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Recent studies on nanoscale field-effect sensors reveal the crucial importance of the low frequency noise for determining the ultimate detection limit. In this letter, the 1/f -type noise of Si nanoribbon field-effect sensors is investigated. We demonstrate that the signal-to-noise ratio can be increased by almost two orders of magnitude if the nanoribbon is operated in an optimal gate voltage range. In this case, the additional noise contribution from the contact regions is minimized, and an accuracy of 0.5 ‰ of a pH shift in one Hz bandwidth can be reached. showed that the SNR increases in the subthreshold regime, which is therefore the preferred regime for high sensitivity. However, a more detailed understanding of the noise properties is needed to optimize the SNR across the full operating range of the FET.In the present work, we measure the low-frequency 1/f noise of a dual-gated NR-FET 17,19-21 in ambient and in a buffer solution and determine the resolution limit expressed in a noise equivalent threshold voltage shift δV th , the latter being the measurement quantity in these types of sensors. We identify two regimes which differ in the relative importance of the contact and intrinsic NR resistance. The lowest value in δV th is found when the working point of the NR-FET is adjusted such that the intrinsic NR resistance dominates.In the other case when the contact resistance dominates the noise can be larger by almost two orders of magnitude for nominally the same overall resistance. This result shows the importance of being able to adjust the operating point properly. In the best possible case we determine a resolution limit of 0.5 ‰ of a pH change in one Hz bandwidth, which is comparable to a commercial pH meter (0. This high-yield process provides reproducible, hysteresis-free FETs with the following dimensions: length × width × height = 10 µm × 700 nm × 80 nm (Fig. 1a). A thin Al 2 O 3 layer was deposited on the device to ensure leakage-free operation in an electrolyte solution. In addition, a liquid channel was formed in a photoresist layer, reducing the total area exposed to the electrolyte. which on its own is more strongly capacitively coupled to the liquid than to the back-gate.We refer to the two regimes as contact and NR dominated. The material dependent parameter α accounts for scattering effects and the constant N denotes the number of fluctuators in the system.In Fig. 3, the normalized noise amplitude S V /V Here, we have made use of the relation δG/G = √ S V /V sd .In Fig. 4a we show δV th when the controlling gate is V bg for data measured in air ( ) together with the data acquired in buffer solution at V ref = −0.3 V ( ). Both curves show a very similar behavior. Since we know that the liquid data obtained atcontact dominated, we conclude that the measurement in air is also contact dominated.In Fig. 4b we summarize δV th for measurements done in an electrolyte. To obtain δV th , we consistently use V lg as the controlling gate for all three data sets in this figure. Interestingly, ...

We demonstrate the bottom-up in-situ formation of organometallic oligomer chains at the single-molecule level. The chains are formed using the mechanically controllable break junction technique operated in a liquid environment, and consist of alternating isocyano-terminated benzene monomers coordinated to gold atoms. We show that the chaining process is critically determined by the surface density of molecules. In particular, we demonstrate that by reducing the local supply of molecules within the junction, either by lowering the molecular concentration or by adding side groups, the oligomerization process can be suppressed. Our experimental results are supported by ab-initio simulations, confirming that the isocyano terminating groups display a high tendency to form molecular chains, as a result of their high affinity for gold. Our findings open the road for the controlled formation of one-dimensional, single coordination-polymer chains as promising model systems of organometallic frameworks.

Conducting atomic force microscopy is an attractive approach enabling the correlation of mechanical and electrical properties in individual molecular junctions. Here we report on measurements of gold-gold and gold-octanedithiol-gold junctions. We introduce two-dimensional histograms in the form of scatter plots to better analyze the correlation between force and conductance. In this representation, the junction-forming octanedithiol compounds lead to a very clear step in the force-conductance data, which is not observed for control monothiol compounds. The conductance found for octanedithiols is in agreement with the idea that junction conductance is dominated by a single molecule.

We investigate conductance fluctuations in molecular junctions using a mechanically controllable break junction setup in a liquid environment. In contrast to conventional break junction measurements, time-dependent conductance signals were recorded while reducing the gap size between the two contact electrodes. Only small amplitude fluctuations of the conductance are observed when measuring in pure solvent. Conductance traces recorded in solutions containing alkanedithiols show significantly larger fluctuations which can take the form of random telegraph signals. Such signals emerge in a limited conductance range, which corresponds well to the known molecular conductance of the compounds investigated. These large-amplitude fluctuations are attributed to the formation and thermally driven breaking of bonds between a molecule and a metal electrode and provide a still poorly explored source of information on the dynamics of molecular junctions formation. The lifetimes of the high and low conductance states are found to vary between 0.1 ms and 0.1 s.