Electron nanoprobe induced oxidation: a simulation of direct-write purification.

Electron beam direct-write has recently taken a large step forward with the advent of methods to purify deposits. This development has opened the door for future direct-write device prototyping and editing. In one such approach, an additional beam scanning procedure removes carbonaceous impurities via oxidation from metal-carbon deposits (e.g., PtC5) in the presence of H2O or O2 after deposition. So far, critical aspects of the oxidation reaction remain unclear; experiments reveal clearly that electron stimulated oxidation drives the process yet it is not understood why H2O purifies by a bottom-up mechanism while O2 purifies from the top-down. The simulation results presented here suggest that the chemisorption of dissolved O2 at buried Pt nanoparticle surfaces controls purification in the top-down case while both the high relative solubility coupled with weak physisorption of H2O explains the bottom-up process. Crucial too is the role that the carbonaceous contaminant itself has on the dissolution and diffusion of O2 and H2O. These results pave the way for simulation driven experiments where (1) the transient densification of the deposit can be accounted for in the initial deposit design stage and (2) the deposition and purification steps can be combined.

Pulsed laser-assisted focused electron-beam-induced etching of titanium with XeF2: enhanced reaction rate and precursor transport.

In order to enhance the etch rate of electron-beam-induced etching, we introduce a laser-assisted focused electron-beam-induced etching (LA-FEBIE) process which is a versatile, direct write nanofabrication method that allows nanoscale patterning and editing. The results demonstrate that the titanium electron stimulated etch rate via the XeF2 precursor can be enhanced up to a factor of 6 times with an intermittent pulsed laser assist. The evolution of the etching process is correlated to in situ stage current measurements and scanning electron micrographs as a function of time. The increased etch rate is attributed to photothermally enhanced Ti-F reaction and TiF4 desorption and in some regimes enhanced XeF2 surface diffusion to the reaction zone.

Some new techniques for applying the housing unit method of local population estimation: further evidence.

The housing unit method of population estimation is often characterized as being imprecise and having an upward bias. In an earlier paper we argued that the method itself cannot be properly characterized by a particular level of precision or direction of bias. Only specific techniques of applying the method can have such characteristics. In that paper we presented several new techniques for estimating the number of households and average number of persons per household (PPH). However, the testing of these new techniques was limited by the lack of census results against which the estimates could be compared. Complete census data on population, households, and PPH are now available and can be used to test alternate estimation techniques. In this paper we replicate the tests reported in our earlier paper using 1980 census data for Florida's 67 counties. These tests provide further evidence that the new techniques produce more precise, less biased estimates than previously used techniques.

Formaldehyde in dentistry: a review of mutagenic and carcinogenic potential.

For many years there has been controversy over the value of antimicrobial drugs for intracanal dressings in endodontics. Formocresol, a formaldehyde compound, has evolved as the preferred drug for routine endodontic procedures, as well as pediatric endodontics. The increase in the use of formaldehyde has been complicated by the introduction of paraformaldehyde pastes for filling root canals. Neither of these formulas has ever been standardized. The doses are arbitrary, and the common dose of formocresol has been shown to be many times greater than the minimum dose needed for effect. The efficacy of paraformaldehyde pastes is questionable and remains clouded by inconclusive evidence, conflicting research, inadequate terminology, and a lack of convincing statistical evidence. The clinical use and delivery of formocresol and paraformaldehyde pastes remain arbitrary and unscientific. Formaldehyde has a known toxic mutagenic and carcinogenic potential. Many investigations have been conducted to measure the risk of exposure to formaldehyde; it is clear that formaldehyde poses a carcinogenic risk in humans. There is a need to reevaluate the rationale underlying the use of formaldehyde in dentistry particularly in light of its deleterious effects.

Some new techniques for applying the housing unit method of local population estimation.

The housing unit method of population estimation is often characterized as being imprecise and having an upward bias. We believe that the method itself cannot properly be characterized by a particular level of precision or direction of bias. Only specific techniques of applying the method can have such characteristics. In this paper we discuss several new techniques we have developed for estimating households and the average number of persons per household. Estimates produced by these techniques are compared to estimates produced by several other techniques. Special census results from Florida provide preliminary evidence that the new techniques produce more precise, less biased estimates than the other techniques.