Myxofibrosarcoma of the thyroid gland

AbstractIntroductionMyxofibrosarcoma of the thyroid is exceptional: a Medline search found a single case report. We report a new case which raised diagnostic and therapeutic problems.ObservationWe report the case of a 74-year-old woman who presented with swelling of the left thyroid lobe and ipsilateral cervical lymphadenopathy. Total thyroidectomy with cervical lymph-node dissection was performed. Histological analysis diagnosed myxofibrosarcoma. Evolution was marked by rapid local recurrence, and chemotherapy based on doxorubicin and ifosfamide was introduced.Discussion/conclusionHead and neck myxofibrosarcoma is rare. MRI is essential and should always precede treatment. Diagnosis is histological. There is elevated risk of local recurrence after resection, accompanied by worsening tumor grade, whence the need for accurate diagnosis, appropriate treatment and regular MRI follow-up

Analysis of Temperature-Programmed Desorption via Equilibrium Thermodynamics

Temperature-programmed desorption (TPD) experiments in surface science are usually analyzed using the Polanyi–Wigner equation and/or transition-state theory. These methods are far from straightforward, and the determination of the pre-exponential factor is often problematic. We present a different method based on equilibrium thermodynamics, which builds on an approach previously used for TPD by Kreuzer et al. (Surf. Sci.1988). Equations for the desorption rate are presented for three different types of surface–adsorbate interactions: (i) a 2D ideal hard-sphere gas with a negligible diffusion barrier, (ii) an ideal lattice gas, that is, fixed adsorption sites without interaction between the adsorbates, and (iii) a lattice gas with a distribution of (site-dependent) adsorption energies. We show that the coverage dependence of the sticking coefficient for adsorption at the desorption temperature determines whether the desorption process can be described by first- or second-order kinetics. The sticking coefficient at the desorption temperature must also be known for a quantitative determination of the adsorption energy, but it has a rather weak influence (like the pre-exponential factor in a traditional TPD analysis). Quantitative analysis is also influenced by the vibrational contributions to the energy and entropy. For the case of a single adsorption energy, we provide equations to directly convert peak temperatures into adsorption energies. These equations also provide an approximation of the desorption energy in cases that cannot be described by a fixed pre-exponential factor. For the case of a distribution of adsorption energies, the desorption spectra cannot be considered a superposition of desorption spectra corresponding to the different energies. Nevertheless, we present a method to extract the distribution of adsorption energies from TPD spectra, and we rationalize the energy resolution of TPD experiments. The analytical results are complemented by a program for simulation and analysis of TPD data

Analysis of Temperature-Programmed Desorption via Equilibrium Thermodynamics

Temperature-programmed desorption (TPD) experiments in surface science are usually analyzed using the Polanyi–Wigner equation and/or transition-state theory. These methods are far from straightforward, and the determination of the pre-exponential factor is often problematic. We present a different method based on equilibrium thermodynamics, which builds on an approach previously used for TPD by Kreuzer et al. (Surf. Sci.1988). Equations for the desorption rate are presented for three different types of surface–adsorbate interactions: (i) a 2D ideal hard-sphere gas with a negligible diffusion barrier, (ii) an ideal lattice gas, that is, fixed adsorption sites without interaction between the adsorbates, and (iii) a lattice gas with a distribution of (site-dependent) adsorption energies. We show that the coverage dependence of the sticking coefficient for adsorption at the desorption temperature determines whether the desorption process can be described by first- or second-order kinetics. The sticking coefficient at the desorption temperature must also be known for a quantitative determination of the adsorption energy, but it has a rather weak influence (like the pre-exponential factor in a traditional TPD analysis). Quantitative analysis is also influenced by the vibrational contributions to the energy and entropy. For the case of a single adsorption energy, we provide equations to directly convert peak temperatures into adsorption energies. These equations also provide an approximation of the desorption energy in cases that cannot be described by a fixed pre-exponential factor. For the case of a distribution of adsorption energies, the desorption spectra cannot be considered a superposition of desorption spectra corresponding to the different energies. Nevertheless, we present a method to extract the distribution of adsorption energies from TPD spectra, and we rationalize the energy resolution of TPD experiments. The analytical results are complemented by a program for simulation and analysis of TPD data

Self-Limiting Adsorption of WO₃ Oligomers on Oxide Substrates in Solution

Electrochemical surface science of oxides is an emerging field with expected high impact in developing, for instance, rationally designed catalysts. The aim in such catalysts is to replace noble metals by earth-abundant elements, yet without sacrificing activity. Gaining an atomic-level understanding of such systems hinges on the use of experimental surface characterization techniques such as scanning tunneling microscopy (STM), in which tungsten tips have been the most widely used probes, both in vacuum and under electrochemical conditions. Here, we present an <i>in situ</i> STM study with atomic resolution that shows how tungsten­(VI) oxide, spontaneously generated at a W STM tip, forms 1D adsorbates on oxide substrates. By comparing the behavior of rutile TiO₂(110) and magnetite Fe₃O₄(001) in aqueous solution, we hypothesize that, below the point of zero charge of the oxide substrate, electrostatics causes water-soluble WO₃ to efficiently adsorb and form linear chains in a self-limiting manner up to submonolayer coverage. The 1D oligomers can be manipulated and nanopatterned <i>in situ</i> with a scanning probe tip. As WO₃ spontaneously forms under all conditions of potential and pH at the tungsten–aqueous solution interface, this phenomenon also identifies an important caveat regarding the usability of tungsten tips in electrochemical surface science of oxides and other highly adsorptive materials

Trapping Nitric Oxide by Surface Hydroxyls on Rutile TiO₂(110)

Hydroxyls are omnipresent on oxide surfaces under ambient conditions. While they unambiguously play an important role in many catalytic processes, it is not well-understood how these species influence surface chemistry at atomic scale. We investigated the adsorption of nitric oxide (NO) on a hydroxylated rutile TiO₂(110) surface with scanning tunneling microscopy (STM), X-ray/ultraviolet photoemission spectroscopy (XPS/UPS), and density functional theory (DFT) calculations. At room temperature adsorption of NO is only possible in the vicinity of a surface hydroxyl, and leads to a change of the local electronic structure. DFT calculations confirm that the surface hydroxyl-induced excess charge is transferred to the NO adsorbate, which results in an electrostatic stabilization of the adsorbate and, consequently, a significantly stronger bonding

Prototypical Organic–Oxide Interface: Intramolecular Resolution of Sexiphenyl on In₂O₃(111)

The performance of an organic semiconductor device is critically determined by the geometric alignment, orientation, and ordering of the organic molecules. Although an organic multilayer eventually adopts the crystal structure of the organic material, the alignment and configuration at the interface with the substrate/electrode material are essential for charge injection into the organic layer. This work focuses on the prototypical organic semiconductor para-sexiphenyl (6P) adsorbed on In₂O₃(111), the thermodynamically most stable surface of the material that the most common transparent conducting oxide, indium tin oxide, is based on. The onset of nucleation and formation of the first monolayer are followed with atomically resolved scanning tunneling microscopy and noncontact atomic force microscopy (nc-AFM). Annealing to 200 °C provides sufficient thermal energy for the molecules to orient themselves along the high-symmetry directions of the surface, leading to a single adsorption site. The AFM data suggests an essentially planar adsorption geometry. With increasing coverage, the 6P molecules first form a loose network with a poor long-range order. Eventually, the molecules reorient into an ordered monolayer. This first monolayer has a densely packed, well-ordered (2 × 1) structure with one 6P per In₂O₃(111) substrate unit cell, that is, a molecular density of 5.64 × 10¹³ cm^–2

Surface Structure of TiO₂ Rutile (011) Exposed to Liquid Water

The rutile TiO₂(011) surface exhibits a (2 × 1) reconstruction when prepared by standard techniques in ultrahigh vacuum (UHV). Here we report that a restructuring occurs upon exposing the surface to liquid water at room temperature. The experiment was performed in a dedicated UHV system, equipped for direct and clean transfer of samples between UHV and liquid environment. After exposure to liquid water, an overlayer with a (2 × 1) symmetry was observed containing two dissociated water molecules per unit cell. The two OH groups yield an apparent “c(2 × 1)” symmetry in scanning tunneling microscopy (STM) images. On the basis of STM analysis and density functional theory (DFT) calculations, this overlayer is attributed to dissociated water on top of the unreconstructed (1 × 1) surface. Investigation of possible adsorption structures and analysis of the domain boundaries in this structure provide strong evidence that the original (2 × 1) reconstruction is lifted. Unlike the (2 × 1) reconstruction, the (1 × 1) surface has an appropriate density and symmetry of adsorption sites. The possibility of contaminant-induced restructuring was excluded based on X-ray photoelectron spectroscopy (XPS) and low-energy He⁺ ion scattering (LEIS) measurements

Following the Reduction of Oxygen on TiO₂ Anatase (101) Step by Step

We have investigated the reaction between O₂ and H₂O, coadsorbed on the (101) surface of a reduced TiO₂ anatase single crystal by scanning tunneling microscopy, density functional theory, temperature-programmed desorption, and X-ray photoelectron spectroscopy. While water adsorbs molecularly on the anatase (101) surface, the reaction with O₂ results in water dissociation and formation of terminal OH groups. We show that these terminal OHs are the final and stable reaction product on reduced anatase. We identify OOH as a metastable intermediate in the reaction. The water dissociation reaction runs as long as the surface can transfer enough electrons to the adsorbed species; the energy balance and activation barriers for the individual reaction steps are discussed, depending on the number of electrons available. Our results indicate that the presence of donor dopants can significantly reduce activation barriers for oxygen reduction on anatase

Nickel Carbide as a Source of Grain Rotation in Epitaxial Graphene

Graphene has a close lattice match to the Ni(111) surface, resulting in a preference for 1 × 1 configurations. We have investigated graphene grown by chemical vapor deposition (CVD) on the nickel carbide (Ni₂C) reconstruction of Ni(111) with scanning tunneling microscopy (STM). The presence of excess carbon, in the form of Ni₂C, prevents graphene from adopting the preferred 1 × 1 configuration and leads to grain rotation. STM measurements show that residual Ni₂C domains are present under rotated graphene. Nickel vacancy islands are observed at the periphery of rotated grains and indicate Ni₂C dissolution after graphene growth. Density functional theory (DFT) calculations predict a very weak (van der Waals type) interaction of graphene with the underlying Ni₂C, which should facilitate a phase separation of the carbide into metal-supported graphene. These results demonstrate that surface phases such as Ni₂C can play a major role in the quality of epitaxial graphene

Water Adsorption at the Tetrahedral Titania Surface Layer of SrTiO₃(110)-(4 × 1)

The interaction of water with oxide surfaces is of great interest for both fundamental science and applications. We present a combined theoretical (density functional theory (DFT)) and experimental (scanning tunneling microscopy (STM) and photoemission spectroscopy (PES)) study of water interaction with the two-dimensional titania overlayer that terminates the SrTiO₃(110)-(4 × 1) surface and consists of TiO₄ tetrahedra. STM and core-level and valence band PES show that H₂O neither adsorbs nor dissociates on the stoichiometric surface at room temperature, whereas it does dissociate at oxygen vacancies. This is in agreement with DFT calculations, which show that the energy barriers for water dissociation on the stoichiometric and reduced surfaces are 1.7 and 0.9 eV, respectively. We propose that water weakly adsorbs on two-dimensional, tetrahedrally coordinated overlayers