  Two-dimensional crystals, single sheets of layered materials, often show
distinct properties desired for optoelectronic applications, such as larger and
direct band gaps, valley- and spinorbit effects. Being atomically thin, the low
amount of material is a bottleneck in photophysical and photochemical
applications. Here, we propose the formation of stacks of two-dimensional
crystals intercalated with small surfactant molecules. We show, using first
principles calculations, that already the very short surfactant methyl amine
electronically decouples the layers. We demonstrate the indirect-direct band
gap transition characteristic for Group 6 transition metal dichalcogenides
experimentally by observing the emergence of a strong photoluminescence signal
for ethoxide-intercalated WSe2 and MoSe2 multilayered nanoparticles with
lateral size of about 10 nm and beyond. The proposed hybrid materials offer the
highest possible density of the two-dimensional crystals with electronic
properties typical for monolayers. Variation of the surfactant's chemical
potential allows fine-tuning of electronic properties and potentially
elimination of trap states caused by defects.
