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1.
Sci Transl Med ; 16(739): eadk9109, 2024 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-38507469

RESUMO

Myasthenia gravis (MG) is a neuromuscular disease that results in compromised transmission of electrical signals at the neuromuscular junction (NMJ) from motor neurons to skeletal muscle fibers. As a result, patients with MG have reduced skeletal muscle function and present with symptoms of severe muscle weakness and fatigue. ClC-1 is a skeletal muscle specific chloride (Cl-) ion channel that plays important roles in regulating neuromuscular transmission and muscle fiber excitability during intense exercise. Here, we show that partial inhibition of ClC-1 with an orally bioavailable small molecule (NMD670) can restore muscle function in rat models of MG and in patients with MG. In severely affected MG rats, ClC-1 inhibition enhanced neuromuscular transmission, restored muscle function, and improved mobility after both single and prolonged administrations of NMD670. On this basis, NMD670 was progressed through nonclinical safety pharmacology and toxicology studies, leading to approval for testing in clinical studies. After successfully completing phase 1 single ascending dose in healthy volunteers, NMD670 was tested in patients with MG in a randomized, placebo-controlled, single-dose, three-way crossover clinical trial. The clinical trial evaluated safety, pharmacokinetics, and pharmacodynamics of NMD670 in 12 patients with mild MG. NMD670 had a favorable safety profile and led to clinically relevant improvements in the quantitative myasthenia gravis (QMG) total score. This translational study spanning from single muscle fiber recordings to patients provides proof of mechanism for ClC-1 inhibition as a potential therapeutic approach in MG and supports further development of NMD670.


Assuntos
Cloretos , Miastenia Gravis , Humanos , Ratos , Animais , Cloretos/uso terapêutico , Miastenia Gravis/tratamento farmacológico , Músculo Esquelético/fisiologia , Junção Neuromuscular , Canais de Cloreto
2.
Psychopharmacology (Berl) ; 239(10): 3313-3323, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-36094619

RESUMO

The pathophysiology of schizophrenia involves abnormal reward processing, thought to be due to disrupted striatal and dopaminergic function. Consistent with this hypothesis, functional magnetic resonance imaging (fMRI) studies using the monetary incentive delay (MID) task report hypoactivation in the striatum during reward anticipation in schizophrenia. Dopamine neuron activity is modulated by striatal GABAergic interneurons. GABAergic interneuron firing rates, in turn, are related to conductances in voltage-gated potassium 3.1 (Kv3.1) and 3.2 (Kv3.2) channels, suggesting that targeting Kv3.1/3.2 could augment striatal function during reward processing. Here, we studied the effect of a novel potassium Kv3.1/3.2 channel modulator, AUT00206, on striatal activation in patients with schizophrenia, using the MID task. Each participant completed the MID during fMRI scanning on two occasions: once at baseline, and again following either 4 weeks of AUT00206 or placebo treatment. We found a significant inverse relationship at baseline between symptom severity and reward anticipation-related neural activation in the right associative striatum (r = -0.461, p = 0.035). Following treatment with AUT00206, there was a significant increase in reward anticipation-related activation in the left associative striatum (t(13) = 4.23, peak-level p(FWE) < 0.05)), but no significant effect in the ventral striatum. This provides preliminary evidence that the Kv3.1/3.2 potassium channel modulator, AUT00206, may address reward-related striatal abnormalities in schizophrenia.


Assuntos
Esquizofrenia , Estriado Ventral , Humanos , Imageamento por Ressonância Magnética , Recompensa , Esquizofrenia/diagnóstico por imagem , Esquizofrenia/tratamento farmacológico , Canais de Potássio Shaw , Estriado Ventral/fisiologia
3.
J Psychopharmacol ; 36(9): 1061-1069, 2022 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-36164687

RESUMO

BACKGROUND: Current treatments for schizophrenia act directly on dopamine (DA) receptors but are ineffective for many patients, highlighting the need to develop new treatment approaches. Striatal DA dysfunction, indexed using [18F]-FDOPA imaging, is linked to the pathoetiology of schizophrenia. We evaluated the effect of a novel drug, AUT00206, a Kv3.1/3.2 potassium channel modulator, on dopaminergic function in schizophrenia and its relationship with symptom change. Additionally, we investigated the test-retest reliability of [18F]-FDOPA PET in schizophrenia to determine its potential as a biomarker for drug discovery. METHODS: Twenty patients with schizophrenia received symptom measures and [18F]-FDOPA PET scans, before and after being randomised to AUT00206 or placebo groups for up to 28 days treatment. RESULTS: AUT00206 had no significant effect on DA synthesis capacity. However, there was a correlation between reduction in striatal dopamine synthesis capacity (indexed as Kicer) and reduction in symptoms, in the AUT00206 group (r = 0.58, p = 0.03). This was not observed in the placebo group (r = -0.15, p = 0.75), although the placebo group may have been underpowered to detect an effect. The intraclass correlation coefficients of [18F]-FDOPA indices in the placebo group ranged from 0.83 to 0.93 across striatal regions. CONCLUSIONS: The relationship between reduction in DA synthesis capacity and improvement in symptoms in the AUT00206 group provides evidence for a pharmacodynamic effect of the Kv3 channel modulator. The lack of a significant overall reduction in DA synthesis capacity in the AUT00206 group could be due to variability and the low number of subjects in this study. These findings support further investigation of Kv3 channel modulators for schizophrenia treatment. [18F]-FDOPA PET imaging showed very good test-retest reliability in patients with schizophrenia.


Assuntos
Dopamina , Esquizofrenia , Biomarcadores , Corpo Estriado/diagnóstico por imagem , Di-Hidroxifenilalanina/farmacologia , Di-Hidroxifenilalanina/uso terapêutico , Dopamina/farmacologia , Humanos , Tomografia por Emissão de Pósitrons/métodos , Canais de Potássio/farmacologia , Canais de Potássio/uso terapêutico , Reprodutibilidade dos Testes , Esquizofrenia/diagnóstico por imagem , Esquizofrenia/tratamento farmacológico , Canais de Potássio Shaw
4.
Nanomaterials (Basel) ; 11(10)2021 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-34684921

RESUMO

We have systematically investigated the effects of hydrogen annealing on Ni- and Al-contacted carbon nanotube field-effect transistors (CNTFETs), whose work functions have not been affected by hydrogen annealing. Measured results show that the electronic properties of single-walled carbon nanotubes are modified by hydrogen adsorption. The Ni-contacted CNTFETs, which initially showed metallic behavior, changed their p-FET behavior with a high on-current over 10 µA after hydrogen annealing. The on-current of the as-made p-FETs is much improved after hydrogen annealing. The Al-contacted CNTFETs, which initially showed metallic behavior, showed unipolar p-FET behavior after hydrogen annealing. We analyzed the energy band diagrams of the CNTFETs to explain experimental results, finding that the electron affinity and the bandgap of single-walled carbon nanotubes changed after hydrogen annealing. These results are consistent with previously reported ab initio calculations.

5.
Hear Res ; 377: 153-166, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-30939361

RESUMO

AUT00063 is an experimental new medicine that has been demonstrated to suppress spontaneous hyperactivity by modulating the action of voltage-gated potassium-channels in central auditory cortical neurons of a rodent model. This neurobiological property makes it a good candidate for treating the central component of subjective tinnitus but this has not yet been tested in humans. The main purpose of the QUIET-1 (QUest In Eliminating Tinnitus) trial was to examine the effect of AUT00063 on the severity of tinnitus symptoms in people with subjective tinnitus. The trial was a randomised, placebo-controlled, observer, physician and participant blinded multi-centre superiority trial with two parallel groups and a primary endpoint of functional impact on tinnitus 28 days after the first drug dosing day. The trial design overcame the scale and logistical challenges of delivering a scientifically robust, statistically powered multi-centre study for subjective tinnitus within the National Health Service in England. The trial was terminated early for futility. Overall, 212 participants consented across 18 sites with 91 participants randomised to groups using age, gender, tinnitus symptom severity and hearing status as minimisation factors. While the pharmacokinetic markers confirm the uptake of AUT00063 in the body, within the expected therapeutic range, with respect to clinical benefit findings indicated that AUT00063 was not effective in alleviating tinnitus symptoms (1.56 point change in Tinnitus Functional Index). In terms of clinical harms, results indicated that a daily dose of 800 mg capsules of AUT00063 taken for 28 days was safe and well tolerated. These findings provide significant advances in the drug development field for hearing sciences, but raise questions about the predictive validity of certain rodent models of noise-induced hearing loss and tinnitus, as least for the mechanism evaluated in the present study. Trial Registration: (EudraCT) 2014-002179-27; NCT02315508.


Assuntos
Percepção Auditiva/efeitos dos fármacos , Audição/efeitos dos fármacos , Imidazóis/uso terapêutico , Pirimidinas/uso terapêutico , Canais de Potássio Shaw/efeitos dos fármacos , Zumbido/tratamento farmacológico , Adulto , Idoso , Método Duplo-Cego , Término Precoce de Ensaios Clínicos , Inglaterra , Feminino , Humanos , Imidazóis/efeitos adversos , Imidazóis/farmacocinética , Masculino , Pessoa de Meia-Idade , Pirimidinas/efeitos adversos , Pirimidinas/farmacocinética , Índice de Gravidade de Doença , Canais de Potássio Shaw/metabolismo , Fatores de Tempo , Zumbido/diagnóstico , Zumbido/metabolismo , Zumbido/fisiopatologia , Resultado do Tratamento
6.
Sci Rep ; 6: 22700, 2016 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-26939862

RESUMO

There have been many successful attempts to grow high-quality large-area graphene on flat substrates. Doing so at the nanoscale has thus far been plagued by significant scalability problems, particularly because of the need for delicate transfer processes onto predefined features, which are necessarily low-yield processes and which can introduce undesirable residues. Herein we describe a highly scalable, clean and effective, in-situ method that uses thin film deposition techniques to directly grow on a continuous basis ultrathin graphite (uG) on uneven nanoscale surfaces. We then demonstrate that this is possible on a model system of atomic force probe tips of various radii. Further, we characterize the growth characteristics of this technique as well as the film's superior conduction and lower adhesion at these scales. This sets the stage for such a process to allow the use of highly functional graphite in high-aspect-ratio nanoscale components.

7.
Wound Repair Regen ; 22(3): 326-33, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24844332

RESUMO

Scars in humans of African continental ancestry heal with an exaggerated inflammatory response and a generally wider scar. Interleukin-10 is an anti-inflammatory and antifibrotic cytokine. A randomized controlled trial in Caucasians found that exogenous interleukin-10 resulted in improved macroscopic scar appearance and reduced scar redness. We investigated the effects of interleukin-10 on cutaneous scarring in volunteers of African ancestral origin in an exploratory, single-center, within-subject, double-blind randomized controlled trial. Fifty-six subjects received two of four potential prerandomized concentrations of interleukin-10 (5, 25, 100, and 250 ng/100 µL) in two full-thickness incisions on the upper inner arms. Anatomically matching incisions on the contralateral arm were treated with placebo. Scars were excised at 1 month for histological analysis and were redosed with the same regimen. Resultant excision scars were followed up for 12 months for scar width measurement and scoring. Scoring was performed by trial doctors, subjects, and a panel. Incisions treated with 100 ng/100 µL interleukin-10 had significantly reduced microscopic scar widths. Incisions treated with 5 and 25 ng/100 µL interleukin-10 were also narrower, but not significantly. There were no differences observed in pro-inflammatory or pro-fibrotic markers between interleukin-10 and placebo treatment. There was no long-term evidence that 100 ng/100 µL interleukin-10 had a therapeutic effect on macroscopic scar width or appearance, as excisions treated with this concentration were significantly wider than placebo between 8 and 12 months of maturation. Doctors showed a trend toward favoring the macroscopic appearance of placebo-treated excisions compared with those treated with 250 ng/100 µL interleukin-10. Panelists scored placebo-treated excisions as significantly better-appearing than those treated with 250 ng/100 µL interleukin-10. Doctors' scores showed a trend toward favoring treatment with 5 ng/100 µL interleukin-10 at 10 and 11 months post-excision. Subjects showed a trend toward favoring treatment with 5 ng/100 µL interleukin-10 between 5 and 9 months postexcision. Analysis of images of markedly improved scars revealed a potential subset of responders among those treated with 5 ng/100 µL interleukin-10. No concentration of interleukin-10 produced a statistically significant improvement in scarring compared with placebo.


Assuntos
População Negra , Cicatriz/patologia , Inflamação/patologia , Interleucina-10/imunologia , Cicatrização , Ferimentos e Lesões/imunologia , Cicatriz/prevenção & controle , Método Duplo-Cego , Feminino , Humanos , Masculino , Resultado do Tratamento , Cicatrização/imunologia , Ferimentos e Lesões/patologia
8.
Dalton Trans ; 43(20): 7391-9, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24637546

RESUMO

In common with rocksalt-type alkali halide phases and also semiconductors such as GeTe and SnTe, SnSe forms all-surface two atom-thick low dimensional crystals when encapsulated within single walled nanotubes (SWNTs) with diameters below ∼1.4 nm. Whereas previous density functional theory (DFT) studies indicate that optimised low-dimensional trigonal HgTe changes from a semi-metal to a semi-conductor, low-dimensional SnSe crystals typically undergo band-gap expansion. In slightly wider diameter SWNTs (∼1.4-1.6 nm), we observe that three atom thick low dimensional SnSe crystals undergo a previously unobserved form of a shear inversion phase change resulting in two discrete strain states in a section of curved nanotube. Under low-voltage (i.e. 80-100 kV) imaging conditions in a transmission electron microscope, encapsulated SnSe crystals undergo longitudinal and rotational oscillations, possibly as a result of the increase in the inelastic scattering cross-section of the sample at those voltages.

9.
Tetrahedron Lett ; 52(48): 6349-6351, 2011 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-22199407

RESUMO

The C21-C34 fragment of the potent FKBP12-binding macrolide antascomicin B was prepared using Ireland-Claisen and allylic diazene rearrangements to establish the C26/C27 and the C23 stereocenters, respectively. Directed hydrogenation installed the C29 ß-configuration. The fragment possesses 7 of the 11 fixed stereocenters contained in the natural product.

10.
Dalton Trans ; 39(3): 711-4, 2010 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-20066213

RESUMO

A novel and rapid and continuous hydrothermal route to the synthesis of extensive ultra-thin 2D sodium titanate (Na(2)Ti(3)O(7)) nano-sheets using a superheated water flow at 450 degrees C and 24.1 MPa as a crystallizing medium is described. High resolution electron microscopy of the sheets revealed that they were a few layers thick and largely uncurled, highly crystalline despite their very short time under hydrothermal flow conditions. The sodium titanate sheets possessed excellent photocatalytic activity for decolourisation of methylene blue dye.

11.
Nanotechnology ; 20(44): 445608, 2009 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-19809115

RESUMO

We present a method to directly align PbS nanocrystals in micron-sized superstructures within a conjugated polymer. First, lead sulfide nanocrystals are directly synthesized in a MEH-PPV suspension via a single pot, surfactant-free method. Post-synthesis precipitation of the composite solution involving mild oxidation of the nanocrystals results in the formation of nanocrystal-polymer and nanocrystal-oxide superstructures. Detailed TEM is used to study the crystallographic nature of these structures and the roles of polymer and lead sulfate. An epitaxial relationship between lead sulfide and lead sulfate at the nanoscale is shown, giving insight into the oxidation rates of the PbS nanocrystals' facets.

12.
Plast Reconstr Surg ; 124(1): 256-265, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19568089

RESUMO

BACKGROUND: Few data are available regarding the psychological impact of scars arising from routine elective/aesthetic surgical procedures. To gain insight into both patients' and clinicians' concerns, the authors have undertaken structured semiquantitative surveys of (1) patients who had recently undergone a routine surgical procedure and (2) a cohort of plastic and aesthetic dermatological surgeons. METHODS: All selected patients had undergone a surgical procedure within 6 to 24 months before survey and had a scar(s) that caused concern. Participants completed a previously validated Self Completion Form that aimed to investigate their concerns. Clinicians were surveyed via telephone interviews using a similar format of questionnaire but with questions tailored to clinicians. RESULTS: Ninety-seven patients and 24 clinicians were interviewed. Patients were dissatisfied with scars resulting from surgery, irrespective of gender, age, ethnicity, or geographical location, and 91 percent would value even small improvements in scarring. Patients had scar(s) that they wished were less noticeable over a wide range of body sites (both "visible" and "nonvisible"). Male and female respondents had similar rates of dissatisfaction about their own scars. The survey revealed issues in the communication between patients and clinicians regarding scars; 71 percent of patients felt that they were more concerned than their surgeon about the scar resulting from a recent surgical procedure. CONCLUSIONS: This preliminary study indicates that patients are highly concerned about scarring following routine surgery, with most patients valuing any improvement in scarring. These data also show that there are disparities in patient-clinician communication regarding expectations following surgery.


Assuntos
Cicatriz/patologia , Inquéritos e Questionários , Adolescente , Adulto , Idoso , Atitude , Cicatriz/psicologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem
13.
Expert Opin Investig Drugs ; 18(8): 1231-9, 2009 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-19604123

RESUMO

Disfiguring scarring in the skin is an area of high medical need. Current treatments for scarring have variable or limited effectiveness and have typically not been evaluated in randomized, controlled, double-blind clinical trials. The prophylactic improvement in scar appearance, through administration of agents around the time of injury, represents a new therapeutic approach for which there are currently no registered pharmaceuticals. Extensive research into the mechanisms of scar-free and scar-forming healing has provided a robust scientific rationale for the development of avotermin (human recombinant TGF-beta3) as a potential therapeutic for the improvement of scar appearance in humans. The pioneering approach used for the clinical development of avotermin in this new indication has explained the efficacy and safety profile of avotermin in several, prospectively randomized, double-blind clinical studies in human volunteers and patients. These studies, which show a clear translation from preclinical efficacy models to the clinical environment, have shown that prophylactic scar improvement is pharmaceutically achievable. It is anticipated that therapeutics such as avotermin, with a sound mechanistic basis and proof of effectiveness in suitably robust clinical trials, will be available to meet the needs of patients in the foreseeable future.


Assuntos
Cicatriz/tratamento farmacológico , Fator de Crescimento Transformador beta3/uso terapêutico , Animais , Cicatriz/patologia , Cicatriz/prevenção & controle , Ensaios Clínicos como Assunto , Descoberta de Drogas , Avaliação Pré-Clínica de Medicamentos , Humanos , Proteínas Recombinantes/administração & dosagem , Proteínas Recombinantes/farmacologia , Proteínas Recombinantes/uso terapêutico , Pele/efeitos dos fármacos , Pele/patologia , Fator de Crescimento Transformador beta3/administração & dosagem , Fator de Crescimento Transformador beta3/farmacologia , Cicatrização/efeitos dos fármacos
14.
Nat Nanotechnol ; 3(9): 563-8, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18772919

RESUMO

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.


Assuntos
Grafite/síntese química , Transição de Fase , Grafite/química , Pirrolidinonas/química , Análise Espectral/métodos
15.
J Colloid Interface Sci ; 319(1): 140-3, 2008 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-18082178

RESUMO

By employing Na2Se as a selenium source, we demonstrate that extremely small ( approximately 1 nm) mercapto acid-stabilized CdSe nanoparticles can be conveniently prepared in water. The as-prepared nanoparticles start to show dominant near band-gap photoluminescence in the blue spectral range and show high photoluminescence in the green spectral range.

16.
J Psychopharmacol ; 22(1): 55-63, 2008 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-17715211

RESUMO

Sexual dysfunction is common during acute and continuation treatment of depressed patients with selective serotonin (5-hydroxytryptamine, 5-HT) re-uptake inhibitors (ssRIs), but there is no consensus on clinical management. Compounds with 5-HT(1A) agonist properties have been proposed as adjuvant agents in patients continuing with ssRIs. Randomized double-blind placebo-controlled parallel-group fixed-dose 4-week treatment study. Previously depressed male or female patients in symptomatic remission receiving stable doses of fluoxetine or paroxetine but experiencing treatment-emergent sexual dysfunction were randomised to double-blind treatment with placebo or VML-670 (a 5-HT(1A) and 5-HT(1D) agonist). sexual dysfunction was assessed by the Arizona sexual Experiences scale (ASEX). Two-hundred and eighty-eight patients (204 women, 84 men; mean age 44.2 years) received VML-670 (n = 149; 107 women, 42 men) or placebo (n = 139; 97 women, 42 men). In the intention-to-treat, last-observation carried forward analysis (n = 282), proportionately more patients became free of sexual dysfunction with VML-670 (34.3% versus 27.9% with placebo) but this difference was not statistically significant. Male patients treated with VML-670 showed a significantly greater (p =0.01) improvement in ability to achieve and maintain penile erection (a secondary outcome measure). A similar proportion of patients reported on-treatment, treatment-emergent adverse events with VML-670 (71.1%) and placebo (68.3%), and a similar proportion experienced at least one treatment-related adverse event (36.9% versus 35.3%). Double-blind treatment with VML-670 offered no significant advantage over placebo on the primary outcome measure in the overall sample. Further studies may be warranted in larger groups of male patients with sexual dysfunction.


Assuntos
Inibidores Seletivos de Recaptação de Serotonina/efeitos adversos , Agonistas do Receptor 5-HT1 de Serotonina , Agonistas do Receptor de Serotonina/uso terapêutico , Disfunções Sexuais Psicogênicas/tratamento farmacológico , Adulto , Idoso , Método Duplo-Cego , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Agonistas do Receptor de Serotonina/administração & dosagem , Agonistas do Receptor de Serotonina/efeitos adversos , Disfunções Sexuais Psicogênicas/induzido quimicamente
18.
Org Lett ; 8(17): 3663-5, 2006 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-16898786

RESUMO

[reaction: see text] The synthesis of an advanced intermediate in the synthesis of the title compound has been achieved. Key steps include an Ireland-Claisen rearrangement to install the C7 tertiary alcohol stereocenter, an SN2' reaction of an alkoxymethyl Cu reagent, and a diastereoselective Re-catalyzed allylic alcohol transposition.


Assuntos
Hidrocarbonetos Aromáticos com Pontes/síntese química , Diterpenos/síntese química , Furanos/síntese química , Hidrocarbonetos Aromáticos com Pontes/química , Catálise , Cobre/química , Ciclização , Diterpenos/química , Furanos/química , Estrutura Molecular
19.
J Microsc ; 223(Pt 1): 1-8, 2006 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-16872425

RESUMO

High Resolution Electron Microscopy (HREM) is often used to characterize objects supported by amorphous substrates, usually amorphous carbon. HREM is currently undergoing step change in performance due to aberration correctors. This paper examines the aberration corrected imaging of objects supported by amorphous substrates. In particular, we show that a substantial increase in the ratio of the object contrast to the substrate contrast can be achieved by utilizing the strong variation of phase contrast with height, which is present when the spherical aberration has been adjusted to a small value. This variation is examined using the familiar Weak Phase Object Approximation model from which it is determined that the contrast ratio achieves a maximum at a small nonzero value of the spherical aberration. This result is confirmed by multislice modelling which allows for deviations from the Weak Phase Object Approximation and delocalization effects. One important practical result of this study is the need to place the object of interest on the correct side of the amorphous carbon substrate.

20.
Phys Rev Lett ; 96(21): 215501, 2006 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-16803245

RESUMO

Using high resolution electron microscopy and first principles quantum mechanical calculations we have explored the fundamental physics and chemistry of the semiconductor, HgTe grown inside single wall carbon nanotubes. This material forms a low-dimensional structure based on a repeating Hg2Te2 motif in which both atom species adopt new coordination geometries not seen in the bulk. Density-functional theory calculations confirm the stability of this structure and demonstrate conclusively that it arises solely as a consequence of constrained low dimensionality. This change is directly correlated with a modified electronic structure in which the low-dimensional form of HgTe is transformed from a bulk semimetal to a semiconductor.

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