bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Controlling Electron and Photon Transport Via Nanoengineering
Authors: Xiong Ze , Tang Jinyao
Published: February 2020

Nanostructured materials behave dramatically different from their bulk counterpart in both electronic properties as well as thermal transport properties. With the immerging low dimensional materials such as nanowires or two-dimensional materials, the research interest has been focused on nanoengineering these materials for different applications including high-performance thermoelectric generator and effective thermal management. On the other hand, these newly developed material systems also arises new scientific questions and offers great opportunities to fundamentally understand the transport physics in nanostructures.

In this work, we would like to present two examples of nanoengineering low dimensional materials to modify their thermoelectric and thermal transport properties which addresses both graphene and semiconductor superlattice nanowires respectively. It is well known that graphene is an excellent candidate electronic material due to its high carrier mobility as well as it is ultrahigh thermal conductivity. Notably, with high thermal conductivity, the thermal management in graphene-based electronic circuit is considered a superior to silicon-based devices. However, this conclusion is based on previous studies on the pristine graphene sheet instead of nanopatterned graphene. We studied the thermal transport behavior of graphene nanomesh with high-density nanoholes and discovered the substantial thermal conductivity suppression with the introduced patterns. This study highlighted the importance of the phonon backscattering inside the two-dimensional graphene system and the thermal management may be more difficult than previously estimated in graphene electronics.

On the other hand, while the thermal conductivity reduction in nanoengineered materials has been demonstrated in many studies, the Seebeck enhancement in nanomaterials was seldom observed. Previously, it has been predicted that the energy filtering effect in superlattice materials may induce an enhanced Seebeck coefficient in nanomaterials. However, since the superlattice materials is usually prepared by high-cost vapor-phase method which cannot be applied to large-scale application. Here, we harnessed the lattice strain of the epitaxy junctions and developed a solution based chemical synthesis method to prepare superlattice nanowires. We compared the Seebeck coefficient and electrical conductivity of the superlattice nanowire which demonstrated energy filter effect and enhanced thermoelectric properties.

Reference:

Z. Xiong, X. Wang, H. K. Lee, J. Zhan, Y. Chen, J. Tang, Thermal Transport in Supported Graphene Nanomesh.
ACS Appl. Mater. Interfaces

Article ASAP (2018)

Z. Xiong, Y. Cai, X. Ren, B. Cao, J. Liu, Z. Huo, J. Tang, Solution-Processed CdS/Cu2S Superlattice Nanowire with Enhanced Thermoelectric Property.
ACS Appl. Mater. Interfaces
9 (38), 32424 (2017)

Figure 1
(Invited) Ionic Thermoelectric Effects and Thermally Chargeable Solid-State Supercapacitors
Authors: Yu Choongho
Published: February 2020

Thermally-induced ion transport has been recently reported to exhibit extremely large thermally induced voltage in contrast to conventional thermoelectrics mainly utilizing thermally-driven electron transport. Here comparative experimental studies about the thermoelectric behaviors of different types of solid-state ionic conductors have been carried out. Their thermopower values have been found to be on the order of 1~10 mV/K. Based on the transport studies, novel methods for generating a large voltage from a temperature gradient and simultaneously storing electrical energy have been developed without losing the benefit of solid-state no-moving part devices like conventional thermoelectrics. Arrays of thermally chargeable supercapacitors have been batch-fabricated, and connected together to linearly raise the output voltage up to 2.1 V, suggesting excellent suitability for roll-to-roll mass manufacturing and practical implementation of thermal energy harvesting. The outcomes suggest that it may be feasible to eliminate needs for battery replacement and wired connections to power lines for various distributed electronic systems whenever and wherever a temperature gradient is present.
Using Copper Ion As the Catalyst Precursor of Electroless Copper Deposition on Polyimide Film
Authors: Li Kuan Shan , Dow Wei-Ping
Published: February 2020

Polyimide film has the desirable properties of thermal stability, good chemical resistance and excellent mechanical strength and has been widely applied to complicated electronic devices and products. Considering the cost issue, we developed a palladium-free process which employs complexed copper ion as catalyst precursor of electroless copper deposition to metallize polyimide film. In this work, electroless Cu was pre-deposited on the polyimide as a seed layer and then followed by copper electroplating. Herein, we used complexed copper ion as the catalyst precursor. After chemical reduction step, the complexed copper ion was reduced to metallic copper (i.e., copper nanoparticle), which is a good catalyst for electroless copper deposition. Therefore, we call the process to be palladium-free process because palladium is a usual and expensive catalyst for electroless copper deposition. The ratio of the complexing agents to the copper ions and optimal temperatures of the solution were investigated in order to enhance the adhesion strength of copper metal film on the polyimide film. The amounts of complexed copper ion on the polyimide surface and the morphology of electroless copper were measured by atomic absorption spectrometry (AA) and imaged by scanning electron microscope (SEM), respectively. X-ray photoelectron spectroscopy (XPS) was used to examine the elements on the polyimide. The results showed that complexed copper ion has the function of catalyst after chemical reduction for the electroless copper deposition on polyimide. The temperature of the catalyst exhibits significant effect on the adhesion strength of the deposited copper metal film on the polyimide film.

Keywords:

Polyimide, Catalyst, Electroless copper deposition

Reference:

[1] Makoto Kohtoku, Hideo Honma and Osamu Takai, J. Electrochem. Soc., 161, D806-D812 (2014).
Using Peg As a Suppressor for High Speed Copper Filling of Microvias
Authors: Chiang Ya-Chi , Dow Wei-Ping
Published: February 2020

Copper electroplating has been widely used for the metallization process of the inner conducting lines in printed circuit boards (PCBs). Short plating process time, which means that the electrochemical deposition is operated at a high current density is always expected because of high yield consideration. However, it is difficult to fill a microvia using copper electroplating at a high current density. The microvias of PCBs have to be fully filled by copper electroplating without void, and the organic plating additives have to overcome breakdown (i.e., electrochemical oxidation) on anode. In this work, we find out a formula employing polyethylene glycol (PEG) as the suppressor can fill the microvias within 20 minutes. The filling performance was assessed through the cross-sections of the filled microvias using optical microscope (OM). Both cyclic voltammetry (CV) and linear sweep voltammetry (LCV) were carried out to explain the fast filling mechanism.

Keywords: High speed copper filling, Microvia, Printed circuit board, Polyethylene glycol.

References

W. P. Dow, M. Y. Yen, S. Z. Liao, Y. D. Chiu and H. C. Huang, Electrochim. Acta, 53, 8228 (2008).
Using Electrochemically Exfoliated Graphene As a Conductive Layer of a Printed Circuit Board
Authors: Chang Shuo-Wen , Dow Wei-Ping
Published: February 2020

Graphene is a popular material because of its unique two-dimensional (2D) structure and intrigued physical and chemical properties. Graphene obtained from chemical exfoliation is usually prepared by oxidizing graphite in a mixing solution containing strong acids and oxidants, which severely destroys the honeycomb lattices of graphene and deteriorates its performance even though these defects could be recovered partly by subsequent reduction process.[1, 2] Recently, electrochemical exfoliation of graphite has attracted attention due to its easy, fast and environmentally friendly nature to produce high quality graphene.[3] In this study, one step electrochemical process not only can synthesize exfoliated graphene oxide (GO) but also can dop in the GO with heteroatoms. After grafting the exfoliated GO on a printed circuit board (PCB), the subsequent reduction of GO sheets to graphene recovers the graphitic structure as a conductive layer. We discussed the effect of electrochemically exfoliated GO on copper electroplating on a PCB. The operating parameters which influence the electron transfer on the electrochemically exfoliated GO, such as electrolytes, operating currents and graphite source, were investigated by using several analysis methods, such as atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy techniques.

Keywords:

Electrochemical exfoliation, Graphene oxide, Conductive layer, Printed Circuit Board

Reference:

[1] S. Park, and R. S. Ruoff, “Chemical methods for the production of graphenes,” Nature nanotechnology, vol. 4, no. 4, pp. 217, 2009.

[2] X. Li, H. Wang, J. T. Robinson, H. Sanchez, G. Diankov, and H. Dai, “Simultaneous nitrogen doping and reduction of graphene oxide,” Journal of the American Chemical Society, vol. 131, no. 43, pp. 15939-15944, 2009.

[3] K. Parvez, R. Li, S. R. Puniredd, Y. Hernandez, F. Hinkel, S. Wang, X. Feng, and K. Müllen, “Electrochemically exfoliated graphene as solution-processable, highly conductive electrodes for organic electronics,” ACS nano, vol. 7, no. 4, pp. 3598-3606, 2013.
(Invited) Fine Temperature Monitoring of Si Wafer for Plasma Processing
Authors: Ito Masafumi , Tsutsumi Takayoshi , Ohta Takayuki , Hori Masaru
Published: February 2020

One of the critical parameters in many semiconductor-processing steps such as plasma etching, chemical vapor deposition, and so on, is the substrate temperature. For example, the etch rate and etch profile are sensitive to the substrate temperature in the plasma etching process. However, contact measurement such as thermo-couples and fluorescent temperature sensor cannot measure the accurate temperature, especially in low pressure due to poor thermal transfer between the wafer and the probe.

We have developed the non-contact temperature measurement of substrates by using optical low-coherence interferometer. [1-6] The low-coherence interferometry is based on Michelson interferometry, and a white light such as a super-luminescent diode (SLD) was used as a low-coherence light source. SLD has the central wavelengths of 1325 nm and the full width at half maximum of 64.5 nm. The light which is reflected at the surface of Si substrate interfered with the light reflected at the scanning reference mirror. The interfered light was detected with a spectrometer and the signal which is a frequency domain spectrum was converted to a time domain signal by inverse Fourier transformation. The temperature of the Si substrate is derived from the change in the optical path length of Si substrate due to thermal expansion and changes in the refractive index.

The temperatures of Si wafer and chamber parts made of Si were successfully monitored in the SiO2 plasma etching using capacitively coupled plasma. The performance was compared with that of fluorescent temperature sensor. From these results, we have demonstrated highly precise and rapid response measurement of the temperature of Si wafer at real time by using Fourier domain low coherence interferometer.

References

[1] K. Takeda et al., “Temperature-Measurement System Using Optical Fiber-Type Low-Coherence Interferometry for MultiLayered Substrate” Jpn. J. Appl. Phys., 43, 7737 (2004).

[2] T. Ohta et al., “Simultaneous measurement of substrate temperature and thin film-thickness on SiO2/Si wafer using optical fiber-type low-coherence interferometry”, J. Appl. Phys., 105, 013110 (2009).

[3] C. Koshimizu et al., “Low-coherence interferometry - based non-contact temperature monitoring of a silicon wafer and chamber parts during plasma etching”, Appl. Phys. Express, 3, 056201 (2010).

[4] C. Koshimizu et al., “Simultaneous In situ Measurement of Silicon Substrate Temperature and Silicon Dioxide Film Thickness during Plasma Etching of Silicon Dioxide Using Low-Coherence Interferometry”, Jpn. J. Appl. Phys., 51 046201 (2012).

[5] H. Yamamoto et al., “Feature Profiles on Plasma Etch of Organic Films by a Temporal Control of Radical Densities and Real-Time Monitoring of Substrate Temperature”, Jpn. J. Appl. Phys., 51 016202 (2012).

[6] T.Tsutsumi et al., “Rapid measurement of substrate temperatures by frequency-domain low-coherence interferometry”, Appl. Phys. Lett. 103, 182102(2013).
(Invited) High Performance & Scalable GaN Device Manufacturing Status on 8-Inch Diameter QST® Platform
Authors: Basceri Cem
Published: February 2020

While developers are making headway with GaN power devices and applications, the existing wafer sizes, yields, cost and performance scaling for both GaN switches and diodes have been limited for volume manufacturing ― creating obstacles for widespread GaN adoption with competitive cost structure thereby preventing access to much larger addressable markets. As the result of significant R&D and pilot-line validation, QROMIS’ groundbreaking and disruptive solution to high volume, low cost and scalable GaN manufacturing is a specially-designed CMOS fab-friendly substrate material called “QST®” (QROMIS Substrate Technology) which supports high quality GaN epitaxy layers (from a few microns to tens of microns thick, including enablement of free-standing GaN) and high performance power device designs thereby paving the way to create a robust GaN power business with large products portfolio (100V to 1,500V lateral or vertical switches, diodes, ICs and more), all manufactured on the same 8-inch or 12-inch production platform. In addition, QST® enables advanced GaN LED devices (e.g. wafer-level chip-scale package (WLCSP) emitters and micro-LEDs) and GaN RF electronics (e.g. vertical devices) which are key features for high volume manufacturing and foundry economics. In this talk, status updates on QST®-based materials and device technologies, and the products development work, covering 8-inch diameter 100V-to-1,500V GaN power switches and diodes, GaN LEDs, and GaN RF devices, will be presented. Also, a detailed review of the company’s volume manufacturing status and 8-inch GaN device wafer foundry services for the industry players, in partnership with Vanguard International Semiconductor and Micron Technology, will be discussed.

Figure 1
(Invited) Integration of Diamond with GaN for Thermal Management in High Power Applications
Authors: Goorsky Mark S. , Wang Yekan Steven , Bai Tingyu , Feygelson Tatyana I , Tadjer Marko J , Hobart Karl D. , Graham Samuel
Published: February 2020

The development of compound semiconductor, wide bandgap electronics based on GaN is poised to impact future rf and advanced power electronic switches. The performance and reliability of these devices is impacted by heat dissipation, which is necessary in order to maintain reasonable device temperatures. Diamond is considered to be a suitable material to promote heat transfer away from the active regions of devices, and recently, several techniques have been developed to integrate diamond with semiconductor materials to achieve effective heat dissipation. We address the properties of polycrystalline diamond, both in thin film and bulk form, to better understand how the polycrystalline nature of diamond impacts thermal conductivity. The deposition of diamond onto, for example, GaN requires the inclusion of interfacial layers; the stability of these layers plays a large role in their effectiveness to protect the semiconductor from the deposition byproducts and to facilitate heat transfer from the GaN to the diamond layer. Novel surface engineering techniques also impact thermal transport across interfaces. We employed transmission electron microscopy imaging and electron energy loss spectroscopy, electron backscattered diffraction (SEM) and precession electron diffraction(TEM), high resolution x-ray scattering, combined with thermal transport measurements to address these issues.
(Invited) III-Nitride UV-Visible Integrated Photonics for Quantum and Biomedical Applications
Authors: Zhao Yuji
Published: February 2020

III-nitride semiconductors have drawn considerable attentions for its wide success in photonic devices including light-emitting diodes, laser diodes, solar cells, and photodetectors. In addition to discrete devices, recent studies on III-nitride waveguides have now opened up new opportunities in integrated photonics for biochemical sensing, beam steering, nonlinear optics, and quantum photonics applications in the UV and visible spectral region. For example, due to their wide bandgap, low material dispersion, and active integration capability, III-nitride materials are particularly attractive for integrated nonlinear optics applications, including second harmonic generation, comb generation, and parametric down conversion. In this talk, I will first present our recent studies on the fundamental nonlinear optical properties of GaN, namely, two photon absorption coefficient, three photon absorption coefficient, and Kerr nonlinear refractive index, and discuss their impacts on the device performance. I will also discuss on-going research at ASU on AlN nanophotonic ring resonators for second order harmonic generation of picosecond UV coherence light, as well as supercontinuum generation from UV to IR. The presented III-nitride integrated photonics platform would enable a wide rangeof applications in biochemical sensing, quantum information, and optical communications.
(Invited) Computer Simulation of Intrinsic Point Defect Distribution Valid for All Pulling Conditions in Large-Diameter Czochralski Si Crystal Growth
Authors: Sueoka Koji , Mukaiyama Yuji , Kobayashi Koji , Fukuda Hiroaki , Yamaoka Shunta , Maeda Susumu , Iizuka Masaya , Mamedov, Vasif M
Published: February 2020

In order to explain and engineer the intrinsic point defect behavior in large-diameter single crystal Si growing by Czochralski (CZ) method, a unified model valid for all pulling processes, crystal resistivities and not electrically active impurity concentrations is needed by coupling the impacts of thermal stress and dopant atoms. This paper provides the thermal equilibrium concentration of intrinsic point defects (vacancy V and self-interstitial Si I) as functions of thermal stresses, type and concentration of dopant, and concentration of interstitial oxygen in CZ-Si crystal. Global heat transfer during crystal growth in a puller was simulated by CGSim package, software of STR Group, Inc. Visual distribution of V and I concentrations inside a growing Si ingot well explains the previous experimental results of impacts of thermal stress and heavy doping.
Solution Based Al2O3 Gate Insulator for Low Temperature Poly Silicon TFT
Authors: Yang Hee Chan , Hwang Sang Ho , Baek Yeong Jo , Lee Sang Min , Okada Tatsuya , Noguchi Takashi , Bae Byung Seong
Published: February 2020

Solution based insulator was applied for low temperature poly silicon thin film transistor (TFT). Solution process has several advantages of low cost, short process time and no plasma damage. Several kinds of solution-based materials were tested for TFTs, including organic insulators. In this paper, we present the aluminum oxide gate insulator based on solution process.

For poly-silicon process, amorphous silicon is deposited by sputtering and crystallized by blue laser diode annealing. After pattering of the poly-silicon, gate insulator of Al2O3 was formed by solution process. After gate insulator etching, source/drain metal was deposited and patterned. Low temperature process below 400℃ for all TFT fabrication with low cost has been developed and reported.

The insulator was characterized with the metal-insulator-semiconductor (MIS) structure. 0.8 M Al(NO3)39H2O solution with DMAC (Di-methyl-acetamide) was coated on the Si-wafer. The surface of silicon wafer was treated with oxygen plasma before coating to improve the adhesion. After spin-coating, it was baked at 150℃ for 5 min. It was annealed finally at 300℃ for 1 h.

To improve the insulator performance, the multi coating was tested. After coating and baking, it was coated again. Figure 1 shows the I-V characteristics for the sample coated for three times. As the number of coating increased, leakage current was reduced and the break down voltage increased.

Figure 1
Clock-Generator Embedded Charge Pump Circuit Using Oxide TFT
Authors: Kang Min Su , Kang In Hye , Han Ye Lin , Hwang Sang Ho , Baek Yeong Jo , Lee Sang Min , Bae Byung Seong
Published: February 2020

Wearable device refers to a device that is always in contact with the body beyond the carrying smartphone. For wearable applications, flexibility is important, which need the integration of the circuit on a substrate. With the discrete devices, it is difficult to bend.

In wearable device, information should be displayed. For the display, drive circuit is necessary. With a battery, we need some boost up circuit such as charge pump for driving of the display. The charge pump need clocks which should be supplied by separate source. In this paper we embedded the clock generator in charge pump circuit.

Charge pump are used in almost all mobile devices and provide a stable output voltage under unstable power condition. Among several types of charge pumps, Dickson type charge pump has been used widely in traditional industrial applications.

In the charge pump circuit, two square waves are alternately applied. At the first stage, the capacitor is charged equal to the supply voltage. In the second stage, the circuit is connected in series with the power supply and the load.

Finally, the voltage across the load increases to twice the sum of the supply voltage and the capacitor voltage. Figure 1 shows proposed charge pump circuit with embedded clock generator and the output voltage of it. The circuit that generates the clocks CK and CKB is necessary for driving the charge pump circuit. The clock generator has the same configuration as the RC oscillator and alternately outputs square wave of 1.5 V.

As shown in Fig. 1, the output voltage is about 6 V when the input voltage is 1.5 V. The output voltage increases linearly with respect to the input voltage. The output voltage variation according to the number of TFTs are also investigated. As the number of TFTs increases, the output voltage increases.

Figure 1
(Invited) Large-Scale Growth of Two-Dimensional Materials Toward Phase-Engineered Hybrid Films Utilizing Low Temperature Plasma-Assisted Chemical Vapor Reaction Method
Authors: Chueh Yu-Lun
Published: February 2020

2D materials have attracted much attention because of frontier electronic materials due to its superior electronic transport properties and mechanical flexibility in the future, making it a potential material for high performance and wearable electronics. Graphene is a typical 2D materials with high carrier mobility; however, it still cannot be applied in transistor due to the lack of bandgap. A new type of 2D semiconducting materials called transition metal dichalcogenides (TMDCs), which are layered structure with the strong in-plane bonding and weak out-of-plane interactions similar to graphite, have been intensively studied. Recent studies have predicted exceptional physical properties upon reduced dimensionality attracting lots of attention due to the versatile physical chemical behaviors. Nevertheless, the synthesis and the study of the fundamental physical properties of TMDs are still in early stages. The lack of a large-area and reliable synthesis method restrict exploring all the potential applications of the TMDs. Chemical vapor deposition (CVD) is a traditional approach for the growth of TMDs; nevertheless, the high growth temperature is a major drawback for its to be applied in flexible electronics. In this talk, an inductively coupled plasma (ICP) was used to synthesize Transition Metal Dichalcogenides (TMDs) through a plasma-assisted selenization process of metal oxide (MOx) at a low temperature, as low as 250 °C. Compared to other CVD processes the use of ICP facilitates the decomposition of the precursors at lower temperatures; therefore, the temperature required for the formation of TMDs can be drastically reduced. WSe2 was chosen as a model material system due to its technological importance as a p-type inorganic semiconductor with an excellent hole mobility. Large-area synthesis of WSe2 on polyimide (30 x 40 cm2) flexible substrates and 8-inch silicon wafers with good uniformity was demonstrated at the formation temperature of 250 °C as confirmed by Raman and X-ray Photoelectron (XPS) spectroscopy. Furthermore, by controlling different H2/N2 ratios, hybrid WOx/WSe2 films can be formed at the formation temperature of 250 ºC as shown by TEM and confirmed by XPS. The applications o including (1) water splitting, (2) gas sensors, (3) photodetectors, (3) anode materials in secondary ion battery will be reported.
(Invited) Nano Scaled 1-D Nanorod and Nested Nanotube Device Structures in Gas Sensing Applications
Authors: Lin Pengtao , Zhang Kai , Baumgart Helmut
Published: February 2020

In this talk the various uses of one-dimensional (1D) nanostructures such as nanorods and nanotubes in gas sensing applications will be reviewed. During recent years semiconducting metal oxide ZnO one-dimensional (1D) nanostructures have been popular because the high surface area- to-volume ratio of these nanostructures is potentially useful for gas sensing applications. ZnO is characterized by a wide band gape of 3.37 eV and a large exciton binding energy (~60 meV). The use of 1-D ZnO nanostructures is attractive due to the availability of low cost synthesis processes and a reasonably good electrical conductivity that can be further modulated and improved by doping with Al to achieve Al doped ZnO (AZO). In general, ZnO 1-D nanorod structures can be successfully synthesized by hydrothermal method in an autoclave with ZnO seed layers deposited on the substrate. The solutions used for ZnO nanorods hydrothermal growth are typically composed of zinc nitrate hexahydrate (Zn(NO3)6H2O) and hexamethylenetetramine ((CH2)6N4) dissolved in DI water. The introduction of 3-D wrap-around coatings with ALD technology enabled recently the fabrication of nested ZnO nanotubes with alternate coatings of Al2O3 and ZnO to synthesize AZO coatings. In order to increase the critical surface-to-volume ratio even further the state-of-the-art was further expanded to include sacrificial ALD alumina coatings that can subsequently be selectively removed by wet chemical means using a Sodium hydroxide (NaOH) etch solution. Such an integrated process sequence produces empty annular rings surrounding the core ZnO nanorod, thereby exposing additional free surfaces of AZO and ZnO for catalytic sensing reactions. In principle several or ultimately n sacrificial coating layers can be added by ALD technology to fabricate coaxial multiple nested nanotube structures with one nanotube inside the other. Each empty sacrificial annular ring adds two additional free reactive surfaces to the sensor. The application potential for MOS gas sensors and photodetectors with 1-D ZnO nanostructures will be reviewed. The physical characterization and sensing performances of ZnO nanorods benchmarked against ZnO multiple nested nanotube structures with AZO coatings and sacrificial layers will be discussed and compared to literature examples.
Quadrupole Gap Surface Plasmon Integrated Bilayer MoS2 for Excellent Photoelectrochemical Hydrogen Evolution
Authors: Sriram Pavithra , Manikandan Arumugam , Chueh Yu-Lun , Yen Ta-Jen
Published: February 2020

Plasmonic nanoantennas with efficient scattering and strong electromagnetic field confinement were integrated to atomically thin transition metal dichalcogenides (TMDC) to shed light on the nanoscale light-matter interactions. Herein, we optimized the quadrupole gap surface plasmonic (QGSP) structure by Taguchi design to maximize field enhancement and integrated to CVD grown bilayer molybdenum disulfide (MoS2), beneficially tuning the optical properties of bilayer MoS2. The optimized QGSP structure with 27.87 factor enhanced performance and advantageous 1cm2 continuous bilayer MoS2 finds potential application for hydrogen evolution reaction (HER) with superior outcome. MoS2@QGSP act as an excellent photocatalyst for HER activity on account of accelerated electron injection process in comparison to electron-hole pair recombination supported from skilled light trapping capacity of QGSP structure and plentiful accepting sites of large surface continuous bilayer MoS2 film. This report demonstrates the gap surface plasmon enhanced intrinsic catalytic properties of bilayer MoS2 for photocatalytic reactions.
Heterostructure a-Carbon Coated Copper Phosphide Peapod Nanotubes As Ultra-High Efficient Hydrogen Evolution Catalyst By Low Temperature Chemical Vapor Reaction
Authors: Manikandan Arumugam , Sriram Pavithra , Wang Yi-Chung , Chen Chia-Wei , Shih Yu-Chuan , Yen Ta-Jen , Chueh Yu-Lun
Published: February 2020

Towards finding the low-cost electrocatalyst with high catalytic properties to replace the noble metal in use of electrochemical hydrogen evolution reaction (HER) of total water splitting is appropriate to approach the green, sustainable energy supply. Here we synthesized a direct growth of novel copper phosphide peapod nanotube structure for first time coated with amorphous carbon/few-layer graphene from chemically synthesized copper nanowire (Cu NW) at a low temperature of 400 °C by chemical vapor reaction (CVR) process. The as-prepared peapod morphology was evidenced by SEM, TEM and the crystallinity was studied by XRD analysis. Raman and XPS were utilized to evaluate the presence of graphitic carbon at the surface and phases of copper phosphide. This nanostructure exhibits superior electrocatalytic activity by achieving lower overpotential of 287 mV at the current density of 10 mA cm-2 with low Tafel slope of 72 mV dec-1 and show excellent stability over 1000 cycles. Besides, the current catalyst prepared from copper save the production cost and could be used as an inexpensive electrocatalyst for all the water splitting systems.
Band Engineering of Quantum Dot Substrates to Utilize QD-Generated Photocarrier for SERS Signal Amplification
Authors: Lim Hunhee , Baek Kwang Min , Jung Yeon Sik
Published: February 2020

Interacting with light, plasmonic materials generate electric fields induced by localized surface plasmon resonance (LSPR) phenomenon. Electric field generated by plasmonic materials can induce optical phenomena such as light scattering, light emissive recombination and surface-enhanced Raman scattering (SERS). These phenomena grant versatile functionalities to plasmonic materials which can be applied to various devices such as photovoltaics, light emitting diode, meta material, SERS and so on. Amplifying electric field of plasmonic materials can improve the optical phenomenon and applications. Injecting external carriers into plasmonic materials can be good solution to improve electric field generation.

In this research, we used incident light to generate photo-carrier and designed the band structure of the materials to extract photo-carrier into the plasmonic materials. We fabricated the substrate consisting of lead sulfide quantum dot/zinc oxide/plasmonic structure. The bottom quantum dot (QD) layer absorbs light and transfer photo-carrier to zinc oxide and plasmonic structure. For the photo-active material, we selected lead sulfide quantum dot (QD) because the band gap of the QD is conveniently tunable by controlling the size of QD. We synthesized the QD with the band gap around 1.3eV to optimize the light absorption ranging from 400nm to 900nm. Upper ZnO layer forms p-n junction with QD and selectively transports electron to top plasmonic materials. To verify the enhancement of electric field in photo-carrier injected plasmonic structure (PCIPS) substrate, we applied PCIPS substrate to SERS device. We measured 4 different molecules and the SERS signals enhanced from 3 to 7 times. Kelvin probe force microcopy (KPFM) measurement showed the change in surface potential of the substrate with and without light incidence. Our device showed great potential in SERS application because the device showed meaningful improvement in SERS signal simply using incident laser used to detect molecules.

Figure 1
Metal Junction Interface and Surface Transport Properties of Halide Perovskite
Authors: Lin Chun-Ho , Li Ting-You , Cheng Bin , Ke Jr-Jian , Wei Tzu-Chiao , He Jr-Hau
Published: February 2020

Trihalide perovskites have arrived at the forefront of next-generation solar technology due to their impressive light absorption coefficients, long carrier lifetimes, high carrier mobility, and intense photoluminescence. The metal/perovskite junction interface and carrier transport behaviors along the perovskite surface were studied on single crystalline CH3NH3PbBr3 by employing transfer length method with lithography patterned Au, Pt, and Ti electrodes. The charge pinning effect and image force were observed at perovskite junction interface for different contact metals. Furthermore, the surface charges at perovskite surface can result in the thermally activated carrier transport with activation energy of 0.2 eV when temperature is above 207 K; meanwhile variable range hopping dominates the transport below 207 K. This fundamental study of metal contact and surface transport of halide perovskite will guide the future electronic applications, and are especially important for low-dimensional perovskites which have high specific surface area.
(Invited) Controlling the Carbon Vacancy in 4H-SiC By Thermal Processing
Authors: Ayedh Hussein M. , Baathen Marianne E. , Galeckas Augustinas , Hassan Jawad Ul , Bergman J. P. , Nipoti Roberta , Hallen Anders , Svensson Bengt G
Published: February 2020

The carbon vacancy (VC) is a major point defect in high-purity 4H-SiC epitaxial layers for bipolar power devices, and it limits the minority charge carrier lifetime. VC exhibits a formation energy of only ~5.0 eV, as confirmed both theoretically and experimentally, and in as-grown layers realized by chemical vapor deposition techniques, the VC concentration is typically in the low 1012 cm-3 range. After high-temperature device processing exceeding 1900 °C, the VC concentration can be enhanced by several orders of magnitude.

Three different approaches are commonly used to minimize the VC content and enhance the carrier lifetime; (i) near-surface ion implantation followed by high-temperature annealing, (ii) thermal oxidation of the Si-terminated epi-layer surface, and the most recent one (iii) ‘equilibrium annealing’ at moderate temperatures (≤1500 °C) under C-rich surface conditions. In the present contribution, we will discuss the advantages and limitations of the different approaches with a particular focus on the approach (iii). New insight into the atomistic processes governing the VC equilibration kinetics is given and how these processes can be tailored by varying the cooling rate after high-temperature treatment. Especially, the diffusivities of both VC and the carbon self-interstitial are found to play a decisive role and where at least the former one displays a substantial anisotropy between directions parallel and perpendicular to the basal c-plane. After thermal treatment of as-grown layers under C-rich surface conditions at 1500 °C for 1 h followed by slow/moderate cooling, the VC concentration is shown to be reduced to ~1x1011 cm-3 enabling a minority carrier lifetime well above 20 µs at room temperature.
(Invited) Microfluidics for Biomedical Devices By Two Examples
Authors: Baysal Oktay
Published: February 2020

The need and the tremendous value of “very small” machines and devices were realized in late 1980’s. In the following decade, the indispensable utility of micro- or even nano-level transport phenomena in these machines was recognized, leading to the start of research and development in microflows. Researchers started investigating from a point where they deemed relevant body of knowledge on macroflows stood. Over the ensuing years, there has been significant amount of resource investment to, for example, the understanding of how the underlying physics differed as compared to macroflows and, just as importantly, what existing transport phenomena tools would be applicable. It was quickly observed that what significantly changed were the relative effects of, for example, very low Reynolds numbers, the domination of surface and interface tension, and even the continuum assumption. Much happened since then, hence, today we enjoy the ever ubiquities micro- and nano-fluidic devices this body of research and development have produced.

The author took interest in this field in the early 2000’s. This presentation will briefly sample a few of our earlier studies which varied from “design optimization of a micro synthetic jet actuator to control microflow separation,” to “electrodiffusiophoretic motion of charged spherical particle in a nanopore.” The emphasis, however, will be on our current research on two biomedical devices, using in silico approach and collaborating with adjoining experimentations: (i) a convective polymerase chain reactor (cPCR); (ii) microfluidics-aided collagen fiber (MCF) fabrication. Our goal in the first project is to develop a methodology for a portable and affordable c-PCR design intended for point-of-care use. Computational fluid and heat transfer models are developed to simulate the prerequisite convective transport fields. The search space for optimality is determined based on a specified range of the selected design variables. The convection-diffusion equations are then recast to determine and minimize the time-to-double the reagent (in our case, the double-stranded DNA) by the candidate design. For the MCF device, we are developing a new microfluidic methodology to fabricate advanced telocollagen fibers. The ultimate goal is to obtain an advanced microfluidic-based telocollagen manufacturing technology suitable to produce ligament and tendon repair and replacement grafts. Our specific goal is to provide the in silico guidance to the fabrication of collagen fibrils, which are much finer and better axially aligned, since prior research has shown that the mechanical strength of such fibers would be more favorable in achieving their purpose.
Weakly Charged Nanochannels Can Generate High Salinity Gradient Power
Authors: Yeh Li-Hsien , Su Yen-Shao , Chen Fu , Chiou Yu-Ting
Published: February 2020

Nanofluidic salinity gradient power (NSGP), in which power associated with the salinity gradient can be generated with ion-selective nanochannels, has recently received considerable attention due to its high power density and power generation process without any chemical pollutants. Developing a novel nanopore/nanochannel material to attain high performance of NSGP device is essential to develop this next generation, renewable, clean energy. A general design guideline is that the higher the nanochannel’s surface charge density, the greater the NSGP performance. However, the present study will report the first evidence that an optimal surface charge density of a nanochannel is required to generate higher performance of salinity gradient power, which challenge the past understanding so far. To explain what we found in experiments, a rigorous model with considering the deportation and protonation reactions on the channel wall is developed to investigate the power conversion from a salinity gradient with a pH-regulated nanochannel. The result from our modeling is in good consistent with the experimental observation of the unexpected charge-density dependent NSGP behavior. It is also found that the nanochannel with lower surface charge density can have remarkably higher NSGP performance. The reason to cause the interesting and unexpected phenomenon is due to the charge-density dependent ion concentration polarization effect, which yields the decrease in the effective concentration ratio (actual driving force) across the nanochannel. The results are informative for designing relevant apparatus in renewable energy applications.
(Invited) Hybrid Microfluidic Cell Sorting for Rare Cell Isolation
Authors: Ai Ye
Published: February 2020

Selective isolation of specific cell subpopulations from highly heterogeneous biological samples is an essential process in various biological studies and clinical applications. The ability to isolate rare cell populations, for example circulating tumor cells, provides unprecedented capabilities for the study of disease progression and better disease assessment. Currently, sorting and isolation of rare cell populations is typically performed using fluorescence-activated cell sorting (FACS) system, a technology developed nearly 60 years ago. These FACS systems are however complex, bulky, and expensive, require highly trained personnel for operation, and may produce bio-hazardous aerosols in open environments.

Microfluidics studies the unique behavior and interactions of fluids and particles at the micrometer length scale, typically in confined microscale channels. Microfluidic technology capable of precise cell manipulation thus has great potential to reinvent the next-generation cell sorting technology. We are currently developing two microfluidic cell sorting technologies including high-throughput hydrodynamic cell sorting and high-accuracy acoustic cell sorting. Hydrodynamic cell sorting is using an interesting inertial particle focusing behavior in an intermediate Reynolds number regime (~100 > Re > ~1). We have designed and fabricated a new type of hydrodynamic sorting device with a series of reverse wavy channel structures. These repeated wavy channels produce periodically reversed Dean secondary flow perpendicular to the main flow direction. The hydrodynamic inertial lift force and the Dean drag force scale with the particle size very distinctively, which leads to distinct equilibrium positions of differently sized particles. We have demonstrated the use of this new hydrodynamic sorting device to isolate cancer cells from blood cells without the use of sheath flows. Acoustic cell sorting is developed based on the study of interactions between high-frequency sound waves and microscale particles. In particular, I will discuss a unique design of a focused interdigital transducer (FIDT) structure, which is able to generate a highly localized acoustic field on the order of 25 µm wide. This highly focused acoustic beam has an effective manipulation area size that is comparable to individual micron-sized particles. We have demonstrated the use of this highly localized acoustic field for fluorescence-activated single cell level sorting with sub-millisecond pulses. By combining the two microfluidic cell sorting technologies, we have demonstrated the capability of enriching target cells by 1,000 to 10,000 times, providing a new solution of rare cell isolation.
Identifying Laser-Induced Plasma Spectra of Particle in Gas-Solid Flow Based on the Standard Deviation of Pixel Intensities
Authors: Yao Shunchun , Li Yuesheng
Published: February 2020

A new method which schemes of conditional data processing named standard deviation (SD) method is present and evaluated for identifying spectral data of gas-solid particle flow based on laser-induced plasma spectroscopy. The SD method is also compared with two conditional analysis methods called the SNR method and the absolute intensity method. First, the effect of three methods identifying the spectral data of the same fly ash sample is compared. Then, the threshold stability of the three methods under different conditions was observed by screening the spectral data of a set of 12 coal samples. The rejection rate, error rejection rate (or error rejection) and missing rejection rate (or missing rejection) were used to evaluate these three different approaches. And probability of false hits is determined by evaluating various conditional processing thresholds. The characteristic peaks used for the analysis of fly ash and coal samples are selected as Si 288.16 nm and C 247.86 nm, respectively. The result shows that for all approaches the SD method has the minimum rejection rate and error rejection (both 0%) when the SD threshold value is 120, the total rejection rate of the SD method is also the lowest of the three under this condition, which is 37.67%. It means that true data and false data could be completely and accurately identified by using the SD method. Moreover, for different samples and experimental conditions, the thresholds of absolute intensity method and SNR method fluctuate in the range of 83 - 135 counts and 2.05 - 4.00, respectively, while the threshold of the SD method has been stable at 55. Compared with other two methods, the SD method is more universal when faced with variable detection conditions. So it has more advantages in the rapid detection and analysis of power plants.
Operando Study of the LiV3O8 Cathode: Coupling Electrochemical and EDXRD Measurements with Mathematical Models
Authors: Brady Nicholas W , Zhang Qing , Bruck Andrea , Bock David C , Gould Christian Alexander , Marschilok Amy C , Takeuchi Kenneth J , Takeuchi Esther S , West Alan C.
Published: February 2020

Building upon a previously validated crystal-scale model, a coupled electrode/crystal-scale mathematical model is used to compare phase-change behavior and electrochemical performance of lithium trivanadate (LiV3O8). The agreement between simulated and observed electrochemical performance is compelling. Observations about the phase-change dynamics of the material were gathered using time and space-resolved operando EDXRD measurements. These observations were compared with simulated concentration and phase profiles. Both simulation and experiment reveal that during lithiation, phase transformations preferentially occur near the separator, while during delithiation the disappearance of the lithium-rich β-phase occurs uniformly across the electrode.