Ion-implantation-caused special damage profiles determined by spectroscopic ellipsometry in crystalline and in relaxed (annealed) amorphous silicon

We previously developed a fitting method of several parameters to evaluate ion-implantation-caused damage profiles from spectroscopic ellipsometry (SE) (M. Fried et al., J. Appl. Phys., 71 (1992) 2835). Our optical model consists of a stack of layers with fixed and equal thicknesses and damage levels described by a depth profile function (coupled half Gaussians). The complex refractive index of each layer is calculated from the actual damage level by Bruggeman effective medium approximation (EMA) using crystalline (c-Si) and amorphous (a-Si) silicon as end-points. Two examples are presented of the use of this method with modified optical models. First, we investigated the surface damage formed by room temperature B+ and N+ implantation into silicon. For the analysis of the SE data we added a near surface amorphous layer to the model with variable thickness. Second, we determined 20 keV B+ implantation-caused damage profiles in relaxed (annealed) amorphous silicon. In this special case, the complex refractive index of each layer was calculated from the actual damage level by the EMA using relaxed a-Si and implanted a-Si as end-points. The calculated profiles are compared with Monte Carlo simulations (TRIM code); good agreement is obtained

Non-destructive characterization of nitrogen-implanted silicon-on-insulator structures by spectroscopic ellipsometry

Silicon-on-insulator (SOI) structures implanted with 200 or 400 keV N+ ions at a dose of 7.5 × 1017cm−2 were studied by spectroscopic ellipsometry (SE). The SE measurements were carried out in the 300–700 nm wavelength (4.13-1.78 eV photon energy) range. The SE data were analysed by the conventional method of using appropriate optical models and linear regression analysis. We applied a seven-layer model (a surface oxide layer, a thick silicon layer, upper two interface layers, a thick nitride layer and lower two interface layers) with good results. The fitted parameters were the layer thickness and compositions. The results were compared with data obtained from Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy. The sensitivity of our optical model and fitting technique was good enough to distinguish between the silicon-rich transition layers near the upper and lower interfaces of the nitride layer, which are unresolvable in RBS measurements

Ion-implantation induced anomalous surface amorphization in silicon

Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model

Comparative investigation of damage induced by diatomic and monoatomic ion implantation in silicon

The damaging effect of mono- and diatomic phosphorus and arsenic ions implanted into silicon was investigated by spectroscopic ellipsometry (SE) and high-depth-resolution Rutherford backscattering and channeling techniques. A comparison was made between the two methods to check the capability of ellipsometry to examine the damage formed by room temperature implantation into silicon. For the analysis of the spectroscopic ellipsometry data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fractions of the amorphous silicon component in the layers) by linear regression. The depth dependence of the damage was determined by both methods. It was revealed that SE can be used to investigate the radiation damage of semiconductors together with appropriate optical model construction which can be supported or independently checked by the channeling method. However, in case of low level damage (consisting mainly of isolated point defects) ellipsometry can give false results, overestimating the damage using inappropriate dielectric functions. In that case checking by other methods like channeling is desirable

Methylene blue: an alternative, multi-purpose stain for detection, analysis and isolation of nucleic acids

A series of experiments was performed utilizing Methylene Blue (MeB) in place of the intercalating dyes ethidium bromide (EtBr) and acridine orange (AO) to stain, visualize, and isolate DNA and RNA. MeB proved to be superior to the other dyes for several purposes: 1) visualization of glyoxalated (chemically denatured) RNA in agarose gels, 2) staining of nucleic acids that are to be used in subsequent hybridization experiments, and 3) isolation and purification of plasmid DNA by CsCl ultracentrifugation. MeB was found to perform at least as well as EtBr or AO for visualization of DNA in agarose of acrylamide gels, and DNA stained with MeB can be purified from agarose gel slices by the Gene Clean protocol. These results indicate that MeB is a very effective nucleic acid stain. Its safety versus conventional intercalating dyes will be discussed.Здійснено серію експериментів з використання метиленового синього (МС) замість інтеркалюючих барвників бромистого етидію (ЕВ) та. акридинового оранжевого (АО) для забарвлен­ня, візуалізації та виділення ДНК і РНК. Показано, що МС переважає інші барвники у використанні для декількох цілей: 1) візуалізації гліоксильовано'і (хімічно денатурованої) РНК в агарозних гелях; 2) забарвлювання нуклеїнових кислот, які в подальшому будуть використані в експериментах з гібри­дизації; 3) виділення та очистки плазмідної ДНК ультрацентрифугуванням в CsCl. Знайдено, що за допомогою МС ДНК так само добре виявляється в гелях агарози або акриламіду, як і з використанням ЕВ і АО, а ДНК, забарвлена МС, може бути очищена із зрізів гелей агарози по протоколу «Gene Clean». Ці результати вказують на те, що МС є дуже ефективним барвником нуклеїнових кислот. Обговорюється його безпека іюрівняно з загальноприйнятними інтеркалюючими барвниками.Проведена серия экспериментов по использованию метилено­вого синего (МС) вместо интеркалирующих красителей бромистого этидия (ЭВ) и акридинового оранжевого (АО) для окрашивания, визуализации и выделения ДНК и РНК. Показано, что МС превосходит другие красители в использовании для нескольких целей: 1) визуализации глиоксилированной (хи­мически денатурированной) РНК в агарозных гелях; 2) окрашивания нуклеиновых кислот, которые впоследствии будут использоваться в экспериментах по гибридизации; 3) выделе­ния и очистки плазмидной ДНК ультрацентрифугированием в CsCl. Обнаружено, что МС так же пригоден для визуализации ДНК в гелях агарозы или акриламида, как ЭВ или АО, а ДНК, окрашенная МС, может быть очищена из срезов гелей агарозы по протоколу «Gene Clean». Эти результаты указывают на то, что МС – очень эффективный краситель нуклеиновых кислот. Обсуждается его безопасность по сравнению с общепринятыми интеркалирующими красителями

Determination of complex dielectric functions of ion implanted and implanted‐annealed amorphous silicon by spectroscopic ellipsometry

Measuring with a spectroscopic ellipsometer (SE) in the 1.8–4.5 eV photon energy region we determined the complex dielectric function (ϵ = ϵ1 + iϵ2) of different kinds of amorphous silicon prepared by self‐implantation and thermal relaxation (500 °C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a‐Si (i‐a‐Si) differs from that of relaxed (annealed) a‐Si (r‐a‐Si). Moreover, its ϵ differs from the ϵ of evaporated a‐Si (e‐a‐Si) found in the handbooks as ϵ for a‐Si. If we use this ϵ to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis–Mott plot based on the relation: (ϵ2E2)1/3 ∼ (E− Eg). The results are: 0.85 eV (i‐a‐Si), 1.12 eV (e‐a‐Si), 1.30 eV (r‐a‐Si). We attribute the optical change to annihilation of point defects

Progesterone Inhibits Epithelial-to-Mesenchymal Transition in Endometrial Cancer

Background: Every year approximately 74,000 women die of endometrial cancer, mainly due to recurrent or metastatic disease. The presence of tumor infiltrating lymphocytes (TILs) as well as progesterone receptor (PR) positivity has been correlated with improved prognosis. This study describes two mechanisms by which

Sequence Homology at the Breakpoint and Clinical Phenotype of Mitochondrial DNA Deletion Syndromes

Mitochondrial DNA (mtDNA) deletions are a common cause of mitochondrial disorders. Large mtDNA deletions can lead to a broad spectrum of clinical features with different age of onset, ranging from mild mitochondrial myopathies (MM), progressive external ophthalmoplegia (PEO), and Kearns-Sayre syndrome (KSS), to severe Pearson syndrome. The aim of this study is to investigate the molecular signatures surrounding the deletion breakpoints and their association with the clinical phenotype and age at onset. MtDNA deletions in 67 patients were characterized using array comparative genomic hybridization (aCGH) followed by PCR-sequencing of the deletion junctions. Sequence homology including both perfect and imperfect short repeats flanking the deletion regions were analyzed and correlated with clinical features and patients' age group. In all age groups, there was a significant increase in sequence homology flanking the deletion compared to mtDNA background. The youngest patient group (<6 years old) showed a diffused pattern of deletion distribution in size and locations, with a significantly lower sequence homology flanking the deletion, and the highest percentage of deletion mutant heteroplasmy. The older age groups showed rather discrete pattern of deletions with 44% of all patients over 6 years old carrying the most common 5 kb mtDNA deletion, which was found mostly in muscle specimens (22/41). Only 15% (3/20) of the young patients (<6 years old) carry the 5 kb common deletion, which is usually present in blood rather than muscle. This group of patients predominantly (16 out of 17) exhibit multisystem disorder and/or Pearson syndrome, while older patients had predominantly neuromuscular manifestations including KSS, PEO, and MM. In conclusion, sequence homology at the deletion flanking regions is a consistent feature of mtDNA deletions. Decreased levels of sequence homology and increased levels of deletion mutant heteroplasmy appear to correlate with earlier onset and more severe disease with multisystem involvement