Local Potential Variations Research Articles

Rare Earth Selectivity and Electric Potentials at Mica Interfaces.

Controlling materials' composition and structure to selectively adsorb rare earth elements (REE) is critical for better separations. Understanding how local electric potentials affect REE adsorption and how they can be modified via chemical substitution is of fundamental importance. We present calculated mean inner potentials for muscovite and phlogopite micas in excellent agreement with measured values of +10.6 V. Natural substituents for aluminum significantly influence the electric potentials at the basal surface, altering the REE adsorption energies (Ead). Nd3+ adsorption is generally favored over that of Yb3+ on both micas. Substituents with lower charge than aluminum increase the Lewis basicity of adjacent oxygen atom lone electron pairs, enhancing Ead by 20 to 30 kcal/mol. These substitutions modify the electric potential's magnitude and spatial extent, highlighting the role of high-resolution electron holography/tomography and the importance of understanding atomic-scale variations in electric potentials for improving REE cation adsorption and selectivity on micas. In summary, the adsorption energies of REE cations are correlated with the substituent charge and local electrostatic potential variations because these factors dictate the electrostatic interactions between the cations and the interface.

Topologically Protected Single Edge Mode Lasing in Photonic Crystal Su–Schrieffer–Heeger Lattice with Directional Loss Control

AbstractTopological photonics is considered to be a robust and flexible platform for the design of nanophotonic devices against structural imperfections and performance degradation. Combining with parity‐time (PT) symmetry systems based on spatially distributed gain and loss, photonic crystal (PhC) lasers with micron‐size carrier reservoirs offer an ideal test bed for lasing mode competition and topological protection in nanophotonic structures. In this study, single topological edge mode (TEM) lasing is demonstrated in PhC lasers with a Su–Schrieffer–Heeger lattice comprised of coupled nanoresonators. By inducing directional loss control, a mode selection strategy is implemented, that achieves single TEM lasing with a side‐mode‐suppression ratio exceeding 30 dB. One of the TEMs exhibits remarkable robustness against local potential variation introduced by additional loss channels. This strategy integrating both topological protection and PT symmetry in nanophotonics would open up new prospects for the development of on‐chip single‐mode topological lasers unperturbed by output channels in nanophotonic integrated circuits.

The local potential variation mapping including thermoelectromotive force in nanocomposite materials under non-thermal equilibrium

Thermoelectric nanocomposite materials are attracting much attention due to their high thermoelectric performance brought by effectively combining thermoelectric properties of the matrix and introduced nanostructures. However, understanding the mechanism of Seebeck coefficient enhancement brought in nanocomposite materials is difficult because there are no measurement methods of thermoelectromotive force V TE on the nanoscale. In this study, we demonstrate that the controlled temperature gradient Kelvin force microscopy (T-KFM) measurement we developed in 2021 can be applied to nanocomposite films. We observe temperature difference ΔT-induced vacuum level V vac variation, which is related to V TE, in PEDOT:PSS/Si nanowire nanocomposite films using T-KFM. The large ΔT-induced V vac variation at the tops of Si nanowires is generated, which is mainly explained by the larger Seebeck coefficient value of the Si nanowire. This application of T-KFM to the nanocomposites highlights that T-KFM will be a powerful tool for the development of nanocomposite materials with controlled thermoelectric properties on the nanoscale.

Compensating for artifacts in scanning near-field optical microscopy due to electrostatics

Nanotechnology and modern materials science demand reliable local probing techniques on the nanoscopic length scale. Most commonly, scanning probe microscopy methods are applied in numerous variants and shades, for probing the different sample properties. Scattering scanning near-field optical microscopy (s-SNOM), in particular, is sensitive to the local optical response of a sample, by scattering light off an atomic force microscopy (AFM) tip, yielding a wavelength-independent lateral resolution in the order of ∼10 nm. However, local electric potential variations on the sample surface may severely affect the probe–sample interaction, thereby introducing artifacts into both the optical near-field signal and the AFM topography. On the other hand, Kelvin-probe force microscopy (KPFM) is capable of both probing and compensating such local electric potentials by applying a combination of ac and dc-voltages to the AFM tip. Here, we propose to combine s-SNOM with KPFM in order to compensate for undesirable electrostatic interaction, enabling the in situ probing of local electric potentials along with pristine optical responses and topography of sample surfaces. We demonstrate the suitability of this method for different types of materials, namely, metals (Au), semiconductors (Si), dielectrics (SiO2), and ferroelectrics (BaTiO3), by exploring the influence of charges in the systems as well as the capability of KPFM to compensate for the resulting electric force interactions.

Community-based integrated care versus hospital outpatient care for managing patients with complex type 2 diabetes: costing analysis.

Objective This study compared the cost of an integrated primary-secondary care general practitioner (GP)-based Beacon model with usual care at hospital outpatient departments (OPDs) for patients with complex type 2 diabetes. Methods A costing analysis was completed alongside a non-inferiority randomised control trial. Costs were calculated using information from accounting data and interviews with clinic managers. Two OPDs and three GP-based Beacon practices participated. In the Beacon practices, GPs with a special interest in advanced diabetes care worked with an endocrinologist and diabetes nurse educator to care for referred patients. The main outcome was incremental cost saving per patient course of treatment from a health system perspective. Uncertainty was characterised with probabilistic sensitivity analysis using Monte Carlo simulation. Results The Beacon model is cost saving: the incremental cost saving per patient was A$365 (95% confidence interval -A$901, A$55) and was cost saving in 93.7% of simulations. The key contributors to the variance in the cost saving per patient course of treatment were the mean number of patients seen per site and the number of additional presentations per course of treatment associated with the Beacon model. Conclusions Beacon clinics were less costly per patient course of treatment than usual care in hospital OPDs for equivalent clinical outcomes. Local contractual arrangements and potential variation in the operational cost structure are of significant consideration in determining the cost-efficiency of Beacon models. What is known about this topic? Despite the growing importance of achieving care quality within constrained budgets, there are few costing studies comparing clinically-equivalent hospital and community-based care models. What does this paper add? Costing analyses comparing hospital-based to GP-based health services require considerable effort and are complex. We show that GP-based Beacon clinics for patients with complex chronic disease can be less costly per patient course of treatment than usual care offered in hospital OPDs. What are the implications for practitioners? In addition to improving access and convenience for patients, transferring care from hospital to the community can reduce health system costs.

Assessment of off-axis and in-line electron holography for measurement of potential variations in Cu(In,Ga)Se2 thin-film solar cells

AbstractElectron holography is employed to study variations of the electrostatic crystal potential in Cu(In,Ga)Se2 (CIGS) thin-film solar cells at different length scales: Long-range potential variations across the layer structure of the solar cell as well as inhomogeneities within the layers are analyzed by off-axis holography. In-line holography is applied to examine the local potential variation across a CIGS grain boundary. The phase reconstruction from a focal series is performed by a modified transport of intensity equation (TIE) which is optimized to reduce common artifacts. For comparison, three different microscopes of different optical configurations were used for in-line holography. Based on the results, the impact of the used microscope as well as further acquisition parameters on the in-line holography measurement is assessed. The measured potential variations are discussed considering the effect of different possible sources that may cause potential fluctuations. It is found that most of the variations are best explained by mean inner potential fluctuations rather than by inhomogeneities of the electronic properties. Finally, the present resolution limit of both methods is discussed regarding the feasibility of future electronic characterization of CIGS by holography.

Remote Control Electrodeposition: Principles for Bipolar Patterning of Substrates without an Electrical Connection

We describe electrolyte design for bipolar electrochemical growth and patterning of a range of materials on an electrically floating substrate using the scanning bipolar cell (SBC). In the SBC, bipolar electrodeposition is driven by local potential variation generated beneath a rastering microjet anode connected to a far-field cathode. Metal reduction occurs beneath the microjet when the substrate is approached, provided the electrolyte possesses a suitable reducing agent that undergoes oxidation across the substrate far-field. We use a series of metal reduction reactions (Ni, Cu, Au, Ag) that cover a wide range of nobility, and couple them to the oxidation of ascorbic acid or ferrous ion, depending upon the metal used. The reversibility or irreversibility of the local metal reduction reaction dictates details of the required electrolyte thermodynamics. For irreversible deposits (Ni, Au), there is a wide thermodynamic operating window for the bipolar counter reaction. Reversible deposits that are easily etched (Cu, Ag) have tight thermodynamic windows; deposit stability requires the use of metastable electrolytes. We provide a simple scaling relationship that incorporates the electrolyte thermodynamics, interfacial charge transfer kinetics, and SBC operating conditions, then demonstrate its use through a 10X reduction in the spatial dimensions of local nickel reduction chemistry.

Effect of the interaction conditions of the probe of an atomic-force microscope with the n-GaAs surface on the triboelectrization phenomenon

Triboelectrization as a result of the scanning of an atomic-force-microscope probe over an n-GaAs surface in the contact mode is investigated. The dependences of the local potential variation on the scanning rate and the pressing force of the probe are obtained. The results are explained by point-defect formation in the surface layers of samples under the effect of deformation of these layers during probe scanning. The charge localized at these defects in the case of equilibrium changes the potential of surface, which is subject to triboelectrization. It is shown that, for qualitative explanation of the observed dependences, it is necessary to take into account both the generation and annihilation of defects in the region experiencing deformation.

One-Dimensional Nature of InAs/InP Quantum Dashes Revealed by Scanning Tunneling Spectroscopy.

We report on low-temperature cross-sectional scanning tunneling microscopy and spectroscopy on InAs(P)/InGaAsP/InP(001) quantum dashes, embedded in a diode-laser structure. The laser active region consists of nine InAs(P) quantum dash layers separated by the InGaAsP quaternary alloy barriers. The effect of the p-i-n junction built-in potential on the band structure has been evidenced and quantified on large-scale tunneling spectroscopic measurements across the whole active region. By comparing the tunneling current onset channels, a consistent energy shift has been measured in successive quantum dash or barrier layers, either for the ground state energy of similar-sized quantum dashes or for the conduction band edge of the barriers, corresponding to the band-bending slope. The extracted values are in good quantitative agreement with the theoretical band structure calculations, demonstrating the high sensitivity of this spectroscopic measurement to probe the electronic structure of individual nanostructures, relative to local potential variations. Furthermore, by taking advantage of the potential gradient, we compared the local density of states over successive quantum dash layers. We observed that it does not vanish while increasing energy, for any of the investigated quantum dashes, in contrast to what would be expected for discrete level zero-dimensional (0D) structures. In order to acquire further proof and fully address the open question concerning the quantum dash dimensionality nature, we focused on individual quantum dashes obtaining high-energy-resolution measurements. The study of the local density of states clearly indicates a 1D quantum-wirelike nature for these nanostructures whose electronic squared wave functions were subsequently imaged by differential conductivity mapping.

Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission.

Heterogeneous processes at solid/gas, liquid/gas and solid/liquid interfaces are ubiquitous in modern devices and technologies but often difficult to study quantitatively. Full characterization requires measuring the depth profiles of chemical composition and state with enhanced sensitivity to narrow interfacial regions of a few to several nm in extent over those originating from the bulk phases on either side of the interface. We show for a model system of NaOH and CsOH in an ~1-nm thick hydrated layer on α-Fe2O3 (haematite) that combining ambient-pressure X-ray photoelectron spectroscopy and standing-wave photoemission spectroscopy provides the spatial arrangement of the bulk and interface chemical species, as well as local potential energy variations, along the direction perpendicular to the interface with sub-nm accuracy. Standing-wave ambient-pressure photoemission spectroscopy is thus a very promising technique for measuring such important interfaces, with relevance to energy research, heterogeneous catalysis, electrochemistry, and atmospheric and environmental science.

Quantitative non-contact voltage profiling of quasi one-dimensional nanoelectronic devices

Local electrical characterization tools, such as Electrostatic force microscopy (EFM), can provide local electrical information of nanoelectronic devices, albeit mostly qualitative. For example, EFM images are convolution of local surface potential, capacitance, and contact potential variations in the device. In this study, we demonstrate a calibration procedure to obtain quantitative local voltage distributions of quasi one-dimensional nanoelectronic devices based on carbon nanotubes and ZnO nanowires. By comparing the results with IV measurements of the same devices, we can obtain local electrical properties of devices such as contact resistance, intrinsic resistivity of the nanomaterial, and resistance of a defect.

Transport and Photoelectric Effects in Structures with Ge and SiGe Nanoclusters Grown on Oxidized Si (001)

Crystalline germanium nanoclusters (NCs) are grown by a molecular-beam epitaxy technique on chemically oxidized Si (100) surface at 700oC. Deposition of silicon on the surface with Ge nanoclusters leads to surface reconstruction and formation of polycrystalline diamond-like Si coverage, while nanoclusters core becomes tetragonal SiGe alloy. Possible mechanisms for nanoclusters growth are discussed. Selective photoexcitation of Ge or SiGe nanoclusters or space-charge layer of underlying Si allows to observe two non-equilibrium steady-states with higher and lower conductivity values as compared to the equilibrium one. The persistent photoconductivity (PPC) behaviour was observed after excitation of electron-hole pairs in Si (001) substrate. This effect may be attributed to spatial carrier separation by macroscopic fields in the depletion layer of the near-surface Si. Decreasing of surface conductivity, driven by optical recharging of NCs and Si/SiO2 interface states, is observed in the spectral range from 0.6 to 1.0 eV. Conductivity drop is discussed in the terms of hole accumulation by Ge-NC states enhancing the local-potential variations and, therefore, decreasing the surface conductivity of p-Si.

A 3-D Statistical Simulation Study of Mobility Fluctuations in MOSFET Induced by Discrete Trapped Charges in SiO $_2$ Layer

The random telegraph signal in nanoscale devices is critically dependent on the spatial distribution and number of trapped charges in the gate oxide. Also, the drain-current fluctuation ΔI <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_D$</tex></formula> therein is known to be made up of the fluctuations in carrier number and mobility. In this paper, the local potential variation (LPV) arising from the single charge is incorporated into well-known mobility model and the effect of discrete trapped charges in the oxide layer is statistically investigated, using the in-house 3-D drift-diffusion and density-gradient device simulators. The LPV model covers the conventional distributed trapped charge mobility model but it can also accurately account for the observed fluctuations in I <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_D$</tex></formula> in terms of carrier number and mobility fluctuations.

Nanogold hollow microsphere-based electrochemical immunosensor for the detection of ferritin in human serum

A simple and sensitive electrochemical immunosensor was designed for the determination of ferritin (FeAg, as a model) in human serum by using a nanogold hollow microsphere (NGHS)-functionalized interface as an immunosensing probe. The presence of NGHSs provided a congenial microenvironment with large surface coverage for the immobilization of ferritin antibodies (FeAb). The formation of the antibody-antigen complex by a simple one-step immunoreaction between the immobilized FeAb and FeAg in sample solution introduced a change of membrane charge on the surface of the immunosensing probe. Thus, local potential variations could be detected by potentiometry. Compared to conventional gold nanoparticle probes, the NGHS-modified immunosensors exhibit wide dynamic range from 1.0 to 500 ng·mL−1 toward FeAg, with a detection limit of 0.1 ng·mL−1 (at 3σ). The selectivity, reproducibility and stability of the immunosensors are acceptable. The assay was evaluated with clinical serum specimens (n = 25), and excellent correspondence with the reference enzyme-linked immunosorbent assay method was obtained.

Single-Electron Force Readout of Nanoparticle Electrometers Attached to Carbon Nanotubes

We introduce a new technique of probing the local potential inside a nanostructure employing Au nanoparticles as electrometers and using single-electron force microscopy to sense the charge states of the Au electrometers, which are sensitive to local potential variations. The Au nanoelectrometers are weakly coupled to a carbon nanotube through high-impedance molecular junctions. We demonstrate the operation of the Au nanoelectrometer, determine the impedance of the molecular junctions, and measure the local potential profile in a looped nanotube.

Impurity scattering effects in STM studies of high- [formula omitted] superconductors

Recent STM measurements have observed many inhomogeneous patterns of the local density of states on the surface of high- T c cuprates. As a first step to study such disordered strong correlated systems, we use the BdG equation for the t– t ′ – t ″ – J model with an impurity. The impurity is taken into account by a local potential or local variation of the hopping/exchange terms. Strong correlation is treated by a Gutzwiller mean-field theory with local Gutzwiller factors and local chemical potentials. It turned out that the potential impurity scattering is greatly suppressed, while the local variation of hoppings/exchanges is enhanced.

Human Fingerprint - Metal Interactions Studied Using a Scanning Kelvin Probe

Human fingerprint friction ridge deposits induce local Volta potential variations on a range of technologically important metals including iron, copper, aluminium and brass, which can be spatially mapped at high resolution using a scanning Kelvin probe (SKP). Because the Volta potential patterns principally derive from a depassivation of the metal surface by inorganic salts in human sweat, fingerprints can be visualized by SKP even after exposure to high temperatures. This property is exploited in the use of SKP to visualize fingerprint patterns on items of forensic significance, such as fired cartridge cases, where the loss of organic fingerprint components upon firing typically renders conventional chemical development techniques ineffective.

Scanning tunneling microscopy/spectroscopy as an atomic-resolution dopant profiling method in Si

The ability of scanning tunneling microscopy and spectroscopy (STM/STS) as a dopant profiling method in Si is demonstrated. We have developed two different methods. One is a simultaneous measurement of potential and dopant atom distributions by conventional STM/STS. Actually acceptor and donor atoms were distinctly detected and the local potential variation was observed at p-n junctions on atomically-flat hydrogenated Si(111) substrates. The comparison between the measured dopant atom and potential distributions at a p-n junction revealed that the potential profile was significantly affected by the fluctuation of dopant atom distributions. The other is a quantitative measurement of carrier distributions by resonance electron tunneling (RET) spectroscopy. The RET peak energy of C60 molecules placed on oxidized Si(001) surfaces was measure by STS and the resulting value systematically varied depending on the doping level of the substrates, enabling us to measure carrier density profiles across p-n junctions.

Scanning gate microscopy investigations on an InGaAs quantum point contact

In recent years, there has been interest in devices created on InGaAs due to the possibility of its use for spintronics. Nonetheless, this material is known for usually presenting some levels of disorder. We have used scanning gate microscopy to study the local potential for an in-plane gated InGaAs quantum point contact and succeeded in obtaining images corresponding to sites where same quantum interference conditions are maintained. Furthermore, we have visualized images of the local potential variations within the confined region near pinch-off condition.

Potential and Impedance Imaging of Polycrystalline BiFeO3 Ceramics

Electrostatic‐force‐sensitive scanning probe microscopy (SPM) is used to investigate grain boundary behavior in polycrystalline BiFeO3 ceramics. Scanning surface potential microscopy (SSPM) of a laterally biased sample exhibits potential drops due to resistive barriers at the grain boundaries. In this technique, the tips acts as a moving voltage probe detecting local variations of potential associated with the ohmic losses within the grains and at the grain boundaries. An approach for the quantification of grain boundary, grain interior, and contact resistivity from SSPM data is developed. Scanning impedance microscopy (SIM) is used to visualize capacitive barriers at the grain boundaries. In SIM, a dc‐biased tip detects the variations of local potential induced by the lateral ac voltage applied to the sample. Unlike the traditional dc and ac transport measurement, both of these techniques are sensitive to the variation of local potential (SSPM) or local voltage oscillation amplitude and phase (SIM), rather than to current. Therefore, special attention is paid to the relationship between SSPM and SIM images and data obtained from traditional impedance spectroscopy and dc transport measurements. For BiFeO3 ceramics excellent agreement between the local SIM measurements and impedance spectroscopy data are demonstrated.