Akinola Oyedele

Oak Ridge National Laboratory | ORNL · Center for Nanophase Materials Sciences

The unique properties of graphene have made it a promising material for integration in future electronic applications. The idealized surface of graphene, atomically-flat and without dangling bonds, offers the opportunity to understand the assembly of organic and inorganic molecules to form a wide range of ordered architectures and functional graphe...

The failure to achieve stable Ohmic contacts in 2D material devices currently limits their promised performance and integration. Here, we demonstrate that a phase transformation in a region of a layered semiconductor, PdSe2, can form a contiguous metallic Pd17Se15 phase, leading to the formation of seamless Ohmic contacts for field-effect transisto...

Most studied two-dimensional (2D) materials exhibit isotropic behavior due to high lattice symmetry; however, lower-symmetry 2D materials such as phosphorene and other elemental 2D materials exhibit very interesting anisotropic properties. In this work, we report the atomic structure, electronic properties, and vibrational modes of few-layered PdSe...

In this work, we show unusual effects of strong interlayer coupling on low-frequency (LF) Raman scattering in exfoliated PdSe2 crystals with different number of layers. Unlike many other layered materials, it is found that the measured frequencies of the breathing modes cannot be simply described by a conventional linear chain model (LCM) that trea...

Defect engineering has been a critical step in controlling the transport characteristics of electronic devices, and ability to create, tune, and annihilate defects is essential to enable the range of next-generation devices. Whereas defect formation has been well demonstrated in three-dimensional semiconductors, similar exploration of the heterogen...

The group-10 noble-metal dichalcogenides have recently emerged as a promising group of two-dimensional materials due to their unique crystal structures and fascinating physical properties. In this work, the resonance enhancement of the interlayer breathing mode (B1) and intralayer Ag 1 and Ag 3 modes in atomically thin pentagonal PdSe2 were studied...

PdSe2, an emerging two-dimensional (2D) material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer-dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few-layer PdSe2 (two to five layers) under the in-plane uniaxial tensile...

Two‐dimensional (2D) palladium diselenide (PdSe2) has strong interlayer coupling and a puckered pentagonal structure, leading to remarkable layer‐dependent electronic structures and highly anisotropic in‐plane optical and electronic properties. However, the lack of high‐quality, 2D PdSe2 crystals grown by bottom‐up approaches limits the study of th...

In article number 1906238, Kai Xiao and co‐workers develop a novel chemical vapor deposition method to successfully synthesize a pentagonal 2D material, PdSe2, which exhibits strong optical anisotropy and high carrier mobility. The growth of high‐quality, anisotropic 2D crystals is essential for the rapid exploration and development of electronic d...

The role of additives in facilitating the growth of conventional semiconducting thin films is well established. Apparently, their presence is also decisive in the growth of two-dimensional transition metal dichalcogenides (TMDs), yet their role remains ambiguous. In this work, we show that the use of sodium bromide enables synthesis of TMD monolaye...

We report atomically precise pentagonal PdSe2 nanoribbons (PNRs) fabricated on a pristine PdSe2 substrate with a hybrid method of top-down and bottom-up processes. The PNRs form a uniform array of dimer structure with a width of 2.4 nm and length of more than 200 nm. In situ four-probe scanning tunneling microscopy (STM) reveals metallic behavior o...

Two-dimensional (2D) crystal growth over substrate features is fundamentally guided by the Gauss-Bonnet theorem, which mandates that rigid, planar crystals cannot conform to surfaces with nonzero Gaussian curvature. Here, we reveal how topographic curvature of lithographically designed substrate features govern the strain and growth dynamics of tri...

Atmospheric and long-term aging effects on electrical properties of WSe2 transistors with various thicknesses are examined. While countless published studies report electrical properties of transition metal dichalcogenide materials, many are not attentive to testing environment or to age of samples, which we have found significantly impacts results...

Two-dimensional materials such as layered transition-metal dichalcogenides (TMDs) are ideal platforms for studying defect behaviors, an essential step towards defect engineering for novel material functions. Here, we image the 3D lattice locations of selenium-vacancy VSe defects and manipulate them using a scanning tunneling microscope (STM) near t...

In-plane heterojuctions formed from two monolayer semiconductors represent the finest control of electrons in condensed matter, and has attracted significant interests. Various device studies have shown the effectiveness of such structures to control electronic processes, illustrating their potentials for electronic and optoelectronic applications....

The formation of an electric double layer in ionic liquid (IL) can electrostatically induce charge carriers and/or intercalate ions in and out of the lattice which can trigger a large change of the electronic, optical and magnetic properties of materials and even modify the crystal structure. We present a systematic study of ionic liquid gating of...

Composite materials possessing both crystalline and amorphous domains, when subjected to X-ray and neutron scattering, generate diffraction patterns that are often difficult to interpret. One approach is to perform atomistic simulations of a proposed structure, from which the analogous diffraction pattern can be obtained for validation. The structu...

In this paper, high performance top-gated WSe2 field effect transistor (FET) devices are demonstrated via a two-step remote plasma assisted ALD process. High-quality, low-leakage aluminum oxide (Al2O3) gate dielectric layers are deposited onto the WSe2 channel using a remote plasma assisted ALD process with an ultrathin (~1 nm) titanium buffer laye...

In this study, high-performance multilayer WSe2 field effect transistor (FET) devices with carrier type control are demonstrated via thickness modulation and a remote oxygen plasma surface treatment. Carrier type control in multilayer WSe2 FET devices with Cr/Au contacts is initially demonstrated by modulating the WSe2 thickness. The carrier type e...

Interpreting the results of scattering data for complex materials with a hierarchical structure in which at least one phase is amorphous presents a significant challenge. Often the interpretation relies on the use of large-scale molecular dynamics (MD) simulations, in which a structure is hypothesized and from which a radial distribution function (...

phenyl)thiophen-2-yl)methylene)malononitrile as an efficient donor molecule in vacuum-processed bulk-heterojunction organic solar cells A comprehensive experimental study is reported on the optical and electrical characteristics of 2-((5-(4-(diphenylamino)phenyl)thiophen-2-yl)methylene)malononitrile (DPTMM) when used as molecular donor in an organi...