Oxygen vacancy induced carrier mobility enhancement in nano-multilayered ZrO_(2):Y_(2)O_(3)/SrTiO_(3)thin films for non-volatile memory devices

The influence of oxygen vacancy-dominated carrier mobility on the performance of memristors has attractedconsiderable attention.The device’s carrier mobility can be significantly improved by forming a nano-multilayeredheterostructure when the individual layer thickness is below a critical value.In this work,Pt/[ZrO_(2):Y_(2)O_(3)(YSZ)/SrTiO_(3)(STO)]n/Nb:SrTiO_(3)(NSTO)memristive devices were configurated through laser pulse deposited YSZ/STO nanomultilayeredactive layer with both Pt and NSTO acting as top and counter electrodes.Specifically,the Pt/[YSZ/STO]5/NSTO device with five consecutive layers of YSZ/STO thin film shows superior memristor performance,and itscorresponding carrier mobility presents a significantly enhanced value compared to that of other periodic numbers ofYSZ/STO composed memristive devices.This can be attributed to the increase of oxygen vacancy concentration in thedevice,as evidenced by both experimental results and theoretical analysis.This work provides a significant approach inimproving the performance of memristor dominated by oxygen vacancy transporting mechanism.

Controllable fabrication of self-organized nano-multilayers in copper–carbon films

In order to clarify the influence of methane concentration and deposition time on self-organized nano-multilayers,three serial copper-carbon films have been prepared at various methane concentrations with different deposition times using a facile magnetron sputtering deposition system. The ratios of methane concentration(CH4/Ar+CH4) used in the experiments are 20%, 40%, and 60%, and the deposition times are 5 minutes, 20 minutes, and 40 minutes, respectively.Despite the difference in the growth conditions, self-organizing multilayered copper-carbon films are prepared at different deposition times by changing methane concentration. The film composition and microstructure are investigated by x-ray photoelectron spectroscopy(XPS), x-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), and high-resolution transmission electron microscopy(HRTEM). By comparing the composition and microstructure of three serial films, the optimal growth conditions and compositions for self-organizing nano-multilayers in copper-carbon film are acquired. The results demonstrate that the self-organized nano-multilayered structure prefers to form in two conditions during the deposition process. One is that the methane should be curbed at low concentration for long deposition time,and the other condition is that the methane should be controlled at high concentration for short deposition time. In particular, nano-multilayered structure is self-organized in the copper-carbon film with copper concentration of 10-25 at.%.Furthermore, an interesting microstructure transition phenomenon is observed in copper-carbon films, that is, the nanomultilayered structure is gradually replaced by a nano-composite structure with deposition time and finally covered by amorphous carbon.

Structure and Anomalous Magnetic Properties in Fe-N/Ti-N Nano-multilayers

DC-magnetron sputtering was employed to prepare Fe-N/Ti-N periodic nano-multilayers . Magnetic properties were studied by vibrating sample magnetometry and structure by TEM and X-ray diffraction for the films. A strong enhancement of the saturation magnetization was found in multilayers containing thinner Fe-N layers. The coercivity was found to be nearly constant. A kind of anomalous hysteresis loops was found in some

Microstructure and mechanical properties of VAlN/Si_(3)N_(4) nano-multilayer coatings

VAlN coating is of particular interest for dry cutting applications owing to its low-friction and excellent abrasiveness.Nano-multilayer structure is designed to tailor the properties of VAlN coating.In this work,a series of VAlN/Si_(3)N_(4) nano-multilayer coatings with varied Si_(3)N_(4) layer thicknesses were prepared by reactive sputtering method.The microstructure and mechanical properties of the coatings were both investigated.It is revealed that Si_(3)N_(4) with a shallow thickness(~0.4 nm)was crystallized and grown coherently with VAlN,showing a remarkable increase in hardness compared to VAlN monolayer coating.The hardness of coherently VAlN/Si_(3)N_(4) nano-multilayer coatings reached to 48.7 GPa.With further increase of Si_(3)N_(4) layer thickness,the coherent growth of nano-multilayers was terminated,showing amorphous structure formed in nano-multilayers and the hardness was declined.On the other hand,when Si_(3)N_(4) layer thickness was 0.4 nm,the friction coefficient of VAlN/Si_(3)N_(4) nano-multilayer coating was almost equal to that of VAlN monolayer coating,which was attributed to the crystallization of Si_(3)N_(4) and the produced coherent interfaces between VAlN and Si_(3)N_(4) for the hardening effect of nano-multilayer coatings.Upon further increase of Si_(3)N_(4) layer thickness,pronounced improvement of friction coefficient in VAlN/Si_(3)N_(4) nano-multilayer coating was observed.

Electromagnetic characteristics and microwave magnetism of Fe_(46)Co_(44)B_(10)/SiO_2 nano-multilayers

Fe46Co44B10/SiO2 nano-multilayers were synthesized by radio frequency magnetron sputtering. The thickness of individual layer was designed and controlled in nano-meter. The effect of thickness of ferromagnetic layer, insulative layer or the total number of layers on the intrinsic characteristics and microwave permeability were investigated respectively. The results show that, saturation magnetization changes obviously with different thicknesses of ferromagnetic layer or insulative layer, but coercivity changes little and remains small. When the thickness of ferromagnetic layer and insulative layer keeps 1.5 and 1.3 nm respectively and the number of the total layers increases from 10 to 90, coercivity reduces and resistivity of the films improves from 0.25 to 2.22 π·m. The resonant frequency locates at the point higher than 2 GHz and the imaginary part of complex permeability at 2 GHz is larger than 150. These multilayer films can be applied in the field of micromagnetic devices or anti-interference of electromagnetic wave.

Fabrication and characterization of NiO films for energetic nano-multilayers by direct current reactive sputtering

NiO films were fabricated by reactive direct current magnetron sputtering on glass and alumina substrates for the application in energetic nano-multilayers. The structural and thermal properties of the films were investigated with the volume ratio of oxygen to argon ranging from 1：9 to 3：2, and the optimized ratio value is obtained as 1：3, which was confirmed by X-ray diffraction （XRD）, atomic force microscopy and ultrafast measure- ment system. The effect of the film thickness, varying from 150 to 900 nm, on the structural properties was characterized by XRD and scanning electron microscopy （SEM）. XRD analysis reveals that the （111） lattice plane is the preferred orientation. The intensities of preferential peaks and the grain sizes increase as the film thicknesses increase.

Deposition of TiN/TiAlN multilayers by plasma-activated EB-PVD:tailored microstructure by jumping beam technology

Plasma-activated electron beam-physical vapor deposition（EB-PVD）was used for depositing nitride multilayer coatings in this work.Different from the conventional coating methods,the multilayers were obtained by manipulating electron beam（EB）to jump between two different evaporation sources alternately with variable frequencies（jumping beam technology）.The plasma activation was generated by a hollow cathode plasma unit.The deposition process was demonstrated by means of tailoring TiN/TiAlN multilayers with different modulation periods（M1：26.5 nm,M2：80.0 nm,M3：6.0 nm,M4：4.0 nm）.The microstructure and hardness of the multilayer coatings were comparatively studied with TiN and TiAlN singlelayer coatings.The columnar structure of the coatings（TiN,TiAlN,M1,M2）is replaced by a glassy-like microstructure when the modulation period decreases to less than 10 nm（M3,M4）.Simultaneously,superlattice growth occurs.With the decrease of modulation period,both the hardness and the plastic deformation resistance（H^3/E^2,H-hardness and E-elastic modulus）increase.M4coating exhibits the maximum hardness of（49.6±2.7）GPa and the maximum plastic deformation resistance of^0.74 GPa.