Substrate Absorption Research Articles

A surface photovoltage spectroscopy study of GaAs∕AlAs complicated nanostructures with graded interfaces

We present a surface photovoltage (SPV) spectroscopy study of the optical properties and the bound states of graded interface AlAs∕GaAs superlattices (SLs) containing two GaAs embedded quantum wells (EQWs) with different widths. SPV spectra are measured in the metal-insulator-semiconductor operation mode under super-band-gap optical excitation at room temperature. In spite of the relatively large absorption of the GaAs substrate, the SPV spectra exhibit clearly resolved features superimposed on the substrate smooth background. These features have been identified as free exciton transitions in the EQWs and in the SL. This interpretation is based on a detailed comparison of the SPV results with those of electronic structure calculations and photoluminescence spectral measurements. The calculations are performed in frames of the envelope function approximation, employing a model structure very similar to the real one and taking into account the interface grading. The mechanisms of the SPV signal generation have been discussed. An experimental confirmation is given to the theoretical model developed by others, about the SPV behavior in quantum wells. Our study demonstrates further the SPV spectroscopy powerful potentialities for nondestructive contactless characterization at room temperature of complicated nanostructures with graded interfaces.

Improvement of the Oral Drug Absorption of Topotecan through the Inhibition of Intestinal Xenobiotic Efflux Transporter, Breast Cancer Resistance Protein, by Excipients

Recently, breast cancer resistance protein (BCRP/ABCG2) has been shown to limit the oral absorption of its substrates in the intestine. The purpose of this study was to examine whether excipients can be used as inhibitors of BCRP, to improve the oral drug absorption of BCRP substrates. In wild-type mice, Pluronic P85 and Tween 20, given orally 15 min before topotecan administration, increased the area under the plasma concentration-time curve (AUC) of topotecan after oral administration (2.0- and 1.8-fold, respectively). In contrast, Pluronic P85 and Tween 20 were less effective (no significant difference) on the AUC of topotecan after oral administration in Bcrp (-/-) mice (1.2- and 1.2-fold, respectively). Pluronic P85 and Tween 20 given orally did not affect significantly the AUC of topotecan after intravenous administration in wild-type and Bcrp (-/-) mice. Moreover, we determined the mucosal-to-serosal absorptive transport of topotecan using everted mouse ileum. Pluronic P85 and Tween 20 significantly increased the intestinal absorption rate of topotecan in everted sacs from wild-type mice whereas, in everted sacs from Bcrp (-/-) mice, the absorption rate was 2.1-fold greater than that in wild-type mice, and these excipients were not significantly effective. There was no significant difference in the intestinal P-glycoprotein (P-gp) expression and serosal-to-mucosal secretory transport of rhodamine 123, a typical P-gp substrate. Taken together, these results suggest that Pluronic P85 and Tween 20 can improve the oral bioavailability of BCRP substrates by inhibiting BCRP function in the small intestine.

Single oscillator energy and dispersion energy of uniform thin chalcogenide films from Cu–As–S–Se system

This paper presents some of the results obtained by using the modified envelope method, which takes substrate absorption into account. Samples investigated in this paper are the series of amorphous thin chalcogenide uniform films from system Cux[As2(S0.5Se0.5)3]100−x. Thin films were deposited under vacuum on glass substrates by thermal evaporation technique, from previously synthesized bulk samples. The dispersion of the refractive index is discussed in terms of the single oscillator model proposed by Wemple and DiDomenico. By using this model, i.e. by plotting (n2−1)−1 against (ℏω)2 and fitting a straight line, oscillator parameters, E0 – the single oscillator energy and Ed – the dispersion energy, were directly determined.

Dynamic simulation of benzene vapor treatment by a two-phase partitioning bioscrubber: Part I: Model development, parameter estimation, and parametric sensitivity

A dynamic, mechanistic model has been developed to predict the performance of a liquid–liquid, two-phase partitioning bioscrubber (TPPB) for removal, and subsequent biodegradation, of toxic volatile organic compounds (VOCs) from industrial waste gases under various conditions of practical relevance. TPPBs, which contain an immiscible and biocompatible organic liquid phase, allow enhanced biodegradation rates to be maintained by partitioning inhibitory substrates away from microorganisms. The system being considered involves the treatment of benzene vapors by Achromobacter xylosoxidans Y234 using n-hexadecane as the organic phase. The model incorporates the following dynamic elements: volatile substrate and oxygen absorption by both liquid phases, partitioning of dissolved substrate and oxygen between liquid phases, and microbial consumption of dissolved substrate and oxygen in the aqueous phase for both growth and maintenance. Part I focuses on the development of the model equations and estimation of relevant parameters. Using parametric sensitivity analysis, the relative influences of the parameters are identified under transient and steady state conditions. Both the organic phase volume fraction and its properties are predicted to have a significant influence on performance. Biocatalysts capable of maintaining high biodegradation rates under dilute substrate concentrations are predicted to be superior for use in TPPBs.

Cu(II) Complexes Conjugated with 9-Aminoacridine Intercalator: Their Binding Modes to DNA and Activities as Chemical Nuclease

New mono- and bis-Cu(II)-triazacyclononane(tacn) complex that conjugated with 9-aminoacridine were synthesized, and their binding modes and DNA cleavage activity were investigated in this study. When the classic intercalator, 9-aminoacridine, was conjugated to mono- and bis-Cu(II)-tacn complexes, a significant red-shift and hypochromism in absorption spectrum was apparent in the acridine absorption region upon binding to DNA. Furthermore, the magnitude of the negative reduced linear dichroism signal in the substrate absorption region appeared to be larger than that in the DNA absorption region. These spectral observations indicated that the acridine moiety intercalated when the Cu(II)-tacn complex was conjugated. In contrast, from a close analysis of the circular and linear dichroism spectrum, the aminoacridine-free bis-Cu(II)-tacn complex was concluded to bind at the phosphate groups of DNA. The 9-aminoacridine-free-bis-Cu(II)-tacn complex produces the nicked and linear DNA. On the other hand, 9-aminoacridine conjugated mono-and bis-Cu(II)-tacn complexes showed unspecific binding with negligible DNA cleavage.

Closed equation for the normal incidence reflectance of thin films on absorbing substrates

The optical constants of thin films can be obtained from inversion of spectrophotometric measurements by using minimization gradient methods. The computational approach of these minimization methods requires closed compact formulas for reflectance and/or transmittance. For normal incidence closed compact formulations for the direct transmittance, both for thin films on transparent or absorbing substrates, and for the reflectance of thin films on transparent substrates, are available in the literature. We report here a closed compact formula to evaluate reflectance spectra of thin films on absorbing substrates, and it is shown that for vanishing substrate absorption this new, to the best of our knowledge, approach gives the same results obtained from the formulation corresponding to thin films supported by transparent substrates.

Are Plasma Citrulline and Glutamine Biomarkers of Intestinal Absorptive Function in Patients With Short Bowel Syndrome?

Sensitive biomarkers for intestinal absorptive function would be clinically useful in short bowel syndrome (SBS). Citrulline (Cit) is a product of the metabolism of glutamine (Gln) and derived amino acids by enterocytes. Cit is produced almost exclusively by the gut, which is also a major site of Gln metabolism. The goals of this study were to examine whether plasma Cit and Gln concentrations are biomarkers of residual small intestinal length and nutrient absorptive functions in adult SBS patients followed prospectively. We studied 24 stable adults with severe SBS receiving chronic parenteral nutrition (PN) in a double-blind, randomized trial of individualized dietary modification +/- recombinant human growth hormone (GH). During a baseline week, intestinal absorption studies (% absorption of fluid, kcal, nitrogen, fat, carbohydrate, sodium, phosphorus, and magnesium) were performed and concomitant plasma Cit and Gln concentrations determined. Individualized dietary modification and treatment with subcutaneous injection of placebo (n = 9) or GH (0.1 mg/kg daily x 21 days, then 3 times/week; n = 15) were then begun. PN weaning was initiated after week 4 and continued as tolerated for 24 weeks. Repeat plasma amino acid determination and nutrient absorption studies were performed at weeks 4 and 12. Residual small bowel length at baseline was positively correlated with baseline plasma Cit (r = 0.467; p = .028). However, no significant correlations between absolute Cit or Gln concentrations and the percent absorption of nutrient substrates at any time point were observed. Similarly, no correlation between the change in Cit or GLN concentration and the change in % nutrient absorption was observed (baseline vs weeks 4 and 12, respectively). By weeks 12 and 24, 7 and 13 subjects were weaned completely from PN, respectively. However, baseline plasma Cit or Gln did not predict PN weaning at these time points. We concluded that plasma Cit (but not Gln) concentrations appeared to be an indicator of small intestinal length in adult SBS. However, neither plasma Cit nor Gln was a biomarker for intestinal absorptive function in this cohort of patients with SBS.

LXR Alpha Transactivates Mouse Organic Solute Transporter Alpha and Beta via IR-1 Elements Shared with FXR

Recently identified organic solute transporter (Ost) alpha and beta are located on the basolateral membrane of enterocytes and may be responsible for the intestinal absorption of many substrates including bile acids. In the present study, the mechanism governing the transcriptional regulation of their expression was investigated. To clarify the transcriptional regulation of Osts, reporter gene assays were performed using mouse Ostalpha/beta promoter-luciferase reporter constructs. Co-transfection of the constructs with farnesoid X receptor (FXR) and retinoid X receptor alpha (RXRalpha) or liver X receptor alpha (LXRalpha) and RXRalpha into Caco-2 cells induced the transcriptional activities of both Ost alpha and beta and further increases were observed following treatment with each agonist. Sequence analyses indicated the presence of IR-1 regions in Ostalpha and Ostbeta promoters, which was confirmed by the finding that the deletion of IR-1 sequences abolished the response to FXR and LXRalpha. Furthermore, mutations in IR-1 reduced the FXR- and LXRalpha-dependent transactivation of Ostalpha/beta. Together with the detection of direct binding of FXR/RXRalpha and LXRalpha/RXRalpha to the IR-1 elements, the presence of functional FXRE/LXRE was revealed in the promoter region of both Ostalpha and Ostbeta. In addition, the stimulatory effect of FXR/RXRalpha and LXRalpha/RXRalpha on Ostalpha, but not on Ostbeta, was further enhanced by HNF-4alpha. It was concluded that LXRalpha/RXRalpha transcriptionally regulate mouse Ostalpha/beta via IR-1 elements shared with FXR/RXRalpha. Exposure to FXR/LXRalpha modulators may affect the disposition of Ostalpha/beta substrates.

Organic Solar Cells Using Transparent SnO2–F Anodes

Organic solar cells have attracted attention as a means to achieve low-cost solar-energy conversion owing to their ease of manufacture and compatibility with flexible substrates. Conventional organic molecular photovoltaic (PV) devices and light-emitting diodes (OLEDs) are typically grown on transparent indium tin oxide (ITO) anodes that are also widely used for flat-panel displays (FPDs). The scarcity of In, along with the rapid expansion of FPD production, has resulted in a soaring price of ITO-coated glass substrates, with the current price up to ten times greater than in 2003. Alternative transparent conducting oxides such as doped SnO2 or ZnO have been used as electrodes in dye-sensitized, CdTe, microcrystalline Si, and amorphous Si PV devices. Organic small-molecule or polymeric devices, with active layers typically < 1000 A thick, can readily be shorted owing to the pronounced surface-roughness characteristic of these oxide variants. Nevertheless, the cost of F-doped SnO2 (SnO2–F)coated glass is less than one third that of ITO-coated glass. While there have been reports of using SnO2–F as the transparent anode for polymeric OLEDs and solar cells, to our knowledge there has yet to be a demonstration of an organic heterojunction (HJ) PV cell based on SnO2–F anodes with an efficiency greater than 0.1 %. Here, we report on copper phthalocyanine (CuPc)/C60 HJ PV cells on SnO2–F anodes [8] with a power conversion efficiency of 2.5 % at 1 sun simulated AM 1.5 G (AM: air mass; G: Global) illumination. The organic layers were grown by organic vapor-phase deposition (OVPD) that enabled complete coverage of the rough oxide surface, effectively preventing shorts between opposing cathode and anode contacts. In addition, we show that by controlling the organic-film morphology, we can grow the donor–acceptor (D–A) interface into a three-dimensional interdigitated bulk HJ (BHJ) structure, resulting in power-conversion efficiencies nearly twice those of analogous devices with a planar heterointerface. As shown in Figure 1a, the 750 nm thick SnO2–F-coated glass substrates have 70–80 % transmittance in the visible range, or approximately 10 % less than that for glass with 150 nm thick ITO coatings. The absorption of both substrates has a high-energy cutoff at wavelengths less than 350 nm, implying a match of the transparency window to that of the solar radiation spectrum. The sheet resistance of SnO2–F-coated glass is less than 12 X/sq., lower than that of ITO-coated glass (15 X/sq.) The high transparency and small resistance C O M M U N IC A TI O N S

Induction of Rat Intestinal P-glycoprotein by Spironolactone and Its Effect on Absorption of Orally Administered Digoxin

The effect of the diuretic spironolactone (SL) on expression and function of intestinal P-glycoprotein (P-gp), as well as its impact on intestinal absorption of digoxin, was explored. Rats were treated with daily doses of 200 micromol/kg b.wt. of SL intraperitoneally for 3 consecutive days. The small intestine was divided into four equal segments of approximately 25 cm, with segment I being the most proximal. Brush-border membranes were isolated and used in analysis of P-gp expression by Western blot analysis. P-gp content increased in the SL group by 526, 292, 210, and 622% over controls for segments I, II, III, and IV, respectively. Up-regulation of apical P-gp was confirmed by immunofluorescence microscopy. P-gp transport activity was explored in intestinal sacs prepared from segment IV using two different model substrates. Serosal to mucosal transport (efflux) of rhodamine 123 was 140% higher, and mucosal to serosal transport (absorption) of digoxin was 40% lower in the SL group, both indicating increased P-gp function. In vivo experiments showed that intestinal absorption of a single dose of digoxin administered p.o. was attenuated by SL pretreatment. Thus, concentration of digoxin in portal and peripheral blood was lower in SL versus control groups, as well as its accumulation in kidney and liver. Urinary excretion of digoxin was significantly decreased in the SL group, probably reflecting decreased systemic availability of digoxin for subsequent urinary elimination. We conclude that SL induces P-gp expression with potential impact on intestinal absorption of substrates with therapeutic application.

Nitride light-emitting diodes grown on Si (111) using a TiN template

Nitride light-emitting diodes (LEDs) are grown on a Si (111) substrate with a TiN template. Transmission electron microscopy and x-ray diffraction indicate that the epitaxial relation follows Si(1,1,1)‖TiN(1,1,1)‖AlN(0,0,1), Si[1,1,0]‖TiN[1,1,0], and Si[0,0,1]‖TiN[0,0,1]. The reflectance measurement and simulation results indicate that the TiN can be adopted as a reflector to mitigate the substrate absorption problem, thus increasing the extraction efficiency of nitride LEDs grown on Si.

Gefitinib Modulates the Function of Multiple ATP-Binding Cassette Transporters In vivo

The 4-anilinoquinazoline (4-AQ) derivative gefitinib (Iressa) is an oral epidermal growth factor receptor tyrosine kinase inhibitor. Oral administration of 4-AQ molecules, such as gefitinib, inhibits ATP-binding cassette (ABC) transporter-mediated drug efflux and strongly increases the apparent bioavailability of coadministered drug molecules that are transporter substrates. Based on in vitro studies investigating 4-AQ interactions with several transporters, these effects have primarily been attributed to the inhibition of breast cancer resistance protein (BCRP; ABCG2). Although 4-AQ shows in vitro inhibition of P-glycoprotein [multidrug resistance protein (MDR1); ABCB1], the in vivo effect on this and other transporters is not known. In our studies, pretreatment of Abcg2(-/-) and Mdr1(a/b)(-/-) mice with gefitinib increased oral absorption and decreased systemic clearance of topotecan, a model substrate, indicating that additional transporters were inhibited. These results were extended to human orthologues using engineered cell lines to show that gefitinib inhibited the efflux of BCRP and MDR1 substrates and restored vincristine sensitivity in MDR1-expressing cells. Although gefitinib inhibited BCRP more potently than MDR1 (10-fold), the inhibition of both transporters occurred at clinically relevant concentrations (e.g., 1-5 micromol/L). These studies illustrate the broad implications for the therapeutic combination of gefitinib or other 4-AQ molecules with agents that are BCRP and MDR1 substrates. 4-AQ molecules may offer a means to increase the low and variable oral drug absorption of transporter substrates while decreasing interpatient variability and reversing tumor drug resistance.

Effects of controlled-release on the pharmacokinetics and absorption characteristics of a compound undergoing intestinal efflux in humans

ObjectiveThe number of active pharmaceutical ingredients (API) undergoing inhibitable and saturable intestinal efflux is considerable. As a consequence, absorption and bioavailability may depend on the intestinal concentration profile of the drug and may vary as a function of dose and release rate of the drug from the dosage form. The impact of controlled versus immediate-release on the absorption of P-glycoprotein substrates is currently unknown. Thus, the main focus of the present study was a comparison of the pharmacokinetics of the P-gp model substrate talinolol following administration of immediate-release (IR) and controlled-release (CR) tablets to healthy human volunteers with a particular focus on the absorption characteristics of the active pharmaceutical ingredients. MethodsTalinolol immediate-release (Cordanum®, 100mg), one controlled-release (100mg) and two controlled-release tablets (200mg) were administered as single doses to fasting healthy volunteers in a crossover design with a 1 week washout period between treatments. Sufficient blood and urine samples were drawn and analysed using a specific HPLC method with UV detection to describe the resulting plasma and urinary excretion versus time profiles. ResultsThe bioavailability of talinolol in term of AUC0→∞ for IR talinolol was approximately twice as high as compared to the administration of the same dose in a controlled-release dosage form. After administration of talinolol IR tablets, the drug was rapidly absorbed and reached maximum concentrations Cmax of 204.5ng/ml±121.8 (means±S.D.) 2h after dosing. The terminal half-life of the drug averaged 19.8h following IR administration in comparison to 32h under CR dosing conditions. Following administration of the IR dosage form, significant secondary peaks were observed in one healthy subject. Secondary peaks were not clearly apparent in the CR plasma profiles. ConclusionThe present study demonstrates a considerable loss of bioavailability of drugs that are substrates of intestinal secretory transporters upon their administration in controlled-release dosage forms.

Polarization of near-forward-scattered light from particulate substrates illuminated at near-grazing angles

Laboratory photopolarimetric measurements of light scattered by substrates consisting of semitransparent particles with sizes significantly larger than the wavelength show a polarization shoulder at small scattering angles near θ = 10 – 30 ° in addition to the Brewster maximum positioned near θ = 50 ° . With ray-tracing simulations, we find that the shoulder appears to be related to light passing through particles in the upper layers of the substrates. We study the dependence on particle absorption and packing density of particulate substrates. The studies show that the shoulder weakens with increased absorption and packing density.

Evaluation of methods for estimating starch digestibility and digestion kinetics in ruminants

The objective of the paper is to review literature concerning the methods used to estimate starch digestibility in different segments of the digestive tract of ruminants and the kinetics of starch digestion. Starch digestibility and site of starch digestion have a profound effect on the amount and profile of substrates absorbed from the digestive tract. The prediction of starch digestibility in the rumen is laborious and also technically difficult because of unrepresentative sampling of digesta from duodenal cannulae. The double-marker technique does not solve the problems related to unrepresentative digesta sampling because any of the particulate markers are not intimately associated with particles rich in starch. Furthermore, physical separation of particles rich in starch and fibre, which is a requisite in applying multiple marker techniques, would be difficult. However, despite problems in the determination of starch flow, the double-marker technique is likely to improve the accuracy of the flow measurements of other components. Mechanistic dynamic models describing digestion and absorption of substrates require reliable estimates of the digestion kinetics of feed components. The in situ technique has been extensively evaluated and used in estimating the digestion rate of starch. Initial particle loss, often described as soluble starch, is the major problem of the technique. Various assumptions have been used for the behaviour of this fraction in the kinetic models. It is also possible that the secondary particle loss during the incubation would overestimate the rate of digestion. Both the patterns of duodenal marker excretion curves and duodenal starch flow strongly suggest that the passage of particles rich in starch do not follow the first-order passage kinetics. This means that the models used to estimate ruminal starch digestibility from the kinetic parameters are incomplete. The published data suggest that the in situ technique underestimates ruminal starch digestibility for slowly degradable starch sources such as maize and overestimates it for rapidly degradable starch sources such as barley. An advantage of the in vitro methods is that the estimates of starch disappearance are not biased by particle loss. In vitro gas production technique may also be used for estimation of the rate of starch digestion for cereal grains by applying the curve subtraction method; i.e. gas production from the cell wall fraction is subtracted from the total gas production curve. Starch represents the major proportion of cell solubles in cereal grains and even a greater proportion of gas production potential. A requisite of the in vitro techniques in estimating the rate of starch digestion is that the system itself is not limiting.

Influence of Dietary Phytate and Exogenous Phytase on Amino Acid Digestibility in Poultry: A Review

The effects of dietary phytate and microbial phytase supplementation on amino acid availability in poultry diets are of considerable practical importance. Published data on the influence of exogenous phytase supplementation on the ileal digestibility of amino acids in poultry are reviewed in this paper, with emphasis on the factors causing variability in amino acid responses. Several modes of action have been proposed by researchers to explain the influence of phytate on protein digestion, but it is hypothesised that the de novo formation of binary protein-phytate complexes in the gut under acidic conditions in the proventriculus may be the main mechanism whereby phytate depresses the digestibility of dietary amino acids as bound protein is refractory to pepsin digestion. It is also likely that phytate promotes the flow of endogenous amino acids. The review demonstrates that the choice of inert marker used in the digestibility assays is a major factor responsible for the variable phytase responses reported in the literature. The important diet-related causes for the variability include differences among ingredients, dietary levels of Ca and nonphytate P and dietary electrolyte balance, and clearly amino acid responses with added phytase may be enhanced by considering these issues in poultry feed formulations. Phytase feed enzymes, however, do not degrade the majority of dietary phytate in poultry and consequently the negative influence of phytate on protein digestibility is not completely removed by phytase supplementation. It is proposed that the experimental use of ‘dephytinised’ feed ingredients may be useful to define the actual extent to which amino acid digestibility is compromised by dietary phytate. The efficacy of current phytase feed enzymes may be further enhanced by the simultaneous use of other exogenous enzymes, which complement their activity, increase substrate access and/or absorption of liberated nutrients.

Extracellular Cleavage of E-Cadherin by Leukocyte Elastase During Acute Experimental Pancreatitis in Rats

Cadherins play an important role in cell-cell contact formation at adherens junctions. During the course of acute pancreatitis, adherens junctions are known to dissociate-a requirement for the interstitial accumulation of fluid and inflammatory cells-but the underlying mechanism is unknown. Acute pancreatitis was induced in rats by supramaximal cerulein infusion. The pancreas and lungs were either homogenized for protein analysis or fixed for morphology. Protein sequencing was used to identify proteolytic cleavage sites and freshly prepared acini for ex vivo studies with recombinant proteases. Results were confirmed in vivo by treating experimental pancreatitis animals with specific protease inhibitors. A 15-kilodalton smaller variant of E-cadherin was detected in the pancreas within 60 minutes of pancreatitis, was found to be the product of E-cadherin cleavage at amino acid 394 in the extracellular domain that controls cell-contact formation, and was consistent with E-cadherin cleavage by leukocyte elastase. Employing cell culture and ex vivo acini leukocyte elastase was confirmed to cleave E-cadherin at the identified position, followed by dissociation of cell contacts and the internalization of cleaved E-cadherin to the cytosol. Inhibition of leukocyte elastase in vivo prevented E-cadherin cleavage during pancreatitis and reduced leukocyte transmigration into the pancreas. These data provide evidence that polymorphonuclear leukocyte elastase is involved in, and required for, the dissociation of cell-cell contacts at adherens junctions, the extracellular cleavage of E-cadherin, and, ultimately, the transmigration of leukocytes into the epithelial tissue during the initial phase of experimental pancreatitis.

Surface characterization of thin titania films prepared at low temperatures

Nanostructured thin films of titanium dioxide were produced on cotton, glass and silicon substrates from alkoxide solutions at low temperatures. The microstructure and elemental composition of these films were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX), respectively. The crystallinity of the films was studied by transmission electron microscopy (TEM) and Raman spectroscopy. The UV absorption of titania-coated cotton substrates was also studied. The leaching stability of the titania films coated on cotton after washing reveals a high level of adhesion which might be attributable to a dehydration reaction between titania and the cellulosic hydroxyl groups of cotton.

Thin-film InGaN multiple-quantum-well light-emitting diodes transferred from Si (111) substrate onto copper carrier by selective lift-off

Crack-free thin-film InGaN multiple-quantum-well light-emitting diodes (LEDs) were successfully transferred from the original Si (111) substrate onto copper carrier by means of metal-to-metal bonding and the selective lift-off (SLO) technique using wet-chemical etching. Crystalline quality was investigated by x-ray diffraction and photoluminescence measurements. No deterioration was found in the thin film after substrate removal due to the fact that the SLO technique minimizes the residual strain relaxation. Substrate removal eliminates not only the substrate absorption but also the large band offset between the AlN buffer layer and substrate. In conjunction with inserting a metal reflector between the LED structure and the copper carrier, the performances of the LED fabricated on the substrate removal region were significantly improved. The operating voltage at 20mA and the series resistance was 3.6V and 27Ω, respectively. The optical power revealed an increase of 49% compared to the LED before substrate removal.

In situ IR reflectance absorption spectroscopy studies of the effect of Nafion on CO adsorption and electrooxidation at Pt nanoparticles

We have synthesized colloidal Pt nanoparticles with a mean particle size of 2.6±0.4 nm by reducing PtCl2 dissolved in N,N-dimethylacetamide with t-BuMe2SiH. The latter compound acted both as a reducing agent and a stabilizer of the Pt nanoparticles. Pt nanoparticles were deposited onto the Au substrate and IR reflectance absorption spectroscopy (IRRAS) was applied to investigate CO adsorption and oxidation at the surface of the catalyst. The reactivity of the catalyst covered with Nafion was compared with the reactivity of the catalyst without Nafion. In addition, the reactivity of the colloidal Pt was compared with the reactivity of bulk polycrystalline Pt. We found that CO oxidation proceeds at lower over-potentials at nanoparticles than at polycrystalline Pt. The IRRAS data indicate that the difference in the reactivity may be explained by a different mechanism of the oxidation reaction; Langmuir–Hinshelwood at Pt nanoparticles and island formation and growth at polycrystalline Pt. We have also observed that a film of Nafion slows down the CO oxidation reaction. The IRRAS spectra for CO adsorbed at Pt nanoparticles covered by Nafion were significantly different from the spectra recorded for the nanoparticles in the absence of Nafion. The spectroscopic features suggest that in the presence of Nafion the nanoparticles experience regions of lower and higher proton concentration.