ICMCTF2019 Session F3-TuA: 2D Materials: Synthesis, Characterization, and Applications

Tuesday, May 21, 2019 1:40 PM in Room Pacific Salon 6-7
Tuesday Afternoon

Session Abstract Book
(294KB, May 5, 2020)
Time Period TuA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2019 Schedule

Start Invited? Item
1:40 PM Invited F3-TuA-1 Roll-to-roll Plasma Chemical Vapor Deposition for Scalable Graphene Production
Timothy Fisher (UCLA, USA); Majed Alrefae (Purdue University, USA)
Recently, roll-to-roll (R2R) chemical vapor deposition (CVD) processes have been implemented to produce graphene with substrate feed rates ranging from 5-100 mm/min. However, this production rate must increase much further to make graphene a feasible product in semiconductor and materials manufacturing industries. Plasma sources can be applied to increase the graphene deposition rate, and additionally, to decrease energy input. This work will describe the implementation of a radio frequency plasma R2R CVD process to deposit graphene on copper and nickel foils, and carbon fibers. The growth process takes advantage of the high-temperature plasma gas that produces active carbon species to accelerate growth kinetics. Thus, supplemental heating of the substrate is unnecessary when using plasma, in contrast to thermal CVD systems that consume energy to heat the substrate and to decompose the carbon gas source. In situ temperature measurements of the substrate in the plasma region confirm the plasma’s ability to heat the substrate to the 1200-1500 K range depending on the plasma power. From these real-time temperature measurements, a heat transfer model is developed and validated to determine the substrate temperature profile during R2R graphene growth. The effects of plasma power and web speed on substrate temperature are explored and correlated to graphene quality. The results indicate that graphene growth on Cu foil is most significantly influenced by the in-plasma substrate temperature, whereas growth on Ni foil is controlled by the substrate cooling rate, which is evaluated from the heat transfer model. Furthermore, the plasma environment is characterized by optical emission spectroscopy (OES) to optimize graphene growth and assess the impact of ion bombardment. The OES results suggest that the quality of graphene deposited on Cu foil is enhanced with increased CH emission and decreased emission from O, H, Ar+, C2, and CN. The process characterization techniques aid in controlling and optimizing graphene growth in a large-scale setup, including graphene quality as a function of reactor pressure and nitrogen mole fraction with associated uncertainties obtained from statistical analysis. The talk will include a discussion of applications of the resulting materials in energy and biosensing technologies, as well as plans for a new MHz plasma R2R system supplemented by solar heating.
2:20 PM F3-TuA-3 Magnetron Sputtered MoS2/C Nanocomposites as Highly Efficient Electrocatalyst in Hydrogen Evolution Reaction
Samuel Rowley-Neale, Marina Ratova (Manchester Metropolitan University, UK); Lukas Fugita (University of Sao Paulo, Brazil); Graham Smith (University of Chester, UK); Amer Gaffar, Justyna Kulczyk-Malecka, Peter Kelly, Craig Banks (Manchester Metropolitan University, UK)

The design and fabrication of an inexpensive and highly efficient electrocatalyst for the hydrogen evolution reaction (HER), were performed by the route of magnetron sputtering. Molybdenum disulfide (MoS2) was coated directly onto the nanocarbon (C) powder support. Sputtering time was explored as a function of physiochemical composition of MoS2/C nanocomposites, and its performance in HER. Increased sputtering time gave rise to materials with different compositions and oxidation states of Mo ions, Mo4+ and Mo6+, associated with sulfur anions (sulfide, elemental and sulfate) and improved HER outputs. The physiochemical characterisation of the MoS2/C nancomposites as a function of sputtering time was evaluated using scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman Spectroscopy. An optimised sputtering time of 45 minutes was used to fabricate MoS2/C nanocomposites. This gave rise to an optimal HER performance in regards to its onset potential (-0.44 mV vs saturated calomel electrode (SCE)), achievable current (-1.45 mVs-1) and Tafel value (43 mVdec-1) for the compositions rich in Mo4+ and sulfide (MoS2). This bespoke fabricated MoS2/C nanocomposites were incorporated into the bulk ink utilised in the fabrication of screen-printed electrodes (SPEs) to allow improved electrical wiring to the MoS2/C and to produce scalable and reproducible electrocatalytic platforms. The MoS2/C-SPEs displayed far greater HER catalysis with a 450 mV reduction in the HER onset potential and a 1.70 mA cm− 2 increase in the achievable current density (recorded at − 0.75 V vs SCE), compared to a bare/unmodified graphitic SPE. The approach of using magnetron sputtering to modify carbon with MoS2 facilitates the mass production of stable and effective electrode materials for possible use in electrolysers, which are cost competitive to platinum (Pt) and mitigate the need to use time consuming and low-yield exfoliation techniques, typically used to fabricate pristine MoS2.

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2:40 PM F3-TuA-4 HIPIMS Graphene on Copper for Heat Spreading
Chun-Ming Chen, En-Yi Liao, Ping-Yen Hsieh, Ying-Hung Chen, Ju-Liang He (Feng Chia University, Taiwan)

The heat generated from electronic devices such as light emitting diodes, batteries, and highly integrated transistors is one of the major causes limiting their performance and reliability. The extraordinarily high thermal conductivity of graphene has let intensive studies for use as a heat spreader. A strategy of further enhancing the thermal conductivity by growing graphene layer on copper will thus proposed in this study. Based on our previous study, it is able to grow graphene layer on copper foil at relative low temperature by using high power impulse magnetron sputtering (HIPIMS) equipped with synchronized substrate bias. The thermal conductivity of the graphene-on-copper (GOC) layer structure was measured, here in this study, based on Angstrom’s method. The thermal conductivity of GOC was significantly enhanced as compared to bare copper foil alone. This is due to epitaxial graphene on copper generated low interfacial thermal resistance, and intrinsic high thermal conductivity of graphene. Finally, a strong correlation between graphene layer thickness and thermal conductivity was reported.

3:00 PM F3-TuA-5 Tailoring Optical Properties of Two-Dimensional Transition Metal Dichalcogenides Via Photonic Annealing
Rachel Rai, Kim Gleibe (University of Dayton, Air Force Research Laboratory, USA); Nicholas Glavin (Air Force Research Laboratory, Wright-Patterson AFB, USA); Robert Wheeler (UES, Inc., Air Force Research Laboratory, USA); Richard Kim (Air Force Research Laboratory, Wright-Patterson AFB, USA); Ali Jawaid (UES, Inc., Air Force Research Laboratory, USA); Luke Bissell (Air Force Research Laboratory, Wright-Patterson AFB, USA); Christopher Muratore (University of Dayton, USA)
Semiconducting transition metal dicahlogenides (TMDs) exhibit unique combinations of physical properties at thicknesses of less than 5 molecular layers. For example, mechanical flexibility and photoluminescence (PL) in the visible to near infrared (NIR) frequencies are not properties that are commonly observed in a single material, but are routinely measured for materials such as 2D MoS2 and WSe2. Such properties make TMDs attractive candidates for the next generation of flexible and wearable opto-electronic technologies. Incorporation of TMDs into commercial applications is currently limited, however, by challenges associated with synthesis of large area, device-quality films with tunable properties. Our work encompasses diverse innovative techniques to tailor optical properties of TMD thin films by controlling their area, thickness, crystalline domain size, defect density and uniformity during and after processing. We begin by application of thin amorphous films of WSe2 and other TMDs on both flexible and rigid substrates via vapor phase and liquid phase application over large areas. We then illuminate the amorphous film with diverse light sources, including lasers (visible-IR), broad-band xenon lamps, and nanoscale electron beams. WSe2 was selected as a model material due to high quantum yield at room temperature. Tailoring the ‘structure’ of the amorphous material via modulation of the energy flux during magnetron sputtering provides an opportunity to model homogeneous or heterogeneous crystallization during illumination by controlling the density of pre-existing nuclei. Crystallization kinetics were examined by in situ analysis of real-time images and electron diffraction patterns. The amorphous-crystalline conversion is correlated to 2D growth theory and contrasting elements of 2D versus 3D growth are highlighted. A significant increase in photoluminescence intensity is accompanied by a change in crystal edge density, consistent with observations that PL originates preferentially from defective regions of 2D WSe2. Furthermore, we examine quantum confinement effects on photoluminescence yield in nanoscale crystalline areas (~10 nm) via electron beam irradiation .
3:20 PM COMPLIMENTARY REFRESHMENTS IN EXHIBIT HALL
4:00 PM F3-TuA-8 Mechanism of Formation of Nitrogenated Doped Graphene Films, Investigated by In situ XPS During Thermal Annealing in Vacuum
Yannick Bleu (Univ. Lyon, Université Jean Monnet, France); Vincent Barnier, Frédéric Christien (Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, France); Florent Bourquard (Univ. Lyon, Laboratoire Hubert Curien, Université Jean Monnet, France); José Avila (Synchrotron SOLEIL & Université Paris-Saclay, France); Florence Garrelie (Univ. Lyon, Université Jean Monnet, France); Maria-Carmen Asensio (Synchrotron SOLEIL & Université Paris-Saclay, France); Christophe Donnet (Université de Lyon, Université Jean Monnet, France)

The introduction of dopants, such as nitrogen, into the graphene network, is paramount for many applications such as nanoelectronics, nanophotonics, sensor devices and green energy technology. One way consists in thermal heating of a doped solid carbon source, such as an amorphous a-C:N film, in the presence of a metal catalyst, to obtain nitrogenated graphene (NG) layers. The control of such a process requires to investigate diffusion and segregation mechanisms of the graphene precursor through the metal catalyst.

In the present study, the mechanism of atomic diffusion and NG film growth through a nickel catalyst thin film was investigated using in situ X-ray photoelectron spectroscopy (XPS) performed during thermal heating responsible for NG synthesis. Amorphous a-C:N films, containing 16%at. nitrogen, 10 nm thick, were synthetized by femtosecond pulsed laser ablation on fused silica substrates. A 150 nm thick nickel film was subsequently deposited by thermal evaporation on the a-C:N films. Thermal annealing at various temperatures (200, 300, 500 and 650°C), with different time durations, were performed in ultra-high vacuum during in situ XPS analysis, to carry out the top surface genesis of the NG film onto the nickel catalyst. FEG-SEM, Raman and X-ray absorption (XAS) spectroscopies were also performed to elucidate the nature and chemical composition of NG films. The diffusion of carbon and nitrogen through the nickel film towards the surface from 300°C was observed, without any graphene signature. Graphene films are formed at the highest temperatures, with a final 3%at. nitrogen content, in both pyrrolic and pyridinic configurations. In addition, the kinetics of carbon surface enrichment observed using in-situ XPS is discussed in the frame of the interface segregation theory and modelled using the Du Plessis approach. The solid-state transformation mechanism responsible for the formation of few-layer NG films is thus investigated.

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4:20 PM Invited F3-TuA-9 Engineering Point and Extended Defects in Transition Metal Dichalcogenides
Hannu-Pekka Komsa (Aalto University, Finland)

Two-dimensional (2D) materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have recently received lots of attention due to their unique material properties and numerous potential applications. The 2D atomic structure can also facilitate distinct defect formation mechanisms and offer new possibilities for defect engineering.

In my talk, I will present the results from layered molybdenum dichalcogenides (MoS2, MoSe2, and MoTe2), where vacancy, substitutional, interstitial, and grain boundary defects are introduced by electron irradiation or by various chemical treatments. Due to the 2D nature, transmission electron microscopy and scanning tunneling microscopy imaging allows direct monitoring of formation and agglomeration of defects as well as of larger structural changes. First-principles calculations are used to provide microscopic insight into the energetics and kinetics of these processes. The gained understanding together with the computationally predicted defect properties can be used to guide future efforts in tailoring the 2D material properties via defect engineering.

5:00 PM F3-TuA-11 Physicochemical and Mechanical Performance of Nylon 6.6 Coated Thin Free-standing Boron-doped Diamond Nanosheets
Robert Bogdanowicz, Mateusz Ficek (Gdansk University of Technology, Poland); Vitezslav Stranak, Jiri Kratochvil (University of South Bohemia, Czech Republic); Marek Szkodo, Jacek Ryl, Michal Sobaszek (Gdansk University of Technology, Poland)

In the following work, we describe studies on the fabrication and the physicochemical performance of thin and free-standing heavy boron-doped diamond (BDD) nanosheets coated by thin nylon 6.6. First, the diamond nanosheets with less than 400 nm of thickness were grown and doped by boron on Ta substrate by using microwave plasma-enhanced chemical vapor deposition technique (MPECVD) [1]. Then, the BDD/Ta samples where covered by 6.6 nylon to improve their stability in harsh environments.

The plasma polymer films, the thickness in the range 500-1000 nm, with different surface energies were obtained by magnetron sputtering of a bulk target. The hydrophilic nitrogen-rich C:H:N :O were prepared by sputtering of nylon 6.6. C:H:N :O as films with high surface energy improves adhesion at ambient condition. However, their disadvantage lays in a natural swelling increasing its volume about of 15% after immersion into an aqueous liquid. This behavior influences diamond-C:H:N :O structure in a wet environment.

The C:H:N :O coated diamond nanosheets were delaminated from Ta substrate creating free-standing nanostructures (Diamond-on-Nylon). The C:H:N :O film fixtures the thin polycrystalline diamond sheets enhancing its mechanical stability and enabling transfer and integration with microelectronic systems.

We have manifested that investigated Diamond-on-Nylon nanostructures possess altered morphology and physicochemical properties, revealed by electron microscopy and Raman spectroscopy. Moreover, the electrical response of investigated nanostructures as conductive electrodes is time-stable and indicates the high activity of the sheets with higher dopant concentrations.

Moreover, the Diamond-on-Nylon is characterized with altered mechanical properties like Young modulus or internal stress. These properties varied strongly with the thickness and density of nylon coverage.

In summary, the Diamond-on-Nylon nanostructures show excellent electrical and thermal conductivity along with high mechanical strength. Composite diamond-on-polymer structures could be further developed for flexible and robust electronic devices or thermal heat spreaders.

Acknowledgments

The authors gratefully acknowledge the financial support of the National Centre for Science and Development Grant Techmatstrateg No. 347324. This work was partially supported by the Science for Peace Programme of NATO (Grant no. G5147). The DS funds of the Faculty of Electronics, Telecommunications, and Informatics are also acknowledged.

References

[1]. Bogdanowicz, Robert, et al. Advanced Functional Materials (2018): 1805242.

[2]. Ryl, Jacek, et al. Carbon 96 (2016): 1093-1105.

Session Abstract Book
(294KB, May 5, 2020)
Time Period TuA Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2019 Schedule