Thomas N. Blanton

Epitaxial LiTaO3 thin films by pulsed laser deposition

Epitaxial LiTaO3 thin films having excellent crystalline properties have been achieved on (0001)‐sapphire substrates using the technique of pulsed laser deposition. X‐ray diffraction analysis revealed that completely single‐phase c‐oriented LiTaO3 films were produced. X‐ray rocking curve analysis showed that the range of misalignment of the c‐axis direction was about 0.2°. Ion channeling studies indicated a minimum backscattering yield of only 4.9%. Channeling also revealed an improvement in crystalline perfection as a function of distance above the interface with the sapphire substrate. Optical waveguiding with losses on the order of 1 dB/cm was demonstrated.

Epitaxial growth of MgO on (100)GaAs using ultrahigh vacuum electron‐beam evaporation

Epitaxial layers of MgO grown on (NH4)xS‐treated (100)GaAs substrates were prepared by electron‐beam evaporation in an ultrahigh vacuum system without introducing additional oxygen. The films deposited at 500 °C were found to grow with stoichiometric composition and have (110) planar orientation. X‐ray pole‐figure analysis showed that the [110] direction in the MgO(110) plane is parallel to the [011] direction in the GaAs(100) plane with a 4: 3 coincident site lattice. The film surface was smooth with no signs of structural defects or microcracks.

Epitaxial growth of lithium niobate thin films from a single‐source organometallic precursor using metalorganic chemical vapor deposition

Lithium niobate thin films were deposited on (0001) sapphire using metalorganic chemical vapor deposition. An organometallic compound, formed by reaction of lithium dipivaloylmethanate and niobium(V) ethoxide, was used as a single‐source precursor. The epitaxial nature of the films was established by x‐ray diffraction and Rutherford backscattering analyses (RBS).

Preparation of silver behenate coatings to provide low- to mid-angle diffraction calibration

A method for the preparation of a well aligned silver behenate sample is described. Multiple (0 0 l) diffraction peaks, (0 0 1) to (0 0 48), are easily observed using a conventional laboratory X-ray diffraction instrument.

X-ray diffraction characterization of polymer intercalated graphite oxide

Graphite oxide (GO) is generated by treating graphite with strong oxidizers. GO retains the structure of graphite, but does so with a larger and irregular basal plane spacing. The oxidation of graphite results in the formation of epoxide groups, as well as C–OH and COOH groups. It is the presence of some of these moieties that allows GO to be dispersed in water, allowing for its use in waterborne formulations. Although GO does not possess the electrical properties of single-sheet graphene, it can be swelled in water, which allows for intercalation of hydrophilic polymer between GO sheets, resulting in a composite that can be coated to produce a continuous film. After coating it may be possible to chemically convert GO to a reduced graphite oxide (r-GO) with improved electrical conductivity. X-ray diffraction (XRD) is ideally suited to evaluate GO–polymer composite samples for evidence of intercalation or exfoliation of GO. Examples of GO–polymer analysis by XRD are presented, along with results that demonstrate the effect of relative humidity (RH) on neat GO. Knowing the ambient RH during XRD data collection was found to be important to correctly assess the extent of polymer intercalation within the GO lattice.

Characterization of proton exchange lithium niobate waveguides

Proton exchanged samples of LiNbO3 have been profiled by micro‐Raman spectroscopy, secondary ion mass spectroscopy, Rutherford backscattering channeling, and by x‐ray diffraction (XRD). Following proton exchange (PE) there are two different phases in addition to pure LiNbO3 detected by XRD. After successive annealing steps the outermost phase disappears and an interfacial region forms progressively between PE and LiNbO3. Specific vibrational bands are correlated to electro‐optic and nonlinear optical properties of the system, and the recovery of these properties upon annealing is correlated to chemical bonding changes.

The processes of formation and epitaxial alignment of SrTiO3 thin films prepared by metallo-organic decomposition

The processes of formation and crystallization of thin films of SrTiO3 prepared by the method of metallo‐organic decomposition have been studied with particular emphasis on the relationship between the thermal decomposition of the metallo‐organic precursors and the eventual epitaxial alignment of the crystallized films. The films are deposited by spin coating onto single‐crystalline silicon and SrTiO3 substrates, pyrolyzed on a hot plate at temperatures ranging from 200 to 450 °C, and subsequently heat treated in a quartz tube furnace at temperatures ranging from 300 to 1200 °C. Heat treatment at temperatures up to 450–500 °C results in the evaporation of solvents and other organic addenda, thermal decomposition of the metallo‐organic (primarily metal‐carboxylates) precursors, and formation of a carbonate species. This carbonate appears to be an intermediate phase in the reaction of SrCO3 and TiO2 to form SrTiO3. Relevant to this work is the fact that the carbonate species exhibits diffraction lines, indi...

Enhancement and suppression of the formation of porous silicon

We present the results of an investigation of various means to enhance or suppress the formation of porous silicon. The first method involves a lithographic process using silicon nitride to produce sub‐0.5 μm light emitting porous silicon (LEPSi) lines adjacent to fully protected silicon regions. The second method consists of amorphizing regions of the wafer prior to anodization with high energy/high dose ion implantation, followed by anodization and annealing. In this method, LEPSi is produced in the unimplanted regions only. Using focused ion‐beam implantation ∼100 nm patterns have been obtained. The third method utilizes low energy/low dose bombardment (ion milling/reactive ion etching) with argon ions prior to anodization. Under appropriate bombardment conditions, we have observed a strong enhancement of the formation rate of LEPSi, possibly due to the generation of a large number of defects on the wafer surface. Our results demonstrate that porous silicon light emitting diodes (LEDS) and silicon elec...

Clay–polymer nanocomposite coatings for imaging application

Aqueous coatings of intercalated smectite clay particles in a polymeric matrix have been evaluated for application in inkjet media. The state of clay intercalation, as measured by X-ray diffraction (XRD) technique, plays a significant role in determining the crystallinity of the polymer and the transparency and gloss of the coatings. Results of practical tests on the nanocomposite coatings operating as inkjet-receiving layers are discussed.

Single-substrate cholesteric liquid crystal displays by colloidal self-assembly

We report a single-substrate method for fabrication of reflective and bistable cholesteric liquid crystal displays on flexible substrates based on self-assembly of uniform droplets of liquid crystal in a polymer matrix to create a close-packed monolayer. The displays may be made on a large scale and exhibit switching voltages, brightness, and contrast approaching two-substrate methods such as the two-substrate polymerization-induced phase separation method.