  Nanomaterials are prone to influence by chemical adsorption because of their
large surface to volume ratios. This enables sensitive detection of adsorbed
chemical species which, in turn, can tune the property of the host material.
Recent studies discovered that single and multilayer molybdenum disulfide
(MoS_2) films are ultra sensitive to several important environmental molecules.
Here we report new findings from ab initio calculations that reveal
substantially enhanced adsorption of NO and NH3 on strained monolyaer MoS2 with
significant impact on the properties of the adsorbates and MoS2 layer. The
magnetic moment of adsobed NO can be turned between 0 and 1 uB, strain also
induces an electronic phase transition between half-metal and metal. Adsorption
of NH3 weakens the MoS2 layer considerably, which explains the large discrepacy
between the experimentally measured strength and breaking strain of MoS2 film
from previous theoretical predictions. On the other hand, adsorption of NO2, CO
and CO2 is insensitive to the strain condition in the MoS2 layer. This
contrasting behavior allows sensitive strain engineering of selective chemical
adsorption on MoS2 with effective tuning of mechanical, electronic and magnetic
properties. These result suggest new design strategies for constructing MoS2
based ultrahigh sensitivity nanoscale sensor and electromechanical devices.
