bluuebunny/crossref_metadata_2025 huggingface dataset:
Hierarchically Designed 3D-Nanostructures Using Surface Engineered Graphene Shells
Authors: Sarigamala Karthik Kiran , Shukla Shobha , Struck Alexander , Saxena Sumit
Published: February 2020

The rational design and fabrication of nanostructured materials with desired electrochemical performance is highly demanded for energy storage applications. Functionalization of graphene based materials using chemical moieties not only alter the electronic structure of the underlying graphene but also enable in only limited enhancement of targeted properties. Surface modification of graphene based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone. In this pursuit we have fabricated bio-inspired hierarchical nanostructures based on Ni-Co layered double hydroxide on the reduced graphene oxide core shells using template based wet chemical approach. The as-obtained materials with tuned morphology have been characterized structurally and electrochemically. The results show that the charge storage capability of the synthesized material is 3 fold higher than that of pristine materials. These characterizations confirm that the obtained material has large effective surface and has promising applications in catalysis and energy storage. This surface modification strategy is not limited to only transition metal based hydroxides but also may pave a way for the fabrication of many other nanostructured materials.
Carbon Nanotube As Conductive Additive for Lithium Ion Batteries
Authors: Kirner Joel , Zhang Linghong , Qin Yan , Jansen Andrew N. , Lu Wenquan
Published: February 2020

Silicon has been extensively studied as an anode material in lithium-ion batteries due to its extremely high theoretical specific capacity of 3578 mAh/g (Li15Si4). However, the huge volume fluctuations associated with this high cycling capacity create great challenges with regard to electrode mechanical integrity and continual electrolyte decomposition. Common strategies to alleviate this volume expansion are to study silicon alloys, silicon oxide, and to blend silicon materials with graphite active materials.

Herein we study graphite-SiO blends in an attempt to achieve stable cycling performance. We study a wide variety of laminate formulations by varying the graphite/SiO ratio, the binder type, the conductive additive type, and the weight percent of each of these components. We find that the use of single-walled carbon nanotubes (SWCNT) as conductive additive is crucial to prevent rapid capacity fade during initial cycling. The use of SWCNT also enables the use of significantly less conductive additive and binder, likely providing both enhanced conductivity and mechanical stability to the electrode during volume fluctuation.

Acknowledgement:

We gratefully acknowledge the support from the U.S. Department of Energy’s Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory, a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357.
(Invited) Applications and Safety of 2D Materials
Authors: Prato Maurizio
Published: February 2020

The organic functionalization of 2D materials, including graphene and MoS2, offers several advantages:

1) Improved solubility and easier handling of otherwise intractable materials;

2) Additional functions can be implanted on the carbon skeleton, such as chromophores, electroactive units, drugs, etc.;

3) Potential toxicity of the carbon materials can be at least partially lifted by organic functionalization, thanks to improved solubility and debundling in physiological media.

During this talk, we will discuss the various approaches to organic functionalization and will also analyze other important challenges in graphene chemistry, such as the toxicological impact and the limitations in translating graphene into advanced materials.

This work was supported by the European Commission, Graphene Flagship project (no. 696656 and 785219).
Biofilms By E.coli & S.Epidermidis and Its Sensing Possibility By Graphene-Dispersed Silane Coating
Authors: Kanematsu Hideyuki , Nakagawa Ryoichi , Sano Katsuhiko , Barry Dana M. , Itoh Reo , Yamada Hirohisa , Hirai Nobumitsu , Miura Hidekazu , Ogawa Akiko , Kogo Takeshi , Kuroda Daisuke , Tsunashima Katsuhiko , Katakura Katsumi
Published: February 2020

We already found that graphene is very sensitive to biofilm formation by bacterial activities. The problem is how to constitute proper sensing systems to detect biofilms in various cases. In this study, we focussed on the silane compound coating in which nano graphene powder would be dispersed in its free volume. The concentration of graphene powders in silane compound coating was changed from 0.1 wt % to 30 wt% and the graphene dispersed silane compounds were coated on glass and pure copper substrates. And biofilms were formed on those specimens in the well plates filled with liquid cultures containing Staphylococcus epidermis (S.epidermidis) as gram-positive bacteria and Escherichia coli (E.coli) as gram-negative ones. And the formation process was checked by the specimens' potential change in liquid cultures, color changes by staining with Crystal violet and some electrical measurement (capacitance etc.). Finally, we compared all of them each other and discussed about the advantage and disadvantage among the methods for the application as sensing method.
(Invited) Targeted Near Infrared Sensing and Imaging with GFP-Nanobody Carbon Nanotube Hybrids
Authors: Kruss Sebastian
Published: February 2020

Fluorescent nanomaterials have many advantages in terms of their photophysics but it is difficult to target them to specific locations in living systems. In contrast, the green fluorescent protein (GFP) can be genetically targeted to proteins in cells or animals. Therefore, GFP can be seen not only as a fluorophore but as a universal target/handle. Moreover, many transgenic organisms or transfected cells are available.

We wanted to combine the advantage of GFP targeting and fluorescent nanomaterials. Therefore, we conjugated a GFP nanobody to near infrared (nIR) fluorescent single-walled carbon nanotubes (SWCNTs). SWCNTs fluoresce in the nIR tissue transparency window (900 nm -1700 nm) and do not bleach. The GFP nanobody serves as recognition unit for GFP and the SWCNT serves as superior nIR fluorophore. These hybrids were then used in biological experiments to demonstrate the versatility of this approach. First, we demonstrated that it is possible to label single GFP-tagged kinesin motors in living drosophila embryos and track their directional movement during embryogenesis. Second, we labeled the cytoskeleton in mammalian cells in the nIR. Finally, we targeted cell surface receptors and used the SWCNTs fluorescence for sensing. We have previously shown that specifically functionalized SWCNTs change their fluorescence in the presence of the neurotransmitter dopamine. Here, we used this property to target SWCNTs to GFP modified cell surface receptors and detect dopamine.

In summary, we show that GFP nanobody conjugated SWCNTs show great potential for targeted nIR imaging, sensing and labeling.
Progress Towards Single-Walled Carbon Nanotube Applications in Biomedicine and the Exoneration of Toxicity
Authors: Heller Daniel A. , Galassi Thomas Vito , Jena Prakrit Vaibhav , Ao Geyou , Roxbury Daniel , Zheng Ming , Williams Ryan M.
Published: February 2020

Single-walled carbon nanotubes exhibit unique photophysical properties that enable the detection of biomarkers, metabolites, and drugs in living cells, tissues, and organisms. The intrinsic near-infrared photoluminescence of nanotubes exhibits unique photostability and sensitivity to the local environment to transduce molecular binding events via changes in the nanotube optical bandgap. We developed carbon nanotube-based optical sensors to detect metabolites and cancer biomarkers in vivo, in order to improve early cancer detection and accelerate drug discovery for cancer and allied diseases. We introduced carbon nanotubes into disease models via implantation within devices, as well as by intravenous injection. In all cases, we found that properly-functionalized single-walled carbon nanotubes exhibit no deleterious effects in live cells or in vivo at concentrations needed for measurement. Via injecting a single-chirality carbon nanotube species responsive to lipids, we found that lipid accumulation in liver Kupffer cell lysosomes tracks the progression of non-alcoholic fatty-liver disease (NAFLD) in a live murine model. Notably, we found that that lipid accumulation is persistent in the Western Diet model of NAFLD after resuming normal feeding, suggesting long-term effects of a poor diet. This finding demonstrates that single-walled carbon nanotubes enable the development of new tools to allow biologists to measure disease states in situ.
(Invited) Purification Using Atpe to Single (n,m) Species in the Large Diameter Single-Wall Carbon Nanotube Limit
Authors: Li Han , Zheng Ming , Flavel Benjamin S. , Fagan Jeffrey A.
Published: February 2020

Separation of single-wall carbon nanotube (SWCNT) populations to completely specified physical structures is a primary milestone necessary for enabling SWCNT-based technologies. Aqueous two-phase extraction (ATPE), in which the spontaneous phase separation of an aqueous polymer mixture is utilized to spatially separate solutes on the basis of their chemical potential difference for the two phases, is a promising technology for achieving this milestone. However, due to the expanded number of (n,m) species with increasing nanotube diameter, and the increased difficulty in optical characterization of aqueous-dispersed samples, isolation of larger diameter SWCNTs, > ~1.4 nm in diameter, has continued to be a difficult proposition. Advances in methodology of separation and sample preparation are now overcoming both these barriers in our laboratories. In this work I will detail improved separation procedures utilizing alkane-filled SWCNT populations for the isolation of individual SWCNT (n,m) structures from > 1.5 nm average diameter SWCNT dispersions. These method developments can readily isolate multiple large diameter (n,m) species, and are enabling new scientific and device application work. The enhanced separation methods, isolated (n,m) species, and applications of those populations will be presented.
(Invited) Photoexcited Electron Transfer from Semiconducting Carbon Nanotubes to Non-Fullerene Acceptors
Authors: Arnold Michael S
Published: February 2020

We have previously demonstrated efficient electron transfer from photoexcited small diameter (< 1 nm) semiconducting carbon nanotubes to C60 fullerene electron acceptors in planar, bilayer heterojunction diode devices, with internal quantum efficiency of 90%. However, the out-of-plane exciton diffusion length in planar nanotube thin films is poor (~ 5 nm), limiting the optical density of nanotube films that can be implemented in these devices, which in turn has limited external quantum efficiency to 50% at the nanotube bandgap and to << 50% off-resonance. Polymer solar cells also face a similar limitation (poor exciton diffusion length) and overcome this problem by blending the polymer and acceptor together into a bulk heterojunction. These bulk heterojunctions are typically formed by co-casting the polymer with a solubilized fullerene derivative, phenyl-C61 (or 71) -butyric acid methyl ester (PBCM) to create the blend. However, this strategy has not yet worked well to create nanotube-based bulk heterojunction devices that are more efficient that bilayered devices. One problem is that the electron affinity of PCBM is shallower than the electron affinity of C60, which detrimentally impacts the nanotube to acceptor charge transfer efficiency. To address this shortcoming, new electron acceptors are needed. We have surveyed several new non-fullerene electron acceptors, including both small molecule and polymers, as potential C60 and PCBM replacements. In this talk, the results of this survey will be presented. Moreover, the use of the most promising new non-fullerene acceptors in bulk heterojunctions with semiconducting nanotubes will be discussed.
(Invited) Photophysics of Cabon Nanostructures
Authors: Zhao Shen , Lavie Julien , Rondin Loïc , Orcin-Chaix Lucile , Rebeyre Grégoire , Diederichs Carole , Chassagneux Yannick , Voisin Christophe , Narita Akimitsu , Campidelli Stephane , Lauret Jean-Sébastien
Published: February 2020

In the last decades, research on graphene has been extensively developed. It is now well established that graphene shows unique physical properties such as extremely high charge-carrier mobility, which promises a wealth of applications in (nano)electronics. However, graphene does not have a bandgap. Therefore, one challenge for scientists is the control and modification of the electronic porperties in order to open a sizable bandgap. In this context nanosized graphene have a lot of assets. The reduction of one dimension of graphene leads to carbon nanotubes (CNT) or graphene nanoribbons (GNRs) while the reduction of the two dimensions leads to graphene quantum dots (GQDs). The size reduction, the topology and the shape of the edges define the electronic and optical properties of this family of objects.

In this presentation, I will show our last results on the photophysics of such nanostructures investigated at the single object level.
Charge Transport in Mixed Semiconducting SWCNT Networks with Tailored Diameter Distributions
Authors: Brohmann Maximilian , Berger Felix Julian , Zaumseil Jana
Published: February 2020

The recent availability of purely semiconducting single-walled carbon nanotubes (SWCNTs) and the ability to prepare dense and uniform SWCNT networks from dispersion has led to promising applications in optoelectronics, e.g. in field-effect transistors (FETs), light-emitting diodes, notch filters and solar cells. Further optimization and controlled tuning of nanotube networks is desirable to establish them as competitive semiconducting materials. The impact of the SWCNT network composition on the overall charge transport was demonstrated recently [1]. The uneven energy landscape of networks with a broad tube diameter and thus bandgap distribution results in inferior transport properties. Contrary to common belief, the charge transport in networks is not solely determined by tube-tube junctions but intra-nanotube transport also has a significant impact on the overall network mobility. Here, we examine this hypothesis in a detailed charge transport study of FETs with SWCNT networks consisting of polymer-sorted small diameter (6,5) SWCNTs (0.76 nm) and large diameter plasma torch SWCNTs (1.2-1.5 nm) with different but controlled mixing ratios. All FETs showed balanced ambipolar transport with low off-currents and negligible hysteresis. The extracted mobilities varied characteristically with network composition. The obtained experimental data are compared to results from numerically simulated networks with analogous SWCNT compositions. The employed random resistor network model was recently shown to adequately describe the carrier density-dependent mobility in SWCNT networks [2].

[1] M Brohmann et al., J. Phys Chem. C
122, 19886-19896 (2018)

[2] S. P. Schießl et al., Phys. Rev. Mater.
1, 046003 (2017)

Figure 1
(Invited) Organic Molecular Tuning of Many-Body Interaction Energies in Air-Suspended Carbon Nanotubes
Authors: Tanaka Shunsuke , Otsuka Keigo , Kimura Kensuke , Ishii Akihiro , Imada Hiroshi , Kim Yousoo , Kato Yuichiro K.
Published: February 2020

Environmental screening effects are large in carbon nanotubes due to their atomically thin nature, and therefore it is possible to control the optical properties with molecular adsorption [1,2]. Here we investigate adsorption effects of copper phthalocyanine molecules on excitons and trions in air-suspended carbon nanotubes [3]. Using photoluminescence excitation spectroscopy, we observe that exciton energy redshifts gradually with the molecular deposition thickness. The trion emission is also observed at large deposition amounts, which suggests charge transfer between the phthalocyanine molecules and carbon nanotubes. Analyzing the spectra for individual tubes, we find a correlation between the exciton-trion energy separation and the exciton emission energy, indicating that the many-body interaction energies scale similarly with the molecular dielectric screening.

Work supported in part by RIKEN (Incentive Research Projects), JSPS (KAKENHI JP16H05962, JP17H07359), and MEXT (Nanotechnology Platform). We acknowledge the Advanced Manufacturing Support Team at RIKEN for technical assistance.

[1] T. Uda, A. Ishii, and Y. K. Kato, ACS Photonics 5, 559 (2018).

[2] T. Uda, S. Tanaka, and Y. K. Kato, Appl. Phys. Lett. 113, 121105 (2018).

[3] S. Tanaka, K. Otsuka, K. Kimura, A. Ishii, H. Imada, Y. Kim, and Y. K. Kato, arXiv:1812.10245 (2018).
Fabrication of Sticky and Slippery Aluminum Alloys Based on Anodic Alumina Nanofibers
Authors: Kikuchi Tatsuya , Kondo Ryunosuke , Nakajima Daiki , Suzuki Ryosuke O. , Natsui Shungo
Published: February 2020

Anodizing aluminum in a pyrophosphoric acid solution (H4P2O7) causes the formation of numerous anodic alumina nanofibers. The nanofiber-covered aluminum surface exhibits superhydrophilicity measuring less than 10° in water contact angle (WCA). In contract, as the alumina surface is modified with a self-assembled monolayer (SAM), the WCA value changes to show superhydrophobicity measuring more than 150°. In the present investigation, the fabrication of highly sticky and slippery aluminum alloys was achieved by optimizing the nanostructure of anodic alumina nanofibers formed on the surface.

Commercially available 3004 aluminum alloys (composition: 1.0-1.5 wt% Mn, 0.8-1.3 wt% Mg, small amounts of Cu, Zn, Fe, and Si) were chemically polished in a 2.5 M NaOH solution at 333 K for 5 min, and then were immersed in a 4.0 M HNO3 solution at room temperature for 30 s. The polished specimens were immersed in a pyrophosphoric acid solution (74.0 wt%) at 293 K, and then were anodized at a constant voltage of 75 V for up to 60 min. After anodizing, the specimens were immersed in a 1.5 mM 3,3,4,4,5,5,6,6,7,7,8,8,8,-tridecafluorooctylphosphonic acid (FOPA)/ethanol solution at 313 K for 48 h. The slipping behavior of the water droplet formed on the anodized specimens was examined by advancing and receding contact angle measurements using an optical contact angle meter.

As the aluminum alloys were anodized in a pyrophosphoric acid solution, numerous anodic alumina nanofibers with the insoluble intermetallic compounds were formed on the surface. The length of the nanofibers increased with the anodizing time, and many nanofiber-tangled intermetallic particles were exposed to the surface. Figure 1 shows the changes in the advancing contact angle, θ
adv, and the receding contact angle, θ
rec, on the SAM-modified aluminum surface with anodizing time, t
a. The θ
adv value increased to approximately 170° by pyrophosphoric acid anodizing, and this superhydrophobicity was maintained upon further anodizing up to 60 min. On the other hand, the θ
rec value drastically changed with anodizing time. As a result, the contact angle hysteresis (θ
adv - θ
rec) was also changed with anodizing time. Therefore, the adhesion interaction between the water droplet and the aluminum surface can easily be controlled by pyrophosphoric acid anodizing.

Figure 1
Electrodeposited 3D Nanomesh Electrodes: Combined High Surface Area, High Porosity and Structural Integrity and Regularity
Authors: Vereecken Philippe M. , Zankowski Stanislaw Piotr
Published: February 2020

We present a nanomesh material that is widely applicable in a variety of sustainable-applications requiring high surface area electrodes such as batteries, electrocatalytic convertors, fuel cells and hydrogen production. The nanomesh material is a three-dimensional nanowire (metal) grid structure with highly regular internal dimensions. The hexagonally organized vertical nanowires are horizontally interconnected to its three neighboring nanowires. As a result, it combines high porosity with an unprecedented surface-to-volume ratio. For each micrometer thickness, there is a 26-fold increase of available surface area. To visualize this: when filling a volume of a small can of soda, it would remain 75% empty while containing a surface area equal to the size of a football field. On top of that, the internal and external dimensions can be tuned to almost any specification, making it potentially compatible with a multitude of application requirements.

The material can be quite easily manufactured through cheap anodization and electroplating processes. First, a mold is formed by anodization of aluminum foil as for the well-known Anodic Aluminum Oxide (AAO) process. The secret for the regular horizontal perforation at the nanoscale lays in the controlled doping of the aluminum metal with copper. The resulting 3D nanoporous structure acts as a mold in which a large variety of metal (compounds) can be electrodeposited. After consecutive chemical dissolution of the alumina template, a mechanically rigid nanomesh structure remains. The nanomesh can be detached from the substrate as a free-standing flexible nanomesh foil. We will show that a 3 micron thick nanomesh easily outperforms a 400 micron thick foam in surface area and electrochemical performance for hydrogen evolution reaction.
Selective Si3N4 Etching in Si3N4/SiO2 Pair-Layer Stack Using Non-H3PO4-Based Superheated Water
Authors: Son Changjin , Lim Sangwoo
Published: February 2020

It is necessary to selectively etch Si3N4 in Si3N4/SiO2 multi-stack structure for the fabrication of 3D NAND [1]. The etching reaction of Si3N4 in phosphoric acid is known as 3Si3N4 + 4H3PO4 + 27H2O → 4(NH4)3PO4 + 9H2SiO3 [2]. However, as the number of Si3N4 etching batch process increases, the Si3N4 etching performance of H3PO4 decreases. Therefore, a fresh H3PO4 solution should be used for each process. As a result, the consumption of H3PO4 and process cost increase. In addition, the etching by-products could be reattached to SiO2 layers, which causes problems in the subsequent processes. In this study, the etching of Si3N4 and SiO2 in superheated water was investigated. In addition, by adding proper additives to superheated water, the Si3N4 etching rate and Si3N4/SiO2 etch selectivity were controlled.

Blanket Si3N4 and SiO2 films on Si wafer were used. A patterned Si3N4/SiO2 pair-layered structure was also used. HCl, NH4OH, H2SiO3 and HF were used as additives. The thicknesses of the Si3N4 and SiO2 films were measured using spectroscopic ellipsometry and FE-SEM. The etching rates of Si3N4 and SiO2 were shown in Figure 1. The etch rate of Si3N4 and SiO2 in superheated water (pH 7) was 23 and 1.5 Å/min, respectively. When HCl was added, the etching rate of Si3N4 was decreased. On the other hand, when NH4OH was added, the etching rate of Si3N4 was increased. Therefore, it is believed that OH- generated from the self-ionization of water in the superheater water plays an important role in the etching of Si3N4. In addition, proper additives were added to superheated water to improve the etching performance. The result of patterned Si3N4/SiO2 structure using superheated water with additive was shown in Fig. 2(a). For comparison, the result of the 85 wt% H3PO4 process was shown in Fig. 2(b). In the superheated water with additive and the H3PO4 process, the lateral etched depths of the Si3N4 were similar. However, in the superheated water process, the thickness of the remaining SiO2 layers was maintained without thinning. Therefore, optimized superheated water without H3PO4 show a very promising selective etch performance at the 3D Si3N4/SiO2 pair-layer structure.

References

[1] S. Aritome, NAND flash memory technologies, p. 273, John Wiley & Sons, Hoboken, NJ (2015).

[2] K.B. Sundaram, R.E. Sah, H. Baumann, K. Balachandran, R.M. Todi, Microelectron. Eng., 70, 109 (2003).

Figure 1
(Invited) High-Speed and Linear Graded-Channel GaN FETs
Authors: Moon Jeong-Sun , Wong Joel , Grabar Bob , Antcliffe Mike , Chen Peter , Corrion Andrea , Arkun Erdem , Khalaf Isaac , Kim Sam , Fay Patrick
Published: February 2020

RF communications with spectral efficiency utilizes complex modulation schemes that

require amplifier linearity [1]. As amplifier operating frequency moves into the millimeter

wave (mm-wave) range, the power added efficiency becomes also important to save the

system prime power. As for 5G applications, high efficiency and linearity of amplifiers are

required to support complex waveforms with high peak-to-average ratio (PAPR) and large

instantaneous bandwidth.

We report the first demonstration of graded-channel GaN HEMTs operating in the

millimeter-wave frequency range. At 30 GHz, these graded-channel GaN HEMTs

demonstrated excellent PAE of 65% at associated power density of 3 W/mm. The measured

PAE and output power density shows great improvement over other mm-wave T-gated

AlGaN/GaN HEMT devices. Under two-tone linearity characterization at 30 GHz, PAE of

about 50% was demonstrated with C/IM3 of 30 dBc, which is very promising for mmwave

linear and efficient amplifiers without digital pre-distortion.

This material is based upon work supported by the DARPA under contract number

FA8650-18-C-7802. The views expressed are those of the author and do not reflect the

official policy or position of the DARPA or the U.S. Government. Any opinions, findings

and conclusions or recommendations expressed in this material are those of the author(s)

and do not necessarily reflect the views of the U.S. Government.
(Invited) Electron Emission Study of Planar-Type Electron Emission Devices Based on Nanocrystalline Silicon
Authors: Shimawaki Hidetaka , Mimura Hidenori , Murakami Katsuhisa , Nagao Masayoshi
Published: February 2020

A planar-type electron emission device having a thin film diode structure such as a metal-oxide-semiconductor (MOS) [1] is a promising candidate as a fine electron source for applications of vacuum nanoelectronic devices, including environment-hard electronic devices, flat panel displays and high-sensitive image sensors. This is because the cathode operates at low extraction voltage and produces uniform and highly directional emission, compared with conventional field emitters with needle structure. Furthermore, the cathode is insensitive to the environment. However, the device is limited in emission current by its low efficiency (i.e., the ratio of the emission current to the total tunneling current) of typically less than 0.1 % due to strong scattering of hot electrons while traveling through the conduction band of both the oxide and the gate metal, after tunneling through the potential barrier in the oxide [2]. The reduction of the work function of the gate electrode by adsorption of alkali metals onto the surface [3] and the use of films containing nano- and micro-crystalline structure taking the place of the oxide layer have been proposed to improve the performance on the MOS cathode [4]. Another strategy is to reduce electron scattering within the topmost metal electrode by decreasing the electrode thickness [5-7].

In order to improve the emission efficiency and understand the emission mechanism we have fabricated the planar-type electron emission devices based on oxidized nanocrystalline Si (nc-Si) prepared by a pulsed laser ablation (PLA) technique and investigated their emission properties. The emission area of the device was designed 500 mm in diameter. The emission current and the efficiency are higher for thinner in the gate electrode, indicating tunneling is sensitive to the thickness of the gate. The electron emission efficiency is predicted to reach ~ 10 % if electron scattering on the inside of the topmost metal electrode is perfectly suppressed. In our presentation, we will discuss the detailed electron emission properties of the nc-Si based planar-type electron emission device.

References

[1] K. Yokoo et al., J. Vac. Sci. Technol. B 11, 429 (1993). [2] K. Yokoo et al., J. Vac. Sci. Technol. B 12, 801 (1994). [3] H. Mimura et al., APL 88, 123514 (2006). [4] H. Shimawaki et al., J. Vac. Sci. Technol. B 24, 971 (2006). [5] K. Yokoo et al., J. Vac. Sci. Technol. B 14, 2096 (1996). [6] H. Shimawaki et al., J. Vac. Sci. Technol. B 26, 864 (2008). [7] H. Shimawaki et al., J. Vac. Sci. Technol. B 28, C2C49 (2010).
(Invited) Engineered Particle-Particle Contacts for Improved Thermal Interface Materials
Authors: Wang Robert Y.
Published: February 2020

I present my group’s ongoing work to use liquid metal to overcome thermal transport bottlenecks in polymer composites. The central premise behind this effort is that liquid metal-coated particle inclusions will have enlarged particle-particle contact regions relative to the point-like contacts between non-coated particle inclusions. In effect, the LM functions as a thermally conductive “solder” between particles.

Polymer composites play an important role for thermal interface materials (TIMs). TIMs improve thermal transport by filling micro air gaps between the rough surfaces of adjacent components (e.g., between a computer chip and heat spreader). These applications require mechanically compliant materials such as polymers that unfortunately also suffer from low thermal conductivity. Consequently high thermal conductivity solid particles are typically added to the polymer to boost thermal transport. Despite these efforts, TIM conductivities still usually fall below 2 W m-1 K-1because the small point-like contacts between solid filler particles lead to large thermal contact resistances that bottleneck thermal transport.

I first present our work on polymer composites with nickel-based particle inclusions. We explore bare nickel particles, nickel particles coated with silver, and nickel particles coated with liquid metal. These coatings impart mechanical compliance to the surface of the hard nickel particles and lead to a 3-fold increase in thermal conductivity of the polymer composite. These studies also reveal that a nanometer-scale native oxide coating on the liquid metal impedes thermal transport.

In order to improve thermal transport for liquid-metal coated particles, we next focus on methods to physically break the native oxide. Rupturing this thin oxide allows liquid metal to flow and yields improved contact between particles. To address this challenge, we conduct a series of thermal-mechanical studies on liquid metal droplets. In order to focus on the key physics, we create beds of liquid metal droplets with their native oxides intact (i.e. no polymer matrix and no solid particle core). We then study thermal transport as a function of applied mechanical pressure. We observe an enhancement in thermal transport that accompanies the rupture of the native oxide. We also find that the oxide rupture follows theoretical predictions for failure of thin-walled pressure vessels. Lastly, we chemically modify the native oxide shell to reduces its strength, promote oxide rupture, and improve thermal transport.
(Invited) Thermionic Transport in Van Der Waals Heterostructures
Authors: Zebarjadi Mona , Rosul Golam , Liu Naiming
Published: February 2020

We show theoretically and computationally that solid-state thermionic devices made out of 2D van der Waals layers could have efficiencies as high as thermoelectric modules. Here, we present experimental results for cross-plane thermoelectric transport in gold-graphene-few layers of WSe2-graphene-gold structures. We present a new measurement technique to extract equivalent device figure of merit in a wide temperature range. A small ZT was estimated at room temperatures using cooling curve measurements. It is noted that despite the small value of ZT (0.002), it is orders of magnitude larger than previously reported ZTs for van der Waals heterostructures. It is also noted that higher ZT values are expected at elevated temperatures and better performances are expected when the substrate is replaced by a good heat sink. We discuss design strategies to improve the efficiency and lay the pathway toward highly efficient thermionic devices.
Improved Switching Stability and Resistance Ratio in SrTiO3-Based Resistive Switches By Ni Nanoparticles Exsolution
Authors: Gonzalez-Rosillo Juan Carlos , Spring Jonathan , Sediva Eva , Carrillo Alfonso J. , Hood Zachary David , Rupp Jennifer L.M.
Published: February 2020

Memristor devices are promising potential hardware components for computer memory and neural network computing. Advances over the last years on understanding and implementing memristor technology had positioned them as a major candidate to overcome current bottlenecks in current electronic-based transistors in terms of downscaling capabilities and energy consumption. In particular, current challenges preventing a widespread implementation of oxygen-based memristors in today’s integrated circuits include the need to address cycle-to-cycle and device-to-device variabilities. These occur due to the random nature of nanoionic conductive filaments, whose rupture and formation govern the device operation. Changes in the filament location, shape and chemical composition during resistance switching are responsible for the cycle-to-cycle variability. Here we tackle the variability challenge by employing a double stabilization mechanism, where we spatially confine the conductive filaments with Ni nanoparticles that are capable of oxygen exchange between the set and reset cycles. Ni nanoparticles are fabricated on the bottom La0.2Sr0.7Ti0.9Ni0.1O3-δ thin film electrode by an exsolution process, during which Ni dopant metal cations exsolve from the perovskite backbone at high temperatures and reducing conditions. This method of nanoparticle fabrication offers great control over particle size and density tuned by the exsolution conditions. Particles with average diameters ranging from 10 to 60 nm were fabricated at 900 and 1000°C under a 5% H2 atmosphere. Exsolution also insures a good particle anchorage into the bottom electrode preventing particle agglomeration and movement. SrTiO3 is deposited on top of the Ni-decorated bottom electrode as the switching material followed by and the device is toped with a platinum top electrode. Cyclic voltammetry shows, that the ratio between the ON and OFF resistance states increases from single units to 180 as the particle diameter increases. Additionally, the variability of the low resistance state decreases below 5% as the average particle diameter increases to 60 nm. These findings offer a straightforward strategy on improving cycle-to-cycle variability in memristive devices, which is a major challenge for commercial application of the technology.
Memristive Devices Formed By ALD Metal Oxide Growth on a Hafnium Layer – Study of the Interfacial HfO2 Formation
Authors: Aussen Stephan , Hardtdegen Alexander , Dittmann Regina , Hoffmann-Eifert Susanne
Published: February 2020

Redox-based memristive devices (ReRAM) are considered for future energy-efficient non-volatile memory. Memristive cells enable high speed data access, low power consumption and high scalability, which is a key requirement for their use as artificial synapses in neuromorphic computing. Applications in networks of up to 106 devices require a scaling of the cell volume to about 103 nm3. For a typical valence-change-mechanism (VCM)-type switching cell with a metal oxide, like HfO2, sandwiched between two metal electrodes of different oxidation enthalpy, this means that the individual layer thickness is in the range of a few nanometers. Therefore, a control of the device properties demands for a control of interfacial reactions during device fabrication. Here, we are going to present a careful analysis of the oxidation of an Hf electrode layer during atomic layer deposition (ALD) of different metal oxides, these are Al2O3, TiO2, and HfO2. The in-situ encapsulation of a reactive metal electrode by means of an ALD metal oxide layer enables a better process control compared to stack structures formed by breaking the vacuum conditions.

In this study, plasma and thermal ALD processes were used to grow ultrathin layers of Al2O3, TiO2, and HfO2 on top of Hf metal films, after transfer under UHV conditions. The growth of homogeneous metal oxide films of a few nanometer in thickness enabled a systematic analysis of the HfO2 formation at the Hf/metal oxide interface by means of angle dependent X-ray photoelectron spectroscopy (XPS). The results show that the properties of the interfacial HfO2 layer can be controlled by the metal oxide deposited on top as well as by the process chemistry and deposition temperature. In contrast to the TiO2 film, the Al2O3 layer clearly serves as oxidation barrier. In addition, the chemistry and structure of the HfO2 interfacial layer were analyzed from XPS and transmission electron microscopy analysis.

Memristive device were fabricated from the Hf/HfO2/MOx stacks by depositing Pt top electrodes. The initial current of the devices scales with the pad size indicating the high quality of the insulating oxide layers. Consistent with VCM-type memristive devices the cells required an electroforming voltage to enable bipolar-type resistive switching. In this presentation, the trade-off between the two functionalities of oxidation protection versus enabling of a low electroforming voltage will be discussed.
Enhancing Surface Flatness and Brightness of Zn/Cu Alloy By Acidic Electroplating Copper
Authors: Chen Chien-Lin , Dow Wei-Ping
Published: February 2020

Conventional hardware plating processes contain metal (e.g., Zn/Cu alloy) injection in a mold, alkaline copper plating, pyrophosphate copper plating, and acidic copper plating. After metal injection in a mold, the metal substrates will be formed with some scratches or pin holes due to the long-term use of the mold. These scratches and pores will make the surface uneven, decrease the brightness of the hardware after electroplating processes. Moreover, it cannot pass the reliability test, such as adhesion and corrosion tests. However, common alkaline copper plating and pyrophosphate copper plating do not have filling ability to solve these problems.

In this work, we are going to use acidic copper plating to improve the surface flatness and solve the problem of pin holes. Blind microvias were used to simulate the pin holes and uneven surface of the hardware. Various plating additives with different concentrations were studied to fill the microvias and simultaneously render the surface to be smooth and bright. We observed the cross-section of the microvia by using an optical microscope (OM) and measured the surface brightness by using a luminance meter to investigate the effect of additives on surface brightness and filling performance.
Selective Cu Electrodeposition for Sub-Micrometer Redistribution Layers
Authors: Lee Jinhyun , Park Kimoon , Yoo Bongyoung
Published: February 2020

The density of integrated circuit (IC) was doubled by shrinking the feature size in semiconductor industry. An improvement in density of standard interconnection and the packaging technology is much slower than the IC trends. To overcome the increasing I/O interconnect gap, the semiconductor packaging technology has been driven by many researchers and companies over the many years. The redistribution layers (RDL), one of the important parts for the package process, play a role to rearrange I/O connections from the die to substrate.

For fine line pitch below 10μm, the damascene RDL process was proposed. The flow of damascene RDL process was composed of photoresist patterning, a metal layer deposition, Cu electrodeposition and chemical-mechanical planarization (CMP). During the Cu electrodeposition for the damascene RDL process, Cu overburdens were formed on top surfaces of sub-micrometer trenches. Typically the CMP process has been used to remove these overburdens in semiconductor industry, however, this surface planarization process caused an increase in process cost. For prevent the Cu overburden at low cost, the selective Cu electrodeposition which is process filling only trench is required. The selective Cu electrodeposition can be achieved by μCP with various additives.

The microcontact printing (μCP) process which transfers the self-assembled monolayers (SAMs) on the top surface of trenches can be one of the solutions preventing the Cu deposition on these top surfaces.[1-2] SAMs are organic molecules that formed spontaneously on the solid surface by chemisorption and organization of alkanethiol, silane, and so forth.[3] In this research, flat polydimethylsiloxane (PDMS) stamp is used for providing on the top surface of patterned substrate.

Selective Cu electrodeposition was proceeded on trench in CuSO4 1 M/H2SO4 0.58M electrolyte with various additives. In this study, electrochemical behavior of additives was studied by cyclic voltammetry and selective electrodeposition process was investigated with various additives, applied potential, charge density. The µCP process show the effective suppression of Cu growth on the top surface of trenches so that Cu overburden thickness was significantly reduced. This result reveals the feasibility of Cu trench-selective deposition below 10 μm. The μCP method with various additives shows the possibility of replacing surface planarization process which removes overburden of Cu for the RDL process..

[1]Y.Xia and G. Whitesides, "Soft lithography", Annu. Rev. Mater. Sci., vol. 28, no. 1, pp. 153-184, 1998.

[2]S.Alom Ruiz and C. Chen, "Microcontact printing: A tool to pattern", Soft Matter, vol. 3, no. 2, pp. 168-177, 2007.

[3]P.Laibinis, G. Whitesides, D. Allara, Y. Tao, A. Parikh and R. Nuzzo, "Comparison of the structures and wetting properties of self-assembled monolayers of n-alkanethiols on the coinage metal surfaces, copper, silver, and gold", J. Am. Chem. Soc., vol. 113, no. 19, pp. 7152-7167, 1991.
(Invited) High Performance Plug-and-Play Nanoelectronic Devices
Authors: Filler Michael A
Published: February 2020

We present a versatile suite of nanomanufacturing processes to fabricate, in an entirely bottom-up fashion, high performance modular semiconductor devices. Our overall approach, which is a distinct departure from the fully integrated nature of conventional wafer-based fabrication, promises dispersions of "plug-and-play" building blocks suitable for all manner of massively-scalable electronic and photonic systems. The vapor-liquid-solid (VLS) mechanism is central to our methodology, allowing for the bottom-up growth and nanoscale compositional encoding of single-crystalline semiconductor materials (i.e., group IV, III-V, and oxide). In a newly developed bottom-up patterning process – Selective CoAxial Lithography via Etching of Surfaces (SCALES) – we leverage the chemical differences between encoded segments to yield surface masks with nanoscale precision. Such masks can subsequently direct the deposition of the thin films (e.g., oxides, metals) needed to complete the construction of fully-functional devices. We also introduce the Geode process to increase the throughput of nanowire manufacturing by orders-of-magnitude beyond the state-of-the-art. This scalable nanowire growth method utilizes an unconventional substrate: the interior surface of hollow silica microcapsules lined with the metal nanoparticles that seed nanowire growth. These processes constitute a powerful new platform with which to fabricate and deploy high performance semiconductor devices and systems.
Enhanced Ionic and Electronic Transport in Nano-TiO2/Sheared CNT Composite Electrode for High Performance Na+ Insertion-Based Pseudocapacitors
Authors: Luo Sainan , Yuan Tao , Soule Luke P , Yang Junhe , Liu Meilin , Zheng Shiyou
Published: February 2020

Ion-insertion based pseudocapacitors show great promise to bridge the gap in performance between capacitors of high power densities and batteries of high energy densities. While Li+ based insertion pseudocapacitors (LICs) have been extensively studied, the exceedingly more abundant and inexpensive Na+ based pseudocapacitors (SICs) have not. Owing to the significantly larger size of Na+ than Li+, finding suitable low-voltage insertion materials for Na+ has been challenging. In this presentation, we will report a new low-voltage Na+ insertion electrode consisting of TiO2 nanocrystals anchored onto N-doped, sheared-carbon nanotubes (SCNTs) that overcomes the poor kinetics, low storage capacity, and limited stability often associated with Na+ based intercalation materials. In a half cell configuration, our anode shows a large capacity of 267 mAh g-1 at a 1C cycling rate and 120 mAh g-1 at a 10C rate while maintaining 87% of the initial capacity after 1000 cycles. When coupled with activated carbon (AC) in a full cell configuration, a remarkable energy density and power density of 54.9 Wh kg-1 and 1410 W kg-1, respectively, can be achieved while maintaining 90% capacity retention over 5000 cycles. The exceptional rate capability, energy and power density, and stability of our SICs are attributed to the dramatically enhanced electronic and Na+ ion conductivity of the TiO2/SCNTs composite electrode with unique architecture created during our synthesis process. The electrode designed in the current work presents an advancement in Na+ insertion electrode design that will ultimately result in cheap, high energy and power density energy storage devices for commercial use.
Carbon Allotropes Grafted with Poly (pyrrole) Derivatives Via Living Radical Polymerizations: Electrochemical Analysis of Nano-Composites for Energy Storage
Authors: Ignaszak Anna
Published: February 2020

In this study two living radical polymerization techniques, e-ATRP and RAFT, were applied for the grafting carbon allotropes such as MWCNT, Graphene and SWCNH with the methacrylate functionalized-poly(pyrrole). The modified carbons were examined as the polymerization initiators in the e-ATRP and RAFT synthesis. Their electrochemical response for the co-catalyst activity revealed the highest activation rate constant for SWCNH, owing to its highest specific surface area, and thus availability of large electrochemical interface for the redox process. The Fourier-transform infrared and Raman spectroscopies were used to identify the reaction products at each phase and for the final composites. TEM imaging showed that: (i) the morphology of composites made from the same carbon allotrope are not significantly different for RAFT and e-ATRP products; (ii) the structure of the ultimate product strongly depends on the type of carbon: for SWCNH the polymer was locally agglomerated between the carbon clusters due to ultra-small carbon particles, and for the Graphene, the polymer formed an uniform layer on the most outer sheets of Graphene; (iii) the poly(pyrrole) film or the particle size was very small (in all cases less than 30 nm), demonstrating the control over the polymer morphology in living polymerization techniques. The high specific gravimetric capacitances over 456 F g-1 and electrochemical stability up to 7500 cycles were obtained for MWCNT-grafted-poly(pyrrole), and slightly less for Graphene-based composites synthetized by e-ATRP, showing the advantages of this method over RAFT. The electrode voltages for all composites were higher as compared to the pure polymer electrodes, with some benefit of RAFT over e-ATRP product, and with significant improvement observed for the MWCNT- and Graphene-based systems. Regardless of the synthesis method, all composites demonstrated enhanced specific capacitance as compared to their individual components, revealing the synergy of double-layer capacitance from the carbon and the pseudo-capacitance generated by the polymer fraction. Both, the RAFT and e-ATRP are polymerization methods that deliver nanomaterials with tailored morphology and desired functions, by creating a stable anchorage between carbon, molecular linker and the polymer, and without unwanted side effects such as the homopolymerization, as indicated in our previous studies on similar carbon/poly(pyrrole systems.

Figure 1