Carrier Plasma Research Articles

GeSi modulator based on two-mode interference

A GeSi modulator based on two-mode interference is designed in this study. A GeSi layer with a height of 0.22 μm is introduced to decrease the optical power overlap of the two modes. A doping region in which the free carrier plasma dispersion effect exists to change the oscillation period for on- and off-state switching is identified. A doping concentration of 1×10¹⁸ cm⁻³ for both n and p type is selected. The single modulation arm for 3 V operation is 1416.3 μm long. The extinction ratio and insertion loss are 15 and 5 dB, respectively. The traveling electrode design shows 3 dB bandwidth as large as 50 GHz.

Influence of processing gases on the properties of cold atmospheric plasma SiO x C y coatings

Abstract Thin layers of SiO x C y ( y = 4− x and 3 ≤ x ≤ 4) were applied using a cold atmospheric plasma torch on glass substrates. The aim was to investigate using Atomic Force Microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (Tof-Sims) the influence of the gases used on the morphology and composition of the deposits. A hexamethyldisilane (HMDS) precursor was injected in post-discharge in an air or nitrogen plasma using a carrier gas (air or nitrogen) and was applied on the substrate previously pre-treated by an air or nitrogen plasma. The carrier gas and plasma gas flows and the distance between the substrate and the plasma torch, the scanning speed, and the precursor flows were kept constant during the study. The gas used during activation pre-treatment showed no particular influence on the characteristics of the deposit. When air is used both as plasma and carrier gas, the coating layer is thicker (96 nm) than when nitrogen is used (64 nm). It was also evidenced that the gas carrying the precursor has little influence on the hydrophobicity of the coating, contrary to the plasma gas. The latter significantly influences the surface characteristics of the coatings. When air is used as plasma gas, a compact coating layer is obtained and the surface has a water contact angle (WCA) of 82°. When nitrogen is used, the deposit is more hydrophobic (WCA of 100°) and the deposit morphology is different. This increase in hydrophobicity could be correlated to the increase of Si O C bonds in the upper surface layers evidenced by XPS analyzes. This observation was then confirmed by Tof-Sims analyzes carried out on these thin layers. A uniform distribution of Carbons in the siloxane coating could also be observed using Tof-Sims 2D reconstruction images of cross sections of the deposited layers.

Proteomics-based identification of plasma proteins and their association with the host–pathogen interaction in chronic typhoid carriers

SummaryBackgroundCurrent diagnostic tests are inadequate to detect typhoid cases, as well as the chronic carrier state, the sole reservoir of Salmonella enterica serovar Typhi. The current study was conducted to find new molecular signatures of pathogen/disease to understand the mechanism behind the host–pathogen interaction in enteric fever.MethodsProteomics-based studies were done to determine the expression of differentially expressed proteins in the plasma of controls, acute typhoid cases, and chronic typhoid carriers. Further, transcriptome-based analysis using reverse-transcriptase PCR (RT-PCR) was done in controls, acute typhoid cases, and chronic typhoid carriers.ResultsResults showed the upregulation of proprotein convertase subtilisin, furin, haptoglobin, and albumin in the plasma of chronic typhoid carriers. The elevation in mRNA expression of four differentially expressed proteins confirms the changes at the transcriptional level. Further, the increase in albumin and haptoglobin in chronic typhoid carriers shows their role in free radical generation, inflammation, and monocyte cell signaling.ConclusionThrough proteomics techniques, this study identified four proteins in the chronic typhoid carrier host that may have a role in the disease pathogenesis of enteric fever.

GaAs/AlGaAs-Based 870-nm-Band Widely Tunable Edge-Emitting V-Cavity Laser

An 870-nm-band wavelength tunable edge-emitting semiconductor laser based on V-coupled cavities in a GaAs/AlGaAs material system is presented. It does not involve any grating or epitaxial regrowth. Using a single electrode control, 31-channel wavelength tuning with a channel spacing of about 0.38 nm is achieved, with a tuning range of 11.4 nm. By additionally varying the temperature from 8°C to 50°C, wavelength tuning of 60 channels over 22.4 nm is demonstrated. At lower tuning current and with a temperature variation of 18°C, wavelength switching by carrier plasma effect is achieved with a tuning range of 8.2 nm. The simple and compact 870-nm-band edge-emitting tunable laser is suitable for multifunctional photonic integration for optical interconnect and biomedical applications.

Non-Drude Behavior in Indium-Tin-Oxide Nanowhiskers and Thin Films Investigated by Transmission and Reflection THz Time-Domain Spectroscopy

A comparative study of indium-tin-oxide (ITO) nanowhiskers (NWhs) and thin films as transparent conductors in the terahertz frequency range are conducted. We employ both transmission-type and reflection-type terahertz time-domain spectroscopies (THz-TDTS and THz-TDRS) to explore the far-infrared optical properties of these samples. Their electrical properties, such as plasma frequencies and carrier scattering times, are analyzed and found to be fitted well by the Drude-Smith model over 0.1-1.4 THz. Further, structural and crystalline properties of samples are examined by scanning electron microscopy and X-ray diffraction, respectively. Non-Drude behavior of complex conductivities in ITO NWhs is attributed to carrier scattering from grain boundaries and impurity ions. In ITO thin films, however, the observed non-Drude behavior is ascribed to scattering by impurity ions only. Considering NWhs and thin films with the same height, mobility of the former is ~ 125 cm2V-1s-1, much larger than those of the ITO thin films, ~ 27 cm2 V-1 s-1. This is attributed to the longer carrier scattering time of the NWhs. The dc conductivities ( ~ 250 Ω-1 cm-1) or real conductivities in the THz frequency region of ITO NWhs is, however, lower than those of the ITO thin films ( ~ 800 Ω-1 cm-1) but adequate for use as electrodes. Partly, this is a reflection of the much higher plasma frequencies of thin films. Significantly, the transmittance of ITO NWhs ( ≅ 60%-70%) is much higher ( ≅ 13 times) than those of ITO thin films in the THz frequency range. The underneath basic physics is that the THz radiation can easily propagate through the air-space among NWhs. The superb transmittance and adequate electrical properties of ITO NWhs suggest their potential applications as transparent conducting electrodes in THz devices.

High-speed delay tuning of slow light in pin-diode-incorporated photonic crystal waveguide

We demonstrate the high-speed electrical delay tuning of slow light pulses using Si photonic crystal waveguides. The device has an i-region-chirped pin diode, within which thermo-optic and carrier plasma effects are generated by forward bias. The former changes the delay up to 62 ps for the DC bias. The latter changes the delay for 1 Gbps pseudo random bit sequence tuning signals, which will be applicable to advanced time-domain optical signal processing.

Free carrier plasma optical response and dynamics in strongly pumped silicon nanopillars

We investigated time-resolved optical properties of the free carrier plasma excited by femtosecond laser pulses in silicon nanopillars. The optical response of the excited nanopillars was modelled by the 2D Maxwell-Garnett mixing rule modified to accommodate a Drude-like contribution of the free carriers. The experimental results of the plasma dynamics pump-probe study suggest that the main mechanism of the decay at high pumping is Auger recombination with a rate similar to that of the bulk silicon. We also show that the low reflective and almost fully transparent layer of the nanopillars becomes strongly absorptive when the pillars are pumped with the free carrier concentration in the range between 8×1020 and 2×1021 cm−3. The enhancement of the absorption is attributed to plasmon resonance at which the probe light and the excited plasma frequencies are matched.

Investigation of the Spatiotemporal Responses of Nanoparticles in Tumor Tissues with a Small-Scale Mathematical Model

The transport and accumulation of anticancer nanodrugs in tumor tissues are affected by many factors including particle properties, vascular density and leakiness, and interstitial diffusivity. It is important to understand the effects of these factors on the detailed drug distribution in the entire tumor for an effective treatment. In this study, we developed a small-scale mathematical model to systematically study the spatiotemporal responses and accumulative exposures of macromolecular carriers in localized tumor tissues. We chose various dextrans as model carriers and studied the effects of vascular density, permeability, diffusivity, and half-life of dextrans on their spatiotemporal concentration responses and accumulative exposure distribution to tumor cells. The relevant biological parameters were obtained from experimental results previously reported by the Dreher group. The area under concentration-time response curve (AUC) quantified the extent of tissue exposure to a drug and therefore was considered more reliable in assessing the extent of the overall drug exposure than individual concentrations. The results showed that 1) a small macromolecule can penetrate deep into the tumor interstitium and produce a uniform but low spatial distribution of AUC; 2) large macromolecules produce high AUC in the perivascular region, but low AUC in the distal region away from vessels; 3) medium-sized macromolecules produce a relatively uniform and high AUC in the tumor interstitium between two vessels; 4) enhancement of permeability can elevate the level of AUC, but have little effect on its uniformity while enhancement of diffusivity is able to raise the level of AUC and improve its uniformity; 5) a longer half-life can produce a deeper penetration and a higher level of AUC distribution. The numerical results indicate that a long half-life carrier in plasma and a high interstitial diffusivity are the key factors to produce a high and relatively uniform spatial AUC distribution in the interstitium.

Presence of N‐glycosylated transthyretin in plasma of V30M carriers in familial amyloidotic polyneuropathy: an escape from ERAD

Familial amyloid polyneuropathy (FAP) is an autosomal dominant disease characterized by deposition of amyloid related to the presence of mutations in the transthyretin (TTR) gene. TTR is mainly synthesized in liver, choroid plexuses of brain and pancreas and secreted to plasma and cerebrospinal fluid (CSF). Although it possesses a sequon for N-glycosylation N-D-S at position 98, it is not secreted as a glycoprotein. The most common FAP-associated mutation is TTR V30M. In a screening for monoclonal antibodies developed against an amyloidogenic TTR form, we detected a distinct TTR with slower electrophoretic mobility in Western of plasma from carriers of the V30M mutation, not present in normal plasma. Mass spectrometry analyses of this slower migrating TTR (SMT) identified both wild-type and mutant V30M; SMT was undetectable upon N-glycosidase F treatment. Furthermore, SMT readily disappeared in the plasma of V30M - FAP patients after liver transplantation and appeared in plasma of transplanted domino individuals that received a V30M liver. SMT was also detected in plasma, but not in CSF of transgenic mice for the human V30M mutation. A hepatoma cell line transduced to express human V30M did not present the SMT modification in secretion media. Glycosylated TTR was absent in fibrils extracted from human kidney V30M autopsy tissue or in TTR aggregates extracted from the intestine of human TTR transgenic mice. Studies on the metabolism of this novel, glycosylated TTR secreted from FAP liver are warranted to provide new mechanisms in protein quality control and etiopathogenesis of the disease.

Nitrogen-oxygen plasma treatment of ITO for performance improvement of blue organic light emitting diodes

Blue organic light-emitting diodes (OLEDs) were fabricated by pre-treating indium-tin-oxide (ITO) glass with a nitrogen-oxygen plasma (N2:O2) carrier gas. The device structure was ITO/α- NPD(4,4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl)/BH140(Idemitsu):BD052(Idemitsu)/BCP (2,9dimethyl-4,7-diphenyl-1,10-phenanthroline) (variable)/LiF/Al:Li. In comparison with conventional O2-treated devices, our N2:O2-treated devices showed increased electroluminescence, current efficiency, brightness, and lifetime. The blue OLED devices showed the optimum working voltage and current density at 5.5 V when the thickness of the BCP was 25 A and high efficiency when the thickness was 100 A.

From bowel to kidneys: the role of cubilin in physiology and disease

Cubilin is a large endocytic receptor serving such diverse functions as the intestinal absorption of the intrinsic factor-B(12) complex and the renal proximal tubule reabsorption of filtered proteins including albumin, transferrin, vitamin D-binding protein and other important plasma carriers. Cubilin is a structurally unique, peripheral membrane protein, which depends on the membrane protein amnionless (AMN) for correct apical translocation. In addition, AMN appears important for efficient internalization of intrinsic factor-B(12) in the intestine, whereas in the proximal tubule cubilin interacts with another endocytic receptor, megalin, for effective reabsorption. The importance of cubilin has been demonstrated in several animal models of cubilin deficiency as well as in a variety of human diseases. Recent demonstration of cubilin in podocytes from various species awaits further clarification with respect to the functional role as well as its role in pathology.

New approach toward transparent and conductive ZnO by atomic layer deposition: Hydrogen plasma doping

A hydrogen plasma doping process was combined with the traditional atomic layer deposition (ALD) technique in order to enhance the transparency and conductivity of ZnO films. The hydrogen plasma was included in situ during each ALD cycle and was found to be more effective at producing highly conductive ZnO when used before the H2O vapor pulse that is standard to thermal-ALD processes. Through the hydrogen plasma doping process, the resistivity and carrier concentration of the ALD ZnO films are improved to levels suitable for transparent conductive oxide applications. These favorable electrical properties, combined with improved transparency, make such H-doped ZnO films comparable to some of the best Al-doped ZnO materials achieved with ALD processes in the literature. At thicknesses well below 200 nm, the H-doped ALD ZnO films maintain optimal resistivities near 7 × 10−4 Ω cm along with average transmittance values of ∼92% from 400 to 1000 nm.

Development of thin film cathodes for lithium-ion batteries in the material system Li–Mn–O by r.f. magnetron sputtering

Today most commercially available lithium ion batteries are still based on the toxic and expensive LiCoO2 as a standard cathode material. However, lithium manganese based cathode materials are cheaper and environmentally friendlier. In this work cubic-LiMn2O4 spinel, monoclinic-Li2MnO3 and orthorhombic-LiMnO2 thin films have been synthesized by non-reactive r.f. magnetron sputtering from two ceramic targets (LiMn2O4, LiMnO2) in a pure argon discharge. The deposition parameters, namely target power and working gas pressure, were optimized in a combination with a post deposition heat treatment with respect to microstructure and electrochemical behavior. The chemical composition was determined using inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The films' crystal structure, phase evolution and morphology were investigated by X-ray diffraction, micro Raman spectroscopy and scanning electron microscopy. Due to the fact that these thin films consist of the pure active material without any impurities, such as binders or conductive additives like carbon black, they are particularly well suited for measurements of the intrinsic physical properties, which is essential for fundamental understanding. The electrochemical behavior of the cubic and the orthorhombic films was investigated by galvanostatic cycling in half cells against metallic lithium. The cubic spinel films exhibit a maximum specific capacity of ~82mAh/g, while a specific capacity of nearly 150mAh/g can be reached for the orthorhombic counterparts. These films are promising candidates for future all solid state battery applications.

Plasma distribution of tetraphenylporphyrin derivatives relevant for Photodynamic Therapy: Importance and limits of hydrophobicity

In the course of a Photodynamic Therapy (PDT) protocol, disaggregation of the sensitizer upon binding to plasma proteins and lipoproteins is one of the first steps following intravenous administration. This step governs its subsequent biodistribution and has even been evoked as possibly orientating mechanism of tumor destruction. It is currently admitted as being mainly dependent on sensitizer’s hydrophobicity. In this context, as far as glycoconjugation of meso-tetraphenylporphyrin (TPP) macrocycle, a promising strategy to improve targeting of retinoblastoma cells confers to the sensitizer an amphiphilic character, we have studied the effect of this strategy on binding to plasma proteins and lipoproteins. With the exception of the majoritary protein binding (more than 80%) of more hydrophilic para-tetraglycoconjugated derivatives, high density lipoproteins (HDL) appear as main plasma carriers of the other amphiphilic glycoconjugated photosensitizers. This HDL-binding is a combined result of binding affinities (logKa ranging from 4.90 to 8.77 depending on the carrier and the TPP derivative considered) and relative plasma concentrations of the different carriers. Evaluation of binding affinities shows that if hydrophobicity can account for LDL- and HDL-affinities, it is not the case for albumin-affinity. Molecular docking simulations show that, if interactions are mainly of hydrophobic nature, polar interactions such as hydrogen bonds are also involved. This combination of interaction modalities should account for the absence of clear relationship between albumin-affinity and hydrophobicity. Taken together, our findings clarify the importance, but also the limits, of hydrophobicity’s role in structure–plasma distribution relationship.

Mosquito Feeding Assays to Determine the Infectiousness of Naturally Infected Plasmodium falciparum Gametocyte Carriers

IntroductionIn the era of malaria elimination and eradication, drug-based and vaccine-based approaches to reduce malaria transmission are receiving greater attention. Such interventions require assays that reliably measure the transmission of Plasmodium from humans to Anopheles mosquitoes.MethodsWe compared two commonly used mosquito feeding assay procedures: direct skin feeding assays and membrane feeding assays. Three conditions under which membrane feeding assays are performed were examined: assays with i) whole blood, ii) blood pellets resuspended with autologous plasma of the gametocyte carrier, and iii) blood pellets resuspended with heterologous control serum.Results930 transmission experiments from Cameroon, The Gambia, Mali and Senegal were included in the analyses. Direct skin feeding assays resulted in higher mosquito infection rates compared to membrane feeding assays (odds ratio 2.39, 95% confidence interval 1.94–2.95) with evident heterogeneity between studies. Mosquito infection rates in membrane feeding assays and direct skin feeding assays were strongly correlated (p<0.0001). Replacing the plasma of the gametocyte donor with malaria naïve control serum resulted in higher mosquito infection rates compared to own plasma (OR 1.92, 95% CI 1.68–2.19) while the infectiousness of gametocytes may be reduced during the replacement procedure (OR 0.60, 95% CI 0.52–0.70).ConclusionsDespite a higher efficiency of direct skin feeding assays, membrane feeding assays appear suitable tools to compare the infectiousness between individuals and to evaluate transmission-reducing interventions. Several aspects of membrane feeding procedures currently lack standardization; this variability makes comparisons between laboratories challenging and should be addressed to facilitate future testing of transmission-reducing interventions.

Characteristics of THz carrier dynamics in GaN thin film and ZnO nanowires by temperature dependent terahertz time domain spectroscopy measurement

We present a comprehensive study of the characteristics of carrier dynamics using temperature dependent terahertz time domain spectroscopy. By utilizing this technique in combination with numerical calculations, the complex refractive index, dielectric function, and conductivity of n-GaN, undoped ZnO NWs, and Al-doped ZnO NWs were obtained. The unique temperature dependent behaviors of major material parameters were studied at THz frequencies, including plasma frequency, relaxation time, carrier concentration and mobility. Frequency and temperature dependent carrier dynamics were subsequently analyzed in these materials through the use of the Drude and the Drude–Smith models.

Preparation of spherical hollow alumina particles by thermal plasma

Spherical hollow particles were prepared from solid alumina powders using DC arc thermal plasma, and then spray coating was performed with the as-prepared particles. Operating variables for the hollow particle preparation process were additional plasma gas, input power, and carrier gas flow rate. The spherical hollow alumina particles were produced in the case of using additive gas of H2 or N2, while alumina surface was hardly molten in the pure argon thermal plasma. In addition, the hollow particles were well produced in high power and low carrier gas conditions due to high melting point of alumina. Hollow structure was confirmed by focused ion beam-scanning electron microscopy analysis. Morphology and size distribution of the prepared particles that were examined by field emission-scanning electron microscopy and phase composition of the particles was characterized by X-ray diffraction. In the spray coating process, the as-prepared hollow particles showed higher deposition rate.

Laterally coupled silicon-germanium modulator for passive waveguide systems

We model a laterally coupled Franz-Keldysh add-drop ring modulator designed to overcome the C-band indirect absorption of silicon-germanium. Although our concept is based on loss-sensitive interferometry, it utilizes the same highly absorptive germanium-rich compositions geared toward complementary metal-oxide semiconductor (CMOS) photodetectors and electroabsorption modulators. The proposed device can be integrated with passive waveguide networks in which the carrier plasma modulation mechanism is ineffective. In addition, unlike previous silicon-germanium modulator schemes, complex butt-coupling between the passive transport and the active silicon-germanium waveguides is not required. Instead, the optical mode remains guided within the transport waveguide, minimizing transition losses.

Pilot-study on the influence of carrier gas and plasma application (open resp. delimited) modifications on physical plasma and its antimicrobial effect against Pseudomonas aeruginosa and Staphylococcus aureus.

Introduction: Physical plasma is a promising new technology regarding its antimicrobial effects. This is especially accounting for treatment of bacterial infection of chronic wounds. Plasma can be generated with different carrier gases causing various biological effects. Screening of different carrier gases and plasma generation setups is therefore needed to find suitable compositions for highly effective antimicrobial plasma treatments and other applications. Method: The plasma source used was a radio-frequency plasma jet which generates tissue tolerable plasma (TTP). The study compared the antimicrobial efficacy of air, argon, or helium plasma alone or admixed with 0.1%, 0.5%, and 1% oxygen against Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). Treatment took place in an environmentally open and delimited system. Therefore, bacteria were plated on agar and treated with plasma in a punctiform manner. The resulting inhibition zones were measured and the reduction factors were calculated by colony counting, respectively. Results: For S. aureus and P. aeruginosa, inhibition zones and overall reduction of colony forming units (CFU) on the agar plate were observed while an accumulative reduction of CFU dominated for S. aureus. The highest antimicrobial effect was shown in form of an inhibition zone for argon plasma with 0.1% oxygen admixture for both species. S. aureus was more sensitive for helium plasma with >0.1% oxygen admixture compared to P. aeruginosa which in turn was more sensitive for argon plasma with and without oxygen. The efficacy of air plasma was very low in comparison to the other gases. The treatment in a closed system predominantly enhanced the antimicrobial effect. The effect intensity varied for each treatment time and gas mixtures. Discussion: As expected, the antimicrobial effect mostly increased when increasing oxygen admixture to the carrier gases. The variation in bacterial growth and inhibition after exposure to different plasma gas compositions could be due to a varying generation of reactive oxygen species or radiation. Conclusion: The applied plasma in a “closed system” accumulates bactericidal plasma species and might increase antimicrobial efficacy in clinical settings as in wound management involving multi-drug resistant bacteria.

Eigenstate localization in an asymmetric coupled quantum well pair

Optical pumping of a type-I/type-II coupled asymmetric quantum well pair induces a spatially separated two dimensional charge carriers plasma in the well’s wide and narrow parts. Treating the two coupled wells as a single system we find that the eigenstate probability distribution localizes exclusively either in the wide or the narrow parts of the well pair. The energy of the narrow-well localized state determines the minimal excitation energy for optically pumped charge carriers separation. In a previously used design [Guliamov et al., PRB 64 035314 (2001)] this narrow well transition energy was measured to correspond to a wavelength of 646nm. We propose modifications to the design suggested earlier with the purpose of pushing up the energy required for the optical pumping of the two-dimensional plasma into the green and blue regions of the visible spectrum.