Journal
PHYSICAL REVIEW LETTERS
Volume 116, Issue 1, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.116.016602
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Funding
- National Key Basic Research Program of China [2013CBA01604, 2015CB921600, 2012CB932704, 2015CB351900]
- National Natural Science Foundation of China [61325020, 61261160499, 11274154, 61521001, 11274380, 91433103, 61229401]
- Research Grant Council of Hong Kong [SAR N_CUHK405/12]
- MICM Laboratory Foundation [9140C140105140C14070]
- Priority Academic Program Development of Jiangsu Higher Education Institutions
- Jiangsu Shuangchuang program
- Jiangsu Shuangchuang Team Program
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One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the dielectric interface. Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered single-crystalline mono- to tetralayer pentacene crystals are realized by van derWaals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to bandlike in subsequent layers. Such an abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only similar to 3 nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals.
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