Fabrication of junction-free Cu nanowire networks via Ru-catalyzed electroless deposition and their application to transparent conducting electrodes.

Over the past few years, metal nanowire networks have attracted attention as an alternative to transparent conducting oxide materials such as indium tin oxide for transparent conducting electrode applications. Recently, electrodeposition of metal on nanoscale template is widely used for formation of metal network. In the present work, junctionless Cu nanowire networks were simply fabricated on a substrate by forming a nanostructured Ru with 80 nm width as a seed layer, followed by direct electroless deposition of Cu. By controlling the density of Ru nanowires or the electroless deposition time, we readily achieve desired transmittance and sheet resistance values ranging from ∼1 kΩ sq-1at 99% to 9 Ω sq-1at 89%. After being transferred to flexible substrates, the nanowire networks exhibited no obvious increase in resistance during 8000 cycles of a bending test to a radius of 2.5 mm. The durability was verified by evaluation of its heating performance. The maximum temperature was greater than 180 °C at 3 V and remained constant after three repeated cycles and for 10 min. Transmission electron microscopy and x-ray diffraction studies revealed that the adhesion between the electrolessly deposited Cu and the seed Ru nanowires strongly influenced the durability of the core-shell structured nanowire-based heaters.

Property Optimization of the Micro-Bolometer Array Designed by Associating Noise Equivalent Temperature Difference and Resistance Equation.

We present how to optimize efficiently the performance of micro-bolometer array with design parameters such as active area and channel length, and minimize simultaneously the channel resistance of bolometer array with a minimum channel area and length in a given technology and technology window. The results demonstrate that the serpentine is very efficient pattern to minimize the channel since it provides a large area or path through which electron or holes conducts as easy as possible, as well as it maintains a relatively large absorption area in a given pixel area. On the other hand, these approach have also much large effects on the flicker noise reduction because amorphous Si active layer has about 20 M ohm/ which causing an insufficient current level in an array circuits, however, any dopants does not need to reduce resistance of micro-bolometer channel.

Single-Crystalline Nanobelts Composed of Transition Metal Ditellurides.

Following the celebrated discovery of graphene, considerable attention has been directed toward the rich spectrum of properties offered by van der Waals crystals. However, studies have been largely limited to their 2D properties due to lack of 1D structures. Here, the growth of high-yield, single-crystalline 1D nanobelts composed of transition metal ditellurides at low temperatures (T ≤ 500 °C) and in short reaction times (t ≤ 10 min) via the use of tellurium-rich eutectic metal alloys is reported. The synthesized semimetallic 1D products are highly pure, stoichiometric, structurally uniform, and free of defects, resulting in high electrical performances. Furthermore, complete compositional tuning of the ternary ditelluride nanobelts is achieved with suppressed phase separation, applicable to the creation of unprecedented low-dimensional materials/devices. This approach may inspire new growth/fabrication strategies of 1D layered nanostructures, which may offer unique properties that are not available in other materials.

Large-area, continuous and high electrical performances of bilayer to few layers MoS2 fabricated by RF sputtering via post-deposition annealing method.

We report a simple and mass-scalable approach for thin MoS2 films via RF sputtering combined with the post-deposition annealing process. We have prepared as-sputtered film using a MoS2 target in the sputtering system. The as-sputtered film was subjected to post-deposition annealing to improve crystalline quality at 700 °C in a sulfur and argon environment. The analysis confirmed the growth of continuous bilayer to few-layer MoS2 film. The mobility value of ~29 cm(2)/Vs and current on/off ratio on the order of ~10(4) were obtained for bilayer MoS2. The mobility increased up to ~173-181 cm(2)/Vs, respectively, for few-layer MoS2. The mobility of our bilayer MoS2 FETs is larger than any previously reported values of single to bilayer MoS2 grown on SiO2/Si substrate with a SiO2 gate oxide. Moreover, our few-layer MoS2 FETs exhibited the highest mobility value ever reported for any MoS2 FETs with a SiO2 gate oxide. It is presumed that the high mobility behavior of our film could be attributed to low charged impurities of our film and dielectric screening effect by an interfacial MoOxSiy layer. The combined preparation route of RF sputtering and post-deposition annealing process opens up the novel possibility of mass and batch production of MoS2 film.

Selective growth of graphene in layer-by-layer via chemical vapor deposition.

Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (∼40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices.

Synthesis and characterization of large-area and continuous MoS2 atomic layers by RF magnetron sputtering.

In this article, we report layer-controlled, continuous and large-area molydenum sulfide (MoS2) growth onto a SiO2/Si substrate by RF sputtering combined with sulfurization. A two-step process was employed to synthesize MoS2 films. In the first step, an atomically thin MoO3 film was deposited by RF magnetron sputtering at 300 °C. Subsequently, the as-sputtered MoO3 film was further subjected to post-annealing and sulfurization processes at 650 °C for 1 hour. It was observed that the number of layers of MoS2 can be controlled by adjusting the sputtering time. The fabricated MoS2 transistors exhibited high mobility values of ∼21 cm(2) V(-1) s(-1) (bilayer) and ∼25 cm(2) V(-1) s(-1) (trilayer), on/off ratios in the range of ∼10(7) (bilayer) and 10(4)-10(5) (trilayer), respectively. We believe that our proposed paradigm can start a new method for the growth of MoS2 in future electronics and optoelectronics applications.

Characterizations of realized metal-insulator-silicon-insulator-metal waveguides and nanochannel fabrication via insulator removal.

We investigate experimentally metal-insulator-silicon-insulator-metal (MISIM) waveguides that are fabricated by using fully standard CMOS technology. They are hybrid plasmonic waveguides, and they have a feature that their insulator is replaceable with functional material. We explain a fabrication process for them and discuss fabrication results based on 8-inch silicon-on-insulator wafers. We measured the propagation characteristics of the MISIM waveguides that were actually fabricated to be connected to Si photonic waveguides through symmetric and asymmetric couplers. When incident light from an optical source has transverse electric (TE) polarization and its wavelength is 1318 or 1554 nm, their propagation losses are between 0.2 and 0.3 dB/µm. Excess losses due to the symmetric couplers are around 0.5 dB, which are smaller than those due to the asymmetric couplers. Additional measurement results indicate that the MISIM waveguide supports a TE-polarized hybrid plasmonic mode. Finally, we explain a process of removing the insulator without affecting the remaining MISIM structure to fabricate ~30-nm-wide nanochannels which may be filled with functional material.

Hybrid Si-LiNbO3 microring electro-optically tunable resonators for active photonic devices.

Hybrid Si-LiNbO3 electro-optic tunable ring resonators have been proposed and demonstrated as a path to achieving ultracompact and high-speed electro-optic devices. Free standing single crystal LiNbO3 microplatelets (~mm long and ~1 µm thick) were obtained from a z-cut LiNbO3 substrate by ion implantation and thermal treatment. The platelets were transferred and thermally bonded on top of Si resonators that were fabricated in a Si-on-insulator platform by a 0.18 µm standard complementary metal-oxide-semiconductor process. For the hybrid microring resonator, a free spectral range of 16.5 nm, a finesse F of ~1.67 × 10², a Q-factor of ~1.68 × 104, and an effective r coefficient of ~1.7 pm/V were achieved for the TE mode. These values are in good agreement with the calculated results.

Silicon photonic temperature sensor employing a ring resonator manufactured using a standard CMOS process.

An ultra-small integrated photonic temperature sensor has been proposed and demonstrated which incorporates a silicon ring resonator linked to a vertical grating coupler. It was manufactured using a 0.18 µm standard CMOS process, rendering a homogeneous integration into other electrical/optical devices. The temperature variation was measured by monitoring the shift in the resonant wavelength of the silicon resonator, which was induced by the thermo-optic effect and the thermal expansion effect. The dependence of its sensing capability upon the waveguide width of the resonator was intensively probed both theoretically and experimentally. The best achieved sensitivity was about 83 pm/°C for a waveguide width of 500 nm, while the sensitivity was boosted by ~10 pm/°C by adjusting the waveguide width from 300 nm to 500 nm. Finally, the response speed of the sensor was as fast as ~6 µs.