John A. Marohn

Professor

150 Baker Lab
john.marohn@cornell.edu
607/255-2004

Education

National Research Council Postdoctoral Associate, US Army Research Laboratory
PhD, California Institute of Technology
BS, Chemistry, University of Rochester
BA, Physics, University of Rochester

Departments and programs

Chemistry and Chemical Biology

Affiliated Colleges

College of Arts and Sciences

Academic interests

Analytical
Biophysical
Materials
Physical
Polymer

Keywords

Pi-conjugated systems, electric force and magnetic resonance force microscopies

Overview

Professor John Marohn's group is focused on imaging the structure and function of materials at the nanometer scale. We are pushing magnetic resonance imaging to nanoscale resolution in order to study individual biomolecules and are developing and applying tools to study charge in thin-film devices -- including the drift, diffusion, trapping, and generation of charge from light.

Research Focus

Detecting and imaging individual electron spins
Quantum measurement
Lead halide perovskites
Organic photovoltaic materials
Unconventional semiconductors

Publications

Search PubMed for articles by “JA Marohn”.
For a current list of publications go here.
For current publications also see Orcid and Google Scholar.

Representative Publications

Nanoscale magnetic resonance imaging

C. E. Isaac, C. M. Gleave, P. T. Nasr, H. L. Nguyen, E. A. Curley, J. L. Yoder, E. W. Moore, L. Chen, and J. A. Marohn, Dynamic nuclear polarization in a magnetic resonance force microscope experiment, Phys. Chem. Chem. Phys., 2016, 18, 8806 – 8819, URL http://dx.doi.org/10.1039/C6CP00084C, PMC5609491.
J. G. Longenecker, H. J. Mamin, A. W. Senko, L. Chen, C. T. Rettner, D. Rugar, and J. A. Marohn, High-gradient nanomagnets on cantilevers for sensitive detection of nuclear magnetic resonance, ACS Nano, 2012, 6, 9637 – 9645, URL http://dx.doi.org/10.1021/nn3030628.
E. W. Moore, S.-G. Lee, S. A. Hickman, S. J. Wright, L. E. Harrell, P. P. Borbat, J. H. Freed, and J. A. Marohn, Scanned-probe detection of electron spin resonance from a nitroxide spin probe, Proc. Natl. Acad. Sci. U.S.A., 2009, 106, 22251 – 22256, URL http://dx.doi.org/10.1073/pnas.0908120106.
S. R. Garner, S. Kuehn, J. M. Dawlaty, N. E. Jenkins, and J. A. Marohn, Force-gradient detected nuclear magnetic resonance, Appl. Phys. Lett., 2004, 84, 5091 – 5093, URL http://dx.doi.org/10.1063/1.1762700.

Nanoscale fluctuations

S. Lekkala, J. A. Marohn, and R. F. Loring, Electric force microscopy of semiconductors: Theory of cantilever frequency fluctuations and noncontact friction, J. Chem. Phys., 2013, 139, 184702, URL http://dx.doi.org/10.1063/1.4828862.
N. Hoepker, S. Lekkala, R. F. Loring, and J. A. Marohn, Dielectric fluctuations over polymer films detected using an atomic force microscope, J. Phys. Chem. B, 2011, 115, 14493 – 14500, URL http://dx.doi.org/10.1021/jp207387d.
S. M. Yazdanian, N. Hoepker, S. Kuehn, R. F. Loring, and J. A. Marohn, Quantifying electric field gradient fluctuations over polymers using ultrasensitive cantilevers, Nano Lett., 2009, 9, 2273 – 2279, URL http://dx.doi.org/10.1021/nl9004332.
S. Kuehn, J. A. Marohn, and R. F. Loring, Noncontact dielectric friction, J. Phys. Chem. B, 2006, 110, 14525 – 145258, URL http://dx.doi.org/10.1021/jp061865n.

Charge and ion motion in unconventional semiconductors

R. P. Dwyer, S. R. Nathan, and J. A. Marohn, Microsecond photocapacitance transients observed using a charged microcantilever as a gated mechanical integrator, Sci. Adv., 2017, 3, e1602951, URL http://dx.doi.org/10.1126/sciadv.1602951.
A. M. Tirmzi, R. P. Dwyer, T. Hanrath, and J. A. Marohn, Coupled slow and fast charge dynamics in cesium lead bromide perovskite, ACS Energy Lett., 2017, 2, 488 – 496, URL http://dx.doi.org/10.1021/acsenergylett.6b00722.
R. P. Dwyer, L. E. Harrell, and J. A. Marohn, Lagrangian and impedance spectroscopy treatments of electric force microscopy, Phys. Rev. Appl., 2019, 11, 064020, URL http://dx.doi.org/10.1103/PhysRevApplied.11.064020.
J. L. Luria, K. A. Schwarz, M. J. Jaquith, R. G. Hennig, and J. A. Marohn, Spectroscopic characterization of charged defects in polycrystalline pentacene by time- and wavelength-resolved electric force microscopy, Adv. Mater., 2011, 23, 624 – 628, URL http://dx.doi.org/10.1002/adma.201003073.
T. N. Ng, W. R. Silveira, and J. A. Marohn, Dependence of charge injection on temperature, electric field, and energetic disorder in an organic semiconductor, Phys. Rev. Lett., 2007, 98, 066101, URL http://dx.doi.org/10.1103/PhysRevLett.98.066101.
J. D. Slinker, J. A. DeFranco, M. J. Jaquith, W. R. Silveira, Y.-W. Zhong, J. M. Moran-Mirabal, H. G. Craighead, H. D. Abruña, J. A. Marohn, and G. G. Malliaras, Direct measurement of the electric-field distribution in a light-emitting electrochemical cell, Nat. Mater., 2007, 6, 894 – 899, URL http://dx.doi.org/10.1038/nmat2021.
E. M. Muller and J. A. Marohn, Microscopic evidence for spatially inhomogeneous charge trapping in pentacene, Adv. Mater., 2005, 17, 1410, URL http://dx.doi.org/10.1002/adma.200401174.