Interstitial sodium and lithium doping effects on the electronic and mechanical properties of silicon nanowires: a DFT study.

In this work, we present a theoretical study of the electronic band structure and the Young's modulus of hydrogen-passivated silicon nanowires (H-SiNWs), grown along the [110] crystallographic direction, as a function of the concentration of interstitial sodium (Na) and lithium (Li) atoms. The study is performed using the supercell scheme and the density functional theory (DFT), within the local density approximation (LDA). The results show that the presence of Na or Li atoms closes the former semiconducting band gap of the H-SiNWs and shifts the Fermi energy into the conduction band. The transition from semiconductor to metal occurs as soon as a single Na or Li atom is added to the nanowire and the number of occupied states near the Fermi level is larger for the H-SiNWs with Li atoms in comparison with those nanowires with the same concentration of Na atoms. The calculated formation energies reveal that the system becomes less stable when the concentration of Na and Li atoms augments. Moreover, the obtained binding energies indicate that Si-Li and Si-Na bonds are formed. It is worth mentioning that the binding energies of H-SiNWs with interstitial Li atoms are larger than those corresponding to the H-SiNWs with interstitial Na atoms. On the other hand, the Young's moduli of H-SiNWs with Na atoms are lower than those of pure H-SiNWs and their values diminish when the concentration of Na atoms increases. In contrast, Young's moduli of H-SiNWs present a non-monotonic behavior as a function of the concentration of interstitial Li atoms and for the largest studied concentration the nanowire fractures. These results give insight into the changes that electronic and mechanical properties of H-SiNWs suffer during the charge-discharge process, which should be taken into account in the design of electrodes of Na or Li-ion batteries.

Confinement effect on the low temperature specific heat for ultrathin silicon nanowires: a first principles study.

This work studied the phonon confinement effects at the low temperature specific heat of Si nanowires from first principles using density functional perturbation theory. The nanowires were modeled in the [0 0 1] direction for three different diameters, with the largest cross section being approximately 10 Å. The results indicate the specific heat can be described at low temperatures using a third-grade polynomial of the form c v = λT + ßT 2 + γT3, where the coefficients of quadratic and cubic terms are almost nonexistent for small diameters. These terms begin to have relevance at larger diameters. Further analysis shows λ > ß > γ, which shows the phonon confinement (λ) and surface atoms (ß) become more important than the volumetric contribution (γ) for ultrathin nanowires at low temperatures.

Lithium effect on the electronic properties of porous silicon for energy storage applications: a DFT study.

Theoretical studies on the effect of Li on the electronic properties of porous silicon are still scarce; these studies could help us in the development of Li-ion batteries of this material which overcomes some limitations that bulk silicon has. In this work, the effect of interstitial and surface Li on the electronic properties of porous Si is studied using the first-principles density functional theory approach and the generalised gradient approximation. The pores are modeled by removing columns of atoms of an otherwise perfect Si crystal, dangling bonds of all surfaces are passivated with H atoms, and then Li is inserted on interstitial positions on the pore wall and compared with the replacement of H atoms with Li. The results show that the interstitial Li creates effects similar to n-type doping where the Fermi level is shifted towards the conduction band with band crossings of the said level thus acquiring metallic characteristics. The surface Li introduces trap-like states in the electronic band structures which increase as the number of Li atom increases with a tendency to become metallic. These results could be important for the application of porous Si nanostructures in Li-ion batteries technology.

Carbon monoxide sensing properties of B-, Al- and Ga-doped Si nanowires.

Silicon nanowires (SiNWs) are considered as potential chemical sensors due to their large surface-to-volume ratio and their possible integration into arrays for nanotechnological applications. Detection of harmful gases like CO has been experimentally demonstrated, however, the influence of doping on the sensing capacity of SiNWs has not yet been reported. For this work, we theoretically studied the surface adsorption of a CO molecule on hydrogen-passivated SiNWs grown along the [111] crystallographic direction and compared it with the adsorption of other molecules such as NO, and O2. Three nanowire diameters and three dopant elements (B, Al and Ga) were considered, and calculations were done within the density functional theory framework. The results indicate that CO molecules are more strongly adsorbed on the doped SiNW than on the pristine SiNW. The following trend was observed for the CO adsorption energies: E A[B-doped] > E A[Al-doped] > E A[Ga-doped] > E A[undoped], for all diameters. The electronic charge transfers between the SiNWs and the adsorbed CO were estimated by using a Voronoi population analysis. The CO adsorbed onto the undoped SiNWs has an electron-acceptor character, while the CO adsorbed onto the B-, Al-, and Ga-doped SiNWs exhibits an electron-donor character. Comparing these results with the ones obtained for the NO and O2 adsorption, the larger CO adsorption energy on B-doped SiNWs indicates their good selectivity towards CO. These results suggest that SiNW-based sensors of toxic gases could represent a clear and advantageous application of nanotechnology in the improvement of human quality of life.

Lithium effects on the mechanical and electronic properties of germanium nanowires.

Semiconductor nanowire arrays promise rapid development of a new generation of lithium (Li) batteries because they can store more Li atoms than conventional crystals due to their large surface areas. During the charge-discharge process, the electrodes experience internal stresses that fatigue the material and limit the useful life of the battery. The theoretical study of electronic and mechanical properties of lithiated nanowire arrays allows the designing of electrode materials that could improve battery performance. In this work, we present a density functional theory study of the electronic band structure, formation energy, binding energy, and Young's modulus (Y) of hydrogen passivated germanium nanowires (H-GeNWs) grown along the [111] and [001] crystallographic directions with surface and interstitial Li atoms. The results show that the germanium nanowires (GeNWs) with surface Li atoms maintain their semiconducting behavior but their energy gap size decreases when the Li concentration grows. In contrast, the GeNWs can have semiconductor or metallic behavior depending on the concentration of the interstitial Li atoms. On the other hand, Y is an indicator of the structural changes that GeNWs suffer due to the concentration of Li atoms. For surface Li atoms, Y stays almost constant, whereas for interstitial Li atoms, the Y values indicate important structural changes in the GeNWs.

Alternating chemotherapy and accelerated split-course irradiation in locally advanced nonsmall cell lung carcinoma.

BACKGROUND: The prognosis of patients with locally advanced nonsmall cell lung carcinoma (NSCLC), which is usually unresectable, is very poor, and patient survival rarely reaches 1 year. However, prolonged survival correlated with objective responses has been observed among patients with intrathoracic disease treated with a combination of cytotoxic drugs and local irradiation despite the lack of consensus regarding the schedule of such combined therapy. From October 1989 to November 1993, a Phase II study was conducted to evaluate the tolerability and efficacy of alternating chemotherapy and accelerated split-course radiotherapy in the treatment of patients with locally advanced NSCLC. METHODS: Sixty-three consecutive patients with unresectable Stage III NSCLC entered this study. The treatment was composed of 3 cycles of combined chemotherapy and radiotherapy at 4-week intervals. Chemotherapy with cisplatin (30 mg/m2/day) and etoposide (100 mg/m2/day) was delivered intravenously on Days 1, 2, and 3, followed by radiotherapy on Days 4-8. A course of radiotherapy consisted of 1.5 gray (Gy) per fraction twice a day (3 Gy per day) for 5 consecutive days, for a total dose of 15 Gy. Response was assessed after 3 courses, for a total irradiation dose of 45 Gy. In cases of objective antitumoral response with operable tumor, surgery was performed. A fourth course of chemotherapy and radiotherapy, for a total dose up to 60 Gy in 12 weeks, was administered to all patients. Two additional courses of chemotherapy were given, for a total of six. RESULTS: Of the 63 patients, 62 were evaluable for response. Six had a complete remission and 36 a partial response, resulting in an overall response rate of 67.7%. Nine patients underwent surgery (pneumonectomy for seven patients and lobectomy for two patients), and the complete disappearance of any residual tumor was documented histologically in four. Of the 290 chemotherapy courses delivered, there were 31 of Grade 3-4 toxicity, mainly leukopenia and vomiting. The median times of freedom from disease progression and overall survival were 8 months (confidence interval [CI], 7-9.5) and 14 months (CI, 10-22), respectively. The 1-, 2-, and 5-year survival rates of the 62 patients were 54%, 35%, and 21%, respectively. Patients who responded had a significantly longer median survival (16 months) than nonresponders (7 months) (P = 0.02). However, there was no difference in the survival of resected and nonresected patients. CONCLUSIONS: This treatment schedule resulted in a high response rate with prolonged survival. However, the toxicity of this approach was not negligible, even though it did not preclude this strategy. This combined modality must be compared with other combinations of alternating or sequential chemoradiotherapy.

[Diagnosis of localized pulmonary opacities by transbronchial biopsy]. / Diagnostic des opacités pulmonaires localisées par biopsie transbronchique.

In order to assess the value of transbronchial biopsy (BTB) in the diagnosis of local pulmonary opacities, we have carried out a prospective study from October 1981 to August 1982 on 180 patients with a localised pulmonary opacity radiographically. 73 presented with a tumour visible fibreoptically in whom the diagnosis was made by bronchial biopsy. In 56 patients the clinical and biological picture were not suggestive of a malignancy and the lesion disappeared in 15 days on antibiotic treatment. Finally in 51 subjects the cancerous nature of the opacity was strongly suspected and the indication for a BTB were met. We obtained the following results: among 51 patients 11 were suffering from the sequelae of non-progressive disease and 40 of progressive disease; namely a sensibility of 80% and a specificity of 100%. The results vary as a function of the size of the tumour and its localisation. The best results were obtained for tumours with a diameter of greater than 3 cm, in the middle third of the lung (diagnosed by BTB 9 times out of 10). Thus transbronchial biopsy seems to be the first invasive examination to contemplate in the diagnosis of localised pulmonary opacities.

[Pleural pressure during thoracocentesis in patients with pleural neoplasms]. / La pression pleurale au cours des ponctions évacuatrices pour pleurésie néoplasique.

In 45 patients with cancerous pleural effusion, thoracocentesis was performed according to the following technique : after local anaesthesia (5 ml of 2% lidocaine) in the posterior part of the 6th intercostal space, thoracocentesis was carried out with a blunt trocar connected to a water manometer. The pleural pressure was measured before removal of the fluid (Po). Then three different techniques of drainage (active suction at -- 80 or -- 40 mmHg or underwater sealed drainage) were randomized. Pleural pressure was measured after removal of every 100 ml and at the end of the procedure (PT). The mean Po +/- SD was respectively -- 4.08 +/- 2.95, -- 3.81 +/- 3.12 and -- 2.53 +/- 2.42 cmH2O for the three different groups of drainage. After drainage, PT was decreased in the three groups, especially after -- 80 mmHg aspiration. In 14 patients, side effects occurred during thoracocentesis and the procedure was stopped. Symptoms, chiefly cough, occurred after a mean removal of 1.1 +/- 0.7 1. PT in these patients was statistically lower (-- 18 +/- 5.59 cmH2O) than in the 31 asymptomatic patients (--11.40 +/- 5.75 cmH2O) (p less than 0.001). In conclusion, the assessment of the pleural pressure during thoracocentesis seems to be convenient in order to prevent any complication of pleural evacuation : pleural evacuation should be stopped if the pleural pressure decreased below -- 18 cmH2O. A depression at -- 80 mmHg is too dangerous for pleural aspiration; -- 40 mmHg or under water sealed drainage are both convenient for a safe and complete evacuation.

[Clinical aspects and course of 38 cases of malignant pleural mesothelioma observed in the Marseilles region]. / Aspects cliniques et évolution de 38 cas de mésothéliomes pleuraux malins observés dans la région marseillaise.

Epithelial or mixed mesotheliomas were detected in 38 patients in the region of Marseilles over a period of 9 years. Though an occupational element was involved in 80% of cases, no history of contact with asbestos could be obtained in certain of the patients. Confirmation of diagnosis requires wide pleural biopsies, because of the high level of false negatives and false positives from cytology and pleural needle biopsy. Hyaluronic acid levels are significant only when they are markedly enhanced. Local and regional tumor spread provides an aid to prognosis, but authentic metastases, with further worsening of prognosis, were detected in more than 75% of patients while still alive. Nodules appeared along the course of punctures of drainage tubes or in thoracotomy scars in 56% of cases, and appear to be a very frequent and characteristic feature of mesothelioma. Their therapy involves preventive irradiation.

[Review of today's treatment of bronchial small cell anaplastic cancers (author's transl)]. / Revue de l'état actuel du traitement des cancers anaplasiques bronchiques à petites cellules.

The median survival time of untreated patients with small cell anaplastic carcinoma of the lung does not exceed three months. An important improvement in survival and disease-free period has been achieved by some new therapeutic combinations including chemotherapy alone or radiotherapy and chemotherapy. These recent results are reviewed in this paper, and a new treatment schedule is presented.