Doping Molecular Monolayers: Effects on Electrical Transport Through Alkyl Chains on Silicon

n‐Si/C_nH_{2n + 1}/Hg junctions (n = 12, 14, 16 and 18) can be prepared with sufficient quality to assure that the transport characteristics are not anymore dominated by defects in the molecular monolayers. With such organic monolayers we can, using electron, UV and X‐ray irradiation, alter the charge transport through the molecular junctions on n‐ as well as on p‐type Si. Remarkably, the quality of the self‐assembled molecular monolayers following irradiation remains sufficiently high to provide the same very good protection of Si from oxidation in ambient atmosphere as provided by the pristine films. Combining spectroscopic (UV photoemission spectroscopy (UPS), X‐ray photoelectron spectroscopy (XPS), Auger, near edge‐X‐ray absorption fine structure (NEXAFS)) and electrical transport measurements, we show that irradiation induces defects in the alkyl films, most likely C?C bonds and C? C crosslinks, and that the density of defects can be controlled by irradiation dose. These altered intra‐ and intermolecular bonds introduce new electronic states in the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of the alkyl chains and, in the process, dope the organic film. We demonstrate an enhancement of 1–2 orders of magnitude in current. This change is clearly distinguishable from the previous observed difference between transport through high quality and defective monolayers. A detailed analysis of the electrical transport at different temperatures shows that the dopants modify the transport mechanism from tunnelling to hopping. This study suggests a way to extend significantly the use of monolayers in molecular electronics.     

Mapping the gene causing hereditary primary hyperparathyroidism in a Portuguese kindred to chromosome 1q22-q31

A Portuguese kindred with autosomal dominant isolated primary hyperparathyroidism (HPT) that was associated with parathyroid adenomas and carcinomas was investigated with the aim of determining the chromosomal location of this gene, designated HPTPort. Leukocyte DNA from 9 affected and 16 unaffected members and 7 parathyroid tumors from 4 patients was used in comparative genomic hybridization (CGH), tumor loss of heterozygosity (LOH), and family linkage studies. The CGH studies revealed abnormalities of chromosomes 1 and 13, and the results of LOH studies were consistent with the involvements of tumor suppressor genes from these regions. Family segregation studies mapped HPTPort to chromosome 1q22-q31 by establishing linkage with eight loci (D1S254, D1S222, D1S202, D1S238, D1S428, D1S2877, D1S422, and D1S412) (peak two-point LOD scores = 3. 46-5.14 at 0% recombination), and defined the location of HPT Port to a 21 cM region flanked centromerically by D1S215 and telomerically by D1S306. Thus, HPTPort has been mapped to chromosome 1q22-q31, and a characterization of this gene will help to elucidate further the mechanisms that are involved in the development of parathyroid tumors.     

天然气稳定碳同位素比值数学模拟

根据理论和实验资料,提出了一种新的烃气稳定碳同位素比值数学模拟方法.动力学模型采用了一系列平行的一级天然气生成反应,发生同位素交换的与未发生同位素交换的化学键相对裂解率用方程式表示为k*/k=(A*f/Af)exp(-△Ea/RT)式中R为气体常量,T为温度.利用量子化学计算估计不同简单分子均裂键裂解的熵(A*f/Af)和焓(△Ea)条件.例如,我们获得短链正构烷烃(≤C6)失去甲基官能团的平均△Ea为42.0 cal/mol,平均A*f/Af为1.021.甲烷的生成存在明显差异,预测在200℃的沉积盆地条件下短链正构烷烃产生13CH4的速率比产生12CH4的速率慢2.4%,但在500℃的实验室加热条件下仅慢0.7%.就其它分子均裂键裂解所进行的类似计算也显示了相似的结果(除少数例外),△Ea值介于0～60 cal/mol之间,A*f/Af值介于1.00～1.04之间.大量数据处理结果揭示(1)在△Ea值和化学键裂解能之间存在弱的波型曲线关系;(2)在△Ea值和A*f/Af值之间存在明显的正相关性.这些发现的重要意义在于可以采用适当的动力学模型阐明在恒温密闭系统条件下正十八烷生成甲烷的化学和同位素数据.根据特殊温度史,校正后的模型可以提供与油型干酪根和原油裂解有关的甲烷碳同位素组成、总甲烷生成量和甲烷产率间的定量关系.不同甲烷源岩动力学反应的明显变化,必须根据特殊研究区域的实验室数据来对这些模型进行应用并充分校准.根据这种方法,天然气碳同位素数据不但可以用于估计沉积盆地中生气的时间,而且可以用于评价形成有效聚集的源岩成熟度,以及恢复圈闭充填史.     

Tumor angiogenesis as a prognostic factor in ovarian carcinoma: quantification of endothelial immunoreactivity by image analysis

BACKGROUND: The growth of a malignant tumor requires the formation of new capillaries. Quantification of these microvessels is difficult. The purpose of this study was to establish an objective technique for quantifying angiogenesis and to evaluate whether microvessel quantity may predict tumor aggressiveness in patients with ovarian carcinoma. METHODS: Endothelial area was used to quantify microvessel density in immunohistochemically stained sections of 28 International Federation of Gynecology and Obstetrics Stage IIIC ovarian carcinomas. The endothelial area was measured with a computer-aided image analysis system in the subepithelial stroma of highest vascularization. The endothelial area in the specimens of 14 patients who survived for > or =6 years was compared with that of 14 patients matched for stage and treatment who died of the disease. RESULTS: The mean tumor area analyzed was 5.04 +/- 0.23 mm2. The mean endothelial area per mm2 of stroma from survivors and dead patients was 0.038 +/- 0.026 mm2 and 0.110 +/- 0.034 mm2, respectively (P < 0.0001). No significant differences were found in histology, tumor grade, status of lymph nodes, and amount of residual tumor. CONCLUSIONS: Image analysis was used to overcome the potential subjectivity of manual counts. Computer-assisted image analysis can evaluate accurately the angiogenic potential in ovarian carcinomas. Tumor angiogenesis may prove to be a prognostic factor in patients with ovarian carcinoma. This study suggests that the measurement of the endothelial area would be clinically useful in determining microvessel density [See editorial on pages 2219-21, this issue.]     

Achieving high hetero-deformation induced(HDI)strengthening and hardening in brass by dual heterostructures

Heterostructured materials,defined as materials that contain multiple zones with dramatically different flow stresses,have the potential to push the envelope of...     

Determining particle-size distributions from chord length measurements for different particle morphologies

A recently proposed model to determine particle-size distributions (PSDs) from chord length measurements has been applied to different particle morphologies, namely compact, platelet- and rod-shaped particles. To study these systems, chord length distributions (CLDs) were measured at varying particle size and solids concentration for each compound and were subsequently utilized to determine the system-specific parameters. Each model was successfully applied to its respective compound such that the experimental PSDs and model predictions were in good agreement. Moreover, the effect of other variables such as agitation rate and solvent composition was investigated and found to be negligible for the specific systems tested. Finally, potential model optimizations of the general model construct have been studied. Two variants of the CLD compression step, namely principal component analysis and a geometric model have been considered as surrogate models. However, neither of these approaches yielded superior results than the previously proposed approach.     

Band alignment at organic-inorganic heterojunctions between P3HT and n-type 6H-SiC

The exact band alignment at organic/inorganic semiconductor heterojunctions is influenced by a variety of properties and is difficult to predict. For organic/inorganic bilayer heterojunctions made of poly(3-hexylthiophene) (P3HT) and n-type 6H-SiC, the band alignment is determined via current-voltage measurements. For this purpose, a model equivalent circuit, combining thermionic emission and space-charge-limited current effects, is proposed which describes the behavior of the heterojunction very well. From the fitting parameters, an interface barrier height of 1.1 eV between the lowest unoccupied molecular orbital (LUMO) of P3HT and the conduction band (CB) of 6H-SiC is determined. In addition, from the maximum open circuit voltage of 6H-SiC/P3HT diodes, a difference of 0.9 eV between the highest occupied molecular orbital (HOMO) of P3HT and the CB of 6H-SiC is deduced. These two values determine the alignment of the energy bands of 6H-SiC relative to the HOMO and LUMO of P3HT. The 6H-SiC/P3HT bilayer heterojunction exhibits an open circuit voltage of ~0.5 V at room temperature, which makes such a materials system a potential candidate for bulk heterojunction hybrid solar cells with 6H-SiC nanoparticles.     

Tailoring the Angular Mismatch in MoS2 Homobilayers through Deformation Fields

Ultrathin MoS₂ has shown remarkable characteristics at the atomic scale with an immutable disorder to weak external stimuli. Ion beam modification unlocks the potential to selectively tune the size, concentration, and morphology of defects produced at the site of impact in 2D materials. Combining experiments, first-principles calculations, atomistic simulations, and transfer learning, it is shown that irradiation-induced defects can induce a rotation-dependent moiré pattern in vertically stacked homobilayers of MoS₂ by deforming the atomically thin material and exciting surface acoustic waves (SAWs). Additionally, the direct correlation between stress and lattice disorder by probing the intrinsic defects and atomic environments are demonstrated. The method introduced in this paper sheds light on how engineering defects in the lattice can be used to tailor the angular mismatch in van der Waals (vdW) solids.