Molecular electronics is a developing area of scientific research where long term objectives are to create active molecular devices that act as computing or sensing devices, for example. Over the past 10 years significant progress has been made in the measurement of single molecule electrical properties such as electrical conductance, electronic energy states, and even single molecule vibration spectroscopy using tunneling electrons. The later phenomena, inelastic electron tunneling spectroscopy (IETS), is potentially a very useful sensing method because it provides a vibrational fingerprint of molecules, has single molecule sensitivity, and has the advantage that it is a solid state technique with potential for large scale, low cost manufacturing using microfabrication methods. Arguably, the most successful experiments to date have been carried out using scanning tunneling microscopy methods, which are not practical outside of the laboratory. In this paper, we present a novel approach to IETS sensors using monolithically nanofabricated tunnel junctions grown using atomic layer deposition (ALD). ALD is used to grow the sensing nanoelectrodes and control the tunnel junction spacing from field emission (> 2 nm electrode separation) to direct tunneling (< 2 nm separation). ALD will be shown to be an ideal nanoelectrode growth technique due to the sub-nm growth precision, ultra-clean growth environment (of special importance for electrode materials other than gold), the potential for controlling electrode atomic structure, and the potential for scalability to manufacturing. In-situ electrical measurements during the tunnel junction growth will be presented to show the transition from field emission to direct tunneling, the effects of temperature variation and thermal expansion, and chemical effects due to oxidation of the electrodes. The electrodes will be shown to have several advantages over existing molecular measurement techniques including stability to voltages up to +/-5 V, and insensitivity to vibration. Moreover, the monolithic tunnel junction approach allows molecular trapping experiments to be carried out in real time. Implications for the extension of these devices to monolithic IETS sensors will be discussed.