29 research outputs found
Ultra-large scale transition metal dichalcogenides: fabrication and exploitation
No full textTwo-dimensional materials have emerged as a versatile platform for exploring novel physical phenomena and enabling innovative device architectures. Among them, transition metal dichalcogenides (TMDCs), such as molybdenum disulfide, are of particular interest due to their unique optical and electronic properties, including a thickness-dependent bandgap, strong excitonic effects, and spin-valley coupling. These characteristics make TMDCs promising candidates for next-generation electronic, optoelectronic, and photonic technologies.
Realizing the full potential of TMDCs requires reliable fabrication methods. This thesis presents the development of two gold-assisted exfoliation techniques designed to produce high-quality monolayer flakes. The first method utilizes APTES-functionalized target substrates to enhance flake adhesion. The second introduces a mechanically constraining layer that enables direct exfoliation onto arbitrary substrates without the need for surface functionalization. A comprehensive characterization confirms the high structural and optical quality of the exfoliated flakes. Imaging spectroscopic ellipsometry is demonstrated as an effective technique for assessing TMDC thickness over large areas.
Additionally, the phenomenon of laser-induced photoluminescence enhancement in molybdenum disulfide monolayers is investigated and attributed to local healing of sulfur vacancies.
Finally, the robustness of the exfoliated monolayers is validated through their integration into nanofabrication workflows. Specifically, thermal scanning probe lithography (t-SPL) is employed to create metallic nanostructures directly on top of monolayer molybdenum disulfide without degrading its optical properties. These results highlight the versatility of gold-assisted exfoliation for 2D material exploitation in advanced devices
Achieving High Visibility of Monolayer MoS2 Using Backside-Illuminated Thin Films
No full textInternational audienceInterference reflection microscopy (IRM) and backside absorbing layer microscopy (BALM) have emerged as powerful optical microscopy methods for the study of nanomaterials and biological samples. These techniques consist in using an inverted optical microscope in reflection mode to observe objects deposited either on glass (IRM) or on a nanometric absorbing metallic film (BALM). The thickness of the BALM absorbing layer and of optional additional transparent layers, as well as the choice of incident wavelength and top medium, act as powerful levers for maximizing the resultant contrast of a given sample. However, the use of BALM to study samples with high absorption coefficient has been limited so far in the literature. Furthermore, the complex refractive index (ñ = n + iκ) of layers in a specific BALM optical stack have so far not been measured, and thus experimentally informed simulations are nonexistent. In this work, we use variable angle spectroscopic ellipsometry (VASE) to measure ñ(λ) of each layer in BALM (and IRM) stacks consisting of different combinations of glass, Cr, Au, and AlOx, with the two-dimensional (2D) transition metal dichalcogenide (TMD) MoS2 as the sample under study. Using the measured values, we simulate contrast spectra and compare them against data. We manipulate the film thicknesses and top media to engineer favorable contrast conditions both in the blue and red regimes of the visible spectrum, with peak contrasts of ≈80%. Finally, we demonstrate how the 2-layer BALM stack can double as both an optically sensitive system and at the same time a metal–oxide–semiconductor structure allowing for electrostatic gating. We use this structure to do in situ local charge density imaging of a 2D MoS2 capacitor, which showcases the versatility of these types of BALM stacks
Fast thickness mapping of large-area exfoliated two-dimensional transition metal dichalcogenides by imaging spectroscopic ellipsometry
No full textTwo-dimensional transition metal dichalcogenides (2D TMDCs) have gained significant attention from the scientific community due to their exceptional properties, making them extremely attractive for optoelectronic and photonic applications. However, many exfoliation or synthesis techniques yield 2D crystals with limited crystalline quality and/or small lateral size. Here, we report a facile Au-assisted exfoliation method, yielding high-quality, large-area monolayers with lateral sizes of hundreds of micrometers. A self-assembled monolayer of (3-aminopropyl)triethoxysilane (APTES) is employed to improve the adhesion between the 2D material and the target substrate, dramatically improving the yield and reliability of the exfoliation process. The monolayer nature of the final sample is then assessed by means of Imaging Spectroscopic Ellipsometry (iSE), which enables a quick and reliable thickness mapping over millimeter-sized areas
Plasmonic-based Label-free Detection and Imaging of Molecules
No full textabstract: Obtaining local electrochemical (EC) information is extremely important for understanding basic surface reactions, and for many applications. Scanning electrochemical microscopy (SECM) can obtain local EC information by scanning a microelectrode across the surface. Although powerful, SECM is slow, the scanning microelectrode may perturb reaction and the measured signal decreases with the size of microelectrode. This thesis demonstrates a new imaging technique based on a principle that is completely different from the conventional EC detection technologies. The technique, referred to as plasmonic-based electrochemical imaging (PECI), images local EC current (both faradaic and non-faradaic) without using a scanning microelectrode. Because PECI response is an optical signal originated from surface plasmon resonance (SPR), PECI is fast and non-invasive and its signal is proportional to incident light intensity, thus does not decrease with the area of interest. A complete theory is developed in this thesis work to describe the relationship between EC current and PECI signal. EC current imaging at various fixed potentials and local cyclic voltammetry methods are developed and demonstrated with real samples. Fast imaging rate (up to 100,000 frames per second) with 0.2×3µm spatial resolution and 0.3 pA detection limit have been achieved. Several PECI applications have been developed to demonstrate the unique strengths of the new imaging technology. For example, trace particles in fingerprint is detected by PECI, a capability that cannot be achieved with the conventional EC technologies. Another example is PECI imaging of EC reaction and interfacial impedance of graphene of different thicknesses. In addition, local square wave voltammetry capability is demonstrated and applied to study local catalytic current of platinum nanoparticle microarray. This thesis also describes a related but different research project that develops a new method to measure surface charge densities of SPR sensor chips, and micro- and nano-particles. A third project of this thesis is to develop a method to expand the conventional SPR detection and imaging technology by including a waveguide mode. This innovation creates a sensitive detection of bulk index of refraction, which overcomes the limitation that the conventional SPR can probe only changes near the sensor surface within ~200 nm.Dissertation/ThesisVideo for Figure 3.2 C to HVideo for Figure 3.5Video for Figure 5.5Video for Figure 6.7Video for Figure 6.11Ph.D. Electrical Engineering 201
Optimizing Gold‐Assisted Exfoliation of Layered Transition Metal Dichalcogenides with (3‐Aminopropyl)triethoxysilane (APTES): A Promising Approach for Large‐Area Monolayers
No full textTwo-dimensional transition metal dichalcogenides (2D TMDCs) have gained significant attention from the scientific community due to their exceptional properties. Recently, the metal-assisted exfoliation technique has emerged as a promising method for producing large-area, high-quality 2D monolayers. However, achieving strong adhesion between metal foil and substrate during the exfoliation process remains a major challenge, preventing successful exfoliation. To overcome this issue, this study explores the application of (3-Aminopropyl)triethoxysilane (APTES) as an adhesion layer to substantially improve adhesion between the monolayers and hydrophilic substrates such as SiO2, allowing for a high yield of mm-sized monolayers. Two sample sets, obtained from the same MoS2 crystal via gold-assisted exfoliation with APTES-treated substrates and from standard scotch tape exfoliation, are statistically compared. APTES significantly improves exfoliation performance, yielding larger monolayers compared to conventional methods. This improvement enables the effective exfoliation with the gold-tape method, which otherwise results in no yield. Through Raman and photoluminescence characterization techniques, it is found that the flakes obtained from gold-assisted exfoliation and APTES are comparable to those obtained by standard scotch-tape exfoliation in terms of defects and optical properties, showing signatures of strain-induced Raman shift and n-type doping
Optimizing Au-Assisted Exfoliation of Layered Materials with (3-Aminopropyl) triethoxysilane (APTES) for Large-Area Monolayers
No full textNILAI MORAL DALAM KUMPULAN CERPEN UNTUK SEJUTA HARAPAN KARYA PEMENANG LOMBA MENULIS CERPEN PECI (PENULIS CILIK) TAHUN 2017 (SEBUAH KAJIAN SOSIOLOGI SASTRA)
No full textTaskiyah, Layyinatusshifa. 2019. The Moral Values of the Prose Collection Untuk Sejuta Harapan Written by the Winners of Prose Writing Competition of Peci (Penulis Cilik/Young Author). 2017: Literature Sociological Studies. Theis. Bachelor Degree of Indonesian Language and Literature Department. Faculty of Humanities of Universitas Diponegoro Semarang. Advisors: Dr. M. Abdullah, M. Hum and Dra. Mirya Anggrahini, M. Hum
The research in the moral values of the prose collection of Untuk Sejuta Harapan (For A Million People) written by the winners of the prose competition of Peci (Penulis Cilik/Young Author) in 2017 studies the moralities found in the short stories. This prose collection consists of eight proses, but the writer studies only three proses which have represented the whole eight proses. The first prose is about the sacrifices of a mother. The second prose tells sincerity and gender equalities. The last prose tells cares and humbleness.
The aims of this research are to describe the intrinsic elements of the prose collection of Untuk Sejuta Harapan (For A Million People) and to describe the moral values found in the prose collection. The method used in this research is the literature sociological method in order to reveal the the moralities found in the short story collection. The theories used in this research are the fictional structural theories, the literature sociological theories, and the moral theories.
The research shows that the prose collection observed contains three good moral values, namely the principles of kindnesses, fairness, and respect to each own self. The principles of kindnesses can be seen in the humbleness and the willingness to take responsibilities, whereas the principles of respect to each own self can be seen in the attitudes of authentic values and the independence of the moral. Through this research, it can be seen how important it is to preach good morals, such as cares and humbleness. Caring attitudes taught to kids will make them be more caring and humbler when they’ve grown up. The readers also can recognize that being each own self is an important thing. Through authentic value attitudes found in the principle of respect to each own self, readers are explained a kid needs to be himself. A kid needs to be independent by respecting and trusting his own opinions.
Key words: Untuk Sejuta Harapan, Literature Sociology, Fiction, Structure, Moral Valu
Adhesion and friction patterns of CVD-grown WS2 monolayer flakes induced by vacancy-rich defect domains
No full textA comprehensive understanding of the relationship between defects concentration, optical properties and mechanical behavior of two-dimensional transition metal dichalcogenides (TMDs) is crucial for their integration as active components in micro- and nanomechanical devices. In this study we characterize the nanoscale contact adhesion and friction of WS2 flakes grown via chemical vapor deposition. We identify two domains named α and β with distinct mechanical properties, which are not apparent in morphological differences but mirror spatial variations of the optoelectronic properties. The α-domains exhibit high photoluminescence (PL) emission, strong Raman response, higher contact adhesion and lower friction, closely resembling the response of pristine WS2 flakes prepared by mechanical exfoliation. Conversely, the β-domains display very low PL emission, weak Raman response with blueshifted fingerprint peaks, lower adhesion and up to six-fold higher friction. Based on experimental evidence and general arguments, we attribute the mechanical heterogeneity between the α- and β-domains to the differentiated densities of sulfur and tungsten atomic vacancies, which are known to selectively populate the two domains. Our results indicate that the tungsten vacancies in the β-domains not only mediate non-radiative recombination processes but also drive a prominent friction enhancement, either by increasing the amplitude and disorder of the WS2 potential energy surface or by impacting the stress distribution within the growing flakes. These findings help identify the type of defects and mechanisms that most significantly affect the properties of TMD monolayer flakes prepared by scalable production routes
A Eletrobrás de hoje e a Eletrobrás do futuro: construindo cenários institucionais e identificando novos negócios
No full textThis dissertation has as objective builds institutional sceneries capable to describe possible future paths they be traveled it by the Centrais Elétricas Brasileiras S.A. - Eletrobrás. Guided for the field of the managerial strategies, the author adopted the PROSPEX method, by Eduardo Marques (2003), and the obtained results pointed three main sceneries: spotlight, light and lamp. To these sceneries, the theory of the strategic business area (SBA) was applied, what allowed to detect new businesses for Eletrobrás.Esta dissertação tem como objetivo construir cenários institucionais capazes de descrever possíveis trajetórias para a Centrais Elétricas Brasileiras S.A. − Eletrobrás. Orientado para o campo das estratégias empresariais, o autor adotou o método PROSPEX, de Eduardo Marques (2003), e os resultados obtidos apontam três cenários principais: holofote, farol e lamparina. A esses cenários foi aplicada a teoria da área estratégica de negócios (AEN), o que permitiu a detecção de alguns novos negócios para a Eletrobrás
Demokrasi dan Dakwah Islam:: Kajian Politisasi Agama pada Pemilu 2024 di Kabupaten Lombok Timur
No full textThis article looks at the politicization of religion in East Lombok Regency during the 2024 elections. The author collected data in the field using three techniques: observation, interviews, and documentation. These three strategies generate primary sources. Meanwhile, secondary sources include scholarly publications such as journals, dissertations, scientific periodicals, and survey findings. After completing research, the author discovered that religion was politicized in East Lombok Regency through the use of religious symbols such as the imamah and white peci as traditional apparel that represents piety. Politicians also employ the narrative of friendship, politics as a platform for da'wah, ukhuwah Islamiyah, piety, and sami'na wa atho'na to politicize religion. Aside from that, their identity as a Tuan Guru is also used on pamphlets, billboards, stickers and even on ballot papers. Artikel ini mengulas politisasi agama di Kabupaten Lombok Timur pada pemilu 2024. Penulis mengumpulkan data di lapangan dengan menggunakan tiga teknik yaitu observasi, wawancara, dan dokumentasi. Ketiga strategi ini menghasilkan sumber primer. Sedangkan sumber sekunder meliputi publikasi ilmiah seperti jurnal, disertasi, terbitan berkala ilmiah, dan temuan survei. Setelah menyelesaikan penelitian, penulis menemukan adanya politisasi agama di Kabupaten Lombok Timur melalui penggunaan simbol-simbol keagamaan seperti imamah dan peci putih sebagai pakaian adat yang melambangkan ketakwaan. Politisi juga memanfaatkan narasi silaturahmi, politik sebagai wadah dakwah, ukhuwah Islamiyah, ketakwaan, dan sami'na wa atho'na untuk mempolitisasi agama. Selain itu identitas mereka sebagai Tuan Guru juga terpampang pada pamflet, baliho, stiker bahkan pada surat suara
