Electron. Mater., Volume 2, Issue 3 (September 2021) – 11 articles

Solid solutions in the Ba(Pb_1−xSr_x)O_3−z system were prepared by aliovalent substitution of Pb⁴⁺ by Sr²⁺ ions to investigate the effect of cation stoichiometry on thermal and electrical properties as x was varied between 0 and 0.4, in the temperature range 300–523 K. The starting compound, barium plumbate (BaPbO₃), has a perovskite structure and is known to exhibit metallic conductivity due to an overlap of the O2p nonbonding and the Pb–O spσ antibonding band, which is partially filled by the available electrons. The large difference in the ionic radii between the Pb⁴⁺ and Sr²⁺ ions introduces significant strain into the (Pb/Sr)O₆ octahedra of the perovskite structure. Additionally, charged defects are created on account of the different oxidation states of the Pb⁴⁺ and Sr²⁺ ions. Evidence of a metal to insulator transition (MIT) of the Mott–Hubbard type has been observed at a critical concentration of Sr²⁺ ions. Full article

Implantable bioelectrodes have the potential to advance neural sensing and muscle stimulation, mainly in patients with peripheral nerve injuries. They function as the transducer at the interface between the damaged nerve and the muscle which is controlled by that nerve. This work reports the fabrication and characterization of novel, low-cost, flexible bioelectrodes based on polyaniline (PANI) and supported with silicone polymer. The fabricated electrodes were evaluated for their electrical and mechanical characteristics. PANI was used as the main transducer component in this fabrication. The characterization methods included electrical conductivity, capacitive behavior, long-term electrical impedance, and mechanical evaluation. The results of the fabricated PANI-silicone-based samples displayed a bulk impedance of 0.6 kΩ with an impedance of 1.6 kΩ at the frequency of 1 kHz. Furthermore, the bioelectrodes showed a charge storage capacity range from 0.0730 to 4.3124 C/cm². The samples were stable when subjected to cyclic voltammetry tests. The bioelectrodes revealed very flexible mechanical properties as observed from the value of Young’s modulus (in the order of MPa) which was less than that of skin. Hence, the PANI-based bioelectrodes reported herein showed promising electrochemical characteristics with high flexibility. Full article

In the field of printed electronics, there is a pressing need for printable resistors, particularly ones where the resistance can be varied without changing the size of the resistor. This work presents ink synthesis and printing results for variable resistance, inkjet-printed patterns of a novel and sustainable carbon nanomaterial—multilayer graphene nanoshells. Dispersed multilayer graphene nanospheres are sterically stabilized by a surfactant (Triton X100), and no post-process is required to achieve the resistive functionality. A surface tension-based adsorption analysis technique is used to determine the optimal surfactant dosage, and a geometric model explains the conformation of adsorbed surfactant molecules. The energetic interparticle potentials between approaching particles are modeled to assess and compare the stability of sterically and electrostatically stabilized multilayer graphene nanoshells. The multilayer graphene nanoshell inks presented here show a promising new pathway toward sustainable and practical printed resistors that achieve variable resistances within a constant areal footprint without post-processing. Full article

Using a combination of first principles and semiempirical calculation, we explore the structural, electronic, and optical properties of a wide range of perovskite ($AB{X}_3$) nanoparticle of different size and composition. The variations of the $B{X}_3$ backbone structure considered include all possible combinations of the cations $B=Pb,Sn$ and the anions $X=Cl,Br,I$, while the interstitial cation A is either methylamonium (MA), or formamidinium (FA), or guanidine amine (GA), or dimethylamine (DEA). Our results indicate that the orientational disorder of the A moieties may affect the structural and electronic properties of the NPs while the optical properties exhibit a clear dependence on the NPs’ size and the types of B cations and X anions, but they are quite insensitive to the type of A cation. Full article

In this study, we undertake a Bayesian optimization of the Hubbard U parameters of wurtzite GaN and InN. The optimized Us are then tested within the Hubbard-corrected local density approximation (LDA+U) approach against standard density functional theory, as well as a hybrid functional (HSE06). We present the electronic band structures of wurtzite GaN, InN, and (1:1) InGaN superlattice. In addition, we demonstrate the outstanding performance of the new parametrization, when computing the internal electric-fields in a series of [InN]${}_1$–[GaN]${}_n$ superlattices (n = 2–5) stacked up along the c-axis. Full article

A multi-level cell (MLC) operation as a 1–3 bit/cell of the FeFET emerging memory is reported by utilizing optimized Si doped hafnium oxide (HSO) and hafnium zirconium oxide (HZO) based on ferroelectric laminates. An alumina interlayer was used to achieve the thickness independent of the HSO and HZO-based stack with optimal ferroelectric properties. Various split thicknesses of the HSO and HZO were explored with lamination to increase the FeFET maximum memory window (MW) for a practical MLC operation. A higher MW occurred as the ferroelectric stack thickness increased with lamination. The maximum MW (3.5 V) was obtained for the HZO-based laminate; the FeFETs demonstrated a switching speed (300 ns), 10 years MLC retention, and 10⁴ MLC endurance. The transition from instant switching to increased MLC levels was realized by ferroelectric lamination. This indicated an increased film granularity and a reduced variability through the interruption of ferroelectric columnar grains. The 2–3 bit/cell MLC levels and maximum MW were studied in terms of the size-dependent variability to indicate the impact of the ferroelectric area scaling. The impact of an alumina interlayer on the ferroelectric phase is outlined for HSO in comparison to the HZO material. For the same ferroelectric stack thickness with lamination, a lower maximum MW, and a pronounced wakeup effect was observed in HSO laminate compared to the HZO laminate. Both wakeup effect and charge trapping were studied in the context of an MLC operation. The merits of ferroelectric stack lamination are considered for an optimal FeFET-based synaptic device operation. The impact of the pulsing scheme was studied to modulate the FeFET current to mimic the synaptic weight update in long-term synaptic potentiation/depression. Full article

Bio-based activated carbons with very high specific surface area of >3.000 m² g⁻¹ (based on CO₂ adsorption isotherms) and a high proportion of micropores (87% of total SSA) are produced by corncobs via pyrolysis and chemical activation with KOH. The activated carbon is further doped with different proportions of the highly pseudocapacitive transition metal oxide RuO₂ to obtain enhanced electrochemical properties and tune the materials for the application in electrochemical double-layer capacitors (EDLC) (supercapacitors). The activated carbon and composites are extensively studied regarding their physico-chemical and electrochemical properties. The results show that the composite containing 40 wt.% RuO₂ has an electric conductivity of 408 S m⁻¹ and a specific capacitance of 360 Fg⁻¹. SEM-EDX, XPS, and XRD analysis confirm the homogenous distribution of partly crystalline RuO₂ particles on the carbon surface, which leads to a biobased composite material with enhanced electrochemical properties. Full article

Tungsten oxide is a widely used electrochromic material with important applications in variable-transmittance smart windows as well as in other optoelectronic devices. Here we report on electrochemical impedance spectroscopy applied to hydrous electrochromic tungsten oxide films in a wide range of applied potentials. The films were able to reversibly bleach and color upon electrochemical cycling. Interestingly, the bleaching potential was found to be significantly higher than in conventional non-hydrous tungsten oxide films. Impedance spectra at low potentials showed good agreement with anomalous diffusion models for ion transport in the films. At high potentials, where little ion intercalation takes place, it seems that parasitic side reactions influence the spectra. The potential dependence of the chemical capacitance, as well as the ion diffusion coefficient, were analyzed. The chemical capacitance is discussed in terms of the electron density of states in the films and evidence was found for a band tail extending below the conduction band edge. Full article

Currently, a large number of neurostimulators are commercially available for the treatment of drug-resistant diseases and as an alternative to pharmaceuticals. According to the current state of the art, such highly engineered electroceuticals require bulky battery units and necessitate the use of leads and extensions to connect the implantable electronic device to the stimulation electrodes. The battery life and the use of wired electrodes constrain the long-term use of such implantable systems. Furthermore, for therapeutic success and patient safety, it is of utmost importance to keep the stimulation current within a safe range. In this paper, we propose an implantable system design that consists of a low number of passive electronic components and does not require a battery. The stimulation parameters and power are transmitted inductively using an extracorporeal wearable transmitter at frequencies below 1 MHz. A simple circuit design approach is presented to achieve a closed-loop control of the stimulation current by exploiting the nonlinear properties of ferroelectric materials in ceramic capacitors. Twenty circuit topologies of series- and/or parallel-connected ceramic capacitors are investigated by measurement and are modeled in Mathcad. An approximately linear increase in the stimulation current, a stabilization of the stimulation current and an unstable state of the system were observed. In contrast to previous results, specific plateau ranges of the stimulation current can be set by the investigated circuit topologies. For further investigations, the consistency of the proposed model needs to be improved for higher induced voltage ranges. Full article

We report an optimized chemical vapor transport method to grow single crystals of (Mn_1−xNi_x)₂P₂S₆ where x = 0, 0.3, 0.5, 0.7, and 1. Single crystals up to 4 mm × 3 mm × 200 μm were obtained by this method. As-grown crystals are characterized by means of scanning electron microscopy and powder X-ray diffraction measurements. The structural characterization shows that all crystals crystallize in monoclinic symmetry with the space group C2/m (No. 12). We have further investigated the magnetic properties of this series of single crystals. The magnetic measurements of the all as-grown single crystals show long-range antiferromagnetic order along all principal crystallographic axes. Overall, the Néel temperature T_N is non-monotonous; with increasing Ni²⁺ doping, the temperature of the antiferromagnetic phase transition first decreases from 80 K for pristine Mn₂P₂S₆ (x = 0) up to x = 0.5 and then increases again to 155 K for pure Ni₂P₂S₆ (x = 1). The magnetic anisotropy switches from out-of-plane to in-plane as a function of composition in (Mn_1−xNi_x)₂P₂S₆ series. Transport studies under hydrostatic pressure on the parent compound Mn₂P₂S₆ evidence an insulator-metal transition at an applied critical pressure of ~22 GPa. Full article

The band alignment of Mg(OH)₂-based heterostructures is investigated based on first-principles calculation. (111)-MgO/(0001)-Mg(OH)₂ and (0001)-wurtzite ZnO/(0001)-Mg(OH)₂ heterostructures are considered. The O 2s level energy is obtained for each O atom in the heterostructure supercell, and the band edge energies are evaluated following the procedure of the core-level spectroscopy. The calculation is based on the generalized gradient approximation with the on-site Coulomb interaction parameter U considered for Zn. For MgO/Mg(OH)₂, the band alignment is of type II, and the valence band edge of MgO is higher by 1.6 eV than that of Mg(OH)₂. For ZnO/Mg(OH)₂, the band alignment is of type I, and the valence band edge of ZnO is higher by 0.5 eV than that of Mg(OH)₂. Assuming the transitivity rule, it is expected that Mg(OH)₂ can be used for certain types of heterostructure solar cells and dye-sensitized solar cells to improve the performance. Full article