Direct observation of delithiation as the origin of analog memristance in LixNbO2

The discovery of analog LixNbO2 memristors revealed a promising new memristive mechanism wherein the diffusion of Li+ rather than O2- ions enables precise control of the resistive states. However, directly correlating lithium concentration with changes to the electronic structure in active layers remains a challenge and is required to truly understand the underlying physics. Chemically delithiated single crystals of LiNbO2 present a model system for correlating lithium variation with spectroscopic signatures from operando soft x-ray spectroscopy studies of device active layers. Using electronic structure modeling of the x-ray spectroscopy of LixNbO2 single crystals, we demonstrate that the intrinsic memristive behavior in LixNbO2 active layers results from field-induced degenerate p-type doping. We show that electrical operation of LixNbO2-based memristors is viable even at marginal Li deficiency and that the analog memristive switching occurs well before the system is fully metallic. This study serves as a benchmark for material synthesis and characterization of future LixNbO2-based memristor devices and suggests that valence change switching is a scalable alternative that circumvents the electroforming typically required for filamentary-based memristors

Studies of minority carrier diffusion length increase in p-type ZnO : Sb

Minority electron diffusion length was measured in p-type, Sb-doped ZnO as a function of temperature using the electron beam induced current technique. A thermally induced increase of electron diffusion length was determined to have an activation energy of 184 +/- 10 meV. Irradiation with a low energy (5 kV) electron beam also resulted in an increase of diffusion length with a similar activation energy (219 +/- 8 meV). Both phenomena are suggested to involve a Sb-Zn-2V(Zn) acceptor complex. Saturation and relaxation dynamics of minority carrier diffusion length are explored. Details of a possible mechanism for diffusion length increase are presented

Electron irradiation-induced increase of minority carrier diffusion length, mobility, and lifetime in Mg-doped AlN/AlGaN short period superlattice

Minority carrier diffusion length in a p-type Mg-doped AlN/Al(0.08)Ga(0.92)N short period superlattice was shown to undergo a multifold and persistent (for at least 1 week) increase under continuous irradiation by low-energy beam of a scanning electron microscope. Since neither the diffusion length itself nor the rate of its increase exhibited any measurable temperature dependence, it is concluded that this phenomenon is attributable to the increase in mobility of minority electrons in the two-dimensional electron gas, which in turn is limited by defect scattering. Cathodoluminescence spectroscopy revealed similar to 40% growth of carrier lifetime under irradiation with an activation energy of 240 meV

Doping level dependence of electron irradiation-induced minority carrier diffusion length increase in Mg-doped GaN

The electron irradiation-induced increase of minority carrier diffusion length was studied as a function of hole concentration in Mg-doped GaN. Variable-temperature electron beam induced current measurements yielded activation energies of 264, 254, 171, and 144 meV for samples with hole concentrations of 2x10(16), 9x10(16), 3x10(18), and 7x10(18) cm(-3), respectively. This carrier concentration dependence of the activation energy for the effects of electron irradiation was found to be consistent with Mg acceptors, indicating the involvement of the latter levels in the irradiation-induced diffusion length increase

Cathodoluminescence studies of carrier concentration dependence for the electron-irradiation effects in p-GaN

Electron-irradiation increase of nonequilibrium carrier lifetime was studied as a function of hole concentration in Mg-doped GaN. Temperature-dependent cathodoluminescence (CL) studies yielded activation energies of 344, 326, 237, and 197 meV for samples with hole concentrations of 2x10(16), 9x10(16), 3x10(18), and 7x10(18) cm(-3), respectively. The systematic decay of activation energy with carrier concentration was found to be consistent with Mg acceptors, indicating the involvement of the latter levels in irradiation-induced lifetime changes

Results of SIVVA assessments for species for all three climate scenarios (SC1-SC3) and across all six regions: Laguna Madre (LM), Western Gulf Coastal Plain (WGCP), Mississippi Alluvial Plain (MAP), Southern Coastal Plain (SCP), Central Florida Coastal Plain (CFCP), and Southern Florida Coastal Plain (SFCP).

<p>Scores are presented for all three modules: Ecosystem Status (ES), Vulnerability (VU), and Conservation Value (CV).</p

Results of SIVVA assessments for natural communities for all three climate scenarios and across all six regions.

<p>Scores are presented for all three modules: Ecosystem Status (ES), Vulnerability (VU), and Conservation Value (CV).</p

Vulnerability and adaptive capacity SIVVA for species scores: Light grey bars are averaged across subregions with whiskers depicting variation across three climate scenarios; darker grey bars are averaged across climate scenarios with whiskers depicting variation across subregions.

<p>Note comparable scores, but greater variation across regions than climate scenarios.</p