Normal Imaging Conditions Research Articles

Probing the beam‐induced heating effect inside a transmission electron microscope by nanoparticle labels

Beam-induced heating effect on nanoscale samples is a crucial question, as it strongly influences the interpretation of observed unusual behaviours. This question is currently under debate without a convincing conclusion. Here, using silver nitride (Ag3N) nanoparticles as temperature labels, we perform an investigation on this heating effect inside a transmission electron microscope (TEM) under normal imaging conditions. Combined with experimental measurements and semi-quantitative calculations, a temperature increase of more than 100 K is estimated and confirmed in the graphite carbon nitride (g-C3N4) films. Strong temperature gradients are found to exist in the single-end fixed g-C3N4 films. The influencing factors of heat accumulation are also investigated and discussed. Findings in this study may shed some light on the understanding of the abnormal behaviours of nano-objects observed inside TEM.

Passive multiple reverse time migration imaging based on wave decomposition and normalized imaging conditions

With the development of seismic exploration, passive-source seismic data has attracted increasing attention. Ambient noise passive seismic sources exists widely in nature and industrial production. Passive seismic data is important in logging while drilling (LWD), large-scale structural exploration, etc. In this paper, we proposed a passive multiple reverse time migration imaging (PMRTMI) method based on wavefield decomposition and normalized imaging conditions method. This method differs from seismic interferometry in that it can use raw passive seismic data directly in RTM imaging without reconstruction of virtual active gather, and we use the wavefield decomposition method to eliminate the low frequency noise in RTM. Further, the energy normalized imaging condition is used in full wavefield decomposition, which can not only enhance the image quality of both edge and deep information but also overcome the wrong energy problem caused by uneven distribution of passive sources; furthermore, this method exhibits high efficiency. Finally, numerical examples with the Marmousi model show the effectiveness of the method.

Practical issues in carrier‐contrast imaging of GaN structures

AbstractScanning capacitance microscopy (SCM), scanning spreading resistance microscopy (SSRM) and secondary electron emission within a scanning electron microscope (SEM) were used to image two magnesium‐doped GaN samples, grown under identical conditions. In only one of these samples were the dopants activated by annealing. Under normal imaging conditions for SCM and SSRM, no discernable change in contrast was observed in the unactivated sample, whilst for SEM imaging contrast increased over ca. 40 s of imaging time, indicating some activation of the dopants by the electron beam. In addition, various sample preparation techniques were attempted in order to minimise the roughness of the GaN cross‐section used for SCM imaging. Some techniques which reduce the surface roughness lead to a poor SCM signal‐to‐noise ratio. However, a cleaving technique is described which produces suffi‐ciently large and flat areas within multi‐layered GaN specimens for the extraction of useful SCM data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modelling the application of adaptive optics to wide‐field microscope live imaging

Wide-field fluorescence microscopy is an essential tool in modern cell biology. Unfortunately the image quality of fluorescence microscopes is often significantly degraded due to aberrations that occur under normal imaging conditions. In this article, we examine the use of adaptive optics technology to dynamically correct these problems to achieve close to ideal diffraction limited performance. Simultaneously, this technology also allows ultra-rapid focusing without having to move either the stage or the objective lens. We perform optical simulations to demonstrate the degree of correction that can be achieved.

Distance-dependent electron hopping conductivity and nanoscale lithography of chemically-linked gold monolayer protected cluster films

Films of monolayer protected Au clusters (MPCs) with mixed alkanethiolate and ω-carboxylate alkanethiolate monolayers, linked together by carboxylate–Cu 2+–carboxylate bridges, exhibit average edge-to-edge cluster spacings that vary with the numbers of methylene segments in the alkanethiolate ligand as determined by a combined atomic force microscopy (AFM)/UV-Vis spectroscopy method. The electronic conductivity ( σ EL) of dry films is exponentially dependent on the cluster spacing, consistent with electron tunneling through the alkanethiolate chains and non-bonded contacts between those chains on individual, adjacent MPCs. The calculated electronic coupling factor ( β) for tunneling between MPCs is 1.2 Å −1, which is similar to other values obtained for tunneling through hydrocarbon chains. Electron transfer rate constants measured on the films reflect the increased cluster–cluster tunneling distance with increasing chainlength. The MPC films are patterned by scanning the surface with an AFM or scanning tunneling microscopy (STM) tip under appropriate conditions. The patterning mechanism is physical in nature, where the tip scrapes away the film in the scanned region. Large forces are required to pattern films with AFM while normal imaging conditions are sufficient to produce patterns with STM. Patterns with dimensions as small as 100 nm are shown. Subsequent heating (300 °C) of the patterned surfaces leads to a metallic Au film that decreases in thickness and is smoother compared to the MPC film, but retains the initial shape and dimensions of the original pattern.

Imaging of symmetry-forbidden fringes with La 1− xCa xMnO 3 as example

It is shown (experimentally and theoretically) with La 1− x Ca x MnO 3 as example that symmetry forbidden fringes can be easily obtained in HREM images due to symmetry breaking in the diffraction process (crystal tilt) or in the non-linear imaging process (e.g. 2 and 3 fold astigmatism, coma, beam tilt, anisotropic information limit). Given the normal imaging conditions of HREM microscopes such forbidden fringes can hardly be prevented.

Safety of intrauterine contraceptive devices during MR imaging.

Three intrauterine contraceptive devices (IUD) were examined in an experimental in vitro setup to test their MR compatibility: Multiload CU375. Nova T (containing copper and silver), and Gyne T. The devices were fixed in a polyacrylamide gel and exposed to the magnetic field and the radiofrequency (RF) of standard MR sequences (spin-echo, turbo-spin-echo, turboFLASH, and magnetization transfer prepared FLASH). The RF power of a turbo-spin-echo sequence was increased by a factor of 5. Temperatures of the IUDs and the gel were measured during the MR examination. No deflection of the IUDs exposed to the magnetic field of 1.5 Tesla was detected. Under normal imaging conditions no temperature increase could be observed. Using an increased RF power, a maximal temperature rise of 0.4 degree C per examination was seen. No differences between the gel and the IUDs were observed, indicating that there is no specific heating of the tested IUDs.