Molecules on Si: Electronics with Chemistry

Basic scientific interest in using a semiconducting electrode in molecule‐based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test‐bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor‐molecule electronics we need reproducible, high‐yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power. To consider these issues and questions we will, in this Progress Report,

• review junctions based on direct bonding of molecules to oxide‐free Si.
• describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified.
• investigate to what extent imperfections in the monolayer are important for transport across the monolayer.
• revisit the concept of energy levels in such hybrid systems.

     

Clarifying Boundary Issues in Psychopathology: The Role of Taxometrics in a Comprehensive Program of Structural Research.

Despite decades of debate, important questions about the boundaries that separate psychological disorder from normality and that distinguish 1 disorder from another remain largely unanswered. These issues pose empirical questions that may be addressed by assessing the latent structure of psychopathological constructs. Because these constructs are likely to be structurally complex, and no single statistical tool addresses all structural questions, it is proposed in this article that boundary issues be examined through programmatic research grounded in the taxometric method and elaborated by complementary analyses. The authors describe how such a program could delimit the structure of disorders and test competing explanations of diagnostic co-occurrence, emphasizing the potential to enhance the reliability and validity of assessment, maximize the power of research designs, and improve diagnostic classification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An Engineered Nanocomplex with Photodynamic and Photothermal Synergistic Properties for Cancer Treatment

Photodynamic therapy (PDT) and photothermal therapy (PTT) are promising therapeutic methods for cancer treatment; however, as single modality therapies, either PDT or PTT is still limited in its success rate. A dual application of both PDT and PTT, in a combined protocol, has gained immense interest. In this study, gold nanoparticles (AuNPs) were conjugated with a PDT agent, meso-tetrahydroxyphenylchlorin (mTHPC) photosensitizer, designed as nanotherapeutic agents that can activate a dual photodynamic/photothermal therapy in SH-SY5Y human neuroblastoma cells. The AuNP-mTHPC complex is biocompatible, soluble, and photostable. PDT efficiency is high because of immediate reactive oxygen species (ROS) production upon mTHPC activation by the 650-nm laser, which decreased mitochondrial membrane potential (^∆ψ_m). Likewise, the AuNP-mTHPC complex is used as a photoabsorbing (PTA) agent for PTT, due to efficient plasmon absorption and excellent photothermal conversion characteristics of AuNPs under laser irradiation at 532 nm. Under the laser irradiation of a PDT/PTT combination, a twofold phototoxicity outcome follows, compared to PDT-only or PTT-only treatment. This indicates that PDT and PTT have synergistic effects together as a combined therapeutic method. Our study aimed at applying the AuNP-mTHPC approach as a potential treatment of cancer in the biomedical field.     

A taxometric investigation of the latent structure of worry.

Researchers have described 2 types of worriers, normal and pathological, who differ in the frequency, intensity, and controllability of their worry experiences. Although normal and pathological worry are generally treated as separate though related phenomena, no study has tested for separateness against the alternative hypothesis that all worry exists along a single dimension. In the present study, worry ratings of 1,588 college students were submitted to taxometric procedures designed to evaluate latent structure. Results provided evidence for the dimensionality of worry. These findings suggest that generalized anxiety disorder (GAD), whose central feature is worry, may also be quantitatively rather than qualitatively different from normal functioning. The authors argue that a focus on normal and pathological extremes has constrained the study of worry phenomena and that dimensional conceptualization of worry may significantly enhance understanding of both worry and GAD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electronic Contact Deposition onto Organic Molecular Monolayers: Can We Detect Metal Penetration?

Using a semiconductor as the substrate to a molecular organic layer, penetration of metal contacts can be clearly identified by the study of electronic charge transport through the layer. A series of monolayers of saturated hydrocarbon molecules with varying lengths is assembled on Si or GaAs and the junctions resulting after further electronic contact is made by liquid Hg, indirect metal evaporation, and a “ready‐made” metal pad are measured. In contrast to tunneling characteristics, which are ambiguous regarding contact penetration, the semiconductor surface barrier is very sensitive to any direct contact with a metal. With the organic monolayer intact, a metal–insulator–semiconductor (MIS) structure results. If metal penetrated the monolayer, the junction behaves as a metal–semiconductor (MS) structure. By comparing a molecule‐free interface (MS junction) with a molecularly modified one (presumably MIS), possible metal penetration is identified. The major indicators are the semiconductor electronic transport barrier height, extracted from the junction transport characteristics, and the photovoltage. The approach does not require a series of different monolayers and data analysis is quite straightforward, helping to identify non‐invasive ways to make electronic contact to soft matter.     

Accelerating image registration with the Johnson-Lindenstrauss lemma: application to imaging 3-D neural ultrastructure with electron microscopy

We present a novel algorithm to accelerate feature based registration, and demonstrate the utility of the algorithm for the alignment of large transmission electron microscopy (TEM) images to create 3-D images of neural ultrastructure. In contrast to the most similar algorithms, which achieve small computation times by truncated search, our algorithm uses a novel randomized projection to accelerate feature comparison and to enable global search. Further, we demonstrate robust estimation of nonrigid transformations with a novel probabilistic correspondence framework, that enables large TEM images to be rapidly brought into alignment, removing characteristic distortions of the tissue fixation and imaging process. We analyze the impact of randomized projections upon correspondence detection, and upon transformation accuracy, and demonstrate that accuracy is maintained. We provide experimental results that demonstrate significant reduction in computation time and successful alignment of TEM images.     

Evaluation of nanoparticle dispersion in polypropylene by small-angle X-ray scattering

A small-angle X-ray scattering method has been developed for the quantitative evaluation of the effectiveness of nanoparticle dispersion in polymer matrices; it is termed the nanoscale dispersion index. This method was applied to dispersions of nanosized TiO₂ fillers in polypropylene. Master batches prepared with lower filler contents showed better dispersion as evaluated by the nanoscale dispersion index. The addition of 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol to the compounds did not affect the degree of nanoscale dispersion as estimated by the nanoscale dispersion index. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Leading us not into temptation: Momentary allurements elicit overriding goal activation.

The present research explored the nature of automatic associations formed between short-term motives (temptations) and the overriding goals with which they interfere. Five experimental studies, encompassing several self-regulatory domains, found that temptations tend to activate such higher priority goals, whereas the latter tend to inhibit the temptations. These activation patterns occurred outside of participants' conscious awareness and did not appear to tax their mental resources. Moreover, they varied as a function of subjective goal importance and were more pronounced for successful versus unsuccessful self-regulators in a given domain. Finally, priming by temptation stimuli was found not only to influence the activation of overriding goals but also to affect goal-congruent behavioral choices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The latent structure of social anxiety disorder: Consequences of shifting to a dimensional diagnosis.

Despite longstanding debate over the nature of the boundary between social anxiety disorder (SAD) and less severe social anxiety, no study has tested directly whether the defining features of the disorder correspond to a latent category or dimension. The present study examined this question using data from the National Comorbidity Survey Replication (NCS-R), a nationally representative survey of the U.S. household population. Indicators representing the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM–IV; American Psychiatric Association, 1994) criteria for SAD were submitted to taxometric analyses in a subsample of adults (n = 2,166) who reported excessive social fear in their lifetime. Multiple taxometric procedures and consistency tests converged on a dimensional solution, suggesting that SAD is continuous with milder social anxiety. In follow-up analyses, a dimensional SAD diagnosis outperformed the DSM–IV diagnosis in predicting the subsequent onset of a range of clinically important outcomes. Large differences in associations with comorbid mood disorders, suicidality, and treatment seeking in particular favored the prognostic value of dimensional over categorical diagnosis. These findings support the validity and potential utility of a dimensional conceptualization of SAD that may inform efforts to revise the diagnosis for DSM–V. (PsycINFO Database Record (c) 2010 APA, all rights reserved)