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Coconut coir, a major type of tropical lignocellulosic waste, has been restricted from higher-value applications due to its chemical complexity and inherent variability. To better disclose the chemical relationships between polysaccharides and lignin in coir and further exploit its high value-added bio-based materials, two lignin-carbohydrate complexes (LCCs) designated as glucan-lignin (GL) and xylan-lignin (XL) were successively isolated from coir via a simplified and quantitative fractionation method. The characterization of chemical composition, molecular weight distribution, and constituent substructures of the isolated LCC fractions were examined, and the lignin-carbohydrate (LC) chemical linkages were revealed as γ-esters by a 2D heteronuclear singular quantum correlation (HSQC) NMR technique. Furthermore, XL was demonstrated as a more competitive candidate than GL for 2,2-diphenyl-1-picryl-hydrazyl (DPPH) removal in comparison with 2,6-di-tert-butyl-4-methylphenol (BHT, a commercial antioxidant), and was also featured as a more promising reinforcing agent for elevating the adsorption property of polyacrylamide-based hydrogels via the synergistic effect of physical and hydrogen bonding adsorptions.

By employing localized surface plasmon resonance (LSPR), the near band edge (NBE) emission intensity of ZnO films were greatly varied, while defect emission remained almost the same. This photoluminescence (PL) intensity enhancement or reduction is tunable by changing the position of Ag nanoparticles (NPs) relative to the ZnO films. The remarkable variation of the NBE emission was investigated deeply. These experimental results reveal that the Ag NPs play a key role in tuning the PL performance of the semiconductor material, where LSPR occurs.

In this study, electroluminescence (EL) from n-ZnO/p-GaN heterojunctions is investigated and tailored. The heterojunctions were obtained by depositing high-quality ZnO films on the p-GaN substrate through pulsed laser deposition (PLD), and the characteristics were analyzed by X-ray diffraction (XRD), photoluminescence (PL) spectra at room-temperature (RT, 300 K), current-voltage (I-V) characteristics curves, and the EL spectra. By means of the band energy theory, a simple and effective way to tailor the luminescent properties of the heterojunction was discussed. The ultra-violet (UV) emission from the n-ZnO was obtained through the improvement of the electrical properties of the films and the substrates. The visible light emissions were tailored through the transition of different defect caused color emissions. Besides, an unexpected yellow light (YL) emission caused by Ga-O interlayer was also studied.

The magnetron sputtering discharge is a highly successful tool for deposition of thin films and coatings. It has been applied for various industrial applications for over four decades. Sustaining a plasma in a magnetron sputtering discharge requires energy transfer to the plasma electrons. In the past, the magnetron sputtering discharge has been assumed to be maintained by cathode sheath acceleration of secondary electrons emitted from the target, upon ion impact. These highly energetic electrons then either ionize the atoms of the working gas directly or transfer energy to the local lower energy electron population that subsequently ionizes the working gas atoms. This leads to the well-known Thornton equation, which in its original form [1] is formulated to give the minimum required voltage to sustain the discharge. However, recently we have demonstrated that Ohmic heating of electrons outside the cathode sheath is typically of the same order as heating due to acceleration across the sheath in dc magnetron sputtering (dcMS) discharges [2]. The secondary electron emission yield $\gamma _{see}$ is identified as the key parameter determining the relative importance of the two processes. In the case of dcMS Ohmic heating is found to be more important than sheath acceleration for secondary electron emission yields below around 0.1. For the high power impulse magnetron sputtering (HiPIMS) discharge we find that direct Ohmic heating of the plasma electrons is found to dominate over sheath acceleration by typically an order of magnitude, or in the range of 87 – 99 % of the total electron heating. A potential drop of roughly 100 – 150 V, or 15 – 25% of the discharge voltage, always falls across the plasma outside the cathode sheath [3].

White light-emitting diode (LED) with effective energy conservation and long service life could be employed in numerous applications. In this study, the high-performance n-ZnO films were first prepared via pulsed laser deposition on p-GaN substrates and then the n-ZnO/p-GaN heterojunction LED was fabricated. This LED exhibits blue and yellow light emission, and their emission intensities can be tuned by adjustment of the fabrication parameters (e.g., oxygen pressure) and/or by introduction of a semi-insulating i-ZnO layer to form a p-GaN/i-ZnO/n-ZnO heterojunction. Thus, a facile approach has been proposed for the preparation of white LED.

A new reactive ionization region model (R-IRM) is developed to describe the reactive Ar/O-2 high power impulse magnetron sputtering (HiPIMS) discharge with a titanium target. It is then applied to ...

Without the use of a metal catalyst in the process, ZnO with nanostructures was successfully prepared on Si (100) substrate by simple chemical vapor-deposition method. In our work, Ar was used as the plasma forming gas, O2 was the reactive gas and metal zinc powder (99.99% purity) vaporized by cylinder hollow-cathode discharge (HCD) acted as the zinc source. The crystal structures of the as-synthesized ZnO nanostructures were characterized by X-ray diffraction (XRD); the ZnO sample growing on the wall of the crucible showed a ‘comb-like’ nanostructure, while the other one at the bottom of the crucible showed a ‘rod-like’ structure, which can be attributed to the difference of the oxygen content. The measurement on the photoluminescence (PL) performance of the ZnO nanostructures was carried out at room temperature. The results indicated that the ‘comb-shape’ ZnO nanomaterial possessed a remarkably strong ultraviolet emission peak centered at 388 nm, while ZnO nanorods, except better ultraviolet emission, also had relatively strong blue-green emission ranging from 470 to 600 nm due to the existence of oxygen vacancies. The growth mechanism of ZnO with nanostructures is also discussed in this paper.

The time-dependent plasma discharge ionization region model (IRM) has been under continuous development during the past decade and used in several studies of the ionization region of high-power imp ...

A nanocomposite, silver nanoparticles embedded into polyethylene oxide (PEO) is synthesized by magnetron sputtering. The embedded silver in PEO matrix is confirmed by transmission electron microscopy (TEM) image, X-ray diffraction (XRD) pattern, and atomic force microscopy (AFM) analysis. By TEM image the sizes of silver nanoparticles are found to be tunable, and the silver crystallization is preferentially grown in facet of (111) by varying the plasma parameters, especially the working pressure. The crystal statue is evidenced by UV–visible spectra where the peak of plasmon absorption is located at ca. 400 nm. This characterization is very important for silver nanocomposite application as an antibacterial reagent based on previous antimicrobial results. By Fourier transform infrared spectroscopy (FTIR) the functional group of C–O–C in PEO films is depicted to be enough retained from the monomer in MS plasma.

The lower deposition rate for high power impulse magnetron sputtering (HiPIMS) compared with direct current magnetron sputtering for the same average power is often reported as a drawback. The often invoked reason is back-attraction of ionized sputtered material to the target due to a substantial negative potential profile, sometimes called an extended presheath, from the location of ionization toward the cathode. Recent studies in HiPIMS devices, using floating-emitting and swept-Langmuir probes, show that such extended potential profiles do exist, and that the electric fields E-z directed toward the target can be strong enough to seriously reduce ion transport to the substrate. However, they also show that the potential drops involved can vary by up to an order of magnitude from case to case. There is a clear need to understand the underlying mechanisms and identify the key discharge variables that can be used for minimizing the back-attraction. We here present a combined theoretical and experimental analysis of the problem of electric fields E-z in the ionization region part of HiPIMS discharges, and their effect on the transport of ionized sputtered material. In particular, we have investigated the possibility of a sweet spot in parameter space in which the back-attraction of ionized sputtered material is low. It is concluded that a sweet spot might possibly exist for some carefully optimized discharges, but probably in a rather narrow window of parameters. As a measure of how far a discharge is from such a window, a Townsend product Pi(Townsend) is proposed. A parametric analysis of Pi(Townsend) shows that the search for a sweet spot is complicated by the fact that contradictory demands appear for several of the externally controllable parameters such as high/low working gas pressure, short/long pulse length, high/low pulse power and high/low magnetic field strength. Funding Agencies|Swedish Research Council||Swedish Foundation for Strategic Research||European Collaboration in Science and Technology (COST Action)|MP0804|ANR HiPPoPP (French Government Research Agency)||Romanian ministry of Education, Research, Youth and Sport|IDEI 540/2009

A time-dependent plasma discharge model has been developed for the ionization region in a high-power impulse magnetron sputtering (HiPIMS) discharge. It provides a flexible modeling tool to explore, e. g., the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, and the gas rarefaction and refill processes. A separation is made between aspects that can be followed with a certain precision, based on known data, such as excitation rates, sputtering and secondary emission yield, and aspects that need to be treated as uncertain and defined by assumptions. The input parameters in the model can be changed to fit different specific applications. Examples of such changes are the gas and target material, the electric pulse forms of current and voltage, and the device geometry. A basic version, ionization region model I, using a thermal electron population, singly charged ions, and ion losses by isotropic diffusion is described here. It is fitted to the experimental data from a HiPIMS discharge in argon operated with 100 mu s long pulses and a 15 cm diameter aluminum target. Already this basic version gives a close fit to the experimentally observed current waveform, and values of electron density n(e), the electron temperature T(e), the degree of gas rarefaction, and the degree of ionization of the sputtered metal that are consistent with experimental data. We take some selected examples to illustrate how the model can be used to throw light on the internal workings of these discharges: the effect of varying power efficiency, the gas rarefaction and refill during a HiPIMS pulse, and the mechanisms determining the electron temperature. QC 20120125

The transport of charged particles in a high power impulse magnetron sputtering (HiPIMS) discharge is of great interest when optimizing this promising deposition technique with respect to deposition rate and control of the ion acceleration. In this study the internal current densities Jϕ (azimuthal direction) and JD⊥ (axial direction) have therefore been spatially and temporally resolved in the bulk plasma region above a cylindrical magnetron using Rogowski coils. From the measurements a phenomenological model has been constructed describing the evolution of the current density in this pulsed plasma. The core of the model is based on six different types of current systems, which characterize the operating transport mechanisms, such as current transport along and across magnetic field lines, as well as the initiation, buildup and steady-state of a HiPIMS plasma. Furthermore, the data also shows that there are spatial and temporal variations of the key transport parameter Jϕ/JD⊥ , governing the cross-B resistivity and also the energy of the charged particles. The previously reported faster-than-Bohm cross-B electron transport is here verified, but is not found to be present during the whole discharge regime as well as for all locations. These results on the plasma dynamics are essential input when modeling the axial electric field, governing the back-attraction of ionized sputtered material, and might furthermore provide a link between the different resistivities reported in HiPIMS, pulsed-DC, and DC magnetron discharges. Funding agencies|Swedish Research Council||Swedish Foundation for Strategic Research

The onset and development of self-sputtering (SS) in a high power impulse magnetron sputtering (HiPIMS) discharge have been studied using a plasma chemical model and a set of experimental data, tak ...

In most models of sputtering magnetrons, the mechanism for energizing the electrons in the discharge is assumed to be sheath energization. In this process, secondary emitted electrons from the cathode surface are accelerated across the cathode sheath into the plasma, where they either ionize directly or transfer energy to the local lower energy electron population that subsequently ionizes the gas. In this work, we present new modeling results in support of an alternative electron energization mechanism. A model is experimentally constrained, by a fitting procedure, to match a set of experimental data taken over a large range in discharge powers in a high-power impulse magnetron sputtering (HiPIMS) device. When the model is matched to real data in this way, one finding is that the discharge can run with high power and large gas rarefaction without involving the mechanism of secondary electron emission by twice-ionized sputtered metal. The reason for this is that direct Ohmic heating of the plasma electrons is found to dominate over sheath energization by typically an order of magnitude. This holds from low power densities, as typical for dc magnetrons, to so high powers that the discharge is close to self-sputtering, i.e. dominated by the ionized vapor of the sputtered gas. The location of Ohmic heating is identified as an extended presheath with a potential drop of typically 100–150 V. Such a feature, here indirectly derived from modeling, is in agreement with probe measurements of the potential profiles in other HiPIMS experiments, as well as in conventional dc magnetrons.

Model studies of 400 mu s long discharge pulses in high-power impulse magnetron sputtering have been made to study the gas dynamics and plasma chemistry in this type of pulsed processing plasma. Da ...