ALD2023 Session NS-MoA: 2D Growth

Monday, July 24, 2023 4:00 PM in Regency Ballroom A-C
Monday Afternoon

Session Abstract Book
(298KB, Jul 29, 2023)
Time Period MoA Sessions | Abstract Timeline | Topic NS Sessions | Time Periods | Topics | ALD2023 Schedule

Start Invited? Item
4:00 PM Invited NS-MoA-11 A Modified ALD-like Approach to Demonstrate Exceptionally Thin Dielectric Layer Growth on 2D Materials
Daire Cott, Stefanie Sergeant, Raf Rennen, Groven Benjamin (IMEC Belgium); Dennis Lin (IMEC, Belgium); Xiangyu Wu (IMEC Belgium); Zaoyang Lin (IMEC Belgium,); Tom Schram, Quentin Smets, Inge Asselberghs, Pierre Morin (IMEC Belgium)

Uniform deposition of extremely thin dielectrics on 2D materials is sought after to exploit the potential of 2D materials in future nano-electronic devices. To that end, significant challenges must be overcome. The surface of thin layers of pristine 2D materials can be seen as fully passivated where all covalent bonding is located parallel to the plane and layers are bound together by Van der Waals forces. To form an effective interface between the 2D material surface and an oxide covering layer a lowering of the overall surface energy must be achieved. Interestingly, 2D materials already possess an extremely low surface energy (~40 mJ/m2)[1] indicating that wetting is a significant challenge. Additionally, when considering ALD - the method of choice to form scaled high-k dielectric layers on Si device technology - which relies on the ability to form a uniform covalently bound atomic layer as the starting surface to nucleate subsequent layers. Conversely, to maximize 2D materials electronic potential the pristine nature of the 2D material should be maintained without damaging the in-plane covalent bonding of the system. This excludes many well-established physical deposition techniques such as PVD sputtering or even plasma enhanced ALD techniques where damage to the 2D layer can be created, inducing defects that although will enhance the nucleation of oxides will simultaneously degrade the electrical performance in nanoscale devices.

In this presentation, a method to overcome the inert nature of 2D materials to support oxide formation without inducing defects into the 2D material will be discussed. Insights into the formation mechanism of thin Aluminum oxide based layers on 2D materials will be outlined with particular focus on two types of transition metal dichalcogenides namely, WS2 and MoS2. Combining our method with 5nm HfO2 to form the top oxide in lab based dual gated MOSFETs a low equivalent oxide thickness (EOT) of 2.1nm was demonstrated [2], Additionally, the upscaling of this approach to large area 300mm 2D material covered substrates will be also discussed [3]

[1]: Gaur et al., Nano Lett. 2014, 14, 4314−4321.

[2]: Wu et al., 2021 IEEE International Electron Devices Meeting (IEDM), 7.4. 1-7.4. 4

[3]: Smets et al., 2021 IEEE International Electron Devices Meeting (IEDM). IEDM21-725

4:30 PM NS-MoA-13 Water-free SbOx-ALD-process for Coating Bi2Te3-particles
Sebastian Lehmann, Fanny Mitzscherling, Shiyang He, Jun Yang, Martin Hantusch, Amin Bahrami, Kornelius Nielsch (Leibniz Institute for Solid State and Materials Research)

We developed a water-free Atomic Layer Deposition (ALD) process to homogeneously deposit SbOx using SbCl5 and Sb-Ethoxide as precursors reported for the first time. The coating is applied on Bi2Te3 particles which were synthesized via the solvothermal route to enhance the thermoelectric properties (i.e. Seebeck coefficient, thermal and electrical conductivity) via interface engineering. The amorphous character of the coating was shown by the missing reflexes on the XRD diffractograms. A shift from the oxidation state +III to +V of the Sb-species was observed towards increasing SbOx-coating layer thickness using XPS. Additionally, a peak shift of the Sb 3d5/2 + O 1s peak indicating increased n-type doping of the material. Electrical measurements of spark plasma sintered bulk samples confirmed the doping effect by a decreased specific resistivity with increasing SbOx-layer thickness. The Seebeck coefficient was improved for the coated samples compared to the uncoated reference sample while the total thermal conductivity remained almost constant resulting in an enhancement of the Power factor and the zT. The results distinctly show that surface engineering via Powder ALD is an effective tool to improve key properties of thermoelectric materials.

4:45 PM NS-MoA-14 2D FeSX Nanosheets by ALD: Electrocatalytic Properties Towards Hydrogen Evolution Reaction
Raul Zazpe, Jhonatan Rodriguez Pereira, Sitaramanjaneya Thalluri, Ludek Hromadko (University of Pardubice); David Pavliňák, Eva Kolíbalová (Brno University of Technology); Hanna Sopha, Jan Macak (University of Pardubice)

In the last years, the search of novel and cost-effective catalysts to replace costly and scarce noble metals drove to explore a wide range of materials, such as transition metal dichalcogenides (TMDCs), phosphides, carbides, nitrides among others.[1] Inspired by the first experimental evidences reported on the catalytic activity of MoS2 edge sites,[2] an intense researching work has been devoted in exploring the catalytic properties of other 2-dimensional (2D) TMDCs, e.g. WS2, MoSe2, and MoTe2.[3–6] 2D materials offer unique structural, optical and electronic properties as compared to the bulk counterparts. In addition, they show significant prospects as catalyst mainly due to the flake-like morphology with minimal thickness, high surface-to-volume ratio, and capability of surface functionalization and tuning the catalytically active edges sites.[7] Among the TMDCs materials, the catalytic properties of iron sulfide and its different phases, namely FeS2, Fe3S4 and FeS, have been largely overlooked and barely explored compared to other TMDCs, despite the relative low cost and toxicity and the high natural abundance of iron and sulfur.

Herein, we present 2-dimensional (2D) FeSx nanosheets of different sizes as an electrocatalyst towards hydrogen evolution reaction (HER) in alkaline media. The 2D FeSx nanosheets were synthesized by applying different numbers of Atomic Layer Deposition (ALD) cycles on TiO2 nanotube layers and graphite sheets as active supporting materials. The electrochemical results confirmed the electrocatalytic activity with an excellent long-term stability and an enhanced catalytic activity reflected by a noteworthy drop of the HER overpotential. Using a range of characterization techniques, it was unveiled that the origin of the enhanced catalytic activity was caused by the synergistic interplay between in situ morphological and composition changes experienced by the 2D FeSx nanosheets during HER. Under the application of a cathodic potential in alkaline media, it was observed that the original 2D FeSx nanosheets transformed to iron oxyhydroxide-iron oxysulfide core-shell nanoparticles, which exhibited a higher active catalytic surface and newly created Fe-based HER catalytic sites. [8]

[1] P. Yu et al, Nano Energy2019, 58, 244–276.

[2] T. F. Jaramillo et al Science (80-. ).2007, 317, 100–102.

[3] J. Bonde et al, Faraday Discuss.2009, 140, 219–231.

[4] J. C. McGlynn et al., Nat. Commun.2019, 10, 4916.

[5] M. Motola et al., Nanoscale2019, 11, DOI 10.1039/c9nr08753b.

[6] R. Zazpe et al., Appl. Mater. Today2021, 23, 101017.

[7] S. H. Noh et al, J. Mater. Chem. A2018, 6, 20005–20014.

[8] R. Zazpe et al, submitted.

5:00 PM NS-MoA-15 300 mm Wafer-Scale and Self-limiting Layer Synthesis of 2D MoSe2 by Atomic Layer Deposition
Angelica Zacatzi, Michael Miller, Ravi Kanjolia, Thong Ngo (EMD Electronics)

2D Transition metal dichalcogenide (TMD) materials have opened a route to continue the down-scaling trend of semiconductor technology. As part of the TMD materials library, MoSe2 has demonstrated itself to be a very promising candidate as a channel material for transistor devices, achieving field-effect mobilities up to ~ 150 - 200 cm2/(V s). [1]

The synthesis of high quality 2D MoSe2 is required to unlock the potential application of this material in electronic devices. However, to date, there are limited reports on MoSe2 synthesis in comparison to the variety of techniques used to obtain MoS2 in the literature. A previous approach describes a two-step MoSe2 deposition, where MoO3 is first deposited by atomic layer deposition (ALD) onto a substrate followed by a selenization process performed at 900°C [2]. While this route produced 2D MoSe2, a single, lower temperature process would be preferred to better meet the high-volume manufacturing demands in the semiconductor industry. In this work, we developed a process to synthesize uniform, 300 mm wafer-scale 2D MoSe2 films using conventional ALD. A detailed study of the MoSe2 ALD process window, from 425 °C - 600 °C, correlated with the composition and structural properties of the MoSe2 film will be presented. The resulting MoSe2 films from the optimized process are stoichiometric and present a 2H phase. Furthermore, this novel optimized ALD process exhibited a self-limiting layer synthesis-like behavior [3], allowing the precise control over the MoSe2 thickness.

The proposed ALD approach presented in this work contributes to the efforts in developing high-quality 2D materials for the realization of atomically thin channel materials.

[1] N. R. Pradhan, D. Rhodes, Y. Xin, S. et al., ACS Nano, 8, 8, 7923–7929 (2014).

[2] T.-J. Dai, X.-D. Fan, Y.-X. Ren, et al. Mater. Sci. 53, 8436–8444, (2018).

[3]Y. Kim, JG. Song, Y. Park, et al. Sci Rep 6, 18754 (2016).

5:15 PM NS-MoA-16 Wafer-Scale Controlled Growth of Two-Dimensional Metal Dichalcogenides Through Atomic Layer Deposition and Top-Bottom Epitaxy
Chanyoung Yoo, Wonho Choi, Jeong Woo Jeon, Byongwoo Park, Gwangsik Jeon, Sangmin Jeon, Cheol Seong Hwang (Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, Seoul National University)

Two-dimensional (2D) metal dichalcogenides (MDCs) are a class of MX2 compounds that exhibit unique electrical, optical, and mechanical properties due to their 2D van der Waals (vdW) structures1. Among them, Sb2Te3 is a p-type semiconductor with a narrow direct bandgap that has the potential for applications in a topological insulator2, thermoelectric3, and optoelectronic. Sb2Te3 is also utilized in phase-change memories, where the pseudobinary GeTe-Sb2Te3 tie line compositions are the primary materials4. To utilize the unique properties of Sb2Te3 and for other 2D MDCs, continuous films with ultrathin thicknesses (<< ~10 nm) must be formed on substrates. However, depositing 2D MDCs such as Sb2Te3 with ultrathin thickness is challenging due to their tendency to grow in an island-type non-uniform manner, exhibiting prominent plate-shaped morphologies.

In this study, a novel atomic layer deposition (ALD) method utilizing amorphous (a-) GeTe as a buffer layer was developed to change the island-type growth of Sb2Te3 film to layer-by-layer growth, enabling precise control of film thickness with high uniformity, as shown in Figure 1. The Ge atoms in the buffer layer act as anchoring sites where the Sb-precursors can adhere uniformly. After forming a uniform Sb2Te3 layer, the growth was self-terminated by the inert vdW surface (Figure 2a), and the substitutional reaction of Ge atoms with the Sb-precursors dominated the growth. The replacement of Sb atoms formed crystalline (c-) GeSbTe and further Sb2Te3 cycles transformed the c-GeSbTe layer into a pure Sb2Te3 film (Figure 2b). The self-terminated thickness of the Sb2Te3 film was determined by the thickness of the a-GeTe buffer layer (Figure 2c). This new ALD method, referred to as top-to-bottom epitaxial growth, involved depositing the Sb2Te3 film through the displacement and diffusion of Sb atoms from the surface to the substrate (see the overall illustrations in Figure 2d). This approach resulted in conformal c-axis-oriented Sb2Te3 films with ideal layer-by-layer growth. Furthermore, layer-by-layer growth was maintained on contact hole structures (compare Figure 3a-c and 3d-f), exhibiting c-axis orientation along the curvature without any protruding plates, as evidenced by the characteristic vdW gaps of Sb2Te3 parallel to the curved corner. This new ALD method utilizing an amorphous buffer layer holds great potential for application to other 2D MDCs and provides a versatile and scalable platform for their growth.


1 S. Manzeli et al., Nat Rev Mater, 2017.
2 H. Zhang et al., Nat Phys, 2009.
3 L. M. Goncalves et al., Thin Solid Films, 2011.
4 H. S. P. Wong et al., Proceedings of the IEEE, 2010.

View Supplemental Document (pdf)
Session Abstract Book
(298KB, Jul 29, 2023)
Time Period MoA Sessions | Abstract Timeline | Topic NS Sessions | Time Periods | Topics | ALD2023 Schedule