My primary research interests focus on the origin ane evolution of elements in the Galaxy and planetary materials within the early Solar System through a variety of isotopic anomalies (radiogenic, spallogenic and nucleosynthetic) preserved in meteoritic components. These isotopically anomalous signals, revealed through analyses of samples by Secondary Ion Mass Spectrometry (SIMS), provide information about the astrophysical environment in which the Solar System formed, the timescales of high temperature processing and chemical evolution during the earliest stages of the Solar System formation, and nucleosynthetic processes inside stars. The research topics I am pursuing can be categorized into two parts:
Origins of short-lived radionuclides and early solar system chronology
    Two big questions in Solar System formation concern the timescales of high temperature processing (e.g., formations of solids, temperature fluctuations in the disk . . . etc) in the early evolutionary stages, and the astrophysical environment in which the solar protoplanetary disk resided. Although how and where the Solar System formed 4.5 Gyr ago is largely unknown, astronomical observations of young stellar objects provide some constraints on the lifetimes of their different evolutionary stages and the environments in which they formed. However, one major deficiency is that astronomical estimates usually have too low a temporal resolution for high temperature processing in the solar nebula. In order to understand the finer scale chronologies of solid formation, I use a laboratory approach — analyses of daughter isotopes from now-extinct, short-lived radionuclides in meteorites.
    Radioactivities with half-lives > 100 Myrs are considered short-lived. Such half-lives are short compared to the age of the Solar System, but are long enough to survive over a sufficient amount of time in the solar nebula to be incorporated into the oldest rocks, namely Ca-Al-rich Inclusions (CAIs). The short lifetimes of these radioactivities make them suitable for fine-scaled chronologies in the early Solar System. Among all short-lived radionuclides, I am particularly interested in four isotope systems: 7Be–7Li (t1/2 = 53 days), 10Be–10B (t1/2 = 1.5 Myr), 26Al–26Mg (t1/2 = 0.7 Myr) and 41Ca–41K (t1/2 = 0.1 Myr). The refractory nature, very short half-lives, and diverse nucleosynthetic origins of the parent isotopes mean that they can potentially provide important constraints on the timescales of the formation of the earliest solids and the astrophysical processes that occurred at the very beginning of the Solar System (within the first several million years).
References: Liu, M.-C., McKeegan, K. D., Goswami, J. N., Marhas, K. K., Sahijpal, S., Ireland, T. R., and Davis, A. M. 2009, Isotopic Records in CM Hibonites: Implications for Timescales of Reservoir Mixing in the Solar Nebula. Geochimica et Cosmochimica Acta, 73, 5051-5079
                   Liu, M.-C., Nittler, L. R., Alexander, C. M. O'D and Lee, T. 2010, Lithium-Beryllium-Boron Isotopic Compositions in Meteoritic Hibonite: Implications for Origin of 10Be and Early Solar System Irradiation. The Astrophysical Journal Letters, 719, L99-L103.
                             Liu, M.-C., Chaussidon, M., Gopel, C., and Lee, T. 2012, A Heterogeneous Solar Nebula as Sampled by CM Hibonite. Earth Planetary 
          Science Letters, 327, 75–83.
                  Liu, M.-C., Chaussidon, M., Srinivasanl, G., and McKeegan, K. D. 2012, A Lower Initial Abundance of Short-lived 41Ca in the Early Solar System and Its Implications for Solar System Formation. The Astrophysical Journal, 761, 137.
             Liu, M.-C., 2014, On the Injection of Short-lived Radionuclides from a Supernova into the Solar Nebula: Constraints from the Oxygen Isotopes. The Astrophysical Journal Letters, 781, L28.
Numerical modeling of spallogenic isotopic anomalies
    Besides isotope meausurements with ion microprobes, I am also interested in understanding the spallation effects on stable isotopes. From 10Be records in refractory inclusions (CAIs and hibonites), it is believed that these solids must have suffered intense irradiation in the solar nebula, which might have also affected the isotope abundances of certain elements. However, earlier studies on irradiation-induced nuclear reactions primarily focused on the production of short-lived radionuclides, such as 10Be, 26Al and 41Ca, to explain the observed abundances in meteorites. Very little attention was paid to investigating how stable isotopic compositions in these refractory solids would have been modified by irradiation-induced nuclear reactions. Interestingly, the ion microprobe analyses revealed apparent 26Mg deficits in 26Al-free CM hibonites, for which stellar nucleosynthetic explanations have not been available. Thus, an irradiation model was constructed, with the first goal of assessing whether the observed Mg anomalies are of spallation origin.
References:  Liu, M.-C. and McKeegan, K. D. 2009, On an Irradiation Origin for Magnesium Isotope Anomalies in Meteoritic Hibonite. The Astrophysical Journal Letters, 697, L145-L148.