PubMed Health⌕ Search

Biomedical subjects

J A Liddle

Publications and source records attributed to J A Liddle.

At least 19 recordsLinked to original sources
PubMed2006

Sub-38 nm resolution tabletop microscopy with 13 nm wavelength laser light.

We have acquired images with a spatial resolution better than 38 nm by using a tabletop microscope that combines 13 nm wavelength light from a high-brightness tabletop laser and Fresnel zone plate optics. These results open a gateway to the development of compact and widely available extreme-ultraviolet imaging tools capable of inspecting samples in a variety of environments with a 15-20 nm spatial resolution and a picosecond time resolution.

Journal Article↗
PubMed2006

A silicon-based, sequential coat-and-etch process to fabricate nearly perfect substrate surfaces.

For many thin-film applications substrate imperfections such as particles, pits, scratches, and general roughness, can nucleate film defects which can severely detract from the coating's performance. Previously we developed a coat-and-etch process, termed the ion beam thin film planarization process, to planarize substrate particles up to approximately 70 nm in diameter. The process relied on normal incidence etching; however, such a process induces defects nucleated by substrate pits to grow much larger. We have since developed a coat-and-etch process to planarize approximately 70 nm deep by 70 nm wide substrate pits; it relies on etching at an off-normal incidence angle, i.e., an angle of approximately 470 degrees from the substrate normal. However, a disadvantage of this pit smoothing process is that it induces defects nucleated by substrate particles to grow larger. Combining elements from both processes we have been able to develop a silicon-based, coat-and-etch process to successfully planarize approximately 70 nm substrate particles and pits simultaneously to at or below 1 nm in height; this value is important for applications such as extreme ultraviolet lithography (EUVL) masks. The coat-and-etch process has an added ability to significantly reduce high-spatial frequency roughness, rendering a nearly perfect substrate surface.

Electrochemistry↗
PubMed2005

Nanoimaging with a compact extreme-ultraviolet laser.

Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a free-standing imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology.

Equipment Design↗
PubMed2005

Integration of scanning probes and ion beams.

We report the integration of a scanning force microscope with ion beams. The scanning probe images surface structures non-invasively and aligns the ion beam to regions of interest. The ion beam is transported through a hole in the scanning probe tip. Piezoresistive force sensors allow placement of micromachined cantilevers close to the ion beam lens. Scanning probe imaging and alignment is demonstrated in a vacuum chamber coupled to the ion beam line. Dot arrays are formed by ion implantation in resist layers on silicon samples with dot diameters limited by the hole size in the probe tips of a few hundred nm.

Bismuth↗
PubMed2005

Parallel fabrication of sub-50-nm uniformly sized nanoparticles by deposition through a patterned silicon nitride nanostencil.

Using low-pressure chemical vapor deposition of silicon dioxide, we have reduced the size of 56-nm features in a silicon nitride membrane, called a stencil, down to 36 nm. Sub-50-nm uniformly sized nanoparticles are fabricated by electron-beam deposition of Pt through the stencil mask. A self-assembled monolayer (SAM) of tridecafluoro-1,1,2,2-tetrahydrooctyl-1-trichlorosilane was used to reduce Pt clogging of the nanosize holes during deposition as well as to protect the stencil during the postdeposition Pt removal. X-ray photoelectron spectroscopy shows that the SAM protects the stencil efficiently during this postdeposition removal of Pt.

Electrons↗
PubMed2005

Metal-induced assembly of a semiconductor island lattice: Ge truncated pyramids on Au-patterned Si.

We report the two-dimensional alignment of semiconductor islands using rudimentary metal patterning to control nucleation and growth. In the Ge on Si system, a square array of submicron Au dots on the Si (001) surface induces the assembly of deposited Ge adatoms into an extensive island lattice. Remarkably, these highly ordered Ge islands form between the patterned Au dots and are characterized by a unique truncated pyramidal shape. A model based on patterned diffusion barriers explains the observed ordering and establishes general criteria for the broader applicability of such a directed assembly process to quantum dot ordering.

Journal Article↗
PubMed1987

A laboratory for handling chemical toxicants safely.

The Centers for Disease Control has a special Chemical Toxicant Laboratory (CTL) for handling very hazardous chemicals. It is designed to protect the workers, prevent the release of the chemical toxicant into the surrounding environment, and provide for the scientific integrity of the experiments conducted. A discussion of laboratory ventilation and special containment devices is presented. The design of the CTL, coupled with a realistic set of safety guidelines, provides for the safe conduct of research involving highly toxic chemicals.

Centers for Disease Control and Prevention, U.S.↗
PubMed1986

The laboratory's role in environmental health emergency investigations.

An emergency environmental health investigation of a mass poisoning of unknown origin is a multidiscipline effort that requires the cooperation and close communication of epidemiologists, toxicologists, and chemists. The laboratory's role in this effort is important; special instruments, knowledge, and experience are needed. Our approach to such an investigation is discussed and past cases are used as illustrations. The role of the analytical chemist is presented, and the major resources needed for these investigations are described.

Animals↗
PubMed1983

Contamination of the food chain by polychlorinated biphenyls from a broken transformer.

In 1979, widespread distribution of chicken and egg food products and grease contaminated with polychlorinated biphenyl (PCBs) occurred across the United States and as far away as Canada and Japan. The contamination was traced to an accidental leakage of PCBs from a transformer stored in a hog slaughtering plant in Montana. Breast milk analyses showed the PCB absorption had occurred among egg consumers. The episode illustrates the need for heightened vigilance over the fate of PCBs still in use.

Abattoirs↗
PubMed1983

Gas-liquid chromatographic determination of polychlorinated biphenyls and a selected number of chlorinated hydrocarbons in serum.

A method is proposed for concurrently determining the levels of multiple intact exogenous compounds in serum, particularly polychlorinated biphenyls (PCBs) as Aroclor (AR) 1254 and chlorinated hydrocarbons (CHs). Bovine serum pools containing in vivo-bound PCBs (as AR 1254) and in vitro-spiked CHs are used to evaluate the method, which encompasses serum denaturation with methanol, mixed solvent extraction, multiple solvent fractionation from activated silica gel, and determination by electron capture gas-liquid chromatography. Mean recoveries of the in vitro-spiked 9 CHs at levels of 2.0-29.1 ppb ranged from 52.8 to 98.4% from trial environmental pools; mean recoveries of the in vivo-bound PCBs (as AR 1254) were 114.1 and 92.6% at levels of 10 and 50 ppb, respectively.

Animals↗
PubMed1983

Assessment of methods to determine PCB levels in blood serum: interlaboratory study.

Twenty-five laboratories participated in a study to determine the levels of polychlorinated biphenyls (PCBs) in 3 bovine serum pools, referred to as trial environmental pools (TEPs). TEPs 2 and 3 contained, respectively, low (9.97 ppb) and high (49.64 ppb) levels of PCBs (as in vivo-bound Aroclor 1254) and the same level of 9 commonly occurring chlorinated hydrocarbons. TEP 1 contained only naturally occurring levels of these analytes. Laboratories analyzed each sample in duplicate by the method used in their laboratory for measuring PCBs in blood serum. The coefficients of variation (CV) for the 12 laboratories reporting quantitative data and the required number of analyses for TEP 2 and TEP 3 were 37.0 and 30.7%, respectively. The mean recoveries for these 12 laboratories were 239.3 and 165.4% for TEP 2 and TEP 3, respectively. Three laboratories reported data with mean values for TEP 2 and TEP 3 within +/- 3 standard deviations of the CDC characterized mean. Their coefficients of variation were 12.4 and 18.8% for TEP 2 and TEP 3, respectively. The mean recoveries for these 3 laboratories were 150.7 and 98.4% for TEP 2 and TEP 3, respectively. Our most significant observations were the laboratories' failure to separate PCBs from DDTs and the excessive background of the reagent blanks. The widely discrepant results indicate a definite need to standardize methodology for this analysis.

Animals↗
PubMed1983

Evaluation of potential analytical approach for determination of polychlorinated biphenyls in serum: interlaboratory study.

Forty-four laboratories participated in evaluation of a method for determining polychlorinated biphenyls (PCBs) as AR 1254 in serum at the parts per billion level. The method involves deproteinating serum with methanol, extracting with hexane-ethyl ether, and eluting PCBs from deactivated silica gel for gas-liquid chromatographic determination with electron capture detection. Compounds are quantitated by using the Webb-McCall factors. Five serum pools, 4 containing in vivo-fortified PCBs (as AR 1254) or 8 in vitro-fortified chlorinated hydrocarbons (CHs), or both, were used. For PCB fortification levels of 9.89 (EP 2), 24.74 (EP 3), and 74.20 ppb (EP 4), interlaboratory coefficients of variation (CVs) for collaborators that adhered to protocol were 92.7, 67.6, and 25.8%, respectively. CVs on the same pools analyzed by the Centers for Disease Control (CDC) were 7.4, 7.8, and 4.6%, respectively. Average interlaboratory recoveries for pools EP 2, EP 3, and EP 4 were 138.1, 111.2, and 91.1%, respectively, and 99.8, 89.6, and 90.4%, respectively, for CDC on the same pools. There was a general decrease in the mean error for those laboratories that had participated in an earlier study in which they were allowed to use their own methods.

Animals↗
PubMed1982

Electron-capture, capillary column gas chromatographic determination of low-molecular-weight diols in serum.

Research on alcoholism has revealed that concentrations of 1,2-propanediol, d,1-2,3-butanediol and meso-2,3-butanediol may be greater in the serum of chronic alcoholics than in the serum of social drinkers and nondrinkers. In connection with one of these studies, we developed methodology to determine these diols at the micromolar levels in 500 serum samples. The procedure consisted primarily of extraction of the serum with acetonitrile containing internal standard. The extract was then concentrated to dryness and reacted with p-bromophenylboric acid. The reaction mixture was injected into a gas chromatograph fitted with a capillary column and an electron-capture detector. The total coefficients of variation were best for 1,2-propanediol, 6.82 and 10.00%, and worst for d,1-2,3-butanediol, 13.64 and 19.22%. The observed means for the analytes were all within 10% of the spiked level.

Alcoholism↗
PubMed1982

Evidence of degradation of polybrominated biphenyls in soil samples from Michigan.

Soil samples obtained from the former polybrominated biphenyls (PBB) manufacturing site in Michigan were analyzed by gas chromatography and gas chromatography with mass spectrometric detection. The results indicate significant degradation of the PBB residue in the soil sample. The soil sample with the highest concentration of PBB had the greatest degree of degradation. Principal degradation products include 2,3', 4,4', 5-pentabromobiphenyl, 2,2', 4,4', 5-pentabromobiphenyl and two unidentified tetrabromobiphenyls. The degradation pattern observed supports a photochemical decomposition mechanism. These degraded residues may be more toxic than the original Firemaster residues. The implications of the results are discussed.

Biodegradation, Environmental↗
PubMed1981

Hyperkeratosis induced by sunlight degradation products of the major polybrominated biphenyl in Firemaster.

Sunlight photodegradation of 2,2', 4,4', 5,5' -hexabromobiphenyl, the major component of Firemaster, gave a mixture that produces severe hyperkeratosis of the rabbit ear. This component in its pure state does not cause hyperkeratosis. One or more of the four major photolysis products must be responsible for this activity. A similar photodegradation pattern was observed for 2,2', 3,4,4', 5,5' -heptabromobiphenyl, the second largest component of Firemaster.

Animals↗