Rhodium Pyrazolate Complexes as Potential CVD Precursors

Reaction of 3,5-(CF3)(2)PzLi with [Rh(mu-Cl)(eta(2)-C2H4)(2)](2) or [Rh(mu-Cl)(PMe3)(2)](2) in Et2O gave the dinuclear complexes [Rh(eta(2)-C2H4)(2)(mu-3,5-(CF3)(2)-Pz)](2) (1) and [Rh-2(mu-Cl)(mu-3,5-(CF3)(2)-Pz) (PMe3)(4)] (2) respectively (3,5-(CF3)(2)Pz = bis-trifluoromethyl pyrazolate). Reaction of PMe3 with [Rh(COD)(mu-3,5-(CF3)(2)-Pz)](2) in toluene gave [Rh(3,5-(CF3)(2)-Pz)(PMe3)(3)] (3). Reaction of 1 and 3 in toluene (1 : 4) gave moderate yields of the dinuclear complex [Rh(PMe3)(2)(mu-3,5-(CF3)(2)-Pz)](2) (4). Reaction of 3,5-(CF3)(2)PzLi with [Rh(PMe3)(4)]Cl in Et2O gave the ionic complex [Rh(PMe3)(4)][3,5-(CF3)(2)-Pz] (5). Two of the complexes, 1 and 3, were studied for use as CVD precursors. Polycrystalline thin films of rhodium (fcc-Rh) and metastable-amorphous films of rhodium phosphide (Rh2P) were grown from 1 and 3 respectively at 170 and 130 degrees C, 0.3 mmHg in a hot wall reactor using Ar as the carrier gas (5 cc min(-1)). Thin films of amorphous rhodium and rhodium phosphide (Rh2P) were grown from 1 and 3 at 170 and 130 degrees C respectively at 0.3 mmHg in a hot wall reactor using H-2 as the carrier gas (7 cc min(-1)).Welch Foundation F-816Petroleum Research Fund 47014-ACSNSF 0741973Chemistr

Surface roughness and thermal conductivity of semiconductor nanowires: going below the Casimir limit

By explicitly considering surface roughness at the atomic level, we quantitatively show that the thermal conductivity of Si nanowires can be lower than Casimir's classical limit. However, this violation only occurs for deep surface degradation. For shallow surface roughness, the Casimir formula is shown to yield a good approximation to the phonon mean free paths and conductivity, even for nanowire diameters as thin as 2.22 nm. Our exact treatment of roughness scattering is in stark contrast with a previously proposed perturbative approach, which is found to overpredict scattering rates by an order of magnitude. The obtained results suggest that a complete theoretical understanding of some previously published experimental results is still lacking.Comment: 11 pages, 4 figure

Patches in a side-by-side configuration: a description of the flow and deposition fields

In the last few decades, a lot of research attention has been paid to flow-vegetation interactions. Starting with the description of the flow field around uniform macrophyte stands, research has evolved more recently to the description of flow fields around individual, distinct patches. However, in the field, vegetation patches almost never occur in isolation. As such, patches will influence each other during their development and interacting, complex flow fields can be expected. In this study, two emergent patches of the same diameter (D = 22 cm) and a solid volume fraction of 10% were placed in a side-by-side configuration in a lab flume. The patches were built as an array of wooden cylinders, and the distance between the patches (gap width Delta) was varied between Delta = 0 and 14 cm. Flow measurements were performed by a 3D Vectrino Velocimeter (Nortek AS) at mid-depth of the flow. Deposition experiments of suspended solids were performed for selected gap widths. Directly behind each patch, the wake evolved in a manner identical to that of a single, isolated patch. On the centerline between the patches, the maximum velocity U-max was found to be independent of the gap width Delta. However, the length over which this maximum velocity persists, the potential core L-j, increased linearly as the gap width increased. After the merging of the wakes, the centerline velocity reaches a minimum value U-min. The minimum centerline velocity decreased in magnitude as the gap width decreased. The velocity pattern within the wake is reflected in the deposition patterns. An erosion zone occurs on the centerline between the patches, where the velocity is elevated. Deposition occurs in the low velocity zones directly behind each patch and also downstream of the patches, along the centerline between the patches at the point of local velocity minimum. This downstream deposition zone, a result of the interaction of neighbouring patch wakes, may facilitate the establishment of new vegetation, which may eventually inhibit flow between the upstream patches and facilitate patch merger

UNDERSTANDING THE PHYSICS OF KAPPA (Κ0): INSIGHTS FROM THE EUROSEISTEST NETWORK

Στην παρούσα μελέτη υπολογίζουμε την παράμετρο απόσβεσης στις υψηλές συχνότητες, κ0, για το δίκτυο EUROSEISTEST. Οι εδαφικές συνθήκες στους 14 επιφανειακούς και 6 υπόγειους επιταχυνσιογράφους κυμαίνονται από μαλακές αποθέσεις έως σκληρό βράχο. Πρώτα διαχωρίζουμε την τοπική από την περιφερειακή απόσβεση και υπολογίζουμε το κ0. Έπειτα, χρησιμοποιούμε την υπάρχουσα γνώση του εδαφικού προφίλ και των δυναμικών εδαφικών ιδιοτήτων για να συσχετίσουμε το κ0 με διάφορες γεωτεχνικές παραμέτρους (Vs30, συχνότητα συντονισμού, βάθος έως το βραχώδες υπόβαθρο). Τέλος, χρησιμοποιούμε τα αποτελέσματά μας για να βελτιώσουμε τη φυσική κατανόηση του κ0. Προτείνουμε ένα μοντέλο που περιλαμβάνει δύο καινοτόμες ιδέες. Αφ’ ενός, παρατηρούμε πως οι τιμές του κ0 σταθεροποιούνται για υψηλές τιμές Vs, κάτι που πιθανώς σημαίνει πως οι τιμές κ0 συγκλίνουν ανά περιοχή για σκληρό βράχο. Σε αυτήν την περίπτωση, προτείνουμε τη χρήση δεδομένων από όργανα εντός γεωτρήσεων για τον υπολογισμό τους. Αφ’ ετέρου, παρατηρούμε πως η εδαφική απόσβεση δεν επαρκεί για να περιγράψει τη συνολική μετρηθείσα απόσβεση. Προτείνουμε την ύπαρξη μιας επιπλέον πηγής απόσβεσης πέραν της εδαφικής: την απόσβεση διασποράς που οφείλεται στις μικρής κλίμακας ετερογένειες του εδαφικού προφίλ. Σε αυτήν την περίπτωση, οι γεωτεχνικές μετρήσεις της απόσβεσης των υλικών ενδέχεται να μην επαρκούν για την εκτίμηση της συνολικής τοπικής απόσβεσης. Ξεκινώντας όμως από μια εκτίμηση της απόσβεσης της περιοχής (από γεώτρηση), και προσθέτοντας την απόσβεση του υλικού, μπορεί κανείς να προσδιορίσει μία ελάχιστη τιμή για το κ0.this study we estimate the spectral decay factor κ0 for the EUROSEISTEST array. Site conditions range from soft sediments to hard rock over 14 surface and 6 downhole accelerographs. First, we separate local and regional high frequency attenuation and measure κ0. Second, we use the existing knowledge of the geological profile and material properties to correlate κ0 with different site characterisation parameters (Vs30, resonant frequency, depth-to-bedrock). Third, we use our results to improve our physical understanding of κ0. We propose a conceptual model comprising two new notions. On the one hand, we observe that κ0 stabilises for high Vs values; this may indicate the existence of regional values for hard rock κ0. If so, we propose that borehole measurements may be useful in determining them. On the other hand, we find that material damping may not suffice to account for the total measured attenuation. We propose that, apart from damping, additional site attenuation may be caused by scattering from small-scale profile variability. If this is so, then geotechnical damping measurements may not suffice to infer overall crustal attenuation under a site; but starting with a regional (borehole) value and adding damping, we might define a lower bound for site-specific κ0