bluuebunny/crossref_metadata_2025 huggingface dataset:
Confined Shear-Based Alignment of Carbon Nanotubes for Thin Film Transistors
Authors: Jinkins Katherine R , Chan Jason , Berson Arganthaël , Arnold Michael S
Published: February 2020

Individual semiconducting single-walled carbon nanotubes (s-SWCNTs) exhibit the high charge-carrier mobility, current carrying capacity, and sensitivity needed for applications based on thin-film transistors (TFTs) such as flexible electronics, displays, and sensors. However, assembling s-SWCNTs into aligned arrays to exploit the exceptional electronic properties of this material has been a major roadblock toward the integration of s-SWCNTs into electronic devices. Here, we are able to use confined shear-based alignment to fabricate aligned arrays of s-SWCNTs across arbitrarily large substrates.

In this study, we demonstrate that large amounts of shear can be used to align s-SWCNTs from solution by forcing s-SWCNT ink at high volumetric flow rates through 20 - 100 µm tall channels on SiO2 substrates. We use Raman spectroscopy to quantify the ratio of the Raman G band (~1590 cm-1) to the Si peak (~520 cm-1) of our films. This ratio provides a measure of the amount of s-SWCNTs deposited. We study the deposition from three concentrations of ink (~70, 35, and 7 µg mL-1) while varying the volume of ink used at a set shear rate of 3.2*105 s-1. The G/Si ratio behavior is similar for each concentration. Initially, there is a steep increase in the G/Si ratio up to 100 µL of ink, after which, the G/Si ratio increases linearly with increasing volume of ink.

Polarized Raman spectroscopy is used to quantify the disorder in the film. We show that for the s-SWCNT ink concentrations used in this study, the concentration does not affect the degree of alignment in the aligned s-SWCNT films and that the shear rate is the main factor affecting the alignment. Assuming the s-SWCNTs are oriented within a Gaussian angular distribution, from polarized Raman spectroscopy, the angular width of distribution was measured to be σ = 30° for a shear rate of 3.2*105 s-1 regardless of ink concentration and volume. This degree of alignment makes this technique non-ideal for fabricating devices with small channel lengths for high-performance applications such as logic or radio-frequency devices. However, for long-channel devices, there must be some amount of disorder in the s-SWCNT films to allow for charge percolation. This means this shear alignment technique is ideal for fabricating films for long-channel devices such as TFTs. Here, we fabricate transistors from films of shear-aligned s-SWCNTs and study the effect of degree of alignment on the transistor performance.

Because of the simplicity of this technique, we are able to scale the deposition of aligned s-SWCNTs to arbitrarily large areas as long as the high shear rate is maintained. This makes the technique ideal for large-area scaling in industry applications. As a demonstration, we show the large-area, uniform alignment of s-SWCNTs via confined shear-based alignment across a 4” wafer.
(Invited) Endohedral Filling Effects for Single-Wall Carbon Nanotubes As a Function of Filler Molecule and Nanotube Size
Authors: Fagan Jeffrey A.
Published: February 2020

Single-wall carbon nanotubes (SWCNTs) with open ends can be readily filled with a wide variety of organic molecules through simple liquid exposure. Ingestion of such molecules affects the extrinsic environment experienced by the SWCNT, and holds promise for controlled modulation of intrinsic SWCNT properties. To date optical linewidth narrowing, transition energy shifts and fluorescence enhancement as well as density modulation have been demonstrated. However, the dependencies of the properties on the filler molecule properties is observed to be non-uniform across filler and SWCNT (n,m) combinations. Of particular note is the combination of filler molecules and SWCNT structures of similar size, for which sieving and non-bulk arrangements of the filler molecules can be anticipated. Results in the small-diameter (n,m) SWCNT limit will be presented isolating the effects of filler insertion on the nanotube properties as a function of diameter, and implications for filling-based nanotube property manipulation.
Constraining Photoluminescent Defect States in Chirality-Sorted Covalently Doped Single-Walled Carbon Nanotubes
Authors: Saha Avishek , He Xiaowei , Ao Geyou , Zheng Ming , Tretiak Sergei , Htoon Han , Doorn Stephen K.
Published: February 2020

Recent developments in carbon nanotube surface chemistry are leading to the emergence of unexpected new optical behaviors. Specifically, introduction of covalently-bound defect sites into the nanotube structure generates a new photoluminescent (PL) emitting state that is significantly red-shifted from the normal excitonic emitting state that results from optical excitation.1 These new states have been shown to significantly increase emission quantum yields and introduce new functionality including room-temperature single photon emission, near-IR photon upconversion, and multifunctionality generated by localization of excitons at these defect sites.2,3,4 The new optical behaviors present a broad range of unexplored photophysics yet to be fully understood. Of particular interest is the use of emerging functionalization chemistries to introduce sp3 defects that have highly tunable properties.

An important challenge arising from the functionalization chemistry is that seemingly similar and structurally simple functionalization can give rise to a broad diversity in observed PL spectral features.1,3,5 Low-temperature spectroscopy along with quantum chemistry calculations demonstrated that these multiple emissive defect states are likely due to the occurrence of multiple possible, chemically distinct, binding configurations on the nanotube surface.6 Following these results, we hypothesize that the diverse emissive states are also influenced by the interplay of nanotube chirality, structure of the dopant, and surface structures on the tube. In this regard, we aim to control the number of emissive states through control of these factors. We have studied a number of different chiral structures for aryldiazonium functionalization, ranging from so-called near-armchair to near-zigzag structures of varying diameter. We have demonstrated that zigzag carbon nanotubes tend to constrain photoluminescent defect states more efficiently than other chiralities. Density functional theory (DFT) calculations suggest that symmetry of the zigzag tube is the primary factor in creating a less diversified emission spectrum. Our findings on controlling the defect peak diversity could enhance the predictable functionality of these doped carbon nanotubes.

References:

Piao, et al. Chem., 5, 840 (2012).

Ma, et al. Nanotech., 10, 671 (2015).

Shiraki, et al., Rep., 6, 28393 (2016).

He, et al., Photonics,
11, 577 (2017).

Maeda, et al., Nanoscale,
8, 16916 (2016).

He, et. al., ACS Nano, DOI:1021/acsnano.7b03022, (2017).
Quantum Yield Effects of Modified DNA Sequences on Single-Walled Carbon Nanotube (SWCNT) Fluorescence
Authors: Gillen Alice Judith , Lambert Benjamin Paul , Molina-Romero Daniel , Boghossian Ardemis Anoush
Published: February 2020

The sensitivity of fluorescent SWCNT-based sensors has been shown to strongly depend on sensor brightness, with the brightest sensors demonstrating enhanced sensitivity capable of single-molecule detection. Although defect-free nanotubes show improved brightness that can enhance sensor sensitivity, the applicability of these nanotubes are often limited by their availability and the sensor preparation procedure, which can introduce defects that diminish quantum yield. Sensor brightness can be tuned to a certain degree through the non-covalent functionalization of SWCNTs with various single-stranded DNA (ssDNA) sequences. However, the correlation between sequence identity and SWCNT brightness remains elusive, and an empirical approach must thus be used to improve brightness. Here, we present a systematic approach to modulating SWCNT brightness through chemical modification of DNA. These modifications can be applied to nearly any DNA sequence, allowing one to enhance SWCNT brightness without significantly altering the sequence-based specificity conferred by the DNA wrapping.
(Invited) Nanotube Excitonic Emitter at the Subwavelength Scale
Authors: Rotkin Slava V. , Sofka Benjamin Joseph
Published: February 2020

It is slightly embarrassing to accept the fact that after a decade of very intensive research on optics of single-wall carbon nanotubes (SWCNT) still there is no complete understanding of fundamental physics behind it. For example, our knowledge of excitonic effects in SWCNTs is limited, nailed at two extremes – sophisticated and often highly idealized numerical simulations of very small systems or rudimentary empirical models of more realistic systems, not even always yielding analytical results.

In this talk, one question arising in the physics of nanotube excitons is addressed: what is the shape of the excitation for a finite size SWCNT object? Since a whole SWCNT is sub-diffraction scale object, one may expect something similar to Hertz dipole, modified for a semiconductor material (as opposed to metal). To the best of our knowledge, such a solution was not known, thus a theory shedding light on the distribution of current of a nanotube excitonic emitter has been developed.

While in our earlier work we considered localization of a free excitonic wave (aka binding) on a single charged impurity[1], in this talk we assume localization effects due to SWCNT end reflections. Unlike many of earlier excitonic works we take this into account via a self-consistent response of the whole nanotube antenna. Unexpectedly, even for a charge neutral SWCNT system, plasmonic resonances were found to develop on top of the excitonic spectral response[2]. We demonstrate that these plasmonic features are robust and should be detectable in near-field experiments.

[1] BO. Tayo, SV. Rotkin, “Charge impurity as a localization center for singlet excitons in single-wall nanotubes”, Phys. Rev. B 86, 125431 (2012).

[2] B. Sofka, SV. Rotkin, “Nanotube exciton-antenna polaritons”, in preparation.

This research is supported by the NSF ECCS-1509786.

Fig. 1. Spectral current density distribution for an excitonic SWCNT emitter: 1d-current density is plotted vs. axial coordinate of a 50 nm long nanotube and vs. the frequency of excitation (in energy units).

Figure 1
(Invited) Multi-Functional Nano-Templates for Solar Spectrum Conversion
Authors: Ko Doo-Hyun
Published: February 2020

We demonstrate novel approaches to harness entire solar spectrum via nano-templates with lanthanide-based upconversion and downshifting materials. The nano-template is prepared using nanoimprint technique that lends itself to large area fabrication of nano-patterns, and it enhances the efficiency of spectrum conversion process through the excitation of resonant modes near the band edge of the materials. For practical applicability of this template, organic solar cells with the lanthanide based nano-template are evaluated showing distinctively improved efficiency, and double imprinting technique are devised to generate color tunability. The material-agnostic nano-patterning methodology is further extended to a sol-gel-based CuInGaS2 (CIGS) solution to improve simultaneously optical and electrical performance in thin film solar cells.
(Invited) Edge-Selectively Functionalized Graphene Nanoplatelets As a Metal-Free Counter Electrode in DSSCs
Authors: Ju Myung Jong , Kim Jae cheon , Yoo Kicheon , Baek Jong-Beom , Lee Jae-Joon
Published: February 2020

Metal-free carbon-based electrocatalysts for dye-sensitized solar cells (DSSCs) are sufficiently active in Co(II)/Co(III) electrolytes but are not satisfactory in the most commonly used iodide/triiodide (I−/I3
−) electrolytes. Thus, developing active and stable metal-free electrocatalysts in both electrolytes is one of the most important issues in DSSC research. Edge-selectively heteroatoms-doped graphene nanoplatelets (XGnPs, X=N, halogens, Se, Te, Sb etc.) were prepared by a simple mechanochemical driven reaction between graphite and target materials. The edge-selective doping and the preservation of the pristine graphene basal plane in the XGnPs were confirmed by various analytical techniques, including atomic-resolution transmission electron microscopy (AR-TEM) and/or time of flight secondary ion mass spectrometry (TOF-SIMS). Here we report the synthesis of edge-selective graphene nanoplatelets (XGnPs) prepared by a simple mechanochemical reaction between graphite and target materials, and their application to counter electrodes (CE) for DSSCs in both Co(II)/Co(III) and I−/I3
− electrolytes. Specifically, tested as the DSSC CE in both Co(bpy)3
2+/3+ (bpy = 2,2′-bipyridine) and I−/I3
− electrolytes, among the XGnPs, the SeGnP-CEs exhibited outstanding electrocatalytic performance with ultimately high stability. The SeGnP-CE–based DSSCs displayed a higher photovoltaic performance than did the Pt-CE–based DSSCs in both SM315-sensitizer with Co(bpy)3
2+/3+ and N719-sensitizer with I−/I3
− electrolytes. Furthermore, the I3
− reduction mechanism, which has not been fully understood on carbon-based CE materials to date, was clarified by an electrochemical kinetics study combined with density functional theory (DFT) and nonequilibrium Green’s function calculations (NEGF). These new findings may pave the way for further development of more practical Pt-free CEs, which may help to accelerate the practical applications of DSSCs.
(Invited) Graphene Oxide Liquid Crystals and Relevant Functional Nanostructures
Authors: Kim Sang Ouk
Published: February 2020

Graphene Oxide Liquid Crystal (GOLC) is a newly emerging graphene based material, which exhibits nematic type colloidal discotic liquid crystallinity with orientational ordering of graphene oxide flakes in good solvents, including water. Since our first discovery of GOLC in aqueous dispersion at 2009, this interesting mesophase has been utilized over world-wide for many different application fields, such as liquid crystalline graphene fiber spinning, highly ordered graphene membrane/film production, prototype liquid crystal display and so on. Interestingly, GOLC also allow us a valuable opportunity for the highly ordered molecular scale assembly of functional nanoscale structures. This presentation will introduce our current status of GOLC research particularly focusing on the nanoscale assembly of functional nanostructures. Besides, relevant research works associated to the nanoscale assembly and chemical modification of various nanoscale graphene based materials will be presented.
Highly Conductive and Stable Graphene/PEDOT:PSS Composites As Metal Free Cathodes for Organic Dye-Sensitized Solar Cells
Authors: Kim Jae cheon , Ju Myung Jong , Rahman Mohammad Mahbubur , Yoo Kicheon , Lee Jae-Joon
Published: February 2020

Graphene is a potential candidate as a counter electrode (CE) material to replace the Pt for long-term stability and low-cost fabrication of dye-sensitized solar cells (DSSC). Although the catalytic activity of graphene towards iodine-based redox mediator is not significantly high, it exhibited excellent electrocatalytic activity for cobalt-based redox mediators. However, the low adhesion capacity of graphene with FTO and low stability is the significant problems of graphene based CE for the development of long-term stable DSSCs. This research demonstrated the fabrication of highly stable with strong adhesion capacity based graphene nanoplatelets (GnP) CEs for organic DSSCs. We used conducting polymer (PEDOT:PSS) together with GnPs to improve the adhesion, stability, and catalytic activity. Different weight percent (%) of GnPs were mixed with PEDOT:PSS (PP), and subsequently dispersed by ultrasonication. The dispersed solutions were deposited on FTO by an electro spray (e-spray) method and their electro-catalytic properties were measured for Co(bpy)3
2+/3+ redox couple (bpy=2,2′-bipyridine). The optimal PP/GnP (PPG) CE with 1wt% GnP mixed PP exhibited the profound improvement in conductivity, eletrocatalytic activity, and electrochemical stability for the Co(bpy)3
2+/3+ redox couple compared to the Pt, GnP, and PP CEs. The charge transfer resistance (R
CT) of the optimal PPG CE at the CE/electrolyte interface was 0.07 W.cm2, which is much lower than that of Pt CE (1.02 W.cm2). Moreover, the optimal PPG CEs showed better electrochemical stability under prolonged potential cycling. The DSSCs based on the Y123 sensitizer and optimal PPG CE showed a higher photovoltaic performance (J
sc, FF, and h of 13.64 mA/cm2, 67.01%, and 8.33%, respectively) than those of Pt-CE (J
sc, FF, and h of 13.27 mA/cm2, 65.52%, and 7.99%, respectively), GnP-CE (J
sc, FF, and h of 12.74 mA/cm2, 65.69%, and 7.61%, respectively), and PP-CE (J
sc, FF, and h of 12.27 mA/cm2, 60.72%, and 7.03%, respectively).
The Dependence of Electrochemical Property on Carbon Cage in Tb2C90 Isomers
Authors: Nie Mengsi , Dong Wei , Lian Yongfu
Published: February 2020

Soot containing Tb2C90 was synthesized in a modified Krätschmer-Huffman generator by vaporizing composite graphite rods (8 × 150 mm) filled a mixture of Tb4O7 (99.99%) and graphite powder (molar ratio of Tb: C = 1 : 15) under 400 mbar He atmosphere. The as-produced soot was collected and dispersed in 1, 2, 4-trichlorobenzene (TCB). After refluxing for 12 h, the resulting brown-yellow solution was distilled to remove TCB and immediately redissolved in toluene, and then subjected to HPLC for the isolation of Tb2C90 isomers. For endohedral fullerenes with two metal atoms, M2@C2n, there are two possible structures, i.e. dimetallofullerene, M2@C2n, and metal carbide fullerene, M2(μ-C2)@C2n-2. The UV-Vis-NIR absorption spectra of endohedral fullerenes are largely dependent on the fullerene cages and their electronic structures,1 since they are mostly due to the π−π* transitions of the fullerenes cages. Because the UV-Vis-NIR absorption spectra of Tb2C90（I）and Tb2C90（II）show much similar absorption features to those of Sm2@
C

1

(21)-C90
and Sc2C2@
C

s(hept)C88,2-3 respectively, Tb2C90（I）isomer is estimated to be of Tb2@
C

1

(21)-C90
structure, and Tb2C90（II）isomer of Tb2C2@
C

s

(hept)-C88structure. Electrochemical characterization confirms that the redox properties of endohedral metallofullerenes are tremendously dependent on the structures of carbon cage.

References

[1] Chen N, Beavers C M, Mulet-Gas M et al. J. Am. Chem. Soc., 2012, 134(18): 7851-7860

[2] Chen CH, Abella L, Cerón MR et al. J. Am. Chem. Soc. 2016, 138(39): 13030-13037

[3] Zhang Y, Ghiassi KB, Deng Q et al. Angew. Chem., Int. Ed. 2014, 54(2): 495-499
(Invited) Isolation and Structural Characterization of Lu2C2n
Authors: Shen Wangqiang , Lu Xing , Li Fang-Fang
Published: February 2020

Endohedral metallofullerenes (EMFs) with a composition of M2C2n may exist as di-EMFs, M2@C2n, or as carbide cluster metallofullerenes (CCMFs), M2C2@C2n-2. EMFs containing such metal atoms with a small ionic radius as scandium were found to prefer the CCMF form some of which had been incorrectly assigned as di-EMFs.[1] Lu-containing EMFs remain largely unexplored in spite that lutecium also takes small ionic radius so that . In this work, we report the single-crystal X-ray crystallographic results of a series of Lu-containing EMFs to show that all of them are di-EMFs, namely Lu2@C2n (2n=76-86). Theoretical results confirm the formation of direct Lu-Lu bonding between the two encapsulated metal atoms.[
2
]

References：

[1] X. Lu, T. Akasaka, S. Nagase, Acc. Chem. Res.
2013, 46, 1627-1635.

[2] W. Shen, L. Bao, Y. Wu, C. Pan, S. Zhao, H. Fang, Y. Xie, P. Jin, P. Peng, F.-F. Li, X. Lu, J. Am. Chem. Soc.
2017, 139, 9979−9984.
(Invited) Structural Studies of Fullerene Cages and Cage Disorder in Crystals
Authors: Olmstead Marilyn M. , Powers Xian B. , Balch Alan L.
Published: February 2020

Recent developments in the structure of fullerenes, endohedral fullerenes, and open cage fullerenes will be discussed. The process of cocrystallization has been widely used ,in order to produce crystals suitable for X-ray diffraction. However, disorder of these highly symmetrical cages is common even in cocrystals. We plan to discuss several factors that may contribute to the formation of disordered crystals.
(Invited) Chemical Isolation of Less Common Metallofullerenes
Authors: Rothgeb Amanda J , Tepper Katelyn Rose , Davison Cody Marshall , Stevenson Steven
Published: February 2020

To date, efforts to chemically purify metallofullerenes have focused primarily on the dominant endohedral species, e.g., M3N@C80. These metallic nitride clusters trapped inside C80 cages often represent the more abundant metallofullerenes in soot extract. We have made progress with chemically isolating di-metal (M2@C82) and metal carbide (M2C2@C80, M3C2@C80, M4C2@C80) metallofullerenes. Other less common endohedrals that we are chemically purifying include M3N@C68, M3N@C78, M3N@C88, and M3N@C92. In this presentation, we will discuss our recent results to chemically isolate these less-common metallofullerenes.
(Invited) Exciplex Formation and Decay in Porphyrin-Carbon Nanotube Ensembles
Authors: Imahori Hiroshi
Published: February 2020

During the last few decades, considerable efforts have been made toward the construction of donor–acceptor (D–A) linked systems that efficiently yield photoinduced charge separation, a basic step in natural photosynthesis and solar energy conversion. Among the building units for such D–A systems, nanocarbons deserves a special attention because it reveals notable electronic conductivity, tenacious mechanical strength, and huge specific surface area. These singular properties place nanocarbon-based D–A systems in an attractive position as the next-generation material for energy-conversion devices. With this in mind, a variety of studies have been conducted to prepare covalently linked systems of electron-accepting nanocarbons with electron-donating units such as pyrenes, porphyrins and phthalocyanines. However, the D–A interface frequently undergoes a rapid relaxation of the exciplex with partially charge-separated (CS) character or the complete CS state to the ground state, failing to form a long-lived CS state that is essential for solar energy conversion. In-depth understanding of the relationship between the structure and photodynamics of the electron donor-nanocarbon electron acceptor linked systems is important for extracting the full potential of such D–A materials toward the future applications.

In this talk I will give an overviw of our recent achievements related to photodynamics of porphyrin- attached single-walled carbon nanotubes connected with oligophenylene bridges.

[1] T. Higashino, T. Yamada, M. Yamamoto, A. Furube, N. V. Tkachenko, T. Miura, Y. Kobori, R. Jono, K. Yamashita, and H. Imahori, Angew. Chem. Int. Ed., 55, 629-633 (2016).

[2] T. Umeyama, T. Hanaoka, J. Baek, T. Higashino, F. Abou-Chahine, N. V. Tkachenko, and H. Imahori, J. Phys. Chem. C, 120, 28337-28344 (2016).

[3] J. Baek, T. Umeyama, K. Stranius, H. Yamada, N. V. Tkachenko, and H. Imahori, J. Phys. Chem. C, 121, 13952-13961 (2016).

[4] J. Baek, T. Umeyama, S. Mizuno, N. V. Tkachenko, and H. Imahori, J. Phys. Chem. C, in press.
Bilayer Dielectrics for RRAM Devices
Authors: Misra Durgamadhab , Sultana Sabiha , Jain Barsha , Bhat Navakanta , Tapily Kandabara , Clark Robert D. , Consiglio Steven , Wajda Cory S. , Leusink Gert J.
Published: February 2020

Non-volatile resistive random-access memory (RRAM) devices are currently being investigated as a low power, high density and high-speed alternative DRAM (1). A transition metal oxide dielectric layer is typically used as an insulating layer in a metal-insulator-metal (MIM) structure. To reduce the large variability of switching parameters and high operation current in these RRAM devices, bilayer dielectric structures are being explored.

In this work we have used several different bilayer structures using different dielectrics. In each device the bottom electrode (BE) was 10nm Ti/50nmTiN followed by 1nm Al2O3. The second dielectric layer or the switching layer was a 7-nm HfO2 (R3), HfZrO2 (R4 with Hf:Zr%=50%) or HfAlO2 (R1 with Hf:Al%= 3%) followed by the top electrode (TE) constituting of 8nm Ti/6nm ALD TiN+50nm PVD TiN. In some cases, the top electrode was varied to 2nm ALD TiN/8nm Ti/6nm ALD TiN+50nm PVD TiN (R5) by adding a 2nm ALD TiN layer prior to 8nm Ti. Some devices with HfZrO2 (R2) were subjected to a post deposition anneal (PDA) at 700oC for 60 s. In all cases, to enhance the switching characteristics on the top electrode 8 nm Ti was used as the cap layer material except in the case of R5 where 2nm of ALD TiN was deposited prior to 8 nm of Ti. The use of thin dielectric layer of 1nm Al2O3 was to suppress the sneak-path problem (3) in the low resistance state (RON).

Comparing the variation of switching layer, it was observed that the device with 1nm Al2O3/7nm HfAlO2 (R1) provided the superior average Roff/Ron values and both set and reset power compared to HfO2 (R3), and HfZrO2 (R4) devices. When the HfZrO2 (R4) devices were compared with the identical device with PDA (R2) Ron increased and Roff decreased for the PDA device, reducing the Roff/Ron value. Variation of cap layer to TiN instead of Ti also showed similar Roff/Ronbehavior.

D. Ielmini, Semicond. Sci. Technol. Vol. 31, 063002, 2016.

Xiaorong Chen and Jie Feng, Appl. Phys. A, vol. 120, 67 2015

U. Chand, K-C. Huang, C-Y. Huang, and T-Y. Tseng, IEEE Trans. on Electron Devices, vol. 62(11), 3665, 2015
(Invited) Crystalline Si Perc Solar Cell Technology
Authors: Wang Qi
Published: February 2020

In p-type crystalline Si solar cells, when the passivated emitter rear contact (PERC) replaces the back surface field (BSF) in the back contact, the cell red response enhances and its efficiency improves. In the laboratory, the research type 6 inch cells have reached their new record of 22.0% and 22.7% for mc-Si and c-Si, respectively. In past a couple of years, PERC solar cells successfully migrate from Lab’s development to factory manufacturing. At current mass production, the average solar cell efficiency is over 21% with high end of 21.8%. The average module wattage of 60-cell (6”) achieves over 300W with high end of 320W.
Light-Induced Plating of Aluminum on Silicon in an Ionic Liquid
Authors: Wang Laidong , Huang Wen-Hsi , Shin Woo Jung , Tao Meng , Deng Bowen , Wang Dihua
Published: February 2020

As the consumption of silver for the front electrode in silicon solar cells continues to grow rapidly, a low-cost low-resistivity Earth-abundant metal is likely needed to replace silver. Besides the widely-studied copper, aluminum is another candidate for front metallization in silicon solar cells. Conventional electroplating of aluminum in a nonaqueous ionic liquid has been carried out on silicon solar cells and about 18% efficiency has been demonstrated with an electroplated aluminum front electrode. However, the high-resistivity silicon substrate requires a nickel seed layer to facilitate aluminum electroplating on it. In this talk, we report light-induced plating of aluminum directly on the n side of a silicon p-n junction in an ionic liquid. Without any seed layer, the deposited aluminum has good adhesion to the silicon surface. The resistivity of the aluminum deposits is as low as 4×10–6 Ω-cm, which is only about 1.5 times that of bulk aluminum. The suitable wavelength for the light source is between 600 nm to 1,000 nm. The effect of plating temperature on morphology of the aluminum deposits is analyzed. Our light-induced aluminum plating process enables simpler, lower-cost metallization on silicon solar cells than the copper plating process.
Voltage Pulse Induced Resistance Change Response of Reram with HfO2 Dielectric layer
Authors: Azuma Atsushi , Yoshida Hayato , Nakajima Ryo , Shimizu Tomohiro , Ito Takeshi , Shingubara Shoso
Published: February 2020

ReRAM is one of promising nonvolatile memories with excellent properties such as low power, high switching speed, and scalability against downsizing. Recently, ReRAM has been attracted attention as artificial neuron devices such as synapse which changes resistance according to input voltage or current signals.

Recently we observed multiple resistance states in the RESET process of Ti/HfOx/Pt ReRAM devices. Then we found that the resistance of the reset state changed according to input of voltage pulses. In this study, we focused resistance change response of the SET as well as RESET processes of the Ti/HfO2/Pt ReRAM device. The size of the cross-point device area was 1×1 μm2. The HfOx layer was deposited by reactive sputtering using Ar and O2 mixture gases.

Fig.1 shows the typical bipolar resistance switching characteristic. Compliance current was SET to 500 μA. We applied voltage pulse train of constant voltage with 1 μsec pulse width and 2 μsec interval. Fig.2 shows resistance changes of the device during 200 pulses at various voltages. There was an initial abrupt increase of resistance followed by gradual increase. Pulse numbers before initiating abrupt increase of resistance was smaller as the absolute voltage value was larger. Fig.2 shows voltage dependence of the r5000 (resistance after 5000 voltage pulses were applied), and r5000 was continuously changed with applied negative voltage.

On the other hand, resistance change behaviors in the set process is completely different as shown in Fg.4. Resistance was high around 106 W when the applied voltage was lower than 1.1 V, ad it changed to low around 103 W when the applied voltage was higher than 1.5 V . In the voltage pulse ranges between 1.2 and 1.4 V, the resistance state indicated only two values of high and low. There were binary resistance states existed. From these experimental results, it maybe suggested that voltage pulse response of the RESET process is suitable for application to artificial synapse.
Оxygen Vacancy Influence on the Stabilization Properties of Ferroelectric Hf0.5Zr0.5O2: First Principle Study
Authors: Perevalov Timofey V. , Islamov Damir R. , Gritsenko Vladimir A.
Published: February 2020

The aim of the study is the investigation of the oxygen vacancy (VO) role for the stabilization of orthorhombic noncentrosymmetric (Pbc21) phase in Hf0.5Zr0.5O2 films. The simulations carried out in terms of the hybrid DFT using Quantum-ESPRESSO code for the four low temperatures Hf0.5Zr0.5O2 crystalline phases: orthorhombic ferroelectric (of-), monoclinic (P21c), orthorhombic oI (Pbca) and orthorhombic oII (Pnma).

It is shown that the VO concentration increasing leads to the fact that the pressure range under which the of-Hf0.5Zr0.5O2 structure can exist is narrowed. It is concluded that high VO concentration has a negative impact on the ferroelectric phase stabilization even for thin Hf0.5Zr0.5O2 films. It is established that of-Hf0.5Zr0.5O2 with O vacancies in any concentration is not stable for bulk crystal at any value of external pressure in which the structure is able to exist. However, it is shown that VO have a positive impact on the stabilization of the centrosymmetric oII phase of Hf0.5Zr0.5O2. Thus, the presence of oxygen vacancies and polyvacancies not only does not contribute to the Hf0.5Zr0.5O2 ferroelectric phase stabilization, but also leads to the destruction of the ferroelectric structure. This is consistent with the hypothesis that the degradation ferroelectric response of FeRAM elements during repeated reprogramming, is caused by the oxygen vacancies generation.

The work is supported by the Russian Science Foundation grant #14-19-00192.
Design of Perpendicular Magnetic-Tunneling-Junction Spin-Valve Including [Co/Pt]n Free Layer As Bulk Perpendicular Magnetic Anisotropy
Authors: Baek Jong Ung , Kondo Kei , Jung SunWha , Park Jea-Gun
Published: February 2020

Recently, dynamic random access memory (DRAM) has scaling limit because of its capacitor area. To replace DRAM, the next generation memory devices are being studied. Among them, perpendicular spin transfer torque magnetic random access memory (p-STT MRAM) is considered as a promising candidate because of easy scaling down, low power consumption, high read and write speed and non-volatility.

p-STT MRAM has several challenges for commercialization. To keep a high retention time (~10 years), STT-MRAM should have thermal stability greater than 74. Although the thickness of free layer is increased with thermal stability, the thickness of free layer is limited to maintain perpendicular magnetic anisotropy (PMA). One of studies, double MgO based p-MTJ spin-valve structure is issued for its large volume because in case of double MgO based p-MTJ spin-valve, PMA of the free layer is originated from two i-PMA between the CoFeB free layer / MgO tunneling barrier and CoFeB free layer / MgO capping layer. The i-PMA induced from the two interfaces increases the total volume of the magnetic free layer which increases the thermal stability, but it is still limited by the thickness of the individual CoFeB free layers. In our study, therefore, we propose a new structure using interfacial Co2Fe6B2 and [Co/Pt]n multi-layer as bulk PMA to achieve higher thermal stability than that of double MgO based p-MTJ spin-valve structure.

The dependence of the magnetic moment and thermal stability on the number of [Co/Pt]n multi-layers was estimated by using vibrating sampling magnetometer (VSM) as shown in Fig.1 b. Magnetic moment t~180μemu/cm2) of i-PMA+[Co/Pt]2 multi-layers is similar to that(~180μemu/cm2) of double MgO based p-MTJ spin-valve structure. Also, magnetic moment (t~366μemu/cm2) of i-PMA+ [Co/Pt]5 multi-layers is about two times more than that of double MgO based p-MTJ spin-valve structure and thermal stability (~181) is two times higher than that (~74) of the double MgO based p-MTJ spin-valve structure. The thermal stability can be modulated by simply changing the number of [Co/Pt]n multi-layers. Obviously, these results show that i-PMA + [Co/Pt]n multilayer as bulk PMA based p-MTJ spin-valve can achieve a high thermal stability.

In our presentation, we report the different characteristics of the p-MTJ spin-valve with [Co/Pt]n multi-layers by examining the static magnetization behavior, TMR ratio and MgO crystallinity. In addition, we present how these properties influence mechanism of p-MTJ spin-valve.

Acknowledgements

This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2017R1A2A1A05001285) and the Brain Korea 21 PLUS Program in 2014.

Figure 1
Design of Double Pinned Perpendicular Magnetic-Tunnel-Junction Spin-Valve Exhibiting Multiple Resistance States
Authors: Choi Jin-Young , Kondo Kei , Baek Jong-Ung , Shim Tae-Hun , Park Jea-Gun
Published: February 2020

Perpendicular spin-transfer-torque magnetic random access memory (p-STT MRAM) cells consist of a perpendicular magnetic tunnel junction and a selective device has been researched intensively because of the possibility of overcoming the scaling limitations of the current dynamic random access memory (DRAM) below the 10-nm design rule [1]. p-STT-MRAM requires high tunneling magnetoresistance (TMR) ratio greater than 150%, sufficient thermal stability (Δ=KuV/kBT) above 75 for a ten-year retention-time, and low switching current (J
C0 ~ 1 MA/cm2) must be achieved for low power consumption [2-3]. However, the thermal stability is hard to maintain when scaling down in 10-nm scale of the p-STT MRAM cells for terabit integration. It requires high interfacial anisotropy K
i
to maintain the thermal stability requirement for 10-year retention time [4].

In this study, we designed a p-MTJ spin-valve with a double pinned structure to realize two-bit operation to secure a larger scaling limit (see Fig. 1(a)). We investigated the dependency of the number of [Co/Pt]n multilayers on the coupling strength to the pinned layers in order to control the spin-electron direction of the pinned layers. The total number of [Co/Pt]n SyAF multilayers ferro-coupled to the bottom pinned layer was reduced from 9 to 3 layers to reduce the roughness of the MgO tunneling barrier to increase the TMR ratio. Also, the number of [Co/Pt]n of the top upper SyAF multilayers was modulated so that the coercive field (H
c) required to switch the spin-electron direction of the top pinned layer increased from about 0.3 kOe to 1 kOe which is sufficient to ensure the memory margin for two-bit operation, as shown in Fig. 1(b). Then, we investigated the multiple resistance states with the R-H loop of the double pinned p-MTJ spin-valve, as shown in Fig. 1(c). It showed four different resistance states depending on the spin-electron direction of the free layers and pinned layers as shown in Fig. 1(d) with a maximum TMR ratio of 166%. This implies that the double pinned p-MTJ spin-valve may be suitable for terabit integration compared to that of the single-bit operating p-STT MRAM memory cells.

Acknowledgements

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No.2017R1A2A1A05001285) and Brain Korea 21 PLUS Program in 2014.

References

[1] K. C. Chun et al., IEEE J. Solid-st. Circ. 48, 598 (2013)

[2] J. G. Park et al., IEEE Int. Electron Devices Meeting, IEDM 2015–February, 19.2.1-19.2.4 (2015).

[3] Amiri, P.K., et al., App. Phys. Lett. 98, 112507 (2011)

[4] Shouzhong Peng, et al., IEEE MAGNETICS LETTERS,
volume 8 (2017).

Figure 1
Magnetic Field Assisted Electrodeposition of Co-Ru Nanorods for Water Splitting Reaction
Authors: Dobosz Iwona , Kutyla Dawid , Kolczyk Karolina , Kowalik Remigiusz , Zabinski Piotr
Published: February 2020

The article presents results of tests on potentiostatic electrodeposition of ruthenium and Co-Ru alloys. The tests applying the method of cyclic voltammetry with the use of gold disk electrode (RDE) allowed to define a potentials range in which it is possible to obtain ruthenium and its alloys with cobalt from acid chloride electrolytes.

The influence of electrodeposition parameters and the electrolyte composition on the composition, morphology and structure of the obtained deposits was determined. Co-Ru alloys underwent XRD tests, an analysis with the XRF method and observations using scanning electron microscopy (SEM). Hydrogen evolution tests have been also performed.

Then, cobalt-ruthenium nanorods have been successfully synthesized by electrochemical deposition using an aluminum oxide membrane template with superimposed external magnetic field. The length and average diameter of cobalt alloy nanorods arrays are 4,5 - 9 μm and 100 nm, respectively. For nanorods deposited in applied external magnetic field of 0.6T we observe higher saturation magnetization and slightly higher coercivity field. This method offers a convenient and efficient path to synthesize metal array nanostructures with designed composition.
Electrochemical Fabrication of Nanostructured Thin-Film for Renewable Energy Applications
Authors: Yang Yang
Published: February 2020

Freestanding and robust thin-film electrodes are the basis for future renewable energy technology owing to their unique merits: i) additive-free features enable facile fabrication route and long lifetime; ii) can be easily recycled; iii) significantly reduce the weight and volume of the energy devices, especially for batteries and supercapacitors; iv) can be integrated into wearable electronic systems. However, previous efforts fail to make significant progress in freestanding metal compound thin-films due to a lack of fundamental understanding and technological breakthrough in freestanding metal compound thin-films. In this work, transformative thin-film nanomanufacturing technology has been developed to fabricate freestanding metal compound thin-films using a facile and scalable electrochemical route. Both experimental and computational studies indicate that a supreme electrochemical performance can be achieved by tuning the microstructure and composition of thin-films. Outstanding energy storage and hydrogen generation properties are therefore obtained by directly using these advanced thin-films as electrodes.
Formic Acid Electrooxidation at Pd Nanoparticles Electrodeposited Onto Glassy-Carbon from Ethaline
Authors: Espino-López Iliana Elizabeth , Montes de Oca-Yemha Maria Guadalupe , Estrada-Arce Elsa Miriam , Palomar-Pardavé Eduardo Eduardo , Romero-Romo Mario Alberto
Published: February 2020

Green and low-cost energy production is an important matter in today society because fossil fuels are running low and burning them is not an efficient process. Therefore, low temperature fuel cells arise as a promising technology, e.g. direct ethanol fuel cells (DEFCs) and direct formic acid fuel cells (DFAFCs). Palladium (Pd) has proven to be an excellent catalyst in the formic acid oxidation reaction (FAOR) and further investigation of methods for its’ synthesis at nanoscale is needed. Several studies have been performed on Pd and other metal nanoparticles (NPs) synthetized from aqueous media and deep eutectic solvents (DESs). The advantage of synthesizing NPs by electrodeposition from DESs over aqueous media is the diminution of oxygen or hydrogen evolution reaction. Thus, the aim of this investigation is to electrodeposit Pd NPs onto glassy carbon (GC) from ethaline and find out their relation to size and morphology to the applied potential. Hence, how these affect the efficiency of the DFAOR. Pd electrodeposition was obtained by chronoamperometry (CA), as shown in Figure 1B. The potentials were set according to the cathodic peak in the cyclic voltammetry (CV), see Figure 1A. All experiments were performed at 25 °C on ethaline media. In both cases, GC was used as the working electrode, silver and platinum wires were used as reference and counter electrodes, respectively. Electrodeposits were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) analysis. Furthermore, the Pd electrochemical response was measured by CV to obtain the electroactive area with carbon monoxide. FAOR was conducted by CV and tested by CA over 20 minutes.

Figure 1
An Investigation of the Electropolishing of Metal Parts Fabricated By Powder Bed Fusion Additive Manufacturing
Authors: O'Neil Christopher , Wu Yan , Lassell Austin , Dobson Sean , Yang Li
Published: February 2020

In this work the use of non-aqueous electropolishing for the surface treatment of the as-received Ti6Al4V and IN718 parts fabricated by laser and electron beam powder bed fusion additive manufacturing (PBF-AM) was investigated. Using the non-aqueous electrolyte, the characteristics of the voltage-current curve of the electropolishing exhibit a general absence of the plateau stage for both materials. Experimental design was carried out to quantify the significance of individual electropolishing parameters on the surface qualities of the samples. The electrolyte flow rate, the temperature and the electropolishing voltage appear to be the most significant input variables, and strong coupling effects among various electropolishing parameters were observed. The surface roughness of the electroplished samples exhibits significant improvement to less than 1μm, although the macroscopic surface texture was not effectively eliminated. In addition, the high-cycle fatigue performance of the electropolished samples exhibit significant improvement, which demonstrated the effectiveness of the surface treatment.
An Entropic Approach for Controlled Testing of Electrochemical Components
Authors: Bruce David Robert
Published: February 2020

Custom-designed electrochemical test systems allow for specific measurements to be generated for isolated variables in advanced materials testing. A well designed first-principle system can give insight into more complex interactions often found in real-world devices. Often, such isolated test systems utilize sub-systems that draw upon external reactants for sustained testing and exhaust reaction products as a result. Practical limitations on delivery of purified feed streams and mediation of exhaust require system operation that can fail unexpectedly, often as a result of failure of the system itself rather than of the materials under investigation.

A novel system for testing of zinc-air fuel cell cathodes is presented as an example system that allows for total internal flows of reactant and product chemical flows. Such systems allow for cyclic purification and analysis of reaction products and establishment of a device in which the only output of the testing is heat and reliable data.

Examination of test system control of state properties and elimination of suspected system contaminants highlight the benefits of the developed self-contained flow systems. Insight into general design characteristics for robust electrochemical test systems are developed in light of the limitations of the presented entropy machines.
Electrochemical Generation of Sulfur Vacancies in the Basal Plane of MoS2 for Hydrogen Evolution
Authors: PARK Sangwook , Tsai Charlie , Li Hong , Nørskov Jens , Abild-Pedersen Frank , Zheng Xiaolin
Published: February 2020

Molybdenum disulfide (MoS2) based catalysts for the electrochemical hydrogen evolution reaction (HER) have been widely studied as alternatives to platinum based catalysts due to the earth-abundance and great catalytic activity. Since the edge sites of 2H phase MoS2 were shown to be the active sites for HER, a great number of studies have focused on maximally exposing catalytically active edge-sites through diverse engineering process. Recently, we demonstrated that active sites could be created on the basal plane of 2H-MoS2 by generating sulfur (S)-vacancies. At the S-vacancy sites, the under coordinated Mo atoms introduce gap states that allow for favorable hydrogen binding, introducing the highest per site turnover frequency (TOF) reported for any MoS2-based catalyst for HER. However, the S-vacancies in the basal plane have so far only been generated using controlled argon (Ar) plasma exposure and H2 annealing. A more industrially viable alternative to the argon plasma desulfurization process is needed. To effectively utilize S-vacancies in MoS2 catalysts for industrial applications, a facile, general, and scalable route for generating S-vacancies in MoS2 of any morphology is needed.

Electrochemical desulfurization is one of the possible methods for generating S-vacancies by removing sulfur atoms from the basal plane of MoS2. This method removes the sulfur atoms in the basal plane of 2H-MoS2 to form hydrogen sulfide (H2S) gas through a desulfurizing activation cycle. In this work, we show an electrochemical (EC) desulfurization method for generating S-vacancies in monolayer as well as polycrystalline multilayer MoS2 supported on diverse electrodes. Density functional theory (DFT) calculations show that S-vacancies are expected to be thermodynamically favorable relative to the pristine basal plane at a sufficient negative potential. The concentration of S-vacancies can be controlled by changing the applied desulfurization voltage. These theoretical predictions are experimentally verified with the continuously grown MoS2 monolayers on gold (Au) showing that electrochemically generated S-vacancies are comparable to the recent work about Ar-plasma treated ones. In addition, we demonstrate the generality of the electrochemical desulfurization approach by generating S-vacancies on MoS2 multilayers supported on flat carbon rods and porous carbon foams leading to a significant HER activity enhancement. Finally, we experimentally show that the HER activity is stable under extended desulfurization durations as well as operating durations and that the concentration of S-vacancies and activity can be varied using the applied potential in polycrystalline multilayer MoS2 on carbon foam electrode.