Controlled modulation of conductance in silicon devices by molecular monolayers

We have controllably modulated the drain current (I(D)) and threshold voltage (V(T)) in pseudo metal-oxide-semiconductor field-effect transistors (MOSFETs) by grafting a monolayer of molecules atop oxide-free H-passivated silicon surfaces. An electronically controlled series of molecules, from strong pi-electron donors to strong pi-electron acceptors, was covalently attached onto the channel region of the transistors. The device conductance was thus systematically tuned in accordance with the electron-donating ability of the grafted molecules, which is attributed to the charge transfer between the device channel and the molecules. This surface grafting protocol might serve as a useful method for controlling electronic characteristics in small silicon devices at future technology nodes.     

Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices

The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques.     

Ultrafast site-specific fluorescence quenching of 2-aminopurine in a DNA hairpin studied by femtosecond down-conversion

The ΔP(-)PBS analog of the DNA primary binding sequence (PBS) of the HIV-1 genome labeled at different positions by 2-aminopurine (2-AP) is investigated by a novel femtosecond fluorescence down-conversion experiment with 0.3-ps time resolution. The high signal-to-noise ratio of the fluorescence kinetics makes it possible to reveal four distinct decay times ranging from 0.8 ps to 2-3 ns for all the three labeling positions. This suggests the existence of at least four different quenching conformations of 2-AP with its nearest neighbors, and underscores the structural heterogeneity of the loop region of ΔP(-)PBS. Sub-5-ps components are found and attributed to stacking interactions of 2-AP with the flanking guanine (G) side chains, consistent with the NMR structure of ΔP(-)PBS. The observation of a significant increase of their total amplitude when 2-AP is positioned close to the rigid 3'-half of the G-rich stem gives further support to this assignment. Only a minor portion of conformations involves slow nanosecond collisional quenching.     

Recent progress on nanovehicles

Nanovehicles are a new class of molecular machines consisting of a molecular scale chassis, axles, and wheels, that can roll across solid surfaces with structurally defined directions making them of interest to synthetic chemists, surface scientists, chemical engineers, and the general car enthusiast. In this tutorial review, following a brief introduction to the development of nanomachines, our recent progress on the nanovehicle project is presented including the design, synthesis, and testing of a series of nanocars, nanotrucks, and motorized nanocars.     

A study of the formation, purification and application as a SWNT growth catalyst of the nanocluster [HxPMo12O40[subset]H4Mo72Fe30(O2CMe)15O254(H2O)98

The synthetic conditions for the isolation of the iron-molybdenum nanocluster FeMoC [HxPMo12O40 [subset]H4Mo72Fe30(O2CMe)15O254(H2O)98], along with its application as a catalyst precursor for VLS growth of SWNTs have been studied. As-prepared FeMoC is contaminated with the Keplerate cage [H4Mo72Fe30(O2CMe)15O254(H2O)98] without the Keggin [HxPMo12O40]n- template, however, isolation of pure FeMoC may be accomplished by Soxhlet extraction with EtOH. The resulting EtOH solvate is consistent with the replacement of the water ligands coordinated to Fe being substituted by EtOH. FeMoC-EtOH has been characterized by IR, UV-vis spectroscopy, MS, XPS and 31P NMR. The solid-state 31P NMR spectrum for FeMoC-EtOH (delta-5.3 ppm) suggests little effect of the paramagnetic Fe3+ centers in the Keplerate cage on the Keggin ion's phosphorous. The high chemical shift anisotropy, and calculated T1 (35 ms) and T2 (8 ms) values are consistent with a weak magnetic interaction between the Keggin ion's phosphorus symmetrically located within the Keplerate cage. Increasing the FeCl2 concentration and decreasing the pH of the reaction mixture optimizes the yield of FeMoC. The solubility and stability of FeMoC in H2O and MeOH-H2O is investigated. The TGA of FeMoC-EtOH under air, Ar and H2 (in combination with XPS) shows that upon thermolysis the resulting Fe : Mo ratio is highly dependent on the reaction atmosphere: thermolysis in air results in significant loss of volatile molybdenum components. Pure FeMoC-EtOH is found to be essentially inactive as a pre-catalyst for the VLS growth of single-walled carbon nanotubes (SWNTs) irrespective of the substrate or reaction conditions. However, reaction of FeMoC with pyrazine (pyz) results in the formation of aggregates that are found to be active catalysts for the growth of SWNTs. Activation of FeMoC may also be accomplished by the addition of excess iron. The observation of prior work's reported growth of SWNTs from FeMoC is discussed with respect to these results.     

Integral resource capacity planning for inpatient care services based on bed census predictions by hour

The design and operations of inpatient care facilities are typically largely historically shaped. A better match with the changing environment is often possible, and even inevitable due to the pressure on hospital budgets. Effectively organizing inpatient care requires simultaneous consideration of several interrelated planning issues. Also, coordination with upstream departments like the operating theatre and the emergency department is much-needed. We present a generic analytical approach to predict bed census on nursing wards by hour, as a function of the Master Surgical Schedule and arrival patterns of emergency patients. Along these predictions, insight is gained on the impact of strategic (ie, case mix, care unit size, care unit partitioning), tactical (ie, allocation of operating room time, misplacement rules), and operational decisions (ie, time of admission/discharge). The method is used in the Academic Medical Center Amsterdam as a decision-support tool in a complete redesign of the inpatient care operations.