Ultrathin undoped tetrahedral amorphous carbon films: thickness dependence of the electronic structure and implications for their electrochemical behaviour.

In this paper we show that the electronic properties of ultrathin tetrahedral amorphous carbon (ta-C) films are heavily dependent on their thickness. By using scanning tunnelling spectroscopy, Raman spectroscopy, and conductive atomic force microscopy, it was found that a decrease of ta-C thickness from 30 to 7 nm leads to (i) the narrowing of the band gap; (ii) appearance of shallower monoenergetic traps as well as the increase of their concentration; (iii) the increase of the equilibrium concentration of free charge carriers and their mobility; which were caused by (iv) the increase in the sp(2) fraction. However, beyond a certain ta-C thickness (7 nm) the electronic properties of the studied samples start to deteriorate, which is highly likely related to titanium oxide formation at the Ti/ta-C interface. The same tendency is observed for the sample with beforehand air-formed native titanium oxide at the interface. With respect to the last point, it is suggested that the ta-C layer has no uniform coverage if its thickness is small enough (less than 7 nm). The experimental results were rationalized by detailed atomistic simulations. By using the so-called "Tauc plot" we introduce the possibility of the coexistence of bulk and surface band gaps originating from the large increase in sp(2) bonded carbon atoms in the surface region compared to that in the bulk ta-C. The results from the simulations were found to be consistent with the experimental measurements. The previously stated variation in the electronic properties of the layers as a function of their thickness was also exhibited in the electrochemical properties of the samples. It appears that the thinner ta-C layers had more facile electron transfer kinetics as determined with a ferrocenemethanol (FcMeOH) outer sphere redox system. However, if the ta-C layer thickness was reduced too much, the films were not stable anymore.

Intra-abdominal localisation of a buschke-lowenstein tumour: case presentation and review of the literature.

Giant condyloma acuminatum or Buschke-Lowenstein tumour is a very rare disease which usually is located in the genital, anorectal, and perianal regions. It is regarded as a type of verrucous carcinoma occurring on anogenital mucosal surfaces where it is locally invasive but displays a benign cytology. We describe a case of a 24-year-old woman with persisting condyloma acuminata progressing to a large intra-abdominal Buschke-Lowenstein tumour. To our knowledge such an advanced stage has only been reported once before. The severity and extent of the tumour both determine the treatment and patient outcome. Treatment was impeded by cachexia, an immunosuppressive state after kidney transplantation and difficulties in establishing a reliable diagnose. Interferon treatment was started which initially led to tumour reduction but was complicated by an interferon-induced pancreatitis, pneumonia, and fasciitis necroticans resulting in death. We present a literature overview on the treatment options for a Buschke-Lowenstein tumour, with emphasis on interferon therapy, with all the advantages and disadvantages.