Paul F. Johnson

High Efficiency Copper Indium Gallium DiSelenide (CIGS) by High Power Impulse Magnetron Sputtering (HIPIMS): A Promising and Scalable Application in Thin-film Photovoltaics

A novel method to deposit Copper Indium Gallium Diselenide (CIGS) using High Power Impulse Magnetron Sputtering (HIPIMS) was demonstrated and compared to the existing DC magnetron sputtering process. The metal-ion assisted thin-film growth inherent to a HIPIMS deposition process was used to advantage in depositing CIGS films. The HIPIMS plasma was characterized by measuring ion currents on a Langmuir probe placed into the plasma sufficiently close to the substrate. The high density plasma consisting of both metal and metal ions resulted in CIGS thin-film solar cells of superior conversion efficiencies (∼13%) as compared to conventional DC magnetron sputtering (∼10%). The efficiency enhancement was attributed to the improvement in the shunt resistance of the solar cell which corresponds to the increase in the density of the CIGS layer. Furthermore, it was also possible to grow large grained CIGS (∼1 micron) with high mobility metal-ions from the HIPIMS process. The scalability potential of the HIPIMS CIGS process was also demonstrated by running a 1.5 m long Copper-Indium-Gallium rotatable in a selenium environment using a HIPIMS power supply. The cylindrical magnetron was run at an average power of 7.8 KW and peak powers of as much as 300 KW with controlled arcing. The existence of a HIPIMS plasma was confirmed by the ion currents on the Langmuir probe and the metal signals from a Plasma Emission Monitor (PEM).

A General Analytical Solution for the Concentration Profiles of Ion-Exchanged Planar Waveguides

During the recent years, a great variety of ion-exchange processes, including one-step or two-step electric field assisted ion-exchange processes, have been developed to fabricate different kinds of passive planar glass waveguides, e.g., surface waveguides, which correspond to surface maximum concentration, or buried waveguides, which correspond to inside maximum concentration [1,2,3]. Theoretical calculation of ionic concentration distribution has been of interest since refractive index is generally a linear function of concentration. A general analytical solution to calculate both surface and buried concentration distributions from different ion-exchange processes, however, has not yet been presented. In addition, traditional ion-exchange has been carried out only with constant surface concentration boundary conditions. Little attention has been paid, either experimentally or theoretically, to ion-exchange processes with variable boundary conditions. In fact, the time-dependent surface concentration is experimentally observed for the ion-exchange of GRIN glass in molten salt bath [4]. Very recently, a novel one-step technique [5,6] involving electric field assisted ion-exchange of Na + in glass by Ag + from molten AgNO 3 bath with decaying silver concentration has been developed to produce buried Ag + concentration profiles in glass. As the accurate and reproducible processes are very important for fabricating ion-exchanged glass waveguides, theoretical modeling and analysis on the new process are needed. In this paper, the one-dimensional field-assisted linear diffusion equation has been analytically solved by Laplace transformation to theoretically calculate concentration profiles produced by field enhanced ion-exchange process with exponentially decaying surface concentration boundary conditions. The applications of the solution to a variety of ion-exchange processes with different boundary or processing conditions for optical waveguide fabrication have been discussed. The theoretical results prove that the solution is a general analytical solution which can be used to calculate either surface concentration profiles or buried concentration profiles.

Incorporation of nitrogen into amorphous silica using a direct plasma reaction technique

Abstract A direct plasma reaction (DPR) technique has been used to surface-nitride amorphous silica. The nitride treatment has been performed over a temperature range of 750 to 1300°C and a low-pressure range of 40 to 268 Pa using a 90:10 nitrogen-hydrogen gas mixture. The plasma is generated by an inductively coupled rf power supply and is used as both a thermal and chemical source. The effects of various process parameters such as surface temperature, gas pressure and treatment time on nitrogen content and weight loss have been studied. Nitrogen is incorporated in both molecular and structural form. A very high nitridation rate has been observed. A good agreement among the nitrogen content, weight loss and microstructures is established. Electron and X-ray diffraction studies showed the treated layers as amorphous. Microblisters form at higher temperatures and this may limit the treatment temperatures to below 900°C. The effect of post-treatment annealing has been investigated. Unlike the case of thermal nitridation, pure nitrogen has also been shown to be a good candidate for surface modification.

Buried Concentration Profiles for Optical Waveguides by One-Step Electro-Diffusion Process: Theoretical Analysis

In recent years, a two-step electric field assisted diffusion or ion-exchange technique has been extensively studied for producing buried concentration profiles in glass [1,2,3], polymer [4,5], electrooptic and semiconducting [6,7] substrate materials to fabricate buried optical waveguide devices. The technique contains two separate diffusion processes and is quite complicated, cost and time consuming. In addition, theoretical analysis of the technique is too complicated to be used for calculating and tailoring concentration profiles. Many efforts have been made to pursue a one-step process for producing buried profiles. Very recently, a novel one-step technique [8] involving electric field assisted diffusion of silver ions into glass from molten AgNO 3 bath with decaying silver concentration has been developed to produce buried Ag + concentration profiles in glass substrate. The new technique is, from the practical operation point of view, relatively simple and is a significant improvement over the conventional two-step process.

Effects Of Trioxane On Silica Gel

Hydrolysis, condensation and thermal reactions of silica gels derived from TEOS with and without 1,3,5-trioxane (C 3 H 6 O 3 ) were studied. Effects of trioxane on viscosity and gelation time of solutions were determined. Specific surface, density, porosity and microhardness of gels were measured. The behavior of gels at elevated temperature was clarified using DTA, TGA, and dilatometry. The properties and structure of trioxane containing sol/gels may be explained by the role trioxane played in the sol-gel transition. The results of this investigation concerning sol-gel/gel-glass transitions, structure and properties of gels are presented.

Inductively-Coupled Plasma Nitriding of Fused Silica

Plasma nitriding of fused silica has been performed over a temperature range of 750°C to 1300°C in a nitrogen-hydrogen plasma generated by an inductively coupled RF discharge. The plasma is used as both thermal and chemical source. The effects of various process parameters such as surface temperature, gas pressure and treatment time on total nitrogen content have been studied. The advantages and the drawbacks of this direct plasma nitriding technique are briefly discussed.

Applications of Analytical Microscopy to Cermaic Research

The objective of this paper is twofold. First, a definition of Analytical Electron Microscopy (AEM) will be developed through consideration of the development of instrumentation and techniques. Second, the usefulness of AEM for the characterization of ceramic materials will be demonstrated through discussion of specific applications. Details of the design and use of instrumentation, specific sample preparation requirements and interpretation of data obtained cannot be presented in a short review paper. However, the references are intended to point the reader to pertinent literature in each of these critical areas. While the recent literature available describing AEM is substantial, it is also specialized. Textbooks have been written covering topics presented in this review in a sentence. So, with the understanding that the field of AEM is ill-defined, broad and deep, let us proceed.