How do electronic carriers cross Si-bound alkyl monolayers?

Electron transport through Si-C bound alkyl chains, sandwiched between n-Si and Hg, is characterized by two distinct types of barriers, each dominating in a different voltage range. At low voltage, current depends strongly on temperature but not on molecular length, suggesting transport by thermionic emission over a barrier in the Si. At higher voltage, the current decreases exponentially with molecular length, suggesting tunneling through the molecules. The tunnel barrier is estimated, from transport and photoemission data, to be ~1.5 eV with a 0.25me effective mass.Comment: 13 pages, 3 figure

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

We compare the charge transport characteristics of heavy doped p- and n-Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p- and n-type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current

Incorporation of cobaltocene as an n-dopant in organic molecular films

© 2007 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.2752145DOI: 10.1063/1.2752145Electrical or chemical doping of molecular films is an efficient means of improving and controlling charge injection and carrier transport in organic devices. Recent work demonstrated that bis(cyclopentadienyl)cobalt(II) (cobaltocene, CoCp₂) efficiently dopes a tris(thieno)hexaazatriphenylene (THAP) derivative, as shown by a 0.56 eV shift of the Fermi level toward the empty states and an increase of current density by a factor of 10³ over undoped THAP devices. In this work, a combination of x-ray photoemission spectroscopy and Rutherford backscattering is used to elucidate the details of dopant incorporation into bulk films. Cobaltocene is observed to codeposit into the THAP matrix in a controllable manner, with preferential adsorption of the dopant onto the surface of the host film. In the case of CoCp₂-doped tris(8-hydroxy-quinolinato) aluminum (Alq₃) films, negligible amounts of the dopant are found in the bulk matrix and on the film surface, resulting in minimal improvements in the electrical characteristics of doped Alq₃ films. The process of CoCp₂ adsorption onto a film surface or the evolving surface of a growing film which leads to dopant incorporation is likely assisted by charge transfer from cobaltocene to the host material, resulting in ion pairing between the dopant and host

A Study of Competing Designs for a Liquidity-Saving Mechanism

We study two designs for a liquidity-saving mechanism (LSM), a queuing arrangement used with an interbank settlement system. We consider an environment where banks are subjected to liquidity shocks. Banks must make the decision to send, queue, or delay their payments after observing a noisy signal of the shock. With a balance-reactive LSM, banks can set a balance threshold below which payments are not released from the queue. Banks can choose their threshold such that the release of a payment from the queue is conditional on the liquidity shock. With a receipt-reactive LSM, a payment is released from the queue if an offsetting payment is received, regardless of the liquidity shock. We find that these two designs have opposite effects on different types of payments. Payments that are costly to delay will be settled at least as early, or earlier, with a receipt-reactive LSM. Payments that are not costly to delay will always be delayed with a receipt-reactive LSM, while some of them will be queued and settled early with a balance-reactive LSM. We also show that parameter values will determine which system provides higher welfare

Quantitative assessment of cardiac load-responsiveness during extracorporeal life support: case and rationale

We describe a case of a patient assisted by extracorporeal life support, in which we obtained the dynamic filling index, a measure for venous volume during extracorporeal life support, and used this index to assess cardiac load-responsiveness during acute reloading. While reloading, the obtained findings on cardiac pump function by the dynamic filling index were supported by trans-esophageal echocardiography and standard pressure measurement. This suggests that the dynamic filling index can be used to assess cardiac load-responsiveness during extracorporeal life support

Overnight RRP Operations as a Monetary Policy Tool: Some Design Considerations

We review recent changes in monetary policy that have led to development and testing of an overnight reverse repurchase agreement (ON RRP) facility, an innovative tool for implementing monetary policy during the normalization process. Making ON RRPs available to a broad set of investors, including nonbank institutions that are significant lenders in money markets, could complement the use of the interest on excess reserves (IOER) and help control short-term interest rates. We examine some potentially important secondary effects of an ON RRP facility, both positive and negative, including impacts on the structure of short-term funding markets and financial stability. We also investigate design features of an ON RRP facility that could mitigate secondary effects deemed undesirable. Finally, we discuss tradeoffs that policymakers may face in designing an ON RRP facility, as they seek to balance the objectives of setting an effective floor on money market rates during the normalization process and limiting any adverse secondary effects

Repos, Fire Sales, and Bankruptcy Policy

The events from the 2007-2009 financial crisis have raised concerns that the failure of large financial institutions can lead to destabilizing fire sales of assets. The risk of fire sales is related to exemptions from bankruptcy's automatic stay provision enjoyed by a number of financial contracts, such as repo. An automatic stay prohibits collection actions by creditors against a bankrupt debtor or his property. It prevents a creditor from liquidating collateral of a defaulting debtor since collateral is a lien on the debtor's property. In this paper, we construct a model of repo transactions, and consider the effects of changing the bankruptcy rule regarding the automatic stay on the activity in repo and real investment markets. We find that exempting repos from the automatic stay is beneficial for creditors who that hold the borrowers' collateral. Although the exemption may increase the size of the repo market by enhancing the liquidity of collateral, it can also lead to subsequent damaging fire sales that are associated with reductions in real investment activity. Hence, policy makers face a trade-off between the benefits of investment activity and the benefits of liquid markets for collateral

Intercomparison of desert dust optical depth from satellite measurements

This work provides a comparison of satellite retrievalsof Saharan desert dust aerosol optical depth (AOD)during a strong dust event through March 2006. In this event,a large dust plume was transported over desert, vegetated,and ocean surfaces. The aim is to identify the differencesbetween current datasets. The satellite instruments consideredare AATSR, AIRS, MERIS, MISR, MODIS, OMI,POLDER, and SEVIRI. An interesting aspect is that the differentalgorithms make use of different instrument characteristicsto obtain retrievals over bright surfaces. These includemulti-angle approaches (MISR, AATSR), polarisationmeasurements (POLDER), single-view approaches using solarwavelengths (OMI, MODIS), and the thermal infraredspectral region (SEVIRI, AIRS). Differences between instruments,together with the comparison of different retrievalalgorithms applied to measurements from the same instrument,provide a unique insight into the performance andcharacteristics of the various techniques employed. As wellas the intercomparison between different satellite products,the AODs have also been compared to co-located AERONETdata. Despite the fact that the agreement between satellite andAERONET AODs is reasonably good for all of the datasets,there are significant differences between them when comparedto each other, especially over land. These differencesare partially due to differences in the algorithms, such as assumptionsabout aerosol model and surface properties. However,in this comparison of spatially and temporally averageddata, it is important to note that differences in sampling, relatedto the actual footprint of each instrument on the heterogeneousaerosol field, cloud identification and the qualitycontrol flags of each dataset can be an important issue

Liquidity-Saving Mechanisms in Collateral-Based RTGS Payment Systems

This paper studies banks' incentives for choosing the timing of their payment submissions in a collateral-based real-time gross settlement payment system and the way in which these incentives change with the introduction of a liquidity-saving mechanism (LSM). We show that an LSM allows banks to economize on collateral while also providing incentives to submit payments earlier. The reason is that, in our model, an LSM allows payments to be matched and offset, helping to settle payment cycles in which each bank must receive a payment that provides sufficient funds to allow the settlement of its own payment. In contrast to fee-based systems, for which Martin and McAndrews (2008a) show that introducing an LSM can lead to lower welfare, in our model welfare is always higher with an LSM in a collateral-based system