Versatile vacuum chamber for in situ surface X‐ray scattering studies

A compact portable vacuum‐compatible chamber designed for surface X‐ray scattering measurements on beamline ID01 of the European Synchrotron Radiation Facility, Grenoble, is described. The chamber is versatile and can be used for in situ investigation of various systems, such as surfaces, nanostructures, thin films etc., using a variety of X‐ray‐based techniques such as reflectivity, grazing‐incidence small‐angle scattering and diffraction. It has been conceived for the study of morphology and structure of semiconductor surfaces during ion beam erosion, but it is also used for the study of surface oxidation or thin film growth under ultra‐high‐vacuum conditions. Coherent X‐ray beam experiments are also possible. The chamber is described in detail, and examples of its use are given.     

Phonons, rotons, and layer modes of liquid 4He in aerogel

We report the first observation of two-dimensional layer modes in both fully filled and partially filled aerogel. Using complementary high-energy resolution and high statistical precision neutron scattering instruments, and two different 87% porous aerogel samples, we show that the three-dimensional (3D) phonon-roton excitation energies and lifetimes of liquid 4He in aerogel are the same as in bulk 4He within current precision. The layer modes are the excitations that distinguish aerogel from the bulk rather than a difference in the 3D roton energy.     

Wavelets on irregular meshes

We construct wavelets associated with a mesh involving local refinements. The first stage consists in the definition of a multiresolution analysis adapted to our non-translation invariant situation. Then, we show that, modulo an optimal condition on the geometry of the mesh, the orthogonal complement of the approximation spaces can be constructed by hand and presents the homogeneous behaviour that we were looking for. Finally, we propose a fast algorithm on irregular meshes, using a second wavelet basis constructed for this purpose. The stability of the synthesis algorithm is proved whereas the stability of the analysis algorithm is still an open problem.     

Dynamics of liquid 4He in vycor

Using inelastic neutron scattering, we have observed well-defined phonon-roton ( p-r) excitations in superfluid 4He in Vycor over a wide wave-vector range, 0.3相似文献   

Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine

Further investigations into the chemistry of the rhenacyclobutadiene complexes (CO)₄Re(η²-C(R)C(CO₂Me)C(X)) (1: R=Me, X=OEt (1a), O(CH₂)₃CCH (1b), NEt₂ (1c); R=CHEt₂, X=OEt (1d); R=Ph, X=OEt (1e)) are reported. Reactions of 1 with alkynes at reflux temperature of toluene and at ambient temperature either under photochemical conditions or in the presence of PdO yield ring-substituted η⁵-cyclopentadienylrhenium tricarbonyl complexes, 2. The symmetrical alkynes R^′CCR^′ (R^′=Ph, Me, CO₂Me) afford the pentasubstituted complexes (η⁵-C₅(Me)(CO₂Me)(OEt)(Ph)(Ph))Re(CO)₃ (2d), (η⁵-C₅(Me)(CO₂Me)(OEt)(Me)(Me))Re(CO)₃ (2e), (η⁵-C₅(Me)(CO₂Me)(OEt)(CO₂Me)(CO₂Me))Re(CO)₃ (2f), and (η⁵-C₅(Me)(CO₂Me)(NEt₂)(CO₂Me)(CO₂Me))Re(CO)₃ (2i) on reaction with the appropriate 1, whereas the unsymmetrical alkynes R^′CCR″ (R^′=Ph; R″=H, Me) give either only one, (η⁵-C₅(Me)(CO₂Me)(OEt)(Ph)H)Re(CO)₃ (2a)), or both, (η⁵-C₅(Me)(CO₂Me) (OEt)(Ph)(Me))Re(CO)₃ (2b) and (η⁵-C₅(Me)(CO₂Me)(OEt)(Me)(Ph))Re(CO)₃ (2c), (η⁵-C₅(Ph)(CO₂Me)(OEt)(Ph)H)Re(CO)₃ (2g) and (η⁵-C₅(Ph)(CO₂Me)(OEt)(H)(Ph))Re(CO)₃ (2h), of the possible products of [3 + 2] cycloaddition of alkyne to η²-C(R)C(CO₂Me)C(X). Thermolysis of (CO)₄Re(η²-C(Me)C(CO₂Me)C(O(CH₂)₃CCH)) (1b) containing a pendant alkynyl group proceeds to (η⁵-C₅(Me)(CO₂Me)(O(CH₂)₃)H)Re(CO)₃ (2j), a η⁵-cyclopentadienyl-dihydropyran fused-ring product. Competition experiments showed that each of PhCCH and MeO₂CCCCO₂Me reacts faster than PhCCPh with 1a. The results with unsymmetrical alkynes are rationalized by steric properties of substituents at the CC and ReC bonds and by a preference of ReC(Me) over ReC(OEt) to undergo alkyne insertion. A mechanism is proposed that involves substitution of a trans CO by alkyne in 1, insertion of alkyne into ReC bond to give a rhenabenzene intermediate, and collapse of the latter to 2. Complexes 1a and 1d undergo rearrangement in MeCN at reflux temperature to give rhenafuran-like products, (CO)₄Re(κ²-OC(OMe)C(CHCR₂)C(OEt)) (R=H (3a) or Et (3b)). The reaction of 1d also proceeds in EtCN, PhCN, and t-BuCN at comparable temperature, but is slower (especially in t-BuCN) than in MeCN. In pyridine at reflux temperature, 1a undergoes a similar rearrangement, with CO substitution, to give (CO)₃(py)Re(κ²-OC(OMe)C(CHCEt₂)C(OEt)) (4). A mechanism is proposed for these reactions. The sulfonium ylides Me₂SCHC(O)Ph and Me₂SC(CN)₂ (Me₂SCRR^′) react with 1a in acetonitrile at reflux temperature by nucleophilic addition of the ylide to the ReC(Me) carbon, loss of Me₂S, and rearrangement to a rhenafuran-type structure to yield (CO)₄Re(κ²-OC(OMe)C(C(Me)CRR^′)C(OEt)) (R=H, R^′=C(O)Ph (5a); R=R^′CN (5b)). All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.     

Chemistry of Fischer-type rhenacyclobutadiene complexes. I. Deprotonation, addition/substitution of nucleophilic reagents at α-carbon, and insertion of heteroatoms into rhenium-carbon bonds

The rhenacyclobutadienes (CO)₄Re(η²- C(R)C(CO₂Me)C(OR^′)) (2) undergo a number of reactions that mirror those of Fischer alkoxycarbene complexes. Thus, (CO)₄Re(η²-C(Me)C(CO₂Me)C(OEt)) (2a) can be deprotonated by LDA, Na[OBu-t], or Na[CH(CO₂Me)₂] to give the ylide-like conjugate base [(CO)₄Re(η²-C(CH₂)C(CO₂Me)C(OEt)]⁻ (3), which was isolated as PPN(3). Li(3) undergoes deuteriation with DCl/D₂O and alkylation with Et₃OPF₆ at ReCCH₂, with the latter reaction affording (CO)₄Re(η²-C(CH₂Et)C(CO₂Me)C(OEt)) (4). Repetition of the sequence deprotonation-ethylation on 4 generates (CO)₄Re(η²-C(CHEt₂)C(CO₂Me)C(OEt)) (5). The nature of the alkoxy substituent in 2 can be varied by use of the rhenacyclobutenones Na[(CO)₄Re(η²-C(R)C(CO₂Me)C(O))] (Na(1)) in conjunction with AcCl and R^′OH to produce a series of new complexes (R=Ph, R^′=Et (2b); R=Me, R^′=CH₂CHCH₂ (2c), (CH₂)₃CCH (2d), Me (2e)). Aminolysis of 2a with the primary and secondary amines PhNH₂, HO(CH₂)₂NH, p-TolNH₂, and Et₂NH yields the aminorhenacyclobutadiene complexes (CO)₄Re(η²-C(Me)C(CO₂Me)C(NHR^′ or NR^′₂)) (R₂^′=Et₂ (6a); R^′=Ph (6b), (CH₂)₂OH (6c), p-Tol (6d)). These complexes display lesser carbene-like character than their alkoxy counterparts 2, as evidenced by ¹H and ¹³C NMR spectroscopic properties and lack of reactivity toward LDA by 6a. Reactions of each 2a and 6a with PPhMe₂ at low temperature afford (CO)₄Re(η²-C(Me)(PPhMe₂)C(CO₂Me)C(OEt)) (7) and (CO)₃(PPhMe₂)Re(η²-C(Me)C(CO₂Me)C(NEt₂)) (9), respectively, further in agreement with the more carbenoid nature of 2a than 6a. 7 undergoes conversion to (CO)₃(PPhMe₂)Re(η²-C(Me)C(CO₂Me)C(OEt)) (8) upon heating. 2a reacts with each of (NH₄)₂[Ce(NO₃)₆], DMSO, EtNO₂/Et₃N, and Me₃NO under various conditions to afford one or both of the oxygen atom insertion products into the ReC bonds, (CO)₄Re(κ²-OC(Me)C(CO₂Me)C(OEt)) (10) and (CO)₄Re(κ²-C(Me)C(CO₂Me)C(OEt)O) (11). In contrast, no reaction occurred between 2a and S₈ on heating. However, 6a was converted to the NH insertion product (CO)₄Re(κ²-NHC(Me)C(CO₂Me)C(NEt₂)) (12) by the action of H₂NNH₂ · H₂O at 0 °C. All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.     

Aggregation-Induced Emission and Temperature-Dependent Luminescence of Potassium Perylenetetracarboxylate

Investigation of temperature-dependent photoluminescent properties of potassium perylene-3,4,9,10-tetracarboxylate (K₄PTC), a molecule with no internal rotational degrees of freedom, shows aggregation-induced enhanced emission at room temperature. The different excitonic emission processes are dependent of temperature, some of which quenches in an intermediate temperature range (from 50 to 150 K). The exciton excited states switching phenomenon from "dark" to "bright" states is observed and its explained using Herzberg-Teller selection rule. K₄PTC is a molecule comparable to the size of its precursor, perylene-3,4,9,10-tetracarboxylic anhydride (PTCDA) and is highly soluble in water, contrary to PTCDA, which is poorly soluble in most solvents. Powder x-ray diffraction measurements corroborate a lesser degree of ordering of bulk K₄PTC compared to bulk PTCDA. The green luminescent molecule could, in principle, be used as a biomarker, or in photodynamic therapy, if further studies show relatively low toxicity.