Differential geometry of the ruled surfaces optically generated by mirror-scanning devices. I. Intrinsic and extrinsic properties of the scan field

Rectilinear propagation of light rays in homogeneous isotropic media makes it possible for optical generation of ruled surfaces as the ray is deflected by a rotatable mirror. Scan patterns on a plane or curved surface are merely curves on the ruled surface. Based on this understanding, structures of the scan fields produced by mirror-scanning devices of different configurations are investigated in terms of differential geometry. Expressions of the first and second fundamental coefficients and the first and second Gauss differential forms are given for an investigation of the intrinsic properties of the optically generated ruled surfaces. The Plücker ruled conoid is then generalized for mathematical modeling of the scan fields produced by single-mirror scanning devices of different configurations. Part II will be devoted to a study of multi-mirror scanning systems for optical generation of well-known ruled surfaces such as helicoids and hyperbolic paraboloids.     

Fatigue failures of austenitic stainless steel orthopedic fixation devices

Failures of four different 300-series austenitic stainless steel biomedical fixation implants were examined. The device fractures were observed optically, and their surfaces were examined by scanning electron microscopy. Fractography identified fatigue to be the failure mode for all four of the implants. In every instance, the fatigue cracks initiated from the attachment screw holes at the reduced cross sections of the implants. Two fixation implant designs were analyzed using finite-element modeling. This analysis confirmed the presence of severe stress concentrations adjacent to the attachment screw holes, the fatigue crack initiation sites. Conclusions were reached regarding the design of these types of implant fixation devices, particularly the location of the attachment screw holes. The use of austenitic stainless steel for these biomedical implant devices is also addressed. Recommendations to improve the fixation implant design are suggested, and the potential benefits of the substitution of titanium or a titanium alloy for the stainless steel are discussed.     

Fracture behaviour of boron filaments

Various types of boron filaments were broken in tension in such a way that primary fracture surfaces, and fragments ejected when fracture occurred, were retained. Fracture surfaces observed in the scanning electron microscope could be placed into one of two broad categories. Type I surfaces exhibited primary fracture characteristics such as mirror, mist and hackle zones. Flaws which initiated failure could frequently be resolved. Type II surfaces appeared to be generated by subsequent fracture immediately following primary failure. The relationship between the fracture surfaces and the stress distributions occurring within the fibres as a result of manufacturing conditions is discussed.     

High-speed noncontact profiler based on scanning white-light interferometry

We describe a system for fast three-dimensional profilometry, of both optically smooth and optically rough surfaces, based on scanning white-light techniques. The system utilizes an efficient algorithm to extract and save only the region of interference, substantially reducing both the acquisition and the analysis times. Rough and discontinuous surfaces can be profiled without the phase-ambiguity problems associated with conventional phase-shifting techniques. The system measures steps to 100 μm, scans a 10μLm range in 5 s, and has a smooth surface repeatability of 0.5 nm.     

相位扫描法制作变栅距光栅

提出了一种制作变栅距(VLS)光栅的相位扫描方法。该方法的主要装置包括一个用于控制刻划机运动的光栅干涉仪和一个相位扫描机构。如果调整光栅干涉仪,保证接收场中只有两条干涉条纹,然后改变用于对条纹进行计数的光电传感器的位置,就可以刻划出具有变栅距的刻槽。对光电式光栅刻划机的控制系统和结构都做了详细论述。按照上述方法成功刻划出了试验性的VLS光栅,它的最小栅距增量为0.33nm,并对在制作过程中产生的误差进行了讨论。采用测量衍射角的方法进行了栅距检测试验,由变栅距光栅和等栅距光栅作出的拟合曲线表明:相位扫描方法是加工具有亚纳米栅距增量的VLS光栅的有效方法,该方法对超精密定位也具有借鉴作用。     

Spatially resolved electronic and vibronic properties of single diamondoid molecules

Diamondoids are a unique form of carbon nanostructure best described as hydrogen-terminated diamond molecules. Their diamond-cage structures and tetrahedral sp3 hybrid bonding create new possibilities for tuning electronic bandgaps, optical properties, thermal transport and mechanical strength at the nanoscale. The recently discovered higher diamondoids have thus generated much excitement in regards to their potential versatility as nanoscale devices. Despite this excitement, however, very little is known about the properties of isolated diamondoids on metal surfaces, a very relevant system for molecular electronics. For example, it is unclear how the microscopic characteristics of molecular orbitals and local electron-vibrational coupling affect electron conduction, emission and energy transfer in the diamondoids. Here, we report the first single-molecule study of tetramantane diamondoids on Au(111) using scanning tunnelling microscopy and spectroscopy. We find that the diamondoid electronic structure and electron-vibrational coupling exhibit unique and unexpected spatial correlations characterized by pronounced nodal structure across the molecular surfaces. Ab initio pseudopotential density functional calculations reveal that much of the observed electronic and vibronic properties of diamondoids are determined by surface hydrogen terminations, a feature having important implications for designing future diamondoid-based molecular devices.     

Isothermal solidification based packaging of biosensors at low temperatures

Thick film Au printed square contact pads are interconnected to Cu substrates at constant pressure and temperature using the isothermal solidification of Bi-In alloy on the joining surfaces. The effect of reaction time on the mechanical strength of the package has been analyzed. Thermal stability of the fabricated specimens have been measured and discussed. The delaminated surfaces examined optically reveal the morphology of the metallization zones on the joining substrates. The scanning electron microscopy of these surfaces is reported in this paper. Tests for thermal shock, pH resistivity and shelf life have been carried out to predict the reliability of the packaging for long term applications.     

Isophote-based ruled surface approximation of free-form surfaces and its application in NC machining

This paper presents a method to approximate free-form surfaces using piecewise ruled surface and its application in five-axis NC machining. New concepts of isophote, iso-inclination curve and iso-inclination angle are introduced to facilitate the generation of the piecewise ruled surfaces. The resulting ruled surfaces are adaptive to the surface features, such as peaks and valleys. Adjusting the isoinclination angle controls the error of this approximation. The application of the isophote-based ruled surface approximation in five-axis NC machining is also studied. The tapered tools are suggested to cut the ruled surfaces. Methods for selecting appropriate tools and generating tool paths are presented. The present case studies show that the new approach may lead to the integration of rough, semi-finish and finish machining of free-form surfaces.     

Optical learning neural network with a pockels readout optical modulator

We have constructed an optical neural-network system with learning capability by using a Pockels readout optical modulator. The system has a two-dimensional structure that permits easy optical alignment and can handle images without scanning. Learning signals are calculated optically with two liquid-crystal devices by a matrix-matrix outer-product method. The calculated learning signals are added directly to the weights memorized on the Pockels readout optical modulator. A two-layer network is implemented, and the learning and recognition of four alphabetical characters are realized according to the delta rule.     

Laser printer optics with use of slant scanning of multiple beams

Simultaneous scanning of multiple beams in an array is an effective method to realize high-speed and high-resolution printers. The arrayed multiple beams can be generated by devices such as grating, Wollaston prism, fiber array, and laser diode array. In any of these devices, the focused spots in an array have a period several tens of times larger than the spot diameter. We propose a simultaneous scanning method suitable for these devices in which the arrayed multiple beams are arranged in a slant angle to the scanning direction to produce consecutive scan lines. Laser print experiments with two or four beams were carried out, and high-performance printing of a 431.8-mm print width, 23.6 dot/mm (i.e., 600 dot/in.) resolution, and of 541-mm/s speed were realized.     

Protein Adhesion at Poly(ethylene glycol) Modified Surfaces

The inhibition of protein adsorption to the surfaces of biomedical devices is a crucial requirement for avoiding implant‐associated infections or thrombus formation on blood‐contacting artificial surfaces and thus for increasing the long‐term biocompatibility of the devices. Here, the use of surface plasmon resonance and scanning force microscopy using protein‐modified tips (see figure) to study protein adhesion on poly(ethylene glycol) (PEG) grafted polymer materials is discussed. The PEG‐rafted materials are revealed to have significantly reduced affinity to proteins.     

Selective binding of dye molecules and CdSe nanocrystals on nanostructures generated by AFM lithography of silicon surfaces

Anchoring optically active molecules or semiconductor nanocrystals on nanostructured surfaces is one of the first steps for building complex structures with variable properties and functions. Electrostatic interactions have been used for selective binding of cationic molecular species on lithographically generated and negatively charged nanostructures. Semiconductor nanocrystals, covered by amphiphilic molecules, have been bound via hydrophobic interactions. Selective binding of cationic Rhodamin 6G molecules to freshly prepared silicon oxide nanostructures as well as the CdSe/ZnS nanocrystals to the surrounding hydrophobic alkyl monolayer could be identified both by optical methods and by atomic force microscopy. The adsorption of CdSe/ZnS nanoparticles was accompanied by self-organization phenomena of the surfactant tri octyl phosphine oxide (TOPO).     

Investigation of the photoluminescence and modification of InGaP/GaAs/InGaAs heterostructures by near-field scanning microscopy

This study deals with the local spectroscopy and modification of semiconducting InGaP/GaAs/InGaAs quantum-well heterostructures by near-field scanning optical microscopy. The spatial distribution of the photoluminescence intensity in these structures is investigated and spatial nonuniformity of the photoluminescence is observed as a result of the nonuniform properties of the InGaP layers. It is shown for the first time that local quenching of the photoluminescence may be achieved by optically induced impurity diffusion near the quantum well, and this may be utilized to develop low-dimension semiconducting devices. Pis’ma Zh. Tekh. Fiz. 23, 20–25 (August 26, 1997)     

Dipole-directed assembly of lines of 1,5-dichloropentane on silicon substrates by displacement of surface charge

One-dimensional nanostructures at silicon surfaces have potential applications in nanoscale devices. Here we propose a mechanism of dipole-directed assembly for the growth of lines of physisorbed dipolar molecules. The adsorbate chosen was a halide, in preparation for the patterned imprinting of halogen atoms. Using scanning tunnelling microscopy, physisorbed 1,5-dichloropentane on Si(100)-2x1 was shown to self-assemble at room temperature into molecular lines that grew predominantly perpendicular to the Si-dimer rows. Line formation was triggered by the displacement of surface charge by the dipolar adsorbate. Experimental and simulated scanning tunnelling microscopy images were in agreement for a range of positive and negative bias voltages. The geometry of the physisorbed molecules and nature of their binding were evident from the scanning tunnelling microscopy images, as interpreted by scanning tunnelling microscopy simulation.     

3D Printed Polymer Photodetectors

Extrusion‐based 3D printing, an emerging technology, has been previously used in the comprehensive fabrication of light‐emitting diodes using various functional inks, without cleanrooms or conventional microfabrication techniques. Here, polymer‐based photodetectors exhibiting high performance are fully 3D printed and thoroughly characterized. A semiconducting polymer ink is printed and optimized for the active layer of the photodetector, achieving an external quantum efficiency of 25.3%, which is comparable to that of microfabricated counterparts and yet created solely via a one‐pot custom built 3D‐printing tool housed under ambient conditions. The devices are integrated into image sensing arrays with high sensitivity and wide field of view, by 3D printing interconnected photodetectors directly on flexible substrates and hemispherical surfaces. This approach is further extended to create integrated multifunctional devices consisting of optically coupled photodetectors and light‐emitting diodes, demonstrating for the first time the multifunctional integration of multiple semiconducting device types which are fully 3D printed on a single platform. The 3D‐printed optoelectronic devices are made without conventional microfabrication facilities, allowing for flexibility in the design and manufacturing of next‐generation wearable and 3D‐structured optoelectronics, and validating the potential of 3D printing to achieve high‐performance integrated active electronic materials and devices.     

Some aspects of the fracture behaviour of Mg65Cu25Y10 bulk metallic glass during room-temperature bending

The fracture behaviour of Mg₆₅Cu₂₅Y₁₀ bulk metallic glass (BMG) during room-temperature three-point bending was investigated. The BMG was initially produced by casting into a wedge-shaped mold which generated an amorphous structure below the ∼4 mm thickness zone of the wedge. Three-point bend testing was then carried out on the BMG with the fracture angles and salient features of the fracture surfaces examined by scanning electron microscopy. Observations indicate that this type of deformation mode results in fracture via crack propagation from both surfaces of the samples where the tensile and compressive stresses are greatest. The direction of crack propagation was also found to deviate considerably from 45° to the length direction of sample. A scanning electron microscopy (SEM) study of the fracture surfaces indicated that deformation banding was a feature of crack propagation within compressive zone whereas the tensile zone generated a featureless surface characteristic of brittle failure. The mechanism of failure of the present alloy is discussed on the basis of the observed features on the fracture surfaces and the direction of propagation of cracks during failure and compared with the failure mechanism of samples fractured under both simple tension and compression.     

Lasing action in organic semiconductor thin films

Lasing action in optically pumped thin films of organic semiconductors has recently been demonstrated in a variety of materials employing a variety of cavity configurations. The excitation intensities required for lasing in optically pumped films are comparable to the electrical current densities achievable in light emitting devices based on these materials, opening the door to the possible realization of organic diode lasers. However, the design of diode laser structures is complicated by the relatively low charge carrier mobilities of organics. It has also been shown that the optical properties of organic films under electrical excitation are affected by the formation of polarons, imposing yet another obstacle for realization of these devices. The continuing research on organic diode lasers is motivated by the unique properties of these devices, such as narrow spectral emission linewidth and the temperature independence of laser output power and emission wavelength, which may be advantageous in a number of applications.     

Photoacoustic holographic imaging of absorbers embedded in silicone

Light absorbing objects embedded in silicone have been imaged using photoacoustic digital holography. The photoacoustic waves were generated using a pulsed Nd:YAG laser, λ=1064 nm, and pulse length=12 ns. When the waves reached the silicone surface, they were measured optically along a line using a scanning laser vibrometer. The acoustic waves were then digitally reconstructed using a holographic algorithm. The laser vibrometer is proven to be sensitive enough to measure the surface velocity due to photoacoustic waves generated from laser pulses with a fluence allowed for human tissue. It is also shown that combining digital holographic reconstructions for different acoustic wavelengths provides images with suppressed noise and improved depth resolution. The objects are imaged at a depth of 16.5 mm with a depth resolution of 0.5 mm.     

Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.     

Development of fast-scanning laser probe system based on knife-edge method for diagnosis of RF surface acoustic wave devices

This paper describes the development of a high-speed laser probe system for surface acoustic wave (SAW) devices. A fast scanning rate of 2.5 kS/s is realized by continuous stage translation and successive acquisition of the detector output by a high-speed data-logger. Trigger pulses are generated from the output of a high-precision linear-scale installed in the translation stage and fed to the data-logger for the synchronization with the stage movement. The phase-sensitive, knife-edge method is used for the optical detection. This makes the system very unsusceptible to low-frequency mechanical vibration caused by the fast stage translation. The system is applied for the characterization of spurious resonance modes in SAW devices. In conjunction with skillful use of image processing in wavenumber domain, it is shown how the present system is effective in the diagnosis and development of SAW devices.