Volume 5, Issue 3 - Special issue: Experimental and computational advances in nano-scale fabrication and characterization / Issue editor: Moh’d Rezeq

The inner workings of semiconductor electronic and photonic devices, such as dopants, free charge carriers, electric potential, and electric field, are playing a crucial role in the function and performance of the devices. Electrical scanning probe microscopy (SPM) techniques have been developed and deployed to measure, with nanometric spatial resolution and high quantitative accuracy, the two-dimensional profiles of dopant, potential, electric field, and free carrier distribution, within unbiased and/or operating electronic and photonic devices. In this review paper, we summarize our latest SPM experimental results, including the scanning spreading resistance microscopy and scanning capacitance microscopy of terahertz quantum cascade lasers, scanning capacitance microscopy of non-volatile memory devices, scanning voltage microscopy of terahertz quantum cascade lasers, and scanning voltage microscopy of interband cascade lasers. Interpretation of the measured quantities are presented and calibrated, demonstrating that important internal physical quantities and inner mechanisms of device operation can be uncovered. It reveals that the novel SPM techniques would find more applications to the emerging semiconductor quantum devices and nanoelectronics.

Nanotips are considered significant elements in some of nanotechnology instruments. They are used in scanning probe microscopes and electron microscopes to characterize materials at the nano and atomic scales. Therefore, the size and profile of the nanotip determines the performance of these microscopes. The advancement of nanotip fabrication techniques has enabled the fabrication of ultra-sharp tips and even single-atom tips. However, the characterization of nanotips with an apex of a few nanometers is still premature, while the conventional characterization methods of the tip size, such as the ring counting method, have shown some limitation at this nano scale. In this paper, we review the various nanotip fabrication methods with a focus on the most recent one, which is called the local electron bombardment method. We demonstrate an approach for estimating the nanotip radius with good approximation using ball crystal models. We also model the overall nanotip profile using finite element simulation tools based on the hyperboloidal geometry. The modeling and radius estimation approach is applied on tips fabricated by the local electron bombardment method, which will be explained in detail as well.

Memristors are one of the emerging technologies that can potentially replace state-of-the-art integrated electronic devices for advanced computing and digital and analog circuit applications including neuromorphic networks. Over the past few years, research and development mostly focused on revolutionizing the metal oxide materials, which are used as core components of the popular metal-insulator-metal memristors owing to their highly recognized resistive switching behavior. This paper outlines the recent advancements and characteristics of such memristive devices, with a special focus on (i) their established resistive switching mechanisms and (ii) the key challenges associated with their fabrication processes including the impeding criteria of material adaptation for the electrode, capping, and insulator component layers. Potential applications and an outlook into future development of metal oxide memristive devices are also outlined.

In recent years, nanoparticle formulations utilizing magnetic materials have started gaining more consideration in the biomedical arena due to their inherent superparamagnetic/paramagnetic nature paving ways to develop assays and sensors benefitting mostly magnetic separation technique. Coupled with the developments in the synthetic field in obtaining controlled-sized particles and surface functionalities, a variety of sensitive and selective assays have been developed ranging from detection/separation/enrichment of antibodies, enzymes, proteins, and nucleic acids to whole cells, virus, and pathogens utilizing a variety of signal transduction mechanisms including fluorescence, surface plasmon resonance, and magnetic resonance. In addition to ongoing research in this field, there are already commercialized products engineered to detect and quantify biomolecules with proper surface formulations. Owing to the immensity of applications of magnetic particles, in this article, recent trends in the design and applications of iron oxide nanoparticles will be reviewed.

Studying the properties of water confined in carbon nanotubes (CNTs) have gained a lot of interest in recent years due to the vast potential applications of systems in nanoscale liquid transport as well as biology functions. This article presents a comprehensive review of recent experimental and theoretical results using nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulations. Different NMR methods including 1 H and 2 H NMR line shapes, relaxation, and diffusion measurements are reviewed. In addition, we present a review of MD studies that explained the driving forces behind water filling, structure of confined water, and its flow in CNTs. Debatable issues in the results are pointed out, and several possible directions for future research, both experimentally and theoretically, are proposed.

Nanometal-semiconductor contacts in the sub-20-nm range have shown some deviations in electrical characteristics compared to conventional diodes. We have used a finite element simulation software to build and analyze a proposed geometrical model. We used two different theoretical approaches to study the enhancements of the electric field at the interface, and then the total current across nano-Schottky junction. The results revealed a significant tunneling current at the reverse bias for low n-doped semiconductor substrates and low current at the forward bias. However, in the case of high n-doped semiconductor substrates, the thermionic current is significant at forward biases and the current is low at the reverse bias. We have used our finite element simulation models based on both approaches to fit the existing experimental data of nano-Schottky contacts.

The potential energy curves for the 45 singlet, triplet, and quintet electronic states in the representation 2s+1 Λ (+/-) of the BF molecule have been investigated using the complete active space self-consistent field (CASSCF) method with multireference configuration interaction (MRCI). The internuclear distance R e , the harmonic frequency ω e , the static dipole moment μ, the rotational constants B e , and the electronic transition energy with respect to the ground state T e have been calculated for the considered electronic states. The comparison between the values of the present work and those available in the literature for several electronic states shows a very good agreement. Twelve electronic states of BF molecule are reported here for the first time that are not yet observed experimentally.