The physics and chemistry of transport in CdSe quantum dot solids

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.Vita.Includes bibliographical references.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Semiconductor quantum dots (QDs) have tunable opto-electronic properties and can be chemically synthesized and manipulated with ease, making them a promising novel material for many diverse applications. An understanding of the physics of charge transport in QDs is not only important for realizing QD based electronic devices, but it also provides crucial insight into the chemical and optical properties of QDs. This thesis highlights how photoconductivity measurements are valuable to advancing our understanding of QD physics because they are exquisitely sensitive to the optical, chemical, and electronic properties of QDs. The work presented in this thesis emphasizes how the chemistry and physics of QD films are deeply entwined. Chapter 2 demonstrates that the photoconductivity and dark conductivity of CdSe QD films are enhanced following annealing at high temperatures. Chapter 3 illustrates that the purity of the QD capping reagent (tri-n-octylphosphine) and the methods used for film preparation can each affect the observed photocurrent by two to three orders of magnitude. In Chapter 4, the methods for CdSe film preparation developed in Chapter 3 are used to make films that exhibit photoconductivity properties consistent with having a low density of trapped charges, in contrast to previous studies. Chapter 5 also uses chemistry to bring CdSe QD films into a new regime of photoconductivity physics. Post-deposition chemical treatments that increase photocurrent by up to three to four orders of magnitude are presented. The voltage dependence of the photocurrent after treatment is consistent with having achieved unity exciton separation efficiency. Furthermore, by bringing CdSe QD films into this(cont.) new regime of higher photoconductivity physics it is found that energetics prevent the facile injection of charges from gold electrodes into CdSe QDs, but there is no barrier to charge extraction.by Mirna Jarosz.Ph.D

Electronic transport in films of colloidal CdSe nanocrystals

We present results for electronic transport measurements on large three-dimensional arrays of CdSe nanocrystals. In response to a step in the applied voltage, we observe a power-law decay of the current over five orders of magnitude in time. Furthermore, we observe no steady-state dark current for fields up to 10^6 V/cm and times as long as 2x10^4 seconds. Although the power-law form of the decay is quite general, there are quantitative variations with temperature, applied field, sample history, and the material parameters of the array. Despite evidence that the charge injected into the film during the measurement causes the decay of current, we find field-scaling of the current at all times. The observation of extremely long-lived current transients suggests the importance of long-range Coulomb interactions between charges on different nanocrystals.Comment: 11 pages, 10 figure

Reuse-based Online Models for Caches

We develop a reuse distance/stack distance based analytical modeling framework for efficient, online prediction of cache performance for a range of cache configurations and replacement policies LRU, PLRU, RANDOM, NMRU. Our framework unifies existing cache miss rate prediction techniques such as Smith’s associativity model, Poisson variants, and hardware way-counter based schemes. We also show how to adapt LRU way-counters to work when the number of sets in the cache changes. As an example application, we demonstrate how results from our models can be used to select, based on workload access characteristics, last-level cache configurations that aim to minimize energy-delay product. Categories andSubjectDescriptor

Additional file 7: Figure S7. of Unique, dual-indexed sequencing adapters with UMIs effectively eliminate index cross-talk and significantly improve sensitivity of massively parallel sequencing

Multiplex captures have comparable uniformity to individual captures. Uniform coverage enables accurate variant calling with minimal sequencing cost. (PDF 115 kb

Additional file 6: Figure S6. of Unique, dual-indexed sequencing adapters with UMIs effectively eliminate index cross-talk and significantly improve sensitivity of massively parallel sequencing

Schematic of the experiment used to measure adapter contamination and multiplexed capture index hopping. Replicate libraries were prepared using 16 unique dual-matched UMI adapters and enriched with the IDT xGen AML Cancer Panel in pools of 1, 4, 8, and 16. Each multiplexing experiment was sequenced on separate Illumina NextSeq runs. (PDF 819 kb

Additional file 10: Figure S10. of Unique, dual-indexed sequencing adapters with UMIs effectively eliminate index cross-talk and significantly improve sensitivity of massively parallel sequencing

Mutation-specific thresholds provide additional improvements to calling accuracy. (a) Number of false positives from 8-oxoguanine errors are found at low frequencies. (b) Increased minimum variant allele frequency thresholds for 8-oxoguanine mutations improves the positive predictive value (PPV) for rare variants without reducing sensitivity. (PDF 168 kb

Cross-oncopanel study reveals high sensitivity and accuracy with overall analytical performance depending on genomic regions.

Targeted sequencing using oncopanels requires comprehensive assessments of accuracy and detection sensitivity to ensure analytical validity. By employing reference materials characterized by the U.S. Food and Drug Administration-led SEquence Quality Control project phase2 (SEQC2) effort, we perform a cross-platform multi-lab evaluation of eight Pan-Cancer panels to assess best practices for oncopanel sequencing. All panels demonstrate high sensitivity across targeted high-confidence coding regions and variant types for the variants previously verified to have variant allele frequency (VAF) in the 5-20% range. Sensitivity is reduced by utilizing VAF thresholds due to inherent variability in VAF measurements. Enforcing a VAF threshold for reporting has a positive impact on reducing false positive calls. Importantly, the false positive rate is found to be significantly higher outside the high-confidence coding regions, resulting in lower reproducibility. Thus, region restriction and VAF thresholds lead to low relative technical variability in estimating promising biomarkers and tumor mutational burden. This comprehensive study provides actionable guidelines for oncopanel sequencing and clear evidence that supports a simplified approach to assess the analytical performance of oncopanels. It will facilitate the rapid implementation, validation, and quality control of oncopanels in clinical use.All SEQC2 participants freely donated their time, reagents, and computing resources for the completion and analysis of this project. Part of this work was carried out with the support of the Intramural Research Program of the National Institutes of Health (to Mehdi Pirooznia), National Institute of Environmental Health Sciences (to Pierre Bushel), and National Library of Medicine (to Danielle Thierry-Mieg, Jean Thierry-Mieg, and Chunlin Xiao). Leming Shi and Yuanting Zheng were supported by the National Key R&D Project of China (2018YFE0201600), the National Natural Science Foundation of China (31720103909), and Shanghai Municipal Science and Technology Major Project (2017SHZDZX01). Donald J. Johann, Jr. acknowledges the support by FDA BAA grant HHSF223201510172C. Timothy Mercer and Ira Deveson were supported by the National Health and Medical Research Council (NHMRC) of Australia grants APP1108254, APP1114016, and APP1173594 and Cancer Institute NSW Early Career Fellowship 2018/ECF013. This research has also been, in part, financially supported by the MEYS of the CR under the project CEITEC 2020 (LQ1601), by MH CR, grant No. (NV19-03-00091). Part of this work was carried out with the support of research infrastructure EATRIS-CZ, ID number LM2015064, funded by MEYS CR. Boris Tichy and Nikola Tom were supported by research infrastructure EATRIS-CZ, ID number LM2018133 funded by MEYS CR and MEYS CR project CEITEC 2020 (LQ1601).S