Magnetic Nanoparticles as MRI Contrast Agents

Magnetic Resonance Imaging (MRI) is a non-invasive imaging modality that offers both anatomical and functional information. Intrinsic longitudinal and transverse relaxation times (T1 and T2, respectively) provide tools to manipulate image contrast. Additional control is yielded when paramagnetic and magnetic particulate materials are used as contrast materials. Superparamagnetic particles are mostly synthesized from iron oxide and are usually coated with polymers and functional particles to offer multifunctional biomedical applications. The latter include not only MRI but also cancer treatment through drug delivery and hyperthermia. This Chapter reviews the fundamental dipole–dipole diamagnetic proton relaxation mechanism dominant in water followed by a brief description of the use of gadolinium complexes as MRI contrast agent. Finally, a description of the important chemical and physical properties of magnetic nanoparticle (MNP) that define their use as MRI relaxation enhancing agents especially for T2. The main governing models are described for the different motional regimes with few simulation results demonstrating the applicability of the given equations

Perovskite-Surface-Confined Grain Growth for High-Performance Perovskite Solar Cells

The conventional post-annealing (CPA) process is frequently employed and regarded a crucial step for high-quality perovskite thin-films. However, most researchers end up with unwanted characteristics because controlling the evaporation rate of perovskite precursor solvents during heat treatment is difficult. Most perovskite thin-films result in rough surfaces with pinholes and small grains with multiple boundaries, if the evaporation of precursor solvents is not controlled in a timely manner, which negatively affects the performance of perovskite solar cells (PSCs). Here, we present a surface-confined post-annealing (SCPA) approach for controlling the evaporation of perovskite precursor solvents and promoting crystallinity, homogeneity, and surface morphology of the resulting perovskites. The SCPA method not only modulates the evaporation of residual solvents, resulting in pinhole-free thin-films with large grains and fewer grain boundaries, but it also reduces recombination sites and facilitates the transport of charges in the resulting perovskite thin-films. When the method is changed from CPA to SCPA, the power conversion efficiency of PSC improves from 18.94% to 21.59%. Furthermore, as compared to their CPA-based counterparts, SCPA-based PSCs have less hysteresis and increased long-term stability. The SCPA is a potentially universal method for improving the performance and stability of PSCs by modulating the quality of perovskite thin-films

Guidelines for Fabricating Highly Efficient Perovskite Solar Cells with Cu2O as the Hole Transport Material

Organic hole transport materials (HTMs) have been frequently used to achieve high power conversion efficiencies (PCEs) in regular perovskite solar cells (PSCs). However, organic HTMs or their ingredients are costly and time-consuming to manufacture. Therefore, one of the hottest research topics in this area has been the quest for an efficient and economical inorganic HTM in PSCs. To promote efficient charge extraction and, hence, improve overall efficiency, it is crucial to look into the desirable properties of inorganic HTMs. In this context, a simulation investigation using a solar cell capacitance simulator (SCAPS) was carried out on the performance of regular PSCs using inorganic HTMs. Several inorganic HTMs, such as nickel oxide (NiO), cuprous oxide (Cu2O), copper iodide (CuI), and cuprous thiocyanate (CuSCN), were incorporated in PSCs to explore matching HTMs that could add to the improvement in PCE. The simulation results revealed that Cu2O stood out as the best alternative, with electron affinity, hole mobility, and acceptor density around 3.2 eV, 60 cm2V−1s−1, and 1018 cm−3, respectively. Additionally, the results showed that a back electrode with high work-function was required to establish a reduced barrier Ohmic and Schottky contact, which resulted in efficient charge collection. In the simulation findings, Cu2O-based PSCs with an efficiency of more than 25% under optimal conditions were identified as the best alternative for other counterparts. This research offers guidelines for constructing highly efficient PSCs with inorganic HTMs

Lead-Free Perovskite Homojunction-Based HTM-Free Perovskite Solar Cells: Theoretical and Experimental Viewpoints

Simplifying the design of lead-free perovskite solar cells (PSCs) has drawn a lot of interest due to their low manufacturing cost and relative non-toxic nature. Focus has been placed mostly on reducing the toxic lead element and eliminating the requirement for expensive hole transport materials (HTMs). However, in terms of power conversion efficiency (PCE), the PSCs using all charge transport materials surpass the environmentally beneficial HTM-free PSCs. The low PCEs of the lead-free HTM-free PSCs could be linked to poorer hole transport and extraction as well as lower light harvesting. In this context, a lead-free perovskite homojunction-based HTM-free PSC was investigated, and the performance was then assessed using a Solar Cell Capacitance Simulator (SCAPS). A two-step method was employed to fabricate lead-free perovskite homojunction-based HTM-free PSCs in order to validate the simulation results. The simulation results show that high hole mobility and a narrow band gap of cesium tin iodide (CsSnI3) boosted the hole collection and absorption spectrum, respectively. Additionally, the homojunction’s built-in electric field, which was identified using SCAPS simulations, promoted the directed transport of the photo-induced charges, lowering carrier recombination losses. Homojunction-based HTM-free PSCs having a CsSnI3 layer with a thickness of 100 nm, defect density of 1015 cm−3, and interface defect density of 1018 cm−3 were found to be capable of delivering high PCEs under a working temperature of 300 K. When compared to formamidinium tin iodide (FASnI3)-based devices, the open-circuit voltage (Voc), short-circuit density (Jsc), fill factor (FF), and PCE of FASnI3/CsSnI3 homojunction-based HTM-free PSCs were all improved from 0.66 to 0.78 V, 26.07 to 27.65 mA cm−2, 76.37 to 79.74%, and 14.62 to 19.03%, respectively. In comparison to a FASnI3-based device (PCE = 8.94%), an experimentally fabricated device using homojunction of FASnI3/CsSnI3 performs better with Voc of 0.84 V, Jsc of 22.06 mA cm−2, FF of 63.50%, and PCE of 11.77%. Moreover, FASnI3/CsSnI3-based PSC is more stable over time than its FASnI3-based counterpart, preserving 89% of its initial PCE. These findings provide promising guidelines for developing highly efficient and environmentally friendly HTM-free PSCs based on perovskite homojunction

Misconceptions about Atomic Models Amongst the Chemistry Students

Bohr’s model is a semi-classical model which involves both classical and quantum principles. Although more sophisticated Schrödinger model has been presented to students, the residual picture in their minds persists to consider Bohr’s model to be the closest to the physical reality. We included few questions about Bohr’s model in tests to assess the students’ understandings of realistic atomic models in general-chemistry courses offered for freshmen in two universities in the Middle-East (namely, Yarmouk University at Irbid, Jordan, and the United Arab Emirates University at Al-Ain, UAE, from both a statistical sample of 687 students was collected). The results reveal the existence of huge misconceptions amongst a large portion of the students’ sample (i.e., ≥ 85%). Alternative solutions are discussed and suggested to draw a strategy to better dissimilate the knowledge in order to overcome the existing learning difficulties

Diethanolamine Modified Perovskite-Substrate Interface for Realizing Efficient ESL-Free PSCs

Simplifying device layout, particularly avoiding the complex fabrication steps and multiple high-temperature treatment requirements for electron-selective layers (ESLs) have made ESL-free perovskite solar cells (PSCs) attractive. However, the poor perovskite/substrate interface and inadequate quality of solution-processed perovskite thin films induce inefficient interfacial-charge extraction, limiting the power conversion efficiency (PCEs) of ESL-free PSCs. A highly compact and homogenous perovskite thin film with large grains was formed here by inserting an interfacial monolayer of diethanolamine (DEA) molecules between the perovskite and ITO substrate. In addition, the DEA created a favorable dipole layer at the interface of perovskite and ITO substrate by molecular adsorption, which suppressed charge recombination. Comparatively, PSCs based on DEA-treated ITO substrates delivered PCEs of up to 20.77%, one of the highest among ESL-free PSCs. Additionally, this technique successfully elongates the lifespan of ESL-free PSCs as 80% of the initial PCE was maintained after 550 h under AM 1.5 G irradiation at ambient temperature

Magnetic studies of vortices in YBaCuO crystals.

Magnetic studies of vortices in YBaCuO crystals

Magnetic Properties of Magnetic Nanoparticles for Efficient Hyperthermia

Localized magnetic hyperthermia using magnetic nanoparticles (MNPs) under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed

Investigating the Role of Shell Thickness and Field Cooling on Saturation Magnetization and Its Temperature Dependence in Fe3O4/γ-Fe2O3 Core/Shell Nanoparticles

Understanding saturation magnetization and its behavior with particle size and temperature are essential for medical applications such magnetic hyperthermia. We report the effect of shell thickness and field cooling on the saturation magnetization and its behavior with temperature in Fe3O4/γ-Fe2O3 core/shell nanoparticles of fixed core diameter (8 nm) and several shell thicknesses. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM, high-resolution transmission electron microscopy (HRTEM)) were used to investigate the phase and the morphology of the samples. Selected area electron diffraction (SAED) confirmed the core/shell structure and phases. Using a SQUID (San Diego, CA, USA), magnetic measurements were conducted in the temperature range of 2 to 300 K both under zero field-cooling (ZFC) and field-cooling (FC) protocols at several field-cooling values. In the ZFC state, considerable enhancement of saturation magnetization was obtained with the increase of shell thickness. After field cooling, we observed a drastic enhancement of the saturation magnetization in one sample up to 120 emu/g (50% larger than the bulk value). In both the FC and ZFC states, considerable deviations from the original Bloch’s law were observed. These results are discussed and attributed to the existence of interface spin-glass clusters which are modified by the changes in the shell thickness and the field-cooling

Perovskite-Surface-Confined Grain Growth for High-Performance Perovskite Solar Cells

The conventional post-annealing (CPA) process is frequently employed and regarded a crucial step for high-quality perovskite thin-films. However, most researchers end up with unwanted characteristics because controlling the evaporation rate of perovskite precursor solvents during heat treatment is difficult. Most perovskite thin-films result in rough surfaces with pinholes and small grains with multiple boundaries, if the evaporation of precursor solvents is not controlled in a timely manner, which negatively affects the performance of perovskite solar cells (PSCs). Here, we present a surface-confined post-annealing (SCPA) approach for controlling the evaporation of perovskite precursor solvents and promoting crystallinity, homogeneity, and surface morphology of the resulting perovskites. The SCPA method not only modulates the evaporation of residual solvents, resulting in pinhole-free thin-films with large grains and fewer grain boundaries, but it also reduces recombination sites and facilitates the transport of charges in the resulting perovskite thin-films. When the method is changed from CPA to SCPA, the power conversion efficiency of PSC improves from 18.94% to 21.59%. Furthermore, as compared to their CPA-based counterparts, SCPA-based PSCs have less hysteresis and increased long-term stability. The SCPA is a potentially universal method for improving the performance and stability of PSCs by modulating the quality of perovskite thin-films