bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Long Cycling Life Aluminum-Ion Batteries By Nanocarbon Electrode Optimization, a Comparative Study for Sustainability in Rechargeable Batteries
Authors: Carvajal-Rossainz Christian Gerardo , Cerro-Lopez Monica , Mendez-Rojas Miguel Angel , Munoz-Sandoval Emilio , Lopez-Urias Florentino , Espinoza-Lopez Thomas Antoine , Perez-Andrade Jonathan , Jimenez-Flores Ivan Guillermo
Published: February 2020

The need for environment-friendly, low cost, long-life, and non-flammable rechargeable batteries is today an active motivation for research in sustainable energy storage all around the world. Aluminum-ion batteries have demonstrated to be a close alternative to lithium-ion based batteries due to their unique advantages, such as, non-flammability, high stability, and cost effectiveness. On the other hand; high surface area carbons have been reported in the literature as active materials for ionic storage to be used as electrodes which motivates the development of green and sustainable Al-based rechargeable batteries. Here, we report a comparative study of three different nanocarbon structures as active materials for optimization in Al-ion batteries; bulk activated carbon (commercially available), multi-wall carbon nanotubes (Synthesized in collaboration with the GNCSL research laboratory of the IPICYT institute), and a so-called-Nano-Cheese activated carbon structure (synthesized in our group) where used as active electrodes for energy storage showing a remarkable cycling life for a potential window of 0.2 to 2.0V (vs. Al3+/Al). Their performance has been compared demonstrating an increase in absolute capacity of approximately 500% for the bulk activated carbon in comparison to multiwall carbon nanotubes and approximately 5,000% increase for the Nano-Cheese structured activated carbon (NCSAC). Moreover, the battery based on this last material (NCSAC) showed an increased stability in cycling life in comparison to the other two active materials. These results were obtained with no need of additional ionic salts added to the electrolyte solution and the methods and mechanisms for the electrode optimization will be discussed and described in detail.
(Invited) What Determines the Composition of Fullerene Porphyrin Cocrystals?
Authors: Roy Mrittika , Olmstead Marilyn M. , Balch Alan L.
Published: February 2020

Cocrystallization of endohedral fullerenes and empty cage fullerenes with Ni(octaethylporphyrin) has become a widely used method to obtain X-ray structural information on these molecules. However, the stoichiometry of composition of these materials is difficult to predict. here we will report some new structures and studies of factors that effect the composition of these cocrystals.
(Invited) Synthesis of Benzothieno[60]Fullerenes through Fullerenyl Cation Intermediates
Authors: Matsuo Yutaka , Yu Yun , Yang Xiao-Yu
Published: February 2020

Benzothieno[60]fullerenes were synthesized by using fullerenyl cation key intermediates. The reaction proceeded through a nucleophilic attack of the sulfur atom as a weak nucleophile to the fullerenyl cation electrophile. A monoarylated fullerene, (2-methylthiophenyl)hydro[60]fullerene, C60ArH (Ar = C6H4-SMe-2, and so on; four derivatives) was subjected to deprotonation with KO
t
Bu to form a fullerenyl anion ArC60
–, followed by oxidation using I2to generate a fullerenyl cation ArC60
+ leading to intramolecular demethylative cyclization via fullerene cation–S interaction to the product. Electrochemical study elucidated low-lying LUMO level of this compound. Computational calculation revealed high-lying HOMO level due to the fused thieno moiety, giving relatively narrower band gap than usual fullerene derivatives.
(Invited) Excited State Dynamics and Ultrafast Electron Transfer in β-Iodo Substituted Bdp and ADP Donor-Acceptor Systems Featuring Fullerene.
Authors: Gobeze Haptom B. , Shao Shuai , D'Souza Francis
Published: February 2020

Novel donor-acceptor systems featuring, as electron donors, triplet sensitizers, viz., β-iodo substituted BDP and ADP, and fullerene as an electron acceptor are designed and synthesized. Iodination of meso-phenyl-tetramethyl-BDP and tetraphenyl-ADP bearing catechol aldehyde groups at the boron center is achieved by treating the precursors with N-iodosuccinimide (NIS) in dry DCM and dry chloroform, respectively, and stirring them for 24 hours under nitrogen at room temperature. Following successful synthesis of pure diiodo-BDP-CHO and diiodo-ADP-CHO, the final donor-acceptor dyads I2BDP-C60 (1) and I2ADP-C60 (2) are synthesized by following Prato reaction using sarcosine in dry toluene and refluxing under nitrogen for 24 hours. The final products which are purified over silica column are achieved as pink-reddish and bluish solid, respectively. Their structural integrity is arrived by both 1H and 13C-NMR, and HR-Mass spectral analysis.

The steady-state and time-resolved excited state study of the dyads and control compounds using UV-vis absorption, fluorescence, phosphorescence, TCSPC and transient absorption both in the femtosecond and nanosecond time domain, in both toluene and benzonitrile, reveals very interesting photochemistry. The interplay of the thermodynamics and the kinetics of the singlet to triplet state intersystem crossing in the donor compounds is found to be decisive to the formation and quantum yield of the charge separated state in the dyads 1 and 2. In the case of dyad 1, with a slower rate of intersystem crossing, kISC= 5.18 x 10 9 S-1 in benzonitrile, the electron transfer seems to out compete the intersystem crossing and an ultrafast electron transfer is observed in benzonitrile with kCS= 1.9 x 1011 S-1. In the case of dyad 2 on the other hand, the fast intersystem crossing in diiodo-ADP seems to aggressively compete with the electron transfer especially for excitation initiated from S1 state while a better electron transfer dynamic is observed for electron transfer originating from the higher excited state. The charge separated states are found to persist up to ca. 1 ns, especially in the case of dyad 1 with a life time of 992.5 ps and a kCR= 1.0 x 109 S-1.

Figure 1
(Invited) Pristine Carbon Nanowires: Are They Five-Fold Symmetry C90, C100 and C120 Fullerenes or [5,5] End-Capped Carbon Nanotubes?
Authors: Stevenson Steven , Seeler Tiffany L. , Koenig Ryan M. , Tepper Katelyn R. , Franklin Hannah M. , Liu Xiaoyang , Wang Xiaoling , Dorn Harry C
Published: February 2020

In contrast to the ubiquitous studies on C60 and C70 fullerenes, few experimental studies have been reported that describe pristine samples of higher fullerenes beyond 90 carbon atoms. Likewise, very few single-walled carbon nanotube reports have focused on pristine SWCNTs studies because of the lack of pristine nanotubes of either zigzag (n,n) or armchair (n,0) forms with respect to diameter and chirality. In this presentation, we describe a series of pristine molecules that can be described as either five-fold symmetry C90, C100 and C120 fullerenes or [5,5] End-Capped Carbon Nanotubes. The isolation, characterization, and physical properties of this pristine carbonaceous series will be the focus of this presentation.
(Invited) Chemical Purification of Nanotubular Fullerenes: Separating Buckyballs from Buckytubes
Authors: Koenig Ryan M. , Tepper Katelyn R. , Franklin Hannah M. , Seeler Tiffany L. , Stevenson Steven
Published: February 2020

The existence of structural isomers is well known for fullerenes. Thousands of publications relate to the “spheroidal” fullerenes. Yet only a trace of experimental findings have been reported for the predicted “tubular” fullerene isomers. There are several reasons. First, the yield of nanotubular fullerenes is less than 0.05 percent in a typical soot extract. Second, there is a purification challenge to overcome. The currently published method necessitate the use of multiple HPLC columns having a variety of stationary phases to resolve co-eluting spheroidal and nanotubular fullerenes.

In this presentation, we discuss our recent results since the Seattle meeting. We will demonstrate that differences in the chemical reactivity of spheroidal versus tubular fullerenes can be used as a separation tool. Using this approach, we now have purified several isomers of nanotubular fullerenes.
(Invited) Actinide Endohedral Fullerenes: Unexpected Cages and Encapsulated Clusters
Authors: Chen Ning , Zhuang Jiaxin , Wang Yaofeng , Yang Wei , Li Xiaomeng
Published: February 2020

Three new isomers of Th@C82 have been isolated and characterized. These novel actinide endohedral fullerenes were fully characterized by mass spectrometry, single crystal X-ray diffractometry, UV-vis-NIR, Raman and cyclic voltammetry. Among them, an unexpected novel Non-IPR C82 cage, Th@Cs-(39701)-C82, has been identified by X-ray crystallography. Though M@C82 fullerenes are most common form of ednoheral fullerenes, which has been known since the discovery of EMFs, Non-IPR M@C82 has never been discovered before. This is the first C82 based Non-IPR monometallic endohedral fullerenes reported so far. This discovery not only presents a novel C82 fullerene cage but also highlights the unique interaction between single actinide ion and carbon cage. In addition, we will report our recent progress on the actinide cluster fullerenes.
(Invited) New Approaches in Computational Modeling of Fullerene/Metallofullerenes
Authors: Liu Xiaoyang , Dorn Harry C
Published: February 2020

Today, computational models are extensively applied in scientific research to address fundamental as well as practical issues in material science. Fullerenes and metallofullerenes are well recognized as potential materials for next-generation electronic devices, such as quantum computers. The rapid advance in fullerene/metallofullerene research requires improved theoretical tools to understand fundamental as well as practical applications of these new members of fullerene/metallofullerene family. In this presentation, we will describe the extension of the famous spiral program by Fowler and Manolopoulos1 to generate new non-classical isomers. We have extended this approach beyond 5 and 6 membered fullerene structures to other polygon faces, such as, heptagons. In addition, we have developed a machine learning tool based on a general relationship between the structure patterns and physical properties. Finally, we will describe our current modeling studies regarding chromatographic retention mechanism(s) of fullerene/metallofullerene molecules.

Reference:

Fowler, Patrick W., and D. E. Manolopoulos. An Atlas of Fullerenes. Clarendon Press-Oxford, 1995.
(Invited) Synthesis and Properties of Giant Molecular Carbon Nanorings and Nanocrowns Based on Nanographenes
Authors: Du Pingwu , Huang Qiang , Jia Hongxing
Published: February 2020

Carbon exists as a variety of nanometer-sized allotropes, such as 0D fullerenes, 1D carbon nanotubes (CNTs), and 2D graphene. So far, it is still a great challenge to construct CNTs with a fixed length and diameter-specified single-chirality. We have synthesized a series of novel large π-extended molecular carbon nanorings and nanocrowns based on nanographene hexa-peri-hexabenzocoronene (HBC) unit (named as [n]CHBCs) and other nanographenes as a finite model of armchair CNTs, including [n]CHBCs (n=4,6,8), TCR, and HCR, et al (Figure 1).1-3 Their tubular structures of these [n]CHBCs have also been characterized using various physical methods, including NMR, STM, PL, crystallographic analysis, and STM images. In addition, the photophysical properties of these nanocarbons are studied in solution and explained by theoretical calculations. TCR and HCR can selectively capture fullerene C60 due to strong supramolecular interactions and the molecular structure of C60@TCR is unambiguously determined by single-crystal X-ray diffraction. Compared to the HBC monomer, obvious redshift in absorption and emission spectra has been observed in these HBC carbon nanorings and nanocrowns. More recently, we constructed a three-dimensional capsule-like HBC-containing carbon nanocage,4 which can be considered as a novel synthetic model of the capped zigzag [12,0] carbon nanotubes.

1. Lu, D. P.; Wu, H. T.; Dai, Y. F.; Shi, H.; Shao, X.; Yang, S. F.; Yang, J. L.; Du, P. W. Chem.
Commun.
2016, 52, 7164-7167.

2. Lu, D.P.; Zhuang, G. L.; Wu, H. T.; Wang, S.; Yang, S. F.; Du, P. W. Angew.
Chem., Int. Ed.
2017, 56, 158-162.

3. Jia, H. X.; Zhuang, G. L.; Wang, J. Y.; Huang, Q.; Wu, Y. Y.; Zhou, Y.; Yang, S. F.; Du, P. W. submitted for publication, 2019.

4. Cui, S. S.; Zhuang, G. L.; Lu, D. P.; Jia, H. X.; Wang, Y.; Yang, S. F.; Du, P. W. Angew.
Chem., Int. Ed.
2018, 57, 9330-9335.

Figure 1
Purification of Nanotubular Fullerenes: Manipulating Reactivity Differences of Carbon Tubes and Spheres
Authors: Seeler Tiffany L. , Koenig Ryan M. , Tepper Katelyn R. , Franklin Hannah M. , Stevenson Steven
Published: February 2020

In this poster presentation, I will discuss advances in our isolation of nanotubular fullerenes. We have found significant differences in the reactivity of nanotubular fullerenes compared to their spheroidal counterparts. By strategically manipulating these differences, we can obtain samples enriched in the tubular species. In this first stage of pre-cleanup, we can improve the percent abundance of tubular fullerenes by several orders of magnitude. In a second stage, we use HPLC and fraction collection for their final purification. Assignment to tubular structures is based on UV-Vis and X-ray crystallographic findings.
Chemical Purification of Lutetium Clusters Entrapped in Less-Common Fullerene Cages
Authors: Franklin Hannah M. , Stevenson Steven , Tepper Katelyn R.
Published: February 2020

Little information exists in the literature for Lu clusters entrapped in less-common fullerene cages. In this research, we describe a separation method that uses reactivity differences to isolate various desired Lu metallofullerenes. In the first stage, the majority of fullerene species are reacted and removed from solution, leaving behind the more chemically resistant metallofullerenes. Injection of these inert metallofullerenes into HPLC for fraction collection provides an array of purified less-common fullerene endohedrals for subsequent characterization experiments (e.g., UV-Vis, etc).
Phosphorene Exfoliated from Black Phosphorous Via Bipolar Electrochemistry
Authors: Rabiei Baboukani Amin , Khakpour Iman , Wang Chunlei
Published: February 2020

Phosphorene as one of the 2D layered materials, has received a great attention for different applications from high performance energy storage to optoelectronic devices. It has tunable band-gap ranging from 0.3 to 2.0 eV and interesting semiconducting properties. Therefore, it is very important to design a facile, cost-effective and scalable method to prepare a single or few-layer phosphorene. Herein, for the first time, we proposed a simple, eco-friendly and fast process to exfoliate a black phosphorous (BP) crystal into phosphorene by using a bipolar electrochemistry in deionized water. Bipolar electrochemistry is based on applying a voltage between two driving electrodes in the presence of bulk black phosphorous in DI water. In this study, Raman spectroscopy and transmission electron microscopy (TEM) have been applied to analyze the exfoliated BP. Raman spectra revealed that the intensity of the vibration bands decreases significantly for the exfoliated BP, confirming successfully exfoliation of BP into 2D phosphorene. The exfoliated BP materials were assembled as a half cell and investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) tests. In this conference, detailed material synthesis and electrochemical characterization will be presented.
Enhancing Electrical and Contact Properties of WSe2 ­­field-Effect Transistors Via Vacuum-Annealed Pt-W Alloy Contacts
Authors: Kim Hyun , Park Hyunik , Kim Jihyun
Published: February 2020

Two-dimensional (2D) materials have been extensively studied as one of the promising post-silicon materials for nano-sized field effect transistors to overcome physical limits of Si-based electronic devices. Semiconducting transition metal dichalcogenides (TMDs) have been studied as attractive candidates with sizeable band structure, in contrast to graphene with zero band gap limiting its implementation into electronics due to large off-currents and low drain-current modulation. Among all, tungsten diselenide (WSe2) has attracted attention as a p-type conducting material with its high current on/off ratio, hole mobility, and environmental stability. Despite the superior electrical properties of WSe2, difficulty in forming of a stable Ohmic contact with a low contact resistance has posed a significant limitation in fabricating WSe2-based devices. It creates van der Waals (vdW) gaps with contact metal and additional tunneling barrier, which increases contact resistance and affects device performance. Efforts have been made to reduce contact resistance such as by work function engineering and charge transfer methods employing various novel technical strategies. However, such approaches still need industrial fabrication compatibility and environmental stability.

In this work, a simple one-step vacuum annealing was used to address vdW gaps and reduce contact resistance. Thermal annealing is extensively incorporated in conventional compound semiconductor fabrication process to facilitate alloying or inter-diffusion of metal to semiconductors and enhance contact properties. Plus, thermal annealing can eliminate interlayer residues originated from the repeated exfoliation and dry transfer processes, which would deteriorate electrical contact between metals and TMDs. Herein, few-layered WSe2 was transferred on to platinum (Pt) electrodes with high work function (>5 eV) to facilitate hole injection. Effects of vacuum annealing on the performance of WSe2 FETs were then investigated. With improved contact properties from the removal of interlayer residues, the device performance including on-current density, hole mobility, and current on/off ratio enhanced up to the temperature of 650 ℃. Especially, p-type conduction was greatly improved after vacuum-annealed at 600 ℃, confirmed by selenium vacancy-aided formation of interlayer PtxW1-x alloy. The alloyed contacts occupied between WSe2 and Pt played a role in improving contact properties and lowering contact resistance. The device performance started to deteriorate when vacuum-annealed above 650 ℃, which is attributed to thermal degradation of WSe2 channel from high annealing temperature. Our work would further pave the way for achieving methods in fabricating a reliable TMDs based devices. Details will be discussed at the presentation.

Figure 1
Synthesis and Surface Modification of Two-Dimensional Mxenes As Potential Magnesium Battery Cathodes
Authors: Fagerli Frode Håskjold , Kaland Henning , Hadler-Jacobsen Jacob , Boge Lars-Arne , Selbach Sverre Magnus , Wang Zhaohui , Vullum-Bruer Fride
Published: February 2020

Rechargeable magnesium batteries may allow for safer and cheaper batteries compared to those based on Li-ion technology, mostly due to the possibility of utilizing magnesium metal as anode material without forming dendrites [1]. However, since the first prototype was reported in 2000 [2], limited improvements on the cathode side have been achieved, where either trapping of magnesium ions or low operating potentials limit the performance [3]. After its discovery in 2011 [4], a new group of two-dimensional materials, known as MXenes, has been proposed as possible cathode materials for rechargeable magnesium batteries, due to their good electronic properties and ion hosting capabilities [5]. Various MXenes have already shown promising behavior in Li-ion batteries [6].

Here, we present data from several compositions of MXenes formed by the selective etching of Al from the initial MAX phase precursor in concentrated HF acid. The MAX phases were produced by solid state reaction synthesis through careful control of temperature and stoichiometry to obtain the desired end compositions. After successful etching, different treatment methods have been investigated in order to control the surface termination groups together with the interlayer distance between the flakes. The materials were characterized by SEM, EDX, XRD and XPS to map out the elemental and structural changes resulting from these treatments. Electrochemical properties have also been assessed through cyclic voltammetry and galvanostatic charge/discharge analysis.

References:

[1] M. Masaki, Journal of Power Sources 196 (2011), 7048-7055

[2] D. Aurbach et al., Nature 407 (2000) 724-727

[3] P. Canepa et al., Chemical Reviews 117 (2017) 4287-4341

[4] Naguib et al., Adv. Mater. 23 (2011) 4248-4253.

[5] Naguib et al., J. Am. Chem. Soc. 135 (2013) 15966-15969

[6] C. Eames, M. S. Islam, J. Am. Chem. Soc. 136 (2015) 16270-16276
(Invited) Atomic Level Investigation of Resistance Switching in 2D Memory Devices
Authors: Hus Saban , Ge Ruijing , Wu Xiaohan , Gu Yuqian , Lee Jack C. , Li An-Ping , Akinwande Deji
Published: February 2020

The last few years have witnessed significant developments in non-volatile resistance switching (NVRS) devices which employ layered 2D materials such as hexagonal Boron Nitride (hBN) and Transitional Metal Dichalcogenides (TMDs) as the active medium. Among these developments, the demonstration of NVRS in vertical metal-insulator-metal (MIM) devices with single layer atomic sheets used as the insulating layer, is particularly intriguing. While it was long believed that leakage currents would prevent observation of this phenomenon for atomically thin insulating layers our previous studies on mesoscopic scale devices demonstrated stable unipolar and bipolar operations. Furthermore, these studies suggest that localized defects and other atomic-scale multiphysics mechanisms are likely to have a key role in NVRS observed in these 2D devices.

Here, we present our current research on the atomic level details of the relationship between the NVRS and heterogeneities in 2D materials. For these investigations, we utilize both single probe and multi-probe scanning electron microscopy (STM) methods, first, to identify the atomic level details of the heterogeneity and then to conduct transport experiments in the vicinity of specific heterogeneities. These studies aim to provide one to one correlation between the structural properties of the heterogeneity and its role on the transport properties of the material. Through these studies, we seek to deduce which particular defect structures are most desirable for NVRS and utilize this information for the development of extremely high-density data storage devices as well as neuromorphic applications and low power RF switches.
(Invited) Graphene-Based Brain Interfaces for Probing Neural Activity
Authors: Kuzum Duygu
Published: February 2020

The complexity of neural dynamics in the brain has challenged both basic neuroscience research and medical practice for decades. Understanding neural dynamics and information processing performed at cellular and population levels require advanced neurotechnologies that provide recording and stimulation capability with high resolution. Clinical neuromodulation therapies widely used for neurological disorders also depend on the ability to manipulate the dynamics of neural circuits. Conventional neural interfaces offering electrical and optical probing of neural activity have greatly advanced our understanding of neural functions. However, most of these technologies are based on a single functionality. That significantly limits the sensing resolution at multiple spatial and temporal scales. Combining multiple functionalities in a single system has recently been pursued as an integrative approach in new neurotechnology development. Graphene has recently emerged as a neural interface material offering several outstanding properties, such as high optical transparency, flexibility, high conductivity, functionalization and biocompatibility. The unique combination of these properties in a single material system makes graphene an attractive choice for multi-modal probing of neural activity. In this talk, I will present our recent work on graphene-based brain interfaces, discuss key applications, and finally highlight future directions and potential advances for graphene-based neurotechnologies in both basic neuroscience research and medical applications.
Molybdenum Disulfides and Diselenides By Atomic Layer Deposition
Authors: Zazpe Raul , Prikryl Jan , Krbal Milos , Ng Siowwoon , Dvorak Filip , Bures Filip , Macak Jan M.
Published: February 2020

The success of graphene opened a door for a new class of chalcogenide materials with unique properties that can be applied in the semiconductor technology [1]. Monolayers of two-dimensional transition metal dichalcogenides (2D TMDCs) possess a direct band gap [2] that is crucial for optoelectronic applications. Additionally, the direct band gap can be easily tuned by either chemical composition or external stimuli. Next to the optoelectronic applications, where a monolayer planar structure is necessary to employ, a layer of standing flakes, which possesses a large surface area, can be used for hydrogen evolution [3] a photodegradation of organic dyes [4] or as electrodes in Li ion batteries [5].

In principle, TMDCs can be prepared by various top-down (e.g. exfoliation) and bottom-up techniques, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) growth techniques [1]. MoS2, a typical representative of TMDCs, has been widely studied for many applications. Recently, the possibility to employ ALD as a technique to grow MoS2 has been reported. In these works (CH3)2S2 [6] or H2S [7, 8] were used as the S precursor and Mo(CO)6 [6], MoCl5 [7] or Mo(thd)3 [8] as the Mo precursors. From the practical point of view, MoSe2 is even more interesting than MoS2 since MoSe2 possesses a higher electrical conductivity than MoS2 [9, 10]. Recently, we have shown that ALD deposition of MoSe2 [11] or Mo-O-Se [12] using ((CH3)3Si)2Se as the Se precursor and the MoCl5 or Mo(CO)6, respectively, as the Mo precursors is feasible.

The presentation will focus on the synthesis of MoS2 and MoSe2 by ALD, their characterization and applications in various fields. Experimental details and some recent photocatalytic and hydrogen evolution results will be presented and discussed.

References:

[1] A. V. Kolobov, J. Tominaga, Two-Dimensional Transition-Metal, Dichalcogenides. Springer Series in Materials Science, Springer International Publishing AG, Switzerland 2016

[2] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, A. Kis, Nat. Nanotechnol. 2011, 6, 147.

[3] L. Wang, Z. Sofer, J. Luxa, M. Pumera, Adv. Mater. Interfaces
2015, 2, 1500041

[4] Y. Wu, M. Xu, X. Chen, S. Yang, H. Wu, J. Pan, X. Xiong, Nanoscale
2016, 8, 440

[5] D. Ilic, K. Wiesener, W. Schneider, H. Oppermann, G. Krabbes, J.Power Sources
1985, 14, 223

[6] Z. Jin, S.Shin,D.H.Kwon, S. J.Han,Y. S.Min,Nanoscale
2014, 6, 14453.

[7] L. K. Tan, B. Liu, J. H. Teng, S. Guo, H. Y. Low, K. P. Loh, Nanoscale
2014, 6, 10584

[8] M. Mattinen et al., Adv. Mater. Interfaces
2017, 4, 1700123.

[9] D. Kong, H. Wang, J. J. Cha, M. Pasta, K. J. Koski, J. Yao, Y. Cui, Nano Lett. 2013, 13, 1341.

[10] A. Eftekhari, Appl. Mater. Today
2017, 8.

[11] M. Krbal et al., Phys. Stat. Sol. RRL,
2018, 12, 1800023

[12] S. Ng et al., Adv. Mater. Interfaces
2017, 1701146.
(Invited) Tuning Optoelectronic Properties of Transition Metal Dichalcogenides for Hydrogen Generation
Authors: Miller Elisa M.
Published: February 2020

We tune the optical and electronic properties of 2D transition metal dichalcogenides (TMDCs) – MoS2, MoSe2, WS2, and WSe­2– to control the surface conductivity, energetics, and ultimately reactivity. The optoelectronic properties of monolayer and few-layered TMDCs are tuned by surface functionalization, environmental control, and phase engineering. These modifications have a direct impact on the surface reactivity for hydrogen generation. Specifically, we directly map the surface energetics, phase, and reactivity with scanning electrochemical microscopy, scanning Kelvin probe microscopy, confocal Raman/photoluminescence, and scanning transmission electron microscopy-electron energy loss spectroscopy. Moreover, we disentangle the influence of O2and H2O molecules on the surface of TMDCs, where these molecules impact the optoelectronic properties and can influence the potential applications of monolayer TMDCs in (photo)electrocatalysis.
(Invited) Atomic-Scale Exploration of Synthetic Low Dimensional Materials
Authors: Guisinger Nathan P
Published: February 2020

Low-dimensional materials functioning at the nanoscale are a critical component for a variety of current and future technologies. From the optimization of light harvesting solar technologies to large-scale catalytic processes, key physical phenomena are occurring at the nanometer and atomic length-scales and predominately at interfaces. For instance, graphene is a nearly ideal two-dimensional conductor that is comprised of a single sheet of hexagonally packed carbon atoms. In order fully realize the potential of graphene for novel electronic applications, large-scale synthesis of high quality graphene and the ability to control the electronic properties of this material on a nanometer length scale are key challenges. In addition to graphene, we are interested in exploring the synthesis of low-dimensional materials that do not occur in nature. This talk will highlight how scanning probe microscopy presents a series of powerful experimental tools that can overcome several challenges and allow for the direct characterization of several advanced materials. This talk will also cover our most recent discovery and synthesis of new two-dimensional (2D) boron allotropes (borophenes). This discovery of metallic 2D sheets of boron presents almost ideal example of the synergy between predictive modeling resulting in the experimental realization of a designer materials.
(Invited) Towards High-Performance Field-Effect Transistors with Atomically Precise Graphene Nanoribbons
Authors: Llinas Juan Pablo
Published: February 2020

It is now possible to grow graphene nanoribbons with atomically precision by employing on-surface organic synthesis techniques [1]. Bottom-up synthesized graphene nanoribbons have promising electronic properties for high performance field effect transistors (FETs) and ultra-low power devices such as tunneling FETs. However, the short length, wide band gap, and random orientation of GNRs have prevented the fabrication of devices with the expected performance and switching behavior [2]. In this talk, I will discuss our progress in integrating bottom-up synthesized graphene nanoribbons into devices. I will show our results on high on-current and high on-off ratio FETs with a 9-atom wide graphene nanoribbon as the channel material [3]. Furthermore, we also fabricated devices with parallel arrays of GNRs transferred from single crystal Au(788), which greatly improves device yield. Finally, I will discuss how we can use graphene nanoribbon heterostructures to design a low-voltage switch [4].

References

[1] Cai, J. et al. Nature
466, 470–473 (2010).

[2] Bennett, P. B. et al. Applied Physics Letters
103, 253114 (2013).

[3] Llinas, J. P. et al. Nature Communications
8, 633 (2017).

[4] Smith, S., Llinás, J. P., Bokor, J. & Salahuddin, S. IEEE Electron Device Letters
39, 143–146 (2018).
Synthesis and Application of Molybdenum Disulphide Thin Layers Grown By Chemical Vapour Deposition
Authors: Mula Raju , Biswas Kaushik , Annapurna Kalyandurg , Jacob Chacko
Published: February 2020

Recently, two-dimensional (2D) molybdenum disulfide (MoS2) thin layers have been considered for the next generation optoelectronic devices, field effect transistors (FETs) and flexible electronics due to their flexibility, ultra-thin dimensions and excellent semiconducting properties. In this study, large area MoS2 mono-layers/ bi-layers/ tri-layers were grown on different types of substrates (SiO2/Si, Si) by chemical vapour deposition (CVD) technique. The MoS2 thin layers were synthesized at high temperatures (800 oC, 900 oC and 1000 oC) by using solid source precursors of molybdenum trioxide and sulphur in an argon atmosphere. The as-grown MoS2 thin layers were systematically characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and to determine the surface morphology, respectively. Further, the thickness and surface roughness of the grown MoS2 thin layers were analysed by atomic force microscopy (AFM). Micro-Raman spectroscopy was used to identify the number of grown MoS2 layers and their crystalline quality. Finally, the electrical properties of the grown MoS2 thin layers were evaluated by using DC I-V measurements at room temperature in order to know the resistance of the grown layers.
Removal of Photoresist Residues and Healing of Defects on Graphene Using H2 and CH4 Plasma
Authors: Park Chong-Yun , Son Yongkeun , Jo Hyeong Ku
Published: February 2020

Residual impurities on the surface of graphene after device fabrication degrade the performance of graphene electronic devices. It is important to solve this issue in order to use graphene in electronic devices. In this study, we removed residues using four plasma treatment methods following the photolithography process. The four plasma treatment methods were hydrogen plasma treatment (Process 1, P1), methane plasma treatment (Process 2, P2), hydrogen plasma pre- and methane plasma post-treatment (Process 3, P3), and hydrogen-methane mixed plasma treatment (Process 4, P4). The results were analyzed using atomic force microscopy and Raman spectroscopy. Of the four treatments, Process 4 showed the most remarkable removal of photoresist residue and healing of the damaged graphene film, thereby improving the mobility of the graphene. The total resistance of the graphene channel in the device was also considerably reduced. These results reveal that a hydrogen-methane mixed plasma treatment (P4) could be a powerful method for removing residue on the surface of graphene after the lithography process.
Scanning Photoelectron Spectroscopy of Tapered Cross Sections of Perovskite Solar Cells: Element Distribution, Band Alignment, Space Charge Layers and Photo-Voltage Distributions
Authors: Jaegermann Wolfram , Mayer Thomas
Published: February 2020

Photoelectron spectroscopy is used for the characterization of chemical and electronic properties of semiconductor interfaces. As the information depth is extremely low, inner interfaces of device stacks are analyzed by depositing sequentially the respective contact material onto the base material in vacuum chambers integrated with the PES system. Thus elemental distribution including ionic state of the materials in contact as well as doping and electronic potential distribution induced by interface charge transfer can be monitored. For devices with non planar architecture or deposition processes not compatible with vacuum as both are given for perovskite solar cells, this procedure is not applicable.

In this paper we demonstrate the photoelectron spectroscopic analysis of a complete working perovskite solar cell ranging from crystalline TiO2 on FTO front contact over perovskite intermixed in meso-TiO2 and the perovskite layer to Spiro-MeoTAD and Au back contact by preparing a tapered cross section of the cell stack. A wet chemically prepared mixed FAPbI3 MAPbBr3 solar cell of 18% efficiency is analyzed. As the analyzed spot size is in the range of the layer thicknesses a small angle tapered edge is prepared by polishing in order to drastically increase the local resolution across the cell stack. The tapered cross section is measured in the dark and under open circuit operando conditions.

Using core level photoelectron spectroscopy the elemental distributions which forms in the wet chemical deposition process of the precursor solution are derived from the measured core level intensities. In addition, the electronic contact potentials are mapped, which allows conclusions on the band diagram of the full stack. We find that the perovskite absorber is n-type and a strong band bending in the p-type spiro-MeOTAD hole transport contact layer. Shifts of the core level emission binding energies under in situ illumination indicate that the cell photo-potential is induced to a large part at this back contact. We conclude that the diffusion voltage of the cells is not formed across the TiO2-perovskite front contact but mostly across the perovskite/SpiroMeOTAD/Au back contact.

This example demonstrates that the wealth of information that can be obtained on full devices applying the method of scanning photoelectron spectroscopy on device cross section using a tapered edge approach.
Improved Efficiency and Stability of Perovskite Solar Cells By Structure Engineering
Authors: Dai Qilin
Published: February 2020

Considering recent highly energy demand of our society, it is obvious that the development of renewable energy sources and high-efficiency devices are very necessary. Solar cells are believed to be a kind of very promising candidate to replace fossil energy to solve the energy crisis problem because solar energy is renewable, free, clean energy. Currently, Perovskite solar cells (PSCs) dominate solar cell research due to their high efficiency, which is reported to achieve an efficiency of ~23%. However, it is still challenging to obtain PSCs with high efficiency and high stability for outdoor applications due to the decomposition of perovskite material under moisture, UV light and thermal conditions. In our work, we used structure engineering including interface layer manipulation and nanoparticle incorporation to improve the stability and efficiency of PSCs. Moisture stability of the devices were improved by hydrophobic layer introduced into PSCs. The hydrophobic layer prevented the moisture penetrating the devices, leading to improved moisture stability. UV light stability was enhanced by light converter, which can convert UV light into visible light. The converted visible light can be absorbed by the perovskite layer to contribute to the photocurrent of the devices. Therefore, both the efficiency and the UV light stability are improved by the UV light converter. Thermal stability of the devices was enhanced by bismuth doping into perovskite film, leading to better crystallinity, uniform morphology, less grain boundaries, and larger grain sizes, which benefited the PSC device performance. To increase the light harvesting, Metallic nanostructures are also introduced into devices to increase the optical path length of the incident light leading to improved light harvesting and increased device efficiency. PSC efficiency was improved to 20% by structure engineering, which is very promising for practical applications. In addition, solar energy storage effect is also obtained by integrating afterglow fluorescence nanomaterials into PSC devices to realize solar cells working in dark conditions.
(Invited) Dynamic Chromism in Metal Halide Perovskites
Authors: Wheeler Lance M.
Published: February 2020

Metal halide perovskite materials feature ionic bonds with low formation energy that are in stark contrast to the highly-covalent bonds found in its semiconductor counterpart, Silicon. This talk will explore the dynamic manipulation of these ionic bonds to control the absorption and emission properties of nanostructured and bulk thin film perovskites. We have demonstrated molecules at the perovskite surface can lock the material into a metastable crystal phase that is visibly-absorbing, thus making it better than the thermodynamically-favored, visibly-transparent phase for photovoltaics. We sho alternative chemistries have the opposite effect - molecular interactions induce a phase transformation into a visibly-transparent state of the material. Chromism may also be controlled using molecular intercalation into the perovskite structure to bleach or blueshift absorption and emission. We show this effect may be driven using electric fields or thermal gradients, which led to the discovery of an unexplored class of "smart" solar cells that dynamically bleach or become colored in response to these stimuli. We conclude with a discussion on the promise of such devices and speculation on what the future holds for them.
(Invited) Designing Novel Organic Small Molecular As Electron Transport Layers for Planar Perovskite Solar Cells
Authors: Zhang Qichun
Published: February 2020

Compared to the traditional-architecture perovskite photovoltaics (n-i-p type), which use metal oxide as electron transport layers(ETLs) and organic semiconducting materials as hole transport layers, the fabrication of metal-oxide-free, solution-processed inverted perovskite solar cells (PSCs) is more desired because of low-temperatures and all-solution-based applications in future commercial PSC modules. In a typical configuration of inverted PSCs, the widely used ETL compound is the fullerene-based phenyl-C61-butyric acid methyl ester (PCBM), which currently is the best organic ETL material. The cost of this compound is very high, and the morphology and electrical properties are very sensitive to experimental conditions. In this talk, I will talk the recent progress of new organic ETL materials in my group for the replacement of PCBM in inverted PSCs. We believe that easily-accessible simple n-type small molecules are promising ETL candidates to further propel inverted PSCs to practical applications.

References

Ning Wang, Kexiang Zhao, Tao Ding, Wenbo Liu, Ali Said Ahmed, Zongrui Wang, Miaomiao Tian, Xiao Wei Sun,* Qichun Zhang*, “Improving Interfacial Charge Recombination in Planar Heterojunction Perovskite Photovoltaics with Small Molecule as Electron Transport Layer”, Adv. Energy Mater. 2017, DOI: 10.1002/aenm.201700522.

Pei-Yang Gu, Ning Wang, Chengyuan Wang, Yecheng Zhou, Guankui Long, Miaomiao Tian, Wangqiao Chen, Xiao Wei Sun,* Mercouri G. Kanatzidis*, Qichun Zhang,* “Pushing up the efficiency of planar perovskite solar cells to 18.2% with organic small molecular as electron transport layer”, J. Mater. Chem. A. 2017, 5, 7339 – 7344.

Pei-Yang Gu, Ning Wang, Anyang Wu, Zilong Wang, Miaomiao Tian, Zhisheng Fu,* Xiao Wei Sun,* Qichun Zhang* “Azaacene Derivative as Promising Electron Transport Layer for Inverted Perovskite Solar Cells”, Chem. Asian J. 2016, 11(15), 2135–2138.
(Invited) Elucidating Proton Migration in Hybrid Organic Inorganic Perovskites and the Effect of Surface Passivation
Authors: Bassani Dario M. , Sadhu Subha , Buffeteau Thierry , Hirsch Lionel
Published: February 2020

Perovskites in general are known to possess ionic conductivity and ion movement has been postulated to be directly or indirectly responsible for their lack of long-term stability and unusual behavior, including hysteresis. Therefore, understanding ion migration in perovskites is of major importance in improving their performance. Ion movement in HOIPs may occur extrinsically, i.e. from one of the contacts, or take the form of ion migration, where an ion is displaced from an occupied to a vacant site. Numerous studies confirmed the rotational movement of the MA ions within the inorganic cage formed by the PbI2octahedra, which has been associated to the temperature and frequency dependence of the complex permittivity.

To test the relationship between MA rotation and the frequency dispersion in the dielectric response in HOIP materials, we conducted a series of experiments in which the hydrogen atoms in MAI were selectively substituted with deuterium. Our results (Figure 1) unambiguously demonstrate that deuteration of the ammonium group leads to a large inverse kinetic isotope effect indicative of proton tunneling in HOIP materials. Deuteration of the methyl group in MA induces a normal secondary KIE that is consistent with these findings.1,2

REFERENCES

1. Y.-F. Chen, Y.-T. Tsai, L. Hirsch, D. M. Bassani J. Am. Chem. Soc., 2017, 139, 16359 – 16364.

2. S. Sadhu, K. Aqueche, T. Buffeteau,J.-M. Vincent,L. Hirsch,D. M. BassaniMat. Horiz., 2018, DOI: 10.1039/C8MH01119B.

Figure 1
(Invited) Novel Plasmonic Nanomaterials for Near Infrared Light Energy Conversion
Authors: Teranishi Toshiharu
Published: February 2020

The structure of nanomaterial determines their individual properties and assembled structures they can form [1,2].Highly efficient photoenergy conversion in heterostructured nanocrystals (HNCs) requires the formation of epitaxial heterointerfaces and band alignment engineering.One of the phases in HNCs should hold the light absorbing ability, such as narrow band gap semiconductor [3-6] and plasmonic material [7-9].Special attention has been given to the HNCs with the combination of plasmonic semiconductor/semiconductor [7-9], where the near infrared plasmon-induced carrier transfer takes place to realize the long-lived charge separation and near infrared light energy conversion into electricity [8] and chemical energy [7,9].

[1] Wu, H.-L.; Teranishi, T. et al.
Science
2016, 351, 1306.

[2] Kanehara, M.; Arakawa, H.; Honda, T.; Saruyama, M.; Teranishi, T. Chem. Eur. J.
2012, 18, 9230.

[3] Saruyama, M.; So, Y.-G.; Kimoto, K.; Taguchi, S.; Kanemitsu, Y.; Teranishi, T. J. Am. Chem. Soc.
2011, 133, 17598.

[4] Sakamoto, M.; Teranishi, T. et al.
Chem. Sci.
2014, 5, 3831.

[5] Teranishi, T.; Samamoto, M. J. Phys. Chem. Lett.
2013, 4, 2867. (Perspective)

[6] Sakamoto, M.; Teranishi, T. et al.
Nanoscale
2016, 8, 9517.

[7] Lian, Z.; Sakamoto, M.; Teranishi, T.et al.
Nat. Commun.
2018, 9, 2314.

[8] Sakamoto, M.; Teranishi, T.et al.
Nat. Commun., accepted.

[9] Lian, Z.; Sakamoto, M.; Teranishi, T. et al.
J. Am. Chem. Soc., accepted.
(Invited) Multi-Electron Harvesting and Catalysis Using Plasmonic Nanoparticles: A Mechanistic Understanding
Authors: Jain Prashant K
Published: February 2020

Multi-electron redox reactions are known to be kinetically sluggish and there has been an ongoing search for synthetic catalysts for such reactions. In recent work from my laboratory, plasmonic nanoparticles have been found to photocatalyze multi-electron processes such as CO2 reduction and the condensation of ethylene to graphene. However, there is a need for mechanistic understanding and improved control of multi-electron-driven chemistry on plasmonic catalysts. We have studied in detail the transfer of hot electrons and holes from plasmonically excited nanoparticles to model redox species. We have found that under continuous light illumination and conditions favoring charge separation, plasmonic nanoparticles become significantly photocharged and multi-carrier harvesting becomes prevalent. Further, to understand the light-driven pathway for CO2 reduction on plasmonic nanoparticles, we have monitored the photoreaction in-situ on the single-nanoparticle-level using surface enhanced Raman scattering. From the reactive intermediate captured in the course of spectroscopic monitoring, the mechanism by which plasmonic excitation activates CO2 is beginning to be understood.