We investigated the overall and site-specific prevalence of pre-S mutations and its clinical significance in patients with genotype C hepatitis B virus (HBV) infection. Three hundred subjects were included: 50 asymptomatic carriers (AC), 87 chronic hepatitis (CH), 91 liver cirrhosis (LC) and 72 hepatocellular carcinoma (HCC). Pre-S mutations were determined by nucleotide sequence analysis. Possible correlations between pre-S mutations and clinical/virological parameters were examined. Pre-S mutations were detected in 82 cases (27.3%); it was more frequently found in HCC (43.1%) and LC (35.2%) group than in the CH (20.7%) and AC (2.0%) group. Pre-S2 deletion was the most commonly found mutation (10.7%), followed by pre-S2 start codon mutation (9.7%), pre-S1-S2 deletion (3.0%) and both pre-S2 deletion and start codon mutation (2.7%). Pre-S2 deletion and pre-S2 start codon mutation were more frequently detected in advanced diseases (LC and HCC). Pre-S mutations were associated with older age and higher rates of positive HBV DNA (>/=0.5 pg/mL). Advanced disease and positive HBV DNA were shown to be independent predictors of pre-S mutations by logistic regression analysis. These findings suggest that pre-S mutations, especially pre-S2 deletions and pre-S2 start codon mutations, are common in patients with genotype C HBV infection and are associated with advanced liver disease and active viral replication.

Atomic layer etching of Si͑100͒ and Si͑111͒ was carried out using Cl 2 adsorption followed by the Ar neutral beam irradiation for the removal of charging damage during the etching. By supplying Cl 2 and Ar neutrals higher than the critical doses, the exact same depth per cycle corresponding to one atomic layer per cycle of 1.36 Å/cycle for silicon ͑100͒ and 1.57 Å/cycle for silicon ͑111͒ could be obtained by a self-limited etching mechanism. The critical Cl 2 pressure and Ar neutral beam irradiation time corresponded to one monolayer chemisorption of chlorine by the dissociative Langmuir isotherm and the irradiation of Ar neutral beam was enough to remove one layer of silicon chloride formed on the silicon surfaces, respectively.Atomic layer etching ͑ALET͒ can be an indispensable method for the fabrication of future devices such as nanoscale devices, quantum devices, etc., 1,2 because current etch technology utilizing reactive ion etching does not have precise etch rate controllability and tends to damage the surface of the devices physically and electrically due to the use of energetic reactive ions to achieve vertical etch profiles.ALET technology has been investigated since the early 1990s for GaAs and Si devices. 3-9 To achieve ALET, many cycles of sequential steps consisting of the adsorption of halogen gas such as chlorine 3-8 or fluorine 9 and the desorption of the formed halide by heat, laser, or Ar + ions are required. For the Si͑100͒ ALET, precise Si etch rates per cycle were obtained by many researchers, however, among the researchers the reported etch rates were different. 1.5-3.0 Å/cycle was reported for the silicon ͑100͒ etching by fluorine gas 9 and 0.68 ϳ 1.36 Å/cycle 6-8 and 0.52 Å/cycle 8 were reported for the silicon ͑100͒ and ͑111͒ etchings by Cl 2 gas, respectively. In addition, for the anisotropic etching of the silicon during the ALET, directional Ar + ions were used in general for the desorption, and which could cause electrical charging damage to the devices similar to that of the conventional reactive ion etching.In fact, the decrease of damage to the semiconductor which occurred during the plasma etching can be obtained by using neutral beam etching instead of conventional reactive ion etching. Figure 1a shows the photoreflectance spectroscopy ͑PRS͒ data of GaAs etched using Cl 2 neutral beam and Cl 2 inductively coupled plasma ͑ICP͒ etching. For comparison, not only the etch depth but also the energy of the neutral beam and the bias voltage of the ICP etching were maintained the same. As shown in the figure, the GaAs etched using the Cl 2 ICP showed the change of the PRS curve compared to nonetched reference GaAs while the GaAs etched using the Cl 2 neutral beam showed a similar PRS curve as the reference. The change of the PRS curve indicates the existence of surface defects, therefore, the surface damage could be decreased significantly by using a neutral beam instead of conventional reactive ion etching. The damage to the gate oxide of metal oxide semiconductor ͑MOS͒ device during t...

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