Search

Evolution of a non-recombining sex-specific region on the Y (or W) chromosome (NRY) is a key step in sex chromosome evolution, but how recombination suppression evolves is not well understood. Studies in many different organisms indicated that NRY evolution often involves several expansion steps. Why such NRY expansions occur remains unclear, although it is though that they are likely driven by sexually antagonistic selection. This paper describes a recent NRY expansion due to shift of the pseudoautosomal boundary on the sex chromosomes of a dioecious plant Silene latifolia. The shift resulted in inclusion of at least 16 pseudoautosomal genes into the NRY. This region is pseudoautosomal in closely related Silene dioica and Silene diclinis, indicating that the NRY expansion occurred in S. latifolia after it speciated from the other species ~120 thousand years ago. As S. latifolia and S. dioica actively hybridise across Europe, interspecific gene flow could blur the PAR boundary in these species. The pseudoautosomal genes have significantly elevated genetic diversity (π ~ 3% at synonymous sites), which is consistent with balancing selection maintaining diversity in this region. The recent shift of the PAR boundary in S. latifolia offers an opportunity to study the process of on-going NRY expansion.

The evolution of plastic responses to external cues allows species to track the environmental variation they regularly experience. However, it remains unclear how plasticity evolves during adaptation. To test whether distinct patterns of plasticity is associated with recent adaptive divergence, we quantified plasticity for two closely related but ecologically divergent Sicilian daisy species (Senecio, Asteraceae). We sampled c.40 genotypes of each species from natural populations on and around Mt Etna and then reciprocally transplanted multiple clones of each genotype into four field sites along an elevational gradient representing each species’ native range, the edge of their range, and conditions outside their native range. At each elevation we quantified survival and measured leaf traits that included investment (specific leaf area), morphology, chlorophyll fluorescence, pigment content and gene expression. As evidence of adaptive divergence, both species performed better at their native site and better than the species from the other habitat. Traits and differentially expressed genes that changed with elevation in one species often showed little change in the other species, or changed in the opposite direction. Adaptive divergence is therefore associated with the evolution of distinct plastic responses to environmental variation, despite these two species sharing a recent common ancestor.

The conditions for obtaining high-quality heavily doped epitaxial Ge:P/Si(001) epitaxial layers by hot wire chemical vapor deposition were determined. The thermal decomposition of GaP was employed to provide the source of P. Extremely high electron concentration in Ge layers (up to 1.3×1020 cm−3) were achieved. According to the secondary ion mass spectroscopy data, the P concentration was constant within the entire thickness of the Ge layers and drops down abruptly at the boundary with the Si buffer. A strong direct bandgap edge photoluminescence line has been observed from the heavily doped n+-Ge:P layers at room temperature.

The stochastic resonance phenomenon has been studied experimentally and theoretically for a state-of-art metal-oxide memristive device based on yttria-stabilized zirconium dioxide and tantalum pentoxide, which exhibits bipolar filamentary resistive switching of anionic type. The effect of white Gaussian noise superimposed on the sub-threshold sinusoidal driving signal is analyzed through the time series statistics of the resistive switching parameters, the spectral response to a periodic perturbation and the signal-to-noise ratio at the output of the nonlinear system. The stabilized resistive switching and the increased memristance response are revealed in the observed regularities at an optimal noise intensity corresponding to the stochastic resonance phenomenon and interpreted using a stochastic memristor model taking into account an external noise source added to the control voltage. The obtained results clearly show that noise and fluctuations can play a constructive role in nonlinear memristive systems far from equilibrium.

As-prepared PbS films independently on the method of preparation are all p-type semiconductors. The intrinsic p-type of PbS thin films without sensibilization is supposed to originate from the native defects i.e. structural imperfections and shallow accepter levels due to Pb vacancies. The large relativistic splitting in band structure of PbS materials makes them preferable for band gap engineering. In this work PbS thin films were prepared via direct plasma-chemical interaction of lead and sulfur vapors. Then, the as-prepared layers were annealed in argon-oxygen plasma. Optical emission spectroscopy (OES) was used to identify the exited species and to assume the possible mechanisms of plasma-chemical reactions. The changes in electrical properties and structure were also studied.

Culture is a display of everything that man has ever created. It determines the course of the society on which the society will be built, and the economy is an indivisible part of this trend, which is guided by culture. Only a person directly influences the development and formation of a culture in which each sphere of society is interconnected and where each of them is an inseparable link. The article presents a brief overview of the mutual influence of two sciences - economics and culture

We report on the results of the experimental investigations of the local resistive switching (RS) in the contact of a conductive atomic force microscope (CAFM) probe to a nanometer-thick yttria stabilized zirconia (YSZ) film on a conductive substrate under a Gaussian noise voltage applied between the probe and the substrate. The virtual memristor was found to switch randomly between the low resistance state and the high resistance state as a random telegraph signal (RTS). The potential profile of the virtual memristor calculated from its response to the Gaussian white noise shows two local minima, which is peculiar of a bistable nonlinear system.

The structure of the electron current through an individual filament of a nanometer-sized virtual memristor consisting of a contact of a conductive atomic force microscope probe to an yttria stabilized zirconia (YSZ) thin film deposited on a conductive substrate is investigated. Usually, such investigation is performed by the analysis of the waveform of this current with the aim to extract the random telegraph noise (RTN). Here, we suggest a new indirect method, which is based on the measurement of the spectrum of the low-frequency flicker noise in this current without extracting the RTN, taking into account the geometrical parameters of the filament. We propose that the flicker noise is caused by the motion (drift/diffusion) of oxygen ions via oxygen vacancies within and around the filament. This allows us to estimate the root mean square magnitude i0 of the current jumps, which are caused by random jumps of oxygen ions, and the number M of these ions. This is fundamental for understanding the elementary mechanisms of electron current flowing through the filament and resistive switching in YSZ–based memristor devices.

We have applied Conductive Atomic Force Microscopy (CAFM) to study the microscopic mechanism of resistive switching in the ultrathin (3 - 5 nm) yttria stabilized zirconia (YSZ) films. Using CAFM, we were able to trace the growth of the individual conductive filaments, which are considered now to be responsible for the resistive switching effect in the transition metal oxides. The growth of the filaments has been proven to be initiated by the defects in the film material including the ones, which are the concentrators of the electric field, in particular, by the roughness (hillocks) of the film/substrate interface. The electron transport via individual filaments has been studied. Besides the butterfly-type hysteresis in the current-voltage (I-V) curves of the probe- to-sample contact typical for the bipolar resistive switching, we have observed the I-V curves with resonant peaks attributed to the resonant electron tunneling via the localized electron states in the filaments.

Resistive switching (RS) is studied in a memristor based on a ZrO2(Y)/Ta2O5 stack under a white Gaussian noise voltage signal. We have found that the memristor switches between the low resistance state and the high resistance state in a random telegraphic signal (RTS) mode. The effective potential profile of the memristor shows from two to three local minima and depends on the input noise parameters and the memristor operation. These observations indicate the multiplicative character of the noise on the dynamical behavior of the memristor, that is the noise perceived by the memristor depends on the state of the system and its electrical properties are influenced by the noise signal. The detected effects manifest the fundamental intrinsic properties of the memristor as a multistable nonlinear system.

The low-frequency noise in a nanometer-sized virtual memristor consisting of a contact of a conductive atomic force microscope (CAFM) probe to an yttria stabilized zirconia (YSZ) thin film deposited on a conductive substrate is investigated. YSZ is a promising material for the memristor application since it is featured by high oxygen ion mobility, and the oxygen vacancy concentration in YSZ can be controlled by varying the molar fraction of the stabilizing yttrium oxide. Due to the low diameter of the CAFM probe contact to the YSZ film (similar to 10nm), we are able to measure the electric current flowing through an individual filament both in the low resistive state (LRS) and in the high resistive state (HRS) of the memristor. Probability density functions (Pdfs) and spectra of the CAFM probe current in both LRS and HRS are measured. The noise in the HRS is found to be featured by nearly the same Pdf and spectrum as the inner noise of the experimental setup. In the LRS, a flicker noise 1/f(gamma) with gamma approximate to 1.3 is observed in the low-frequency band (up to 8kHz), which is attributed to the motion (drift/diffusion) of oxygen ions via oxygen vacancies in the filament. Activation energies of oxygen ion motion determined from the flicker noise spectra are distributed in the range of [0.52; 0.68] eV at 300K. Knowing these values is of key importance for understanding the mechanisms of the resistive switching in YSZ based memristors as well as for the numerical simulations of memristor devices.

We report on the investigation of the resistive switching (RS) in the ultrathin (≈5 nm in thickness) yttria-stabilized zirconia (YSZ) films with single layers of Au nanoparticles (NPs) by conductive atomic force microscopy (CAFM). Besides the butterfly-type hysteresis loops in the current-voltage (I-V) curves of the contact of the CAFM probe to the investigated film surface corresponding to the bipolar RS, the negative differential resistance (NDR) has been observed in the I-V curves of the AFM probe contact to the YSZ films with Au NPs in the conductive (“ON”) state. The NDR has been related to the resonant tunneling of electrons through the size-quantized energy states in the ultrafine (1 to 2 nm in diameter) Au NPs built in the conductive filaments in the YSZ films.

We report the investigations of the ion migration polarization in the yttria stabilized zirconia (YSZ) thin films in the Metal-Oxide-Metal (MOM) and Metal-Oxide-Semiconductor (MOS) stacks due to the drift of the oxygen vacancies under the external bias voltage applied between the electrodes. The parameters characterizing the drift of the oxygen vacancies in YSZ such as the ion drift activation energy, mobile ion concentration, and the drift mobility have been determined in the temperature range 300–500 K. These data are important for deeper understanding of the fundamental mechanisms of the electroforming and resistive switching in the YSZ-based MOM and MOS stacks, which are promising for the Resistive Random Access Memory (RRAM) and other memristor device applications.

Ballistic Electron/Hole Emission Microscopy (BEEM/BHEM) has been applied to imaging and spectroscopy of Au nanoclusters (NCs) embedded into ultrathin (≈6 nm thick) yttria-stabilized zirconia (YSZ) films on Si substrates prepared using magnetron sputtering and annealing. Such structures are promising for resistive switching in non-volatile memory applications. According to the High Resolution Cross-sectional Transmission Electron Microscopy (HR X-TEM) data, the nearly spherical Au NCs of 1.5 to 3.5 nm in diameter were arranged almost in a single sheet between the YSZ layers. The BEEM images demonstrated the spots of increased collector current of 1 to 2.5 nm in size which are related to ballistic electron tunnelling via the Au NCs. The BEEM/BHEM spectra of the NCs demonstrated stepwise features attributed to the quantum confined states in the Au NCs. By using the best fit between the quantum confined energy states determined from the BEEM/BHEM spectra, the estimate of the NC diameter and the ones calculated for a spherical quantum dot yielded 1.7 to 3.3 nm which is consistent with the HR X-TEM data. The results of the present study demonstrate the capabilities of BEEM/BHEM in characterizing ultrathin dielectric films with metal NCs in research and also in industry.

Bipolar resistive switching phenomenon in the Au/Zr/ZrO2-Y2O3/TiN/Ti memristive devices deposited by magnetron sputtering has been studied. The structure of devices and electrical measurements data for the temperature range from 77 to 490 K are analyzed. The stable switching is demonstrated at room temperature, but the decrease in the resistive switching performance at elevated temperatures is observed.