scholarly journals Method for fabricating large-area gratings with a uniform duty cycle without a spatial beam modulator

2021 ◽  
Author(s):  
Jiujiu liang ◽  
CHONGYU WANG ◽  
Haiou Lu ◽  
Xiaohao Wang ◽  
Kai Ni ◽  
...  
Keyword(s):  
Duty Cycle ◽  
Large Area ◽  
Spatial Beam

Electrochemical micromachining of large-area micro-dimple arrays with high machining accuracy

2016 ◽  
Vol 232 (11) ◽  
pp. 1918-1927 ◽  
Author(s):  
Zhibao Hou ◽  
Ningsong Qu ◽  
Xiaolei Chen
Keyword(s):  
Duty Cycle ◽  
Applied Voltage ◽  
Electrical Discharge Machining ◽  
Electrochemical Micromachining ◽  
Machining Accuracy ◽  
Large Area ◽  
Machining Time ◽  
Pillar Arrays ◽  
Micro Dimples ◽  
Micro Dimple

Surface textures, especially micro-dimple arrays, can significantly improve the friction performance of engineering parts. Through-mask electrochemical micromachining is an effective method for generating micro-dimple arrays. In this article, a new method is introduced to fabricate a large-area polydimethylsiloxane mask containing micro through-holes. Using this technique, a stainless steel mould with micro-pillar arrays is generated by wire electrical discharge machining. A combination of pressure and weight of electrolyte is then proposed to keep the polydimethylsiloxane mask closely attached to the workpiece, which helps to achieve high machining accuracy. The effects of applied voltage, effective machining time and pulse duty cycle on the micro-dimples are investigated. The profiles of the micro-dimples are not sensitive to applied voltage, but pulse duty cycle is a significant factor influencing the depth of the micro-dimples. Micro-dimples of width 95 µm, depth 19 µm and a machining area of diameter 40 mm are successfully generated using a polydimethylsiloxane mask, and the standard deviations of the micro-dimple width and depth are only 0.84 and 0.23 µm, respectively. The present experiments verify that it is feasible to obtain large-area micro-dimple arrays with high machining accuracy using this technique.

Projection-Based Continuous 3D Printing Process With the Grayscale Display Method

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Yancheng Wang ◽  
Dai Xue ◽  
Deqing Mei
Keyword(s):  
High Resolution ◽  
3D Printing ◽  
Duty Cycle ◽  
Excitation Power ◽  
Pixel Size ◽  
Significant Progress ◽  
Large Area ◽  
Light Power ◽  
Printing Process ◽  
Uniform Ratio

Abstract The printing resolution and scale of projection-based 3D printing are affected by the pixel size and projected light power. An effective and versatile method to print complex constructs with high resolution and large area is still required since light distribution in printing systems is generally non-uniform. Here, we propose a projection-based continuous 3D printing with the grayscale display method to serve as an effective and precise way to improve printing resolution and area. The light characterization results demonstrated that the power density presented a non-uniform distribution, and the power values are linear to the excitation power. After modifying the masks into grayscale according to the duty cycle of the digital micro-mirror device (DMD) display, projected light exhibited improved uniformity along with expected light power and uniform ratio. To validate this developed printing process, the grayscale continuous printing of mesh and hexahedron frame constructs enabled a remarkable increase in the printing area and alleviation of under/over curing. This work reveals significant progress in printing of constructs at larger area and higher resolution in projection-based continuous 3D printing under non-uniform light.

Convergent Beam Electron Diffraction

1978 ◽  
Vol 36 (3) ◽  
pp. 304-315
Author(s):  
G. Lehmpfuhl
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Crystal Surface ◽  
Diffraction Spot ◽  
Crystal Thickness ◽  
Large Area ◽  
Electron Microscopic ◽  
Additional Information ◽  
Microscopic Investigations

Introduction In electron microscopic investigations of crystalline specimens the direct observation of the electron diffraction pattern gives additional information about the specimen. The quality of this information depends on the quality of the crystals or the crystal area contributing to the diffraction pattern. By selected area diffraction in a conventional electron microscope, specimen areas as small as 1 µ in diameter can be investigated. It is well known that crystal areas of that size which must be thin enough (in the order of 1000 Å) for electron microscopic investigations are normally somewhat distorted by bending, or they are not homogeneous. Furthermore, the crystal surface is not well defined over such a large area. These are facts which cause reduction of information in the diffraction pattern. The intensity of a diffraction spot, for example, depends on the crystal thickness. If the thickness is not uniform over the investigated area, one observes an averaged intensity, so that the intensity distribution in the diffraction pattern cannot be used for an analysis unless additional information is available.

TEM Study of a Tilt Boundary in Hot-Pressed Silicon

1981 ◽  
Vol 39 ◽  
pp. 160-161
Author(s):  
C. B. Carter ◽  
J. Rose ◽  
D. G. Ast
Keyword(s):  
Electron Diffraction ◽  
Imaging Technique ◽  
Interface Structure ◽  
Large Area ◽  
Weak Beam ◽  
Lattice Fringe ◽  
Electron Diffraction Technique ◽  
Tilt Boundaries ◽  
Beam Technique ◽  
Twist Boundaries

The hot-pressing technique which has been successfully used to manufacture twist boundaries in silicon has now been used to form tilt boundaries in this material. In the present study, weak-beam imaging, lattice-fringe imaging and electron diffraction techniques have been combined to identify different features of the interface structure. The weak-beam technique gives an overall picture of the geometry of the boundary and in particular allows steps in the plane of the boundary which are normal to the dislocation lines to be identified. It also allows pockets of amorphous SiO2 remaining in the interface to be recognized. The lattice-fringe imaging technique allows the boundary plane parallel to the dislocation to be identified. Finally the electron diffraction technique allows the periodic structure of the boundary to be evaluated over a large area - this is particularly valuable when the dislocations are closely spaced - and can also provide information on the structural width of the interface.

Two-photon excitation microscopy in cellular biophysics

1995 ◽  
Vol 53 ◽  
pp. 62-63
Author(s):  
David W. Piston ◽  
Brian D. Bennett ◽  
Robert G. Summers
Keyword(s):  
Confocal Microscopy ◽  
Laser Beam ◽  
Duty Cycle ◽  
Excited Electronic State ◽  
Input Power ◽  
Two Photon ◽  
Simultaneous Absorption ◽  
Photon Excitation ◽  
Very High ◽  
Two Photon Excitation

Two-photon excitation microscopy (TPEM) provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging and photochemistry. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10-5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

P20 phosphor on polyimide as a large area high-resolution transmission screen for slow scan CCD systems

1995 ◽  
Vol 53 ◽  
pp. 20-21
Author(s):  
C. C. Ahn ◽  
S. Karnes ◽  
M. Lvovsky ◽  
C. M. Garland ◽  
H. A. Atwater ◽  
...  
Keyword(s):  
Mechanical Stability ◽  
High Energy ◽  
Practical Implementation ◽  
Line Pair ◽  
Modulation Transfer ◽  
Large Area ◽  
Ccd Imaging ◽  
Transmission Electron ◽  
The One ◽  
Beam Broadening

The bane of CCD imaging systems for transmission electron microscopy at intermediate and high voltages has been their relatively poor modulation transfer function (MTF), or line pair resolution. The problem originates primarily with the phosphor screen. On the one hand, screens should be thick so that as many incident electrons as possible are converted to photons, yielding a high detective quantum efficiency(DQE). The MTF diminishes as a function of scintillator thickness however, and to some extent as a function of fluorescence within the scintillator substrates. Fan has noted that the use of a thin layer of phosphor beneath a self supporting 2μ, thick Al substrate might provide the most appropriate compromise for high DQE and MTF in transmission electron microcscopes which operate at higher voltages. Monte Carlo simulations of high energy electron trajectories reveal that only little beam broadening occurs within this thickness of Al film. Consequently, the MTF is limited predominantly by broadening within the thin phosphor underlayer. There are difficulties however, in the practical implementation of this design, associated mostly with the mechanical stability of the Al support film.

Study of Tip-Surface Interactions in Scanning Tunneling Microscopy (STM) by Reflection Electron Microscopy (REM)

1990 ◽  
Vol 48 (1) ◽  
pp. 320-321
Author(s):  
W. Lo ◽  
J.C.H. Spence ◽  
M. Kuwabara
Keyword(s):  
High Resolution ◽  
Elastic Strain ◽  
Tunneling Current ◽  
Surface Damage ◽  
Surface Interactions ◽  
Graphite Surface ◽  
Scanning Tunneling ◽  
Large Area ◽  
Tunneling Microscopy ◽  
High Resolution Tem

Work on the integration of STM with REM has demonstrated the usefulness of this combination. The STM has been designed to replace the side entry holder of a commercial Philips 400T TEM. It allows simultaneous REM imaging of the tip/sample region of the STM (see fig. 1). The REM technique offers nigh sensitivity to strain (<10−4) through diffraction contrast and high resolution (<lnm) along the unforeshortened direction. It is an ideal technique to use for studying tip/surface interactions in STM.The elastic strain associated with tunnelling was first imaged on cleaved, highly doped (S doped, 5 × 1018cm-3) InP(110). The tip and surface damage observed provided strong evidence that the strain was caused by tip/surface contact, most likely through an insulating adsorbate layer. This is consistent with the picture that tunnelling in air, liquid or ordinary vacuum (such as in a TEM) occurs through a layer of contamination. The tip, under servo control, must compress the insulating contamination layer in order to get close enough to the sample to tunnel. The contaminant thereby transmits the stress to the sample. Elastic strain while tunnelling from graphite has been detected by others, but never directly imaged before. Recent results using the STM/REM combination has yielded the first direct evidence of strain while tunnelling from graphite. Figure 2 shows a graphite surface elastically strained by the STM tip while tunnelling (It=3nA, Vtip=−20mV). Video images of other graphite surfaces show a reversible strain feature following the tip as it is scanned. The elastic strain field is sometimes seen to extend hundreds of nanometers from the tip. Also commonly observed while tunnelling from graphite is an increase in the RHEED intensity of the scanned region (see fig.3). Debris is seen on the tip and along the left edges of the brightened scan region of figure 4, suggesting that tip abrasion of the surface has occurred. High resolution TEM images of other tips show what appear to be attached graphite flakes. The removal of contamination, possibly along with the top few layers of graphite, seems a likely explanation for the observed increase in RHEED reflectivity. These results are not inconsistent with the “sliding planes” model of tunnelling on graphite“. Here, it was proposed that the force due to the tunnelling probe acts over a large area, causing shear of the graphite planes when the tip is scanned. The tunneling current is then modulated as the planes of graphite slide in and out of registry. The possiblity of true vacuum tunnelling from the cleaned graphite surface has not been ruled out. STM work function measurements are needed to test this.

Acoustic-Reflex Dynamics for Pulsed Signals

1978 ◽  
Vol 21 (2) ◽  
pp. 295-308
Author(s):  
Terry L. Wiley ◽  
Raymond S. Karlovich
Keyword(s):  
Duty Cycle ◽  
Acoustic Impedance ◽  
Normal Hearing ◽  
Broadband Noise ◽  
Threshold Shift ◽  
Temporary Threshold Shift ◽  
Acoustic Reflex ◽  
Stapedius Muscle ◽  
Duty Cycles

Contralateral acoustic-reflex measurements were taken for 10 normal-hearing subjects using a pulsed broadband noise as the reflex-activating signal. Acoustic impedance was measured at selected times during the on (response maximum) and off (response minimum) portions of the pulsed activator over a 2-min interval as a function of activator period and duty cycle. Major findings were that response maxima increased as a function of time for longer duty cycles and that response minima increased as a function of time for all duty cycles. It is hypothesized that these findings are attributable to the recovery characteristics of the stapedius muscle. An explanation of portions of the results from previous temporary threshold shift experiments on the basis of acoustic-reflex dynamics is proposed.

Illumination from Large Area Light Sources—II

1914 ◽  
Vol 77 (1988supp) ◽  
pp. 82-83
Author(s):  
Herbert E. Ives
Keyword(s):  
Light Sources ◽  
Large Area
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