Ambient NO2 adsorption onto copper(II) phthalocyanine (CuPc) monolayers is observed using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) to elucidate the molecular sensing mechanism in CuPc chemical vapor sensors. For low doses (1 ppm for 5 min) of NO2 at ambient temperatures, isolated chemisorption sites on the CuPc metal centers are observed in STM images. These chemisorbates almost completely desorb from the CuPc monolayer after annealing at 100 °C for 30 min. Conversely, for high NO2 doses (10 ppm for 5 min), the NO2 induces a fracture of the CuPc domains. This domain fracture can only be reversed by annealing above 150 °C, which is consistent with dissociative chemisorption into NO and atomic O accompanied by surface restructuring. This high stability implies that the domain fracture results from tightly bound adsorbates, such as atomic O. Existence of atomic O on or under the CuPc layer, which results in domain fracture, is revealed by XPS analysis and ozone-dosing experiments. The observed CuPc domain fracturing is consistent with a mechanism for the dosimetric sensing of NO2 and other reactive gases by CuPc organic thin film transistors (OTFTs).

The megasonic cleaning efficiency is evaluated as a function of the angle of incidence of acoustic waves on a Si wafer. Acoustic Schlichting streaming alone is not able to remove nanoparticles smaller than 400 nm. It is shown that oscillating or collapsing behavior of bubbles are responsible for removing nanoparticles smaller than 400 nm during a cleaning process with ultrasound. Optimal particle removal efficiency is obtained around the angle of acoustic transmission of the silicon wafer.

Direct selective detection of hydrogen peroxide and di-tert-butyl peroxide vapors was demonstrated using organic thin-film transistor (OTFT) threshold voltage shifts. Positive threshold voltage shifts are observed during peroxide vapor sensing for metal phthalocyanine (MPc)- and naphthalocyanine (Nc)-based OTFTs. The positive threshold voltage shift observed for peroxides is not evident with nonoxidizing analytes such as dimethyl methylphosphonate (DMMP) and water. MPc and Nc OTFT sensors operating at room temperature have distinct responses in mobility and threshold voltage to peroxide vapors. The mobility changes are reversible under dry air flow, whereas positive threshold voltage shifts are reversed by counter dosing with a polar, electron-donating analyte. The peroxide induced threshold voltage shifts suggest an accumulation of positive charge in the MPc/Nc film The results are consistent with a dual-response mechanism in which the peroxide molecularly chemisorbs and subsequently catalytically decomposes, forming reactive products and increasing fixed positive charge.

Air-stable organic thin-film transistor (OTFT) sensors fabricated using spin-cast films of 5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine (OBNc) demonstrated improved chemical vapor sensitivity and selectivity relative to vacuum-deposited phthalocyanine (H(2)Pc) OTFTs. UV-vis spectroscopy data show that annealed spin-cast OBNc films exhibit a red-shift in the OBNc Q-band λ(max) which is generally diagnostic of improved π-orbital overlap in phthalocyanine ring systems. Annealed OBNc OTFTs have mobilities of 0.06 cm(2) V(-1) s(-1), low threshold voltages (|V(th)| < 1 V), and on/off ratios greater than 10(6). These air-stable device parameters are utilized for sensing modalities which enhance the sensitivity and selectivity of OBNc OTFTs relative to H(2)Pc OTFTs. While both sensors exhibit mobility decreases for all analytes, only OBNc OTFTs exhibit V(th) changes for highly polar/nonpolar analytes. The observed mobility decreases for both sensors are consistent with electron donation trends via hydrogen bonding by basic analytes. In contrast, V(th) changes for OBNc sensors appear to correlate with the analyte's octanol-water partition coefficient, consistent with polar molecules stabilizing charge in the organic semiconductor film. The analyte induced V(th) changes for OBNc OTFTs can be employed to develop selective multiparameter sensors which can sense analyte stabilized fixed charge in the film.

Organic thin film transistor (OTFT) chemical sensors rely on the specific electronic structure of the organic semiconductor (OSC) film for determining sensor stability and response to analytes. The delocalized electronic structure is influenced not only by the OSC molecular structure, but also the solid state packing and film morphology. Phthalocyanine (H2Pc) and tetrabenzoporphyrin (H2TBP) have similar molecular structures but different film microstructures when H2Pc is vacuum deposited and H2TBP is solution deposited. The difference in electronic structures is evidenced by the different mobilities of H2TBP and H2Pc OTFTs. H2Pc has a maximum mobility of 8.6×10−4cm2V−1s−1 when the substrate is held at 250°C during deposition and a mobility of 4.8×10−5cm2V−1s−1 when the substrate is held at 25°C during deposition. Solution deposited H2TBP films have a mobility of 5.3×10−3cm2V−1s−1, which is consistent with better long-range order and intermolecular coupling within the H2TBP films compared to the H2Pc films. Solution deposited H2TBP also exhibits a textured film morphology with large grains and an RMS roughness 3–5 times larger than H2Pc films with similar thicknesses. Despite these differences, OTFT sensors fabricated from H2TBP and H2Pc exhibit nearly identical analyte sensitivity and analyte response kinetics. The results suggest that while the interactions between molecules in the solid state determine conductivity, localized interactions between the analyte and the molecular binding site dominate analyte binding and determine sensor response.

Kelvin probe force microscopy (KPFM) is a unique technique that can provide two-dimensional potential profiles inside a working device. A procedure is described to obtain high-resolution KPFM results on ultra-high vacuum (UHV) cleaved III-V MOSCAPs. Two tip preparation methods: field emission and Cr coating show reproducible high spatial and energy resolution KPFM images. A unique sample design has been developed which is compatible with UHV cross-sectional KPFM (x-KPFM). Key design features are high density of devices on the cleave face, a buried device interface, and a cleavable gate contact. Using x-KPFM, the first UHV cleaved MOSCAP surface potential mapping is demonstrated.

Copper phthalocyanine (CuPc) thin film transistors were fabricated using a tapered edge bottom contact device geometry, and mobility saturation was observed for devices with CuPc thicknesses of 12 monolayers (MLs) and greater. The mobility saturation is attributed to a significantly decreased contact resistance resulting from a bilayer resist lift-off method, as compared with a single layer resist lift-off method. Threshold voltages are also found to saturate above 12 ML CuPc thicknesses.

Chemical sensing properties of phthalocyanine thin-film transistors have been investigated using nearly identical n- and p-channel devices. P-type copper phthalocyanine (CuPc) has been modified with fluorine groups to convert the charge carriers from holes to electrons. The sensor responses to the tight binding analyte dimethyl methylphosphonate (DMMP) and weak binding analyte methanol (MeOH) were compared in air and N(2). The results suggest that the sensor response involves counterdoping of pre-adsorbed oxygen (O(2)). A linear dependence of chemical response to DMMP concentration was observed in both n- and p- type devices. For DMMP, there is a factor of 2.5 difference in the chemical sensitivity between n- and p-channel CuPc thin-film transistors, even though it has similar binding strength to n- and p-type CuPc molecules as indicated by the desorption times. The effect is attributed to the difference in the analyte perturbation of electron and hole trap energies in n- and p-type materials.

The electrical degradation (aging) of copper phthalocyanine (CuPc) organic thin film transistors (OTFTs) was investigated. Thick (1000 ML) and ultrathin (4 ML) channel thicknesses were used in bottom contact OTFTs to correlate the electrical effects of aging with film microstructure. Proper TFT saturation behavior was unattainable in thick devices subject to ambient aging; however ultrathin devices were significantly less susceptible and maintained good saturation and subthreshold behavior. Therefore 1000 monolayer (ML) CuPc OTFTs were characterized in ambient air, clean dry air, clean humidified air, and NO(x) environments to isolate the ambient components that induce aging. Thick channel devices which had been aged in ambient air to the point of losing all saturation behavior could be restored to proper saturation behavior by exposure to clean humidified air. The data are consistent with aging resulting primarily from adsorption of strong oxidants from ambient air within the grain boundaries of the CuPc films.

To decrease gastric volume and acidity prior to anesthesia and surgery and decrease the risk of aspiration, a prospective double-blind trial comparing two H2 receptor blockers, cimetidine and ranitidine, was performed. Analysis of gastric contents revealed both drugs to be extremely effective in raising gastric pH to the 6–7 range. However, ranitidine was shown to be more effective in decreasing gastric volume.

A patient with a rare manifestation of phenytoin-induced hyperplasia is reported. Severe maxillary and mandibular gingival hyperplasia occurred prior to the eruption of the dentition and without evidence of any predisposing local irritation factors.