Large Third-Order Nonlinearities in Atomic Layer Deposition (ALD) Grown Nitrogen-Enriched TiO2 Nanoscale Films & A Career Encompassing Optical Physics, Diversity and Mentoring

Dr. Anthony M. Johnson, Director for the Center for Advanced Studies in Photonics Research (CASPR)

Professor of Physics, Professor of Computer Science & Electrical Engineering

University of Maryland Baltimore County (UMBC)

 Recorded Talk

ABSTRACT:  The next-generation of high-speed photonics devices, such as ultrafast integrated modulators and wavelength converters, require materials with large third-order optical nonlinearities. Typically nonlinear materials are cut from bulk crystals or liquids that are not suitable for integration with complementary metal-oxide-semiconductor (CMOS) technology. In addition to all-optical on-a-chip device applications, materials that exhibit high nonlinear absorption and a fast response time are useful in optical limiting applications, for the protection of optical sensors and the human eye from high intensity light such as lasers. TiO₂ films, with a 120-nm nominal thickness, were deposited by ALD at temperatures ranging from 100-300ºC on quartz substrates, and were studied using a femtosecond thermally managed Z-scan technique. TiO₂ films prepared by physical vapor deposition (PVD) at room temperature were used as control samples. The as-grown ALD films deposited at 150-300ºC exhibited values for n₂, the nonlinear index of refraction, between 0.6 x 10^-10 and 10 x 10^-10 cm²/W, which is 4-6 orders of magnitude larger than previously reported. Annealing the films for 3 hours at 450ºC in air reduced the nonlinearities below the detection limit of the experimental setup. Similarly, as-grown 100ºC ALD and PVD films did not produce a discernable Z-scan trace. The samples were also characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and UV-Vis absorption. Compositional analysis using XPS reveals the presence of ~ 1 atomic % of Ti-O-N metallic bonds in the films that exhibit the largest nonlinearity. Annealing the samples results in the oxidation of the metallic bonding and is accompanied by a large decrease in the nonlinearity. XRD analysis indicates that the as-deposited films are amorphous and the annealed films are partially crystallized. These results demonstrate the possibility of a new class of thin-film nonlinear materials in which their properties can be tailored by controlling the film composition.

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This talk is about my professional journey which started at AT&T Bell Laboratories in the early 1970s. The Bell Laboratories Cooperative Research Fellowship Program for Minorities (CRFP) founded in 1972, followed closely in 1974 by the Graduate Research Program for Women (GRPW) and the Summer Research Program for Minorities and Women (SRP), were among the first programs of their kind in the US to address the issue of underrepresentation of women and minorities in the STEM fields and had a particularly strong impact in Physics. In 1981, four PhDs were awarded to African-Americans in the US in Physics and two (including me) were Bell Labs CRFP Fellows. In addition to striving to produce leading edge research, these Diversity Programs (then called Affirmative Action) made me a strong proponent of the recruitment and retention of women and underrepresented minorities into the scientific enterprise.

BIO:  Anthony M. Johnson, Director of the Center for Advanced Studies in Photonics Research (CASPR),Professor of Physics and Professor of Computer Science & Electrical Engineering at the University of Maryland Baltimore County (UMBC) since 2003. He received a B.S. in Physics (1975) from Polytechnic Institute of New York and a PhD in Physics (1981) from City College of New York.  His PhD thesis research was conducted at AT&T Bell Laboratories with support from the Cooperative Research Fellowship Program for Minorities. He was a Distinguished Member of Technical Staff in the Photonic Circuits Research Department at Bell Labs where he spent 14 years before joining New Jersey Institute of Technology (NJIT) in1995, where he was Chairperson and Distinguished Professor of Physics until 2003. His research career spans ultrafast optical and optoelectronic phenomena in both academia and industry. He has nearly 85 refereed publications, 2 book chapters and 4 US patents. His current research interests include the ultrafast photophysics and nonlinear optical properties of bulk, nanostructured and quantum well semiconductor structures, ultrashort pulse propagation in fibers and high-speed lightwave systems. He was 2002 President of the OSA (the Optical Society); Editor-in-Chief of Optics Letters (95-01); CLEO 1990 Program Co-Chair and CLEO 1992 Conference Co-Chair (Conference on Lasers and Electro-Optics). He was a Member of the Board of Directors of the APS (American Physical Society) [94-97 & 13-14], the Board of Governors IEEE Photonics Society [93-95], the OSA Board of Directors [93-96 & 00-03] and the Governing Board AIP (American Institute of Physics) [02-08]. A Member of the DOE Basic Energy Sciences Advisory Committee [BESAC] (99-08); Member of the NRC/NAS Committee on AMO2010: Atomic, Molecular and Optical Science (05-06);  Deputy Director (06-16) of the NSF Engineering Research Center MIRTHE (Mid-Infrared Technologies for Health and the Environment); Member, APS Division of Laser Science (DLS) Executive Committee (11-14) and APS Executive Board (13-14); Member, NRC Committee on Atomic, Molecular and Optical Science (CAMOS) [13-15]; Founding

Editorial Board Member of Physical Review X (11-18); Sigma Xi Distinguished Lecturer (11-13);

Member, Steering Committee of the International Year of Light and Light-based Technologies (IYL2015);

Member (2016-2018) IEEE Corporate Innovation Award Committee; Member (2016-2018) of the APS

Nominating Committee; Member, Advisory Council for the Princeton Institute for the Science

and Technology of Materials (PRISM) at Princeton University (2018-2021); Member of the 2020 National

Academies Panel on Materials and Manufacturing Sciences at the Army Research Laboratory. Member

and Co-Founder, OSA Ad Hoc Committee on Women and Minorities in Optics (1988-1993); Co-Chair,

OSA Committee on Women and Minorities in Optics (1994-1998); Chair, APS Committee on Minorities in

Physics (1992-1993); OSA Representative to the AIP Liaison Committee for Under-Represented

Minorities (LCURM) (2007-2019); Steering Committee Member and National Advisory Board Member of

the APS Minority Bridge Program (2010-2015), Chair, APS Bridge Program’s National Advisory Board

(2015-2018); Member, OSA Diversity, Equity and Inclusion Rapid Action Committee (DEI RAC) (2020-

2021); (Member, IEEE Technical Activities Board (TAB) Committee on Diversity and Inclusion (CDI)

(2021-). He is a Fellow of the APS, OSA, IEEE, AAAS (American Association for the Advancement

of Science) and the National Society of Black Physicists (NSBP). Awards and honors include the 1996

APS Edward Bouchet Award; CCNY Honorary Doctorate (June 2011); History Makers/Science Makers

(2013) http://www.thehistorymakers.com/biography/anthony-johnson; 2020 IEEE Life Fellow; 2021

Stephen D. Fantone Distinguished Service Award of The Optical Society (OSA) now Optica. Election to

the American Academy of Arts and Sciences (2021).