bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observation of Wake-up Effect on Ferroelectric Y:HfO2 Thickness Scaling
Authors: Mizutani Kazuto , Lin Yu Wei , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki 
Published: December 2020

Ferroelectric HfO2 films have attracted lots of attention because they can be applied to various devices, including memories and logics, with reduced power consumption1. Some of the issues of ferroelectric HfO2 films are the wake-up effect and the thickness scaling to the ferroelectricity. The wake-up effect is the increase in the remnant polarization (Pr
) during the cycling test, and the physical explanation in the film has been reported so far. Also, the crystal structure change after the cycling test has been detected2. The thickness scaling includes both roll-up and off of the Pr
on the film thickness. The physical phenomena are still not known, and the combination of the wake-up effect and the thickness scaling may give a clue to understanding the physics. In this study, we investigated the thickness-dependent wake-up effect of Y-doped atomic-layer-deposited (ALD) HfO2 films.
Metal-insulator-metal (MIM) capacitors with 5 mol% Y-doped-HfO2 (Y:HfO2) films were sandwiched by W electrodes. A post metallization annealing (PMA) is performed at 600oC (1 min) to crystallize the films. Figure 1 shows the initial Pr
of the capacitors on the HfO2 thickness. One can observe a peak in the Pr
at a thickness of 8 nm. The existence of a peak in Pr
on thickness is in good agreement with references3. The switching cycle dependence on the switching polarization (PSW
), the difference between positive and negative Pr
, shown in figure 2, indicates a strong wake-up effect, especially for the 8-nm-thick film. The cross-sectional transmission electron microscope (TEM) image of the 12-nm-thick capacitor, shown in figure 3, indicates the presence of an amorphous interfacial layer at Y:HfO2/W. The magnitude of the wake-up effect might be influenced by the presence of the interface layer.
This work is supported by JST-COI (JPMJCE1309).
[1] T. S. Boscke, et al., Appl. Phys. Lett., 99, 102903 (2011). [2]Y. Tashiro, et al., The JSAP Autumn Meeting, 20a-C309-5, (2019). [3]X. Tian, et al., Appl. Phys. Lett., 112, 102902 (2018).

Figure 1
Robustness of Ferroelectricity in Hafnium-Zirconium Dioxide Films Deposited By Sputtering and Chemical Solution Deposition for Ferroelectric Transistor Applications
Authors: Mohit Mohit , Migita Shinji , Ota Hiroyuki , Morita Yukinori , Tokumitsu Eisuke 
Published: December 2020

Since the discovery of ferroelectricity in HfO2 in 2011, extensive work begin to burst forth on HfO2-based ferroelectric materials and devices. Orthorhombic phase is responsible for ferroelectricity in HfO2, which is usually stabilized by the dopant such as Al, Zr, Si, la and Y. In particular, Zr doped HfO2 (HZO) has large Pr around 20 µC/cm2 and ferroelectricity can be obtained in a wide range of Zr composition. The orthorhombic phase is a metastable phase and Migita et al. [1] reported that the orthorhombic phase of sputtered HZO film was transferred to monoclinic phase by further annealing. In this work, robustness of ferroelectric phase against the further annealing process has been investigated using sputtered HZO and solution-derived Y-doped HZO films [2].
Sputtered HZO films were prepared by room temperature deposition followed by 600 oC, 10 min annealing in N2. Y-doped HZO films were prepared by chemical solution deposition (CSD) by annealing the samples at 800 oC for 3 min in O2.[2] Ferroelectric properties were confirmed by polarization-electric field (P-E) and capacitance-voltage (C-V) measurements for both samples before the second time annealing. Then, both samples were further annealed in 400 and 600 oC in N2 to examine the robustness of ferroelectricity. It was found that sputtered HZO films become paraelectric and that X-ray diffraction (XRD) pattern shows diffraction peak from orthorhombic phase disappeared. On the other hand, CSD HZO films shows ferroelectric nature even after second time annealing with negligible monoclinic phase. Such a significant difference in robustness is presumably due to residual carbon in the CSD films.
In addition, In2O3/(Y-)HZO structures are also fabricated for oxide channel thin film transistor applications and characterized, which will be presented at the conference.
[1] Shinji Migita et al, Jpn. J. Appl. Phys. 58 SBBA07, 2019.
[2] Mohit et al, Jpn. J. Appl. Phys. 59 SMMB02, 2020.
Conformal and Smooth TiN Film Growth By Using ALD Method
Authors: Cho Hyunchol , Jung Sung-Hoon , Nie Ben , Nair Anu , Chen Zhigang , Rathi Somilkumar , Mukherjee Niloy 
Published: December 2020

As the generation of memory devices evolve, the successful fabrication of high aspect ratio (HAR) features becomes more and more challenging. Apart from the traditional patterning, deposition and etch related issues, conformal film deposition onto these HAR structures becomes a critical parameter in determining the overall device yields. It is well established now that compared to conventional deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), atomic layer deposition (ALD) offers a pathway to highest conformality and step-coverage. On the other hand, film conformality, especially roughness property has trade-off relationship to step-coverage property. High-pressure process is appropriate to obtain high step-coverage performance in short ALD cycle time process, but roughness value becomes worse due to higher chance of crystalline film growth at high-pressure process condition. High roughness causes local variations in step-coverage and poses problems for deposition of subsequent layers and device performance.
In the present study, we report that it is possible to obtain conformal and smooth TiN film by using low/high pressure two-step growth, initially low-pressure TiN growth, and secondly high-pressure TiN growth on the non-pattern and HAR pattern wafers. Eugenus’s versatile 300mm mini-batch system and HAR structures with approximately 120:1 (Dimension of bottom opening, and total height are approximately 17nm and 2μm, respectively) were used in this research, respectively. TiCl4 and NH3 were used as the precursors for TiN film deposition and grown TiN films were analyzed by using ellipsometry, atomic force microscopy (AFM) and transmission electron microscopy (TEM) to study the film properties and step-coverages. In addition, reactor-scale computational fluid dynamics (CFD) simulations were performed and correlated to on-wafer experimental results and utilized as a predictive tool.
It was found that TiN film grown at low-pressure condition was more conformal and smoother than that grown at high-pressure condition, although step coverage value grown at low-pressure condition was worse than that grown at high-pressure condition. By optimizing low/high pressure two-step TiN growth condition, it was achieved that not only better roughness than that of pure high-pressure TiN, but also, better step coverage value than that of pure low-pressure TiN as well as than that of pure high-pressure TiN (Figure 1).

Figure 1
Silicene Growth through Island Migration and Coalescence
Authors: Cherukara Mathew Joseph , Narayanan Badri , Chan Henry , Sankaranarayanan Subramanian K. R. S. 
Published: December 2020

Silicene, the Si based counterpart to graphene is predicted to demonstrate similar desirable features to graphene, possessing a Dirac cone in the band-structure and Fermi velocities comparable to graphene. It has also been predicted to demonstrate several exotic properties such as the quantum spin Hall effect, chiral superconductivity and giant magnetoresistance. It has the added benefit of being easy to integrate into current industrial device engineering processes. Silicene monolayers have been grown on Ag (111) and Ir (111) substrates and recently a working field-effect transistor has been demonstrated at room temperature. While it is possible to characterize the final monolayer structure, it is impossible to probe experimentally the evolving atomic structure during growth.
We perform massively-parallel molecular dynamics (MD) simulations to study long time monolayer silicene growth on an Ir (111) surface. We observe an intricate multi-stage growth process driven by atomic and cluster migration on the surface. Initial growth involves formation of sub-nanometer clusters via adatom surface diffusion. Subsequently, these clusters rearrange spontaneously with each additional Si atom, forming clusters containing 4–7 member rings. Growth of each cluster through adatom adhesion is accompanied by the formation of larger islands through cluster migration and coalescence. Coalescence of smaller, more mobile islands into larger clusters is aided by the internal rearrangement of rings within each cluster. This flexibility, both of clusters and their constituent atoms, allows the impinging clusters to reorient after first contact and form a more perfect union. We also report on the effect of temperature and flux on the growth process and the final nanostructure. Our study provides atomistic insights into the early stage growth mechanisms of silicene which can be significant for controlled synthesis of its 2D monolayers.

Reference:

Cherukara, M. J., Narayanan, B., Chan, H., & Sankaranarayanan, S. K. (2017). Silicene growth through island migration and coalescence. Nanoscale, 9(29), 10186-10192.

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Microwave Photon Detection Using a Topological Josephson Junction
Authors: Pan Wei 
Published: December 2020

Single photon detection (SPD) has found increasingly important applications in many forefront areas of fundamental science and advanced engineering applications, ranging from studying the galaxy formation though cosmic infrared background to entanglement of superconducting qubits, single molecular spectroscopy, and remote sensing. In recent years, the rapid developments in superconducting quantum computation, high fidelity quantum measurement, quantum key distribution, and quantum network call for SPD in the microwave frequency range.
In this talk, I will first present our recent experimental work on topological Josephson junctions in Dirac semimetal Cd3As2. In high quality aluminum-Cd3As2-aluminum Josephson junctions, we observe both π and 4π periodic supercurrents. The π period is manifested by both the magnetic-field dependence of the critical supercurrent and the appearance of half-integer Shapiro steps in the ac Josephson effect. Our simulation by a resistively shunted junction model suggests that the π period arises from interference between the induced bulk superconductivity and the induced Fermi-arc surface superconductivity. In the second part of the talk, I will discuss microwave photon detection using these topological Josephson junctions. The temperature dependence and microwave power dependence of the junction resistance are studied. It is observed the effective temperature of the junction device under microwave radiation increases with microwave power, suggesting a promising potential for photon number-resolving capability.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under Contract No. DE-NA-0003525.
(Invited) Area-Selective Spatial ALD of SiO2 Interleaved with Etch-Back Supercycles: Quantification of Area Selectivity By Low Energy Ion Scattering
Authors: Mameli Alfredo , Brüner Philipp , Roozeboom Fred , Grehl Thomas , Poodt Paul 
Published: December 2020

Area-selective ALD interleaved with etch-back steps in a supercycle fashion has recently been reported as very effective in achieving high selectivity. Such supercycles can result in lower defectivity on the non-growth area and thicker layers on the growth area, as compared to solely area-selective ALD.1, 2

Here, we use low energy ion scattering (LEIS) to probe the selectivity of the first supercycle, consisting of plasma-enhanced selective spatial-ALD of SiO2 and conventional CF4-based reactive ion etching (RIE). Given its extreme sensitivity to the top monolayer(s) of a thin film, LEIS can reliably quantify the selectivity/defectivity on the non-growth areas in terms of surface coverage and derived thickness.
A three-step approach was used for the area-selective spatial ALD of SiO2,3 which consisted of inhibitor, silicon precursor (BDEAS), and O2 plasma exposures. The process selectivity as a function of the number of cycles was probed using LEIS to monitor the SiO2 surface coverage on the non-growth area. After 20 spatial ALD cycles, no silicon was detected on the non-growth area (detection limit 2 % SiO2 surface coverage), implying excellent process selectivity. Increasing the number of ALD cycles resulted in a gradual loss of selectivity. Interestingly after 110 ALD cycles, the SiO2 coverage was 86%, indicating a not yet closed layer. At the same time, a SiO2 thickness of 11 nm was measured on the growth area, using spectroscopic ellipsometry. As the last step of the super-cycle, a 3 seconds RIE was sufficient to bring the SiO2 coverage back to zero on the non-growth area, while an 8 nm thick SiO2 layer was left on the growth area.
The data presented in this work demonstrate the effectiveness of combining area-selective spatial ALD + etch-back corrections to achieve extreme SiO2 selectivity while retaining high deposition rates. Finally, we have extended the plasma-enhanced area-selective spatial ALD of SiO2 to other oxides and metals non-growth areas.

REFERENCES

1. R. Vallat et al., JVSTA, 35, 01B104 (2017).
2. S. K. Song et al., Chem. Mater. 31 4793-4804 (2019).
3. A. Mameli et al., ACS Nano, 11, 9303-9311 (2017).

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(Invited) Intercalation Chemistry of Oxides
Authors: Manthiram Arumugam 
Published: December 2020

The lithium-ion battery technology is based on intercalation chemistry phenomenon. The 2019 Chemistry Nobel Laurette Stanley Whittingham was the first to show in 1976 how the intercalation phenomenon can be utilized to realize a rechargeable lithium battery. He demonstrated the concept with a lithium-metal anode and a layered titanium sulfide cathode. Since then the field of intercalation chemistry for electrical energy storage has evolved during the past four decades, encompassing a variety of materials and intercalation working ions, such as monovalent lithium, sodium, and potassium, divalent magnesium, calcium, and zinc, and trivalent aluminum ions. Among the intercalation materials, oxides are at the forefront with rich fundamental structural chemistry and electrochemistry as well as with profound technological and societal impact. Accordingly, this presentation will focus on the richness and complexities of the intercalation chemistry of transition-metal oxides.
The scientific and technological impact of the intercalation chemistry of oxides is illustrated by the three families of cathodes for practical lithium-ion batteries: layered oxides, spinel oxides, and polyanion oxides. The presentation will first provide a comparison of these three families of oxides, pointing out the pros and cons with respect to employing them as electrodes in rechargeable batteries as well as their limiting features from a fundamental solid-state chemistry point of view. Particularly, the structural and chemical features that impact the charge-storage capacity, operating voltage, rate capability, and practical energy density will be discussed.
As we move forward, the layered oxide cathodes have become the prime candidates from an energy density consideration point of view, particularly for portable electronics and electric vehicles. However, bulk and surface instabilities during charge-discharge limit their practical energy density and cycle life, while the use of significant amounts of cobalt in them poses concerns on sustainability, cost, and supply-chain issues. Therefore, the presentation will then focus on layered oxide cathodes with high nickel contents and very low or no cobalt content to increase the energy density and lower the cost. Particularly, the role of modifications in chemical compositions through cationic substitutions on the cycle, thermal, and air instabilities will be discussed from a fundamental solid-state chemistry point of view. The use of advanced analytical techniques, such as in-situ x-ray diffraction, x-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry, scanning electron microscopy, high-resolution transmission electron microscopy, and differential scanning calorimetry in understanding the intricacies of the cathodes and mitigating the problems will be presented.
Freestanding TaN Nanotubular Architecture Based Photoelectrochemical Behavior
Authors: Kang Soon Hyung 
Published: December 2020

Nowadays, the exploration of new photoelectrode architectures to improve the light-harvesting and charge-collection properties of photoelectrochemical cells and related devices have been regarded as a challenging work. Here, we prepared the TaN nanotubular architecture for photoelectrochemical water splitting by RF sputtering and electrochemical anodization. Free-standing TaN nanotube electrode showed the great light harvesting in the visible light, showing the potential PEC performance.
Herein, it is expected that an optimal TaN layer takes part in a role as a photoactive material. Furthermore, the materials combination should be considered to make a synergetic effect to overcome the original weak points of each material. Therefore, the electrocatalysts based on photoelectrode can be suggested using the visible-active TaN and Ag materials.
Electrochemical Fabrication of MoOx@NiMo Heterostructure Catalysts for Hydrogen Evolution Reaction
Authors: Park Juhae , Kim Hyunki , Han Gyeong Ho , Ahn Sang Hyun 
Published: December 2020

In spite of environmental contamination due to the indiscriminate fossil fuel use, energy demand is rapidly increasing globally. The world is focusing on research on clean and renewable energy resources that do not emit pollutants. Among them, hydrogen has been referred to as a rising energy resource because its large energy density and zero carbon footprint. Water electrolysis is considered to be one of the most efficient methods of producing hydrogen in high purity. The water electrolysis is composed of the cathode where hydrogen evolution reaction (HER) occurs and the anode where oxygen evolution reaction (OER) occurs. Pt is well known as a catalyst for good performance in cathode, but there are problems of shortage and high cost. Therefore, there are many studies on non-noble metal, especially about transition metal. In addition, researches on catalysts with heterostructure that have good performance in HER have been conducted. However, some catalysts with heterostructure have the disadvantage of being manufactured over a long period of time at high temperature and high pressure. There is an electrodeposition method to solve this problem. Electrodeposition method has the advantage of adjusting morphology, structure and composition variously by easily controlling variables such as concentration of precursor in deposition bath, deposition time, and voltage, using only a small amount of time and energy.
In this study, we fabricated heterostructure MoOx@NiMo catalysts by electrodeposition method. First, NiMo with various ratios was electrodeposited by varying Ni concentration in deposition bath. Secondly, surface of NiMo was etched by applying constant potential. In this way, excess Ni on surface removed and Mo was oxidized to MoOx which plays a crucial role on HER catalytic activity, and heterostructure of core and shell was manufactured easily. The heterostructure of catalyst was confirmed by transmission electron microscopy (TEM). Through X-ray photoelectron spectroscopy depth profile (XPS), core composition was determined. And the effect of the core composition on the intrinsic activity was investigated. After leaching, the Mo oxidation state and crystal structure generated on the surface were scrutinized through TEM. In addition, using XPS, we identified the ratio of Mo oxidation state on the surface and confirmed how the ratio of MoOx affects performance. Consequently, catalyst with Ni/Mo ratio of 2.6 in core showed the highest intrinsic activity, and when more MoO2 is formed on surface, the catalyst showed higher intrinsic activity. Also, HER activity and stability of all catalysts were evaluated in acidic media.
Fabrication of Expanded Layered Double Hydroxide for Toxic Anion Elimination
Authors: Song Yoseb , Yoo Su-been , Park Ji Young , Choa Yong-Ho 
Published: December 2020

Layered double hydroxide (LDH), known as a toxic ion absorber, is layered structured material composed by metal hydroxide cation layer and anion layer. As followed process, LDH can selectively absorb cations or anions such as As5+, Cl-, NO3
- , and so on. This absorption materials have been highlighted as a critical factor to treat of wastewater.
In this research, we suggest new structure of LDH which is called expanded LDH for enhancing anion absorption efficiency. The expanded LDH is synthesized by heat treatment at relatively low temperature than calcined LDH. At heat treatment temperature, water of crystallization and part of anions are eliminated as gases. The cation layer of expanded LDH is partially anchored by remained anions. Because of anchored region, cationic layer is not able to move away freely from another cationic layer. The unique structure of expanded LDH cause recovery to initial LDH structure through anion absorption as refolding process.
Fabricated expanded LDH is characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometer, thermogravimetry-mass spectroscopy and Fourier transmission infrared analysis.

Figure 1
(Invited) Three-dimensional Free-standing Assemblies of Electrodeposited Nanowires for Photoelectrochemical and Catalytical Applications
Authors: Li Mohan , Ulrich Nils , Maimaitituerxunjiang Abudukade , Wagner Michael , Toimil Molares Maria Eugenia 
Published: December 2020

The implementation of metal and semiconductor nanostructures in devices for catalysis, sensing, and energy conversion requires an excellent control on geometry, crystallinity and composition of the individual nanostructures, as well as its successful assembly into 2-D and 3-D architectures. In particular, nanowire ensembles offer important advantages compared to planar films including e.g. larger surface area and surface to volume ratio, and better crystalline quality.
Ion-track nanotechnology is a powerful technique to create templates for the controlled synthesis of such 3-D nanowire architectures. Etched ion-track membranes are fabricated in two separate process steps: (i) sequential irradiation of polymer foils from one or various directions with swift heavy ions resulting in the creation of tracks; (ii) converting the ion tracks into nanochannels by selective chemical etching. Channel density and orientation, as well as diameter and geometry are adjusted by the irradiation and etching conditions, respectively. Afterwards, by electrodeposition in the nanochannels and subsequent removal of the polymer template 3-D assemblies of nanowires are synthesized. Since the nanowires adopt the exact shape of the host channel, their diameter can be adjusted between ~15 nm and a few µm, and their length between ~1 and several tens of µm.
In this talk, we will discuss the electrochemical deposition of Au1-xAgx, Cu, and Cu2O in interconnected nanochannel networks, the characterization of the resulting 3-D nanowire assemblies, and the investigation of their photoelectrochemical and catalytical properties.