Browsing by Department "OtaNano"

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  • Accelerated Engineering of ELP-Based Materials through Hybrid Biomimetic-De Novo Predictive Molecular Design
    (2024-07-11) Laakko, Timo; Korkealaakso, Antti; Yildirir, Burcu Firatligil; Batys, Piotr; Liljeström, Ville; Hokkanen, Ari; Nonappa; Penttilä, Merja; Laukkanen, Anssi; Miserez, Ali; Södergård, Caj; Mohammadi, Pezhman
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Efforts to engineer high-performance protein-based materials inspired by nature have mostly focused on altering naturally occurring sequences to confer the desired functionalities, whereas de novo design lags significantly behind and calls for unconventional innovative approaches. Here, using partially disordered elastin-like polypeptides (ELPs) as initial building blocks this work shows that de novo engineering of protein materials can be accelerated through hybrid biomimetic design, which this work achieves by integrating computational modeling, deep neural network, and recombinant DNA technology. This generalizable approach involves incorporating a series of de novo-designed sequences with α-helical conformation and genetically encoding them into biologically inspired intrinsically disordered repeating motifs. The new ELP variants maintain structural conformation and showed tunable supramolecular self-assembly out of thermal equilibrium with phase behavior in vitro. This work illustrates the effective translation of the predicted molecular designs in structural and functional materials. The proposed methodology can be applied to a broad range of partially disordered biomacromolecules and potentially pave the way toward the discovery of novel structural proteins.
  • Alpha helical surfactant-like peptides self-assemble into pH-dependent nanostructures
    (2021-03-21) Castelletto, Valeria; Seitsonen, Jani; Ruokolainen, Janne; Hamley, Ian W.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A designed surfactant-like peptide is shown, using a combination of cryogenic-transmission electron microscopy and small-angle X-ray scattering, to have remarkable pH-dependent self-assembly properties. Peptide Arg3-Leu12(R3L12) forms a network of peptide nanotubes at pH 9 and below. These are associated with α-helical conformation in a “cross-α” nanotube structure, in which peptide dimers lie perpendicular to the nanotube axis, with arginine coated inner and outer nanotube walls. In contrast, this peptide forms decorated vesicular aggregates at higher pH values, close to the pKaof the arginine residues. These structures are associated with a loss of α-helical order as detected through X-ray scattering, circular dichroism and FTIR spectroscopy, the latter technique also revealing a loss of ordering of leucine side chains. This suggests a proposed model for the decorated or patchy vesicular structures that comprises disordered peptide as the matrix of the membrane, with small domains of ordered peptide dimers forming the minority domains. We ascribe this to a lipid-raft like phase separation process, due to conformational disordering of the leucine hydrophobic chains. The observation of the self-assembly of a simple surfactant-like peptide into these types of nanostructure is remarkable, and peptide R3L12shows unique pH-dependent morphological and conformational behaviour, with the potential for a range of future applications.
  • Amorphous carbon modulated-quantum dots NiO for efficient oxygen evolution in anion exchange membrane water electrolyzer
    (2024-12-05) Jin, Benjin; Wang, Qian; Sainio, Jani; Saveleva, Viktoriia A.; Jiang, Hua; Shi, Junjie; Ali, Basit; Kallio, Antti Jussi; Huotari, Simo; Sundholm, Dage; Han, Nana; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Developing efficient electrocatalysts of elements that are abundant on earth crust is crucial for green hydrogen generation technologies. In particular, the oxygen evolution reaction (OER) under alkaline plays a key role in anion exchange membrane (AEM) electrolyzer to produce green hydrogen but suffers from low kinetic. Herein, nickel oxide quantum dots with highly uniform size distribution on ultrathin amorphous carbon nanosheets (NiO dots/a-carbon) were successfully prepared by a one-step method. Introducing NiO quantum dots onto amorphous carbon modifies the local coordination environment of Ni promoting it into a higher valence state. Benefitting from the promoted Niδ+ (2<δ<3) and the strong connection between Ni and amorphous carbon though Ni-O-C and Ni-C bonds, NiO dots/a-carbon exhibits excellent activity and stability towards OER in 0.1 M KOH using the rotating disk electrode. Moreover, a challenging current density of 500 mA cm−2 is achieved at 1.7 V with a lab-scale AEM electrolyzer.
  • Apparent ferrimagnetism in Sr(Fe0.2Mn0.2Co0.2Ti0.2V0.2)O3 high-entropy oxide perovskite thin films
    (2024-02-01) Regmi, Balaram; Miertschin, Duncan; Cocconcelli, Maria; Stramaglia, Federico; Crater, Davis; Yao, Lide; Piamonteze, Cinthia; van Dijken, Sebastiaan; Farhan, Alan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present a study on the structural and magnetic properties of Sr(Fe0.2Mn0.2Co0.2Ti0.2V0.2)O3 (S5BO) high-entropy oxide perovskite thin films. We use synchrotron-based x-ray absorption spectroscopy employing x-ray magnetic circular dichroism (XMCD) and reveal an enhanced presence of high-spin Co2+, which appears to feature a magnetic response opposing that of the two other magnetic transition metal elements, Fe and Mn. This is marked by both opposite XMCD signals and an inverted XMCD hysteresis loop for Co, while Fe and Mn show regularly shaped hysteresis curves, as the picture of a ferrimagnetic ground state emerges for S5BO.
  • Atomic layer deposition of magnetic thin films : Basic processes, engineering efforts, and road forward
    (2023-12-29) Jussila, Topias; Philip, Anish; Tripathi, Tripurari; Nielsch, Kornelius; Karppinen, Maarit
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    Atomic layer deposition (ALD) is known as a key enabler of the continuous advances in device engineering for microelectronics. For instance, the state-of-the-art transistor technology depends entirely on ALD-grown high-κ materials. Another application branch where ALD could potentially play a similar important role in future is the magnetic thin film devices. Spin-based devices based on high-quality magnetic thin films are anticipated to provide high-efficiency operations with low power consumption. The strict quality demands the magnetic thin films must fulfill in the next-generation applications form the strong bases for the efforts to implement ALD in this application area. In this first comprehensive review on the topic, our aim is to provide an insightful account of the ALD processes so far developed for magnetic materials and to highlight the application-relevant magnetic properties of the thus fabricated thin films. Moreover, we discuss the various innovative engineering efforts made toward different multi-layered and nanostructured composite materials and complex architectures uniquely enabled by the sophisticated self-terminated film-growth mechanism of ALD. The review is finished with a brief outlook toward the future prospects and challenges in the field.
  • Benzene tricarboxamide derivatives with lipid and ethylene glycol chains self-assemble into distinct nanostructures driven by molecular packing
    (2021-08-28) Aljuaid, Nada; Tully, Mark; Seitsonen, Jani; Ruokolainen, Janne; Hamley, Ian W.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The self-assembly in aqueous solution of benzene-1,3,5-tricarboxamide (BTA) bearing one alkyl chain and two PEG (polyethylene glycol) chains or two alkyl chains and one PEG chain yields completely distinct nanostructures. Two series of derivatives were synthesized and extensively characterized and electron microscopy and small-angle X-ray scattering (SAXS) reveal micelle structures for derivatives with one alkyl and two PEG chains, but nanotapes and nanoribbons for the series with two alkyl and one PEG chain.
  • Broadband miniaturized spectrometers with a van der Waals tunnel diode
    (2024-01-17) Uddin, Md Gius; Das, Susobhan; Shafi, Abde Mayeen; Wang, Lei; Cui, Xiaoqi; Nigmatulin, Fedor; Ahmed, Faisal; Liapis, Andreas C.; Cai, Weiwei; Yang, Zongyin; Lipsanen, Harri; Hasan, Tawfique; Yoon, Hoon Hahn; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Miniaturized spectrometers are of immense interest for various on-chip and implantable photonic and optoelectronic applications. State-of-the-art conventional spectrometer designs rely heavily on bulky dispersive components (such as gratings, photodetector arrays, and interferometric optics) to capture different input spectral components that increase their integration complexity. Here, we report a high-performance broadband spectrometer based on a simple and compact van der Waals heterostructure diode, leveraging a careful selection of active van der Waals materials- molybdenum disulfide and black phosphorus, their electrically tunable photoresponse, and advanced computational algorithms for spectral reconstruction. We achieve remarkably high peak wavelength accuracy of ~2 nanometers, and broad operation bandwidth spanning from ~500 to 1600 nanometers in a device with a ~ 30×20 μm2 footprint. This diode-based spectrometer scheme with broadband operation offers an attractive pathway for various applications, such as sensing, surveillance and spectral imaging.
  • Cell Adhesion Motif-Functionalized Lipopeptides: Nanostructure and Selective Myoblast Cytocompatibility
    (2023-01-09) Rosa, Elisabetta; De Mello, Lucas; Castelletto, Valeria; Dallas, Mark L.; Accardo, Antonella; Seitsonen, Jani; Hamley, Ian W.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The conformation and self-assembly of four lipopeptides, peptide amphiphiles comprising peptides conjugated to lipid chains, in aqueous solution have been examined. The peptide sequence in all four lipopeptides contains the integrin cell adhesion RGDS motif, and the cytocompatibility of the lipopeptides is also analyzed. Lipopeptides have either tetradecyl (C14, myristyl) or hexadecyl (C16, palmitoyl) lipid chains and peptide sequence WGGRGDS or GGGRGDS, that is, with either a tryptophan-containing WGG or triglycine GGG tripeptide spacer between the bioactive peptide motif and the alkyl chain. All four lipopeptides self-assemble above a critical aggregation concentration (CAC), determined through several comparative methods using circular dichroism (CD) and fluorescence. Spectroscopic methods [CD and Fourier transform infrared (FTIR) spectroscopy] show the presence of β-sheet structures, consistent with the extended nanotape, helical ribbon, and nanotube structures observed by cryogenic transmission electron microscopy (cryo-TEM). The high-quality cryo-TEM images clearly show the coexistence of helically twisted ribbon and nanotube structures for C14-WGGRGDS, which highlight the mechanism of nanotube formation by the closure of the ribbons. Small-angle X-ray scattering shows that the nanotapes comprise highly interdigitated peptide bilayers, which are also present in the walls of the nanotubes. Hydrogel formation was observed at sufficiently high concentrations or could be induced by a heat/cool protocol at lower concentrations. Birefringence due to nematic phase formation was observed for several of the lipopeptides, along with spontaneous flow alignment of the lyotropic liquid crystal structure in capillaries. Cell viability assays were performed using both L929 fibroblasts and C2C12 myoblasts to examine the potential uses of the lipopeptides in tissue engineering, with a specific focus on application to cultured (lab-grown) meat, based on myoblast cytocompatibility. Indeed, significantly higher cytocompatibility of myoblasts was observed for all four lipopeptides compared to that for fibroblasts, in particular at a lipopeptide concentration below the CAC. Cytocompatibility could also be improved using hydrogels as cell supports for fibroblasts or myoblasts. Our work highlights that precision control of peptide sequences using bulky aromatic residues within "linker sequences"along with alkyl chain selection can be used to tune the self-assembled nanostructure. In addition, the RGDS-based lipopeptides show promise as materials for tissue engineering, especially those of muscle precursor cells.
  • Cellulose fiber and nanofibril characteristics in a continuous sono-assisted process for production of TEMPO-oxidized nanofibrillated cellulose
    (2022-11) Levanič, Jaka; Svedström, Kirsi; Liljeström, Ville; Šernek, Milan; Osojnik Črnivec, Ilja Gasan; Poklar Ulrih, Nataša; Haapala, Antti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A hardwood dissolving pulp and bleached softwood Kraft pulp were subjected to continuous ultrasonic cavitation assisted TEMPO-mediated oxidation. The effects of such processing on the yield of carboxylic groups, morphological changes of the fibers as well as the effects on the final nanocellulose dispersion were studied. Ultrasonic cavitation in the TEMPO-mediated oxidation phase enhanced the yield of carboxylic groups on both pulps while having a negligible effect on materials losses due to fiber fines formation. The effect of ultrasonic cavitation was purely mechanical and acted as an additional high-shear mixer in the pre-treatment phase. As a result, the morphological changes on the fibers were enhanced, with additional swelling and fiber straightening being observed. Furthermore, the ultrasonic cavitation also influenced the properties of the nanocellulose dispersion obtained from subsequent microfluidization. The sonicated samples exhibited higher optical clarity, higher elasticity in gels while also having somewhat lower viscosities. On nanoscale, ultrasonic cavitation helped the subsequent microfluidization in releasing better individualized nanofibrils as they had smaller diameters than in non-sonicated samples. Sonication also had no effect on the crystallinity properties of the nanocellulose, the observed slight reduction was a result of intense microfluidization that was used to produce the nanocellulose dispersion. Ultrasonic cavitation in the TEMPO-oxidized pre-treatment phase was shown to be a method that can increase the throughput in lab-scale by mechanical activation of pulps and enabling shorter processing times for TEMPO-mediated oxidation. Graphical abstract: [Figure not available: see fulltext.].
  • Chirality and pH Influence the Self-Assembly of Antimicrobial Lipopeptides with Diverse Nanostructures
    (2024-08-19) Adak, Anindyasundar; Castelletto, Valeria; Mendes, Bruno; Barrett, Glyn; Seitsonen, Jani; Hamley, Ian W.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Chirality plays a crucial role in the self-assembly of biomolecules in nature. Peptides show chirality-dependent conformation and self-assembly. Lipidation of peptides occurs in vivo and has recently been exploited in designed conjugates to drive self-assembly and enhance bioactivity. Here, a library of pH-responsive homochiral and heterochiral lipidated tripeptides has been designed. The designed lipopeptides comprise homochiral C16-YKK or C16-WKK (where all the amino acids are l-isomers), and two heterochiral conjugates C16-Ykk and C16-Wkk (where the two lysines are d-isomers). The self-assembly of all the synthesized lipopeptides in aqueous solution was examined using a combination of spectroscopic methods along with cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). Interestingly, it was observed that at acidic pH all the lipopeptides self-assemble into micelles, whereas at basic pH the homochiral lipopeptides self-assemble into nanofibers, whereas the heterochiral lipopeptides self-assemble into nanotapes and nanotubes. A pH switch was demonstrated using a thioflavin T fluorescence probe of β-sheet structure present in the extended structures at pH 8. We demonstrate that both chirality and pH in lipopeptides influence the self-assembly behavior of the model tripeptides, which also show promising bioactivity. Good cytocompatibility is observed in hemolytic assays and antimicrobial activity against both Gram-negative and Gram-positive bacteria is shown through the determination of minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) values and live/dead bacteria staining assay.
  • Colorants Detected by HPLC-PDA in Textiles from 13th Century Lieto Ristinpelto, Finland
    (2023-02) Wright, Krista; Vanden Berghe, Ina; Sahramaa, Jenni; Suomela, Jenni A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Organic colorants of textiles found in the female burial of Lieto Ristinpelto, SW Finland, were analyzed by HPLC-PDA. The textiles’ visible colors varied from different brownish shades to blueish, greenish, and reddish hues. The aim of the chromatographic analysis was to deepen the current understandings of the dyes used in Finland at the transition between the 12th and 13th centuries AD, i.e., at the beginning of the local Medieval period, and to contribute important new information about dyes and clothing from this less-known period of textile history of Finland. The textile finds consisted of a bronze spiral ornamented shawl, an apron tied at the waist, two tablet-woven bands, and a diagonally plaited band with plaited tassels. A unique find was a textile possibly made using the sprang technique. Other textile finds were an orange wool tabby and twill fragments. Analysis of thirty samples from fourteen different textiles indicated that woad colorants were present in most samples, accompanied with lichen compounds, and dyer’s madder was in two visually orange fragments. The visually reddish samples contained luteolin, but no red colorants.
  • Comparison of the self-assembly and cytocompatibility of conjugates of Fmoc (9-fluorenylmethoxycarbonyl) with hydrophobic, aromatic, or charged amino acids
    (2024-06) Castelletto, Valeria; de Mello, Lucas; da Silva, Emerson Rodrigo; Seitsonen, Jani; Hamley, Ian W.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The self-assembly in aqueous solution of three Fmoc-amino acids with hydrophobic (aliphatic or aromatic, alanine or phenylalanine) or hydrophilic cationic residues (arginine) is compared. The critical aggregation concentrations were obtained using intrinsic fluorescence or fluorescence probe measurements, and conformation was probed using circular dichroism spectroscopy. Self-assembled nanostructures were imaged using cryo-transmission electron microscopy and small-angle X-ray scattering (SAXS). Fmoc-Ala is found to form remarkable structures comprising extended fibril-like objects nucleating from spherical cores. In contrast, Fmoc-Arg self-assembles into plate-like crystals. Fmoc-Phe forms extended structures, in a mixture of straight and twisted fibrils coexisting with nanotapes. Spontaneous flow alignment of solutions of Fmoc-Phe assemblies is observed by SAXS. The cytocompatibility of the three Fmoc-amino acids was also compared via MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] mitochondrial activity assays. All three Fmoc-amino acids are cytocompatible with L929 fibroblasts at low concentration, and Fmoc-Arg shows cell viability up to comparatively high concentration (0.63 mM).
  • Configurable anti-ambipolar photoresponses for optoelectronic multi-valued logic gates
    (2024-07-29) Cui, Xiaoqi; Kim, Sunmean; Ahmed, Faisal; Du, Mingde; Liapis, Andreas C.; Muñoz, Juan Arias; Shafi, Abde Mayeen; Uddin, Md Gius; Ali, Fida; Zhang, Yi; Kang, Dong Ho; Lipsanen, Harri; Kang, Seokhyeong; Yoon, Hoon Hahn; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Anti-ambipolar transistors (AATs) are the leading platform for the paradigm shift from binary to multi-valued logic (MVL) circuits, increasing circuit integration density and data processing capacity. However, most AATs with p-n heterojunctions present limited controllability of the transconductance peak, which is key to MVL operation. Here, we report optically configurable AAT/bi-AAT photoresponses implemented with an InSe field-effect transistor for potential MVL operations. The charge trapping and detrapping processes incorporated with manually introduced trap states form the AAT peaks. Furthermore, leveraging a symmetric device configuration, the dark current is significantly suppressed, and AAT photoresponses are highlighted. Contributed by two pathways of trap states, the AAT/bi-AAT photoresponses are switchable by incident optical wavelength. This dependence facilitates optical wavelength to be one of the logic inputs for MVL, based on which we propose circuit-free ternary logic gates in a single device that can achieve more than ∼ 6 and ∼ 19 times improved data density (1 bit per transistor) for NMAX and XNOR, compared with such circuits in a traditional binary design. This work realizes optically controlled AAT photoresponses, paving the way to exploit optical wavelength as a new degree of freedom in MVL computing, offering a route toward ultra-high-density, ultra-low-power, and optically programmable optoelectronic integrated circuits.
  • Controlling the Nematic Liquid Crystallinity of Cellulose Nanocrystals with an Alcohol Ethoxy Sulfonate Surfactant
    (2024-07-08) Majoinen, Johanna; Gustavsson, Lotta; Wani, Owies; Kiefer, Samira; Liljeström, Ville; Rojas, Orlando J.; Rannou, Patrice; Ikkala, Olli
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Cellulose nanocrystals (CNCs) are biobased colloidal nanorods that have unlocked new opportunities in the area of sustainable functional nanomaterials including structural films and coatings, biomedical devices, energy, sensing, and composite materials. While selective light reflection and sensing develop from the typical chiral nematic (cholesteric, Nem*) liquid crystallinity exhibited by CNCs, a wealth of technologies would benefit from a nematic liquid crystal (LC) with CNC uniaxial alignment. Therefore, this study answers the central question of whether surfactant complexation suppresses CNC chirality in favor of nematic lyotropic and thermotropic liquid crystallinity. Therein, we use a common surfactant having both nonionic and anionic blocks, namely, oligo(ethylene glycol) alkyl-3-sulfopropyl diether potassium salt (an alcohol ethoxy sulfonate (AES)). AES forms complexes with CNCs in toluene (a representative for nonpolar organic solvent) via hydrogen bonding with an AES’ oligo(ethylene glycol) block. A sufficiently high AES weight fraction endows the dispersibility of CNC in toluene. Lyotropic liquid crystallinity with Schlieren textures containing two- and four-point brush defects is observed in polarized optical microscopy (POM), along with the suppression of the cholesteric fingerprint textures. The results suggest a nematic (Nem) phase in toluene. Moreover, thermotropic liquid crystallinity is observed by incorporating an excess of AES, in the absence of an additional solvent and upon mild heating. The Schlieren textures suggest a nematic system that undergoes uniaxial alignment under mild shear. Importantly, replacing AES with a corresponding nonionic surfactant does not lead to liquid crystalline properties, suggesting electrostatic structural control of the charged end group of AES. Overall, we introduce a new avenue to suppress CNC chirality to achieve nematic structures, which resolves the long-sought uniaxial alignment of CNCs in filaments, composite materials, and optical devices.
  • Correct Identification of the Core-Shell Structure of Cell Membrane-Coated Polymeric Nanoparticles
    (2022-12-06) Liu, Lizhi; Yu, Wei; Seitsonen, Jani; Xu, Wujun; Lehto, Vesa Pekka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Transmission electron microscopy (TEM) observations of negatively stained cell membrane (CM)-coated polymeric nanoparticles (NPs) reveal a characteristic core-shell structure. However, negative staining agents can create artifacts that complicate the determination of the actual NP structure. Herein, it is demonstrated with various bare polymeric core NPs, such as poly(lactic-co-glycolic acid) (PLGA), poly(ethylene glycol) methyl ether-block-PLGA, and poly(caprolactone), that certain observed core-shell structures are actually artifacts caused by the staining process. To address this issue, fluorescence quenching was applied to quantify the proportion of fully coated NPs and statistical TEM analysis was used to identify and differentiate whether the observed core-shell structures of CM-coated PLGA (CM−PLGA) NPs are due to artifacts or to the CM coating. Integrated shells in TEM images of negatively stained CM−PLGA NPs are identified as artifacts. The present results challenge current understanding of the structure of CM-coated polymeric NPs and encourage researchers to use the proposed characterization approach to avoid misinterpretations.
  • Correlation between microstructure and surface chemistry of carbon nanofibers grown using different adhesive layers
    (2023-03) Pande, Ishan; Sainio, Sami; Sainio, Jani; Liljeström, Ville; Jiang, Hua; Laurila, Tomi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Carbon nanofibers (CNFs) have applications in a wide range of technological and scientific fields. The connections between their micro- and macrostructure and observed performance are, however, currently lacking. This hinders the realization of their full potential. In this paper, we correlate the microstructure of CNFs grown on two types of substrates: (1) Si + 20 nm Ti + 20 nm Ni, and (2) Si + 80 nm Cr + 20 nm Ni, to their surface chemistry. We use transmission electron microscopy (TEM), supported by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis, to describe the morphology and structure of CNFs as well as the underlying interfacial layers. Then, we study the similarities and differences in chemistry of these two types of CNFs using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) and correlate them with the observed structural features of the fibers. Vertically aligned, tip-type fiber growth was observed on both substrates. TEM micrographs show that the CNFs grown on the Cr + Ni substrates have a slightly distorted herringbone-like structure, whereas fibers grown on the Ti + Ni substrates have relatively ill-defined structure with basal planes pointing outwards. Consequently, the latter possess a richer surface chemistry, which is apparent from the wider peaks and more spectral features observed during XAS and XPS measurements. This analysis provides us with some of the missing structure-chemistry connections, which can subsequently be expanded towards including correlations of these features with observed performance of the CNFs in different applications. Ultimately, this enables us to tailor features of the CNFs for specific target fields.
  • Deterministic Polymorphic Engineering of MoTe2 for Photonic and Optoelectronic Applications
    (2023-08-15) Ahmed, Faisal; Rodríguez-Fernández, Carlos; Fernandez, Henry A.; Zhang, Yi; Shafi, Abde Mayeen; Uddin, Md Gius; Cui, Xiaoqi; Yoon, Hoon Hahn; Mehmood, Naveed; Liapis, Andreas C.; Yao, Lide; Caglayan, Humeyra; Sun, Zhipei; Lipsanen, Harri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Developing selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic 2D materials by locally inducing metallic 1T′-MoTe2 on the semiconducting 2H-MoTe2 host layer. In the polymorphic-engineered MoTe2, 2H- and 1T′- crystalline phases exhibit strong optical contrast from near-infrared to telecom-band ranges (1–1.5 µm), due to the change in the band structure and increase in surface roughness. Sevenfold enhancement of third harmonic generation intensity is realized with conversion efficiency (susceptibility) of ≈1.7 × 10−7 (1.1 × 10−19 m2 V−2) and ≈1.7 × 10−8 (0.3 × 10−19 m2 V−2) for 1T′ and 2H-MoTe2, respectively at telecom-band ultrafast pump laser. Lastly, based on polymorphic engineering on MoTe2, a Schottky photodiode with a high photoresponsivity of 90 AW−1 is demonstrated. This study proposes facile polymorphic engineered structures that will greatly benefit realizing integrated photonics and optoelectronic circuits.
  • Direct GaAs Nanowire Growth and Monolithic LightEmitting Diode Fabrication on Flexible Plastic Substrates
    (2022-08) Khayrudinov, V; Sorokina, A; Raj, V; Gagrani, N; Koskinen, T; Jiang, H; Tittonen, I; Jagadish, C; Tan, HH; Lipsanen, H; Haggren, T
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The growth of self-catalyzed GaAs nanowires (NWs) and monolithic light-emitting diode (LED) directly on flexible plastic substrates is reported. Dense GaAs NW forest is attained in self-catalyzed mode using metalorganic vapor phase epitaxy. The NWs are shown to be crystalline with a zinc-blende phase. The optical properties of the GaAs NWs are found to be promising in both photoluminescence emission and light-trapping based on reflectance and transmittance measurements. The LED is fabricated from p-type NWs by depositing Au as Ohmic contact and TiO2/ITO as an electron-selective contact. The demonstrated NW growth and LED fabrication represent a significant step toward low-cost, industrially feasible flexible III–V NW optoelectronic applications, as plastic is inexpensive, and the fabrication steps are compatible with roll-to-roll processing.
  • Directed Assembly of Cellulose Nanocrystals in Their Native Solid-State Template of a Processed Fiber Cell Wall
    (2021-06) Solala, Iina; Driemeier, Carlos; Mautner, Andreas; Penttilä, Paavo A.; Seitsonen, Jani; Leppänen, Miika; Mihhels, Karl; Kontturi, Eero
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nanoparticle assembly is intensely surveyed because of the numerous applications within fields such as catalysis, batteries, and biomedicine. Here, directed assembly of rod-like, biologically derived cellulose nanocrystals (CNCs) within the template of a processed cotton fiber cell wall, that is, the native origin of CNCs, is reported. It is a system where the assembly takes place in solid state simultaneously with the top-down formation of the CNCs via hydrolysis with HCl vapor. Upon hydrolysis, cellulose microfibrils in the fiber break down to CNCs that then pack together, resulting in reduced pore size distribution of the original fiber. The denser packing is demonstrated by N2 adsorption, water uptake, thermoporometry, and small-angle X-ray scattering, and hypothetically assigned to attractive van der Waals interactions between the CNCs.
  • Effect of atomic layer deposited zinc promoter on the activity of copper-on-zirconia catalysts in the hydrogenation of carbon dioxide to methanol
    (2023-02) Arandia, Aitor; Yim, Jihong; Warraich, Hassaan; Leppäkangas, Emilia; Bes, René; Lempelto, Aku; Gell, Lars; Jiang, Hua; Meinander, Kristoffer; Viinikainen, Tiia; Huotari, Simo; Honkala, Karoliina; Puurunen, Riikka L.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The development of active catalysts for carbon dioxide (CO2) hydrogenation to methanol is intimately related to the creation of effective metal-oxide interfaces. In this work, we investigated how the order of addition of copper and zinc on zirconia influences the catalytic properties, the catalytic activity and selectivity toward methanol. Regarding the carbon dioxide conversion and methanol production, the catalysts on which the promoter (zinc) was atomically deposited after copper impregnation (i.e., ZnO/Cu/ZrO2 and ZnO/Cu/ZnO/ZrO2) were superior catalysts compared to the reverse copper-after-zinc catalyst (Cu/ZnO/ZrO2). Temperature-programmed experiments and in situ diffuse reflectance infrared Fourier transform-spectroscopy (DRIFTS) experiments allowed us to elucidate the benefits of the zinc-after-copper pair to store CO2 as carbonate species and further convert them into formate species, key intermediates in the formation of methanol. This research provides insights into the potential of atomic layer deposition in the development of tailored heterogeneous catalysts for efficient CO2 valorization to methanol.