Irving P. Herman

Cerium oxide nanoparticles: Size-selective formation and structure analysis

Nanoparticles of cerium oxide with a narrow size distribution (±15%) are prepared by mixing cerium nitrate solution with an ammonium reagent. High-resolution transmission electron microscopy (TEM) indicates that over 99% of the synthesized particles are single crystals. TEM and photon absorption are used to monitor particle size. The lattice parameter increases up to 0.45% as the particle size decreases to 6 nm, as observed with x-ray diffraction. Raman spectra also suggest the particle-size effect and concomitant lattice expansion. The lattice expansion can be explained by increased concentrations of point defects with decreasing particle size.

Raman analysis of light‐emitting porous silicon

Porous silicon that strongly emits in the visible was analyzed using Raman scattering. The spectrum peaks near 508 cm−1, has a width of ∼40 cm−1, and is very asymmetric. Using a model of phonon confinement, this suggests that the local structure of porous silicon is more like a sphere than a rod and has a characteristic diameter of 2.5–3.0 nm. Polarization Raman measurements suggest that the structure does not consist of a series of parallel columns.

Raman Analysis of Mode Softening in Nanoparticle CeO2−δ and Au-CeO2−δ during CO Oxidation

Oxygen vacancy levels are monitored during the oxidation of CO by CeO(2-δ) nanorods and Au-CeO(2-δ) nanorods, nanocubes, and nanopolyhedra by using Raman scattering. The first-order CeO(2) F(2g) peak near 460 cm(-1) decreases when this reaction is fast (fast reduction and relatively slow reoxidation of the surface), because of the lattice expansion that occurs when Ce(3+) replaces Ce(4+) during oxygen vacancy creation. This shift correlates with reactivity for CO oxidation. Increases in the oxygen deficit δ as large as ~0.04 are measured relative to conditions when the ceria is not reduced.

Diagnostics of inductively coupled chlorine plasmas: Measurement of Cl2 and Cl number densities

The absolute densities of positive ions (Cl2+ and Cl+) are obtained over a 2–20 mTorr pressure range and 5–1000 W input radio-frequency rf power range in a transformer-coupled Cl2 plasma. The relative number density of Cl2+ is measured by laser-induced fluorescence. These laser-induced fluorescence data are calibrated by Langmuir-probe measurements of total positive-ion density at low powers to yield absolute values for nCl2+ and are corrected for changes in rotational temperature with rf power. In turn, the nCl2+ data are used to determine the effective-mass correction for refined Langmuir-probe measurements of the total positive-ion density. The density of Cl+ is then the difference between the total positive-ion and Cl2+ densities. For all the pressures, Cl2+ is found to be the dominant ion in the capacitively coupled regime (input powers below 100 W), while Cl+ is the dominant ion at higher powers (>300 W) of the inductively coupled regime. Experimental results are compared to those from a simple glob...

Wafer‐scale laser pantography: Fabrication of n‐metal‐oxide‐semiconductor transistors and small‐scale integrated circuits by direct‐write laser‐induced pyrolytic reactions

A complete set of processes sufficient for manufacture of n‐metal‐oxide‐semiconductor (n‐MOS) transistors by a laser‐induced direct‐write process has been demonstrated separately, and integrated to yield functional transistors. Gates and interconnects were fabricated of various combinations of n‐doped and intrinsic polysilicon, tungsten, and tungsten silicide compounds. Both 0.1‐μm and 1‐μm‐thick gate oxides were micromachined with and without etchant gas, and the exposed p‐Si [100] substrate was cleaned and, at times, etched. Diffusion regions were doped by laser‐induced pyrolytic decomposition of phosphine followed by laser annealing. Along with the successful manufacture of working n‐MOS transistors and a set of elementary digital logic gates, this letter reports the successful use of several laser‐induced surface reactions that have not been reported previously.

Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties

Advanced applications for high k dielectric and ferroelectric materials in the electronics industry continues to demand an understanding of the underlying physics in decreasing dimensions into the nanoscale. We report the synthesis, processing, and electrical characterization of thin (<100nm thick) nanostructured thin films of barium titanate (BaTiO3) built from uniform nanoparticles (<20nm in diameter). We introduce a form of processing as a step toward the ability to prepare textured films based on assembly of nanoparticles. Essential to this approach is an understanding of the nanoparticle as a building block, combined with an ability to integrate them into thin films that have uniform and characteristic electrical properties. Our method offers a versatile means of preparing BaTiO3 nanocrystals, which can be used as a basis for micropatterned or continuous BaTiO3 nanocrystal thin films. We observe the BaTiO3 nanocrystals crystallize with evidence of tetragonality. We investigated the preparation of wel...

Deuterium separation at high pressure by nanosecond CO2 laser multiple‐photon dissociation

Photochemical deuterium separation is evaluated at pressures up to 1 atm using 2 ns duration CO2 laser pulses to achieve multiple‐photon dissociation (MPD) as the isotopic separation step. Photochemical performance is compared for Freon 123 (2,2‐dichloro‐1,1,1‐trifluoroethane), difluoromethane, and trifluoromethane based on deuterium optical selectivity in absorption, photoproduct yield, and single‐step deuterium enrichment factor. The absorption coefficient versus energy fluence is measured from 0.01 to 3 J/cm2 fluence for CF3CDCl2, CDF3, and CHDF2; added buffer gas results in an order‐of‐magnitude increase in the CDF3 absorption coefficient. The deuterium optical selectivity in absorption at 0.5 J/cm2 fluence with added buffer is 80 for CF3CDCl2 at 10.65 μ, 800 for CHDF2 at 10.48 μ, and 2500 for CDF3 at 10.21 μ. The absorption coefficients and hence optical isotopic selectivities are dependent on fluence, and the optical selectivity attains a maximum value of 8000 for CDF3 below 0.01 J/cm2 fluence. The ...

The qualitative effects of laser irradiation on human arteriosclerotic disease

To determine the effects of laser irradiation upon human coronary atherosclerotic disease, coronary plaques were extracted from fresh human cadaver hearts. Seventy-four diseased artery samples were sectioned either transversely or longitudinally and subjected to laser treatment from argon-ion and carbon dioxide sources. The laser beam affected vaporization and patency in fibrous, lipoid, and calcified plaques as observed histologically. Calcified blockage showed greater extent of charred remnants following controlled thermal injury than did fibrous or lipoid obstructions. The area and depth of penetration varied directly with intensity and duration of photoirradiation and inversely with the density of the atherosclerotic tissue. This study supports further research work on the use of lasers to effect relief of atherosclerotic obstructions.

Electrodeposition of patterned CdSe nanocrystal films using thermally charged nanocrystals

A dc electric field is used to attract charged CdSe nanocrystals in hexane to rapidly form very smooth, robust, large-area, several micron-thick films of equal thickness on both electrodes. This deposition on both electrodes implies there are both positively and negatively thermally charged dots, unlike conventional electrophoretic deposition. With patterned electrodes, controllable and locally selective assembly is achieved.

In situ pulsed laser‐induced thermal desorption studies of the silicon chloride surface layer during silicon etching in high density plasmas of Cl2 and Cl2/O2 mixtures

We have used laser‐induced thermal desorption, combined with laser‐induced fluorescence of SiCl(g) to study, in real time, the Si‐chloride (SiClx(ads)) layer that is present on the surface during Si etching in a high‐plasma density, low pressure Cl2 helical resonator plasma. The SiClx(ads) layer that builds up during etching contains about twice as much Cl as the saturated layer that forms when Si is exposed to Cl2 gas. By varying the laser repetition rate we determined that the surface is chlorinated with an apparent first‐order time constant of ∼6 ms at 1.0 mTorr, and 20 ms at 0.3 mTorr. Therefore in the plasma at pressures above ∼0.5 mTorr, the SiClx(ads) layer reaches saturated coverage on a time scale that is short compared to the time required to etch one monolayer (40 ms). From the weak dependence of the SiClx(ads) layer coverage on discharge power (0.2–1 W/cm3), substrate bias voltage (from 0 to −50 V dc), and pressure (0.5–10 mTorr), we conclude that ion flux, and not neutral etchant flux (i.e., ...