Surface Energy Levels Research Articles

Experimental investigation of plasma-immersion ion implantation treatment for biocompatible polyurethane implants production

Modification of the surface layer of polyurethane with plasma-immersion ion implantation (PIII) and studying its physical and chemical changes have been discussed in this paper. The goal of the research was to obtain carbonized layer allowing creating biocompatible polyurethane implants. The experiments of PIII treatment in various modes were performed. The investigation of the modified surface characteristics was carried out by observing the kinetics of free surface energy for two weeks after treatment. The regularities between treatment time and the level of free surface energy were detected. The explanation of high energy level was given through the appearance of free radicals in the surface layer of material. The confirmation of the chemical activation of the polyurethane surface after PIII treatment was obtained.

Reversible superhydrophilicity and superhydrophobicity on a lotus-leaf pattern.

A facile approach of fabricating a temperature-responsive coating capable of switching reversibly from being superhydrophobic to superhydrophilic is presented. The approach combines micromolding, layer-by-layer assembly of the polymer macroinitiators, and surface-initiated polymerization. Changing between superhydrophobicity and superhydrophilicity depends heavily on the surface roughness and the switching of the surface energy levels. In this study, surface roughness was introduced by replicating the surface morphology of a lotus leaf. The switching of surface energy levels was made possible by grafting a temperature-responsive polymer brush. Wetting studies reveal that the reported approach not only replicates nature but also improves its property by making it responsive to stimulus.

Orientation effect on GaAs/ultrathin polymer/PEDOT:PSS hybrid solar cell

The surface orientation of inorganic semiconductors affects the density of surface states, energy levels, and other intrinsic properties of the semiconductor, all of which would have an impact on the performance of related polymer/inorganic hybrid solar cells. With a set of conjugated polymers having different energy levels and band gaps (P3HT, PNDT-DTffBT, and PBnDT-DTffBT), we show that the photovoltaic behavior of GaAs/ultrathin polymer layer/PEDOT:PSS planar solar cells is noticeably affected by the surface orientation of n-GaAs, (111)B or (100). In all of these hybrid solar cells, a Schottky barrier is formed between the GaAs and the anode, with these ultrathin polymer layers serving as the electron blocking layer (EBL) and the hole transport layer (HTL). The lower density of surface states of GaAs(111)B helps reduce the surface recombination and results in a higher short circuit current for (111)B based hybrid solar cells than for (100) based ones. However, the higher valence band maximum (VBM) of (111)B compared to that of (100) could lead to increased recombination from blocked hole transport, if the highest occupied molecular orbital (HOMO) level of the HTL polymer is lower than the VBM of GaAs. Considering all these effects, P3HT stands out as the best polymer to pair with GaAs in the studied set, with an efficiency of 4.2% achieved for the device based on P3HT/GaAs(111)B.

Giant diamagnetism of gold nanorods

The presence of giant diamagnetism in Au nanorods, NRs, is shown to be a possible consequence of field induced currents in the surface electrons. The distance, Δ, between quantum surface energy levels has been calculated as a function of the NRs radius. Note that those electrons occupying states for which Δ > kBT are steadily orbiting with constant orbital moment. The diamagnetic response induced when a field is turned on remains constant during the time the field is acting. As the NRs radius increases, Δ decreases and accordingly the electron fraction available to generate constant currents decreases, consequently the surface diamagnetic susceptibility decreases towards its bulk value. The surface electronic motion induced by the axial applied field on electrons confined into a cylindrical surface accounts with extremely good quantitative agreement for the giant diamagnetism recently measured and reported.

Universal and Versatile MoO3-Based Hole Transport Layers for Efficient and Stable Polymer Solar Cells

Two solution-processed and highly dispersed MoO3 called d-(MoO3)120 and d-(MoO3)15 with sizes of 120 nm and extremely smaller 15 nm, respectively, are applied into polymer solar cells, and the evaporated MoO3 as hole transport layers (HTLs) in devices is also compared. It is the first time it has been found that the different size of MoO3 can induce the quite different morphologies of the HTLs and their upper active layers due to the unexpectedly caused difference in the surface energy levels. It is worthy to note that the performance of the device with solution-processed d-(MoO3)15 is higher than that of the device with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTLs and even comparable to that of the device with optimized evaporated-MoO3. Simulated by the transfer matrix method, the light intensity and the exciton generation rate in the active layer are found to be greatly enhanced by incorporation of an ultrathin MoO3 combined with PEDOT:PSS. As a result, by inserting a layer of evaporated MoO3 (e-MoO3) between the ITO and PEDOT:PSS, power conversion efficiency (PCE) can be dramatically improved to 7.10% for PBDTTT-C-T:PC71BM. Moreover, the e-MoO3/PEDOT:PSS bilayer also ensures good stability for the devices, due to the MoO3 preventing moisture and oxygen attack and protecting ITO from corrosion caused by the acid PEDOT:PSS.

Interface Modification of ZnO-Based Inverted PTB7:PC71BM Organic Solar Cells by Cesium Stearate and Simultaneous Enhancement of Device Parameters

We used cesium stearate (CsSt) to modify the interface of the electron-extracting contact in inverted organic solar cells. Surface microstructure, optical properties, and electrical characterization as well as exciton generation rate and dissociation probability were investigated to understand the impact of CsSt on the interface contact. The results indicated that by incorporation of CsSt, the surface morphology and energy level as well as conductivity of a zinc oxide (ZnO) film were improved. On the basis of the above properties, highly efficient inverted organic solar cells have been demonstrated by using a ZnO nanoparticle film and CsSt stacked bilayer structure as the cathode interfacial layer. The insertion of a CsSt layer between the ZnO film and active layer improved the electron extraction efficiency, and a high power conversion efficiency (PCE) of 8.69% was achieved. The PCE was improved by 20% as compared to the reference device using a ZnO-only electron extraction layer.

Novel ruthenium sensitizers with a dianionic tridentate ligand for dye-sensitized solar cells: the relationship between the solar cell performances and the electron-withdrawing ability of substituents on the ligand

Five novel ruthenium sensitizers (TUS sensitizers) with a dianionic tridentate ligand (pyridine-2,6-dicarboxyamidato and its derivatives) have been synthesized for application to dye-sensitized solar cells (DSCs). These TUS sensitizers have much larger molar absorption coefficients in the wavelength range below 600 nm compared with those of Black dye which is a structural analog and a highly efficient ruthenium sensitizer. The energy levels of HOMOs and LUMOs of TUS sensitizers shifted to the positive direction with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The energy levels of HOMO and LUMO showed linear correlation with respect to the Hammett constant of the substituents. The DSCs with TUS sensitizers showed much lower performances than that of Black dye. Both inferior adsorptivity on the TiO2 surface and unfavorable energy levels of HOMOs and LUMOs for the effective electron transfer reactions in the DSCs are considered to be the main reasons for the much lower performances of TUS sensitizers. The conversion efficiency of the DSC with a TUS sensitizer increased with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The observed linear relationship between the conversion efficiency and the driving force of the reduction process of the oxidized form of dyes by I(-) suggests that the dye regeneration process is a rate-determining step in the DSCs with TUS sensitizers.

Simulation of the luminescence spectrum of CdSe quantum dots

CdSe quantum dots were prepared via a colloidal route using an organic capping agent consist thiol group (SH). We explicitly calculated the exciton binding energy and we incorporate the exciton contribution then combined it with quantum confinement model and surface states to see its effect on photoluminescence. The results obtained by using MATLAB programming. Calculations took place at room temperature on small quantum dots (1 - 5 nm). In conclusion, our results are quite new and it effect some of the feature that has quite close correspondence with the experimental. The results are also in conformity with other theoretical and experimental investigations. This study shows the applications of photoluminescence spectrum in determination the size of nano particle, distribution of size and surface energy level of CdSe quantum dots.

New vision to CuO, ZnO, and TiO2 nanoparticles: their outcome and effects

Nanomaterials and nanotechnology have attracted more and more attention due to their wide ranges of applications in various fields. With a high level of surface energy, high magnetism, high surface area, and low melting point, engineered nanoparticles (ENPs) has been widely used in industry for various applications. Metal nanoparticles, in particular, have been shown to cause significant biological effects. Review discusses cytotoxic to neurotoxic effects of CuO, ZnO, and TiO2 nanoparticles based on the scenario drawn from various in vitro and in vivo studies. ENPs such as TiO2 and ZnO NPs have great practical importance in industrial applications. CuO NPs is also widely used in biomedical applications as catalyst supports, drug carriers, and gene delivery. However, study conducted on TiO2 NPs have forecast that oxidative DNA damage could be attributed due to reduced glutathione levels with concomitant increase in lipid peroxidation and reactive oxygen species generation. Moreover, there are many evidences showing that ZnO NP and CuO NPs generates ROS production and can cause cell death in different types of cultured cell. Nanoparticle toxicity is assessed by set of tests designed to characterize a given risk and also the mechanism for related outcomes. Conclusively, it becomes more and more important for nanotechnologist to understand the potential health effects of ENPs and what new methodology can be applied to reveal problems like gene silencing and inhibition in antioxidant defense mechanism which can be occurred on severe effects to oxidative stress by ENPs.

Application of hybrid SiO2‐coated CdTe nanocrystals for sensitive sensing of Cu2+ and Ag+ ions

A new ion sensor based on hybrid SiO2 -coated CdTe nanocrystals (NCs) was prepared and applied for sensitive sensing of Cu(2+) and Ag(+) for the selective quenching of photoluminescence (PL) of NCs in the presence of ions. As shown by ion detection experiments conducted in pure water rather than buffer solution, PL responses of NCs were linearly proportional to concentrations of Cu(2+) and Ag(+) ions < 3 and 7 uM, respectively. Much lower detection limits of 42.37 nM for Cu(2+) and 39.40 nM for Ag(+) were also observed. In addition, the NC quenching mechanism was discussed in terms of the characterization of static and transient optical spectra. The transfer and trapping of photoinduced charges in NCs by surface energy levels of CuS and Ag2 S clusters as well as surface defects generated by the exchange of Cu(2+) and Ag(+) ions with Cd(2+) ion in NCs, resulted in PL quenching and other optical spectra changes, including steady-state absorption and transient PL spectra. It is our hope that these results will be helpful in the future preparation of new ion sensors.

Computational analysis and predictive modeling of polymorph descriptors

BackgroundA computation approach based on integrating high throughput binding affinity comparison and binding descriptor classifications was utilized to establish the correlation among substrate properties and their affinity to Breast Cancer Resistant Protein (BCRP). The uptake rates of Mitoxantrone in the presence of various substrates were evaluated as an in vitro screening index for comparison of their binding affinity to BCRP.The effects of chemical properties of various chemotherapeutics, such as antiviral, antibiotic, calcium channel blockers, anticancer and antifungal agents, on their affinity to BCRP, were evaluated using HEK (human embryonic kidney) cells in which 3 polymorphs, namely 482R (wild type) and two mutants (482G and 482T) of BCRP, have been identified. The quantitative structure activity relationship (QSAR) model was developed using the sequential approaches of Austin Model 1 (AM1), CODESSA program, heuristic method (HM) and multiple linear regression (MLR) to establish the relationship between structural specificity of BCRP substrates and their uptake rates by BCRP polymorphs.ResultsThe BCRP mutations may induce conformational changes as manifested by the altered uptake rates of Mitoxantrone by BCRP in the presence of other competitive binding substrates that have a varying degree of affinities toward BCRP efflux. This study also revealed that the binding affinity of test substrates to each polymorph was affected by varying descriptors, such as constitutional, topological, geometrical, electrostatic, thermodynamic, and quantum chemical descriptors.ConclusionDescriptors involved with the net surface charge and energy level of substrates seem to be the common integral factors for defining binding specificity of selected substrates to BCRP polymorph. The reproducible outcomes and validation process further supported the accuracy of the computational model in assessing the correlation among descriptors involved with substrate affinity to BCRP polymorph. A quantitative computation approach will provide important structural insight into optimal designing of new chemotherapeutic agents with improved pharmacological efficacies.

Nonlinear Electrothermal GaN HEMT Model Applied to High-Efficiency Power Amplifier Design

Gallium Nitride (GaN) high electron-mobility transistors (HEMTs) can operate at very high power-density levels, which may cause a significant temperature rise in the transistor channel. In addition, surface and substrate energy levels, or “traps,” can cause strong dispersion effects from pulsed I-V down to dc timescales. Such effects, for both simulation accuracy and device reliability purposes, must be accounted for in any nonlinear device model. In this paper, a novel nonlinear high-power GaN HEMT equivalent circuit electrothermal model is described. Features of the model include a nonlinear thermal subnetwork that is capable of capturing the well-known inherent nonlinear thermal resistance and capacitance of GaN material. Also included is a comprehensive dispersion model that can be extracted and modeled from simple measurements. The model can very accurately predict the pulsed I -V curves at different pulse widths and duty cycles from isothermal up to the safe-operating area limit. Large-signal one-tone, two-tone, and frequency sweep tests show excellent agreement with measurements. Finally, a continuous class-F amplifier is fabricated, and large-signal frequency sweeps are performed. Comparison between the measured and modeled amplifier metrics demonstrate that the model remains accurate over a 50% bandwidth under real-world conditions.

Surface band structure of aryl-diazonium modified p-Si electrodes determined by X-ray photoelectron spectroscopy and electrochemical measurements

The influence of grafted organic layers, obtained by aryldiazonium cations reduction, on the surface properties of p-type silicon was investigated. These layers were characterized by X-ray photoelectron spectroscopy (XPS), infrared spectroscopy and electrochemical methods. The results indicate a passivation of the silicon surface, a decrease of the oxidation of silicon. The results from electrochemical and XPS measurements can be used together to quantify the shift of the surface energy bands of the semiconductor caused by the presence of these layers at the surface. These measurements are important to understand the interfacial properties of the semiconductor and this grafting method can thus be used to adjust the surface energy levels positions toward those of different chemical reactions.

Potential energy surface and rovibrational energy levels of the H2-CS van der Waals complex

Owing to its large dipole, astrophysicists use carbon monosulfide (CS) as a tracer of molecular gas in the interstellar medium, often in regions where H(2) is the most abundant collider. Predictions of the rovibrational energy levels of the weakly bound complex CS-H(2) (not yet observed) and also of rate coefficients for rotational transitions of CS in collision with H(2) should help to interpret the observed spectra. This paper deals with the first goal, i.e., the calculation of the rovibrational energy levels. A new four-dimensional intermolecular potential energy surface for the H(2)-CS complex is presented. Ab initio potential energy calculations were carried out at the coupled-cluster level with single and double excitations and a perturbative treatment of triple excitations, using a quadruple-zeta basis set and midbond functions. The potential energy surface was obtained by an analytic fit of the ab initio data. The equilibrium structure of the H(2)-CS complex is found to be linear with the carbon pointing toward H(2) at the intermolecular separation of 8.6 a(o). The corresponding well depth is -173 cm(-1). The potential was used to calculate the rovibrational energy levels of the para-H(2)-CS and ortho-H(2)-CS complexes. The present work provides the first theoretical predictions of these levels. The calculated dissociation energies are found to be 35.9 cm(-1) and 49.9 cm(-1), respectively, for the para and ortho complexes. The second virial coefficient for the H(2)-CS pair has also been calculated for a large range of temperature. These results could be used to assign future experimental spectra and to check the accuracy of the potential energy surface.

Surface characterisation and bonding of Y-TZP following non-thermal plasma treatment

Objectives(1) To chemically characterise Y-TZP surface via X-ray photoelectron spectroscopy (XPS) and evaluate the surface energy levels (SE) after non-thermal plasma (NTP). (2) To test the microtensile bond strength (MTBS) of Y-TZP bonded to cured composite disks, after a combination of different surface conditioning methods. MethodsTwenty-four Y-TZP discs (13.5mm×4mm) were obtained from the manufacturer and composite resin (Z-100) discs with similar dimensions were prepared. All discs were polished to 600 grit and divided into 8 groups (n=3 disks each), four control (non-NTP treated) and four experimental (NTP treated for 10s) groups. All groups received one of the four following treatments prior to cementation with Rely×Unicem cement: sand-blasting (SB), a Clearfil ceramic primer (MDP), sand-blasting+MDP (SBMDP), or baseline (B), no treatment. SE readings and surface roughness parameters were statistically analysed (ANOVA, Tukey's, p<0.05). Mixed model and paired samples t-tests were used to compare groups on MTBS. ResultsXPS showed increase in O and decrease in C elements after NTP. The polar component increased for BP (42.20mN/m) and SBP (43.77mN/m). MTBS values for groups BP (21.3MPa), SBP (31MPa), MDPP (30.1MPa) and SBMDPP (32.3MPa) were significantly higher in specimens treated with NTP than their untreated counterparts B (9.1MPa), SB (14.4MPa), MDP (17.8MPa) and SBMDP (24.1MPa). Conclusions(1) Increase of O and decrease of C led to higher surface energy levels dictated by the polar component after NTP; (2) NTP application increased MTBS values of Y-TZP surfaces.

Ti-49.5Ni (at%)합금의 다공성 구조가 뼈 세포 흡착에 미치는 영향

Ti-Ni alloys are widely used in numerous biomedical applications (e.g., orthodontics, cardiovascular science, orthopaedics) due to their distinctive thermomechanical and mechanical properties, such as the shape memory effect, superelasticity and low elastic modulus. In order to increase the biocompatibility of Ti-Ni alloys, many surface modification techniques, such as the sol-gel technique, plasma immersion ion implantation (PIII), laser surface melting, plasma spraying, and chemical vapor deposition, have been employed. In this study, a Ti-49.5Ni (at%) alloy was electrochemically etched in 1M <TEX>$H_2SO_4$</TEX>+ X (1.5, 2.0, 2.5) wt% HF electrolytes to modify the surface morphology. The morphology, element distribution, crystal structure, roughness and energy of the surface were investigated by scanning electron microscopy (SEM), energy-dispersive Xray spectrometry (EDS), X-ray diffractometry (XRD), atomic force microscopy (AFM) and contact angle analysis. Micro-sized pores were formed on the Ti-49.5Ni (at%) alloy surface by electrochemical etching with 1M <TEX>$H_2SO_4$</TEX>+ X (1.5, 2.0, 2.5) wt% HF. The volume fractions of the pores were increased by increasing the concentration of the HF electrolytes. Depending on the HF concentration, different pore sizes, heights, surface roughness levels, and surface energy levels were obtained. To investigate the osteoblast adhesion of the electrochemically etched Ti-49.5Ni (at%) alloy, a MTT test was performed. The degree of osteoblast adhesion was increased at a high concentration of HF-treated surface structures.

Assessment of a chair-side argon-based non-thermal plasma treatment on the surface characteristics and integration of dental implants with textured surfaces

The biomechanical effects of a non-thermal plasma (NTP) treatment, suitable for use in a dental office, on the surface character and integration of a textured dental implant surface in a beagle dog model were evaluated. The experiment compared a control treatment, which presented an alumina-blasted/acid-etched (AB/AE) surface, to two experimental treatments, in which the same AB/AE surface also received NTP treatment for a period of 20 or 60 s per implant quadrant (PLASMA 20′ and PLASMA 60′ groups, respectively). The surface of each specimen was characterized by electron microscopy and optical interferometry, and surface energy and surface chemistry were determined prior to and after plasma treatment. Two implants of each type were then placed at six bilateral locations in 6 dogs, and allowed to heal for 2 or 4 weeks. Following sacrifice, removal torque was evaluated as a function of animal, implant surface and time in vivo in a mixed model ANOVA. Compared to the CONTROL group, PLASMA 20′ and 60′ groups presented substantially higher surface energy levels, lower amounts of adsorbed C species and significantly higher torque levels (p=.001). Result indicated that the NTP treatment increased the surface energy and the biomechanical fixation of textured-surface dental implants at early times in vivo.

Positronium formation via excitonlike states on Si and Ge surfaces

Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an excitonlike positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect-band-gap semiconductor with dangling-bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down. © 2011 American Physical Society.

Fabrication and photoelectrochemical study of Ag@TiO 2 nanoparticle thin film electrode

Ag@TiO 2 nanoparticle thin film was fabricated for photoelectrochemical water splitting in the visible light region. Under the irradiation of UV light, positive photocurrent was enhanced in both electrolytes of 0.1 M HNO 3 and 0.1 M NaOH owing to the excitation of photoelectrons within the TiO 2 shells. However, under the irradiation of visible light, the enhancement of positive photocurrent was observed only in 0.1 M HNO 3 because of the formation of a Schottky barrier band bending at the Ag–TiO 2 core-shell interface and the generation of photoelectrons resulted from the surface plasmon resonance of Ag cores. In 0.1 M NaOH, significant negative photocurrent was enhanced due to the influences of higher pH on the surface state and energy level of TiO 2 shells. Such a visible light-induced photoresponse enhancement and photocurrent direction switching made the Ag@TiO 2 nanoparticle thin film useful not only as a photoelectrode for water splitting but also as a photo-switch in a basic electrolyte.

Synthesis, Control, and Characterization of Surface Properties of Cu2O Nanostructures

The ability to control nanostructure shape can strongly affect the overall properties of that system. Here we report the ability to deterministically control nanostructure shape, surface facet orientation, and surface potentials of the oxide semiconductor Cu(2)O. Epitaxial Cu(2)O nanostructures with different shapes and geometries-from boxes to pyramids to huts-have been grown via pulsed laser deposition. By varying the adatom energy and flux per laser pulse we can tune the nature of the nanostructure geometry, the total density of features, the relative surface area to volume ratio, and can create polar, nonequilibrium surfaces. In addition to detailed structural analysis of the nanostructures, high-resolution Kelvin probe force microscopy has been used to systematically analyze the surface potential and electronic structure of the (100), (110), and (111) surfaces of Cu(2)O. These studies suggest that each surface, possessing a unique atomic structure, gives rise to different surface energy levels of conduction and valence bands and the formation of electronic surface junctions. The implication of these findings in terms of a range of applications is discussed.