Ms Contact Research Articles

Tailored HZSM-5 catalyst modification via phosphorus impregnation and mesopore introduction for selective catalytic conversion of polypropylene into light olefins

The waste polyolefin composition varies regionally due to different sorting technologies, emphasizing the necessity for a robust catalyst capable of selectively converting pyrolysis vapors into valuable light olefins while maintaining stability. HZSM-5, a microporous catalyst, efficiently cracks polyethylene (PE) pyrolysis vapors rich in linear aliphatics. However, polypropylene (PP) pyrolysis typically yields branched olefins, potentially hindering effectiveness of HZSM-5 due to mass transfer constraints and coke blockage in micropores. This study modifies HZSM-5 through phosphorus impregnation, mesopore introduction, and steam treatment to evaluate the impact of acidity, pore size, and surface modifications on catalyst stability and light olefin selectivity during PP pyrolysis vapor cracking. Subsequent experiments reveal the superior stability of modified catalysts. Phosphorus-modified (P-HZSM-5ss) and mesoporous phosphorus-modified (P-mesoHZSM-5ss) catalysts retain 72 % and 80 % of their initial activity after 150 runs, respectively, while the parent HZSM-5 experiences a rapid 44 % activity loss. P-mesoHZSM-5ss demonstrates the highest light olefin selectivity (63 wt%) after 150 runs, attributed to improved accessibility of branched olefinic products to active sites within catalyst pores. Further optimization achieves exceptional light olefin selectivity of 84 wt% at 117 ms contact time and 550 °C, surpassing maximum selectivity of the parent catalyst. Comparative analyses of PP, PE, and mixed polyolefinic waste pyrolysis vapor cracking revealed the influence of polyolefin type on optimal operational conditions, stressing the need for flexibility in operating conditions to scale up the proposed polyolefin recycling method. This study highlights the potential of tailored catalyst modifications and process optimization to efficiently convert PP into valuable light olefins, advancing sustainable polyolefin recycling technologies.

Interfacial characteristics, metal-semiconductor contact and optical properties of CSe and BX (X=B, As and Sb) monolayers

Two dimensional (2D) materials with large family recently drawn tremendous attention due to their versatile applications. Appreciating the smooth surface and atomic thickness of 2D materials, which can be constructed in the form of heterostructures, resulting interesting chemical and physical properties in many fields. Particularly, 2D metal-semiconductor contact (MS contact), shown great promise in nanodevices and optoelectronic devices application. In this work, we have constructed the MS contact of CSe and BX (X = P, As and Sb) monolayers and investigated the interfacial characteristics, Schottky contact and optical properties, using density functional theory. Our calculated binding energies and thermal stability confirm that CSe-BX (X = P, As and Sb) MS contact are dynamically and thermally stable. Our prediction shows that CSe-BX (X = P, As and Sb) MS contact forms n-type contact, while well preserved the properties of both monolayers. A small band gap opening in CSe having high carrier mobilities, indicated that CSe-BX (X = P, As and Sb) MS contact are good candidates for high speed nanoelectronics applications. Electrostatic potential and Bader charge analysis confirm that electrons are transfer from CSe layer to the BS monolayers and the potential drops separates charge carrier at the interface, play crucial rule in power conversion efficiency. The imaginary part shows an intense absorption peak near the visible region, hence shows appalling application in photoelectronic and optical transmissions.

Structural and electronic characterization of silicon based MIS contact by xanthene dye molecules (Erythrosine B)

The effect of erythrosine B (ERY) organic material as an interface layer on the electronic characteristics of the Al/p-Si junction is examined in the present work. AFM, NMR, UV–Vis and FTIR measurements have been conducted on the ERY dye molecule. The ERY film on the surface of the substrate is coated with nanoparticles, according to the surface analysis performed using the AFM technique. The basic diode parameters of Al/p-Si and Al/ERY/p-Si junctions were measured by utilizing current-voltage (I–V) and capacitance-voltage (C-V) techniques. The junctions with and without organic interfacial layers were found to have ideality factors of 1.931 and 1.925, respectively. For MS and MIS contacts, the estimated values of barrier height were 0.592 eV and 0.937 eV, respectively. Additionally, the series resistances for the MS and MIS structures by utilizing Norde function, were determined to be 0.14 kΩ and 322.85 kΩ, respectively. In addition, the reverse bias 1/C2-V characteristics were used to analyze the barrier height values and compare the findings to those from I-V method. The experimental findings demonstrated that the Al/ERY/p-Si MIS diode has a barrier height that is remarkably greater than that of the reference Al/p-Si junction. Placement of the ERY dye interlayer between a metal and a semiconductor could enhance and regulate the performance and characteristic of these types of junctions.

Comprehensive Schottky Barrier Height Behavior and Reliability Instability with Ni/Au and Pt/Ti/Pt/Au on AlGaN/GaN High-Electron-Mobility Transistors.

The reliability instability of inhomogeneous Schottky contact behaviors of Ni/Au and Pt/Ti/Pt/Au gate contacts on AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated via off-state stress and temperature. Under the off-state stress condition, Pt/Ti/Pt/Au HEMT showed abruptly reduced reverse leakage current, which improved the Schottky barrier height (SBH) from 0.46 to 0.69 eV by suppression of the interfacial donor state. As the temperature increased, the reverse leakage current of the Pt/Ti/Pt/Au AlGaN/GaN HEMT at 308 K showed more reduction under the same off-state stress condition while that of the Ni/Au AlGaN/GaN HEMT increased. However, with temperatures exceeding 308 K under the same off-state stress conditions, the reverse leakage current of the Pt/Ti/Pt/Au AlGaN/GaN HEMT increases, which can be intensified using the inverse piezoelectric effect. Based on this phenomenon, the present work reveals the necessity for analyzing the concurrent SBH and reliability instability due to the interfacial trap states of the MS contacts.

Gas-phase thermolysis of azines. Part 3. Kinetics and mechanism of pyrolysis of substituted arylidenepyrazin-2-yl- and pyrimidin-2-ylhydrazines

Five N-arylidene-N’-pyrazin-2-ylhydrazines, series (1a-e) and five N-arylidene-N’-pyrimidin-2-ylhydrazines, series (2a-e) were synthesized and characterized: four of the former series and two of the latter are novel compounds. The ten substrates were then subjected to: (i) flow flash vacuum pyrolysis (FVP) at 700 °C and short (ms) contact time; (ii) static sealed-tube pyrolysis (STP) at temperatures in the range of 300–380 °C, and relatively longer substrate residence time of 15–60 min. The products of thermolysis were analyzed, identified, characterized and compared. Further, the kinetics of pyrolysis was investigated over the temperature range ca 550–620 K and 500–615 K, respectively, for substrates (1a,c,e) and (2a,c,e). Rates, Arrhenius log A and Ea, and entropy of activation (∆S≠) were calculated. The nature and composition of the products of pyrolysis were ascertained, and substrate molecular reactivities were adequately explained based on plausible reaction mechanisms, and further rationalized using known effects of common substituent groups and specific nitrogen replacement (N = ) substituents.

Can coronavirus disease 2019 (COVID-19) trigger exacerbation of multiple sclerosis? A retrospective study

I have read the paper entitled “Can Coronavirus Disease 2019 (COVID-19) Trigger Exacerbation of Multiple Sclerosis? A Retrospective Study” by Barzegar et al., 2021Barzegar M. Vaheb S. Mirmosayyeb O. Afshari-Safavi A. Nehzat N. Shaygannejad V. Can coronavirus disease 2019 (COVID-19) trigger exacerbation of multiple sclerosis? A retrospective study.Mult. Scler. Relat. Disord. 2021; 52102947Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar with great interest, and I do believe that such studies should be conducted in order to further our knowledge, and to identify the possible post-COVID-19 complications in patients with MS (PwMS). However, there are a few points that I would like to share with the scientific community regarding this study. First of all, in the methods section, the presence of gadolinium enhancement is stated as a criterion of definition for an MS relapse: “Relapse was defined as … and confirmed by presence of gadolinium enhancement on magnetic resonance imaging (MRI).”. However, in the one to last paragraph of the discussion section (the limitations paragraph), lack of information regarding gadolinium enhancement in all patients is stated as a limitation of this study: “…lack of information on presence of gadolinium enhancement on MRI in all patients are other limitations of this study.”, which contradicts the previous statement and might be a source of confusion. Furthermore, in various instances in this paper, an episode of MS relapse was considered an effect of COVID-19 infection, which considering the limited data in this regard and the preliminary nature of this study, might be too soon to conclude. On this matter, in the first paragraph of the discussion section, the authors state that that the conclusion of this study is in line with previous studies regarding upper respiratory tract infections:“Our findings are in line with previous observation that upper respiratory viral infections (Edwards et al., 1998Edwards S. Zvartau M. Clarke H. Irving W. Blumhardt L.D. Clinical relapses and disease activity on magnetic resonance imaging associated with viral upper respiratory tract infections in multiple sclerosis.J. Neurol. Neurosurg. Psychiatry. 1998; 64 (Psychiatry): 736-741Crossref PubMed Scopus (150) Google Scholar; Kriesel et al., 2004Kriesel J.D. white A. Hayden F.G. Spruance S.L. Petajan J. Multiple sclerosis attacks are associated with picornavirus infections.Mult. Scler. J. 2004; 10: 145-148Crossref PubMed Scopus (36) Google Scholar), of which 10-30% are caused by coronaviruses (Paules et al., 2020Paules C.I. Marston H.D. Fauci A.S. Coronavirus infections—more than just the common cold.JAMA. 2020; 323: 707-708https://doi.org/10.1001/jama.2020.0757Crossref PubMed Scopus (1163) Google Scholar), is associated with risk of MS relapse.”. However, this statement may be inaccurate, confusing, and a source of a possible confirmation bias, as SARS-CoV-2, in contrast with most other coronaviruses, infects the lower respiratory tract, not to mention that in the first two cited papers in this statement (Edwards et al., 1998Edwards S. Zvartau M. Clarke H. Irving W. Blumhardt L.D. Clinical relapses and disease activity on magnetic resonance imaging associated with viral upper respiratory tract infections in multiple sclerosis.J. Neurol. Neurosurg. Psychiatry. 1998; 64 (Psychiatry): 736-741Crossref PubMed Scopus (150) Google Scholar, Kriesel et al., 2004Kriesel J.D. white A. Hayden F.G. Spruance S.L. Petajan J. Multiple sclerosis attacks are associated with picornavirus infections.Mult. Scler. J. 2004; 10: 145-148Crossref PubMed Scopus (36) Google Scholar), coronaviral infections were not among the studied/detected infections. Furthermore, it is worth mentioning that another preliminary study showed no increase in relapse rates of PwMS after COVID-19 contraction (Etemadifar et al., 2021Etemadifar M. Sedaghat N. Aghababaee A. Kargaran P.K. Maracy M.R. Ganjalikhani-Hakemi M. Rayani M. Abhari A.P. Khorvash R. Salari M. Nouri H. COVID-19 and the risk of relapse in multiple sclerosis patients: a fight with no bystander effect?.Mult. Scler. Relat. Disord. 2021; 51102915Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar). Most important of all, the inclusion of patients in this study was stated to be based on an MS clinic visit or contact after a COVID-19 infection: “All relapsing-remitting MS (RRMS) patients with a confirmed COVID-19 diagnosis based on reverse transcription-polymerase chain reaction (RT-PCR) who visited our outpatient MS clinic or contacted the center were included.”. This might be a major source of selection bias, as the COVID-19-infected PwMS who experienced a relapse are more likely to visit or contact an MS clinic, in comparison to PwMS who did not experience a relapse after their COVID-19 infection. There is also a lack of clarification regarding the chronology of the study and the participant flow e.g., when the study was conducted, if any patients were excluded etc. Nevertheless, I appreciate the work from the authors in conducting this study and sharing it with the scientific community. I am hoping that more controlled studies in the future would clarify the possible relationship between MS relapses and COVID-19, informing and alerting PwMS and physicians.

Catheter Ablation of Ventricular Tachycardia Guided by Substrate Electrical Inexcitability.

Catheter Ablation of Ventricular Tachycardia Guided by Substrate Electrical Inexcitability.

Three dimensional polyvinyl alcohol scaffolds modified with collagen for HepG2 cell culture.

The creation of in vitro functional hepatic tissue simulating micro environmental niche of the native liver is a keen area of research due to its demand in bioartificial liver. However, it is still unclear how to maintain benign cell function while achieving the sufficient cell quantity. In this work, we aim to prepare a novel scaffold for the culture of HepG2 cells, a liver cell line, by modifying polyvinyl alcohol (PVA) scaffold with collagen (COL). PVA is a kind of synthetic biostable polymer with high hydrophilicity in the human body, has been widely used in the biomedical field. However, the use of PVA is limited in cell cultures due to lack of biologically active functional groups. In this study, amino silane (KH-550), glutaraldehyde and native type I collagen were used to modify three-dimensional PVA scaffold to establish a suitable composite scaffold for hepatocyte culture. Three types of composite scaffolds were prepared for different collagen content, named as PVA/COL (0.2%), PVA/COL (0.5%) and PVA/COL (0.8%), respectively. The composite scaffolds were characterized by SEM, XPS, FTIR, MS, porosity estimation and water contact angle measurement. The PVA/COL (0.8%) scaffolds had the highest collagen content of 12.13%. The composite scaffold showed high porosity with interconnected pores. Furthermore, the biocompatibility between HepG2 cells and scaffolds was evaluated by the ability of cell proliferation, albumin secretion, as well as urea synthesis. The coating of collagen on PVA scaffolds promoted hydrophilicity and HepG2 cell adhesion. Additionally, enhanced cell proliferation, increased albumin secretion and urea synthesis were observed in HepG2 cells growing on collagen-coated three-dimensional PVA scaffolds.

Interface controlling study of silicon based Schottky diode by organic layer

The organic layer-on- insulator–semiconductor structures have attracted most attention owing to their great significance on technological applications. The interface of silicon based metal/semiconductor diode was improved using an organic layer. In this study, Sn/p-Si MS contact and Sn/C14H15N3/p-Si MIS heterojunction were fabricated via spin coating method. The electrical parameters of both devices have been investigated, and compared using the current–voltage (I–V) and capacitance–voltage (C–V) data at room temperature. The ideality factor of diodes with and without organic interfacial layer was calculated as 1.33 and 1.28, respectively. The values of barrier height were estimated as 0.69 and 0.81 eV for the MS and MIS type structure, respectively. Additionally, the values of series resistances for both diodes were determined as 1.27 and 1.19 kΩ from Norde functions, respectively. The barrier height values were also examined using the reverse bias C−2–V characteristics for both diodes, and compared with results obtained from I to V data. The experimental results confirmed that the barrier height of Sn/C14H15N3/p–Si MIS structure is considerably higher than that of traditional Sn/p-Si MS diode. The performance and quality of these type devices could be improved and controlled by inserting the organic interfacial layer between the metal and semiconductor.

Barrier enhancement of Al/n-InP Schottky diodes by graphene oxide thin layer

In the present work, the surface morphology, structural and optical features of graphene oxide (GO) films are investigated. The Al/GO/n-InP MIS diode is formed by depositing GO layer on n-InP wafer for the barrier enhancement. Interfacial properties of the MIS diode with GO interlayer are extracted from current–voltage (I–V) measurement. The simple diode parameters such as barrier height and ideality factor are extracted from I–V plots, and the values are compared with those of conventional Al/n-InP MS contact. The value of barrier height (BH) for the Al/GO/n-InP contact is found as 0.85 eV. The BH value of 0.85 eV of the Al/GO/n-InP MIS structure is as high as around 100% compared to the value of 0.43 eV of the Al/n-InP reference contacts. We have showed that the value of 0.85 eV is one of the highest values presented for reference contacts with an interlayer.

Self-powered single semiconductor nanowire photodetector

Self-powered photodetectors have been fabricated from a single germanium nanowire (NW) in the metal–semiconductor–metal (MSM) device configuration. The self-powered devices show a high photoresponse (responsivity ∼ 103–105 A W−1) in the wavelength range 300–1100 nm. It has been established from I–V characteristics that asymmetry exists in the Schottky barrier height (SBH) at the two MS contacts. We have used simulation to establish that the asymmetric SBH at the metal contacts in an MSM device is a major cause for the ‘built-in’ axial field that leads to separation of a light generated electron–hole pair in the absence of an applied bias. Thus, even in the absence of external bias, the photogenerated carriers can be separated, which then diffuse to the appropriate electrodes driven by the ‘built-in’ axial field. We also point out the physical origins that can lead to unequal barrier heights in seemingly identical NW/metal junctions in a MSM device.

Elimination of Boron from Soluble Silica Via Solvent Extraction with 2,2,4-Trimethyl-1,3-Pentanediol Using a Multistage Flow-Type Reactor

The sustainable production of solar-grade silicon (SOG-Si) with inexpensive refining process is highly demanded for Si photovoltaic power generation. Diatomaceous earth, an Earth-abundant silica resource, with aqueous chemical refining is a candidate for high-purity source, which could be directly reduced to SOG-Si.1 Since boron and phosphorus act as dopant in Si semiconductor, efficient way of elimination of these light elements is strongly required. We have proposed the application of microchannel device for the solvent extraction of boron with 2-ethyl-1,3-hexanediol (EHD).2,3 While the short diffusion distance as well as the large specific interfacial area of microchannel enabled fast and efficient elimination of boron to SOG-purity, however, improvement of throughput was required for the practical application. In order to take the advantage of microchannel device together with large productivity, further improvement of the elimination efficiency and increase of the area of liquid-liquid interface for the reaction with maintaining short diffusion distance comparable to the microchannel, is necessary. Here, we report the optimization of the extraction reaction and the channel design for increasing the throughput on the boron elimination from soluble silica via solvent extraction using the flow-type reactor. A flow-type reactor with 0.10 mm depth and 1.0 mm width was fabricated on a silicon and glass substrate using photolithography techniques. The number of stages was one or two, and each channel length was 10 mm or 25 mm. As model solution sample, the refined silica spiked with a trace amount of boric acid was dissolved in 2.5M NaOH aqueous solution prior to adjusting pH to 1.0 with 4.0M HCl aqueous solution. In order to improve the elimination efficiency, 2,2,4-trimethyl-1,3-pentanediol (TMPD) was used instead of EHD and added to toluene to be 0.5 M solution. The model solution sample was injected to the flow-type reactors with the flow rate of 1.5 mL·min-1 and the flow rate of the extractant was adjusted to form parallel flow and be separated at the outlet. The residual boron content was determined with inductively coupled plasma mass spectroscopy (ICP-MS). Table 1 shows representative results. The contact duration, i.e., the reaction period was estimated to be 20 ms for 10 mm length and 50 ms for 25 mm length. In the both cases of EHD and TMPD with 25 mm length, elimination rate was almost same and the residual boron content decreased to less than 0.1 ppm. On the other hand, the elimination rate with TMPD on other cases was higher than that with EHD. In addition, the residual boron content decreased to almost 0.1 ppm in the case of TMPD with 40 ms contact duration. These results indicate that the contact duration on the extraction with TMPD could be optimized between 40 ms and 100 ms. Thus, increase of the flow rate with the optimized total duration and area of liquid–liquid interface can improve the throughput. The application of optimized channel design and extraction condition with TMPD based on these results will be discussed.This study was financially supported in part by CREST program by Japan Science and Technology Agency (JST).M. Bessho, Y. Fukunaka, H. Kusuda, T. Nishiyama, Energy & Fuels, 23, 4160(2009).N. Matsuo, Y. Matsui, Y. Fukunaka, T. Homma, ECS Trans. 50, 103(2013).N. Matsuo, Y. Matsui, T. Ishihara, Y. Fukunaka, T. Homma, 224th ECS Meeting, #2261 (2013).

Ethanol Dehydration to Ethylene in a Stratified Autothermal Millisecond Reactor

The concurrent decomposition and deoxygenation of ethanol was accomplished in a stratified reactor with 50-80 ms contact times. The stratified reactor comprised an upstream oxidation zone that contained Pt-coated Al(2)O(3) beads and a downstream dehydration zone consisting of H-ZSM-5 zeolite films deposited on Al(2)O(3) monoliths. Ethanol conversion, product selectivity, and reactor temperature profiles were measured for a range of fuel:oxygen ratios for two autothermal reactor configurations using two different sacrificial fuel mixtures: a parallel hydrogen-ethanol feed system and a series methane-ethanol feed system. Increasing the amount of oxygen relative to the fuel resulted in a monotonic increase in ethanol conversion in both reaction zones. The majority of the converted carbon was in the form of ethylene, where the ethanol carbon-carbon bonds stayed intact while the oxygen was removed. Over 90% yield of ethylene was achieved by using methane as a sacrificial fuel. These results demonstrate that noble metals can be successfully paired with zeolites to create a stratified autothermal reactor capable of removing oxygen from biomass model compounds in a compact, continuous flow system that can be configured to have multiple feed inputs, depending on process restrictions.

Catalytic partial oxidation of ethane to ethylene and syngas over Rh and Pt coated monoliths: Spatial profiles of temperature and composition

The catalytic partial oxidation of C 2H 6 over Pt and Rh coated monolithic supports (4.7 wt% M/α-Al 2O 3 45 PPI) was investigated with a capillary sampling technique for a range of C 2H 6/air ratios at constant inlet flow (∼8 ms contact time), with and without H 2 addition. Effluent data clearly indicate the differences in product distribution between catalysts and equilibrium. Rh effectively converts the reactant mixtures to syngas with ∼80% selectivity, whereas Pt produces C 2H 4 with ∼55% C-atom selectivity, while neither produces thermodynamically favored C. Spatially resolved measurements provide direct evidence of the multi-zone nature of the reactors. With Rh, complete conversion of O 2 occurs to produce mostly CO, H 2 and H 2O within the first 3 mm of catalyst, followed by a reforming zone to produce additional syngas. Pt consumes O 2 more slowly, which results in a steady increase in temperature along the reactor. Ethylene formation correlates to reactor temperatures >750 °C, regardless of C/O, in line with the onset of homogeneous reactions. Hydrogen addition tests (C 2H 6/O 2/H 2=2/1/2) clearly exhibit preferential oxidation of H 2 with O 2 over Pt, which shifts the maximum in temperature upstream while preserving a portion of the C 2H 6 for C 2H 4 production. H 2 addition modifies the concentration and temperature profiles minimally on Rh. The main differences between catalysts are the high reforming and O 2 consumption activity with Rh compared to Pt, which are likely responsible for differences in C 2H 4 yields.

From seconds to milliseconds to microseconds through tailored microchannel reactor design of a steam methane reformer

Conventional steam methane reformers operate with contact times exceeding 1 s. Recent literature has suggested that microchannel reactors may reduce the contact time to a few or tens of milliseconds. This report shows both experimentally and theoretically that the 1 ms barrier for steam methane reforming (SMR) has been broken with the aid of a tailored microchannel reactor design, where the catalyst is coated on a relatively thick porous engineered structure. While 1 ms contact time reactions have been approached by the partial oxidation of methane to synthesis gas, steam reforming has historically been considered a slow reaction. Methane steam reforming experiments at contact times of 90–900 μs were conducted. Greater than 98% approach to equilibrium methane conversion was demonstrated at 900 μs, and 19.7% approach to equilibrium was measured at 90 μs. Both cases were supported with good model agreement. Further, the model explores microchannel reactor structures that minimize heat and mass transfer and results suggest that at a contact time of 500 μs a high approach to equilibrium is possible.

Increasing olefins by H 2 and CH 4 addition to the catalytic partial oxidation of n-octane

The catalytic partial oxidation (CPO) of n-octane over Rh and Pt-coated α-Al 2O 3 catalysts at approximately 5 ms contact times is examined with H 2 and CH 4 addition to the reactor feed. The aim is to preferentially oxidize H 2 or CH 4 and allow more octane to react in the gas phase to form high value chemicals such as ethylene and other olefins. The addition of H 2 increases olefin selectivities on both 80 and 45 ppi foams coated with Rh or Pt, and the highest increase in olefin selectivity occurs at H 2/O 2 = 3/1 on Pt-coated 45 ppi catalysts. In this case, the selectivity to ethylene increases from a maximum of 38 to 51%, and total olefin selectivity increases from 75 to 83% without a decrease in octane conversion. The effect of adding CH 4 is heavily dependent on the catalyst metal and average pore size of the support structure. On Pt catalysts and 45 ppi Rh-coated catalysts, the addition of methane can increase olefin selectivities by several percent. However, on 80 ppi Rh-coated foams, adding methane actually suppresses the formation of olefins and increases selectivity to H 2 and CO.

Temperature dependence of barrier heights of Au/n-type GaAs Schottky diodes

The forward bias current–voltage (I–V) and reverse bias capacitance–voltage (C–V) characteristics of the Au/n-GaAs Schottky diodes (SDs) are investigated over a wide temperature range of 80–400K. According to thermionic emission theory (TE) mechanism, the zero bias barrier height ΦI−V calculated from forward bias I–V characteristics was found to increase with increasing temperature. Such behavior is an obvious disagreement with negative temperature coefficient of the Schottky barrier height. However, the barrier height determined from the C2−V characteristics at high frequency decreased linearly with increasing temperature. This discrepancy between ΦI−V and Φb(C−V) can be explained by the existence of excess capacitance at MS contacts due to interfacial insulator layer or interface states. The existence of barrier height inhomogeneity offers other explanation. Therefore barrier height ΦI−V has been corrected by taking into account quality factors (n) and the electron tunneling factor (αχ1/2δ) in the expression of reverse saturation current (I0) of the diodes. Thus, corrected effective barrier height Φbef(I−V) is in good agreement with the reported negative temperature coefficient of the barrier height of Au/n-GaAs Schottky diodes.

Properties of polyunsaturated phosphatidylcholine membranes in the presence and absence of cholesterol.

Mixtures of cholesterol with phosphatidylcholine species containing the polyunsaturated acyl chains arachidonoyl or docosahexaenoyl were studied by (13)C magic angle spinning (MAS) NMR using both cross-polarization and direct polarization, by (31)P NMR and by differential scanning calorimetry. Several unique features of these systems were observed. The separation of cholesterol in crystalline form occurred at much lower molar fractions than with other forms of phosphatidylcholine. The crystals that were formed were sensitive to the history of the sample. At cholesterol molar fractions below 0.5, they dissolved into the membrane by sequential heating and cooling scans. With higher molar fractions of cholesterol, larger amounts of anhydrous crystals were formed after the first heating. This was accompanied by the formation of non-lamellar phases. The cholesterol crystals that were formed generally were not observed by direct polarization (13)C MAS NMR, even with delay times of 100 s. This suggests that the cholesterol crystals are in a more rigid state in mixtures with these lipids. This is in contrast with the terminal methyl group of the acyl chains that is too mobile to allow cross-polarization using 1 ms contact times.

Impact of Remote Protonation on 13C CPMAS NMR Quantitation of Charred and Uncharred Wood

The impact of inefficient cross polarization (long T CH values), caused by long 13C– 1H internuclear distances, on 13C CPMAS NMR spectra of charred and uncharred woods is determined by simultaneously fitting data from complementary variable spin lock and variable contact time experiments. As expected, the impact is minimal for uncharred woods, but is very significant for the charred woods. Quantification of the decrease in CPMAS signal intensity caused by both inefficient cross polarization and rapid T 1 ρH relaxation is achieved using an advanced spin counting methodology, for which the term “spin accounting” is proposed. 13C CPMAS NMR observabilities determined using the spin accounting methodology were close to 100% for the uncharred samples, and 69–82% for the charred samples. This represents a large improvement on the 30–40% observabilities determined using other spin counting techniques. Furthermore, it is shown that remote protonation and rapid T 1 ρH relaxation are roughly equally responsible for the low signal intensity of standard (1 ms contact time) 13C CPMAS spectra of charcoal.

Electrical properties of sulfur-passivated III–V compound devices

The results of numerous studies since 1987 show that sulfur passivation improves the electrical parameters of III–V compound devices. In this article, we examine the electrical parameters of metal–semiconductor contacts (MS), MS contacts with thin interfacial layer (MIS), and metal-oxide–semiconductor structures (MOS).