Germanium Plate Research Articles

Widely tunable single-frequency Er-doped ZBLAN fiber laser with emission from 3.37 to 3.72 µm.

We demonstrate a widely tunable single-frequency Er-doped ZBLAN fiber laser operating on a 4F9/2→4I9/2 transition band. An uncoated germanium (Ge) plate serves as a narrow-bandwidth etalon and is inserted in the cavity to achieve a single longitudinal mode selection. Wavelength tuning from 3373.8 nm to 3718.5 nm was demonstrated by using a blazed diffraction grating at 3.5 µm. At the emission peak of 3465.6 nm, the laser yields over 100 mW single-frequency output power, with a 3 dB linewidth <6.9 MHz, and a slope efficiency (with respect to the incident 1990 nm pump power) of 20.3%. Such a tunable mid-infrared single-frequency fiber laser may serve as a versatile laser source in spectroscopy and sensing applications.

Nonlinear compression of naturally down-chirped superradiance pulses from a free-electron laser oscillator by thick germanium plates.

Naturally down-chirped superradiance pulses, with mirco-pulse energy, peak wavelength, and micropulse duration of 40 µJ, 8.7 μm, and 5.1 optical cycles, respectively, emitted from a free-electron laser (FEL) oscillator were nonlinearly compressed down to 3.7 optical cycles using a 30-mm-thick Ge plate. The peak power enhancement owing to nonlinear compression was found to be 40%. The achieved peak power and pulse duration were comparable to those of recently developed high-intensity and few-cycle long-wavelength infrared sources based on solid-state lasers. FEL oscillators operating in the superradiance regime can serve as unique tools for studying strong-field physics in long-wavelength infrared regions.

Synthesis and Properties of Nanosized Germanium Particles Obtained in Acetone under the Influence of Laser Radiation

Stable nanosized germanium particles were synthesized in a liquid medium (acetone) by laser irradiation of single-crystal germanium plates under aerobic and anaerobic conditions at room temperature. Various experimental methods—optical spectrophotometry, atomic force microscopy, and dynamic light scattering—made it possible to detect stable nanosized Ge particles in acetone and record optical absorption and luminescence spectra depending on the time of laser irradiation in the presence and absence of oxygen. Particular attention is paid to the results of the effect of laser irradiation on the physicochemical properties of pure acetone.

Electrical Properties of SiGe/W Plate Node in DRAM Capacitor

Recently DRAM(Dynamic Random Access Memory) industry is continuously scaling down to improve productivity and create low power memory products. This trend reduces the capacitance for storing data and increases the unwanted parasitic capacitance, which causes problems in data storage of DRAM. In addition, the plate structure of the node on the current DRAM capacitor further reduces the data storage capacity by causing voltage noise during product operation.In this paper, electrical properties were evaluated using SiGe/W(tungsten) structure instead of the existing SiGe(silicon germanium) plate, based on the fact that when the resistance of the plate node on the capacitor decreases, the plate noise can be improved during product operation by RC model. W was deposited on the high-doped SiGe by PVD(Physical Vapor Deposition), and it was confirmed that an Ohmic contact between SiGe and W was formed. Sheet resistance and contact resistance were decreased by 86.6% and 51.1%, respectively, compared to the existing SiGe plate structure under the voltage condition of 3 volts. As a result, it was confirmed that the value of capacitance for storing data increased by 20%. In order to confirm the improvement of failure, we conducted a test that caused plate noise by continuously inversion of adjacent data, and confirmed that the failure was improved by 36% in the SiGe/W plate structure. Figure 1

Dynamics of a liquid crystal-based modulator with germanium substrates for mid-infrared radiation

ABSTRACT We demonstrate modulation of polychromatic mid-infrared radiation using a liquid crystal layer embedded between Germanium plates. The latter can serve both as transparent substrates and as electrodes for electro-optic addressing. The observed contrast ratios and response times make these modulators promising candidates for mid-infrared radiation control, for example, in chemical sensing applications.

Analysis of nanostructured cobalt ion beam-modified Ge surface for high capacity Li-ion battery anodes by X-ray photoelectron spectroscopy

The results of the study of nanostructured germanium (Ge), intended for its subsequent use as electrodes of lithium-ion batteries are presented. Single-crystal germanium plate was irradiated by cobalt ions with an energy of 40 keV in the dose 4×1016 Co+ / cm2 for the nanostructuring. The changes in the elemental composition occurring during the electrochemical lithiation of manufactured germanium electrode were investigated by X-ray photoelectron spectroscopy (XPS).

Porous Germanium Anode Material for Lithium-Ion Batteries

This work is devoted to the development of porous germanium anode material for lithium-ion batteries. Samples of porous germanium were fabricated by ion implantation of Co+ ions in single-crystal germanium plates. The surface morphology of porous germanium samples with an increase in the implantation dose of Co+ ions was studied. Scanning electron microscopy study revealed that the implantation leaded to the formation of porosity of the surface and the surface morphology differed for different doses of implantation. It is assumed that the obtained Ge material with a porous surface can be used as effective anode material in lithium-ion batteries and will show an increased capacity and charge / discharge rate relative to traditionally used graphite.

Hydrogen in optical germanium and reduction of its negative impact on the crystal properties by ultrasonic processing

Hydrogen content and its effect on the properties of optical germanium has been first investigated. Large coarse-grained plates of Na-doped optical germanium, grown in an inert atmosphere, are shown to contain dissolved hydrogen in a concentration about 1.9 × 1017 cm− 3. It is shown that the presence of hydrogen can lead to the porosity of the plates, to the plate cracking and to the release of toxic gases during plate machining, as well as to some other negative effects. A technique for ultrasonic plate processing has been developed, which leads to a decrease in the hydrogen content by about 7 times, to an increase in the mechanical strength of the plates, to an increase in the material density, to a decrease in the Ge lattice parameter, and ultimately to eliminating all listed negative effects caused by the presence of hydrogen. The developed method of plate processing has found a successful application in the industrial production of protective screens for thermal imaging systems of night vision based on optical germanium plates.

Effect of Cholesterol on Membrane Pore Formation by Amyloid β25-35

One of the cytotoxicity mechanisms of amyloid β (Aβ) peptide in Alzheimer's disease is membrane permeabilization, yet the mechanism of pore formation remains unclear. Here, Ca2+-permeable membrane pore formation by a cytotoxic fragment of Aβ (Aβ25-35) has been analyzed by biophysical methods. Quin-2-loaded lipid vesicles composed of 0.3 mole fraction of anionic lipid 1-palmitoyl-2-oleoyl-phosphatidylglycerol, xchol mole fraction of cholesterol, and (0.7 - xchol) mole fraction of zwitterionic lipid 1-palmitoyl-2-oleoyl-phosphatidylcholine were prepared at xchol = 0, 0.05, 0.1, 0.2 and 0.4. CaCl2 was added externally so that Quin-2 was sequestered from Ca2+ ions. Quin-2 fluorescence increased exponentially upon addition of Aβ25-35, which was interpreted as membrane pore formation by the peptide, calcium influx and binding to intravesicular Quin-2. The kinetics and the magnitude of fluorescence enhancement were used to evaluate the second order rate constant of pore formation (ka), the affinity constant between the peptide molecules (Kp), and the number of peptide units in the pore (n). Circular dichroism suggested mostly β-sheet structure for the peptide in the presence of lipid vesicles. Attenuated total reflection Fourier transform infrared experiments were performed on Aβ25-35 embedded in lipid multilayers deposited on a germanium plate. These data suggested α-helical and β-sheet structures for the peptide in a lipid environment. The structure of the peptide, i.e., the α-helix/β-sheet ratio, varied as a function of cholesterol content in the membranes. These conformational transitions correlated with changes in pore formation parameters (Kp, ka, n). The data suggest that cholesterol affects Aβ membrane pore formation by multiple mechanisms. At moderate concentration (xchol< 0.1), cholesterol supports pore formation possibly through cholesterol-peptide interactions. Further increase in xchol causes pore inhibition by a membrane solidification mechanism. At xchol = 0.4, cholesterol causes lipid disorder and membrane destabilization.

Origin of quasi-mosaic effect for symmetric skew planes in a silicon or germanium plate

Bent silicon and germanium crystals are used for several modern physics applications, above all for focusing of hard X-rays and for steering of charged particle beams by means of channeling and related coherent phenomena. In particular, anisotropic deformations are effectively exploited for these applications. A typical anisotropic deformation that is used is the quasi-mosaic (QM) curvature. It involves the bending of crystallographic planes that would be otherwise flat in the case of an isotropic medium. Here, the curvature the {110} planes was obtained through the quasi-mosaic effect in the symmetric configuration for the first time. This achievement is important because the {110} family of planes is highly efficient for both the applications mentioned above. Until now, the curvature of {110} planes in the QM configuration has not been used because it vanishes if the direction of the planes is aligned with the applied moment that bends the crystal plate. Indeed, to obtain the curvature of this particular family of crystallographic planes, the 〈110〉 direction has not to be aligned with respect to the imparted moment that bends the plate, i.e. the {110} planes have to be skew planes. Experimental verification of the quasi-mosaic curvature for the {110} planes was provided through hard X-ray diffraction at beamline ID15A of the European Synchrotron Radiation Facility in Grenoble, France, showing good agreement with the theoretical expectation.

High-sensitivity ultrashort mid-infrared pulse characterization by modified interferometric field autocorrelation.

We report on spectral phase retrieval of 43MHz, ∼100 fs, 3.3μm pulses at energies down to 8.9pJ by a modified interferometric field autocorrelation method. The simple setup consists of a Michelson interferometer, a 266μm thick AgGaSe2 crystal, and a homemade spectrometer with an InGaAs point detector, which is readily applicable to measuring a 20fs (1.8 cycles) pulse at 3.3μm. The feasibility is verified by comparing with the results obtained by simulation and frequency-resolved optical gating for the spectral phase modulation because of a 4mm thick germanium plate.

The “accumulation effect” of positrons in the stack of foils, detected by measurements of the positron implantation profile

The profiles of positrons implanted from the radioactive source 22Na into a stack of foils and plates are the subject of our experimental and theoretical studies. The measurements were performed using the depth scanning of positron implantation profile method, and the theoretical calculations using the phenomenological multi-scattering model (MSM). Several stacks consisting of silver, gold and aluminum foils, and titanium and germanium plates were investigated. We notice that the MSM describes well the experimental profiles; however when the stack consisting of silver and gold foils, the backscattering and linear absorption coefficients differ significantly from those reported in the literature. We suggest the energy dependency of the backscattering coefficient for silver and gold. In the stacks which comprise titanium and germanium plates, there were observed the features, which indicate the presence of the “accumulation effect” in the experimental implantation profile. This effect was previously detected in implantation profiles in Monte Carlo simulations using the GEANT4 tool kit, and it consists in higher localization of positrons close the interface. We suppose that this effect can be essential for positron annihilation in any heterogeneous materials.

Effect of Membrane Cholesterol on the Structure of Alzheimer's Amyloid β Peptide in Lipid Bilayers

A hallmark feature of Alzheimer's disease is formation of extracellular plaques of the amyloid β (Aβ) peptide. There is evidence that the Aβ peptide inserts into the membranes of surrounding neuronal cells, causing membrane permeabilization or rupture. The level of cholesterol in membranes has been shown to affect the extent and toxicity of Aβ plaques, as well as the mode of membrane insertion of Aβ and its structure. Here we analyze the effect of cholesterol on the secondary structure of the 40-residue Aβ peptide in artificial lipid bilayers. Multilayers composed of 0.3 mol fraction of 1-palmitoyl-2-oleoyl-phosphatidylglycerol, (0.7 - Xchol) mol fraction of 1-palmitoyl-2-oleoyl-phosphatidylcholine, and Xchol mol fraction of cholesterol were deposited on a germanium plate, with Xchol = 0, 0.05, 0.1, 0.2 and 0.4, containing Aβ at a 1:15 peptide/lipid molar ratio. Fourier transform infrared spectra were collected on lipid-peptide samples under three conditions, i) dry multilayers, ii) humidified with D2O vapors, and iii) in the presence of a bulk D2O-based buffer. In all cases, the amide I bands of the peptide indicated comparable fractions of α-helical and β-sheet structures. Increase of Xchol from 0 to 0.2 resulted in a significant decrease in the β-sheet structure and a slight increase in α-helix content. Further increase in Xchol to 0.4 reversed the β-sheet content and increased the α-helical structure; the latter effect was much stronger in hydrated samples. Considering that cholesterol at Xchol > 0.2 causes a fluid-disordered to fluid-ordered transition in membranes, the observed structural effects may reflect either conformational changes in membrane-bound Aβ peptide or a squeezing-out effect. These possibilities, as well as the effect of cholesterol on membrane permeabilization will elucidate the role of cholesterol in Aβ structure and function.

Lipid Composition Regulates the Orientation of Transmembrane Helices in HorA, an ABC Multidrug Transporter

ATP-binding cassette (ABC) transporters constitute a large class of molecular pumps whose central role in chemotherapy resistance has highlighted their clinical relevance. We investigated whether the lipid composition of the membrane affects the function and structure of HorA, a bacterial ABC multidrug transporter. When the transporter was reconstituted in a bilayer where phosphatidylethanolamine (PE), the main lipid of the bacterial membrane, was replaced with phosphatidylcholine (PC), ATP hydrolysis and substrate transport became uncoupled. Although ATPase activity was maintained, HorA lost its ability to extrude the prototypical substrate Hoechst33342. Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR) revealed that, although the secondary structure of the protein was unaffected, the orientation of the transmembrane helices (TM) was modified by the change in lipid composition. The orientation of the backbone carbonyls indicated that the helices opened wider in PE versus PC-containing liposomes, with 10 degrees difference. This was supported by hydrogen/deuterium exchange studies showing increased protection of the backbone from the solvent in PC-containing liposomes. Electron Paramagnetic Resonance was used to further probe the structural change. In the PC-containing liposomes we observed increased mobility of the spin label in TM4, along with increased exposure to molecular oxygen, used as a hydrophobic quencher. This indicates that the lipid change induced modification of the orientation of TM4, exposing Cys-180 to the lipid phase. The lipid composition of the bilayer thus modulates the structure of HorA, and in turn its ability to extrude its substrates.

The interaction of the Bax C-terminal domain with negatively charged lipids modifies the secondary structure and changes its way of insertion into membranes

Fourier transform infrared spectroscopy (FTIR) was used to study the secondary structure of peptides which imitate the amino acid sequences of the C-terminal domain of the pro-apoptotic protein Bax (Bax-C) when incorporated into different lipid vesicles with or without negatively charged phospholipids. The infrared spectroscopy results showed that while the beta-sheet components are predominant in the membrane-free Bax-C secondary structure as well as in the presence of phosphatidylcholine vesicles, the peptide changes its secondary structure in the presence of negatively charged membranes, including phospholipids such as phosphatidylglycerol or phosphatidylinositol, depending on both the lipid composition and their molar ratio. The negative charges in the model membrane surface caused a marked change from beta-sheet to alpha-helix structure. Moreover, using attenuated total reflection infrared spectroscopy (ATR-FTIR), we investigated the orientation of Bax-C alpha-helical structures with respect to the normal to the internal reflection element. The orientation of Bax-C in membranes was also affected by negatively charged lipids, the presence of phosphatidylglycerol reduced the angle it forms with the normal to the germanium plate from 45 degrees in phosphatidylcholine to 27 degrees in phosphatidylglycerol vesicles. These results highlight the importance of lipid-protein interaction for the correct folding of membrane proteins and they suggest that the C-terminal domain of Bax will only span membranes with a net negative charge in their surface.

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We have developed a new type of dual-wavelength transversely excited atmospheric pressure (TEA) CO 2 laser that possesses space overlap and time synchronization. Our experiments have proven that the time interval of two output pulses with different frequencies can be adjusted from 1000 ns to 200 ns. In this way, the requirement of dual-wavelength excitation in a material can be achieved for isotope separation purposes. This TEA CO 2 laser contains a grating-plate cavity formed by one germanium plate and two gratings, where the two gratings partially overlap in the space. The gratings, which are placed in tandem, are mutually beneficial via the germanium plate and establish double-frequency oscillation. The dual-wavelength laser is exported from the germanium plate. It is a changing of the effective area of two gratings that enables us to adjust the space overlap of the two output pulses. By simultaneously adjusting the quantity of misalignment in the gratings angle to vary the spectral line geometry loss, which can be used to reduce the time interval of the two output pulses, a time synchronization can be achieved.

Mode of Membrane Interaction and Fusogenic Properties of a de Novo Transmembrane Model Peptide Depend on the Length of the Hydrophobic Core

Model peptides composed of alanine and leucine residues are often used to mimic single helical transmembrane domains. Many studies have been carried out to determine how they interact with membranes. However, few studies have investigated their lipid-destabilizing effect. We designed three peptides designated KALRs containing a hydrophobic stretch of 14, 18, or 22 alanines/leucines surrounded by charged amino acids. Molecular modeling simulations in an implicit membrane model as well as attenuated total reflection-Fourier transform infrared analyses show that KALR is a good model of a transmembrane helix. However, tryptophan fluorescence and attenuated total reflection-Fourier transform infrared spectroscopy indicate that the extent of binding and insertion into lipids increases with the length of the peptide hydrophobic core. Although binding can be directly correlated to peptide hydrophobicity, we show that insertion of peptides into a membrane is determined by the length of the peptide hydrophobic core. Functional studies were performed by measuring the ability of peptides to induce lipid mixing and leakage of liposomes. The data reveal that whereas KALR14 does not destabilize liposomal membranes, KALR18 and KALR22 induce 40 and 50% of lipid-mixing, and 65 and 80% of leakage, respectively. These results indicate that a transmembrane model peptide can induce liposome fusion in vitro if it is long enough. The reasons for the link between length and fusogenicity are discussed in relation to studies of transmembrane domains of viral fusion proteins. We propose that fusogenicity depends not only on peptide insertion but also on the ability of peptides to destabilize the two leaflets of the liposome membrane.

Hybrid seeded femtosecond optical parametric amplifier

We propose and demonstrate a novel hybrid seeded optical parametric amplifier (OPA) that incorporates an external CW seeding at signal wavelength in the first stage and difference-frequency mixing between the idler and pump in the second stage. By using a germanium plate to block the CW seeding background, spectrally and temporally clean signal pulses with duration less than 150 fs and energy up to 17 muJ are obtained with a MgO:LiNbO3-based hybrid seeded OPA. The device may provide direct tunability to some extent and delivers signal pulses tunable from 1.01 mum to 1.08 mum.

Femtosecond photodeflection spectroscopy in thin monocrystalline plates of germanium

A highly sensitive photodeflection spectroscopy technique with femtosecond time resolution has been developed. Using this technique, we have measured accurately the shape of acoustic pulses, which were generated from the ultrafast phonon emission in a germanium plate. Supersonic expansion of photoexcited electron-hole plasma was observed. The characteristic velocity of plasma diffusion was evaluated. It exceeded the longitudinal sound velocity in germanium by a factor of 4.0.

Infrared external reflection absorption spectroscopic study on the structures of the Langmuir–Blodgett films of palmitoyl-l and dl-lysine on a Ge plate

The p-polarized infrared reflection absorption spectra were observed for the Langmuir–Blodgett (LB) film of palmitoyl-l-lysine (l-PL) and the film of a 1:1 mixture of palmitoyl-l- and d-lysine (dl-PL) prepared on a germanium plate as a function of incident angles. The spectra were simulated by assuming a three-layered model consisting of an air/optically anisotropic LB film/Ge substrate, to determine the orientation angles relative to the surface normal for the transition moments of the CH2 asymmetric stretching, CH2 symmetric stretching, amide I, and amide II modes. The results gave detailed information about the orientation of the palmitoyl as well as peptide groups in the LB-films of l-PL and dl-PL, elucidating the structural difference between the two LB films. In the l-PL film the palmitoyl groups exist in a uniaxial orientation state with the tilt angle of about 29° relative to the surface normal and the peptide groups form an ordered hydrogen-bonded network with the peptide plane tilting from the surface normal of about 19°. On the other hand, the peptide groups form an ordered hydrogen-bonded network with the tilt angle of about 49°, while the palmitoyl groups exist in an irregularly orientated state. A structural model consistent with the above-mentioned results was proposed to the dl-PL film.