsten
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Optical detection of two-color-fluorophore barcode for nanopore DNA sensing2015Conference paper (Refereed)
    Abstract [en]

    A simple schematic on parallel optical detection of two-fluorophore barcode for single-molecule nanopore sensing is presented. The chosen two fluorophores, ATTO-532 and DY-521-XL, emitting in well-separated spectrum range can be excited at the same wavelength. A beam splitter was employed to separate signals from the two fluorophores and guide them to the same CCD camera. Based on a conventional microscope, sources of background in the nanopore sensing system, including membranes, compounds in buffer solution, and a detection cell was characterized. By photoluminescence excitation measurements, it turned out that silicon membrane has a negligible photoluminescence under the examined excitation from 440 nm to 560 nm, in comparison with a silicon nitrite membrane. Further, background signals from the detection cell were suppressed. Brownian motion of 450 bps DNA labelled with single ATTO-532 or DY-521-XL was successfully recorded by our optical system.

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