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1.
Molecules ; 28(4)2023 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-36838883

RESUMO

Two-dimensional materials have wide ranging applications in electronic devices and catalysts owing to their unique properties. Boron-based compounds, which exhibit a polymorphic nature, are an attractive choice for developing boron-based two-dimensional materials. Among them, rhombohedral boron monosulfide (r-BS) has recently attracted considerable attention owing to its unique layered structure similar to that of transition metal dichalcogenides and a layer-dependent bandgap. However, experimental evidence that clarifies the charge carrier type in the r-BS semiconductor is lacking. In this study, we synthesized r-BS and evaluated its performance as a semiconductor by measuring the Seebeck coefficient and photo-electrochemical responses. The properties unique to p-type semiconductors were observed in both measurements, indicating that the synthesized r-BS is a p-type semiconductor. Moreover, a distinct Fano resonance was observed in Fourier transform infrared absorption spectroscopy, which was ascribed to the Fano resonance between the E(2) (TO) phonon mode and electrons in the band structures of r-BS, indicating that the p-type carrier was intrinsically doped in the synthesized r-BS. These results demonstrate the potential future application prospects of r-BS.


Assuntos
Boro , Eletrônica , Elétrons , Excipientes , Semicondutores
2.
Gan To Kagaku Ryoho ; 50(5): 643-645, 2023 May.
Artigo em Japonês | MEDLINE | ID: mdl-37218330

RESUMO

A man in his seventies underwent endoscopic mucosal resection(EMR)of a rectal cancer 3 years ago. Histopathological examination showed that the specimen had been resected curatively. However, a routine follow-up colonoscopy revealed a submucosal mass on the EMR scar. Computed tomography imaging revealed a mass in the posterior wall of the rectum, with suspected invasion of the sacrum. We performed a biopsy during endoscopic ultrasonography and diagnosed a local recurrence of the rectal cancer. After preoperative chemoradiotherapy(CRT), laparoscopic low anterior resection with ileostomy was performed. Histopathological examination revealed invasion of the rectal wall from the muscularis propria to the adventitia and tissue fibrosis at the radial margin, which was devoid of cancerous cells. Subsequently, the patient received adjuvant chemotherapy with uracil/tegafur and leucovorin for 6 months. No recurrence has been reported over a postoperative follow- up period of 4 years. Preoperative CRT may be an effective treatment for locally recurrent rectal cancer after endoscopic resection.


Assuntos
Laparoscopia , Neoplasias Retais , Masculino , Humanos , Reto/patologia , Recidiva Local de Neoplasia/cirurgia , Neoplasias Retais/cirurgia , Neoplasias Retais/patologia , Quimiorradioterapia , Laparoscopia/métodos , Resultado do Tratamento
3.
Gan To Kagaku Ryoho ; 50(13): 1477-1478, 2023 Dec.
Artigo em Japonês | MEDLINE | ID: mdl-38303313

RESUMO

A 74-year-old woman underwent colonoscopy for positive fecal occult blood test. A colonoscopy revealed a Type 1 tumor in the rectosigmoid region. The tumor was diagnosed as well-differentiated adenocarcinoma(tub1)by biopsy. Laparoscopic high anterior resection was performed. The final diagnosis was MiNEN(adenocarcinoma:NEC=6:4), RS, pT4a(SE), INF c, Ly1c, V1b, Pn1b, BD2, pN2a(5/28), cM0, pStage Ⅲc. All lymph node metastases were of NEC origin. This case was considered to be at high risk of recurrence and require adjuvant chemotherapy focused on NEC. She was referred to an advanced medical institution for carboplatin and etoposide therapy. MiNEN is a rare disease, and has a poor prognosis. In order to establish a therapeutic strategy of MiNEN, it is important to accumulate further cases and evidence.


Assuntos
Adenocarcinoma , Laparoscopia , Protectomia , Neoplasias Retais , Feminino , Humanos , Idoso , Neoplasias Retais/tratamento farmacológico , Neoplasias Retais/cirurgia , Neoplasias Retais/patologia , Reto/patologia , Adenocarcinoma/cirurgia
4.
Langmuir ; 38(47): 14422-14429, 2022 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-36383433

RESUMO

In general, randomly oriented ice crystallites are formed by heating amorphous solid water (ASW) films at ∼160 K via homogeneous nucleation. Here, we demonstrate that monolayers of methanol and 1-propanol additives incorporated in the multilayer ASW film lead to heterogeneous nucleation at the substrate interface of Pt(111), as evidenced by the occurrence of epitaxial ice growth. The mobility of water in direct contact with the Pt(111) substrate is decreased relative to that in the bulk, but it can be increased via interactions with hydrophobic moieties of alcohols that are segregated to the interfacial region. As a result, heterogeneous nucleation occurs at ca. 160 K along with homogeneous nucleation in the film interior. However, the template effect is quenched when the alcohols are in direct contact with the substrate. The methanol adspecies deposited onto the ASW film surface induces heterogeneous nucleation at a temperature as low as 145 K, but the 1-propanol adspecies has no such an effect. Their different ability of heterogeneous nucleation at the free ASW film surface, as well as their uptake behaviors in the near surface region, is associated with the hydrophobic hydration of the alcohols resulting from different lengths of the aliphatic moiety.

5.
Biochem Biophys Res Commun ; 568: 37-42, 2021 09 03.
Artigo em Inglês | MEDLINE | ID: mdl-34175688

RESUMO

Cancer-associated fibroblasts (CAFs) are a major component of the tumor microenvironment and have been shown to promote cancer aggressiveness. In our previous study, analysis of expression profiles obtained from paired CAFs and normal fibroblasts from colorectal cancer (CRC) tissue revealed that gene sets related to the Wnt signaling pathway were highly enriched in colorectal CAFs. Furthermore, among the components of the ß-catenin-independent Wnt pathway, Wnt5a was highly expressed in CAFs. Since Wnt5a is considered to be a regulator of CRC progression in CAFs, we performed immunohistochemical analysis on Wnt5a in 171 patients who underwent surgery for CRC. Positive staining for Wnt5a was often found in cancer stroma, particularly in fibromatous areas, although the immunoreactivity for Wnt5a was weak in cancer cells. Wnt5a status in CAFs was significantly associated with tumor size, depth of invasion, lymphatic and vascular invasion, lymph node metastasis, TNM stage, and recurrence. Subsequent in vitro analyses using human recombinant Wnt5a protein revealed that cancer cell proliferation and migration were significantly increased by stimulation with Wnt5a. Our findings suggest that Wnt5a-derived CAFs play a crucial role in CRC progression and have potential as a target of anti-cancer therapies.


Assuntos
Fibroblastos Associados a Câncer/patologia , Neoplasias Colorretais/patologia , Proteína Wnt-5a/análise , Fibroblastos Associados a Câncer/metabolismo , Linhagem Celular Tumoral , Movimento Celular , Proliferação de Células , Neoplasias Colorretais/genética , Progressão da Doença , Regulação Neoplásica da Expressão Gênica , Humanos , Células Tumorais Cultivadas , Proteína Wnt-5a/genética
6.
Phys Chem Chem Phys ; 22(36): 20515-20523, 2020 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-32966413

RESUMO

We have investigated how nucleation and growth processes of ice are influenced by interfacial molecular interactions on some oxide surfaces, such as rutile TiO2(110), TiO2(100), MgO(100), and Al2O3(0001), based on the diffraction patterns of electrons transmitted through ice crystallites under the experimental configuration of reflection high energy electron diffraction (RHEED). The cubic ice Ic grows on the TiO2(110) surface with the epitaxial relationship of (110)Ic//(110)TiO2 and [001]Ic//[11[combining macron]0]TiO2. The epitaxial ice growth tends to be disturbed on the TiO2(110) surface under the presence of oxygen vacancies and adatoms. The result is not simply ascribable to small misfit values between TiO2 and ice Ic lattices (∼2%) because ice grains are formed randomly on TiO2(100). No template effects are identified during ice nucleation on the pristine MgO(100) and Al2O3(0001) surfaces either. The water molecules are chemisorbed weakly on these surfaces as a precursor to dissociation via the acid-base interaction. Such anchored water species act as an inhibitor of epitaxial ice growth because the orientation flexibility of physisorbed water during nucleation is hampered at the interface by the preferential formation of hydrogen bonds.

7.
Phys Chem Chem Phys ; 21(35): 19585-19593, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31464304

RESUMO

How interfacial molecular interactions influence nucleation and growth processes of water ice is explored using pristine, oxygenated, and CO-adsorbed Ni(111) substrates based on RHEED, together with the effects of high-energy electron irradiation on the crystallization kinetics. A monolayer of amorphous solid water deposited onto the pristine Ni(111) substrate crystallizes into ice Ic at ca. 150 K, whereas ice Ih (Ic) is formed preferentially during water vapor deposition at 135 K (125 K). The ice nucleation tends to be hampered on the oxygenated Ni(111) surface because of the hydrogen bond formation with chemisorbed oxygen, leading to the growth of randomly-oriented ice Ic crystallites via spontaneous nucleation. The amorphization and recrystallization of initially crystalline ices are observed during prolonged RHEED measurements at 20 and 70 K, respectively, signifying that high-energy electron irradiation has both thermal and non-thermal effects on the water phase transition. The epitaxial growth (non-epitaxial growth) of ice occurs during electron irradiation of amorphous solid water formed on the pristine and oxygenated Ni(111) substrates (CO-adsorbed Ni(111) substrate) even at 100 K (120 K) because nucleation and growth are initiated at the substrate interface (in the ASW film interior).

8.
Phys Chem Chem Phys ; 21(3): 1123-1130, 2019 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-30607420

RESUMO

This paper describes nucleation, epitaxial growth, and wettability of water on Pt(111) and how they are influenced by oxygen and carbon-monoxide adspecies, based on reflection high energy electron diffraction (RHEED), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and temperature-programmed desorption (TPD). Amorphous solid water deposited onto the pristine Pt(111) substrate crystallizes into ice Ih together with a 2D layer at 150 K, whereas ice Ic (stacking disordered ice or a mixture of ice Ic and Ih) is formed preferentially onto oxygenated Pt(111) (CO-adsorbed Pt(111)) at 155-160 K (150 K). The ice nucleation and epitaxial growth tend to be hampered on the oxygenated Pt(111) surface via hydrogen bond formation with chemisorbed oxygen. The CO-adsorbed Pt(111) surface is hydrophobic, as evidenced by the fact that water forms a complex with CO during evaporation of crystallites at 160-165 K. A disordered 2D layer remains on pristine Pt(111) up to 175 K, whereas an ordered 2D layer exhibiting the (√3 ×√3)R30° structure formed on oxygenated Pt(111) up to 200 K.

9.
Phys Chem Chem Phys ; 20(34): 21856-21863, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-30094449

RESUMO

Graphite is hydrophobic in nature, but the crystallization kinetics and dewetting transition of thin water films deposited onto graphite are distinct from those on typical hydrophobic substrates. To clarify the origin of these behaviors, we investigated the crystallization kinetics of thin water films on graphite in terms of the initial film thickness, deposition temperature, and template effects of adspecies based on reflection high-energy electron diffraction (RHEED) images; the film morphology change was analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The water monolayer nucleates after surface diffusivity occurs at ca. 120 K; the nucleation temperature and time increase with increasing initial film thickness. Crystallites of cubic and hexagonal ices are formed, having preferred orientation [cubic (111) or hexagonal (001)] along the surface normal direction; their relative quantity depends on the initial film thickness and the way of crystallization. Randomly oriented crystallites finally grow via spontaneous nucleation when the film thickness exceeds 7-10 monolayers. The template ordering effects of graphite are quenched when a monolayer of ordered n-octane preexists at the substrate interface. The crystalline ice tends to wet the graphite substrate immediately after nucleation, and the film morphology changes gradually at 130 K because of premelting. The crystallites are ripened via molecular transport through the quasiliquid layer formed at the free surface, grain boundaries, and substrate.

10.
Gan To Kagaku Ryoho ; 45(13): 1931-1933, 2018 Dec.
Artigo em Japonês | MEDLINE | ID: mdl-30692401

RESUMO

A woman in her 40s who presented to a local hospital with bloody stool was referred to our hospital. Colonoscopy showed a rectal tumor, and histological examination showed moderately differentiated adenocarcinoma. CT and MRI revealed that the tumor was 65mm in diameter with no distant metastasis. After the construction of ileostomy, neoadjuvant chemoradiothera- py(NACRT: 45 Gy/25 Fr, S-1 80mg/m2)was performed. The tumor shrank remarkably, and then we performed laparoscopy- assisted low anterior resection. Pathological examination revealed complete disappearance of the cancer cells in the primary site and no appearance of cancer cells in all dissected lymph nodes. NACRT has been recently reported to provide pathological complete response, and these patients are supposed to have a good prognosis. In our case, NACRT enhanced the performance of laparoscopic curative resection while preserving anal function. NACRT should contribute to the curative resection while preserving anal function in patients with locally advanced rectal cancer.


Assuntos
Adenocarcinoma , Laparoscopia , Neoplasias Retais , Adenocarcinoma/tratamento farmacológico , Adenocarcinoma/cirurgia , Adulto , Quimiorradioterapia , Feminino , Humanos , Terapia Neoadjuvante , Neoplasias Retais/tratamento farmacológico , Neoplasias Retais/cirurgia
11.
J Chem Phys ; 135(14): 144704, 2011 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-22010728

RESUMO

CO, O(2), and H(2) adsorption on a clean W(2)C(0001)√13×√13 R ± 13.9° reconstructed surface at room temperature (RT) were investigated using high-resolution electron energy loss spectroscopy (HREELS). The W(2)C(0001) adsorbs CO molecularly and adsorbs O(2) dissociatively, but does not adsorb H(2) at RT. In the CO adsorption system, two C-O stretching (antisymmetric CCO stretching) modes were found at 242.3 meV (1954 cm(-1)) and at 253.0 meV (2041 cm(-1)). The low-frequency site is occupied at first with subsequent conversion to the high-frequency site with increasing coverage. Additionally, a small peak was apparent at 104.5 meV (843 cm(-1)), and a middle peak at 50-51 meV (400-410 cm(-1)), which are assignable to a symmetric stretching mode and a hindered translational mode, respectively, of a CCO (ketenylidene) species. These observations are consistent with the CO adsorption model on top of the surface carbon. For oxygen adsorption, two adsorption states were found at 65.2-68.1 meV (526-549 cm(-1)) and 73.6 meV (594 cm(-1)): typical frequencies to oxygen adsorption on metal surfaces. Results suggest that atomic oxygen adsorption occurred on a threefold hollow site of the second W layer.

12.
Front Chem ; 9: 642388, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34386477

RESUMO

Thin-film growth is a platform technique that allows the preparation of various undeveloped materials and enables the development of novel energy generation devices. Preferred phase formation, control of crystalline orientation and quality, defect concentration, and stoichiometry in thin films are important for obtaining thin films exhibiting desired physical and chemical properties. In particular, the control of crystalline phase formation by utilizing thin-film technology favors the preparation of undeveloped materials. In this study, thin-film growth of transition metal nitride and rare-earth metal boride was performed using remote plasma-assisted molecular beam epitaxy and hybrid physical-chemical vapor deposition techniques, and was successfully achieved by tuning the competition between thermodynamics and kinetics during vapor-phase thin-film growth. Growth conditions of high crystalline quality titanium nitride thin films and high phase purity ytterbium boride thin films were not thermodynamically favorable. Appropriate control of the contribution degree of thermodynamics and kinetics during vapor-phase thin-film growth is crucial for fabricating high phase purity and high crystalline quality thin films.

13.
J Surg Case Rep ; 2020(8): rjaa150, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32855787

RESUMO

Urinary incontinence is one of the common complications after radical prostatectomy along with inguinal hernia. Artificial urethral sphincter implantation is widely accepted as a treatment option. We report two surgical cases of inguinal hernia after artificial urethral sphincter implantation for urinary incontinence following radical prostatectomy. In Case 1, since the device went through the inguinal canal, adhesion around the pubis was extremely hard. In Case 2, the device was placed on the ventral side of the rectus abdominis muscle, so it was operable almost as normal. In each case, the surgical procedure was considered carefully after confirming the location of the device by preoperative computed tomography and ultrasonography. Hernia repair was successfully performed using the Lichtenstein method. There are few reports regarding surgical repair of inguinal hernia following artificial urinary sphincter implantation. Preoperative image and appropriate choice of approach could facilitate safe and secure surgery.

14.
Cancer Med ; 8(14): 6370-6382, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31468733

RESUMO

Recent studies have shown that the tumor microenvironment plays a significant role in the progression of solid tumors. As an abundant component of the tumor microenvironment, cancer-associated fibroblasts (CAFs) have been shown to promote tumorigenesis and cancer aggressiveness, but their molecular characteristics remain poorly understood. In the present study, paired CAFs and normal fibroblasts (NFs) were isolated from five colorectal cancer (CRC) tissues from patients who underwent surgical resection. The gene expression profiles of CAFs and NFs identified by RNA sequencing were compared to understand the complex role of CAFs in cancer progression. Gene Set Enrichment Analysis revealed that the gene sets related to the Wnt signaling pathway were highly enriched in CAFs, as well as TGFß signaling, which is considered to be a regulator of CAFs. Among the components of this pathway, Wnt2 was specifically expressed. The observations led us to speculate that Wnt2 is extremely involved in regulating CRC progression by CAFs. Thus, we performed immunohistochemical analysis on Wnt2 in 171 patients who underwent surgery for colorectal adenocarcinoma. Positive staining for Wnt2 was mainly observed in cancer stroma, although the immunoreactivity was weak in cancer cells. Wnt2 expression in CAFs was significantly correlated with depth of tumor (P < .001), lymph node metastasis (P = .044), TNM stage (P = .010), venous invasion (P < .001), and recurrence (P = .013). Subsequent in vitro analyses were conducted using conditioned medium (CM) from immortalized CAFs transfected with siRNA targeting Wnt2. As a result, cancer cell invasion and migration were significantly decreased in the CM from immortalized CAFs transfected with siRNA targeting Wnt2. Our findings indicated that Wnt2 protein released from CAFs enhances CRC cell invasion and migration. In conclusion, Wnt2 secreted by CAFs plays a key role in cancer progression and is a potential therapeutic target for CRC.


Assuntos
Fibroblastos Associados a Câncer/metabolismo , Neoplasias Colorretais/metabolismo , Proteína Wnt2/biossíntese , Idoso , Fibroblastos Associados a Câncer/patologia , Linhagem Celular Tumoral , Movimento Celular/genética , Proliferação de Células , Neoplasias Colorretais/genética , Neoplasias Colorretais/mortalidade , Neoplasias Colorretais/patologia , Biologia Computacional/métodos , Progressão da Doença , Feminino , Perfilação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Humanos , Imuno-Histoquímica , Masculino , Pessoa de Meia-Idade , Prognóstico , Interferência de RNA , Transcriptoma , Microambiente Tumoral , Via de Sinalização Wnt
16.
Tokai J Exp Clin Med ; 42(1): 58-63, 2017 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-28413873

RESUMO

OBJECTIVE: To assess the feasibility of apparent diffusion coefficient analysis in evaluating the inflammatory severity of extracranial abscesses. METHODS: This retrospective study included 23 patients with solitary body abscesses (except those in the brain) who underwent 1.5-T diffusion-weighted magnetic resonance imaging (DWI) at b-values of 0 and 1000 s/mm2. Three types of the Apparent Diffusion Coefficient (ADC) measurements of abscesses were performed: the mean ADC value in region of interest (ROI), volume of interest (VOI), and histogram analysis of the ADC distribution in the VOI. Furthermore, two different areas were used: high-intensity area on b = 0 and b = 1000 s/mm2 images. Subsequently, correlations between ADC data and C-reactive protein (CRP) levels were assessed using Pearson's correlation coefficient (R) analyses. RESULTS: The strongest correlation was observed between the mean ADC value in VOI and CRP level (R = 0.78, P < 0.01), followed by ROI (R = 0.77, P < 0.01) by using the high-intensity area on the b = 0 s/mm2 images. CONCLUSION: The mean ADC value in the ROI encompassing the abscess at a b-value of 0 s/mm2 may be useful to assess the inflammatory activity of an abscess in daily practice.


Assuntos
Abscesso/diagnóstico por imagem , Biomarcadores , Imagem de Difusão por Ressonância Magnética/métodos , Inflamação/diagnóstico por imagem , Abscesso/complicações , Adulto , Idoso , Proteína C-Reativa/análise , Estudos de Viabilidade , Feminino , Humanos , Inflamação/etiologia , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Índice de Gravidade de Doença
17.
Cancer Med ; 6(6): 1264-1274, 2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28544335

RESUMO

p62/sequestosome 1 (p62) is a multi-domain protein that functions as a receptor for ubiquitinated targets in the selective autophagy and serves as a scaffold in various signaling cascades. p62 have been reported to be up-regulated in several human malignancies, but the biological roles and significance of p62 are still poorly understood in colorectal carcinoma. We immunohistochemically evaluated p62 in 118 colorectal adenocarcinoma and 28 colorectal adenoma cases. We used four colon carcinoma cells (HCT8, HT29, COLO320, and SW480) in the in vitro studies. p62 immunoreactivity was detected in 11% of colorectal adenoma cases and 31% of adenocarcinoma cases, while it was negligible in the normal epithelium. The immunohistochemical p62 status was significantly associated with synchronous liver metastasis, and it turned out to be an independent adverse prognostic factor in colorectal cancer patients. Following in vitro studies revealed that HCT8 and HT29 cells transfected with p62-specific siRNA showed significantly decreased cell proliferation activity, whereas COLO320 and SW480 cells transfected with p62 expression plasmid showed significantly increased cell proliferation activity. The p62-mediated cell proliferation was not associated with the autophagy activity. These findings suggest that p62 promotes the cell proliferation mainly as a scaffold protein, and that the p62 status is a potent prognostic factor in colorectal carcinoma patients.


Assuntos
Adenocarcinoma/metabolismo , Adenoma/metabolismo , Neoplasias Colorretais/metabolismo , Proteína Sequestossoma-1/metabolismo , Adenocarcinoma/genética , Adenocarcinoma/patologia , Adenoma/genética , Idoso , Linhagem Celular Tumoral , Proliferação de Células , Neoplasias Colorretais/genética , Neoplasias Colorretais/patologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Plasmídeos , Prognóstico , RNA Mensageiro/metabolismo , Proteína Sequestossoma-1/genética , Transfecção
18.
J Phys Condens Matter ; 23(30): 305007, 2011 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-21734332

RESUMO

A single crystal surface of ditungsten carbide, W(2)C(0001) was investigated using low-energy (LEED) and high-energy electron diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy (XPS), and high-resolution electron energy loss spectroscopy (HREELS). A new reconstruction, √13 x √13R ± 13.9◦, was found as a clean surface structure after annealing the W(2)C at > 1900 K. The surface carbon content is shown as larger than that in the bulk. Our preliminary results showed that the same structure is realized also on WC(0001). The same surface periodicity is described for an Mo(2)C(0001) LEED pattern in the literature. This reconstruction phase is presumably common on the (0001) surface of hexagonal group-6 transition-metal carbides. In the off-specular HREELS, an atomic vibration of 44.8 meV (361 cm( - 1)) appeared within the gap energy region of the bulk phonon bands, which was assigned to a surface carbon vibration perpendicular to the surface. One possible explanation of the low vibrational frequency is very low adsorption height of the surface carbon atoms.

19.
J Am Chem Soc ; 129(1): 202-9, 2007 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-17199300

RESUMO

Crystallization behaviors of anatase nanocrystallites from an ultrathin two-dimensional reactant composed of exfoliated titania nanosheets have been studied by monitoring the heating process of their well-organized films, with which the film thickness can be controlled from a molecularly thin monolayer to a stacked multilayer structure with a stepwise increment of approximately 1 nm. The heated products were identified by means of total reflection fluorescence X-ray absorption near-edge structure analysis and in-plane X-ray diffraction measurements using a synchrotron radiation source. The films composed of five or more layers of stacked nanosheets were transformed into anatase at 400-500 degrees C, which is a normal crystallization temperature of anatase from bulk reactants. As the film became thinner by decreasing the number of nanosheet layers to five or less, the crystallization temperature was found to increase and finally reached 800 degrees C for the monolayer film. Interestingly, preferential growth of anatase along the c-axis was strongly promoted for these ultrathin films. These unusual behaviors may be understood in terms of crystallization from the two-dimensional system of scarcely distributed reactants. The titania nanosheet crystallite is much thinner than the unit cell dimensions of anatase, and therefore, extensive atomic diffusion is required for the transformation particularly for the ultrathin films with a critical number (2-3) of stacked nanosheet layers. There is some structural similarity between anatase and titania nanosheet, which may account for the oriented growth of anatase nanocrystallites.

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