Inelastic electron tunneling spectroscopy for molecular detection

Inelastic electron tunneling spectroscopy (IETS) [R. C. Jaklevic and J. Lambe, Phys. Rev. Lett. 17, 1139 (1966); R. G. Keil et al., Appl. Spectrosc. 30, 1 (1976); K. W. Hipps and U. Mazur, J. Phys. Chem. 97, 7803 (1993); U. Mazur et al., Anal. Chem. 64, 1845 (1992); P. K. Hansma, Tunneling Spectroscopy (Plenum, New York, 1982)] measurements are performed on Si nanowire (NW)/SiO2/Al NW tunnel junctions. The tunnel junction area is 50 120 nm and tunneling occurs across a 10 nm thick SiO2 layer. IETS measurements are performed at 300 K for ammonium hydroxide (NH4OH), acetic acid (CH3COOH), and propionic acid (C3H6O2) molecules. The I–V, dI/dV–V, and d2 I/dV2 –V characteristics of the tunnel junction are measured before and after the adsorption of molecules on the junction using vapor treatment or immersion. Peaks can be observed in the d2 I/dV2 –V characteristics in all the cases following molecules adsorption. These peaks may be attributed to vibrational modes of N–H and C–H bonds

A philosophical context for methods to estimate origin-destination trip matrices using link counts.

This paper creates a philosophical structure for classifying methods which estimate origin-destination matrices using link counts. It is claimed that the motivation for doing so is to help real-life transport planners use matrix estimation methods effectively, especially in terms of trading-off observational data with prior subjective input (typically referred to as 'professional judgement'). The paper lists a number of applications that require such methods, differentiating between relatively simple and highly complex applications. It is argued that a sound philosophical perspective is particularly important for estimating trip matrices in the latter type of application. As a result of this argument, a classification structure is built up through using concepts of realism, subjectivity, empiricism and rationalism. Emphasis is put on the fact that, in typical transport planning applications, none of these concepts is useful in its extreme form. The structure is then used to make a review of methods for estimating trip matrices using link counts, covering material published over the past 30 years. The paper concludes by making recommendations, both philosophical and methodological, concerning both practical applications and further research

Single-electron and quantum confinement limits in length-scaled silicon nanowires

Quantum-effects will play an important role in both future CMOS and 'beyond CMOS' technologies. By comparing single-electron transistors formed in un-patterned, uniform-width silicon nanowire (SiNW) devices with core widths from ~5–40 nm, and gated lengths of 1 μm and ~50 nm, we show conditions under which these effects become significant. Coulomb blockade drain–source current–voltage characteristics, and single-electron current oscillations with gate voltage have been observed at room temperature. Detailed electrical characteristics have been measured from 8–300 K. We show that while shortening the nanowire gate length to 50 nm reduces the likelihood of quantum dots to only a few, it increases their influence on the electrical characteristics. This highlights explicitly both the significance of quantum effects for understanding the electrical performance of nominally 'classical' SiNW devices and also their potential for new quantum effect 'beyond CMOS' devices

High ON/OFF ratio and multimode transport in silicon nanochains field effect transistors

We have observed multimode transport and high ON/OFF ratio in silicon nanochain devices. Silicon nanochains grown by thermal evaporation of SiO solid sources consisted of chains of silicon nanocrystals ~10 nm in diameter, separated by SiO2 regions. The devices were fabricated using electron beam lithography on SiO2 thermally grown on silicon substrate. These devices exhibited high ON/OFF current ratio up to 104. The inverse subthreshold slope as small as ~500 mV/decade was observed in these devices. Therefore, we believe silicon nanochains hold great potential to be used in field effect transistors