Perfect Flatness Research Articles

Effects of Stretch-Bending Straightening on the Tensile Properties of Cold Rolled Packaging Steel

Achieving perfect flatness, tension-free surfaces, and exceptional resistance to spring back are important characteristics of packaging steel, setting the standard for high-quality material performance. To guarantee these crucial parameters, the implementation of the stretch-bending process at the final stage of the production route is indispensable. Besides improving the flatness properties, the induced plastic deformation results in an accompanying change in the mechanical properties. This investigation focuses on understanding this change in mechanical properties due to different stretch-bending straightening process parameters. A multivariate predictive model is created to calculate a process window for achieving the desired flatness and also mechanical properties in the production of packaging steel. This model is validated by experiments with a laboratory facility.

Magic in twisted transition metal dichalcogenide bilayers

The long-wavelength moiré superlattices in twisted 2D structures have emerged as a highly tunable platform for strongly correlated electron physics. We study the moiré bands in twisted transition metal dichalcogenide homobilayers, focusing on WSe2, at small twist angles using a combination of first principles density functional theory, continuum modeling, and Hartree-Fock approximation. We reveal the rich physics at small twist angles θ < 4∘, and identify a particular magic angle at which the top valence moiré band achieves almost perfect flatness. In the vicinity of this magic angle, we predict the realization of a generalized Kane-Mele model with a topological flat band, interaction-driven Haldane insulator, and Mott insulators at the filling of one hole per moiré unit cell. The combination of flat dispersion and uniformity of Berry curvature near the magic angle holds promise for realizing fractional quantum anomalous Hall effect at fractional filling. We also identify twist angles favorable for quantum spin Hall insulators and interaction-induced quantum anomalous Hall insulators at other integer fillings.

Superword: A honeyword system for achieving higher security goals

Generating honeywords for each user’s account is an effective way to detect whether password databases are compromised. However, there are several underlying security issues associated with honeyword techniques that need to be addressed, for example, (1) How to make it more difficult for an attacker to find an accurate match of “username-real password”? (2) How to prevent the intersection attack in multiple systems caused by password reuse without reducing usability? (3) How to reduce the success rate of targeted password guessing? In this study, we first propose a “matching attack” model and find that although Erguler’s honeyword system can achieve perfect flatness, the success rate of the attacker is 100% under matching attack. Secondly, we propose a new honeyword approach named Superword that isolates the direct relationship between username and the corresponding hashed password in password files. Additional honeypots are mixed with real accounts to detect online guessing attacks. The analysis reveals that our approach makes a matching attacker difficult to find a real password from N password hashes. Since there is no connection between the username and password in password files, our honeyword system also alleviates the multiple systems intersection attack and targeted password guessing.

СУБСТАНЦИИ КОМПОЗИТНОЙ ФОРМЫ

Architecture as a language of social communication embodies the artistic content in various forms that are associated with the organization of professional work. During the period of handicraft production, the architect-the main builder, expressed the cosmic harmony of the Universe made by the Creator. Being a designer, an architect expressed mathematical proportions in the composite forms of the building drawing. The division of labor in design led to the differentiation of the composite form into a functional form, compositional form and constructive form. Industrialization of design led a composite concept to the development of spatial concepts and the formation of an environmental approach. The development of formative thinking of the architect led to the creation of new innovative eco-friendly architectural materials. Unique manufacturing techniques allow to create perfect flatness and flexibility of composite materials associated with the absence of internal stress. This led to the creation of spatial structures without seams in different temperature and climatic conditions. The article systematizes professional design experience concentrated in the concept of composite form, calling the integrated, differentiated and multilayer superpositions of design graphics and the construction body.

Highly flat optical frequency comb generation based on pulse carving and sinusoidal phase modulation

We investigate the relationship between an optical pulse shape and a time lens implemented by means of sinusoidal phase modulation. Based on this investigation, two schemes are proposed to obtain an optical frequency comb (OFC) with exceptionally high flatness and a large number of spectral lines by carving an optical pulse shape to result in a quasilinear chirp via a simple sinusoidal phase modulation technique. The first scheme utilizes an intensity modulator with a single-drive port or with dual-drive ports to carve a narrow pulse. The experimental results show very good spectral profiles with 38 OFC lines at 1.2-dB flatness and 53 lines at 1.5-dB flatness when the intensity modulator is combined with two and three phase modulators for sinusoidal phase modulation, respectively. The second scheme is implemented by replacing the intensity modulator by a dual-parallel Mach–Zehnder modulator (DP-MZM). In this case, we obtain 35 OFC lines at nearly perfect flatness of less than 1 dB and 53 lines at 1.5-dB flatness after combining the DP-MZM with two and three phase modulators, respectively.

Classification of flat bands according to the band-crossing singularity of Bloch wave functions

We show that flat bands can be categorized into two distinct classes, that is, singular and nonsingular flat bands, by exploiting the singular behavior of their Bloch wave functions in momentum space. In the case of a singular flat band, its Bloch wave function possesses immovable discontinuities generated by the band-crossing with other bands, and thus the vector bundle associated with the flat band cannot be defined. This singularity precludes the compact localized states from forming a complete set spanning the flat band. Once the degeneracy at the band crossing point is lifted, the singular flat band becomes dispersive and can acquire a finite Chern number in general, suggesting a new route for obtaining a nearly flat Chern band. On the other hand, the Bloch wave function of a nonsingular flat band has no singularity, and thus forms a vector bundle. A nonsingular flat band can be completely isolated from other bands while preserving the perfect flatness. All one-dimensional flat bands belong to the nonsingular class. We show that a singular flat band displays a novel bulk-boundary correspondence such that the presence of the robust boundary mode is guaranteed by the singularity of the Bloch wave function. Moreover, we develop a general scheme to construct a flat band model Hamiltonian in which one can freely design its singular or nonsingular nature. Finally, we propose a general formula for the compact localized state spanning the flat band, which can be easily implemented in numerics and offer a basis set useful in analyzing correlation effects in flat bands.

Ultraflat and broadband optical frequency comb generator based on cascaded two dual-electrode Mach–Zehnder modulators

A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM). The first DE-MZM can generate a four-comb-line OFC, then the OFC is injected into the second DE-MZM as a carrier, which can increase the number of comb lines. Our modified scheme finally can generate a broadband OFC with high flatness by simply modifying the electrical power and the bias voltage of the DE-MZM. Theoretical analysis and simulation results reveal that a 16-comb-line OFC with a frequency spacing that two times the frequency of the RF signal can be obtained. The power fluctuation of the OFC lines is 0.48 dB and the unwanted-mode suppression ratio (UMSR) can reach 16.5 dB. Additionally, whether the bias drift of the DE-MZMs has little influence on the power fluctuation is also analyzed. These results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness.

Design of All-Normal Dispersion Microstructured Optical Fiber on Silica Platform for Generation of Pulse-Preserving Supercontinuum Under Excitation at 1550 nm

We investigated numerically the possibility of all normal dispersion fiber design for near-infrared supercontinuum generation based on a standard air-silica microstructure. The design procedure includes finding of target dispersion profile and subsequent finding of appropriate geometrical fiber design by inverse dispersion engineering. It was shown that the tailoring of dispersion profile could increase the spectral width of generated supercontinuum while maintaining perfect spectral flatness. Conditions necessary for wide and flat supercontinuum generation as well as restrictions imposed by chosen materials were discussed. As a result of design and optimization procedure, an air-silica design was found providing normal dispersion up to $\text{3}\;\mu {\text{m}}$ . Simulation results with 10 nJ, 100 fs pulses demonstrate supercontinuum generation up to 1.3 octave; whereas pumping with 30 nJ, 100 fs pulses could provide 1.8 octavse supercontinuum.

Metallic TIM Testing and Selection for IC, Power, and RF Semiconductors

Metallic TIM Testing and Selection for IC, Power, and RF Semiconductors

Perfectly Flat-Top and Equiripple Flat-Top Cosine Windows

This paper describes a new method for designing flat-top cosine time windows. New perfectly flat-top windows, i.e., having monotonically decaying main lobe, and new equiripple flat-top windows, i.e., with some minor ripples of equal amplitude in the main lobe, are proposed. Perfect flatness (monotonic main lobe) is obtained by zeroing frequency derivatives of the window’s spectrum at the origin. Perfect flatness is a new quality in flat-top windows, as all known flat-top windows have some ripples in the main lobe. New equiripple flat-top windows are designed based on the conditions imposed on the window’s frequency response. The new flat-top windows are compared with the existing ones through the figures of merit, amplitude estimation example, and noise propagation analysis, showing superior performance of the former. The new windows are an excellent choice for popular digital waveform (spectrum) analyzers, as sine-waves amplitudes can be accurately estimated directly from the discrete Fourier transform spectrum without any further postprocessing.

High flatness optical frequency comb generator based on the chirping of modulators

A novel scheme for generation of an optical frequency comb (OFC) based on the chirping of two cascaded modulators is proposed. The first modulator is a dual-electrode Mach–Zehnder modulator (MZM), while the other modulator is an integrated MZM composed of two parallel MZMs that increases the number of comb lines. Our modified scheme can generate a large number of frequency lines with excellent flatness by simply modifying the chirp factor, and it is shown that up to 54 frequency lines could be observed. Theoretical analysis and simulation results show that under the variety of conditions that can be used in this scheme, the power fluctuations of the OFC lines are less than 0.5 dB in all cases; these results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness. Additionally, our modified scheme has the merit of tunable frequency spacing, which is practical for experimental realization of the OFC.

Probing the flat band of optically trapped spin-orbital-coupled Bose gases using Bragg spectroscopy

Motivated by the recent efforts in creating the flat band in ultracold atomic systems, we investigate how to probe the flat band in an optically-trapped spin-orbital coupled Bose-Einstein condensate using Bragg spectroscopy. We have found that the excitation spectrum and the dynamic structure factor of the condensate alter dramatically, when the band structure exhibits various level of flatness. In particular, when the band exhibits perfect flatness around the band minima corresponding to a near infinite effective mass, a quadratic dispersion emerges in the low-energy excitation spectrum; in sharp contrast, for the opposite case when an ordinary band is present, the familiar linear dispersion arises. Such linear-to-quadratic crossover in the energy spectrum presents a striking manifestation of the transition of an ordinary band into a flat band, thereby allows the direct probe of the flat band by using Bragg spectroscopy.

Automated Tool for Measuring Nanotopography of 300 mm Wafers at early Stages of Wafer Production

Leading edge lithography processes require silicon wafers of nearly perfect flatness. In order to improve wafer manufacturing processes as well as the wafer quality, already early manufacturing processes like grinding and lapping have to be monitored. Assessment of nanotopography (NT) is an established approach to analyze surface features in a spatial wavelength range of 0.2 to 20 mm on silicon wafers end of line. This paper presents a fully automated measurement tool to measure NT on wafers with low reflectivity and wafer sizes up to 300 mm, based on the FRT MicroProf® MFE series. The system features a newly developed white-light interferometry sensor with a field of view of approximately 85 x 85 mm2. 16 single measurements are stitched to cover the entire surface of a 300 mm wafer. An NT analysis optimized stitching algorithm was developed in order to combine the individual images to a complete wafer map. The stitched map of the non-polished wafer is subsequently high-pass filtered and analyzed to quantify NT. Measurement system analysis studies provided repeatability values below 1 nm at a throughput of &gt; 20 wafer/h.

Effect of contact angle between retaining ring and polishing pad on material removal uniformity in CMP process

This paper presents the effect of the contact angle between the retaining ring and the polishing pad in chemical mechanical polishing (CMP) on the profile of the material removal rate (MRR) around the wafer edge and on the within-wafer nonuniformity (WIWNU). This study demonstrates that the mechanical interaction among the polishing pad, wafer, and retaining ring influences the ability to achieve planarization from the CMP process. In particular, the purpose of this study is to understand the effect of the contact conditions between the retaining ring and the pad on the CMP process. In order to verify the mechanical aspects of the MRR near the wafer edge, retaining rings with different contact angles were prepared. Finite element analysis (FEA) verified the effect of the contact angle between the retaining ring and the polishing pad on the stress distribution around the edge of the wafer. The results of the analysis were corroborated by conducting CMP experiments with 200-mm blanket oxide wafers. As expected, the FEA results were in good agreement with the MRR profile around the edge area. Through simulations and experiments, we concluded that the contact angle is an important factor to achieve a flatter edge profile and the material removal profile around the edge of the wafer was optimum at a 0o contact angle. In particular the WIWNU was below 4% when a flat retaining ring was used. The results of this study make it possible to improve the yield of chip production by ensuring the retaining ring maintains perfect flatness without making any special design changes to the CMP equipment.

Using an Interferometric Profiler and Gage Block to Determine Sample Thickness

Preshot characterization of the thickness and form of material samples in targets for dynamic materials properties experiments presents unique challenges. Because of design limitations, the measurement tools currently used introduce increasing error as samples deviate from perfect flatness or thickness uniformity. Contact measurements such as height gages and micrometers, for example, are insensitive to thickness variations occurring over spatial scales smaller than the contact probes. In addition, they measure thickness but not form and often damage samples. Standard confocal microscopes overcome some of these problems but can only measure form on the side of the sample that they see. Also, by design, they consistently overestimate thickness because form errors on the side of the sample against the reference surface always prevent perfect contact with it. We are developing a technique that may prove to be superior to both of these methods at characterizing both thickness and form of samples with both imperfect flatness and nonuniform thickness using only an interferometric optical profiler, an inexpensive fixture, a gage block, and a commercial three-dimensional modeling software. The end result is a computer model of the actual sample.

Reducing Thermal Contact Resistance for Rigid Insulation Thermal Measurements

H EAT transfer through fibrous insulation has been the subject of great interest in the aerospace community because of the use of fibrous insulation in thermal protection systems. Measurement and modeling of heat transfer in rigid and flexible fibrous insulation has been the subject of various studies [1–6]. Heat transfer through a high-porosity rigid insulation is composed of combined radiation and conduction heat transfer. Conduction consists of both solid and gaseous conduction. Solid conduction is a significant component of heat transfer in rigid insulations, with its relative significance increasing with increasing insulation density, but generally decreasing with increasing temperature. Radiation’s significance increases with increasing temperature and decreases with increasing insulation density. Gas conduction is negligible in a vacuum and increases with increasing static pressure and temperature. A simple measurement and modeling technique for heat transfer in a rigid fibrous insulation was investigated. As part of this study, the thermal contact resistance for thermal measurements on rigid fibrous insulation was also investigated. For flexible fibrous insulation, the flexibility of the insulation and negligible solid-conduction mode of heat transfer in the insulation result in negligible thermal contact resistance at the boundaries of test sample [7]. For rigid insulation, the solid-conduction mode of heat transfer is significant and obtaining perfect flatness on sample and test-setup surfaces is not easily achievable. Even a sample with a flat surface may bow from thermal deformations due to temperature gradients across the sample thickness during testing; therefore, thermal contact resistance at the boundaries of the test sample may be significant. For the thermal test setup used in the present study with large temperature differences maintained across the sample thickness, thermal contact resistance on the sample hot side is ignored because on the sample hot side the main mode of heat transfer is radiation. Conversely, on the sample cold side, the main mode of heat transfer is solid conduction; therefore, thermal contact resistance can be significant, which manifests itself as radiation and gas conduction in the void spaces between the bottom of the test sample and the top of the test-setup cold-side surface. Therefore, one objective of the present study is to investigate whether thermal contact resistance is significant for thermal measurements on rigid-insulation samples and, if so, to investigate a technique for eliminating it.

Bulk ammonothermal GaN

In this work, results of structural characterization of high-quality ammonothermal GaN are presented. Besides expected low dislocation density (being of the order of 10 3 cm −2) the most interesting feature seems perfect flatness of the crystal lattice of studied crystals. Regardless the size of crystals, lattice curvature radius exceeds 100 m, whereas better crystals reveal radius of several hundred meters and the best above 1000 m. Excellent crystallinity manifests in very narrow X-ray diffraction peaks of full-width at half-maximum (FWHM) values about 16 arcsec.

Pulse compression using segmented grating in Gekko MII system, ILE

A segmented (tiled) grating array is now investigated as a new compressor system for the reason of manufacturing cost of large aperture single grating. However the considerable freedom of motion of segment arises new difficulties on pulse compression and focusing. We constructed a real compressor system using a segmented grating for 15cm aperture laser beam at Gekko MII 100TW laser system, ILE, for investigating several alignment techniques. In order to produce clean pulse shape and focused pattern generated by misalignments or line density mismatching between segment gratings, we applied the image rotation technique as a compressor arrangement. In addition to reduce uncertainness of motion of all optics, we introduced several sensor/detector such as laser level meter or position sensor. It is also shown that a capacitance detector can keep the perfect flatness of segmented grating surface. Using these techniques we demonstrated pulse compression close to Fourier transform limit.

Effect of substrates on the molecular orientation of silicon phthalocyanine dichloride thinfilms

Molecular orientations of silicon phthalocyanine dichloride(SiPcCl2) thin films deposited on three different substrates have been measured by near-edge x-rayabsorption fine structure (NEXAFS) spectroscopy using linearly polarized synchrotron radiation.The substrates investigated were highly oriented pyrolitic graphite (HOPG), polycrystallinegold and indium tin oxide (ITO). For thin films of about five monolayers, the polarizationdependences of the Si K-edge NEXAFS spectra showed that the molecular planes ofSiPcCl2 on three substrates were nearly parallel to the surface. Quantitative analyses ofthe polarization dependences revealed that the tilted angle on HOPG was only2°, whichis interpreted by the perfect flatness of the HOPG surface. On the other hand, the tilted angle on ITOwas 26°. Atomic force microscopy (AFM) observation of the ITO surface showed that the periodicity of thehorizontal roughness is of the order of a few nanometres, which is larger than the molecular size ofSiPcCl2. It isconcluded that the morphology of the top surface layer of the substrate affects the molecular orientationof SiPcCl2 molecules not only for mono-layered adsorbates but also for multi-layered thinfilms.

Chemical polishing of CdZnTe substrates fabricated from crystals grown by the vertical-gradient freezing method

Chemical polishing is a process of crucial importance in the manufacture of epiready substrates for molecular beam epitaxy (MBE) of high-quality HgCdTe layers. With the aim of fabrication of (211) CdZnTe substrates, we focused on the fundamental research of polishing processes with respect to reducing subsurface damage. Wafers of the orientation (211) were prepared from the as-grown crystals by a process flow including oriented slicing, several steps of mechanical polishing, and finally chemical polishing. In the prechemical polishing process, several free and bound abrasives were applied to reach the surface roughness close to 1 nm. The surface polishing treatment included testing of the surface quality after each polishing step. We used an interferometer profiler, which yields detailed surface maps. Within chemical polishing processing, we have looked for an optimum composition of etchant based on the bromine-methanol/ethylene glycol solution and adequate polishing pad. We studied the substrate surface quality dependence on the rotation speed of the plate, sample loading weights, and duration of polishing. Correlation between the final surface roughness and layer thickness removed was established. The chemical polishing with a very low concentration of Br-methanol/ethylene glycol solution was found to yield very good CdZnTe surfaces with a perfect flatness.