bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
Application of Ag Nanoparticles That Anchored on F-Graphene into NiO/Ni(OH)2 for Improvements in Storage Capacity and Energy Density: Nanotechnology Offers Higher Storage Ability
Authors: Ryu Su Young , Hoffmann Michael R 
Published: February 2020

AgNP is synthesized on the surface of F-graphene as anchored, and characterized to form less than 20 nm in size having quantized physical properties. Application of AgNP has been investigated its effects on NiO/Ni(OH)2 supercapacitor from the comparison of specific capacitance (F g-1) and capacity (mA h g-1). It shows to be beneficial to the energy and power density of NiONi(OH)2 with reversible AgNP multi redox reactions. The specific capacitance of NiONi(OH)2 is highly enhanced by applied AgNP anchored on F-graphene (AgNP/F-graphene) from 148 F g-1 to 356 F g-1
while it results in 226 F g-1 by applied silver without F-graphene. The best result is obtained with the nafion free electrode of AgNP/F-graphene/NiONi(OH)2, as it results in 1,153 F g-1
at the experimental condition of 5 mV/s scan rate in 1M KOH.
For the specific capacity of NiO/Ni(OH)2, the identical result is observed as it improved from 266 mA h g-1
up to 545 mA h g-1
by applied AgNP anchored on F-graphene.
The performance of AgNP combined NiONi(OH)2 leads us to explore the secondary battery of Zn-Ni that combined with Zn-Ag. A preliminary galvanic-charge/discharge test using a single cell of AgNP/F-graphene/NiONi(OH)2 coupled with Zn plate demonstrates to be a potential hybrid rechargeable battery having a high power and energy density, as it resulted in about 3,433 W kg-1 for the power density and 958 W h kg-1 for the energy density, respectively, on the basis of Ni and Silver as the active material.