  Pairs of electrodes with nanometer separation (nano-gap) are achieved through
an electromigration-induced break-junction (EIBJ) technique at room
temperature. Lithographically defined gold (Au) wires are formed by e-beam
evaporation over oxide coated silicon substrates silanized with
(3-Mercaptopropyl)trimethoxysilane (MPTMS) and then subjected to
electromigration at room temperature to create a nanometer scale gap between
the two newly formed Au electrodes. The Si-O-Si covalent bond at the SiO$_2$
surface and the Au-sulphur (Au-S) bond at the top evaporated Au side, makes
MPTMS as an efficient adhesive monolayer between SiO$_2$ and Au. Although the
Au wires are initially 2$\mu$m wide, gaps with length $\sim$1nm and width
$\sim$5nm are observed after breaking and imaging through a field effect
scanning electron microscope (FESEM). This technique eliminates the presence of
any residual metal interlink in the adhesion layer (chromium or titanium for Au
deposition over SiO$_2$) after breaking the gold wire and it is much easier to
implement than the commonly used low temperature EIBJ technique which needs to
be executed at 4.2 K. Metal-molecule-metal structures with symmetrical
metal-molecule contacts at both ends of the molecule, are fabricated by forming
a self-assembled monolayer of -dithiol molecules between the EIBJ created Au
electrodes with nanometer separation. Electrical conduction through single
molecules of 1,4-Benzenedimethanethiol (XYL) is tested using the Au/XYL/Au
structure with chemisorbed gold-sulfur (Au-S) coupling at both contacts.
