Overview of the Project and Objectives This project involves a collaboration between a surface physicist (Bartynski, Rutgers University-New Brunswick, NJ)  and a synthetic organic chemist (Galoppini, Rutgers University-Newark, NJ). The objective of this interdisciplinary research is to develop controlled, tunable,  and modular methodologies to decorate the surface of nanostructured or crystalline inorganic semiconductors  (i.e. metal oxides such as titanium dioxide) as well as single-crystal organic semiconductors (polyaromatic hydrocarbons, or PAHs,  such as rubrene).  The electronic properties of these solid materials, and their ability to transport an electron or a hole, are influenced by  the presence of molecules bound their surface.  These organic/organic or organic/inorganic hybrid materials are important to develop  emerging types optoelectronic devices including  solar cells, sensors or  organic electronics. 

The research is based on the hypothesis that designing the organic/semiconductor interfaces at the molecular level will enable the control of energy level alignment, interfacial chemistry, and allows to tune charge donation and withdrawal of the semiconductor. To this end, the team, together with international collaborators from Germany and Italy, has explored fundamental aspects of the bonding between organic molecules and the semiconducting substrates (i.e. the metal oxides or the PAHs) and has tested new concepts of surface modification.   

Highlights of this work include the encapsulation of dye molecules into large molecular hosts, which are in turn bound onto the surface of the  semiconductors, the exploration of an unprecedented step-by-step process to decorate the surface of PAHs crystals, and the study of interactions and reactions of molecules on metal surfaces in ultrahigh vacuum environment. 

Intellectual Merit:

This work   underpins the two groups long-term  efforts to enhance the fundamental understanding and performance of organic-organic hybrid materials that are used in a wide variety of application areas including organic semiconductor devices and photovoltaics.   Determining the fundamental principles that govern the bonding and electronic interactions between molecules and semiconductor substrates will facilitate significant advancements in these important technologies.

Effective ways to functionalize the surfaces and to tune interfacial properties of the semiconductors explored in this research are still little developed, and the NSF-sponsored research effort has  addressed  this need through new creative approaches.  

Broader Impacts:

The proposed research, though fundamental in scope,  will impact fundamental research in areas of science and technology beyond the specific properties of molecule-semiconductor materials  that were  measured in this work. For instance, organic semiconductors are already finding applications in printed electronics, sensors, solar cells, light-emitting diodes, and other devices. Critical device functions depend on material characteristics, such as charge carrier mobility, which in turn depend on the semiconductor surface properties. These are the  interfaces and properties that are addressed in this  research program.  In summary, the work enhances emerging organic semiconductor capabilities and aids in developing new device concepts. 

The educational component of the proposed program involved graduate and undergraduate students from both groups  in a truly interdisciplinary collaboration. Student exchanges between the labs, joint meetings and and co-advising was strengthened by national and  international collaborations  that allowed  students training  in the laboratories of international collaborators in Germany and Italy, and at US national labs. Two undergraduate students completed their Honors theses working on this project and two graduate students already defended their PhD theses based on this research. The graduate and undergraduate students, half of which are female, are co-authors of peer-reviewed publications and have learned to operate in a truly interdisciplinary and international environment that will further improve their professional development.   The results were presented by the PI and their students   at numerous national and international meetings, at seminars at numerous  universities  in the US and abroad,  at US national labs, and at workshops.  Presentations at open houses and during outreach to local high  schools offered the opportunity to describe this work to the broader public.

The work is still in progress, as two more students will defend their thesis based on this work, and both  teams continues to publish and collaborate internationally.   

Last Modified: 11/29/2016
Modified by: Elena Galoppini