Stability Of Charged States Research Articles

Charge-state stability of color centers in wide band gap semiconductors

Charge-state stability of color centers in wide band gap semiconductors

Charge Stability and Charge-State-Based Spin Readout of Shallow Nitrogen-Vacancy Centers in Diamond.

Spin-based applications of the negatively charged nitrogen-vacancy (NV) center in diamonds require an efficient spin readout. One approach is the spin-to-charge conversion (SCC), relying on mapping the spin states onto the neutral (NV0) and negative (NV-) charge states followed by a subsequent charge readout. With high charge-state stability, SCC enables extended measurement times, increasing precision and minimizing noise in the readout compared to the commonly used fluorescence detection. Nanoscale sensing applications, however, require shallow NV centers within a few nanometers distance from the surface where surface related effects might degrade the NV charge state. In this article, we investigate the charge state initialization and stability of single NV centers implanted ≈5 nm below the surface of a flat diamond plate. We demonstrate the SCC protocol on four shallow NV centers suitable for nanoscale sensing, obtaining a reduced readout noise of 5-6 times the spin-projection noise limit. We investigate the general applicability of the SCC for shallow NV centers and observe a correlation between the NV charge-state stability and readout noise. Coating the diamond with glycerol improves both the charge initialization and stability. Our results reveal the influence of the surface-related charge environment on the NV charge properties and motivate further investigations to functionalize the diamond surface with glycerol or other materials for charge-state stabilization and efficient spin-state readout of shallow NV centers suitable for nanoscale sensing.

Charge stabilization of shallow nitrogen-vacancy centers using graphene/diamond junctions

We studied the charge-state stabilization of shallow nitrogen-vacancy (NV) centers in (111) diamond using graphene/diamond junctions. Measurement of the fluorescence stability and evaluation of the charge-state stability were conducted on the NV centers at the graphene and the graphene-free region. The results revealed that about half of the total NV centers (NV0 + NV−) at the graphene-free region were unstable, while over 90% of the measured NV centers at the graphene region were stabilized as NV− centers. Graphene/diamond junctions contribute significantly to charge-state stabilization of shallow NV− centers in (111) diamond.

Improved process intermediate stability through the identification and elimination of reactive glycation residues – a monoclonal antibody case study

ABSTRACT The manufacturing of therapeutic biologics can result in a heterogeneous population of charge variants, encompassing many quality attributes which could impact activity and pharmacokinetics. Monitoring the relative abundance of these charge variants to demonstrate process consistency is an expectation of regulatory agencies. Control of the relative abundance of charge variants is also necessary to ensure product comparability across the product lifecycle. We have observed a significant shift in the relative abundance of charged species, as measured by capillary isoelectric focusing, during clarified cell culture fluid holds for several monoclonal antibodies. This lack of stability requires that the hold time for this process intermediate be significantly curtailed, eliminating manufacturing flexibility. We have identified the cause of this shift in relative abundance of charged species as changes in glycation levels, focused predominantly on three conserved, solvent accessible, lysine residues. Mutants of a model protein were generated that show increased charge state stability can be gained by eliminating these reactive lysines. Further, characterization studies were conducted on these mutants to determine the impact to biological activity and stability of the molecule, with no detrimental effects observed. Incorporating this knowledge into the assessments of candidate drugs could allow for the selection of molecules less susceptible to this product degradation pathway, allowing for greater manufacturing flexibility. This process of identifying and removing reactive lysine residues could be useful in the design of drug candidates with improved charge state stability, across a range of modalities.

Site-Dependent Properties of Quantum Emitters in Nanostructured Silicon Carbide

Deep defects in silicon carbide (SiC) possess atom-like electronic, spin and optical properties, making them ideal for quantum-computing and -sensing applications. In these applications, deep defects are often placed within fabricated nanostructures that modify defect properties due to surface and quantum confinement effects. Thus far, theoretical studies exploring deep defects in SiC have ignored these effects. Using density functional theory, this work demonstrates site-dependence of properties of bright, negatively-charged silicon monovacancies within a SiC nanowire. It is shown that the optical properties of defects depend strongly on the hybridization of the defect states with the surface states and on the structural changes allowed by proximity to the surfaces. Additionally, the analysis of the first principles results indicates that the charge-state conversion and/or migration to thermodynamically-favorable undercoordinated surface sites can deteriorate deep-defect properties. These results illustrate the importance of considering how finite-size effects tune defect properties, and of creating mitigating protocols to ensure a defect's charge-state stability within nanostructured hosts.

Charge stability of shallow single nitrogen-vacancy centers in lightly boron-doped diamond

Nitrogen vacancy (NV) centers in diamond must be in a stable negatively charged state for their application to quantum sensing and quantum information processing. In this study, we investigated the charge-state stability of single NV centers in lightly boron-doped diamond ([B] ≈ 1 × 1015 cm−3). Photoluminescence and optically detected magnetic resonance measurements indicated that single NV centers near the diamond surface are negatively charged despite the presence of boron acceptors. This unique phenomenon can be explained by charge transfer between the NV centers and their local environment under laser excitation. This study provides a new perspective on the charge stability of single NV centers in lightly doped diamond and insights for further development of high-performance diamond quantum devices.

Charge‐Assisted Engineering of Color Centers in Diamond

Owing to its unique optical and spin properties, the nitrogen‐vacancy (NV) center holds the promise of a diamond‐based room‐temperature scalable quantum computer, but the numerous technical and physical issues are not yet overcome, especially the poor N to NV conversion. The NV and other color centers are, however, successfully used as multitasking quantum sensors, and open new routes in quantum sensing technologies. Most recently, several breakthroughs and demonstrations were achieved, shedding a new light on the feasibility of a NV‐based quantum computer. Herein, the recently developed method of charge‐assisted single defect engineering is reviewed. With a controlled charging of the involved species, it modifies the diffusion or kinetics of defect formation and acts as a catalyzer of the NV creation while hindering the formation of competing and perturbing defects such as divacancies or NVH. Very high NV creation yields up to 75% are obtained and the method is suitable to other impurity‐vacancy defects. Furthermore, it has positive consequences on the charge state stability and coherence time of the NV centers, which is as well discussed. Together with the possibility to nowadays deterministically implant single ions, this powerful method brings the scalability of NV qubits closer.

Effects of Nitrogen Impurity Concentration on Nitrogen-Vacancy Center Formation in 4H-SiC

Spin defects of which states can be manipulated in Silicon Carbide (SiC) have drawn considerable attention because of their applications to quantum technologies. The single negatively-charged pairs of VSi and nitrogen atom (N) on an adjacent C site (NCVSi- center) in SiC is suitable for them. This paper reports the formation of NCVSi- centers on 4H-SiC epilayers with different nitrogen concentrations using light/heavy ion irradiation and subsequent thermal annealing. The formation of NCVSi- centers is characterized by the near infrared photoluminescence (PL) spectroscopy. It is shown that the PL intensity from NCVSi- centers depends on the N concentration and the ion irradiation conditions. The PL intensity increases monotonically with increasing the N concentration when the N concentration is above 2.6×1016 cm-3, whereas no linear correlation between them does not appear below that N concentration. Although the PL intensity increases with increasing defects induced by ion irradiation, the PL quenching due to neighboring residual defects appear at above the areal vacancy concentration of 1017 vac/cm2 and the broad Raman scattering spectra originated from vibration modes of amorphized regions hinder the PL from NCVSi- centers at above 1018 vac/cm2. The formation mechanism and the charge state stability of NCVSi- centers are discussed based on the obtained results.

Relaxation, Thermal, and Interphase Effects in Polymer–Ferroelectric-Piezoelectric Ceramic Composites of Different Structures

The relaxation and thermal processes and interphase phenomena in composites based on ferroelectrics and a polymer matrix are studied. It is shown that the charge stabilized at the interface of the composite during its electrothermopolarization is mainly determined by the structure of the polymer matrix and the piezoelectric phase. The results obtained make it possible to reveal the main factors affecting the piezoelectric properties of the heterogeneous polymer–ferroelectric ceramic system. Polyolefins and fluorine-containing polar polymers are used as the organic phase, and ferroelectric ceramics of rhombohedral, tetragonal, and mixed structures serve as the inorganic phase. The relaxation processes and interphase phenomena are studied using a differential scanning calorimeter, and the charge state is analyzed by recording the thermally stimulated depolarization current. The charge-state stability is determined by the electret potential difference of the composites. The molecular relaxation is analyzed by the dielectric method. It is established that the composites in which the interphase interaction is more pronounced are characterized by high piezoelectric properties.

Релаксационные, термические и межфазные эффекты в композитах полимер-сегнетопьезокерамика различной структуры

AbstractThe relaxation and thermal processes and interphase phenomena in composites based on ferroelectrics and a polymer matrix are studied. It is shown that the charge stabilized at the interface of the composite during its electrothermopolarization is mainly determined by the structure of the polymer matrix and the piezoelectric phase. The results obtained make it possible to reveal the main factors affecting the piezoelectric properties of the heterogeneous polymer–ferroelectric ceramic system. Polyolefins and fluorine-containing polar polymers are used as the organic phase, and ferroelectric ceramics of rhombohedral, tetragonal, and mixed structures serve as the inorganic phase. The relaxation processes and interphase phenomena are studied using a differential scanning calorimeter, and the charge state is analyzed by recording the thermally stimulated depolarization current. The charge-state stability is determined by the electret potential difference of the composites. The molecular relaxation is analyzed by the dielectric method. It is established that the composites in which the interphase interaction is more pronounced are characterized by high piezoelectric properties.

Ab Initio Magneto-Optical Spectrum of Group-IV Vacancy Color Centers in Diamond

Group-IV -- Vacancy color centers in diamond are fast emerging qubits that can be harnessed in quantum communication and sensor applications. There is an immediate quest for understanding their magneto-optical properties, in order to select the appropriate qubits for varying needs of particular quantum applications. Here we present results from cutting edge \emph{ab initio} calculations about the charge state stability, zero-phonon-line energies, spin-orbit and electron-phonon couplings for Group-IV -- Vacancy color centers. Based on the analysis of our results, we develop a novel spin Hamiltonian for these qubits which incorporates the interaction of the electron spin and orbit coupled with phonons beyond perturbation theory. Our results are in good agreement with previous data and predict a new defect for qubit applications with thermally initialized ground state spin and long spin coherence time.

Research Update: Ab initio study on resistive memory device optimization trends: Dopant segregation effects and data retention in HfO2−x

Segregation energy trends and their charge state dependence were established for Group II to Group VI substitutional metal dopants in HfO2 using density functional theory. Corroborating the segregation energy with dopant-oxygen bond lengths and charge state stability, strong effects are predicted for Group II and Group III p-type dopants, which can easily reverse their segregation trend due to −2 charge state preference. Transitions between segregation and isolation may occur around 1.5 eV above the valence band maximum, with the exception of Al, which remains barely stable in its segregated form. In Al-doped HfOx, the switching characteristics of filaments formed near Al dopants show subtle changes and the OFF state data retention is degraded. A comprehensive assessment on configurational Al-VO interaction, charge state dependence, and migration energy changes points to the fact that to achieve OFF state data retention improvements, it will be necessary to engineer the filament interaction with Al to stabilize configurations that favor vacancy filament dissolution. Another mode of failure can result from subsequent charge trapping during the operation of the device, which ultimately prohibits the filament dissociation.

Improving Defect-Based Quantum Emitters in Silicon Carbide via Inorganic Passivation.

Defect-based color centers in wide-bandgap crystalline solids are actively being explored for quantum information science, sensing, and imaging. Unfortunately, the luminescent properties of these emitters are frequently degraded by blinking and photobleaching that arise from poorly passivated host crystal surfaces. Here, a new method for stabilizing the photoluminescence and charge state of color centers based on epitaxial growth of an inorganic passivation layer is presented. Specifically, carbon antisite-vacancy pairs (CAV centers) in 4H-SiC, which serve as single-photon emitters at visible wavelengths, are used as a model system to demonstrate the power of this inorganic passivation scheme. Analysis of CAV centers with scanning confocal microscopy indicates a dramatic improvement in photostability and an enhancement in emission after growth of an epitaxial AlN passivation layer. Permanent, spatially selective control of the defect charge state can also be achieved by exploiting the mismatch in spontaneous polarization at the AlN/SiC interface. These results demonstrate that epitaxial inorganic passivation of defect-based quantum emitters provides a new method for enhancing photostability, emission, and charge state stability of these color centers.

Charge state stabilization of shallow nitrogen vacancy centers in diamond by oxygen surface modification

We investigated the charge state stability and coherence properties of near-surface single nitrogen vacancy (NV) centers in 12C-enriched diamond for potential use in nanoscale magnetic field sensing applications. The stability of charge states in negatively charged NV centers (NV−) was evaluated using one of the pulsed optically detected magnetic resonance measurements, Rabi oscillation measurements. During the accumulation of Rabi oscillations, an unstable shallow NV− was converted to a neutral state. As a result, the contrast of Rabi oscillations degraded, depending on charge state stability. We stabilized the NV− state of very shallow NV centers (∼2.6 ± 1.1 nm from the surface) created by 1.2 keV nitrogen ion implantation by diamond surface modification, UV/ozone exposure, and oxygen annealing. This improvement indicates that we can suppress the upward surface band bending and surface potential fluctuations through Fermi level pinning originating from oxygen-terminated diamond surfaces.

Interplay between strain, defect charge state, and functionality in complex oxides

We use first-principles calculations to investigate the interplay between strain and the charge state of point defect impurities in complex oxides. Our work is motivated by recent interest in using defects as active elements to provide novel functionality in coherent epitaxial films. Using oxygen vacancies as model point defects, and CaMnO3 and MnO as model materials, we calculate the changes in internal strain caused by changing the charge state of the vacancies, and conversely the effect of strain on charge-state stability. Our results show that the charge state is a degree of freedom that can be used to control the interaction of defects with strain and hence the concentration and location of defects in epitaxial films. We propose the use of field-effect gating to reversibly change the charge state of defects and hence the internal strain and corresponding strain-induced functionalities.

Electronic Structure Changes As Source of Chemical and Interfacial Instability in LiCoPO4 As Positive Electrode for High Voltage Li-Ion Batteries

The energy storage capability of a battery scales with the potential difference between its electrodes. Yet operation of positive electrode materials at high potentials introduces challenges of stabilization of charged states. As of today, no positive electrode material has been demonstrated to durably and safely operate above 4.5 V vs. Li+/Li0. LiCoPO4-based electrodes theoretically offer high specific capacity and high potentials of operation, around 4.8V vs. Li+/Li0, but these electrodes are prone to failure during cycling. Failure occurs through chemical and structural degradation in the bulk of the active material or at its interfaces with cell components, especially the electrolyte. The development of Li-ion battery electrodes operating at high potential is indispensable to meet the specific energy target of 250 kWh/kg at the packaged cell level. Changes in the electronic structure and chemical stability of olivine-type LiCoPO4 and Fe-substituted LiCoPO4 were explored as both a function of ion substitution and oxidation state. Soft Ex situX-Ray absorption spectroscopy (XAS) made it possible to compare the changes in chemical bonding between electrode bulk and surface as a function of lithium content. This technique can probe the density of states at the transition metal and O levels. The evolution of these levels revealed changes in the metal-oxide covalence when lithium was deintercalated from the structure, and, thus, the material was oxidized. An increase in covalence can lead to the destabilization of the anions. If this process takes place in the bulk of the material, this destabilization can lead to thermal degradation via oxygen loss. At the surface, even small degrees of destabilization are sufficient to produce oxidizing species that attack the electron-rich solvent molecules in the electrolyte, leading to irreversible capacity loss. Increased metal-oxygen covalence was universally observed in the spectroscopy in the form of a rising pre-O K-edge peak at ~530 eV as a function of lithium deintercalation in both bulk and surface. However, accompanying changes in the Co spectroscopy were only observed in the Fe-substituted sample. These changes are also indicative of increased hybridization between Co 3d and O 2p orbitals. Co K-edge XANES and EXAFS experiments further corroborated these findings, in which virtually no changes in the Co K-edge were observed upon oxidation of unsubstituted LiCoPO4. Fe doping appears to play a substantial role in getting Co to participate in redox chemistry, and the mechanism by which it occurs is currently being explored using Density Functional Theory. Fe-substituted LiCoPO4 is an exciting new positive electrode material that may prove useful in advancing Li-ion battery technology.

5 V driving organic non-volatile memory transistors with poly(vinyl alcohol) gate insulator and poly(3-hexylthiophene) channel layers

Organic non-volatile memory devices were fabricated by employing organic field-effect transistors (OFETs) with poly(vinyl alcohol) (PVA) and poly(3-hexylthiophene) as a gate insulating layer and a channel layer, respectively. The 10-nm-thick nickel layers were inserted for better charge injection between the channel layer and the top source/drain electrodes. The fabricated PVA-OFET memory devices could be operated at low voltages (≤5 V) and showed pronounced hysteresis characteristics in the transfer curves, even though very small hysteresis was measured from the output curves. The degree of hysteresis was considerably dependent on the ratio of channel width (W) to channel length (L). The PVA-OFET memory device with the smaller W/L ratio (25) exhibited better retention characteristics upon 700 cycles of writing-reading-erasing-reading operations, which was assigned to the stability of charged states in devices.

Fabrication and Scintillation Performance of Nonstoichiometric LuAG:Ce Ceramics

Nonstoichiometric LuAG:Ce Ceramics ([Lu(1–x)Cex]3Al5O12, x = 0.005) with different excess of Lu3+ were designed on the basis of Lu2O3‐Al2O3 phase diagram and fabricated by a solid‐state reaction method. Without using any traditional sintering aids, pure phase and good optical performance were obtained in such a Lu‐rich LuAG:Ce ceramics. In addition, scintillation efficiency and light yield of 1% excess of Lu3+ ceramic sample were found 16 times and 1.82 times higher than that of commercial Bi4Ge3O12 (BGO) single crystals, respectively. Such values are comparable or even better than those in most of LuAG:Ce single crystals. However, antisite defects were also induced by excess of Lu doping, whose luminescence was found at 350–410 nm in Lu‐rich LuAG:Ce ceramics. The relationship of excess content of Lu and the microstructure, optical quality, and scintillation performance were clarified and discussed. Furthermore, by utilizing X‐ray absorption near edge spectroscopy technique, the charge state stability of cerium in Lu‐rich LuAG:Ce ceramics was examined. It appears that the excess of isovalence Lu3+ doping has a negligible effect on the cerium valence instability and creation of stable Ce4+ center.

The stabilization of charged states at phenazine-like units in polyaniline under p-doping: an in situ ATR-FTIR spectroelectrochemical study

The structure and stabilization of charged states during p-doping of polyaniline (PANI) were studied by in situ ATR-FTIR spectroelectrochemistry. The role of phenazine-like units in several copolymers of aniline and a phenazine derivative (3,7-diamino-5-phenylphenazinium chloride, phenosafranine) was investigated by spectroelectrochemistry. PANI and three copolymers with different aniline to phenosafranine ratio were electrochemically prepared. FTIR spectra of as-prepared polymers as well as in situ FTIR spectra during the oxidation of the polymers give evidence of the presence of phenazine-like units in the structure of electrochemically prepared PANI, as shown by vibrations of the phenazine rings. New bands corresponding to the in-plane and out-of-plane C-H vibration of 1,2,4-trisubstituted benzene nuclei in the phenazine skeleton are found at 1033, 957, 880, 766 and 681 cm(-1). The potential dependence of IR bands observed during oxidation of the polymers was compared to that of the ESR intensity and the absorption data and points to the diamagnetic species like π-dimers formed at higher oxidation level of PANI. This charged state is shown to be fixed at the link of the phenazine-like units with the linear segments of PANI.

Charged States of α,ω-Dicyano β,β′-Dibutylquaterthiophene as Studied by in Situ ESR UV−Vis NIR Spectroelectrochemistry

The influence of the molecular structure on the stabilization of charged states was studied in detail by in situ ESR UV-vis NIR spectroelectrochemistry at a novel α,ω-dicyano substituted β,β'-dibutylquaterthiophene (DCNDBQT) and the electrochemically generated cation and anion radicals have been proved for the first time. The voltammetry of DCNDBQT results in two separate oxidation steps with the reversible first one. The experimental absorption maxima at 646 and 1052 nm together with the calculated ones (by DFT method) as well as an ESR signal at the first anodic step prove the presence of a radical cation. Three additional optical bands (554, 906, and 1294 nm for CT-transition) can be attributed to the formation of cation radical dimer. The dicationic structure formed in the second oxidation step is not stable. The stabilization proceeds via a dimer formation in two chemical follow-up reactions. The existence of the dimeric structures was proved by ex situ MALDI TOF mass spectrometry. As the substitution by cyano groups opens the route to cathodic reductions, DCNDBQT shows a single quasi-reversible reduction step. Here, the in situ ESR UV-vis NIR spectroelectrochemical measurements and theoretical calculations let us confirm the electrochemical generation of an anion radical. As we found a low number of anion radicals by quantitative ESR spectroelectrochemistry and an appearance of additional bands in the UV-vis NIR absorption spectra, the formation of dimeric structures must be considered and was corroborated by mass spectrometry. The role of dimerization in the reaction mechanism of the DCNDBQT oxidation and reduction are discussed in general. The experimental results were interpreted using the quantum chemical calculations based on density functional theory.