Explore: Dichroism

1Towards an Unambiguous Electron Magnetic Chiral Dichroism (EMCD) Measurement in a Transmission Electron Microscope (TEM)

By Christian Hurm

The intention of the ChiralTEM project (2004-2007) was the detection of electron (energy loss) magnetic chiral dichroism in a transmission electron microscope (TEM), in analogy to X-ray magnetic circular dichroism (XMCD). For the experiments, single-crystal electron transparent specimen's with magnetic induction perpendicular to the specimen's plane are required. In this thesis, different preparation techniques are evaluated regarding their usability to produce ideal specimen's for a verification of EMCD. After the demonstration of a dichroic measurement, an obvious way to prove the chiral effect is to invert the specimen's magnetization from parallel to antiparallel to the electron beam trajectory, leaving all other parameters of the experimental setup unchanged. For this case, one would - according to theory - expect a change in the dichroic signal measured. In the magnetic field of the objective lens of a 300kV TEM, typical ferromagnetic specimens will be close to saturation perpendicular to the specimen's plane. Reversing the current through the coils of the objective lens will then simply invert the magnetization of the specimen. In consequence, any magnetic chiral effect is expected to change sign. A switching unit for Tecnai microscopes has been constructed for save commutation of the lens currents. The direct sensitivity of the dichroic signal to the direction of the magnetization gives evidence to the magnetic origin of the effect.

“Towards an Unambiguous Electron Magnetic Chiral Dichroism (EMCD) Measurement in a Transmission Electron Microscope (TEM)” Metadata:

• Title: ➤  Towards an Unambiguous Electron Magnetic Chiral Dichroism (EMCD) Measurement in a Transmission Electron Microscope (TEM)
• Author: Christian Hurm
• Language: English
• Number of Pages: 122
• Publisher: Logos Verlag Berlin GmbH
• Publish Date: 2009
• Genres: Science

Edition Identifiers:

• Google Books ID: YqiBd9DjAQQC
• ISBN-13: 9783832521080
• ISBN-10: 3832521089
• All ISBNs: 9783832521080 - 3832521089

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• Public Domain: No
• Availability Status: Partially available
• Availability Status for country: US.
• Available Formats: Text is not avialbe, image copy is available.
• Google Books Link: Google Books

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2Photoreceptor Optics

By Allan W. Snyder and Randolf Menzel

The above consideration indicates that at present many of the experi mental facts on PS in animals can be quantitatively explained within the limits of the "universal" photoreceptor membrane concept. Of course, existence of preferential orientation of the absorbing dipoles in the tubuli of the rhabdomeres can not be totally rejected. We hope that the concept of the "universal" photoreceptor membrane may serve as the useful instrument when dealing with newly discovered properties of visual cells so that true mechanisms of electrical and optical coupling will be searched for instead of assumptions being made on additional properties of the photoreceptor membrane in every new animal under study. 5. Absorption Spectrum of the Universal Photoreceptor Membrane and Spectral Sensitivity of the Photoreceptor 5. 1 Preliminary Notes It seems nearly self-evident that the absorption spectrum of the pho toreceptor membrane coincides exactly with that of the visual pigment it contains. Hence, the membrane must exhibit three bands of absorp tion - the principal band with its peak within the limits of visible spectrum (or a-peak); the secondary band between 340 and 380 nm (S peak); and the third, protein band, in the ultraviolet (UV) at 280 nm (COLLINS et al. , 1952). The main peak of absorption is located within the range 433-575 nm for retinol-based pigments and between 438 and 620 nm for 3-dehydroretinol-based pigments, the position of Amax de pending on many ecological factors.

3Electric Field Induced Dichroism of CN ̄in Various Alkali Halides

By Robert Louis Pompi

The above consideration indicates that at present many of the experi mental facts on PS in animals can be quantitatively explained within the limits of the "universal" photoreceptor membrane concept. Of course, existence of preferential orientation of the absorbing dipoles in the tubuli of the rhabdomeres can not be totally rejected. We hope that the concept of the "universal" photoreceptor membrane may serve as the useful instrument when dealing with newly discovered properties of visual cells so that true mechanisms of electrical and optical coupling will be searched for instead of assumptions being made on additional properties of the photoreceptor membrane in every new animal under study. 5. Absorption Spectrum of the Universal Photoreceptor Membrane and Spectral Sensitivity of the Photoreceptor 5. 1 Preliminary Notes It seems nearly self-evident that the absorption spectrum of the pho toreceptor membrane coincides exactly with that of the visual pigment it contains. Hence, the membrane must exhibit three bands of absorp tion - the principal band with its peak within the limits of visible spectrum (or a-peak); the secondary band between 340 and 380 nm (S peak); and the third, protein band, in the ultraviolet (UV) at 280 nm (COLLINS et al. , 1952). The main peak of absorption is located within the range 433-575 nm for retinol-based pigments and between 438 and 620 nm for 3-dehydroretinol-based pigments, the position of Amax de pending on many ecological factors.

4Optical Activity Studies of Nucleic Acid Conformation and Stability

By Neil Philip Johnson

The above consideration indicates that at present many of the experi mental facts on PS in animals can be quantitatively explained within the limits of the "universal" photoreceptor membrane concept. Of course, existence of preferential orientation of the absorbing dipoles in the tubuli of the rhabdomeres can not be totally rejected. We hope that the concept of the "universal" photoreceptor membrane may serve as the useful instrument when dealing with newly discovered properties of visual cells so that true mechanisms of electrical and optical coupling will be searched for instead of assumptions being made on additional properties of the photoreceptor membrane in every new animal under study. 5. Absorption Spectrum of the Universal Photoreceptor Membrane and Spectral Sensitivity of the Photoreceptor 5. 1 Preliminary Notes It seems nearly self-evident that the absorption spectrum of the pho toreceptor membrane coincides exactly with that of the visual pigment it contains. Hence, the membrane must exhibit three bands of absorp tion - the principal band with its peak within the limits of visible spectrum (or a-peak); the secondary band between 340 and 380 nm (S peak); and the third, protein band, in the ultraviolet (UV) at 280 nm (COLLINS et al. , 1952). The main peak of absorption is located within the range 433-575 nm for retinol-based pigments and between 438 and 620 nm for 3-dehydroretinol-based pigments, the position of Amax de pending on many ecological factors.

5ORD and CD in Chemistry and Biochemistry

An Introduction

By Pierre Crabbé

Ord and Cd in Chemistry and Biochemistry ...

6Electric Dichroism and Polymer Conformation

By Terry Charles Troxell

Ord and Cd in Chemistry and Biochemistry ...

7Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry

By Pierre Crabbé

Ord and Cd in Chemistry and Biochemistry ...

8Electric Dichroism and Electric Birefringence

By E. Fredericq and C. Houssier

Ord and Cd in Chemistry and Biochemistry ...

9Dichroism of Dyed Cellulose Fibres

By Derk Heikens

Ord and Cd in Chemistry and Biochemistry ...

10A Note on Dichroic Gratings for Colour Encoding

By K. Hacking and BBC Research Department

Ord and Cd in Chemistry and Biochemistry ...