scholarly journals Ultrathin Single-crystalline MgO (111) Nanosheets

2020 ◽  
Author(s):  
Pengxin Liu ◽  
Paula M. Abdala ◽  
Guillaume Goubert ◽  
Marc Willinger ◽  
Christophe Copéret
Keyword(s):  
Low Temperatures ◽  
Oxygen Vacancies ◽  
High Energy ◽  
Grand Challenge ◽  
High Quality ◽  
Dynamic Vacuum ◽  
Single Crystalline ◽  
Oh Groups ◽  
Single Electrons ◽  
Energy Surfaces

Synthesizing high-quality two-dimensional nanomaterials of non-layered metal oxide is a grand challenge because it requires long range single-crystallinity and clean high-energy surfaces. Here, we report the synthesis of single-crystalline MgO(111) nanosheets via a two-step process involving the formation of ultrathin Mg(OH)<sub>2</sub> nanosheets as precursor and their selective topotactic conversion upon heating under dynamic vacuum. The defect-rich surface displays terminal -OH groups, 3-coordinated O<sup>2-</sup> sites, low-coordinated Mg<sup>2+</sup> sites as well as single electrons trapped at oxygen vacancies, that render MgO nanosheets highly reactive as evidenced by the activation of CO molecules at low temperatures and pressures, with formation of strongly adsorbed red-shifted CO and coupling of CO molecules into C<sub>2</sub> species.

Ultrathin Single-crystalline MgO (111) Nanosheets

2020 ◽  
Author(s):  
Pengxin Liu ◽  
Paula M. Abdala ◽  
Guillaume Goubert ◽  
Marc Willinger ◽  
Christophe Copéret
Keyword(s):  
Low Temperatures ◽  
Oxygen Vacancies ◽  
High Energy ◽  
Grand Challenge ◽  
High Quality ◽  
Dynamic Vacuum ◽  
Single Crystalline ◽  
Oh Groups ◽  
Single Electrons ◽  
Energy Surfaces

Synthesizing high-quality two-dimensional nanomaterials of non-layered metal oxide is a grand challenge because it requires long range single-crystallinity and clean high-energy surfaces. Here, we report the synthesis of single-crystalline MgO(111) nanosheets via a two-step process involving the formation of ultrathin Mg(OH)<sub>2</sub> nanosheets as precursor and their selective topotactic conversion upon heating under dynamic vacuum. The defect-rich surface displays terminal -OH groups, 3-coordinated O<sup>2-</sup> sites, low-coordinated Mg<sup>2+</sup> sites as well as single electrons trapped at oxygen vacancies, that render MgO nanosheets highly reactive as evidenced by the activation of CO molecules at low temperatures and pressures, with formation of strongly adsorbed red-shifted CO and coupling of CO molecules into C<sub>2</sub> species.

scholarly journals Evidence for a conducting surface ground state in high-quality single crystalline FeSi

2018 ◽  
Vol 115 (34) ◽  
pp. 8558-8562 ◽  
Author(s):  
Yuankan Fang ◽  
Sheng Ran ◽  
Weiwei Xie ◽  
Shen Wang ◽  
Ying Shirley Meng ◽  
...  
Keyword(s):  
Electronic Transport ◽  
Ground State ◽  
Low Temperatures ◽  
Magnetic Order ◽  
Energy Gap ◽  
Charge Carriers ◽  
Conducting Surface ◽  
High Quality ◽  
Metallic Behavior ◽  
Single Crystalline

We report anomalous physical properties of high-quality single-crystalline FeSi over a wide temperature range of 1.8–400 K. The electrical resistivity ρ(T) can be described by activated behavior with an energy gap Δ = 57 meV between 150 and 67 K, below which the estimated energy gap is significantly smaller. The magneto-resistivity and Hall coefficient change sign in the vicinity of 67 K, suggesting a change of dominant charge carriers. At ∼19 K, ρ(T) undergoes a cross-over from semiconducting to metallic behavior which is very robust against external magnetic fields. The low-temperature metallic conductivity depends strongly on the width/thickness of the sample. In addition, no indication of a bulk-phase transition or onset of magnetic order is found down to 2 K from specific heat and magnetic susceptibility measurements. The measurements are consistent with one another and point to complex electronic transport behavior that apparently involves a conducting surface state in FeSi at low temperatures, suggesting the possibility that FeSi is a 3D topological insulator.

Epitaxial growth manner and structure of superconducting oxide films

1990 ◽  
Vol 48 (4) ◽  
pp. 2-3
Author(s):  
Yoshichika Bando ◽  
Takahito Terashima ◽  
Kenji Iijima ◽  
Kazunuki Yamamoto ◽  
Kazuto Hirata ◽  
...  
Keyword(s):  
Ultrathin Films ◽  
Film Surface ◽  
High Energy ◽  
Epitaxial Films ◽  
Layer By Layer ◽  
Initial Growth ◽  
In Situ Growth ◽  
High Quality ◽  
Activated Reactive Evaporation

The high quality thin films of high-Tc superconducting oxide are necessary for elucidating the superconducting mechanism and for device application. The recent trend in the preparation of high-Tc films has been toward “in-situ” growth of the superconducting phase at relatively low temperatures. The purpose of “in-situ” growth is to attain surface smoothness suitable for fabricating film devices but also to obtain high quality film. We present the investigation on the initial growth manner of YBCO by in-situ reflective high energy electron diffraction (RHEED) technique and on the structural and superconducting properties of the resulting ultrathin films below 100Å. The epitaxial films have been grown on (100) plane of MgO and SrTiO, heated below 650°C by activated reactive evaporation. The in-situ RHEED observation and the intensity measurement was carried out during deposition of YBCO on the substrate at 650°C. The deposition rate was 0.8Å/s. Fig. 1 shows the RHEED patterns at every stage of deposition of YBCO on MgO(100). All the patterns exhibit the sharp streaks, indicating that the film surface is atomically smooth and the growth manner is layer-by-layer.

scholarly journals The Catalytic Oxidation of Formaldehyde by FeOx-MnO2-CeO2 Catalyst: Effect of Iron Modification

Catalysts ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 555
Author(s):  
Yaxin Dong ◽  
Chenguang Su ◽  
Kai Liu ◽  
Haomeng Wang ◽  
Zheng Zheng ◽  
...  
Keyword(s):  
Low Temperatures ◽  
Oxygen Vacancies ◽  
Catalytic Performance ◽  
Active Oxygen ◽  
Molar Ratio ◽  
N2 Adsorption ◽  
Structure Activity ◽  
Iron Modification ◽  
Surface Active ◽  
Catalyst Effect

A series of FeOx-MnO2-CeO2 catalysts were synthesized by the surfactant-templated coprecipitation method and applied for HCHO removal. The influence of Fe/Mn/Ce molar ratio on the catalytic performance was investigated, and the FeOx-MnO2-CeO2 catalyst exhibited excellent catalytic activity, with complete HCHO conversion at low temperatures (40 °C) when the molar ratio of Fe/Mn/Ce was 2/5/5. The catalysts were characterized by N2 adsorption and desorption, XRD, H2-TPR, O2-TPD and XPS techniques to illustrate their structure–activity relationships. The result revealed that the introduction of FeOx into MnO2-CeO2 formed a strong interaction between FeOx-MnO2-CeO2, which facilitated the improved dispersion of MnO2-CeO2, subsequently increasing the surface area and aiding pore development. This promotion effect of Fe enhanced the reducibility and produced abundant surface-active oxygen. In addition, a great number of Oα is beneficial to the intermediate decomposition, whereas the existence of Ce3+ favors the formation of oxygen vacancies on the surface of the catalyst, all of which contributed to HCHO oxidation at low temperatures.

Line-Shaped Electron Beam System and Soi Films Prepared by The System

1985 ◽  
Vol 45 ◽  
Author(s):  
Y. Hayafuji ◽  
A. Shibata ◽  
T. Yanada ◽  
A. Sawada ◽  
S. Usui ◽  
...  
Keyword(s):  
Electron Beam ◽  
Crystalline Silicon ◽  
Semiconductor Industry ◽  
High Energy ◽  
Silicon Films ◽  
High Energy Density ◽  
Present System ◽  
Single Crystalline ◽  
Beam System ◽  
Scanning Area

ABSTRACTThe line-shaped electron beam annealing system which generates an electron beam of a length of 4 cm and a width af less than 100 um with a high energy density exceeding well over 100 kW/cm2 was developed for the first time with a purpose of SOI processing as its primary application. An pccelaration voltage of up to 20 kV can be used in this system. Seeded single crystalline islands with areas several mm long and 30 to 100 um in width were obtained by a single scan of the electron beam. The electron beam is generated in a pulsed way in the system due to the power restriction of the power supplies. An area of 4×5 cm2 was processed by a single scan of an electron beam at a sample speed of 530 cm/sec and a beam duration of 9.5 msec. The scanning area for one scan is determined by the beam length and the duration of the beam and sample speed.The present system could give single crystalline silicon films without any grain boundaries. The electron mobility of the electron beam recrystallized films, obtained from FETs made as a vehicle to test the electrical properties of the films, was comparable to that of the bulk silicon. A very rapid migration of silicon atoms in solid polycrystalline silicon films, which is controllable by process parameters, was also found with a migration speed of the order of 1 m/sec in a capped structure. The present electron beam system is useful in studying basic mechanisms of crystal growth in thin films. The system can have a very high throughput, a desirable feature in semiconductor industry. The present system can also be used to study the rapid thermal treatment of materials other than semiconductors including rapidly solidified materials.

Properties of Epitaxial SrTiO3 Thin Films Grown on Silicon by Molecular Beam Epitaxy

1999 ◽  
Vol 567 ◽  
Author(s):  
Z. Yu ◽  
R. Droopad ◽  
J. Ramdani ◽  
J.A. Curless ◽  
C.D. Overgaard ◽  
...  
Keyword(s):  
Thin Films ◽  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
High Energy ◽  
State Density ◽  
Unit Cell ◽  
Ex Situ ◽  
Silicon Oxide Layer ◽  
Single Crystalline ◽  
X Ray

ABSTRACTSingle crystalline perovskite oxides such as SrTiO3 (STO) are highly desirable for future generation ULSI applications. Over the past three decades, development of crystalline oxides on silicon has been a great technological challenge as an amorphous silicon oxide layer forms readily on the Si surface when exposed to oxygen preventing the intended oxide heteroepitaxy on Si substrate. Recently, we have successfully grown epitaxial STO thin films on Si(001) surface by using molecular beam epitaxy (MBE) method. Properties of the STO films on Si have been characterized using a variety of techniques including in-situ reflection high energy electron diffraction (RHEED), ex-situ X-ray diffraction (XRD), spectroscopic ellipsometry (SE), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). The STO films grown on Si(001) substrate show bright and streaky RHEED patterns indicating coherent two-dimensional epitaxial oxide film growth with its unit cell rotated 450 with respect to the underlying Si unit cell. RHEED and XRD data confirm the single crystalline nature and (001) orientation of the STO films. An X-ray pole figure indicates the in-plane orientation relationship as STO[100]//Si[110] and STO(001)// Si(001). The STO surface is atomically smooth with AFM rms roughness of 1.2 AÅ. The leakage current density is measured to be in the low 10−9 A/cm2 range at 1 V, after a brief post-growth anneal in O2. An interface state density Dit = 4.6 × 1011 eV−1 cm−2 is inferred from the high-frequency and quasi-static C-V characteristics. The effective oxide thickness for a 200 Å STO film is around 30 Å and is not sensitive to post-growth anneal in O2 at 500-700°C. These STO films are also robust against forming gas anneal. Finally, STO MOSFET structures have been fabricated and tested. An extrinsic carrier mobility value of 66 cm2 V−11 s−1 is obtained for an STO PMOS device with a 2 μm effective gate length.

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