代表性著作

  1. H. H. J. Chang, T.W. Chen, J.W. Chen, W. C. Hong, W. C. Tsai, Y. F. Chen*, and G.Y. Guo,“Current and Strain-Induced Spin Polarization in InGaN/GaN Superlattices”, Phys. Rev. Lett.,98, 136403, (2007)

FIG. 1. The schematic diagram of the edge photoluminescence measurement with different angle of polarizer.

FIG. 2. (a) The theoretical effective Rashba coupling αe = λ + a (eV Å) (О) and BIA coupling β (eV Å3) (●) vs the inplane strain. (b) The theoretical spin Hall conductivity (σs xy) (■) and the degree of circular polarization (CP) (▲) vs the in-plane strain. The in-plane electric field is applied in -y direction.

  1. K.J. Wu, K.C. Chu, C.Y. Chao, Y.F. Chen*, C.W. Lai, C.C. Kang, C.Y. Chen, P.T. Chou, “CdS nanorods imbedded in liquid crystal cells for smart optoelectronic devices”, Nano Lett., 7, 1908 (2007)

Light-emitting devices: In the right direction

A device combining semiconductor nanorods with liquid crystals can produce tunable color emission via electric field control

Fig. 1: A color-tunable light-emitting device. The active region is a mixture of liquid crystals, CdSe nanorods and quantum dots (QDs) between indium tin oxide (ITO) electrodes. An applied electric field (E) rotates the liquid-crystal molecules and attached nanorods to change the color of emission. © 2010 Y.-F. Chen.

.Electrons move freely along one-dimensional nanostructures such as nanorods, quantum wires or nanotubes, but their motion in the other two spatial directions is governed by quantum effects. One important implication of this behavior is that the optical response of these structures is strongly dependent on their orientation. A device that takes advantage of this phenomenon by using liquid crystals to rotate cadmium selenide (CdSe) nanorods has now been constructed by Yang-Fang Chen and co-workers at the National Taiwan University.

Chen and his co-workers mixed CdSe nanorods, just 25 nm long and 7 nm in diameter, with a liquid crystal known as E7 and CdSe quantum dots (QDs) — 5 nm-wide zero-dimensional structures in which electron motion is quantized in all three directions. To apply an electric field across the mixture while allowing any emission to be observed, the team injected the mixture between two glass slides coated with the transparent conductor indium tin oxide (ITO). The nanorods cling to the liquid-crystal molecules because the large surface areas involved generate a strong anchoring force. The liquid crystals — and therefore nanorods — can then be aligned in any direction by applying an electric field (Fig. 1). “We discovered that the physical properties of nanomaterials could be manipulated by an external bias due to the coupling between nanorods and liquid crystal molecules,” explains Chen.

The nanorods and QDs emit light when excited by a laser beam. The peak emission from the rods, which is yellow with a wavelength of 580 nm, is highly polarized because of the rod’s one-dimensional structure. The 650 nm red light from the dots, on the other hand, remains randomly polarized. This means that the contribution of the two light-emitting components — and thus the color of the emission — is dependent on which polarization, relative to the orientation of the nanorods, is measured.

Chen and his colleagues measured the optical output over a range of polarization angles and demonstrated that this approach enabled them to tune the color of light from the device. Chen hopes that further refinement of this approach, such as introducing photonic-crystal structures, will see an increase in device efficiency.

  1. Y.P. Hsieh, H.Y. Chen, M.Z. Lin, S.C. Shiu, M.Y. Chern, X.T. Jia, H. J. Chang, H.M. Huang, S.C. Tseng, L.C. Chen, K.H. Chen, C.F. Lin, C.T. Liang and Y.F. Chen*, “Electroluminescence from ZnO/Si-nanotips light emitting diodes”, Nano Lett., 9 (5), pp 1839–1843 (2009)

Figure 1. Schematic diagrams showing the fabrication technique of our ZnO/Si-nanotips LED array.

Figure 2. (a) SEM picture of silicon nanotips after coating ZnO using pulsed laser deposition. (b) CL spectrum taken from the square region drawn in the middle of the nanotip array as shown in Figure 2(a). (c) TEM image of ZnO/Si-nanotips and (d) SAED pattern taken from the square region drawn in the middle of the nanotip array as shown in panel c. (e) PL spectra and (f) multiphonon Raman spectra of ZnO film coated on silicon nanotips and flat substrate.

  1. Chun-Ying Huang, Di-Yan Wang, Chun-Hsiung Wang, Yung-Ting Chen, Yaw-Tyng Wang, You-Ting Jiang, Ying-Jay Yang, Chia-Chun Chen, and Yang-Fang Chen*, “Efficient Light Harvesting by Photon Downconversion and Light Trapping in Hybrid ZnS Nanoparticles/Si Nanotips Solar Cells”, ACS Nano 4, 10, 5849–5854 (2010)

Figure 1. Schematic diagram of Si nanotips solar cell structure with ZnS NPs.

Figure 2. (a) Current densityvoltage characteristics demonstrating the superior power conversion efficiency of the photovoltaic device spreading 6 mg/mL ZnS NPs as compared to the one without ZnS NPs (- - -) under AM1.5. (b) Current densityvoltage characteristics with different concentration of ZnS NPs.

  1. Meng-Lin Lu, Chih-Wei Lai, Hsing-Ju Pan, Chung-Tse Chen, Pi-Tai Chou, Yang-Fang Chen*, “A Facile Integration of Zero- (I-III-VI Quantum Dots) and One- (Single SnO2 Nanowire) Dimensional Nanomaterials: Fabrication of a Nanocomposite Photodetector with Ultrahigh Gain and Wide Spectral Response”, Nano Letters, 13, 1920−1927 (2013)

FIG. Demonstration of the high sensitivity under the illumination of photon energy smaller than the band gap of nanowire. The most important underlying mechanism arises from typeII band alignment between QDs and NW.

  1. Y.C. Lai, J.Y. Chen, T.C. Chang, Y.T. Yang, F.C. Hsu, and Y.F. Chen*, “Transferable and Flexible Label-Like Macromolecular Memory on Arbitrary Substrates with High Performance and a Facile Methodology ”, Advanced Materials, 25, 2733–2739 (2013)

FIG. Demonstration of memory sticker on various non-conventional substrates with excellent switching performance.
  1. Che-Wei Chang, Wei-Chun Tan, Meng-Lin Lu, Tai-Chun Pan, Ying-Jay Yang, Yang-Fang Chen*, “Graphene/SiO2/p-GaN Diodes: An Advanced Economical Alternative for Electrically Tunable Light Emitters”, Advanced Functional Materials, 23, 4043-4048 (2013)

FIG. a) Schematics of graphene/SiO2/p-GaN MIS-LED and AFM image (inset) of the graphene electrode and photograph of the device. b) EL spectra of graphene/SiO2/p-GaN MIS-LEDs under forward bias at different injection currents at room temperature. The inset shows a photograph of the light emission from MIS-LEDs under forward bias. 

  1. J. Y. Chen, C. Y. Ho, M. L. Lu, L. J. Chu, K. C. Chen, S. W. Chu, W. Chen, C. Y. Mou, and Y. F. Chen*, “Efficient Spin-Light Emitting Diodes Based on InGaN/GaN Quantum Disks at Room Temperature: A New Self-Polarized Paradigm”, Nano Letters, Nano Letters, 14, 3130 (2014)

FIG. Band diagram of (a) spin-down and (b) spin-up electrons in InGaN and Fe3O4. It enables selective transfer of spin polarized electrons and holes and leads to the enhanced output spin polarization of LED.

  1. Ju-Ying Chen, Tong-Ming Wong, Che-Wei Chang, Chen-Yuan Dong, and Yang-Fang Chen* “Self-polarized spin-nanolasers”, Nature Nanotechnology, 9, 845 (2014)

FigureSchematics of band alignment of spin-down and spin-up electrons between GaN and Fe3O4. a, Band alignment of spin-down electrons between GaN and Fe3O4. The imperfection of spin orientation of the electrons at the Fermi energy of Fe3O4 is shown explicitly to reflect the true situation. b, Band alignment of spin-up electrons between GaN and Fe3O4. Owing to the population imbalance of spin alignment, the recombination of electron and hole generates spin-polarized emissions. EF, Fermi energy; up and down arrows, spin orientation of the electrons; shaded areas, energy states occupied by electrons; HH+, heavy holes; LH+, light holes.

  1. Cih-Su Wang, Chuan-Hsien Nieh, Tai-Yuan Lin andYang-Fang Chen*, “Electrically driven random laser memory”, Advanced Functional Materials, DOI: 10.1002/adfm.201500734 (2015)

The first proof-of-concept presentation of random laser memory possesses several advantages of dual memory and lasing functions, which enables to open up new avenues to practical applications, such as light emitting memories for electrical and optical communication.

  1. Meng-Jer Wu, Shang-Cheng Wu, Tien-Lin Shen, Yu-Ming Liao, and Yang-Fang Chen*, “Anderson Localization Enabled Spectrally Stable Deep-Ultraviolet Laser Based on Metallic Nanoparticle Decorated AlGaN Multiple Quantum Wells”, ACS Nano, 15, 330-337 (2021)

 
  1. Chi‐Yuan Chang, Hsin‐Hsiang Huang, Hsinhan Tsai, Shu‐Ling Lin, Pang‐Hsiao Liu, Wei Chen, Fang‐Chi Hsu, Wanyi Nie*, Yang‐Fang Chen*, Leeyih Wang*, “Facile Fabrication of Self‐Assembly Functionalized Polythiophene Hole Transporting Layer for High Performance Perovskite Solar Cells”, Advanced Science, 8, 2002718 (2021)

 

Spin coating and self-assembly route to prepare PEDOT:PSS and P3HT-COOH on ITO substrates. Schematic illustration for spin coated polymer thin film of b) PEDOT:PSS (top), P3HT-COOH (bottom), and c) self-assembled P3HT-COOH. The insets are the contact angle images of deionized water on fabricated HTMs from (b)–(c). d) Contact angle plot with HTMs with different fabrication methods. e) Surface SEM images and f) GIWAXS patterns showing the evolution of the three perovskite grain types under different HTMs. g) GIWAXS line-cut from f with their FWHM on the characteristic peaks of (110) plane in MAPbI3 on three different HTMs. Zoom-in profiles for h) (110) and i) (200) peaks. j) Integral breadth (IB) analysis using Halder–Wagner plots, where β is the integral breadth of the diffraction peak and S is defined as S = 2 s i n θ λ.

 

  1. Shu-Yuan Chiang, Yueh-Yuan Li, Tien-Lin Shen, Mario Hofmann*, Yang-Fang Chen*, “2D Material-Enabled Nanomechanical Bolometer”, Nano Lett., 20, 2326 (2020)

Photoresponse to different wavelengths with indication of mechanism; (inset) extracted responsivity at different wavelengths.

 
  1. Tien-Lin Shen, Han-Wen Hu, Wei-Ju Lin, Yu-Ming Liao, Tzu-Pei Chen, Yu-Kuang Liao, Tai-Yuan Lin, Yang-Fang Chen*, “Coherent Förster resonance energy transfer: A new paradigm for electrically driven quantum dot random lasers”, Science Advances, 6, eaba1705 (2020)

 

Structure of the QD random laser device.(A) Schematic of the QD random laser device. (B) Side-view SEM image of the device structure showing each layer is well deposited. Scale bar, 200 nm. (C) Schematic illustration of CFRET. (D) SEM topography of the mixture QD film. Scale bar, 100 nm. The inset shows the real photo of the red-light emission from the QD random laser device.

 

 
  1. Krishna Prasad Bera, Golam Haider, Yu-Ting Huang, Pradip Kumar Roy, Christy Roshini Paul Inbaraj, Yu-Ming Liao, Hung-I Lin, Cheng-Hsin Lu, Chun Shen, Wan Y Shih, Wei-Heng Shih, Yang-Fang Chen*“Graphene Sandwich Stable Perovskite Quantum-Dot Light-Emissive Ultrasensitive and Ultrafast Broadband Vertical Phototransistors”, ACS Nano, 13, 12540-12552 (2019)

Schematic design of a vertical phototransistor.