Low-voltage cross-sectional EBIC for characterisation of GaN-based light emitting devices

Electron beam induced current (EBIC) characterisation can provide detailed information on the influence of crystalline defects on the diffusion and recombination of minority carriers in semiconductors. New developments are required for GaN light emitting devices, which need a cross-sectional approach to provide access to their complex multi-layered structures. A sample preparation approach based on low-voltage Ar ion milling is proposed here and shown to produce a flat cross-section with very limited surface recombination, which enables low-voltage high resolution EBIC characterisation. Dark defects are observed in EBIC images and correlation with cathodoluminescence images identify them as threading dislocations. Emphasis is placed on one-dimensional quantification which is used to show that junction delineation with very good spatial resolution can be achieved, revealing significant roughening of this GaN p-n junction. Furthermore, longer minority carrier diffusion lengths along the c-axis are found at dislocation sites, in both p-GaN and the multi-quantum well (MQW) region. This is attributed to gettering of point defects at threading dislocations in p-GaN and higher escape rate from quantum wells at dislocation sites in the MQW region, respectively. These developments show considerable promise for the use of low-voltage cross-sectional EBIC in the characterisation of point and extended defects in GaN-based devices and it is suggested that this technique will be particularly useful for degradation analysis.     

X-ray contact microscopy using an excimer laser plasma source with different target materials and laser pulse durations

Soft X-ray contact microscopy (SXCM), using a pulsed X-ray source, offers the possibility of imaging the ultrastructure of living biological systems at sub-100 nm resolution. We have developed a table-top pulsed plasma X-ray source for this application, generated by a large-volume XeCl laser, achieving a good conversion efficiency to 'water-window' X-rays (hν≈280–530 eV).
Optimum plasma conditions for SXCM are discussed, including the effect of pulse duration, target material and resist development time on image resolution. Soft X-ray contact images of Chlamydomonas dysosmos (unicellular alga) and of the cyanobacterium Leptolyngbya are shown.     

The use of laser scanning confocal microscopy (LSCM) in materials science

Laser scanning confocal microscopes are essential and ubiquitous tools in the biological, biochemical and biomedical sciences, and play a similar role to scanning electron microscopes in materials science. However, modern laser scanning confocal microscopes have a number of advantages for the study of materials, in addition to their obvious uses for high resolution reflected and transmitted light optical microscopy. In this paper, we provide several examples that exploit the laser scanning confocal microscope's capabilities of pseudo-infinite depth of field imaging, topographic imaging, photo-stimulated luminescence imaging and Raman spectroscopic imaging.     

Quantitative determination of electric field strengths within dynamically operated devices using EBIC analysis in the SEM

Although electron beam-induced current (EBIC) technique was invented in the seventies, it is still a powerful technique for failure analysis and reliability investigations of modern materials and devices. Time-resolved and stroboscopic microanalyses using sampling Fourier components decomposed by modulated charge carrier excitation are introduced. Quantitative determination of electric field strengths within dynamically operated devices in the scanning electron microscope (SEM) will be demonstrated. This technique allows investigations of diffusion and drift processes and of variations of electric field distributions inside active devices.     

Lorentz phase microscopy of magnetic materials

We propose a method of Lorentz phase microscopy for in situ studies and imaging magnetic materials in transmission electron microscopy (TEM) based on the solution of the magnetic transport-of-intensity equation. We also describe the appropriate way of solving this equation that may be useful for understanding and practical use of non-holographic methods for phase retrieval in electron microscopy, especially in imaging magnetic materials. The method is simple, since it is primarily based on classical Fresnel imaging. On the other hand, it is quantitative and can be applied in any TEM without changing the basic hardware. Therefore, it may well find important practical applications in ultramicroscopy and modern magnetic materials research.     

Electron microscopy and diffraction of radiation-sensitive nanostructured materials

Soft matter research of natural organic and synthetic nanomaterials is an area in nanoscience and technology that has been growing particularly quickly in recent years. The materials under investigation are sensitive to high‐energy electrons. Any structure characterization using electron microscopy thus requires special care. First, we illustrated this on naturally grown nanotubes observed by normal and cryogenic scanning electron microscopy. Second, we studied the ordering and orientation of the mesophase in template‐grown nanotubes and nanorods containing discotic liquid crystals without and with doping, as desired. For these studies, we mainly used transmission electron diffraction and microscopy at low‐dose conditions, high‐efficiency image acquisition, and cryoprotection of the structures at liquid helium temperature. Additional analytical information was obtained by electron energy filtering observations.     

Three-dimensional laser scanning two-photon fluorescence confocal microscopy of polymer materials using a new,efficient upconverting fluorophore

Three-dimensional confocal imaging of polymer samples was achieved by the use of two-photon excited fluorescence in both positive and negative contrast modes. The fluorophore was a new and highly efficient two-photon induced upconverter, resulting in improved signal strength at low pumping power. Because of the relatively long wavelength of the excitation source (798 nm from a mode-locked Ti:Sap-phire laser), this technique shows a larger penetration depth into the samples than provided by conventional single-photon fluorescence confocal microscopy. Single-photon and two-photon images of the same area of each sample show significant differences. The results suggest the possibility of using two-photon confocal microscopy, in conjunction with highly efficient fluorophores, as a tool to study the surface, interface, and fracture in material science applications.     

Selection of structural materials for precision devices

The selection of material suitable for providing the structure of precision devices is considered in terms of some of their mechanical properties, particularly thermal ones. It is proposed that selection be guided by the position of various materials in a mathematical map having as axes combinations of properties which occur in formulae describing important behavioural phenomena. The approach is demonstrated using a three dimensional map through which are compared the merits of a variety of metals, ceramics and semiconductors.     

Internet-based robotic laser scissors and tweezers microscopy

We have engineered a robotic laser ablation and tweezers microscope that can be operated via the internet using most internet accessible devices, including laptops, desktop computers, and personal data assistants (PDAs). The system affords individual investigators the ability to conduct micromanipulation experiments (cell surgery or trapping) from remote locations (i.e., between the US and Australia). This system greatly expands the availability of complex and expensive research technologies via investigator-networking over the internet. It serves as a model for other "internet-friendly" technologies leading to large scale networking and data-sharing between investigators, groups, and institutions on a global scale. The system offers three unique features: (1) the freedom to operate the system from any internet-capable computer, (2) the ability to image, ablate, and/or trap cells and their organelles by "remote-control," and (3) the security and convenience of controlling the system in the laboratory on the user's own personal computer and not on the host machine. Four "proof of principle" experiments were conducted: (1) precise control of microscope movement and live cell visualization, (2) subcellular microsurgery on the microtubule organizing center of live cells viewed under phase contrast and fluorescence microscopy, (3) precise targeting of multiple sites within single red blood cells, and (4) optical trapping of 10 microm diameter polystyrene microspheres.     

Organic optoelectronics ： materials, devices and applications

1Introduction Beforethediscoveryofelectricallyconduc tivepropertiesthroughdoping,polymerswere widelyusedaselectricalinsulatorsduetothesu periorinsulatingpropertiestheyexhibited.In1977,thediscoveryofthefirsthighlyconductive polymer,chemicallyandelectrochemicallydoped polyacetylene,wasreported[12].Thediscovery ofdopedpolyacetylenehasopenedanentirenew fieldforpolymersandorganicmaterialsintheir applicationstobothconductorsandsemiconduc tors.Althoughtheinitialemphasiswasonthe conductivepropertiesob…     

Development of laser scanning microscopy using a near ultraviolet laser

We have developed a legitimate fluorescence con-focal scanning microscope (CLSM) using a near ultraviolet (UV) laser. This system has almost no chromatic aberration from the near UV region to the visible region (350–600 nm), and the objectives are designed as water-immersion type. Therefore this system provides the high-quality fluorescence image excited by the near UV laser, and high-quality image of deep points in a sample.     

A method and devices of electron microtomography in scanning electron microscopy

A method of microtomography of layered microstructures during detection of backscattered electrons in a scanning electron microscope is described. This method is based on the formation of layer-by-layer images hidden under the surfaces of microstructures using reflected electrons filtered within a narrow energy window. An improved deflector-type spectrometer with toroidal electrostatic sector electrodes is applied for microtomography and spectroscopy. To improve the sharpness and accuracy of separation of individual buried heteroboundaries, the modulation principle of video-signal detection is implemented.     

Low-voltage scanning electron microscopy of low-density materials

Delicate microstructures in low-density polymer foams and silica aerogel are susceptible to coating damage, artifact structures induced by coating, and electron-beam damage when they are examined by conventional scanning electron microscopy (SEM) techniques. These problems can be reduced significantly and even eliminated when these materials are examined directly with no coating using low-voltage scanning electron microscopy (LVSEM). Much of the fine structure in these materials also can be resolved at low voltage in a SEM equipped with a field-emission gun (FESEM).     

Applications of quantitative microscopy in materials engineering

Among the examples reviewed are volume-fraction measurements in phase diagram and kinetic studies, properties dependent upon internal surface area, the characterization of phase arrangements by contiguity, proximity and dihedral-angle measurements. The use of grain boundary and particle spacings in studies of mechanical properties is discussed in relation to current theories of strengthening mechanisms. Applications of size-distribution analysis in kinetic studies and in the assessment of inclusion contents in steels are surveyed.     

Phase contrast electron microscopy of biological materials

The properties of two electron microscope phase contrast imaging methods are compared. The first is the conventional bright-field method in which dark phase contrast is created by defocusing; the second is a phase plate method in which bright phase contrast is created by means of a suitably shaped electric field. Using some negatively stained biological specimens which have a well-known repeating structure as the test object, it is shown that the phase plate method has some important advantages over the bright-field method. Its contrast transfer characteristics are such that it can provide a more faithful representation of the high resolution detail in the object. Moreover, by producing bright, rather than the normal dark, phase contrast it is able to simultaneously enhance the detail in the specimen and weaken the detail in the stain; this latter property enables the method to display information about the specimen that it would not be possible to detect with the bright-field method.     

Resolution in nonlinear laser scanning microscopy

The lateral and depth resolution of nonlinear microscopy was studied systematically. Nonlinear microscopy can be classified into several categories depending on the coherence properties of the process that generates the imaging signal from the illuminating light, on whether a single- or a two-beam geometry is used, and whether the optical setup is Type I or Type II. An evaluation of the imaging equations shows that (i) lateral and depth resolution improve with increasing nonlinearity, (ii) the differences between coherent and incoherent imaging diminish, and (iii) nonlinear imaging allows depth discrimination in Type I microscopy.     

High-resolution scanning near-field EBIC microscopy: application to the characterisation of a shallow ion implanted p+-n silicon junction

High-resolution electron beam induced current (EBIC) analyses were carried out on a shallow ion implanted p⁺–n silicon junction in a scanning electron microscope (SEM) and a scanning probe microscope (SPM) hybrid system. With this scanning near-field EBIC microscope, a sample can be conventionally imaged by SEM, its local topography investigated by SPM and high-resolution EBIC image simultaneously obtained. It is shown that the EBIC imaging capabilities of this combined instrument allows the study of p–n junctions with a resolution of about 20 nm.