Stefan Zollner - US grants

9413492 Zollner It is proposed to convert an existing single-wavelength ellipsometer with a rotating analyzer to a spectroscopic ellipsometer and to investigate the optical properties of ternary silicon-germanium-carbon alloys which may have optoelectronic applications. Preliminary ellipsometric measurements will be performed on other classes of emerging materials, such as titanium-silicon-tin, which has possible applications in the automotive industry as a thermocouple material. %%% Same ***

This grant provides support for the acquisition of an infrared spectroscopic ellipsometer for materials research and student training at Arizona State University. The instrument will be equipped with a cryostat attachment allowing variable temperature operation. Such capability is extremely rare: the new instrument will be the first of its kind manufactured in the United States. A spectroscopic ellipsometer measures the real and imaginary parts of a material's index of refraction as a function of wavelength. In the infrared range of the spectrum, the dominant optical excitations are phonons (vibrations), plasmons (collective electronic oscillations) in doped materials, and band-to-band electronic excitations in narrow gap semiconductors. Accordingly, the new ellipsometer will play a key role in the characterization of oxides, ferroelectric materials, and semiconductors, areas of active research at Arizona State University and of great interest to industrial partners. Spectroscopic ellipsometry has significant advantages over light transmission or reflection experiments. The latter measure a single quantity at each wavelength (the intensity of the transmitted or reflected light), whereas ellipsometry measures the change in polarization of the light reflected at a surface. Because this change is characterized by an amplitude ratio and a phase shift (related to the reflection coefficients for light polarized in the plane and perpendicular to the plane of incidence),
ellipsometry is highly accurate and reproducible, even for low light levels. In addition, it requires no reference sample, is less affected by sample scattering of light, and can be used to determine absolute values for the optical constants without independent thickness measurements.

The project is expected to have a broad societal impact. One of its unique aspects will be the synergistic collaboration between ASU and industrial collaborators, who play a key role in the training of ASU personnel. Special emphasis will be placed on fostering scientific education. Funds are requested to support the operation of the instrument during the first year, and these funds will be expended primarily for the training of students. Industrial collaborators will play a key role in these activities, supervising students, providing samples, and teaching short courses on ellipsometry.

In collaboration with Motorola and Freescale Semiconductor, we propose the fabrication and study of novel nanostructures based on highly organized, three-dimensional arrays of size and shape controlled silicon nanocrystals (NCs). These three-dimensional nanostructures will be prepared in the form of pyramid-dot complexes where nearly spherical Si NCs (i.e., quantum dots) will be placed directly on top of laterally ordered Si pyramids. Using this technique, we intend to exploit these novel structures in new memory devices. These devices utilize resonant carrier injection from nanoscale Si pyramids via discrete energy levels of nanometer diameter Si quantum dots. The exciting but challenging goals of this project are:

(i) Development of a nanofabrication technique focused on highly ordered three- dimensional network of Si NC pyramid-dot complexes.

(ii) Experimental studies and theoretical modeling of resonant carrier injection in a system of coupled pyramid-dot Si NCs.

(iii) Fabrication and testing of ultra-fast, non-volatile memory device prototypes based on Si NC pyramid/dot complexes.

By achieving these goals, we will constitute fundamental advances in faster Si NC-based non-volatile memories and novel circuit functionalities.

Broader Impact

The integration of research and education in this proposal will be done (i) via integrating the proposed research advances into the undergraduate and graduate NJIT curriculum, and (ii) by offering outreach programs to pre-college students and school teachers in our local area. For the youngest students, our new project at NJIT will reach out to the local K-12 community with state-of-the art laboratory tours and mentoring high school teacher summer classes with focus on modern electronic devices and circuits. With its ethnically diverse student body and urban location, NJIT has a unique opportunity to pursue groups historically under-represented in science and engineering.

Technical: This GOALI project is to study optical properties of transition metals and related intermetallic compounds, especially silicides. Metal and intermetallic compound films are grown on silicon and silicon oxide using physical vapor deposition at IBM. Samples are annealed to encourage grain growth, intermetallic reactions, and agglomeration (Ostwald ripening). The complex dielectric functions of the thin film materials are investigated using spectroscopic ellipsometry over a wide spectral range from the far infrared to the vacuum ultraviolet. Optical measurements are combined with semiconductor metrology techniques, particularly x-ray measurements and atomic force microscopy, to understand the film properties, intermetallic formation, and evolution of the films during materials and device processing.
Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. Low-resistance contacts to nanoelectronic devices require ultrathin Ohmic metal-semiconductor junctions with superior chemical, physical, and thermal stabilities. Ellipsometry allows non-contact investigations of the properties of thin metal films, intermetallic formation, and materials evolution during processing. Graduate and undergraduate students, including those in under-represented groups, will be trained for ellipsometry, metrology, semiconductor processing, and device fabrication, and learn about materials physics in industry. Well-designed capstone design projects for senior undergraduate students are an important component of the project.

This project is jointly funded by the Electronic and Photonic Materials (EPM) and Ceramic (CER) Programs in the Division of Materials Research.

NON-TECHNICAL DESCRIPTION: This project trains students, including underrepresented minorities and women, in optical and X-ray thickness measurements of thin films (such as those used for advanced manufacturing in Rio Rancho, NM) and connects students with research at National Laboratories, especially the Center for Integrated Nanotechnologies at Sandia National Laboratories. The project determines the refractive index and absorption coefficient of novel crystalline oxides and studies the interaction of localized d- and f-electrons with atomic vibrations and itinerant s- and p-electrons in complex metal oxides. This research aims to develop new types of lasers and light detectors based on metal oxide hetero¬structures.

TECHNICAL DETAILS: This project measures the optical constants of a broad range of complex metal oxides from the mid-infrared to the ultraviolet spectral region. The data is analyzed to draw conclusions on the vibrational, electronic, and transport properties of such oxides. Quantum confinement and stress effects in oxide heterostructures and intersubband transitions in oxide superlattices are also studied. Temperature is used a parameter to tune the oxide properties. Results are compared with theory to achieve a comprehensive understanding of correlated oxides. Experimental results provide adjustable parameters (such as the Hubbard U value) needed for band structure calculations. Undergraduate students engaged in this project visit local and regional high schools and perform materials physics classroom demonstrations. They also organize a week-long physics summer day camp in the New Mexico State University Physics Department.