Daryoosh Vashaee

This paper investigates the microscale engineering aspects of n-type doped GaSb to address the challenges associated with achieving high electrical conductivity and precise dopant distribution in this semiconductor material. AC impedance spectroscopy is employed as a reliable technique to characterize the microstructural and electrical properties of GaSb, providing valuable insights into the impact of grain boundaries on overall electrical performance. The uneven distribution of dopants, caused by diffusion, and the incomplete activation of introduced dopants pose significant obstacles in achieving consistent material properties...

Two-dimensional (2D) topological insulators (TIs) hold great promise for future quantum information technologies. Among the 2D-TIs, the TiNI monolayer has recently been proposed as an ideal material for achieving the quantum spin Hall effect at room temperature. Theoretical predictions suggest a sizable bandgap due to the spin-orbit coupling (SOC) of the electrons at and near the Fermi level with a nontrivial 2 topology of the electronic states, which is robust under external strain. However, our detailed first-principles calculations reveal that, in contrast to these predictions, the TiNI monolayer has a trivial bandgap in the equilibrium state with no band inversion, despite SOC opening the bandgap...

Bismuth telluride-based alloys possess the highest efficiencies for the low-temperature-range (<500 K) applications among thermoelectric materials. Despite significant advances in the efficiency of p-type Bi2 Te3 -based materials through engineering the electronic band structure by convergence of multiple bands, the n - type pair still suffers from poor efficiency due to a lower number of electron pockets near the conduction band edge than the valence band. To overcome the persistent low efficiency of n-type Bi2 Te3 -based materials, we have fabricated multiphase pseudobinary Bi2 Te3 -Bi2 S3 compounds to take advantages of phonon scattering and energy filtering at interfaces, enhancing the efficiency of these materials...

In this study, we investigate the enhancement of exchange bias in core/shell/shell structures by synthesizing single inverted core/shell (Co-oxide/Co) and core/shell/shell (Co-oxide/Co/Co-oxide) nanostructures through a two-step reduction and oxidation method. We evaluate the magnetic properties of the structures and study the effect of shell thickness on the exchange bias by synthesizing various shell thicknesses of Co-oxide/Co/Co-oxide nanostructures. The extra exchange coupling formed at the shell-shell interface in the core/shell/shell structure leads to a remarkable increase in the coercivity and the strength of the exchange bias by three and four orders, respectively...

Bismuth telluride-based thin films have been investigated as the active material in flexible and micro thermoelectric generators (TEGs) for near room-temperature energy harvesting applications. The latter is a class of compact printed circuit board compatible devices conceptualized for operation at low-temperature gradients to generate power for wireless sensor nodes (WSNs), the fundamental units of the Internet-of-Things (IoT). CMOS and MEMS compatible micro-TEGs require thin films that can be integrated into the fabrication flow without compromising their thermoelectric properties...

We report the topological phase, thermal, and electrical properties of bialkali bismuthide compounds (Na,K)2RbBi, as yet hypothetical. The topological phase transitions of these compounds under hydrostatic pressure are investigated. The calculated topological surface states and Z2 topological index confirm the nontrivial topological phase. The electronic properties and transport coefficients are obtained using the density functional theory combined with the Boltzmann transport equation. The relaxation times are determined using the deformation potential theory to calculate the electronic thermal and electrical conductivity...

Thermal fluctuation of local magnetization intercoupled with charge carriers and phonons offers a path to enhance thermoelectric performance. Thermopower enhancement by spin fluctuations (SF) has been observed before. However, the crucial evidence for enhancing thermoelectric-figure-of-merit (zT) by SF has not been reported until now. Here we report that the SF leads to nearly 80% zT enhancement in ferromagnetic CrTe near and below T C ∼ 335 K. The ferromagnetism is originated from the collective electronic and localized magnetic moments...

Using first-principles calculations, we predict highly stable cubic bialkali bismuthides Cs(Na, K)2 Bi with several technologically important mechanical and anisotropic elastic properties. We investigate the mechanical and anisotropic elastic properties under hydrostatic tension and compression. At zero pressure, CsK2 Bi is characterized by elastic anisotropy with maximum and minimum stiffness along the directions of [111] and [100], respectively. Unlike CsK2 Bi, CsNa2 Bi exhibits almost isotropic elastic behavior at zero pressure...

A detailed theoretical model and experimental study are presented that formulate and prove the existence of a robust ponderomotive force (PMF) near the interfaces in a granular dielectric material under microwave radiation. The model calculations show that the net direction of the PMF is pore angle-dependent. For most of the pore angles, the net force is towards the interface creating a mass transport that fills the interfacial pores and facilitates densification. For small ranges of angles, near 180o and 360o , PMF drives the ions in the reverse direction and depletes the pores...

The purpose of this study was to produce and characterize Hydroxyapatite/Zinc Oxide/Palladium (HA/0.05 wt% ZnO/0.1 wt% Pd) nanocomposite scaffolds and study their mechanical and antibacterial properties, biocompatibility and bioactivity. The initial materials were developed using sol-gel and precipitation methods. Scaffolds were characterized using atomic absorption analysis (AA), scanning electron microcopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM), atomic force microscopy (AFM) and Brunauer-EmmeS-Teller (BET) method...

Magnesium (Mg) alloys are being investigated as a biodegradable metallic biomaterial because of their mechanical property profile, which is similar to the human bone. However, implants based on Mg alloys are corroded quickly in the body before the bone fracture is fully healed. Therefore, we aimed to reduce the corrosion rate of Mg using a double protective layer. We used a magnesium-aluminum-zinc alloy (AZ91) and treated its surface with micro-arc oxidation (MAO) technique to first form an intermediate layer...

Thermoelectric materials could play a crucial role in the future of wearable electronic devices. They can continuously generate electricity from body heat. For efficient operation in wearable systems, in addition to a high thermoelectric figure of merit, zT , the thermoelectric material must have low thermal conductivity and a high Seebeck coefficient. In this study, we successfully synthesized high-performance nanocomposites of n-type Bi2 Te2.7 Se0.3 , optimized especially for body heat harvesting and power generation applications...

OBJECTIVE: Design of bioactive scaffolds with osteogenic capacity is a central challenge in cell-based patient-specific bone tissue engineering. Efficient and spatially uniform seeding of (stem) cells onto such constructs is vital to attain functional tissues. Herein we developed heparin functionalized collagen gels supported by 3D printed bioceramic scaffolds, as bone extracellular matrix (ECM)-mimetic matrices. These matrices were designed to enhance cell seeding efficiency of mesenchymal stem cells (MSCs) as well as improve their osteogenic differentiation through immobilized bone morphogenic protein 2 (BMP2) to be used for personalized bone regeneration...

Nanoporous bimetallic Fe-Ag nanoparticles (NPs) were synthesized using a facile chemical reduction method and used to decorate the surface of multi-walled carbon nanotubes (MWCNTs) for hydrogen sorption and storage. The effect of TiO2 nanoparticles on the hydrogen storage properties of Fe-Ag/CNTs was further studied in detail. For this purpose, several nanocomposites of nanoporous bimetallic Fe-Ag/TiO2 nanoparticles with different amounts of bimetallic Fe-Ag NPs were prepared via a hydrothermal method. The hydrogen storage capacity of the as-prepared nanocomposites was studied using electrochemical methods...

Magnesium (Mg) alloys as a new group of biodegradable metal implants are being extensively investigated as a promising selection for biomaterials applications due to their apt mechanical and biological performance. However, as a foremost drawback of Mg alloys, the high degradation in body fluid prevents its clinical applications. In this work, a bioceramic composite coating is developed composed of diopside, bredigite, and fluoridated hydroxyapatite on the AZ91 Mg alloy in order to moderate the degradation rate, while improving its bioactivity, cell compatibility, and mechanical integrity...

Early diagnosis of diseases (before they become advanced and incurable) is essential to reduce morbidity and mortality rates. With the advent of novel technologies in clinical laboratory diagnosis, microbead-based arrays have come to be recognized as an efficient approach, that demonstrates useful advantages over traditional assay methods for multiple disease-related biomarkers. Multiplexed microbead assays provide a robust, rapid, specific, and cost-effective approach for high-throughput and simultaneous screening of many different targets...

In recent years, there has been growing interest in optically-encoded or tagged functionalized microbeads as a solid support platform to capture proteins or nucleotides which may serve as biomarkers of various diseases. Multiplexing technologies (suspension array or planar array) based on optically encoded microspheres have made possible the observation of relatively minor changes in biomarkers related to specific diseases. The ability to identify these changes at an early stage may allow the diagnosis of serious diseases (e...

OBJECTIVE: A systematic characterization of hybrid scaffolds, fabricated based on combinatorial additive manufacturing technique and freeze-drying method, is presented as a new platform for osteoblastic differentiation of dental pulp cells (DPCs). METHODS: The scaffolds were consisted of a collagenous matrix embedded in a 3D-printed beta-tricalcium phosphate (β-TCP) as the mineral phase. The developed construct design was intended to achieve mechanical robustness owing to 3D-printed β-TCP scaffold, and biologically active 3D cell culture matrix pertaining to the Collagen extracellular matrix...

Significant amount of research efforts have been dedicated to the development of scaffolds for tissue engineering. Although at present most of the studies are focused on non-load bearing scaffolds, many scaffolds have also been investigated for hard tissue repair. In particular, metallic scaffolds are being studied for hard tissue engineering due to their suitable mechanical properties. Several biocompatible metallic materials such as stainless steels, cobalt alloys, titanium alloys, tantalum, nitinol and magnesium alloys have been commonly employed as implants in orthopedic and dental treatments...

In this research, a new electrochemical biosensor was constructed for the glucose detection. Iron oxide nanoparticles (Fe3 O4 ) were synthesized through co-precipitation method. Polyvinyl alcohol-Fe3 O4 nanocomposite was prepared by dispersing synthesized nanoparticles in the polyvinyl alcohol (PVA) solution. Glucose oxidase (GOx) was immobilized on the PVA-Fe3 O4 nanocomposite via physical adsorption. The mixture of PVA, Fe3 O4 nanoparticles and GOx was drop cast on a tin (Sn) electrode surface (GOx/PVA-Fe3 O4 /Sn)...