Ohmic contact engineering in few-layer black phosphorus: approaching the quantum limit.

Achieving good quality Ohmic contacts to van der Waals materials is a challenge, since at the interface between metal and van der Waals material different conditions can occur, ranging from the presence of a large energy barrier between the two materials to the metallization of the layered material below the contacts. In black phosphorus (bP), a further challenge is its high reactivity to oxygen and moisture, since the presence of uncontrolled oxidation can substantially change the behavior of the contacts. Here we study three of the most commonly used metals as contacts to bP, chromium, titanium, and nickel, and investigate their influence on contact resistance against the variability between different flakes and different samples. We investigate the gate dependence of the current-voltage characteristics of field-effect transistors fabricated with these metals on bP, observing good linearity in the accumulation regime for all metals investigated. Using the transfer length method, from an analysis of ten devices, both at room temperature and at low temperature, Ni results to provide the lowest contact resistance to bP and minimum scattering between different devices. Moreover, we observe that our best devices approach the quantum limit for contact resistance both for Ni and for Ti contacts.

Two pathways of proton transfer reaction to (triphos)Cu(η(1)-BH4) via a dihydrogen bond [triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane].

The interaction of the η(1)-tetrahydroborate copper(i) complex (triphos)Cu(η(1)-BH4) () with proton donors [CF3CH2OH (TFE), (CF3)2CHOH (HFIP), (CF3)3COH (PFTB), PhOH, p-NO2C6H4OH (PNP), p-NO2C6H4N[double bond, length as m-dash]NC6H4OH (PNAP), CF3OH] was a subject of a combined IR spectroscopic and theoretical investigation. Spectral (Δν) and thermodynamic (ΔH) parameters of dihydrogen bond (DHB) formation were determined experimentally. The terminal hydride ligand (characterized by the basicity factor Ej(BH) = 0.87 ± 0.01) is found to be a site of proton transfer which begins with nucleophilic substitution of BH4(-) by the alcohol oxygen atom on the copper center (BH pathway). The activation barrier computed for (CF3)2CHOH in CH2Cl2 - ΔG = 20.6 kcal mol(-1) - is in good agreement with the experimental value (ΔG = 20.0 kcal mol(-1)). An abnormal dependence of the reaction rate on the proton donor strength found experimentally in dichloromethane is explained computationally on the basis of the variation of the structural and energetic details of this process with the proton donor strength. In the second reaction mechanism found (CuH pathway), DHB complexes with the initial ROH coordination to the bridging hydride lead to B-Hbr bond cleavage with BH3 elimination. "Copper assistance" via the CuO interaction is not involved. This mechanism can be evoked to explain the occurrence of proton transfer in coordinating solvents.

Chemical curing in alkyd paints: an evaluation via FT-IR and NMR spectroscopies.

A study aimed at determining the time necessary for an alkyd paint to attain chemical curing is presented. In particular, the object of our investigation was an oil paint made by Winsor & Newton, namely French ultramarine (PB29) in the Griffin Alkyd "fast drying oil colour" series. Using this paint, we prepared several mock-ups on glass. These were left in the laboratory at room temperature in a piece of furniture with glass doors for a total of 70 days. Samples were taken at different times, and the changes in their composition were monitored by means of FT-IR and multinuclear NMR spectroscopic analyses. Since the cross-linking reactions involved in the formation of the pictorial film mainly affect the amount of carbon-carbon double bonds, we monitored the decrease in allyl, diallyl and vinyl protons and carbons. The data obtained from the use of both techniques led us to conclude that, in our particular experimental conditions, the chemical curing of the paint layer is reached within the first 70 days, thus establishing the beginning of the ageing phenomena.

Cyclotriphosphorus complexes: solid-state structures and dynamic behavior of monoadducts with carbonyl fragments.

Treatment of the cyclo-P3 complexes [(triphos)MP3] [triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane; M = Co (1), Rh (2)] with stoichiometric amounts of [M'(CO)5(thf)]n+ (n = 0, M' = Cr, Mo, W; n = 1, M' = Re) and [W(CO)4(PPh3)(thf)] yields the compounds [[(triphos)M](mu,eta 3:1-P3) [M'(CO)5]] [M = Co; M' = Cr (3a), Mo (3b), W (3c). M = Rh; M' = W (4)], [[(triphos)Co](mu,eta 3:1-P3)[Re(CO5)]]BF4.C7H8 (5) and [[(triphos)Rh](mu,eta 3:1-P3)[W(CO)4PPh3]].2CH2Cl2 (6). The X-ray structures of 5 and 6 have been determined. Crystal data: 5, monoclinic space group P2(1)/n, a = 14.754(2) A, b = 24.886(4) A, c = 15.182(2) A, beta = 103.38(1) degrees, Z = 4; 6, monoclinic space group P2(1)/n, a = 14.872(3) A, b = 27.317(6) A, c = 16.992(4) A, beta = 111.75(5) degrees, Z = 4. The effects of eta 1 coordination on the MP3 core are discussed by comparing the MP3 skeletons in the above structures with those of the previously characterized bis and tris end-on adducts of organometallic fragments of 1. Variable temperature NMR data for the compounds provide evidence for fluxional processes in solution that may be interpreted as [(triphos)M] rotation about its C3 axis and [M'(CO)5] or [M'(CO)4PPh3] scrambling over the P3 cycle. The activation parameters of the fragment scrambling process are determined.

1H- and 2H-T1 relaxation behavior of the rhodium dihydrogen complex [(triphos)Rh(eta 2-H2)H2]+.

Protonation of the classical trihydride [(triphos)RhH3] (2) at 210 K in either THF or CH2Cl2 by either HBF4.OMe2 or CF3SO2OH gives the nonclassical eta 2-H2 complex [(triphos)Rh(eta 2-H2)H2]+ (1) [triphos = MeC(CH2PPh2)3]. Complex 1 is thermally unstable and highly fluxional in solution. In THF above 230 K, 1 transforms into the solvento dihydride complex [(triphos)Rh(eta 1-THF-d8)H2]+ (5) that, at room temperature, quickly converts to the stable dimer trans-[[(triphos)RhH]2(mu-H)2]2+ (trans-6). In CH2Cl2, 1 is stable up to 240 K. Above this temperature, the eta 2-H2 complex begins to convert into a mixture of trans- and cis-6, which, in turn, transform into the bridging-chloride dimers trans- and cis-[[(triphos)RhH]2(mu-Cl)2]2+ at room temperature. Complex 1 contains a fast-spinning H2 ligand with a T1min of 38.9 ms in CD2Cl2 (220 K, 400 MHz). An NMR analysis of the bis-deuterated isotopomer [(triphos)RhH2D2]+ (1-d2) did not provide a J(HD) value. At 190 K, the perdeuterated isotopomers [(triphos)RhD3] (2-d3) and 1-d4 show T1min values of 16.5 and 32.6 ms (76.753 MHz), respectively, for the rapidly exchanging deuterides. An analogous 2-fold elongation of T1min is also observed on going from [(triphos)IrD3] to [(triphos)Ir(eta 2-D2)D2]+. A rationale for the elongation of T1min in nonclassical polyhydrides is proposed on the basis of both the results obtained and recent literature reports.

[Role of transesophageal echocardiography in the evaluation of the potential embolic risk in left atrial thrombosis. Report of a clinical case]. / Ruolo dell'ecocardiografia transesofagea nella valutazione del potenziale rischio embolico della trombosi atriale sinistra. Descrizione di un caso clinico.

We describe the case of a 73-year-old man with cardiac failure due to hypertensive heart disease, chronic atrial fibrillation, prior ischemic stroke and acute ischemia of the left leg probably embolic in nature, in whom transthoracic echocardiography (TTE) detected a large left atrial mass compatible with thrombus. Transesophageal echocardiography (TEE) was performed to better evaluate the atrial mass. TTE showed a mass that was firmly attached to the wall of the left atrium, compact, homogeneous and stationary, indicating a relatively low embolic risk. On the other hand TEE clearly detected a marked motility and echographic unhomogeneity of the atrial mass, suggesting a poorer prognosis and urgent surgical referral due to high impending embolik risk. This case further supports the superiority of TEE to TTE in the assessment of intracardiac masses and, in particular, of embolik risk in a patient with left atrial thrombosis.