Rayid Mojumder

Soft electronics, known for their bendable, stretchable, and flexible properties, are revolutionizing fields such as biomedical sensing, consumer electronics, and robotics. A primary challenge in this domain is achieving low power consumption, often hampered by the limitations of the conventional von Neumann architecture. In response, the development of soft artificial synapses (SASs) has gained substantial attention. These synapses seek to replicate the signal transmission properties of biological synapses, offering an innovative solution to this challenge. This review explores the materials and device architectures integral to SAS fabrication, emphasizing flexibility and stability under mechanical deformation. Various architectures, including floating-gate dielectric, ferroelectric-gate dielectric, and electrolyte-gate dielectric, are analyzed for effective weight control in SASs. The utilization of organic and low-dimensional materials is highlighted, showcasing their plasticity and energy-efficient operation. Furthermore, the paper investigates the integration of functionality into SASs, particularly focusing on devices that autonomously sense external stimuli. Functionalized SASs, capable of recognizing optical, mechanical, chemical, olfactory, and auditory cues, demonstrate promising applications in computing and sensing. A detailed examination of photo-functionalized, tactile-functionalized, and chemoreception-functionalized SASs reveals their potential in image recognition, tactile sensing, and chemosensory applications, respectively. This study highlights that SASs and functionalized SAS devices hold transformative potential for bioelectronics and sensing for soft-robotics applications; however, further research is necessary to address scalability, long-time stability, and utilizing functionalized SASs for prosthetics and in vivo applications through clinical adoption. By providing a comprehensive overview, this paper contributes to the understanding of SASs, bridging research gaps and paving the way toward transformative developments in soft electronics, biomimicking and biointegrated synapse devices, and integrated systems.

Of late, inorganic perovskite material, especially the lead-free CsGeBr3, has gained considerable interest in the green photovoltaic industry due to its outstanding optoelectronic, thermal, and elastic properties. This work systematically investigated the strain-driven optical, electronic, and mechanical properties of CsGeBr3 through the first-principles density functional theory. The unstrained planar CsGeBr3 compound demonstrates a direct bandgap of 0.686 at its R-point. However, incorporating external biaxial tensile (compressive) strain can be tuned the bandgap lowering (increasing) to this perovskite. Moreover, due to the increase of tensile (compressive) strain, a red-shift (blue-shift) behavior of the absorption-coefficient and dielectric function is found in the photon energy spectrum. Strain-induced mechanical properties also reveal that CsGeBr3 perovskites are mechanically stable and highly malleable material and can be made suitable for photovoltaic applications. The strain-dependent optoelectronic and mechanical behaviors of CsGeBr3 explored here would benefit its future applications in optoelectronics and photovoltaic cells design.

The high electronegativity between the atoms of two-dimensional (2D) group-III nitrides makes them attractive to demonstrating a strong out-of-plane piezo-electricity effect. Energy harvesting devices can be predicted by cultivating such salient piezoelectric features. This work explores the tribo-piezoelectric properties of 2D-indium nitride (InN) as a promising candidate in nanogenerator applications by means of first-principles calculations. In-plane interlayer sliding between two InN monolayers leads to a noticeable rise of vertical piezoelectricity. The vertical resistance between the InN bilayer renders tribological energy by the sliding effect. During the vertical sliding, a shear strength of 6.6–9.7 GPa is observed between the monolayers. The structure can be used as a tribo-piezoelectric transducer to extract force and stress from the generated out-of-plane tribo-piezoelectric energy. The A–A stacking of the bilayer InN elucidates the highest out-of-plane piezoelectricity. Any decrease in the interlayer distance between the monolayers improves the out-of-plane polarization and thus, increases the inductive voltage generation. Vertical compression of bilayer InN produces an inductive voltage in the range of 0.146–0.196 V. Utilizing such a phenomenon, an InN-based bilayer compression-sliding nanogenerator is proposed, which can tune the generated tribo-piezoelectric energy by compressing the interlayer distance between the InN monolayers. The considered model can render a maximum output power density of   73 mWcm−2 upon vertical sliding.

Developing van der Waals heterostructures (vdWHs) utilizing vertical mounting of diverse two-dimensional (2D) materials is an efficient way of achieving favorable characteristics. Using first-principles calculations, we demonstrated the geometric configurations and electronic properties of germanene/2D-AlP vdWHs. We considered four high symmetric patterns that show a bandgap opening in the heterostructures of 200 meV–460 meV. The incorporation of spin-orbital coupling reduces the bandgap by 20 meV–90 meV. Both direct and indirect bandgaps were found from these high symmetric patterns, depending on the structural patterns. The charge density distribution and the partial density of states confirmed that germanene was the property builder of the heterostructure, in which 2D-AlP could be a decent substrate. The heterostructure bandgap can be widely tuned in the range 0 meV–500 meV by changing the interlayer separation between the two monolayers. The application of strain and external electric fields also significantly tailored the electronic structures of the heterostructures. Intriguingly, an exceptionally high carrier mobility of more than 1.5 × 105 cm2 V−1 s−1 was observed, which outperforms compared to other studies on germanene heterostructures. All these promising properties make the germanene/2D-AlP heterostructure a viable candidate for FETs, strain sensors, nanoelectronics, and spintronic devices.