The hydrogenation of C-rich Si leads to the formation of two (almost) energetically degenerate H * 2 (C) complexes, each containing one substitutional C (Cs) and two interstitial H atoms which are located at a bond-centered (bc) and an anti-bonding (ab) site, respectively. The two defects are trigonal: Cs − H bc · · · Si − H ab and H ab − Cs · · · H bc − Si. Fourier-transform infrared (FTIR) absorption spectra of these two defects should show two Cs − H and two Si − H stretch modes, but the H ab − Cs mode was absent in earlier studies. The missing line has now been observed by FTIR in especially C-rich Si material. The line is unexpectedly broad, suggesting a very short vibrational lifetime. Partial D substitutions result in the formation of a H ab − Cs · · · D bc − Si center. In this defect, the H ab − Cs line shifts by only 0.3 cm −1 but becomes very sharp, suggesting a long lifetime. The IR line widths show that the vibrational lifetime of the H ab − Cs mode in H ab − Cs · · · D bc − Si is about 16 times longer than that of the same H ab − Cs mode in H ab − Cs · · · H bc − Si. This paper contains experimental data and first-principles calculations which explain this isotope effect.

No abstract

Porokeratosis (PK) is a disorder of keratinization with a clinical presentation of an atrophic center surrounded by a hyperkeratotic border. Lesions of porokeratosis carry a risk of malignant transformation with giant porokeratosis (GPK) being a high-risk variant. We report a case in which a single, large, erythematous, scaly plaque in an immunocompromised patient showed initial histopathological features consistent with psoriasis and subsequent histological features consistent with GPK. This plaque underwent malignant transformation to SCC on three occasions. This case highlights that specimens taken from central portions of porokeratosis may resemble a variety of dermatoses histologically, including psoriasis, resulting in misdiagnosis as seen in our patient. When a patient presents with a diagnosis previously made that isn’t responding to therapy as expected, repeat biopsy is appropriate.

No abstract