Jumei Zhou

Spectral characterization of two-dimensional Thue–Morse quasicrystals realized with high resolution lithography

One-dimensional Thue–Morse (ThMo) lattices are examples of self-similar structures that exhibit bandgap phenomena. ThMo multilayers may also possess fractal photonic bandgaps that give rise to large omnidirectional reflectance and light-emission enhancement effects. Two-dimensional (2D) ThMo aperiodic quasicrystals possess interesting properties for photonic applications too. Here we demonstrate the experimental fabrication of large area 2D ThMo lattices into polymeric substrates at nanometre scale by electron beam lithography (EBL). Far field diffraction patterns of the experimental ThMo structures have been measured and compared with the calculated theoretical Fourier spectra. Scanning electron microscopy and far field diffraction are used to characterize the experimental structures.

Proton conducting zeolite films for low-voltage oxide-based electric-double-layer thin-film transistors and logic gates

Three-dimensional nanoporous zeolite films with Linde Type A (LTA) structure prepared by a seeding-free synthesis strategy exhibited high room-temperature proton conductivity and large electric-double-layer (EDL) capacitance. In-plane-gate indium-zinc-oxide thin-film transistors gated by such proton conducting zeolite LTA films were fabricated by a simple self-assembled method. Due to the strong EDL capacitive coupling triggered by mobile protons in zeolite LTA, such transistors showed a low-voltage operation of 1.5 V and a high performance with a large field-effect mobility of 13 cm2 V−1 s−1 and a small subthreshold swing of 95 mV per decade. Furthermore, AND logic operation was also experimentally demonstrated on the dual in-plane-gate EDL transistors. Our results strongly indicate that zeolite LTA films are promising gate dielectric candidates for application in low-voltage and low-cost electronics, which greatly expands the application areas of zeolites.

A novel hybrid organic/inorganic photonic crystal slab showing a resonance action at the band edge

Here we propose and experimentally demonstrate a hybrid photonic crystal (PC) slab consisting of air rods in a nanocomposite prepared by incorporating CdSe/CdS core/shell NRs (NR) in a polymer. Since the styrene methyl acrylate based polymer (ZEP) is transparent in the visible spectral range and is an electron-sensitive material, it was chosen as the embedding matrix for the NRs. Scanning electron microscopy and luminance measurements were used to characterize the experimental structure. The vertical extraction of the light, by the coupling of the modes guided by the PC slab to the free radiation via Bragg scattering, consists of a narrow orange emission band at 592 nm with a full width at half-maximum (FWHM) of 17 nm. The original characteristics of hybrid materials based on polymers and colloidal NRs, able to combine the unique optical properties of the inorganic moiety with the processability of the host matrix, are extremely appealing in view of their technological impact on the development of new high performing optical devices such as organic light-emitting diodes, ultra-low threshold lasers and non-linear devices.

Low-voltage protonic/electronic hybrid indium zinc oxide synaptic transistors on paper substrates

Low-voltage (1.5 V) indium zinc oxide (IZO)-based electric-double-layer (EDL) thin-film transistors (TFTs) gated by nanogranular proton conducting SiO2 electrolyte films are fabricated on paper substrates. Both enhancement-mode and depletion-mode operation are obtained by tuning the thickness of the IZO channel layer. Furthermore, such flexible IZO protonic/electronic hybrid EDL TFTs can be used as artificial synapses, and synaptic stimulation response and short-term synaptic plasticity function are demonstrated. The protonic/electronic hybrid EDL TFTs on paper substrates proposed here are promising for low-power flexible paper electronics, artificial synapses and bioelectronics.

Transparent In-Plane-Gate Junctionless Oxide-Based TFTs Directly Written by Laser Scribing

A laser-scribing process without any mask and photolithography is developed for transparent junctionless oxide based in-plane-gate thin-film transistor (TFT) fabrication at room temperature. Such junctionless TFTs feature that the channel and the source/drain electrodes are of the same thin indium-zinc-oxide films. Good electrical performance with an Ion/Ioff ratio of 4 × 105, a field-effect mobility of 15 cm2/V · s, and a subthreshold swing of 0.12 V/dec is obtained. AND logic is realized with a reliable logic operation in a dual in-plane-gate configuration. The developed laser-scribing technology is highly desirable in terms of the low-cost fabrication process.

Low-Voltage Junctionless Oxide-Based Thin-Film Transistors Self-Assembled by a Gradient Shadow Mask

A gradient shadow-mask diffraction method is proposed for the fabrication of junctionless indium-tin-oxide (ITO) and indium-zinc-oxide (IZO) thin-film transistors (TFTs) with different channel thicknesses on one glass substrate during one-batch radio-frequency magnetron sputtering. The operation mode and saturation field-effect mobility of the room-temperature-processed oxide-based junctionless TFTs are channel thickness dependent, and the threshold voltages shift from negative to positive when the self-assembled channel thickness is reduced to a critical thickness.

Engineered nanopatterned substrates for high-sensitive localized surface plasmon resonance: an assay on biomacromolecules

In this paper, we report on novel iso-Y-shaped-nanopillar based photonic crystals (PCs) engineered for plasmonic lab-on-a-chip advanced diagnostics. The iso-Y shaped units are selected on the basis of their plasmonic properties, analyzed numerically and experimentally. We show that by accurately choosing the nanopillar shape, dimensions and their geometrical disposal it is possible to obtain efficient optical 2D structures for biomolecule detection by high-sensitive localized surface plasmonic resonance (LSPR). In particular, an assay is realized by using bovine serum albumin (BSA), a widely recognized model for biosystem studies. BSA was simply deposited on a self-assembled monolayer (SAM) of 4-mercaptobenzoic acid (4-MBA) previously grown-up on the plasmonic substrate. We demonstrate that the geometries considered allow the design of LSPR nano-assays working in the visible-NIR region based on both intensity interrogation and the resonance peak shift permitting the sensing of BSA with a limit of detection in the order of picomoles (LOD = 233 pM).

Dodecagonal plasmonic quasicrystals for phage-based biosensing

In this work, we fabricate and characterize a novel sensitive two-dimensional surface enhanced Raman spectroscopy (SERS) substrate made of plasmonic nanocavities in a photonic quasicrystal arrangement characterized by a 12-fold rotational symmetry. Our SERS device is capable of detecting chemisorbed bacteriophages at a femtomolar range. Most importantly, the paper presents for the first time a study on the procedure to functionalize the plasmonic quasicrystal with bacteriophages of the Podoviridae family. The immobilization of the phages on the plasmonic substrate has been studied and verified through SERS measurements. A new stable peak, visible in the SERS spectra at 1326 cm-1 at a greater than 60 times amplification, confirms the immobilization of the phages on the substrate. This functionalization approach can be used also for other types of phages or plasmonic sensors and hence, our achievements could allow the development of novel systems for the specific detection of different species of bacteria.

Magnetically modulated refractive index of a magnetic fluid film based on cigar-shaped ferrite submicron particles

Light beam propagation at a prism-magnetic fluid film interface is experimentally studied. The magnetic fluid is made through dispersion of synthesized cigar-shaped sub-micron particles of Fe2O3 in an oil solution. This was injected into a glass cell with an active area of 10mm2 and a depth ranging from 10 microns to 30 microns whose base is a glass microscope slide and on the top it was covered with a glass prism. The set up was developed by one of the authors to measure light switching at a prism-liquid crystal interface in a previous publication.1 Polarized Light (TE or TM) from a He-Ne laser impinges at the prism-magnetic film interface. The external reflected light is detected by a photodiode connected to a data acquisition system. Since the properties of the magnetic fluid can be modulated by external magnetic fields, we investigated the effects of the magnetic field on the refractive index of the magnetic fluid. For our magnetic fluid, the reflection of light has been investigated as a function of particles concentration and thickness of the films with a wavelength of 633nm and both TE and TM polarization, and applied magnetic fields up to 25 Oe. It was found that the intensity of reflected light increases with increasing magnetic field up to 4 times the initial value, and saturates at 20 Oe for TE light, while decreases with increasing magnetic field up to 4 times less for TM light with the same saturation value. Moreover, under a given magnetic field, the output light increases with the increasing film thickness in TE polarization, and decreases with the increasing film thickness in TM case. The refractive index of the magnetic fluid depends on the concentration of the dilute oil-based magnetic fluid under zero field. These behaviors are explained in terms of the organization of the submicron particles when the magnetic field is applied.2 The cigar-shaped sub-micron particles are oriented along their long axis to form an organized mesostructure. The different aggregation ability of the magnetic fluid particle is responsible for the variation of the optical properties under different magnetic fields and for different polarization of the incident light. It is noteworthly that the magnetically modulated refractive index of the magnetic fluid film could have great potential in electro-optical applications. In particular, according to the experimental results, we believe that the fluid films that we are proposing, thanks to the optical responses and the relative times, is a very good candidate to design Fiber Optical Sensors (FOS) for magnetic fields.