Increase In Beam Size Research Articles

Microcolumn design for a large scan field and pixel number

A different approach in microcolumn design is presented, aiming at a large number of pixels at minimal probe size for the deflected beam. An optimization routine resulted in a seven times magnifying column featuring a more than 7×7mm2 scan field at 40mm working distance. Simulations for 1keV electrons from a field emission source predict an increase in beam size from 85nm on axis up to only about 200nm for a beam deflected 3mm off axis. Within a 1mm scan field this microcolumn could address over 100Mpixels of less than 100nm in size. Tests of this design using the 130nm electron probe of a scanning electron microscope as the electron source resulted in a beam size of ∼930nm on axis up to ∼1000nm for a beam deflected 3mm off axis.

Characterisation of a pre-cell hit detector to be used in single cell irradiation experiments at the Lund Nuclear Microprobe

This paper describes the characterisation of an ultra-thin silicon semiconductor Δ E detector to be used as a pre-cell ion hit detector in single ion experiments on individual, living cells. The characteristics of interest for this specific application are the hit detection efficiency, which has to be close to 100% to enable bombardment with either a single ion or a counted number of ions, the beam spreading, which should be as small as possible to maintain the targeting accuracy, and the vacuum tightness, since the detector is intended, if possible, to be used simultaneously as vacuum window. The hit detection efficiency was shown to be above 99% when detecting alpha particles or 2 MeV protons, the increase in beam size was about 1 μm and the vacuum tightness was comparable to that of the Si 3N 4 wafer which is normally used as vacuum window, thus the Δ E detector fulfils the main criteria to function properly as a single ion hit detector.

Finite-difference-time-domain analysis of finite-number-of-periods holographic and surface-relief gratings

The total-field-scattered-field formulation of the finite-difference time-domain method (FDTD) is used to analyze the diffraction of finite incident beams by finite-number-of-periods holographic and surface-relief gratings. Both second-order and fourth-order FDTD formulations are used with various averaging schemes to treat permittivity discontinuities and a comparative study is made with alternative numerical methods. The diffraction efficiencies for gratings of several periods and various beam sizes, for both TE and TM polarization cases, are calculated and the FDTD results are compared with the finite-difference frequency-domain (FDFD) method results in the case of holographic gratings, and with the boundary element method results in the case of surface-relief gratings. Furthermore, the convergence of the FDTD results to the rigorous coupled-wave analysis results is investigated as the number of grating periods and the incident beam size increase.

Effect of beam size and FRP thickness on interfacial shear stress concentration and failure mode of FRP-strengthened beams

This paper presents the results of an experimental research program designed to study the interfacial shear stress concentration at FRP cut-off points and the failure modes of RC beams strengthened in flexural with externally bonded carbon fibre reinforced polymer (CFRP) sheets. The test variables include the RC beam size and the CFRP thickness. The objectives are to investigate the effects of reduced scaling and the influence of the FRP thickness on the interfacial shear stresses and the failure modes of the FRP-strengthened beams as well as to confirm the validity of proposed analytical models for the prediction of intermediate crack-induced interfacial debonding and interfacial shear stresses at FRP cut-off points. The experimental works involve flexural testing of 17 FRP-strengthened beams under third-point loading. Three different effective beam depths and two CFRP thicknesses are considered. Two main conclusions are drawn from this study. First, the increase in beam size and/or FRP thickness is found to increase the interfacial shear stresses in the FRP curtailment region. In the present study, however, the peak shear stresses are not high enough to cause a change in the failure mode of the beams. Second, the size of the beam does not seem to affect the extent (measured in term of a strengthening ratio, SR) to which a reinforced concrete beam can be strengthened.

Angle-Resolved Laser-Induced Breakdown Spectrometry for Depth Profiling of Coated Materials

The combination of angle-resolved laser ablation with the use of a collimated beam is presented as a new approach to increase the depth-resolved capabilities of laser-induced breakdown spectrometry (LIBS). The effect of beam conditioning and the reduction of the effective sampling depth due to the angular dependence of laser ablation allow ablation rates lower than 2 nm/pulse for coated materials (Sn-coated steels and Cr-coated samples). Spectral information is obtained on a single-laser-shot basis. The effect of incidence angle has been examined from differentiated emission profiles, demonstrating the beneficial effect of working at incidence different from normal. A compromise between depth resolution and emission signal must be found at large angles due to the lower irradiance resulting from the increase in beam size at the interface for large angles of incidence. A comparison of the proposed approach with the analysis provided by a commercial glow-discharge device [glow discharge optical emission spectroscopy (GD-OES)] demonstrated quite satisfactory results.

A High-Resolution Multiple-Crystal Monochromator for X-ray Diffraction Studies

This work proposes a new four-crystal monochromator particularly indicated for applications in the field of high-resolution X-ray diffraction. The monochromator is made of two monolithic crystal elements. The first one is a channel-cut crystal consisting of two symmetrically cut components set in a parallel nondispersive geometry. The second monolithic crystal is composed of two crystal components in a parallel nondispersive geometry but the crystal surfaces are miscut with respect to the diffraction planes. The diffraction geometry for both components of the second monochromator crystal element is the glancing-incidence condition. The peculiar properties of this monochromator are investigated theoretically. An appropriate rotation of the second component of the second monolithic block with respect to the first components corrects the beam deviation caused by the refraction effect. This monochromator system may allow one to obtain highly monochromated and collimated beams with high angular resolution (about 0.01 mrad) and wavelength dispersion of about 4 × 10−5. The intensity reduction of the proposed crystal arrangement in comparison with other monochromators is discussed, including wavelength spread and beam size increase.

Comparison of three lasers on dental pulp chamber temperature change.

Previous studies have reported dental pulp chamber temperature changes using only one beam size per laser. This study was designed to evaluate the effects of beam size, wattage, and energy density on pulp chamber temperature changes of extracted human teeth for three lasers (CO 2, Argon, Nd:YAG). During laser irradiation of the outer enamel surface, a thermocouple was placed in the pulp chamber which measured and recorded the temperature changes. This was done for each combination of lasing dosimetry parameters. In all cases the recorded temperatures increased with the increase in beam size for a given energy density (J/cm 2) and wattage. Also, the recorded temperatures increased with increased energy density for a given wattage and beam size.

Size effect tests of torsional failure of plain and reinforced concrete beams

The current design code formulae for the torsional failure of plain or longitudinally reinforced beams exhibit no size effect, i.e. the failure of geometrically similar beams of different sizes is supposed to occur at the same nominal stress. Experiments on reduced-scale beams were carried out, and the results confirm that there is a significant size effect, such that the nominal stress at failure decreases as the beam size increases. This is found for both plain and longitudinally reinforced beams. The results are consistent with the recently proposed Bažant's size-effect law. However, the scatter of the results and the scope, and range limitations prevent it from being concluded that the applicability of this law is proven.

Submicron electron-beam lithography using a beam size comparable to the linewidth control tolerance

Presently available electron‐beam lithography systems for submicron lithography have minimum beam sizes or edge resolution on the order of 0.1–0.2 μm. Satisfactory proximity correction, linewidth control, and profile quality are critically dependent on beam size. Moreover, variations in beam size about the expected size can result in severe degradation of linewidth control. In this paper, we will examine the relationships between linewidth control, beam size, and proximity correction and show that it is possible, but difficult, to successfully use electron‐beam lithography under these conditions. High resolution vector scan electron‐beam systems with known Gaussian beam sizes are used to produce features down to 0.25 μm in single and multilayer resist. It is shown that the beam size and forward scattering must be included in the proximity correction of submicron patterns. The effects of varying the beam size are also investigated and it is shown, for example, that an increase in beam size of only 0.02 μm can significantly reduce the developed resist linewidth of sub‐half‐micron features in 1.0 μm thick resist.

Scattered radiation distributions around computed tomography scanners and the associated radiation hazard to personnel.

A programme has been set up to monitor the exposure of personnel during specific diagnostic procedures. This programme includes the investigation of radiation hazard associated with the operation of computed tomography scanners. The first-generation CT scanners employed a rotatetranslate geometry where both the detectors and the X-ray tube moved around the patient. Since then, there have been many advances in the design of CT scanners, such as the introduction of a fan-beam geometry coupled with a multi-detector array. These design changes have had little effect on the number of photons employed in producing an image; any reduction in exposure time in later-generation units is balanced by an increase in beam size. However, the decrease in time of exposure and picture reconstruction has enabled the number of tomographic sections in any given period of time to be increased. This increase allows either a larger throughput of patients and/or more slices per patient. Consequently, the total magnitude of scatte...

Crossing of resonance in a relativistic electron ring with discrete and continuous eigenvalue spectrum

The Vlasov formalism is used to calculate the first and second order perturbations of a ring of relativistic electrons after crossing the betatron resonance v r = 1. The presence of coherent self-fields may result in separate crossing of the coherent and incoherent integral resonances associated with the discrete and continuous eigenvalues. The quantity χ giving the ratio of the spread in the single particle frequencies to the coherent frequency shift characterizes the excitation of the continuous spectrum, the eigenmodes of which are similar to the singular von Kampen modes in the theory of plasma oscillations. Compared with an existing approach the present derivation is valid for arbitrary values of χ and is selfconsistent in that it correctly includes the dynamics of the variable giving rise to the finite spread in v r . The increase in beam size resulting from crossing of the incoherent integral resonance is compared with that due to crossing of the half-integral resonance, for which an improved formula is derived with the Vlasov formalism.

The 1.5-GeV synchrotron of the Polytechnical Institute of Tomsk

The synchrotron construction and some experimental results from the synchrotron are described. A decrease of the pressure in the vacuum chambers from 1 × 10 −5 Torr upto 3 × 10 −6 Torr does not change the synchrotron intensity. As the pressure increases upto 8 × 10 −5 Torr, the intensity becomes 8 times less and the vertical beam size increases. The electrons are accelerated by means of two cavities at a mean frequency of 36.46 MHz. It was established that the synchrotron intensity changes largely, if one cavity is distuned for + 50 kHz from the resonance value. According to theory, the influence of the quantum character of the synchrotron radiation upon betatron oscillations, was observed, when the energy of the electrons is above 630 MeV.

Diffraction Loss and Beam Size in Lasers with Spherical Mirrors

The diffraction loss and beam size of the TEM00 mode in gas lasers have been determined experimentally. The results are in agreement with theoretically predicted values to within the experimental error, except that the increase in beam size with reduction of mirror size was found to be less than predicted.