Ge Ions Research Articles

Isomorphous incorporation of tin ions into extra-large pore framework with high-stannum content as efficient Lewis acid catalyst

Germanium-rich *CTH zeolite without organic molecules located inside pore channels experienced only partial structural collapse and subsequently repaired to high-silica structure analogous to the original topology in a short time. The surprise acid-hydrolysis process has caused a large amount of framework Ge ions were removed, giving rise to abundant hydroxyl nests. Benefiting from the unexpected variation of framework structure and chemical composition, stannosilicates Sn-*CTH with extra-large pores and various Sn loadings (Si/Sn molar ratio in the range of 30-∞) were post-prepared depending on the reaction between the added (NH4)2SnCl6 species and the formed silanol groups in the hydroxyl nests. The resultant Sn-*CTH zeolites were able to release significantly the diffusion limitations encountered by the bulky substrates and oxidants, exhibiting promising activities to catalyze the Baeyer-Villiger (B-V) oxidation of ketones with single oxidant either hydrogen peroxide (H2O2) or large-sized tert-butyl hydroperoxide (TBHP). Especially, high ε-caprolactone product selectivity was also obtained in the B-V oxidation of cyclohexanone using H2O2 oxidant through reducing the H2O2/cyclohexanone molar ratio as well as controlling appropriate reaction time, which was more efficient than the traditional Sn-Beta-F catalyst.

Heavy ion single event effect in double-trench SiC metal-oxide-semiconductor field-effect transistors

In this paper, experiments on 208 MeV Ge ion irradiation with different source-drain bias voltages are carried out for the double-trench SiC metal–oxide–semiconductor field-effect transistors, and the physical mechanism of the single event effect is analyzed. The experimental results show that the drain leakage current of the device increases more obviously with the increase of the initial bias voltage during irradiation. When the bias voltage is 400 V during irradiation, the device has a single event burned at a fluence of 9×10<sup>4</sup> ion/cm<sup>2</sup>, and when the bias voltage is 500 V, the device has a single event burned at a fluence of 3×10<sup>4</sup> ion/cm<sup>2</sup>, so when the LET value is 37.3 MeV·cm<sup>2</sup>/mg, the SEB threshold of DUT does not exceed 400 V, which is lower than 34% of the rated operational voltage. The post gate-characteristics test results show that the leakage current of the device with a bias voltage of 100 V does not change significantly during irradiation. When the bias voltage is 200 V, the gate leakage and the drain leakage of the device both increase, so do they when the bias voltage is 300 V, which is positively related to bias voltage. In order to further analyze the single particle effect mechanism of device, the simulation is conducted by using TCAD tool. The simulation results show that at low bias voltage, the heavy ion incident device generates electron-hole pairs, the electrons are quickly swept out, and the holes accumulate at the gate oxygen corner under the effect of the electric field, which combines the source-drain bias voltage, leading to the formation of leakage current channels in the gate oxygen layer. The simulation results also show that at high bias voltage, the electrons generated by the incident heavy ion move towards the junction of the N<sup>–</sup> drift layer and the N<sup>+</sup> substrate under the effect of the electric field, which further increases the electric field strength and causes significant impact ionization. The local high current density generated by the impact ionization and the load large electric field causes the lattice temperature to exceed the melting point of silicon carbide, causing single event burnout. This work provides a reference and support for studying the radiation effect mechanism and putting silicon carbide power devices into aerospace applications.

The local crystallization thresholds under laser irradiation of the Cu+‐ion implanted Ge layers with various thicknesses

AbstractPorous Ge layers were fabricated by implanting Cu+ ions of various acceleration energies into c‐Ge substrate. This made it possible to form amorphous porous Ge layers of thicknesses from 18.6 to 50.5 nm. The distribution depth profiles of implanted Cu+ ions in Ge were simulated by SRIM‐2013 program. The formed layers were studied by Raman spectroscopy. The excitation was carried out by a laser with a wavelength of 488 nm, which has a small penetration depth of ∼20 nm. In the Raman spectra, there is a possibility to distinguish the contribution from the amorphous Ge film, the crystalline c‐Ge substrate, and Ge nanocrystals, which appear under intense laser excitation due to local crystallization. The decomposition of the spectra into individual components makes it possible to subtract the contribution of the substrate and estimate the crystalline volume fraction in the layers. The results obtained confirm the hypothesis of low thermal conductivity of the porous layer, due to which local crystallization occurs.

Temperature dependence of germanium vacancy centers in high-quality diamond after 300 keV ion implantation

In this work, the temperature dependence of diamond GeV centers that were formed by germanium (Ge) ion implantation and annealed in a hydrogen atmosphere at 1000 °C was investigated by photoluminescence spectroscopy. It was found that the intensity of the GeV centers had a thermal quenching effect with the increase in temperature, and the activation energy was fitted at 62.32 meV. Then, the laser power dependence was mainly dependent on radiative recombination so that the diamond GeV center intensity increased with the laser power. Furthermore, the electron-phonon coupling and thermal softening effect were found between Ge ions and vacancies chemical bonds, which made the GeV center peak position red shift with the increase of temperature. Finally, the FWHM of the diamond GeV center exhibited both homogeneous (Lorentzian component) and inhomogeneous broadening (Gaussian component) at 80–280 K, indicating that the Lorentzian component was dominant in the FWHM of the GeV center.

Influence of Ge or Fe Ions on the Magneto-Optical Response of CdMnTe in a Broad Spectral Range

Influence of Ge or Fe Ions on the Magneto-Optical Response of CdMnTe in a Broad Spectral Range

Single event upset reinforcement technology of DICE flip-flop based on layout design

D flip-flop is the basis of timing logic circuit, and SEMU phenomenon tends to be serious with the integrated circuit process size shrinking to nanometer scale. The anti-SEU ability based on DICE structure for D flip-flop cannot meet the requirements of aerospace engineering. Based on the SEU reinforcement technology of D flip-flop under nano-technology and the SEU mechanism of DICE structure, a layout-level anti-SEU flip-flop design method based on DICE circuit structure is proposed considering the circuit performance, area, power consumption and other resource costs. And then a D flip-flop with SEU resistance is designed by commercial 65 nm process, and the designed flip-flop area is 1.8 times that of commercial structure flip-flop. The function and and radiation simulation results indicate that the establishment time and transmission delay of the flip-flop are equivalent to those of the commercial one, and no SEU occurs under the Ge ion bombardment with the LET threshold of approximately 37 MeV·cm2/mg. The performance of the flip-flop circuit and the ability to resist single particle soft error are excellent. In the anti-radiation ASIC design, the area, wiring resources and timing overhead caused by the reinforcement of the D flip-flop circuit are greatly saved.

Insight into OLPT model conduction mechanism and dielectric relaxation of lead borate glass containing Cr and Ge ions

Lead borate glass with compositions 25B2O3–73.8PbO–xGeO2-(1.2 − x) Cr2O3 (x ≤ 1.2 mol. %) is fabricated by the melt quenching procedure. The electrical conductivities (σdc, σac) of fresh samples are measured in the frequency range 100 Hz–1.0 MHz and temperature range 303–393 K. The anomalous behavior observed in the dc activation energy at x = 0.6 mol% is argued to the formation of bridging and non-bridging oxygen bonds. These bonds are formed due to substitution of GeO2 to the expense of Cr2O3 ions in the PbO–B2O3 network. The dependence of ac conductivity on frequency is analyzed through the power law: σacαωs where s ≤ 1.0. The experimental results of s for the considered samples have shown that overlapping large polaron tunneling (OLPT) is the possible conduction model in the considered frequency and temperature ranges. The strength of the OLPT model established on the normal Mayer–Neldel (MN) rule is analyzed and discussed. Furthermore, results of the real and imaginary dielectric constant composed with Cole–Cole diagrams for investigated samples are presented and discussed.

Suppression of Kondo spin-fluctuations as the origin of metamagnetic transition in the new ternary intermetallic Ce3Pd2Ge7

The metamagnetic transition in cerium-based intermetallics is a very common intriguing phenomenon that has remained the subject of close study for several decades. We report crystal structure, magnetization and resistivity of a new ternary cerium germanide Ce3Pd2Ge7 with an orthorhombic structure of La3Co2Sn7-type (space group Cmmm, cell dimensions a = 4.3257(3), b = 26.339(2), c = 4.3594(3) Å, V = 496.69(2) Å3). Low-temperature magnetic properties are characterized by a two-step metamagnetic transition, which can be associated with two nonequivalent positions of Ce ions in the lattice. The first metamagnetic transition occurs in weak magnetic fields below T1 ≈ 11 K and then moves to higher fields when the temperature goes down (B ∼ 1.5 T at T = 2 K). The second transition manifests itself below T2 ≈ 8 K as a rapid increase of magnetization, which starts from zero field and reaches saturation at fields B ≈ 0.1 T. The magnitude of each transition increases with decreasing temperature and the polarized magnetization ΔM reaches 0.13 μB/Ce and 0.08 μB/Ce upon the first and second transitions respectively. The interchange of nonmagnetic Pd and Ge ions (≈ 0.8 %) leads to the appearance of a hysteresis of metamagnetic transitions, as well as to the splitting of the field cooled (FC) and zero field cooled (ZFC) magnetization curves in hysteresis area. The dependence of the polarized magnetization ΔM on temperature which persists up to high fields as well as the continuation of the hysteresis well above the metamagnetic transition (at least up to B ∼ 9 T) indicates a new type of spin-glass-like state, which is caused by the suppression of spin fluctuations and the localization of magnetic moments during the metamagnetic transition.

Localized vibrational modes of GeV-centers in diamond: Photoluminescence and first-principles phonon study

The vibrational behaviour of the germanium-vacancy (GeV) in diamond is studied through its photoluminescence spectrum and first-principles modelled partial phonon density of states. The former is measured in a region below 600 cm−1. The latter is calculated for the GeV center in its neutral, charged, and excited state. The photoluminescence spectrum presents a previously unobserved feature at 248 cm−1 in addition to the well-known peak at 365 cm−1. In our calculations, two localized modes, associated with the GeV center and six nearest carbon atoms (GeC6 cluster) are identified. These correspond to one vibration of the Ge ion along with the [111] orientation of the crystal and one perpendicular to this direction. We propose these modes to be assigned to the two features observed in the photoluminescence spectrum. The dependence of the energies of the localized modes on the GeV-center and their manifestation in experimental optical spectra is discussed.

Opto-electro-structural properties of Ge-doped Sb65Se35 alloys

The microstructural, and opto-electrical characteristics of Ge-doped antimony selenide alloys with the chemical composition Sb65Se35-xGex (0 ≤ x ≤ 20) which prepared by the melt quenching method have been studied here. In all of the investigated samples, structural studies using an X-ray diffraction pattern verified the polycrystalline nature with a simple characteristic peak of Sb2Se hexagonal rhombohedral phase. FE-SEM equipped with EDS was used to explore the morphology and composition of the samples. Raman spectra show a small shift in wave number with the addition of dopant, which could be due to lattice distortion. Electrical conductivity results demonstrate that the samples are degenerate semiconductors. The Eopt of Ge-doped Sb65Se35 alloys was derived using the KM function from DR spectra, and it changed as the Ge ion concentration rises. Ge-doped Sb65Se35 alloys have an optical band gap in the visible sector, making them a potential material for optoelectronic data storage applications.

Ge-codoping effect on X-ray-induced photodarkening in Al-doped and Dy-Al-doped silica glass

X-ray-induced photodarkening and its suppression by Ge-codoping were investigated in Al-doped, Dy-doped, and Dy-Al-doped silica glasses. Absorption bands of 4f-4f5d transition of Dy2+ were determined in Dy-Al-doped silica glass fabricated by Si nano-powders as a reducing agent, and it was found that pair generation of Dy2+ and Al-OHC was occurred in X-ray irradiated Dy-Al-doped silica glass. Ge-codoping suppresses the above-mentioned pair generation and instead forms the pair of GEC and GLPC+. A similar suppression effect of Ge-codoping was observed in Al-Ge-doped silica glass, where pair generation of Al-OHC and Al-E′ center was suppressed. To investigate the stability of defects, annihilation processes during thermal annealing were measured. Al-OHC and Dy2+ are destabilized by Ge-codoping in Al-doped and Dy-Al-doped silica glasses, while GEC is stabilized in Al-Ge-doped and Dy-Al-Ge-doped silica glasses. Based on these results, local structure models around Al, Ge, and Dy ions and possible mechanisms of photodarkening were proposed.

Ge Ion Implanted Photonic Devices and Annealing for Emerging Applications.

Germanium (Ge) ion implantation into silicon waveguides will induce lattice defects in the silicon, which can eventually change the crystal silicon into amorphous silicon and increase the refractive index from 3.48 to 3.96. A subsequent annealing process, either by using an external laser or integrated thermal heaters can partially or completely remove those lattice defects and gradually change the amorphous silicon back into the crystalline form and, therefore, reduce the material’s refractive index. Utilising this change in optical properties, we successfully demonstrated various erasable photonic devices. Those devices can be used to implement a flexible and commercially viable wafer-scale testing method for a silicon photonics fabrication line, which is a key technology to reduce the cost and increase the yield in production. In addition, Ge ion implantation and annealing are also demonstrated to enable post-fabrication trimming of ring resonators and Mach–Zehnder interferometers and to implement nonvolatile programmable photonic circuits.

Unprecedented severe atomic redistribution in germanium induced by MeV self-irradiation

We present a pronounced unprecedented surface modification of a crystalline Ge layer under ion irradiation with a Ge ion beam at the energy of 2.5 MeV. Samples were covered by a thin SiN-protection layer to protect from sputtering and surface redeposition phenomena. Under the irradiation conditions, the Ge layer did not become porous as observed for other projectiles and lower energies but develops into a severely uneven morphology with characteristic length scales of several hundred nanometers. The observed roughness monotonically increases with the irradiation doses. We show that this phenomenon is caused neither by the surface erosion effect nor by a non-uniform volumetric expansion. Rather, atomic redistribution in the bulk of the material is the major drive for the uneven surface. Furthermore, the deformation of the Ge layer likely occurs to the largest extent after irradiation, as indicated by the very flat interface around the end-of-range region. The observed morphology modification is discussed based on irradiation-induced plastic flow, coupled with a larger contribution of the electronic component in the ion–solid interactions.

A DFT study of formic acid decomposition on the stoichiometric SnO2 surface as a function of iso-valent doping

In the present work, we have studied the effect of iso-valent dopants on the chemical reactivity of the stoichiometric SnO2 (110) surface. Si, Ge, Pb, Ti, Zr, Hf, and Ce ions have been placed at the Sn lattice sites (substitutional doping) in bulk, sub-surface, and surface positions. The results show that surface or sub-surface sites are clearly preferred over the bulk ones. Next, we studied the effect of the iso-valent dopants on the adsorption and decomposition reaction of HCOOH molecule. On this basis, four paths with desorption of: (a) H2, (b) CO, (c) H2O, or (d) CO2 can occur. Comparing the results of this decomposition reaction on the SnO2 surface with the same process on rutile TiO2 (110) having the same structure and morphology, reveals that SnO2 is considerably more reactive in all reaction steps of the formic acid decomposition.

Chemoheteroepitaxy of 3C‐SiC(111) on Si(111): Influence of Predeposited Ge on Structure and Composition

Secondary ion mass spectroscopy, Fourier transformed infrared spectroscopy, ellipsometry, reflection high energy diffraction and transmission electron microscopy are used to gain inside into the effect of Ge on the formation of ultrathin 3C‐SiC layers on Si(111) substrates. Accompanying the experimental investigations with simulations it is found that the ultrathin single crystalline 3C‐SiC layer is formed on top of a gradient Si1–x–yGexCy buffer layer due to a complex alloying and alloy decomposition processes promoted by carbon and germanium interdiffusion and SiC nucleation. This approach allows tuning residual stress at very early growth stages as well as the interface properties of the 3C‐SiC/Si heterostructure. Useful yields of secondary ions of Ge in Si matrix and Si dimer are estimated.

Iso-valent doping of reducible oxides: a comparison of rutile (110) and anatase (101) TiO2 surfaces

We studied the role of iso-valent heteroatoms replacing Ti4+ cations in the lattice of two titania polymorphs, rutile (r-) and anatase (a-) by means of first principles calculations. The r-TiO2(110) and the a-TiO2(101) surfaces have been considered and Ti ions in the bulk, sub-surface, and surface sites have been replaced with Si, Ge, Sn, Pb, Zr, Hf, and Ce ions: surface or sub-surface sites are clearly preferred. Since the dopants have the same number of valence electrons as the replaced Ti atom, they can have only two effects: one is steric, related to the different size of the dopant compared to Ti4+; the other is an orbital effect, due to the energy levels associated to the dopant not present on the pristine surface. Both these effects can modify locally the geometric and electronic structure of the surface, in particular by introducing new states in the band gap. To check the effect of the dopants on the surface reactivity we studied as an example the decomposition of HCOOH which can follow four different paths with desorption of (a) H2, (b) CO, (c) H2O, or (d) CO2. The results show the very different behavior of the two titania polymorphs considered, rutile and anatase: rutile is more reactive and more easily reduced than anatase. For specular reasons, the presence of the dopants has in general more pronounced effects on anatase, as they can deeply modify the surface reactivity and the HCOOH decomposition path.

The heavy ions irradiation effects on advanced spin transfer torque materials

We investigate the heavy ions irradiation effect on the spin transfer torque film stacks with perpendicular magnetic anisotropy. Samples are exposed to 175 MeV Cl ion and 235 MeV Ge ion at the fluence of 1x105 ions/cm2 and 1x106 ions/cm2. Measurements of magnetization vs. magnetic field are performed on the film stacks before and after irradiation. The results exhibit that magnetic properties of free layer (CoFeB) in the spin transfer torque film keeps unchanged while magnetic properties of the synthetic antiferromagnet layer (Co/Pt) and the ferromagnetic exchange coupling between reference layer (CoFeB) and synthetic antiferromagnet layer through W layer have changed significantly when the fluence of the two kinds of ions reach 1x106 ions/cm2. We analysis the irradiation damage of the film stacks by SRIM simulation and give a reasonable explanation for this phenomenon. Thus, our work demonstrates that perpendicular spin transfer torque MRAM technology itself, the memory element construction, is subject to damage from heavy ions irradiation.

Enhancement of concentration of XeV and GeV centers in microcrystalline diamond films through He+ irradiation

Atomic defect centers in diamond have been widely exploited in numerous quantum applications like quantum information, sensing, quantum photonics and so on. In this context, there is always a requirement to improve and optimize the preparation procedure to generate the defect centers in controlled fashion, and to explore new defect centers which can have the potential to overcome the current technological challenges. Through this work we report enhancing the concentration of Ge and Xe vacancy centers in microcrystalline diamond (MCD) by means of He+ irradiation. We have demonstrated controlled growth of MCD by chemical vapor deposition (CVD) and implantation of Ge and Xe ions into the CVD-grown samples. MCDs were irradiated with He+ ions and characterized through optical spectroscopy measurements. Recorded photoluminescence results revealed a clear signature of enhancement of the Xe-related and Ge vacancies in MCDs.

Influence of co-doping germanium ions on the long persistent near-infrared luminescence of ZnAl2O4:Cr3+

A series of infrared long persistent phosphor samples of ZnAl2O4: Cr3+ with various doping concentrations of Ge4+ ions were synthesized via a high temperature solid state reaction method. Powder X-ray diffraction, persistent spectra, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Ge4+ ions on the luminescence in the spinel structure. The results define an optimal co-doping of germanium ions (2 mol%) in the ZnAl2O4: Cr3+ can enhance the afterglow time of the phosphor. With the increase of co-doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Thermoluminescence data emphasise there are modifications from the presence of the Ge ions. The phenomenon that the long-wave emission reaches the maximum value of the spectral spread before the short-wave signal provides interesting insights into the charge transfer process.

Pressure evolution of the electronic structure of non-centrosymmetric EuRhGe3

Among europium compounds, pressure induced valence transitions and/or intermediate valence states are often observed. In such systems, applying pressure of several GPa can drive a Eu valence from divalent to almost trivalent. Non-centrosymmetric EuRhGe3 possesses magnetic Eu2+ ions and exhibits antiferromagnetic ordering at ∼11 K at ambient pressure. Pressure resistant magnetic ordering and stable divalent Eu state have been reported in EuRhGe3. Here, we study the pressure evolution of the Eu valence of EuRhGe3 by high resolution x-ray absorption spectroscopy using the partial fluorescence yield method. Our study reveals a successive increase of the Eu valence with increasing pressure without any valence transition. The obtained mean Eu valence approaches ∼2.4 around 40 GPa at 300 K. The experimental data are also analyzed by a full multiplet configuration interaction calculation based on the single impurity Anderson model. The analysis reveals a decrease of the Eu 4f orbital occupation by applying pressure. Pressure evolution of the electronic structure studied by density functional theory suggests that the Rh ions have little contribution to the pressure evolution of the Eu valence, while it implies an active involvement of the Ge ions.