In Situ Observations of Beam-Induced Effects During High-Resolution Electron Microscopy

1990 ◽  
Vol 201 ◽  
Author(s):  
David J. Smith ◽  
Ping Lu ◽  
M. R. McCartney ◽  
R. Sharma
Keyword(s):  
Electron Irradiation ◽  
Rapid Development ◽  
Compound Semiconductors ◽  
High Resolution Electron Microscopy ◽  
Ex Situ ◽  
Oxidation Reduction ◽  
Resolution Electron ◽  
Irradiation Level ◽  
In Situ Observations

AbstractA variety of electron-beam-induced effects, including oxidation, reduction and surface rearrangements are observed to occur at surfaces of oxides, fluorides and compound semiconductors during electron irradiation within the electron microscope. The extent and type of surface modifications observed are shown to depend upon the irradiation level, the residual microscope vacuum and the specimen temperature. For example, ex situ annealing of compound semiconductors leads to different end-products compared with in situ irradiation, thus showing that residual gas components can have a strong influence on the surface reactions. Electron irradiation of rutile during annealing at high temperature under ultrahigh vacuum conditions caused the rapid development of well-facetted holes without the usual intermediary phase seen at room temperature in conventional vacuum.

Studies of Material Reactions by In Situ High-Resolution Electron Microscopy

MRS Bulletin ◽  
1994 ◽  
Vol 19 (6) ◽  
pp. 26-31 ◽  
Author(s):  
Robert Sinclair
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Ex Situ ◽  
New Materials ◽  
Kinetic Measurements ◽  
Transmission Electron ◽  
Resolution Electron

Processing has always been a key component in the development of new materials. Basic scientific understanding of the reactions and transformations that occur has obvious importance in guiding progress. Invaluable insight can be provided by observing the changes during processing, especially at high magnification by in situ microscopy. Now that this can be achieved at the atomic level by using high-resolution electron microscopy (HREM), atomic behavior can be seen directly. Accordingly, many deductions concerning reactions in materials at the atomic scale are possible.The purpose of this article is to illustrate the level reached by in situ HREM. The essential procedure is to form a high-resolution image of a standard transmission electron microscope (TEM) sample and then to alter the structure by some means in a controlled manner, such as by heating. Continual recording on videotape allows subsequent detailed analysis of the behavior, even on a frame-by-frame (1/30 second) basis. The most obvious advantage is to follow the atomic rearrangements directly in real time. However, in addition, by continuous recording no stages in a reaction are missed, which can often occur in a series of conventional ex situ annealed samples because of the limited number of samples that can realistically be examined by HREM. One can be sure that the same reaction, in the same area, is being studied. Furthermore, by changing the temperature systematically, extremely precise kinetic measurements can be made (e.g., for activation energies and kinetic laws) and the whole extent of a material transformation can be investigated in one sample, something that would take months of work if studied conventionally. The information provided by in situ HREM is often unique and so it can become an important technique for fundamental materials investigations.

HREM of electron-irradiated silicas

1993 ◽  
Vol 51 ◽  
pp. 1102-1103 ◽  
Author(s):  
L.C. Qin
Keyword(s):  
Electron Irradiation ◽  
Structural Changes ◽  
High Resolution Electron Microscopy ◽  
Nucleation And Growth ◽  
Sharp Boundary ◽  
Quartz Crystals ◽  
Resolution Electron ◽  
Silica Crystals ◽  
Crystalline Matrix

Silica (SiO2) crystals exist in various polymorphs which have different densities and different crystal structures, such as quartz, tridymite, and cristobalite, though all of these have in common the network structure which is formed by corner-sharing of SiO4 tetranedra. All these structures are sensitive to electron irradiation. Amorphization occurs when they are irradiated by energetic electrons.In the present study three polymorphs of silica crystals, α-quartz, α-tridymite and α-cristobalite crystals2 were used as starting materials. Electron irradiation experiments were carried out in situ in the electron microscope. The structural changes of the specimens were monitored using high-resolution electron microscopy (HREM).The amorphization of α-quartz crystals was found to progress through two morphologies: (a) nucleation and growth of amorphous nuclei with a sharp boundary with the crystalline matrix (figure 1); and (b) crystallinity lost gradually and more uniformly. Figure 2 shows a series of HREM images showing the amorphization of a tridymite crystal.

Quantification of CeO2 Reduction By In Situ Electron Energy-Loss Spectroscopy

2000 ◽  
Vol 6 (S2) ◽  
pp. 12-13
Author(s):  
Renu Sharma ◽  
Peter Crozier
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Mixed Oxides ◽  
High Resolution Electron Microscopy ◽  
Reduction Behavior ◽  
Oxidation Reduction ◽  
Resolution Electron ◽  
Electron Energy Loss

CeO2 is an important material in many catalyst applications. CeO2, PrO2 and TbO2 are the only lanthanides known to exist as oxides in both 3+ and 4+ oxidation states. The high oxygen mobility at low temperature (≈300°C) results in easy oxidation-reduction cycles; a property utilized in the catalyst industry, especially for CeO2. Studying the oxidation-reduction behavior is thus very important to understanding the reactivity of CeO2 as a catalyst. We have studied CeO2 by in situ electron diffraction, high resolution electron microscopy (HREM) and electron energy-loss spectroscopy (EELS), not only to understand the reduction behavior but also to develop a method to quantify the reducibility of CeO2 or mixed oxides containing CeO2 by EELS. We have applied this method to study the behavior of ZrO2-CeO2 catalyst during reduction.Experiments were performed on a PHILIPS-430 electron microscope operated at 300KV, fitted with a differentially pumped environmental cell and a Gatan Imaging Filter (GIF).

scholarly journals In situ measurements of oxidation–reduction potential and hydrogen peroxide concentration as tools for revealing LPMO inactivation during enzymatic saccharification of cellulose

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Adnan Kadić ◽  
Anikó Várnai ◽  
Vincent G. H. Eijsink ◽  
Svein Jarle Horn ◽  
Gunnar Lidén
Keyword(s):  
Reduction Potential ◽  
Enzymatic Saccharification ◽  
The State ◽  
Enzyme Inactivation ◽  
Ex Situ ◽  
Process Economics ◽  
Complete Inactivation ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential

Abstract Background Biochemical conversion of lignocellulosic biomass to simple sugars at commercial scale is hampered by the high cost of saccharifying enzymes. Lytic polysaccharide monooxygenases (LPMOs) may hold the key to overcome economic barriers. Recent studies have shown that controlled activation of LPMOs by a continuous H2O2 supply can boost saccharification yields, while overdosing H2O2 may lead to enzyme inactivation and reduce overall sugar yields. While following LPMO action by ex situ analysis of LPMO products confirms enzyme inactivation, currently no preventive measures are available to intervene before complete inactivation. Results Here, we carried out enzymatic saccharification of the model cellulose Avicel with an LPMO-containing enzyme preparation (Cellic CTec3) and H2O2 feed at 1 L bioreactor scale and followed the oxidation–reduction potential and H2O2 concentration in situ with corresponding electrode probes. The rate of oxidation of the reductant as well as the estimation of the amount of H2O2 consumed by LPMOs indicate that, in addition to oxidative depolymerization of cellulose, LPMOs consume H2O2 in a futile non-catalytic cycle, and that inactivation of LPMOs happens gradually and starts long before the accumulation of LPMO-generated oxidative products comes to a halt. Conclusion Our results indicate that, in this model system, the collapse of the LPMO-catalyzed reaction may be predicted by the rate of oxidation of the reductant, the accumulation of H2O2 in the reactor or, indirectly, by a clear increase in the oxidation–reduction potential. Being able to monitor the state of the LPMO activity in situ may help maximizing the benefit of LPMO action during saccharification. Overcoming enzyme inactivation could allow improving overall saccharification yields beyond the state of the art while lowering LPMO and, potentially, cellulase loads, both of which would have beneficial consequences on process economics.

In-Situ Studies of Epitaxial Thin-Film Growth

1964 ◽  
Vol 19 (7-8) ◽  
pp. 835-843 ◽  
Author(s):  
H. Poppa
Keyword(s):  
Film Growth ◽  
High Resolution Electron Microscopy ◽  
Thin Film Growth ◽  
Continuous Observation ◽  
Epitaxial Thin Film ◽  
Epitaxial Thin Film Growth ◽  
Resolution Electron ◽  
Substrate Surfaces ◽  
Kinetics Of

Early stages of oriented overgrowth of Ag, Au, and Pd on thin, single-crystal substrates of mica, molybdenite, Au and Pd were studied by high-resolution electron microscopy and diffraction. Cleaning of substrate surfaces and deposition of evaporated materials were conducted inside an electron microscope. High-magnification, continuous observation during growth permitted investigation of the kinetics of growth. A number of probably elementary epitaxial processes were studied in detail. Nucleation and growth behavior was examined for different supersaturations and free surface energies of substrate and overgrowth materials. The influence of alloying on growth and the spacing of parallel moiré structures was investigated.

In Situ HREm of Reactions at Interfaces

1997 ◽  
Vol 3 (S2) ◽  
pp. 621-622 ◽  
Author(s):  
R. Sinclair ◽  
T. Itoh ◽  
H. J. Lee ◽  
K. W. Kwon
Keyword(s):  
Chemical Interaction ◽  
High Resolution Electron Microscopy ◽  
Point Of View ◽  
Interface Chemistry ◽  
Amorphous Phases ◽  
Resolution Electron ◽  
Analogous Manner ◽  
The Stability ◽  
Basic Studies

Reactions at solid-solid interfaces are important both scientifically and technologically. Firstly, there is quite a wide variety of possibilities. Materials can react with one another, forming equilibrium, meta-stable or even amorphous phases. The interface can provide a means to promote phase reactions kinetically, in an analogous manner to catalysis. Even when the materials are mutually compatible chemically, the interface topography and atomic structure can evolve over the course of time. From the practical point-of-view, changes in the interface chemistry and structure can profoundly alter the physical properties. This is especially notable in thin film technology, whereby the interfaces constitute a signigicant proportion of the whole device. In this article, contributions to understanding this field are illustrated through application of in situ and high-resolution electron microscopy (HREM).Basic studies of metal-semicoductor interfacial reactions have been successfully carried out for a number of years. of increasing importance in microelectronics is the stability of layers which prevent chemical interaction, namely the diffusion barriers.

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