Investigations on Substrate Temperature-Induced Growth Modes of Organic Semiconductors at Dielectric/semiconductor Interface and Their Correlation with Threshold Voltage Stability in Organic Field-Effect Transistors.

Influence of substrate temperature on growth modes of copper phthalocyanine (CuPc) thin films at the dielectric/semiconductor interface in organic field effect transistors (OFETs) is investigated. Atomic force microscopy (AFM) imaging at the interface reveals a change from 'layer+island' to "island" growth mode with increasing substrate temperatures, further confirmed by probing the buried interfaces using X-ray reflectivity (XRR) and positron annihilation spectroscopic (PAS) techniques. PAS depth profiling provides insight into the details of molecular ordering while positron lifetime measurements reveal the difference in packing modes of CuPc molecules at the interface. XRR measurements show systematic increase in interface width and electron density correlating well with the change from layer + island to coalesced huge 3D islands at higher substrate temperatures. Study demonstrates the usefulness of XRR and PAS techniques to study growth modes at buried interfaces and reveals the influence of growth modes of semiconductor at the interface on hole and electron trap concentrations individually, thereby affecting hysteresis and threshold voltage stability. Minimum hole trapping is correlated to near layer by layer formation close to the interface at 100 °C and maximum to the island formation with large voids between the grains at 225 °C.

Probing molecular packing at engineered interfaces in organic field effect transistor and its correlation with charge carrier mobility.

Surface engineering of SiO2 dielectric using different self-assembled monolayer (SAM) has been carried out, and its effect on the molecular packing and growth behavior of copper phthalocyanine (CuPc) has been studied. A correlation between the growth behavior and performance of organic field effect transistors is examined. Depth profiling using positron annihilation and X-ray reflectivity techniques has been employed to characterize the interface between CuPc and the modified and/or unmodified dielectric. We observe the presence of structural defects or disorder due to disorientation of CuPc molecules on the unmodified dielectric and ordered arrangement on the modified dielectrics, consistent with the high charge carrier mobility in organic field effect transistors in the latter. The study also highlights the sensitivity of these techniques to the packing of CuPc molecules on SiO2 modified using different SAMs. Our study also signifies the sensitivity and utility of these two techniques in the characterization of buried interfaces in organic devices.

Perforating pilomatricoma: transepithelial elimination or not.

We present a 56-year-old woman with a perforating pilomatricoma in the left eyebrow region. Histologically, the tumor consisted mainly of basophilic cells and shadow cells, and the tumor components were being eliminated through an ulcer with damage to the epithelial structures. In past reports of perforating pilomatricoma, this elimination pattern has often been described as transepithelial elimination. In many patients with perforating pilomatricoma, elimination is accompanied by ulceration and epithelial damage. Mehregan recently stated that elimination accompanied by epidermal necrosis and superficial ulceration constituted one form of transepithelial elimination. Epidermal necrosis and ulceration generally constitute severe damage. However, when Mehregan first proposed the concept of transepithelial elimination, it was defined as a phenomenon with relatively little or no damage to the epithelial structures, differentiating it from other types of elimination. This original definition makes transepithelial elimination a unique and interesting phenomenon, and its most important feature is that there is relatively little or no damage to the epithelial structures. Therefore, the terms "epidermal necrosis" and "ulceration" should not be used in association with transepithelial elimination. Hence, in patients with perforating pilomatricoma, the elimination of tumor components from ulcers with damage to the epithelial structures, as seen in the present case, should not be described as transepithelial elimination.

Juvenile temporal arteritis is a manifestation of Kimura disease.

An asymptomatic nodule appeared in the right temporal region of an 81-year-old woman. Histopathologic examination confirmed significant thickening of the vascular wall, constriction of the vessel lumen, and infiltration of numerous eosinophils and lymphocytes. Giant cells were not seen. Lymphoid follicles and capillaries surrounded the large vessel. Elastica van Gieson staining revealed a laceration of the internal elastic lamina. Based on these clinical and histologic findings, the patient was diagnosed as having juvenile temporal arteritis (JTA), a disease first proposed by Lie and his colleagues in 1975. Three years later, a new eruption, again asymptomatic, appeared in the posterior region of the patient's right ear. Subsequently, she was referred to our department. Histologic examination of the new lesion confirmed the infiltration of lymphocytes and eosinophils, which was accompanied by numerous lymphoid follicles, and the proliferation of endothelial cells and capillaries from the deep dermis to the subcutaneous tissue. The patient was diagnosed as having Kimura disease, which is a persistent and recurrent illness. We hypothesized that JTA was a partial expression of Kimura disease and investigated whether past cases of JTA could be considered Kimura disease. As a result, we found that most cases of JTA could indeed be considered Kimura disease. Furthermore, we examined the vascular changes in the routinely and elastic fiber-stained sections of three cases with Kimura disease and two cases with angiolymphoid hyperplasia with eosinophilia. The results showed occlusive vascular changes in most samples from these cases, supporting the hypothesis that JTA is an accessory lesion of Kimura disease.