Robert Alan Bellman

Nanoporous structure of a GdF 3 thin film evaluated by variable angle spectroscopic ellipsometry

As excimer lasers extend to deep-ultraviolet and vacuum-ultraviolet wavelengths at 193 and 157 nm, optical coatings experience the challenge of eliminating possible environmental contamination, reducing scattering loss, and increasing laser irradiation durability. Wide bandgap metal fluorides become the materials of choice for the laser optics applications. To understand the optical properties of nanostructure fluoride films, thin GdF(3) films grown on CaF(2) (111) substrates were evaluated by variable angle spectroscopic ellipsometry. An effective medium approximation model was used to determine both the film porosity and the surface roughness. Structural evolution of the GdF(3) film was revealed with improved ellipsometric modeling, suggesting the existence of multilayer structure, a densified bottom layer, middle layers with increasing porosity, and a rough surface. The nanostructure of the film and the surface roughness were confirmed by atomic force microscopy. The attraction of the nanostructure to environmental contamination was experimentally demonstrated.

Fabrication and performance of a one-to-one erect imaging microlens array for fax

Microlens arrays which image a full size document onto a photoreceptor for copying or transmitting purposes are currently of much interest. In particular those arrays which have total conjugate distances less than 10 mm are important because of the compactness they afford in the contact image sensor (CIS) unit design. In this paper the fabrication of such a one-to-one array utilizing the photosensitive glass-based SMILE tm process is described. The performance of the array in terms of contrast vs. spatial frequency for a facsimile document reader application is tested in a commercial CIS unit. The overall measured performance is examined in terms of the process parameters involved in the lens fabrication. Advantages and disadvantages of the microlens array relative to other methods are considered.

Time-resolved, nonequilibrium carrier dynamics in Si-on-glass thin films for photovoltaic cells

Here, a femtosecond pump–probe spectroscopy method was used to characterize the growth process and transport properties of amorphous silicon-on-glass, thin films, intended as absorbers for photovoltaic cells. We collected normalized transmissivity change (ΔT/T) waveforms and interpreted them using a comprehensive three-rate equation electron trapping and recombination model. Optically excited ~300–500 nm thick Si films exhibited a bi-exponential carrier relaxation with the characteristic times varying from picoseconds to nanoseconds depending on the film growth process. From our comprehensive trapping model, we could determine that for doped and intrinsic films with very low hydrogen dilution the dominant relaxation mode was carrier trapping; while for intrinsic films with large hydrogen content and some texture, it was the standard electron–phonon cooling. In both cases, the initial nonequilibrium relaxation was followed by Shockley–Read–Hall recombination. An excellent fit between the model and the ΔT/T experimental transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.

48.2: The Chemical Durability of EAGLE XG™ in LCD Dry Etch Processes

This work compared the chemical durability of EAGLE XG™, EAGLE2000™ and Code 1737 glasses in typical TFT dry etch processes. Active, dielectric, and metal films were etched with a resist mask. Glass surfaces were evaluated by dark field microscopy, SEM/EDX, and AFM. The results show dry etch durability is comparable for all three compositions.

Nonequilibrium carrier dynamics in ultrathin Si-on-glass films

We present a femtosecond pump-probe spectroscopy approach for characterization of amorphous and microcrystalline silicon films grown on glass substrates. Such films are presently being considered as absorbers in tandem-type, Si-based photovoltaic cells. Our experiments consisted of time-resolved, two-colour femtosecond optical measurements, performed in the transmission mode in a wide range of delay times. Depending on the sample growth process, collected normalized transmissivity change (ΔT/T) waveforms exhibited a bi-exponential relaxation dynamics with the characteristic times varying from picoseconds to nanoseconds. Experimental data were interpreted using a three-rate-equation models, and the relaxation was identified as, depending on the Si film type, being dominated by either carrier trapping or electron-phonon cooling and followed by electron-hole recombination. An excellent fit between the model and the ΔT/T transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.

Nanostructure of GdF3 thin film evaluated by variable angle spectroscopic ellipsometry

As excimer lasers extend to deep-ultraviolet and vacuum-ultraviolet wavelengths at 193nm and 157nm, optical coatings experience the challenge of eliminating possible environmental contamination, reducing scattering loss, and increasing laser irradiation durability. Wide band-gap metal fluorides become the materials of choice for the laser optics applications. In order to understand the optical properties of nanostructured fluoride films, thin GdF3 films grown on CaF2 (111) substrates were evaluated by variable angle spectroscopic ellipsometry. An effective medium approximation model was used to determine both the film porosity and the surface roughness. Structural evolution of the GdF3 film was revealed with improved ellipsometric modeling, suggesting the existence of 3-layer structure, a densified bottom layer, a porous middle layer and a rough top surface. The nanostructure of the film and the surface roughness were confirmed by atomic force microscopy. The attraction of the nano-structure to environmental contamination was experimentally demonstrated.