The statistical sputtering contribution to resolution in concentration-depth profiles

The statistical contribution to resolution in concentration-depth profiles by sputtering combined with Auger electron spectroscopy and secondary ion mass spectrometry is evaluated using a modified form of the sequential layer sputtering model. The modification makes allowance for the fact that each surface atom has a sputtering probability which is inversely proportional to its instantaneous bonding with the matrix, as predicted by Sigmund's theory, instead of being constant. Thus the sputtering is site dependent with the most exposed atoms having the highest sputtering probability. The theory shows that the statistical contribution to the depth resolution for depths greater than 10 nm is approximately constant and, depending on the precise choice of parameters, will probably be in the range 1–2 nm instead of increasing with the square root of depth. Thus the statistical contribution, instead of being the dominant term in the resolution of concentration-depth profiles, may often have only a minor effect when compared with the atomic mixing, diffusional and instrumental terms.     

Atomic structure of collision cascades in ion-implanted silicon and channeling effects

We have investigated the atomic structures of collision cascades in Bi⁺-implanted silicon. The formation of subcascades or bunching of the primary cascades is clearly observed. The central regions of the cascades were found to be amorphous with a high density of disorder in the surrounding regions. The experimental results are discussed in terms of the computer simulation of the deposited damage energy profiles. The effect of channeling on the deposited damage energy profile is examined. The peak and integrated damage energies are considerably lower in channeling directions compared to random directions.     

The fidelity of repair of radiation damage

Ionising radiation (IR) induces a range of DNA damage similar to that which arises endogenously from reactive oxygen species generated as by-products of metabolism. However, due to non-homogeneous energy deposition, the damage from IR frequently occurs in clusters producing unique 'complex' lesions. Cells have evolved a range of mechanisms to respond to DNA damage, which include pathways of DNA repair and processes that prevent the proliferation of damaged cells. However, the repair mechanisms are not fool proof and clustered radiation-induced lesions pose a particular problem. Whether DNA damage created by IR can be repaired accurately, mis-repaired or not repaired at all is of utmost importance in considering the impact of radiation exposure. Here, the current knowledge is discussed of the repair of double strand breaks, a biologically important lesion induced by IR, in the context of the fidelity of the repair mechanisms and the consequences of mis-repair or lack of repair.     

交叉模态对结构随机振动疲劳损伤的贡献

以小阻尼简支梁为例,讨论了交叉模态对随机振动疲劳损伤累积的贡献;结构的响应分析采用模态叠加方法,随机振动疲劳损伤累积分析采用M iner线性疲劳损伤准则。数值模拟结果表明,即使是小阻尼稀疏模态结构,交叉模态对结构振动疲劳损伤累积的贡献也是不容忽视的。     

On damage and nucleation in sputtering of MgO and NbN

In sputter deposition the chemistry of interfaces is of crucial importance, e.g., for wear resistance, for the material to be grown or for tunnel barriers. Similarly, in sputter etching the damage, the serration and the chemistry of the surface controls the reactions and thus the sputter profiles. With ARXPS (angle-resolved X-ray photoelectron spectroscopy) first reliable information on interface chemistry of NbN-MgO and MgO-NbN interfaces was obtained. These results show that particle impact and chemical reactions cause damage, nucleation and growth of MgO and NbN:

• 1.(1) rf magnetron sputtering of MgO onto NbN oxidizes NbN to Nb₂O₅ (≈ 2 nm);
• 2.(2) reactive dc magnetron sputtering of NbN onto MgO reduces MgO to Mg up to depths of 10 nm, where NbN is oxidized partly to perturbed Nb₂O₅.

Mg alloys to NbN_1-xO_xMg_y nucleating the forthcoming δ-NbN phase. This alloy bulges into δ-NbN using up the metallic Mg. This oxidation, the damage and the alloying is the reason for the deterioration of MgO tunnel barriers, for the deterioration of superconductivity of NbN counter electrodes and for the epitaxy of δ-NbN on MgO and of MgO on δ-NbN, being of chemical nature. These effects depend sensitively on sputter conditions, i.e. on interaction of the whole plasma cloud with the target.     

Observations of sputtering damage using the field-ion microscope

The field-ion microscope has been used to study the effects of bombarding tungsten surfaces with low energy noble gas ions. This technique is particularly useful because the collision events which contribute to the process of sputtering occur essentially on the atomic scale. By bombarding with neon, argon and xenon ions in the energy range 100 eV to 1 keV it has been possible to obtain information on the type and distribution of the lattice damage produced, together with the effects of annealing. These results are relevant to those surface techniques such as LEED, AES and XPS which employ low energy ion bombardment as a means of removing surface contamination. Although surfaces treated in this way may be chemically clean their exact topography has previously remained undefined.     

Study of radiation damage to long BGO crystals

Results are presented on the decrease of the scintillation light output of long bismuth germanate (BGO) crystals at room temperature due to irradiation by ⁶⁰Co photons and 25 MeV electrons with doses from 50 to 5000 rad. After irradiation the light output recovers spontaneously. This recovery can be described by the sum of a minimum of three exponential functions. The shortest time constant is of the order of several hours, while the longest time constant is several hundred hours. The initial decrease in light output depends non-linearly on the dose applied and saturation effects have been observed. The damage induced by irradiation with 25 meV electrons is similar to the damage caused by ⁶⁰Co photons. The data are consistent with the view that only the absorption properties of BGO are changed by irradiation. For comparison, a NaI(Tl) crystal and a CsI(Tl) crystal have also been irradiated. Also, the effects on light transmission due to radiation damage to BGO are reported.     

A proposed method of predicting ship collision damage

In the past, research on ship collision strength has centered on nuclear ship structures, but now emphasis is shifting to low-energy collisions of ordinary ships carrying hazardous cargoes including crude oil.A ship collision is too complex to study using theoretical methods alone, yet tests with small-scale models of thin steel plate fail to duplicate actual ship collision damage for the following reasons:

1. (1) The fracture of actual ship shell plate and model shell plate defies the law of similarity;

2. (2) Some structural members are usually omitted for ease of fabrication in relatively small models.

Accordingly, the authors propose a method for predicting ship collision damage that resorts to three combined experiments:

1. (1) A fundamental test determining the initiation of plate fracture;

2. (2) A local structure model test evaluating the effects of structural details;

3. (3) A structural model test investigating the deformation of a ship hull.

This paper reviews, by way of example, some results of the experimental studies which the authors have performed.The laws of similarity proved very important in the study of plate fracture.The authors believe that the proposed method will prove useful especially in dealing with low-energy ship collisions.     

The physics of radiation damage in particle detectors

Intense high-energy particle beams cause damage to semiconductor detectors and signal-conditioning electronics by displacement and long-term ionization effects. While first-principles prediction of effects are not practical, the magnitude of each effect can be scaled approximately between particle energy and type by using an appropriate scaling parameter.     

Investigation of radiation damage to microcapsules in environmental SEM

Abstract

The radiation damage to a specimen in the chamber of electron microscopes has been studied extensively in the past few years. However, for the specific case of specimens with a core/shell structure, such as microcapsules and biological cells, there has been little experimentation devoted to understanding how the radiation may affect their mechanical properties. In the present work, single melamine formaldehyde (MF) microcapsules were imaged using an environmental electron microscope (ESEM) under both dry and wet modes under conditions of different accelerating voltages. The changes in the morphology (shape) were monitored as a function of radiation time. In addition, a newly developed ESEM based nanomanipulation technique was used to measure how the force imposed on single MF microcapsules for a given deformation changed with radiation time, in order to identify a time window within which the radiation damage to the microcapsules may be negligible in order to be able to study the mechanical properties of the particles. Based on the findings, the nanomanipulation technique was applied to measure the force versus displacement for compressing single microcapsules to rupture, including determination of their rupture mode.     

Application of high-density plasma to sputtering and reactive sputtering processes

An investigation of thin-film preparation processes by sputtering technique has been carried out utilizing the high-density plasma induced by the microwave power coupled in the surface wave mode. The high sputtering rate arising from the high ion current to the target is expected to be advantageous for processes of nitride surface and compounds. An independent control of the external bias potential to the target and of the gas mixture ratio is demonstrated to be possible by the mode-locking mechanism. Ferromagnetic films of FeNi alloy were deposited on glass substrates. Films of TiN and of AlN were produced on plastic substrates and on glasses.     

Workplace monitoring of mixed neutron-photon radiation fields and its contribution to external dosimetry

Workplace monitoring is a common procedure for determining measures for routine radiation protection in a particular working environment. For mixed radiation fields consisting of neutrons and photons, it is of increased importance because it contributes to the improved accuracy of individual monitoring. An example is the determination of field-specific correction factors, which can be applied to the readings of personal dosemeters. This paper explains the general problems associated with individual dosimetry of neutron radiation, and describes the various options for workplace monitoring. These options cover a range from the elaborate field characterisation using transport calculations or spectrometers to the simpler approach using area monitors. Examples are given for workplaces in nuclear industry, at particle accelerators and at flight altitudes.     

Computer simulation of defects and radiation damage

In this paper, we describe the computer simulation technique and its application to the study of radiation damage. Details of two important methods: the static and the dynamic methods have been discussed. Applications to the study of point defect formation and stability, their clusters, diffusion, dislocations and dislocation-point defect interaction are discussed drawing from our own work wherever possible. A short mention is made of the importance of the interatomic potential. Examples for the case of magnesium and other hcp metals, bcc iron and fcc Ni are cited and numbers for various quantities like formation energy, dipole tensor, interaction energy etc are quoted.     

Primary and secondary damage to biological tissue induced by laser radiation

A simple analytic model describing the evolution of the thermal injury during and after exposure of biological tissue to pulses of intense laser radiation is presented. Estimates for the upper and lower bounds of the extent of the thermal injury associated with protein and enzyme denaturization (secondary damage) relative to the extent of burned tissue (primary damage) are presented. The energy necessary for burn threshold and the energy required to induce both types of thermal injury increase with laser pulse duration. An optimal duration of laser pulse exists at which the extent of the secondary damage relative to the primary damage is the smallest.     

Small-punch and TEM-disc testing techniques and their application to characterization of radiation damage

The present paper summarizes the development of miniaturized small-punch (SP) and TEM-disc (TD) testing techniques and shows their applicability in characterizing the mechanical properties of irradiated materials. The yield strength, ductility and fracture toughness,J _lc, were empirically estimated by analysing the deformation and fracture behaviour observed in the miniaturized specimen tests. The ductile-brittle transition temperature (DBTT) was determined from the variation of the SP or TD fracture energy with temperature. A linear correlation between the DBTT obtained from the SP and Charpy V-notched specimen tests has been theoretically and experimentally established. The problems of cracking detection and data scattering often observed in the SP or TD specimen tests are discussed in terms of heterogeneous embrittlement behaviour of materials. It has been demonstrated that these miniaturized testing techniques are capable of evaluating hardening, DBTT shifts andJ _lc decreases caused by neutron irradiation.     

Mechanistic simulation of radiation damage to DNA and its repair: on the track towards systems radiation biology modelling

The biophysical simulation code PARTRAC enables, by combining track structure calculations with DNA models on diverse genomic scales, prediction of DNA damage yields and patterns for various radiation qualities. To extend its applicability to later endpoints such as mutagenesis or cell killing, a continuative model for repair of radiation-induced double-strand break (DSB) via non-homologous end-joining has complemented the PARTRAC code by about 12 orders of magnitude on a temporal scale. The repair model describes step-by-step by the Monte Carlo method the attachment and dissociation of involved repair enzymes and diffusion motion of DNA ends. The complexity of initial DNA lesion patterns influences the repair kinetics and outcome via additional cleaning steps required for dirty DNA ends. Model parameters have been taken from measured attachment kinetics of repair enzymes and adaptation to DSB rejoining kinetics after gamma irradiation. Application of the DNA repair model to damage patterns following nitrogen ion irradiation and comparison with experimental results reveal the need for further model refinements. Nevertheless, already the present model represents a promising step towards systems modelling of cellular response to radiation.     

Nanoscale detection of ionizing radiation damage to DNA by atomic force microscopy

The detection and quantification of ionizing radiation damage to DNA at a single-molecule level by atomic force microscopy (AFM) is reported. The DNA damage-detection technique combining supercoiled plasmid relaxation assay with AFM imaging is a direct and quantitative approach to detect gamma-ray-induced single- and double-strand breaks in DNA, and its accuracy and reliability are validated through a comparison with traditional agarose gel electrophoresis. In addition, the dependence of radiation-induced single-strand breaks on plasmid size and concentration at a single-molecule level in a low-dose (1 Gy) and low-concentration range (0.01 ng microL(-1)-10 ng microL(-1)) is investigated using the AFM-based damage-detection assay. The results clearly show that the number of single-strand breaks per DNA molecule is linearly proportional to the plasmid size and inversely correlated to the DNA concentration. This assay can also efficiently detect DNA damage in highly dilute samples (0.01 ng microL(-1)), which is beyond the capability of traditional techniques. AFM imaging can uniquely supplement traditional techniques for sensitive measurements of damage to DNA by ionizing radiation.     

The designers contribution to company success

For the past 25 years Dieter Rams has worked for just two companies. The reason for this deliberate decision will become clear in the following articles.In this, the first in a series of three, Professor Rams discusses the definition and prerequisites of good design. The second article will describe the qualifications and education of designers and the final article will examine the future role of designers.The two companies are Braun AG who manufacture domestic electrical goods and Vitsoe who make furniture. When Dieter Rams joined Braun in 1955 the company employed just under 2000 people and had a turnover of 50 million DM. Now the company employ 9000 and have sales totalling more than 800 million DM.Vitsoe was founded in 1959 to manufacture furniture designed by Rams. Today the company employs 50 people and has sales of 6 million DM.     

Suppression of damage to organic light-emitting layers during deposition of Al-doped ZnO thin films by radio-frequency magnetron sputtering

Conditions for deposition of Al-doped ZnO (AZO) films on an organic light-emitting layer with a radio-frequency magnetron sputtering system were optimized to realize high deposition rate and low resistivity of the films. Damage inflicted on the organic layer by depositing the AZO film under the optimized deposition conditions was studied from photoluminescence, UV-Vis and Fourier transform infrared spectroscopy spectra using tris(8-hydroxyquinolinato)aluminium as a model organic compound. We found that damage to the organic layer was lessened by increasing the magnetic field from a normal intensity of 0.02 T to 0.1 T. The damage to the organic layer was further lessened by inserting a grounded grid electrode between a target and the substrate.