The influence of an intense electron beam on a nonstoichiometric oxide HfO
x
(
) layer of a TaN/HfO
x
/Ni memristor on its electrophysical properties is studied. It is found that the crystalline
h
...-Hf,
m
‑HfO
2
,
o
-HfO
2
, and
t
-HfO
2
phases are formed in the HfO
x
film under this impact. It is established that memristors demonstrate resistive switching at certain electron fluence values. At the same time, such memristors have resistive switching voltages several times lower than those of unirradiated memristors. In addition, they exhibit a multiple decrease in the spread of resistive switching voltages, as well as resistances in low- and high-resistance states. The current–voltage curves of the obtained memristors indicate that the charge transport in them is described by the space-charge-limited current mechanism.
It is shown that the treatment of stoichiometric HfO
2
, which is synthesized by atomic layer deposition, in electron cyclotron resonance hydrogen plasma leads to a significant depletion of the film ...in oxygen and the formation of nonstoichiometric HfO
x
(
). The longer the treatment time, the higher the degree of oxygen depletion. The charge transfer in the films under study occurs by phonon-assisted tunneling between oxygen vacancies serving as traps. It has been found that the
-Si/HfO
x
/Ni structures, where the oxide layer is treated in the electron cyclotron resonance hydrogen plasma, have memristor properties: they are reversibly switched between high and low resistance states. The fabricated memristor structures are forming-free.
The silicon oxide thin films obtained by thermal SiO
2
treatment in hydrogen electron cyclotron resonance plasma at various exposure times are investigated. Using X-ray photoelectron spectroscopy, we ...have established that such treatment leads to a significant oxygen depletion of thermal SiO
2
, the more so the longer the treatment time. The atomic structure of the SiO
x
< 2
films obtained in this way is described by the random bonding model. The presence of oxygen vacancies in the plasma-treated films is confirmed by comparing the experimental valence band photoelectron spectra and those calculated from first principles, which allows the parameter
x
to be estimated. We show that thermal silicon oxide films treated in hydrogen plasma can be successfully used as a storage medium for a nonvolatile resistive memory cell.
Currently, a new generation of high-speed, information-intensive resistive memory based on nonstoichiometric dielectrics is being developed. The electron structure of nonstoichiometric silicon oxide ...SiO
x
is set by the value of parameter
x
. It is found that the treatment of thermal SiO
2
in hydrogen plasma electron cyclotron resonance leads to the enrichment of silicon oxide with excess silicon, which in turn leads to the appearance of electron and hole traps in SiO
x
. SiO
x
conductivity is bipolar: electrons are injected from negatively biased silicon and holes are injected from positively biased silicon. Cathodoluminescence (CL) experiments confirm the assumption that the traps in SiO
x
are due to the excess silicon.
p
++-Si(100)/SiO
x
/Ni memristor metal-dielectric-semiconductor (MDS) structures are fabricated based on the developed procedure for the preparation of nonstoichiometric oxide in hydrogen plasma of electron cyclotron resonance. Such structures have the properties of resistive switching of SiO
x
that do not require a forming operation.
The phase transformations of stoichiometric HfO
2
and non-stoichiometric HfO
x
oxides grown by ion-beam sputtering-deposition during their electron beam crystallization were investigated. It was ...found that the sequences of crystalline phase formations in stoichiometric and non-stoichiometric oxides are significantly different. An amorphous HfO
2
film crystallizes first to form monoclinic
α
-HfO
2
phase nanocrystals and then tetragonal
β
-HfO
2
phase nanocrystals. In non-stoichiometric HfO
x
oxides (
x
= 1.82), in contrast to HfO
2
oxides, hexagonal
α
-Hf phase metal clusters were initially present. During the crystallization process, the metallic
α
-Hf phase growth was observed first with the simultaneous appearance of the monoclinic
α
-HfO
2
phase. Then the orthorhombic-I
γ
-HfO
2
phase appeared, while the
α
-Hf phase growth ceased. The composition of the investigated non-stoichiometric HfO
x
oxides was chosen to be the same as in the dielectric layer of resistive memory cells (ReRAM). The crystallization of oxides was carried out in a local region, the sizes of which are comparable with the size of the ReRAM filament. This made it possible to partially project the crystallization results onto the forming and switching processes in ReRAM cells.
The optical properties and composition of thermal silicon oxide thin films processed in a hydrogen electron cyclotron resonance plasma have been studied by ellipsometry, quantum-chemical modeling, ...and photoluminescence spectroscopy. It has been found that the plasma processing of the films leads to their oxygen depletion and the formation of nonstoichiometric oxide SiO
x
< 2
. The parameter
x
of the obtained SiO
x
films has been determined by comparing the experimental spectral dependence of the refractive index with the dependence obtained theoretically using the ab initio calculation. It is shown that an increase in the time of processing of thermal dioxide SiO
2
in a hydrogen plasma leads to an increase in the refractive index of the film, as well as in the degree of its oxygen depletion. The dependence of the parameter
x
of the investigated films on the hydrogen plasma processing time is plotted.
The optical properties of the HfOx films of different chemical composition (x ≤ 2) deposited by ion beam sputtering-deposition (IBSD) method were studied. Spectral dependencies of refractive index ...n(λ) and extinction coefficient k(λ) were determined with ellipsometry in λ = 250-1100 nm wavelength region. The x values (i.e. O/Hf ratio) for the films were derived from x-ray photoelectron spectroscopy (XPS) data. The spectral dependences of optical constants n(λ) and k(λ) were found to undergo radical changes with x = 1.78-1.82. The films with x < 1.78 demonstrated high extinction coefficient k > 1 with the metallic-like behavior of optical constants spectral dependences. The films with x > 1.82 were found to be transparent, with k = 0 and n(λ) being well approximated by a Cauchy polynomial dependence for dielectrics. Using a sample with a gradient of x, it was established that the transition from the metallic to the dielectric-like behavior of the optical constants occurs not smoothly, but is discontinuous. A sharp jump in the optical constants is observed at x 1.8. According to XPS data, the transparent films were found to consist of two components only: HfO2 and Hf4O7 suboxide. Cauchy polynomial coefficients for Hf4O7 suboxide and HfO2 were found by using the Bruggeman effective medium approximation.
Amorphous nonstoichiometric ZrOx films of different composition have been synthesized by the method of ion-beam sputtering deposition of metallic zirconium in the presence of oxygen at different ...partial oxygen pressures in the growth zone, and their optical properties have been studied in the spectral range of 1.12–4.96 eV. It is found that light-absorbing films with metallic conductivity are formed at the partial oxygen pressure below 1.04 × 10–3 Pa and transparent films with dielectric conductivity are formed at the pressure above 1.50 × 10–3 Pa. It is shown that the spectral dependences of optical constants of ZrOx films are described well by the corresponding dispersion models: the Cauchy polynomial model for films with dielectric conductivity and the Lorentz–Drude oscillator model for films with metallic conductivity.
•Nanometer silica films were synthesized by different methods and processed in hydrogen plasma.•Low-temperature luminescence excited by synchrotron radiation in VUV region was studied.•The conversion ...of hydrogen passivated emission centers was observed.•The luminescence of quantum dots was manifested in the emission spectra.
Optically active defects in modified silicon oxide films on a silicon substrate have been studied by low-temperature photoluminescence (PL) spectroscopy using excitation by synchrotron radiation in the vacuum ultraviolet region. Films of dry thermal silicon oxide obtained by treatment of stoichiometric SiO2 in hydrogen plasma, films of wet thermal silicon oxide, and films with low dielectric constant (so called "low-k" dielectrics) have been studied. Investigations of various type SiO2 films detect the PL centers, which can be conditionally divided into two groups. The first group includes intrinsic point defects, the different variants of oxygen-deficient centers (ODCs). The second group contains centers like the spatially confined excitons in silicon quantum dots (SiQDs). It is shown that SiQDs differ in spectral characteristics, are formed in different ways, due to the transformation and clustering of point defects such as E'-centers, ODC(I) and ODC(II). In this case, the size and spectral properties of quantum dots depend on the mechanism of their formation. Schemes for the conversion of these defects are proposed.
It was found that for wet films and nonstoichiometric SiOx films treated in hydrogen plasma, "metastable" centers ODC(I) and ODC(II) arise only under the action of synchrotron radiation in the region of interband or exciton absorption and then they decay because of radiative relaxation. The absence of stable ODC centers in these films is due to their clustering and the formation of SiQDs. In "low-k" mesoporous films, on the contrary, silicon quantum dots SiQDs are not formed, but ODC(I) and ODC(II) centers are clearly manifested. A scheme of electronic transitions upon indirect excitation of silicon quantum dots through exciton states of the SiO2 matrix is considered. The presented results demonstrate the possibility of controlling the optical properties of silicon thin-film structures by creating in them both oxygen-deficient point defects and quantum dots of various sizes.
The catalytic activity of natural and synthetic mordenites modified with Cu
2+
, Zn
2+
, and Pd
2+
cations via ion exchange was studied in the oxidative conversion of
n
-amyl alcohol to valeric acid ...under the action of oxygen. It is established that the highest activity and selectivity in this reaction is exhibited by mordenite hydrothermally synthesized from kaolinite and containing 3.0 wt % Cu
2+
, 0.1 wt % Pd
2+
, and 2.0 wt % Zn
2+
. The kinetics of this catalytic reaction is studied. Based on the experimental data, a possible stepwise mechanism is proposed, and a theoretically grounded kinetic model of the process is developed.
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