bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Low-Temperature Microwave-Based Plasma Oxidation of Ge and Oxidation of Silicon Followed by Plasma Nitridation
Authors: Lerch Wilfried , Schick T. , Sacher N. , Kegel W. , Niess J. , Czernohorsky M. , Riedel Stefan
Published: February 2020

Oxidation is a key process step in semiconductor device fabrication. Oxides are widely used in the production process as gate dielectrics, interfacial layers for high-k deposition, pad oxides, sacrificial oxides, screen oxides, protection oxides etc. Even though the used oxide thicknesses become thinner the thermal budget (roughly time at temperature) is generally not scalable with the thickness decrease due to the thermally activated oxidation process. However, for future sub-22 nm device structures a continuous reduction of oxidation temperatures is required to minimize dopant redistribution or deactivation, boron depletion, and oxidant enhanced diffusion effects. At the same time physical, chemical and electrical oxide quality has to be maintained. This is valid also for all process steps after device formation where high quality oxides are needed. BEOL applications like surface conditioning by oxidation is only one example.

In this contribution we show that oxides can be grown and/or in a subsequent process step nitridized with an excellent electrical quality for planar Si and Ge devices but also conformally on 3D Si devices at very low temperatures (T < 400 °C). First the oxide growth with or without subsequent nitridation as a multi-step process is studied as function of time, and gas ambient on silicon and germanium, second the electrical characteristics of these various films are demonstrated. In the industry Ge is expected as the promising channel material for future CMOS because of its highest hole mobility among common elemental and compound semiconductors, and an electron mobility that is two times larger than that of Si. Therefore it is important to show outstanding electrical results of the Ge passivation layers grown at very low temperatures.
High-K Metal-Gate Nanowire Junctionless FinFET with Nickel Silicide by Microwave Annealing
Authors: Tsai Wan-Ting , Lin Yu-Hsien
Published: February 2020

Background/ Objectives and Goal

Silicide techniques are widely used for high-performance logic devices as the device dimensions become small towards sub-100 nm due to the source / drain sheet resistance issue.NiSiprocess has several advantages.They are (1) low temperature silicidation process, (2) low silicon consumption, (3) no bridging failure property, (4) smaller mechanical stress, (5) no adverse narrow line effect on sheet resistance,and(6) smaller contact resistance for both n- and p-Si[1].We, therefore, propose a nickel silicide junctionlessFinFETdevices.

     2.  Methods

Fig.1. depicts schematically view of the high-K metal-gate nanowire junctionlessFinFETwere fabricated on a 6-inch wafer with a 40 nm-thick silicon dioxide layer.The active layer with ten strips of NWs was defined by electron beam (e-beam) and transferred by reactive ion etching.An 33 nm dry SiO2 layer was grown on the active layer. Next,implanted (boron for pFETs and phosphorus for nFETs,dosage of 2 × 1014 cm2)  and followed by thermal anneal in the channel.The samples were then dipped in HF solution for NWs. 3 nm of HfO2was deposited by ALD on the nanowires as gate dielectric, followed by the PVD 50 nm TiN for gate metal.After the deposition,electron  beam (e-beam) defined gate contact and transferred by reactive ion etching.Next, 15 nm of titanium followed by 15 nm of nickel was deposited on the sample.NickelSilicide was formed after twice microwave anneal.First annealed by microwave with 360W for 300 sec , and1300W for 300sec. The temperature profiles versus annealing time are shown in Fig. 2[2].

    3. ExpectedResults/Conclusion/Contribution

The ID–VGcharacteristics of a 15 nm gate-length high-k metal-gate nanowire junctionlessFinFET Fig. 3.The on-current value is comparableto that of a junctionlessfinfetwith the same bias conditions.In our experiment,there was no metallization past the silicide layer, therefore the resistance of the devices was large.This is the reasons why devices without silicide showed less on-current presented here.

We have demonstrated high-k metal-gate nanowire junctionlessFinFET with nickel silicide fabricated with a low-temperature process.The devices have exhibited a competitive short-channel behavior and a much-improved drive current.These results indicate that silicide S/D is a promising option for a nanowire junctionlessFinFET device.We believe that this letter significantly advances the state of the art for low-temperature silicide junctionlessFinFET.

REFERENCES

[1] H. Iwai, T. Ohguro, and S. Ohmi, “NiSi salicide technology for scaled CMOS,” Microelectron. Eng., vol. 60, no. 1/2, pp. 157–169, Jan. 2002

[2] Y.-J. Lee et al., “Low-temperature microwave annealing processes for future IC fabrication—A review,” IEEE Trans. Electron Devices, vol. 61, no. 3, pp. 651–665, Mar. 2014.

Figure 1
Novel Oxidants and Sources of Nitrogen for Atomic Layer Deposition
Authors: Alvarez Daniel , Spiegelman Jeffrey , Heinlein Ed , Holmes Russell , Ramos Chris , Leo Mark , Webb Sean
Published: February 2020

Significant effort has gone into developing novel metal precursors for Atomic Layer Deposition (ALD). This effort has been primarily driven by the industry need for new high K materials and metals films.  The need for novel oxidants and sources of nitrogen has been largely ignored.  This paper focuses on delivery of anhydrous hydrogen peroxide and anhydrous hydrazine for ALD applications.

Hydrogen Peroxide (H2O2) in aqueous form is commonly used in semiconductor manufacturing for cleaning and surface preparation operations.  Thirty percent and fifty percent two-component mixtures have been investigated in a few ALD studies with moderate success.  Especially noteworthy are Kummel’s findings that the use of hydrogen peroxide leads to a 3x increase in nucleation density on Ge versus water.  However, H2O2 has limited general utility in aqueous form due to the volatility of water.  At 30C, Raoult’s law predicts a headspace concentration of 294ppm H2O2 and  32373ppm for water, where the H2O/H2O2 ratio is over 100.  Clearly these are not optimal conditions for hydrogen peroxide ALD. However, in its pure state, hydrogen peroxide is highly unstable and has a propensity to decompose, forming water and oxygen.  Our approach entails the use of a membrane delivery system where 99.6% hydrogen peroxide is dissolved in an organic solvent.  Hydrogen peroxide permeates the membrane and is delivered to the ALD chamber, while the solvent does not permeate and remains in the liquid state.  In this way, concentrations much higher than predicted by Raoult’s law for aqueous mixtures are delivered to the process chamber in the absence of water.

Next generation devices have low thermal budgets and high aspect ratio structures that create new challenges for ALD grown nitride films. The use of ammonia is limited due to temperature constraints. Known Plasma  methods cannot uniformly coat the side walls of the device structures and create surface damage. Hydrazine (H2NNH2) has been proposed as a thermal ALD low temperature nitride source. Hydrazine is highly flammable and its flash point decreases with reduced water content. In an analogous approach, we have developed a new method and formulation for the delivery of anhydrous Hydrazine by the use of an inert organic solvent and membrane delivery system.  Precursor vapor pressure is maintained at levels viable for ALD.  Moreover, the addition of a high boiling solvent lowers the risk of explosion by raising the solution flash point.

 Preliminary ALD data will be presented showing unique properties of these new precursors along with theoretical data on precursor delivery under variable ALD conditions.
(Invited) Rapid In-Situ Carbon and Oxygen Cleaning of In0.53Ga0.47As(001) and Si0.5Ge0.5(110) Surfaces via a H2 RF Downstream Plasma
Authors: Wolf Steven , Edmonds Mary , Jiang Ximan , Droopad Ravi , Yoshida Naomi , Dong Lin , Galatage Rohit , Siddiqui Shariq , Sahu Bhagawan , Kummel Andrew
Published: February 2020

Channel passivation of SiGe and InGaAs requires removal of dangling bonds and formation of a thermally stable interface.  On InGaAs, one solution is the deposition by self-limiting CVD or ALD of a few monolayer of silicon, silicon oxide, or silicon nitride.  To form an Si-OH terminated In0.53Ga0.47As(001) surface, two monolayers of Si were deposited at 350°C with self-limiting CVD using Si2Cl6  dosing following by dosing anhydrous HOOH(g).  Scanning tunneling microcopy (STM) shows and ordered surface is form while scanning tunneling spectroscopy (STS) shows the surface Fermi level position moves towards midgap due to a surface dipole formation from –OH groups and oxygen bonding to the surface.  TMA was dosed at 250°C onto the Si-OH terminated InGaAs(001), and XPS shows the emergence of the Al 2p and C 1s peaks indicative of TMA surface nucleation.  The TMA shifts the InGaAs Fermi level back towards the conduction band, consistent with unpinning.   MOSCAPs were fabricated to further demonstrate Fermi level unpinning using the Si-OH termination of InGaAs.

While this same Si deposition process could be employed on SiGe, a  simple annealing process can be employed to form a silicon terminated SiGe surface. A saturation dose of H2O2(g) at 25oC chemisorbs to on Si0.5Ge0.5(110) and Si0.47Ge0.53(001)  surfaces leaving the Fermi level on the surface unpinned, and the surface is functionalized with mainly Si-OH, Ge-OH and Si-O-Ge bond.  After a subsequent TMA dose at 25oC and annealing at 300oC, XPS and STM verify that a thermally stable and well-ordered monolayer of Al2O3 is formed on SiGe(110) and (001) surfaces with only Al-O-Si bonds and no detectable Ge-O-Si bonds. The H2O2(g) functionalization provides 3 times higher  O sites on the surface and 3 times higher TMA nucleation density than H2O(g) at 25°C and 120°C. 

A variety of strongly bound passivating atoms can induce formation of a nearly pure Si interfacial layer between high-k dielectrics and SiGe. This annealing procedure was employed to form MOSCAP on SiGe(001) using Al2O3 and HfO2 gate oxides after either (NH4)2S or NH3 plasma passivation.  For NH3 plasma passivation, angle-resolved XPS showed that the annealing allows formation of nearly Ge-free SiON layer.  For higher Ge concentrations, the annealing process is unlikely to form a nearly Ge-free SiON layer so a novel plasma-free chemistry has been develop to deposit SiON using  ALD with N2H4(g) as a precursor.

Figure 1
Comparison of SiNx and AlN Passivations for AlGaN/GaN Hemts
Authors: Yang Song , Lei Lei , Yu Kun , Zhang Anping , Chen Kevin J
Published: February 2020

We present a comparative study of suppressing AlGaN/GaN HEMTs’ current collapse by two types of passivation materials: amorphous SiNx (grown by PECVD and LPCVD) and epitaxial AlN (grown by plasma enhanced atomic layer deposition (PEALD). The motivation of this study stems from the different mechanisms underlying the two passivation techniques, namely, surface-charge-compensation by shallow donors (with SiNx) and polarization charge (with epitaxial AlN). Since de-trapping from the shallow donor levels is a time-dependent process and the polarization charge compensation is a time-indepdent phenomenon, AlN-passivated AlGaN/GaN HEMTs was found to exhibit improved dynamic switching behavior than SiNx-passivated devices. The results show that the depletion region is much narrower in AlN-passivated devices than SiNx-passivated and un-passivated devices. The transient characteristics reveal the superiority of AlN passivation as the formation of depletion region is predominantly a field effect while the de-trapping from the shallow donor levels in SiNx-passivated devices is limited by their intrinsic time constant. AlN-passivated devices show much smaller dynamic RON variation under both fast and slow switching operations.
(Invited) Room Temperature Spin Electronic Devices Based on Mn and Cr Doped GaN
Authors: El-Masry Nadia A , Bedair Salah M
Published: February 2020

Doping of GaN with Mn and Cr has been achieved by metal organic chemical vapor deposition (MOCVD). Hysteretic behavior was observed at room temperature and structural measurements, X-ray diffraction, and atomic force microscopy gave no evidence of second phases in the transition metal-doped epitaxial layers. Multilayer structures grown by MOCVD were used to determine the dependence of magnetic ordering in GaMnN and GaCrN epilayers upon the availability of free holes. Based on these results a prototype spin devices were designed and fabricated in which holes, adjacent to a GaMnN or GaCrN layer, could be modulated by an applied electric field. The devices demonstrated that enhancement of ferromagnetic behavior could be switched on and off electrically at room temperature. Such current-controlled FM in GaMnN or GaCrN devices would have important applications at room temperature, especially in nonvolatile memory storage systems.
(Invited) Electric-Double-Layer-Gated AlGaN/GaN High Electron Mobility Transistors (HEMTs) for Biosensors
Authors: Chu Chia-Ho , Sarangadharan Indu , Regmi Abiral , Chen Yen-Wen , Hsu Chen-Pin , Wang Yu-Lin
Published: February 2020

Electric double layer was proved to modulate the channel of field-effect transistors, which is called electric-double-layer transistors (EDLTs) and have been reported previously. One of the unique property of the electric double layer is the much higher capacitance compared to that of silicon dioxide or other high dielectric constant materials. EDLTs are attractive not only because of its high capacitance, but also because of its other properties in solution, which is very different from conventional dielectric materials. In this study, we investigate the EDLTs using AlGaN/GaN HEMTs, with different designs of the devices and in solutions with different ionic strength. We find out that the channel conductivity is relevant to these parameters and the EDLT model becomes different from conventional FETs. By using the electric-double-layer AlGaN/GaN high electron mobility transistors, we successfully detect several proteins in physiological environment (1xPBS) with high ionic strength and in serum as well. Our devices and methods do not suffer from the charge screening effect, which is usually a critical issue for conventional FET-based biosensors. Direct detection of proteins in serum without any dilution or washing process can largely simplify the use of the FET-based biosensors for point-of-care or homecare. The results reveal future possible applications of the EDLTs.
Structural and Elemental Analysis of Degraded Single Junction Amorphous Silicon Solar Module
Authors: Osayemwenre Gilbert
Published: February 2020

Photovoltaic solar modules have different defects and degradation characteristic modes. These degradation modes normally heats up some regions in the PV module. Depending on the degree and size of the localised heat, the localized heat can rise above the temperature limit of the module and cause damage to the structural orientation. The presence of severe defect and degradation correlates with high temperature gradients that usually results in morphological damage especially under outdoor conditions. The present study investigates the effect of defect/degradation on the surface morphology of single junction amorphous silicon modules (a-Si:H) during outdoor deployment. The observed structural damage was analysed using scanning electron microscope (SEM) and energy dispersion X-ray (EDX) to ascertain the elemental composition. Results show huge discrepancies in the chemical composition constitute alone different regions. The presence of high concentration of carbon and oxygen was found in the affected region.
(Invited) Development of β-Ga2O3 Materials
Authors: Speck James
Published: February 2020

β-Ga2O3 has attracted significant recent attention for its large bandgap of 4.8 eV which leads to a high breakdown electric field, predicted to be 8 MV/cm.  With a predicted maximum bulk electron mobility of 300 cm2/Vs, β-Ga2O3 yields a Baliga figure of merit (BFOM) that is higher than that of 4H-SiC and GaN.  β-Ga2O3 has a monoclinic crystal structure (usually represented with the b-axis as the unique axis) with strong anisotropy in physical properties.  The crystal cleaves easily on the (100) and (201) planes.  MBE growth on cleavage planes yields low growth rates due to a strong propensity for Ga loss via suboxides [M.-Y. Tsai et al., J. Vac Sci. Tech. A 28, 354 (2010).].  Growth on non-cleavage planes, such as (010), however, yields high growth rates [K. Sasaki et al., J. Cryst. Growth 378, 591 (2013).].  In this presentation, we review our work on development of growth of β-Ga2O3 (010) by plasma-assisted MBE.  We present the development of high temperature homoepitaxial growth of β-Ga2O3 (010) and preliminary Sn doping [H. Okumura et al., Appl. Phys. Express 7, 095501 (2014)]; the development of coherent β-(AlxGa1-x)2O3/Ga2O3 heterostructures [Kaun et al., J. Vac. Sci. Tech. 33, 041508 (2015)]; and viable RIE and ICP etch processes [J. Hogan et al., in preparation].
The SnO2 nanowires Synthesis and Characterization
Authors: Lu Fang-Chun , Wang Chiu-yen
Published: February 2020

Tin dioxide (SnO2) nanowires grow by the thermal vapor deposition method. Vapor-liquid-solid method grows nanowires to product uniform nanowire’s diameter, because this method can control nanowire’s diameter. There are many parameters to affect the nanowire’s growth. These parameters are temperature (source area), flow rate, pressure, source mass, grow time, distance between the source and growth area and the thickness of gold films. The purpose of this study is to find the relationship between the nanowire’s growth and these parameters. Also, by using these parameters to grow the nanowires with specific size of diameter and length.

We find the suitable condition to grow the nanowires and the relationship between growth condition and effect of parameters. This condition grows nanowires is controllable and can be reproduced. In SEM images, it shows the straight nanowires with uniform diameter is 60~120 nm. Here, we discuss the effect of the temperature (source area), flow rate, pressure, source mass…etc. The temperature influences the precursor’s vapor pressure: when the temperature is high, the vapor pressure will be increased and will be caused nanowire to be dense. Similarly, precursor’s mass also affects the density of NWs. Because more precursor will supply more vapor at the moment, it let the density to increase. The growth time is the parameter to control the nanowire’s length when it supplies enough precursor. Pressure, gas flow rate and distance which determine the nanowires grow or not. Nanowires will grow only at the suitable environment. The thick of gold film which controls the nanowire’s diameter, because we grow the nanowires by VLS mechanism. In this study, we can get the specific SnO2 nanowires by tuning growth parameters, such as length, diameter, density ...etc. So it’s possible to support the suitable SnO2 nanowires to make the semiconductor devices.
Investigation of SiC Polytypes for PVT Process Control Using Ultraviolet Fluorescence Technique
Authors: Jeong Seong Min , Yoon Ji-Young , Choi Hyoung-Seuk , Byeon Dae-Seop , Jung Eunjin , Kwon Yong Jin , Kim Jungyu , Kim Younghee , Seo Won Seon , Lee Myung Hyun
Published: February 2020

Silicon carbide (SiC) is a wide-bandgap semiconductor with high saturation velocity and thermal conductivity. So, It is well-known as a potential substrate for high-power, high-temperature and high-frequency devices. Commercial 4H- and 6H-SiC wafers are commonly grown by physical vapor transport (PVT) method and some emerging techniques such as high temperature chemical vapor deposition (HTCVD) and top seeded solution growth (TSSG) is still under developing.

Because SiC has large number of polytypes determined by their stacking order during crystal growth, the polytype inclusion has been a common issue during SiC growth, especially at the early stage of development of new process or new equipments. When photon is incident on the surface of SiC crystal and the energy of photon is larger than the band gap of SiC (2.9 ~ 3.3eV in the UV range), the photon excites the electron in the valence band to the conduction band. Excited electron goes to the lower states emitting heat and relaxes to the valence band emitting photon that has longer wavelength that the incident light. The phenomena that wavelength is shifted to the longer wavelength by material is called fluorescence. Thus, polytypes with different energy band gap can be identified with the fluorescence color if UV ray is incident ray with sufficient energy for excite electron in the valence band.

In this study, we observed the fluorescent color of various SiC polytypes with a lab-developed UV fluorescence equipment. The UV fluorescence is non-destructive technique to characterize the grown sample without any further sample preparations, so that this technique is applied to develop a new PVT process in the early stages. SIMS, Photoluminescence and Raman spectroscopy were used for identify the fluorescence color considering polytypes, dopants and defects. Stress mapping using high resolution X-ray diffraction and Raman spectroscopy were used for analyzing the effect of polytype formation on residual stress distribution on the grown crystal. Glazing-incidence X-ray topography using white beam were conducted for evaluating the grown SiC crystals at Pohang accelerator laboratory.
(Invited) Why Are Nanowire BioFETs More Sensitive than Their Large-Scale Counterparts?
Authors: Shoorideh Kaveh , Chui Chi On
Published: February 2020

FET-based biosensors (bioFETs) are transistors that can detect and quantify charged molecules, such as DNA, RNA, or proteins, in an aqueous environment. The detection is via the electric charge that such molecules intrinsically carry in aqueous environments, so extra labeling molecules and techniques are not required. As such, these devices hold promise for a rapid, portable, and cheap method for measuring biomolecule concentrations in liquid human samples at very low concentrations.

BioFETs have been around for a long time, but they really captured the attention of the scientific community in 2001, when a nanowire-shaped bioFET demonstrated protein detection at concentrations much lower than what had been demonstrated before. The invention was hailed as a breakthrough, and the extreme sensitivity of the nanowire bioFET compared to its non-nanoscale ancestors was attributed to the high surface-area-to volume ratio of the nanowire structure.

The surface-area-to-volume ratio argument has been put into very simple mathematical terms using basic electrostatic arguments. These arguments show that nanowire bioFETs become ever more sensitive as the size of the nanowire shrinks. This result has been widely accepted by the scientific community. Almost every new paper published on the topic cites the surface-area-to-volume ratio argument in its introduction as the justification for using a bioFET with a nanowire structure.

These mathematical equations fail to take into account the effect of Debye screening, which is detrimental to sensor performance because it screens the electric field emanating from the charged biomolecules. Using basic electrostatic arguments, and including the effect of Debye screening, we prove that when a nanowire is surrounded from all sides by the aqueous medium, its sensitivity actually decreases as its diameter shrinks, even while its surface-area-to-volume ratio increases. This result effectively disproves the justification given for the enhanced sensitivity of the nanowires.

We go a bit further, and use simulations to study nanowires that are placed on insulating substrates, as is more commonly encountered in experimental works. We show that within the concave corners created between the sides of the nanowire and the surface on which it sits, Debye screening is significantly weakened, so much so that the majority of the response of the nanowire bioFET is due to the detection of electric charges in these corners. In our simulations, the sensitivity of nanowires decreases with decreasing size when the nanowire is suspended in, and surrounded by, the aqueous medium, in agreement with analytical calculations. However, the trend is reversed for nanowires placed on insulating substrates, in qualitative agreement with experimental results reported in the literature.

These results disprove the surface-area-to-volume ratio argument as the cause of the enhanced sensitivity seen in nanowire bioFETs, and suggest that the concave corners are responsible instead.
(Invited) Oxide Neuron Transistor for High-Performance Biochemical Sensors
Authors: Wan Qing , Liu Ning , Shi Yi
Published: February 2020

Synergic integration of presynaptic inputs from the dendrites plays an important role for sensory information process and cognitive computation, and the idea of building bio-inspired solid-state devices has been around for decades. In 1992, Shibata et al proposed the Si-based neuron transistors with multiple input gates that are capacitively coupled to a floating gate . The “on” or “off” state of the neuron transistors depends on the integrated effect of the multiple input gates. One of the unique features of the neuron transistors is the ultralow power dissipation during the calculation due to the gate-level sum operation in a voltage mode. From then on, Si-based neuron transistors have attracted much attention for chemical and biological detection due to the easy adjustment of threshold voltage. But, up to now,  electrolyte-gated neuron transistors with amorphous oxide channel layers for biochemical sensing applications are not reported. For portable applications, low-voltage operation is preferred. Electrolyte gated electric-double-layer (EDL) transistors can act as potential candidates with a low operation voltage due to the strong EDL modulation at the electrolyte/channel interface. Recently, oxide-based EDL transistors gated by solid-state inorganic electrolytes were proposed by our group. At the same time, artificial synapses and neuron transistors with low power consumption and fundamental biological functions were mimicked in individual device. The sensitivity of a standard ion-sensitive field-effect transistor is limited to be 59.2 mV/pH (Nernst limit) at room temperature. Here, inspired by the dendritic integration and spiking operation of a biological neuron, oxide-based neuron transistors with multiple input gates are fabricated on flexible plastic substrates for pH sensor applications. When the neuron transistor sensor is operated in a quasi-static dual-gate synergic sensing mode, it shows a high pH sensitivity of ~105 mV/pH, which is higher than the Nernst limit. Our results also demonstrate that single-spike dynamic mode can remarkably improve pH sensitivity and reduce response/recover time and power consumption. At last, we find that appropriate depression applied on the sensing gate electrode can further enhance the pH sensitivity and reduce the power consumption. Our flexible neuron transistors provide a new-concept sensory platform for biochemical detection with high sensitivity, rapid response and ultralow power consumption.
(Invited) A Soft Approach to Electronics: From Stretchable Systems to 3D Structures
Authors: Xu Sheng
Published: February 2020

Wearable device that matches the soft human body represents an important trend for bio-integration; the resulting search for pliable electronic materials calls for strategies to bridge the gap between hard and soft – among which advanced engineering of the geometry and architecture of materials presents unique opportunities. A prominent example of materials engineering is that the compressive straining of an elastic substrate can be used to fabricate previously inaccessible classes of 3D structures in monocrystalline materials. Conversely, rationally designed 2D geometries can buckle to form 3D layouts to accommodate tensile strain, resulting in unprecedented stretchability. This enables a series of device possibilities in stretchable electronics, including lithium ion batteries with record stretchability and integrated soft health monitoring systems.
Grating-Structured Freestanding Triboelectric-Layer Nanogenerator for Harvesting Biomechanical Energy
Authors: Xie Yannan
Published: February 2020

Recently, triboelectric nanogenerator (TENG) has emerged as an important energy harvesting technology and attracted extensive attention. In this work, we report a newly-designed TENG that is composed of a grating-segmented freestanding triboelectric layer and two groups of interdigitated electrodes with the same periodicity. The sliding motion of the grating units across the electrode fingers can be converted into multiple alternating currents through the external load due to the contact electrification and electrostatic induction. With more grating segments being introduced to the structure, the amount of accumulated charges, current density, and output frequency were enhanced substantially, which was demonstrated by both of the theoretical and experimental investigations. Working in non-contact mode, the device showed excellent stability and the total conversion efficiency reached as high as 85% at low operation frequency. On basis of these unique characteristics, the TENG was applied to harvest a variety of biomechanical energy, such as sliding of a human hand and human walking, demonstrating the practicability of using TENG to harness a wide range of ambient motion with high efficiency.
Interpenetrated Graphene/WSe2 Lateral Heterostructures for Barrierless Ohmic-Contacted p-FETs
Authors: Tang Hao-Ling , Chiu Ming-Hui , Tseng Chien-Chih , Lien Chen-Hsin , Li Lain-Jong
Published: February 2020

High contact resistance between TMDs and metals has been identified as an outstanding issue. TMDs tend to form a substantial Schottky barrier (SB) with commonly used metals. Air-stable graphene electrodes stacked on the WSe2 by transfer technique have been reported. However, unipolar conduction has not been achieved in FETs based on TMD materials and graphene electrodes. Here we report a synthetic process to directly grow WSe2 monolayers along the edge of patterned few-layered graphene, forming the lateral heterojunction between the graphene and monolayer WSe2. The few-layered WSe2 bridges the few-layer graphene and monolayer WSe2, and an interpenetrating layered structure is formed between graphene and WSe2. As a result, the WSe2 monolayer channel and the junction to the graphene can be formed at the same time by the synthesis method, where graphene serves as source and drain. Graphene is in-situ heavily p-doped by H2 with covent bond during WSe2 growing process. Such a unique junction structure leads to a barrier less ohmic contact between doped graphene and WSe2. Unipolar WSe2 PFET with laterally contacted p-doped graphene source/drain (p-G/WSe2 PFET) can be achieved for the first time. With Pd contacted source/drain metal, the unipolar PFET perform Ion/Ioff > 105 and field effect mobility ~20 cm2/Vˑs. Moreover we can still have unipolar PFET with Ti source/drain metal exceeds 103 Ion/Ioff ratio even Ti work function is low (4.3 eV)  and close to the conduction band edge of WSe2 (electron affinity of WSe2~ 4.03 eV).
A Controllable Method for Electrochemical Deposition Formed Crystalline MoS2 As a Counter Electrode for Dye-Sensitized Solar Cells
Authors: Cheng Chao-Kuang , Lin Che-Hsien , Yeh Tsung-Kuang , Tsai Chuen-Horng , Hsieh Chien-Kuo
Published: February 2020

In this study, the two-dimensional nanomaterials of molybdenum disulfide (MoS2) were synthesized onto the fluorine-doped tin oxide (FTO) glass substrate via the electrochemical deposition (ECD) method. By controlling the potential during the ECD processes, the MoS2 thin films were deposited homogenously onto a large area of FTO glass. It was observed that the edge planes of MoS2 provided plenty active sites for an efficient counter electrode (CE) of the dye-sensitized solar cells (DSSCs). The electrochemical properties of the controllable the MoS2 thin films were characterized and compared with the Platinum (Pt) films prepared by the e-gun technology. The electrochemical activity of the MoS2 CE was performed by cyclic voltammetry (CV), electrochemical impedance spectroscope (EIS) and also assembled as the Pt-free DSSCs. In combination with a dye-sensitized TiO2 working electrode and an iodine-based electrolyte, the DSSC with the MoS2 CE showed a photovoltaic conversion efficiency of 6.089 % under the illumination of AM 1.5 (100 mWcm-2). The results demonstrated that the ECD method displayed a facile and economical process to synthesize the low-cost MoS2 CE for the cost-effective DSSCs.
Pseudocapacitive Electrodes Produced By Oxidant-Free Polymerization of Pyrrole Between the Layers of 2D Titanium Carbide (MXene)
Authors: Boota Muhammad , Anasori Babak , Voigt Cooper , Zhao Meng-Qiang , Barsoum Michel W. , Gogotsi Yury
Published: February 2020

Pseudocapacitive electrodes based on electrochemically active organic materials are emerging for the energy storage applications.1 Organic materials are renewable, relatively inexpensive, lightweight, and their electrochemical properties can be tuned by changing their functional groups. Despite aforementioned advantages, they tend to degrade rapidly upon cycling mainly due to their poor conductivity. One option to improve their cycling performance is to graft/deposit them onto conductive carbon particles.2 Two-dimensional carbides and carbonitirides called MXenes, which generally offer metallic conductivity, may become a suitable option to replace carbon in pseudocapacitve electrodes to improve the electrochemical performance of the organic materials.3,4 

Herein, we present simultaneous intercalation, alignment and oxidant-free polymerization of the pyrrole between the Ti3C2Tx MXene layers by mixing pyrrole monomer with the Ti3C2Tx colloidal solution. The optimized composition of the resulting composite yielded high volumetric and gravimetric capacitances of 1000 F/cm3and 416 F/g, respectively, at 5 mV/s. Furthermore, excellent capacitance retention of 92% was observed after 25,000 cycles at 100 mV/s. 

1. M. Boota et al., Adv. Mater. (2015). DOI: 10.1002/adma.201504705

2. M. Boota et al., ChemSusChem, 8, 3576–3581 (2015)

3. M. R. Lukatskaya et al., Science., 341, 1502–1505 (2013)

4. M. Ghidiu, M. R. Lukatskaya, M.-Q. Zhao, Y. Gogotsi, and M. W. Barsoum, Nature, 516, 78–81 (2014)
(Invited) Designing Two-Dimensional Hybrid Materials for Electrochemical Energy Storage
Authors: Yu Guihua , Peng Lele , Zhu Yue
Published: February 2020

Two-dimensional materials represent a promising material platform for next-generation energy storage and conversion devices. Owing to their advantageous features of large surface area, widely open ion transport pathway within 2D layers, and mechanical flexibility, graphene and other transition-metal oxides and phosphates based nanosheet materials show great promise in next-generation high-density energy storage devices. Here we will present examples on inorganic 2D materials and their hybrids for advanced energy storage devices including alkali-ion batteries and supercapacitors. The first set of examples is inorganic VOPO4 ultrathin nanosheets for ultraflexible solid-state supercapacitors, as well as for both Li-ion and Na-ion storage. And we will also discuss a novel synthetic strategy towards controlled synthesis of porous inorganic nanosheet materials as a promising class of alkali-ion battery electrodes with high capacity and rate capability.
(Invited) Interesting 1-D and 2-D Phases of MoS2
Authors: Loh Kian Ping
Published: February 2020

Tailoring the dimension of nanomaterials to achieve precise tuning of optical, electronic and catalytic properties have been the major goals of researchers for decades.  Two dimensional metal chalcogenides of the MX2 (M=Mo, W and Ti, X= Se, Te) family represent the ultimate control of material dimension in the vertical direction, and exhbits unique quantum confined optoelectronic properties.  At the 1-D level, MoS2 quantum wires display quasi one-dimensional metallic state and novel ferromagnetic behavior that is tunable by its width and edge configurations. Unlike graphene nanoribbons which have been successfully synthesized using bottom–up molecular techniques, there are scant reports on the growth of MoS2 nanoribbons. Herein, we report two novel phases of sub-stochiometric MoS2 (MoSx) grown on Au (111) and Cu (111), respectively. We performed the templated growth of well-aligned, sub-stoichiometric MoSx molecular wire on Au(111) vicinal surface.  Interestingly, we observed the dynamic assembly of MoSx molecular wires and its phase transition into stoichiometric MoS2 nanoribbon. On Cu (111) surfaces, we studied the growth of a novel MoSx 2-D phase which shows catalytic activities for the oligomerization of small molecules on its basal planes. Due to the in-plane rotational freedom and greater diversity of bonding arrangements in MoS2, a plethoras of different polytypes may be possible when the structural assembly is mediated by metal substrate. Thus a whole new class of alternative 2D structures, uniquely different to the classical chalcogenides in terms of electronic and physical properties, may be possible.
(Invited) Defect Engineering in 2-Dimensional Materials: From Theory to Applications
Authors: Terrones Maurcio
Published: February 2020

This talk will first provide an overview of different defects in 2-Dimensional materials such as graphene and Chalcogenides. In particular, we will focus on: 1) defining the dimensionalities and atomic structures of defects; 2) pathways to generating structural defects during and after synthesis and, 3) the effects of having defects on the physico-chemical properties and applications. We will then discuss the synthesis of large-area, high-quality monolayers of nitrogen-, boron- and silicon-doped graphene sheets on Cu foils using ambient-pressure chemical vapor deposition (AP-CVD). Scanning tunneling microscopy (STM) and spectroscopy (STS) demonstrate that defects in doped graphenes arrange in different geometrical configurations exhibiting different electronic and chemical properties. Interestingly, these doped layers could be used as efficient molecular sensors and electronic devices. Finally, we will discuss the controlled synthesis and assembly of chalcogenide monolayers on different substrates. The electronic performance of monolayers of MoS2, WS2 and hetero-systems operating under flexural strain will also be presented. Our findings demonstrates that it is now possible to use chalcogenide layers for the fabrication of flexible electronic devices, however, defect control is required to tailor their performance.
Photocatalytic Hydrogen Production Via Water Splitting Using Different Gold-Based Catalysts
Authors: Arango Juan C. , Machín Abniel , Márquez Francisco
Published: February 2020

In order to avoid serious environmental and economic damages from energy use, humans must stop using fossil fuels altogether, as soon as possible. One possible strategy to cut the dependence of fossil fuels and, at the same time create a new economic force, is to develop a hydrogen based energy economy. A potentially viable way forward is to produce H2 from water by combining solar energy and heterogeneous photocatalysts. For these reasons the objectives of this investigation were: 1) synthesize a high surface area TiO2 nanowires (NWs) catalyst in the rutile phase, 2) incorporate different amount of gold nanoparticles into the as-synthesized catalyst and into the commercial form of TiO2 (Degussa P-25) using a chemical reduction method, 3) produce hydrogen via water splitting using visible and ultraviolet light. The hypotheses of the study were: a) The catalyst with the biggest surface are will produce the biggest amount of hydrogen, and b) The gold nanoparticles will enhance the hydrogen production and will allow the use of visible light, diminishing the semiconductor’s band gap and working as an electron trap. Interestingly, the incorporation of gold nanoparticles into the titania surface enhanced the surface area in both P25 and TiO2 NWs. The hydrogen production obtained by using Au/P25 catalysts was measured to be 800 μmolg-1h-1 under irradiation at 400 nm and 1,436 μmolg-1h-1 using Au/TiO2 NWs at the same wavelength. Both of the hypotheses were correct and all the objectives achieved. The characterization of the synthetized compounds were performed with: 1) X-ray diffraction (XRD) to confirm the crystalline form of the TiO2 synthetized nanowires. 2) Field emission Scanning Electron Microscopy (FESEM), to confirm the morphology of the synthetized compound. 3) Brunauer, Emmett and Teller (BET) instrument to measure the surface area of the gold based nanowires and the commercial TiO2 form P-25. 4) The hydrogen production was measured using a Gas Chromatographer with a Thermal Conductive detector (GC-TCD) attached to a solar simulator. 5) Ultra Violet Visible spectroscopy (UV-VIS) was used to obtain the absorption spectrums of the synthetized TiO2 rutile phase nanowires before and after the gold deposition.  Finding renewable sources of energy is one of the biggest challenges of the 21st century and this investigation contributes into that.
(Invited) Heterogonous Mixed Ion and Electron Conducting Membranes for Efficient Electrochemical CO2 Capture and Conversion
Authors: Huang Kevin
Published: February 2020

Cost competitive and easily accessible fossil fuels are the dominant energy source powering our society. However, burning fossil fuels emits significant amount of CO2, a greenhouse gas that can cause global warming and climate change. Therefore, mitigating CO2 emissions from the use of fossil fuels is imperative. Among all the options, carbon capture and storage (CCS) is considered the best near-term solution.

The CO2 capture technologies currently being developed are targeting three point sources related combustion and gasification processes: post-combustion, oxyfuel combustion and pre-combustion. The state-of-the-art CO2 capture methods are primarily based on reversible chemical/physical absorptions/ adsorptions principles. A grand challenge to these technologies is the high cost and energy penalty. Developing advanced cost-effective and energy-efficient carbon capture technologies is therefore highly desirable.

In this presentation, we show by extensive experimental data and theoretical analysis that two classes of mixed ion and electron conductors are promising candidate membranes for high-flux, high-selectivity, cost-effective and energy-efficient carbon capture based on the electrochemical principles. By combining these membranes with proper conversion mechanisms, the captured CO2 can be instantly converted back to a fuel form, making the overall process carbon neutral.
Transition Metal Phosphides As CO2 Reduction Catalysts
Authors: Calvinho Karin U. D. , Laursen Anders B. , Goetjen Timothy A. , Garlapati Avinash B. , Dismukes Gerard Charles
Published: February 2020

The development of efficient catalysts for converting water and CO2 selectively to hydrocarbons using renewable (electrical) energy is considered the “holy grail” of a sustainable energy economy. Electrochemical CO2 reduction has been demonstrated to form CO, HCOOH, C1 and C2 alcohols on noble metals,1,2 and alkanes on copper.3 These technologies are still pre-commercial and limited by three main problems: 1) atom efficiency: significant H2 production at the expense of the desired product; 2) selectivity: low for a single hydrocarbon product, and 3) electrical efficiency: high overpotential for the reaction. Among the proposed mechanisms on copper, two steps have been postulated as rate-limiting: 1) reductive binding to form adsorbed CO2
-* and, 2)  hydrogen addition to adsorbed CO* forming HCO*4.

To overcome these barriers, we used three strategies which involve use of catalyst surfaces comprised of binary solids (MxPy) in which: 1) phosphorous is chosen for its high P-O bond energy needed to stabilize side-on binding of the HCO* and CO2
-* intermediates via O atom; 2) the M-C bond energy is controlled (choice of M); and 3) an adjustable M-P interatomic spacing that allows C to adopt its favored trigonal binding geometry (ideal sp2 C hybridized orbitals).  We have synthesized four distinct binary transition metal phosphides, having pure and stable crystalline phases and evaluated their performance as catalysts for CO2 reduction using low surface area (flat) electrodes. This allows for direct observation of catalytic activity on the most stable crystal termination and is directly comparable to Cu-foils reported in the literature. Herein we present results that show CO2 reduction to CH4 at -0.6 V, the lowest potential seen thus far to our knowledge. Furthermore, using metal phosphides there is no formation of carbon monoxide, a poisonous gas that is produced in large quantities when copper is employed as catalyst.

Supported by Rutgers University and the Science Without Borders CAPES fellowship.

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(2)       Barton, E. E.; Rampulla, D. M.; Bocarsly, A. B. J. Am. Chem. Soc.
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Electrochemical Microfluidic Immunoarray for Assessment of Aggressive Vs Indolent Forms of Prostate Cancer
Authors: Otieno Brunah A , Mercer Conan P , Jones Abby L , Krause Colleen E , Sherafeldin Mohammed , Joshi Amit A , Leech Dónal , Rusling James F
Published: February 2020

Prostate cancer is the most common cause of cancer-related death in men in the US and throughout the world.  Current practices for detection and staging of prostate cancer often fall short in terms of sensitivity, specificity and inability to distinguish between aggressive and indolent forms of prostate cancer.  These limitations lead to unnecessary treatments that adversely affect the patients’ quality of life with minimal or no gain.  Measurement of small panels of molecular signature biomarkers in serum holds tremendous potential for cancer diagnostics and personalized therapy. Here we describe a simple, low-cost, modular microfluidic system for on-line capture and detection of prostate cancer protein biomarkers. The protein panel includes PSA, CD-14, ERG, GOLM-1, PEDF-1, IGF-1, VEGF-D and IGFBP-3, many of which are thought to be specific for aggressive prostate cancer. The system features a small chamber for on-line protein capture from serum by magnetic beads labeled with many copies of analyte-specific antibodies and signal-transducing enzyme labels, positioned upstream of a detection chamber housing a nanostructured 8-electrode sensor array. Gold immunoarrays fabricated by ink-jet printing ($0.2) or commercial screen printed carbon arrays ($5) are fitted into the microfluidic detection chamber to achieve high sensitivity. Ultralow detection limit in the low fM range was achieved for multiplexed detection of the cancer biomarker proteins from as little as 5 uL. Measurements of this panel of selected biomarkers will be tested with prostate cancer patient samples in future to assess its diagnostic capability.

Figure 1