Speaker: Prof. Zakaria (Zak) Y. Al Balushi, Assistant Professor at the University of California, Berkeley.
Title: "Direct Integration of 2D Materials for Next Generation Electronic Devices."
Date: Monday, December 8, 2025 - Time: 4 PM
Hi Tea & Coffee: 5 PM
Venue: CeNSE Seminar Hall

Abstract:

Two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS2), are emerging 
as key materials for next-generation electronics, addressing challenges in the miniaturization 
of silicon-based technologies. Despite progress in scaling-up 2D materials, integrating them 
into functional devices remains challenging, particularly in the context of three-dimensional 
integration. In the first part of my talk, I will present a scalable method for growing high-quality 
mono- to few-layer MoS2 on large wafers using a spin-on precursor, molybdenum ethyl xanthate. 
This approach facilitates the formation of a metastable amorphous molybdenum trisulfide phase, 
which we can then be leveraged for direct heterogeneous integration. We thoroughly investigate 
the growth dynamics and associated versatile features using comprehensive characterization, 
reactive force-field molecular dynamics simulations, and Density Functional Theory. 
Our method allows precise control over film thickness, grain size, and defect density, 
yielding wafer-scale monolayer MoS2 with reliable optical properties comparable to as-exfoliated 
samples. Additionally, we achieve area-selective formation of MoS2 and the direct deposition 
of sub-5 nm high-k oxides using atomic layer deposition, without the need for seeding or surface 
functionalization. This process enables the fabrication of complex superlattice structures, 
top-gated FETs, and memristor devices, all from a single-source chemistry. Our findings 
highlight the versatility of spin-on metal xanthate chemistries for the synthesis and integration 
of transition metal dichalcogenides (MoS2, WS2, NbS2, ReS2, etc.), paving the way for advanced 
nanoscale fabrication processes and enhancing the commercial viability of 2D materials in electronics.

Moreover, forming heavily doped regions in two-dimensional materials, like graphene, is a 
steppingstone to the design of emergent devices and heterostructures. In the second part of my talk, 
I will present a selective-area approach to tune the work-function and carrier density in monolayer 
graphene by spatially synthesizing sub-monolayer gallium beneath the 2D-solid.  Localized metallic 
gallium is formed via precipitation from an underlying diamond-like carbon (DLC) film that was 
spatially implanted with gallium ions. Controlling the interfacial precipitation process with 
annealing temperature allows for spatially precise ambipolar tuning of the graphene work-function 
that remains stable even in ambient conditions. Our theoretical studies corroborated the role of 
gallium at the heterointerface on charge transfer and electrostatic doping of the graphene overlayer, 
with charge carrier densities from ~1.8×10^10 cm^(-2) (hole-doped) to ~7×10^13 cm^(-2) (electron-doped) 
as measured by in-situ and ex-situ measurements. The extension of this doping scheme to 
other implantable elements into DLC provides a new means of exploring the physics and 
chemistry of highly doped overlayed two-dimensional materials.

Finally, metalorganic chemical vapor deposition (MOCVD) has become a pivotal technique for developing 
wafer-scale TMD 2D materials. If time permits, I will discuss our recent findings on the impact 
of MOCVD growth conditions on achieving uniform and selective polymorph phase control of 
MoTe2 over large wafers. We demonstrated the controlled and uniform growth of few-layer 
MoTe2 in pure 2H, 1T’, and mixed-phases at various temperatures on up to 4-inch C-plane 
sapphire wafers with hexagonal boron nitride templates. At 600oC, high-quality 2H-MoTe2 
was obtained within a narrow temperature window, verified with absorption and TEM analysis. 
In addition, we observed strong exciton-phonon coupling effects in multiwavelength Raman 
spectroscopy when the excitation wavelength was in resonance with the C-exciton. Our findings 
indicate that temperature-induced Te vacancies play a crucial role in determining the MoTe2 phase. 
This study highlights the importance of precise control over the MOCVD growth temperature to 
engineer the MoTe2 phase of interest for device applications.

Biography:

Zak Al Balushi is an assistant professor in the department of Materials Science and Engineering 
at University of California, Berkeley, and a faculty scientist in the Materials Science Division 
at the Lawrence Berkeley National Laboratory. Zakaria received his B.S. (2011), M.S. (2012) 
in Engineering Science and his Ph.D. (2017) in Materials Science and Engineering all from The 
Pennsylvania State University. His early work focused on integration and fabrication of silicon
 nanowire devices, then on the growth of group-III nitride semiconductors, in situ metrology during 
MOCVD growth, epitaxial graphene and the discovery and characterization of unconventional low-dimensional
 materials and heterostructures. Prior to his appointment at the University of California, Berkeley, 
he held two postdoctoral fellowships: the Resnick Prize Fellowship in Applied Physics and Materials 
Science and the NSF Alliances for Graduate Education and the Professoriate (AGEP) Fellowship both at 
the California Institute of Technology under the supervision of Professor Harry Atwater. At the University
 of California, Berkeley, his research group continues to expand in this area and beyond, creating new 
synthesis and integration schemes for emerging low-dimensional materials. He is currently serving on the
 editorial board of Communications Materials, is an elected executive committee member for the American 
Association for Crystal Growth and recently named “Four rising stars who are reshaping nanoscience” by 
Nature [Nature 608, S12-S13 (2022)]. He is also a SK Hynix Faculty Fellow, Society of Hellman Fellow, 
a CIFAR Azrieli Global Scholar in Quantum Materials and a recipient of the NSF CAREER and Micron 
Corporation Early Career Awards in 2022.


Host Faculty:  Prof. Srinivasan Raghavan