A VLSI compatible conducting polymer composite based "electronic nose" chip

The focus of this work would be to exploit the vapor detection technology developed recently at Caltech that forms the basis for a low power, simple "electronic nose". In this work we have integrated the sensors, signal preprocessing, signal processing, and data analysis functions into a single, low power, low cost, "nose chip". Such a device could be implantable covertly or overtly onto suspect sites, deployable through remote delivery methods, worn by soldiers for CW alerts and in principle for IFF or military/nonmilitary identification purposes, and for other areas of national security where low power, lightweight, small, chemical sensing is of importance

Powering the Planet [2007 MRS Spring Meeting Plenary Address]

I am humbled and honored to be here to tell you about a topic that is dear to everyone’s heart — and vital to the future of our planet. My colleague, Richard Smalley, gave a presentation1 on this topic several years ago, at a similar MRS plenary session. Over the last few years of Dr. Smalley’s life, he and I worked together, traveling across our country to deliver a message about a subject that we — like many others, both scientists and lay people — have come to believe is unequivocally the most important technological problem in the world: our global energy future. That is an incredibly powerful statement, one that during the next hour I hope to ably defend

Behavior of Electrodeposited Cd and Pb Schottky Junctions on CH3-Terminated n-Si(111) Surfaces

n-Si/Cd and n-Si/Pb Schottky junctions have been prepared by electrodeposition of Cd or Pb from acidic aqueous solutions onto H-terminated and CH3-terminated n-type Si(111) surfaces. For both nondegenerately (n-) and degenerately (n+-) doped H–Si(111) electrodes, Cd and Pb were readily electroplated and oxidatively stripped, consistent with a small barrier height (Phib) at the Si/solution and the Si/metal junctions. Electrodeposition of Cd or Pb onto degenerately doped CH3-terminated n+-Si(111) electrodes occurred at the same potentials as Cd or Pd electrodeposition onto H-terminated n+-Si(111). However, electrodeposition on nondegenerately doped CH3-terminated n-Si(111) surfaces was significantly shifted to more negative applied potentials (by −130 and −347 mV, respectively), and the anodic stripping of the electrodeposited metals was severely attenuated, indicating large values of Phib for contacts on nondegenerately doped n-type CH3–Si(111) surfaces. With either Cd or Pb, current–voltage measurements on the dry, electrodeposited Schottky junctions indicated that much larger values of Phib were obtained on CH3-terminated n-Si(111) surfaces than on H-terminated n-Si(111) surfaces. Chronoamperometric data indicated that CH3–Si(111) surfaces possessed an order-of-magnitude lower density of nucleation sites for metal electrodeposition than did H–Si(111) surfaces, attesting to the high degree of structural passivation afforded by the CH3–Si surface modification

Studies of silicon photoelectrochemical cells under high injection conditions

The behavior of Si/CH3OH-dimethylferrocene+/0 junctions has been investigated under high injection conditions. Open circuit voltages of (626±5) mV were obtained at short circuit photocurrent densities of 20 mA/cm^2 for samples with an n + -diffused back region, point contacts on the back surface, and with a base of thickness 390 µm and a 1 ms hole lifetime. The diode quality factor and recombination current density were 1.8±0.1 and (2.6±1.5)×10–8 A/cm^2, respectively. These data are consistent with recombination dominated by the base and back contact regions, and not at the Si/CH3OH interface

Proton exchange membrane electrolysis sustained by water vapor

The current–voltage characteristics of a proton exchange membrane (PEM) electrolyzer constructed with an IrRuOx water oxidation catalyst and a Pt black water reduction catalyst, under operation with water vapor from a humidified carrier gas, have been investigated as a function of the gas flow rate, the relative humidity, and the presence of oxygen. The performance of the system with water vapor was also compared to the performance when the device was immersed in liquid water. With a humidified Ar(g) input stream at 20 °C, an electrolysis current density of 10 mA cm^(−2) was sustained at an applied voltage of ~ 1.6 V, with a current density of 20 mA cm^(−2) observed at ~ 1.7 V. In the system evaluated, at current densities >40 mA cm^(−2) the electrolysis of water vapor was limited by the mass flux of water to the PEM. At <40 mA cm^(−2), the electrolysis of water vapor supported a given current density at a lower applied bias than did the electrolysis of liquid water. The relative humidity of the input carrier gas strongly affected the current–voltage behavior, with lower electrolysis current density attributed to dehydration of the PEM at reduced humidity values. The results provide a proof-of-concept that, with sufficiently active catalysts, an efficient solar photoelectrolyzer could be operated only with water vapor as the feedstock, even at the low operating temperatures that may result in the absence of active heating. This approach therefore offers a route to avoid the light attenuation and mass transport limitations that are associated with bubble formation in these systems

Transmission Infrared Spectra of CH_3-, CD_3-, and C_(10)H_(21)-Ge(111) Surfaces

The surface chemistry of CH_3–, CD_3–, and C_(10)H_(21)–Ge(111) surfaces prepared through a bromination/alkylation method have been investigated by infrared spectroscopy. Well-ordered CH_3–Ge(111) surfaces could be prepared only if, prior to bromination, the surface was etched with 6.0 M HCl or with a two-step etch of H_2O_2 (1.5 M)/HF (5.1 M) followed by a short HF (6.0 M) etch. The etching method used to make the Ge precursor surface, and the formation of a bromine-terminated intermediate Ge surface, were of critical importance to obtain clear, unambiguous infrared absorption peaks on the methyl-terminated Ge surfaces. Polarization-dependent absorption peaks observed at 1232 cm^(–1) for CH_3–Ge(111) surfaces and at 951 cm^(–1) for CD_3–Ge(111) surfaces were assigned to the methyl “umbrella” vibrational mode. A polarization-dependent peak at 2121 cm^(–1) for CD_3–Ge(111) surfaces was assigned to the symmetric methyl stretching mode. Polarization-independent absorption peaks at 755 cm^(–1) for CH_3–Ge(111) and at 577 cm^(–1) for CD_3–Ge(111) were assigned to the methyl rocking mode. These findings provide spectroscopic evidence that the methyl monolayer structure on the alkylated Ge is well-ordered and similar to that on analogous Si(111) surfaces, despite differences in the composition of the precursor surfaces. The X-ray photoelectron spectra of CH_3–Ge(111) surfaces, however, were not highly dependent upon the etching method and showed a constant C 1s:Ge 3d ratio, independent of the etching method. The infrared spectra of C_(10)H_(21)–Ge(111) surfaces were also not sensitive to the initial etching method. Hence, while the final packing density of the alkyl groups on the surface was similar for all etch methods studied, not all methods yielded a well-ordered Ge(111)/overlayer interface

Chemical, Electronic, and Electrical Properties of Alkylated Ge(111) Surfaces

The use of Ge in semiconductor electronics has been constrained by the lack of a simple method of passivating the crystal surface. Toward that end, we have explored the utility of chemically bonded hydrocarbon monolayers. Alkylated Ge(111) surfaces have been prepared by addition of 1-alkenes to the H-terminated Ge(111) surface as well as by a two-step halogenation/alkylation procedure. The chemical compositions of the resulting methyl-, ethyl-, and decyl-terminated surfaces have been evaluated using X-ray photoelectron spectroscopy (XPS). Thermal addition of 1-decene produced hydrophobic surfaces with 0.3 ± 0.1 monolayer of Ge oxide detected by XPS, whereas no oxide was observed on the methyl-, ethyl-, or decyl-terminated surfaces that were prepared using the two-step halogenation/alkylation method. Methyl-terminated Ge(111) surfaces prepared by the two-step method displayed a well-resolved C 1s XPS peak at a binding energy of 284 eV, consistent with carbon bonded to a less electronegative element such as Ge. The electronic properties of all of the alkylated surfaces were characterized by measurements of the surface recombination velocity as a function of an externally applied gate voltage. Treatment of HF-etched Ge(111) surfaces with Br2 vapor, followed by reaction with alkylmagnesium or alkyllithium reagents, yielded air-stable surfaces that had surface recombination velocities of 100 cm s^(−1) or less under flat-band conditions. The field-dependent surface recombination velocity experiments indicated that, in contact with air, methyl-terminated n-type Ge(111) samples had a negative surface potential approaching 300 mV, in contrast to the oxidized Ge(111) surface, which exhibited a strongly positive surface potential under the same conditions. Mercury contacts to n-type methyl-, ethyl-, or decyl-terminated Ge(111) substrates that were alkylated using the two-step method formed rectifying junctions with barrier heights of 0.6 ± 0.1 eV, whereas no measurable rectification was observed for Hg contacts to p-type Ge(111) substrates that were alkylated by the two-step method, to n-type Ge(111) substrates that were alkylated through addition of 1-decene, or to oxidized n-type Ge(111) samples

Scanning tunneling microscopy studies of monolayer templates: alkylthioethers and alkylethers

Scanning tunneling microscopy has been used to determine the molecular ordering in stable, ordered monolayers formed from long-chain normal and substituted alkanes in solution on highly oriented pyrolytic graphite surfaces. Monolayers were initially formed using an overlying solution of either a symmetrical dialkylthioether or a symmetrical dialkylether. Initially pure thioether solutions were then changed to nearly pure solutions of the identical chain-length ether, and vice versa. The direct application of a pure solution of long-chain symmetrical ethers onto graphite produced a lamellate monolayer within which the individual molecular axes were oriented at an angle of ~65° to the lamellar axes. In contrast, a pure solution of long-chain symmetrical thioethers on graphite produced a monolayer within which the molecular axes were oriented perpendicular to the lamellar axes. When ethers were gradually added to solutions overlying pure thioether monolayers, the ethers substituted into the existing monolayer structure. Thus, the ether molecules could be forced to orient in the perpendicular thioether-like manner through the use of a thioether template monolayer. Continued addition of ethers to the solution ultimately produced a nearly pure ether monolayer that retained the orientation of the thioether monolayer template. However, a monolayer of thioether molecules formed by gradual substitution into an ether monolayer did not retain the 65° orientation typical of dialkylethers, but exhibited the 90° orientation typical of dialkylthioether monolayers. The thioethers and ethers were easily distinguished in images of mixed monolayers, allowing both an analysis of the distribution of the molecules within the mixed monolayers and a comparison of the monolayer compositions with those of the overlying solutions. Substitution of molecules into the template monolayer did not proceed randomly; instead, a molecule within a monolayer was more likely to be replaced by a molecule in the overlying solution if it was located next to a molecule that had already been replaced

Aspects of science and technology in support of legal and policy frameworks associated with a global carbon emissions-control regime

The delegates to COP21 in Paris, in conjunction with nationally formulated commitments and pledges, resolved that countries should take actions to “hold the increase in global temperature to well below 2 °C above pre-industrial levels” and to achieve “a balance between anthropogenic emissions by sources and removal by sinks of greenhouse gases in the second half of this century”. This resolution for action suggests a step towards a global carbon emissions-control regime which, due to regional variabilities and remaining uncertainties as to the exact effects of atmospheric CO_2 concentrations, must be considered within the purview of risk management. In this Opinion, four topics are discussed that intertwine science, technology, legal, and policy issues critical to the implementation of any global carbon emissions-control regime: (i) What to regulate and at what levels; (ii) Regulating short-term versus long-term emissions; (iii) Validation of compliance in a regulated global emissions regime; and, (iv) Legal aspects of geoengineering