bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epitaxy of Hexagonal Ge-2H : Lessons from in Situ TEM Observations
Authors: Vincent Laetitia , Verheijen Marcel A. , Peeters Wouter , Melhem Hassan , Van den Berg Theo , Ameziane Hafssa , Patriarche Gilles , Dursap Thomas , Travers Laurent , Renard Charles , Panciera Federico , Bakkers Erik P.A.M. 
Published: December 2024

Silicon and Germanium crystallize in the cubic diamond structure 3C with which they dominate definitely the electronics. Playing on crystal phases in semiconductors occurs to be a valuable mean of electronic band engineering. Remarkably, the hexagonal 2H phase of SiGe turns to get a direct band gap with light emission capabilities within a specific composition range (Si<35%). This material holds the promise to fill the gap between electronics and photonics industry using group IV semiconductors.
We use GaAs NWs with the wurtzite structure as a template to create both (1) core/shell and (2) trunk/nanobranches heterostructures [2,3]. The GaAs-wurtzite is an ideal template to copy the structure by epitaxy forcing the Ge to adopt the hexagonal crystal phase and in turn it is used here as a textbook case
The growths are followed using the in situ TEM NANOMAX. This unique microscope can be implemented either with molecular beam epitaxy (MBE) sources or with a gas injector for chemical vapor deposition (CVD). Real time TEM observations at the atomic scale show the fundamental aspects of the epitaxy and the formation of growth-related staking faults in Ge-2H.
1) On core/shell configuration[1], depending on growth conditions, different growth regimes highly impact the crystal quality of the of Ge-2H shell. On {1-100} prismatic surfaces, a regular step flow supports a flat surface and a perfect replication of the hexagonal structure However, when the step flow is destabilized, original intrinsic I3 basal stacking faults (BSF) are formed during growth. We evidence their correlation with the growth modes related to surface diffusion. Understanding the nucleation of these defects is necessary to prevent their formation during epitaxy. Possible scenarios of I3 BSF formation are discussed. Theses defects show a faulted stacking ABACABAB with only one faulted basal plane bounded by a pair of partial dislocations along <11-20> with opposite Burger vectors b=+/-1/3<1-100>. Thermal annealing induces a motion of the dislocation and an expansion of the I3 BSF resulting in a 4H stacking in the core/shell structure.
2) On wurtzite GaAs nanowires, Au catalysts are deposited on the sidewalls. Nanobranches grow with an axial direction along <1-100> and exhibit a hexagonal crystal structure[2] . With in situ observations, we study the VLS and VSS growths of Au catalyzed Ge-2H branches depending on the growth temperature.
[1] L. Vincent et al. Adv. Mat. Inter. 9-16 (2022) 2102340, doi.org/10.1002/admi.202102340
[2] A Li et al. Nanotechnology 34 (2023) 015601 doi: 10.1088/1361-6528/ac9317

Figure 1
(Invited) Recent Progress on Heteroepitaxy of Si-Sn Alloy Thin Films
Authors: Kurosawa Masashi , Shibayama Shigehisa , Sakashita Mitsuo , Nakatsuka Osamu 
Published: December 2024

The realization of silicon-tin (Si1−x
Sn
x
) alloys with various compositions has been expected to open up a higher degree of freedom for designs of the electron and phonon energy band structure in group-IV alloy systems [1-4]. Theoretically, it has been predicted that a Si1-xSnx becomes a direct transition semiconductor with a sufficient Sn content, although the Sn content was varied (25–90%) among reports. Additional interest is that the Sn incorporation in Si should dramatically decrease its thermal conductivity, leading to high thermoelectric performance. One serious problem with the Si1-xSnx synthesizing is Sn precipitation during the growth because of the extremely low solid solubility of Sn in Si (0.1%), a tenth of that in Ge. Thus, the growth conditions—especially growth temperature—need to be chosen carefully. In this talk, we will review the recent progress on the crystal growth techniques of Si1−x
Sn
x
thin films [5-11] and discuss the key point to prevent Sn precipitation during the growth.

References

[1] R. A. Soref and C. H. Perry, J. Appl. Phys. 69, 539 (1991).
[2] S. N. Khatami and Z. Aksamiji, Phys. Rev. Appl. 6, 014015 (2016).
[3] Y. Nagae et al., Jpn. J. Appl. Phys. 56, 04CR10 (2017).
[4] M. Tomita et al., Jpn. J. Appl. Phys. 57 04FB04 (2018).
[5] M. Kurosawa et al., Appl. Phys. Lett. 106, 171908 (2015).
[6] M. Kurosawa et al., Appl. Phys. Lett. 111, 192106 (2017).
[7] M. Kurosawa et al., Jpn. J. Appl. Phys. 58, SAAD02 (2019).
[8] R. Yokogawa et al., ECS Trans. 98, 291 (2020).
[9] K. Fujimoto et al., Appl. Phys. Express 16, 045501 (2023).
[10] T. Oiwa et al., Ext. Abst. 2022 SSDM, Makuhari, 2022, pp. 95-96.
[11] T. Oiwa et al., Ext. Abst. 2023 SSDM, Nagoya, 2023, pp. 535-536.
Development of a Machine Learning Model for Quantifying SEM Images of Electrode Materials Based on AFM Topography Image
Authors: Choi Youngwoo , Hong Seungbum 
Published: December 2024

Scanning electron microscopy (SEM) is a tool that allows for easy visualization of surface morphology of materials, but it has the drawback of difficulty in quantitative shape analysis. On the other hand, atomic force microscopy (AFM) enables quantitative analysis of material surface morphology with very high precision; however, it suffers from long analysis times and difficulties in analyzing a wide area. In particular, materials like graphite, used in electrode materials for batteries, possess high roughness, which poses additional challenges for AFM analysis.
To extend the spatial precision of AFM across a wide range of material surfaces, we developed a machine learning model to quantify SEM images. Based on the dependency of SEM image brightness on the quantity of scattered electrons, we devised an algorithm to generate corresponding topography. By utilizing SEM and AFM images from the same area of a single sample, we trained the machine learning model to produce a unique topography image. With this model, it becomes feasible to reliably quantify SEM images of the material using only pairs of AFM-SEM images.
In this study, we utilized a graphite anode electrode and acquired AFM and SEM images from an 80 x 80 μm area. To obtain AFM images over a wide area, we divided the entire region into 16 sections of 20 x 20 μm each for analysis. Subsequently, we further divided each section into four parts, resulting in a total of 256 pairs of images for training the machine learning model. Through the machine learning process, we inversely calculated the contributions of height and gradient of the topography in graphite material to SEM brightness. Simultaneously, we derived the boundary conditions necessary for the algorithm to calculate topography from SEM images. By applying this trained model, we were able to quantify SEM images in areas where AFM image analysis previously had not been conducted.
Quantifying SEM images has long been considered a significant drawback in SEM analysis due to its complexity. However, applying such methodologies makes SEM image quantification remarkably straightforward. This approach is not limited to electrode materials but can be widely applicable in various material fields such as nano-materials and thin films where quantification is essential. Furthermore, by extending the utilization of AFM data in model training, it is anticipated that combining various AFM modes such as Lateral Force Microscopy (LFM), Piezoelectric Force Microscopy (PFM), and Conductivity AFM (C-AFM) with SEM surface images will enable even higher-dimensional material surface analysis.
(Invited) The Synthesis and Optical Properties of 2D Janus Quantum Layers
Authors: Tongay Sefaattin , Povilus Blake 
Published: December 2024

Named after the two faced Roman God Janus, 2D Janus layers contain two different atomic types on its top and bottom faces. Previous theoretical studies have shown that broken mirror symmetry together with large change transfer across the top and bottom face opens up completely new quantum properties including Rashba effect, colossal Janus field, dipolar excitons, and Skyrmion formation. Despite the theoretical advances in the field, experimental results are still limited due to limitations in high quality 2D Janus layer synthesis. In this talk, I will introduce recent discoveries made at Arizona State University towards different types of Janus layers. The growth process relies on Plasma enhanced low pressure chemical vapor deposition (PE-LPCVD). With this all room temperature technique, our team can synthesize different Janus layers as well as their vertical / lateral heterojunctions, and Janus nanoscrolls. Further studies from our team will introduce on-demand fabrication of 2D Janus layers with unique in-situ growth capabilities that allows us to collect spectroscopy data during the course of Janus material growth. Results are presented along with microscopy, spectroscopy, high -pressure studies, and electronic transport datasets for complete understanding of these systems1-5.
References

Petrić, M. M.; Kremser, M.; Barbone, M.; Qin, Y.; Sayyad, Y.; Shen, Y.; Tongay, S.; Finley, J. J.; Botello-Méndez, A. R.; Müller, K., Raman spectrum of Janus transition metal dichalcogenide monolayers WSSe and MoSSe. Physical Review B
2021,
103 (3), 035414.

Hajra, D.; Sailus, R.; Blei, M.; Yumigeta, K.; Shen, Y.; Tongay, S., Epitaxial Synthesis of Highly Oriented 2D Janus Rashba Semiconductor BiTeCl and BiTeBr Layers. ACS Nano
2020,
14 (11), 15626–15632.

Trivedi, D. B.; Turgut, G.; Qin, Y.; Sayyad, M. Y.; Hajra, D.; Howell, M.; Liu, L.; Yang, S.; Patoary, N. H.; Li, H.; Petrić, M. M.; Meyer, M.; Kremser, M.; Barbone, M.; Soavi, G.; Stier, A. V.; Müller, K.; Yang, S.; Esqueda, I. S.; Zhuang, H.; Finley, J. J.; Tongay, S., Room Temperature Synthesis of 2D Janus Crystals and Their Heterostructures. Advanced Materials
2020, 2006320.

Li, H.; Qin, Y.; Ko, B.; Trivedi, D. B.; Hajra, D.; Sayyad, M. Y.; Liu, L.; Shim, S.-H.; Zhuang, H.; Tongay, S., Anomalous Behavior of 2D Janus Excitonic Layers under Extreme Pressures. Advanced Materials
2020, (32), 2002401.

Yagmurcukardes, M.; Qin, Y.; Ozen, S.; Sayyad, M.; Peeters, F. M.; Tongay, S.; Sahin, H., Quantum properties and applications of 2D Janus crystals and their superlattices. Applied Physics Reviews
2020,
7 (1).

Figure 1
High Quality Carbon Nanotube Thin Films for Transistor Application
Authors: Li Yi , Xi Meiqi , Zhu Xuehao , Bai Lan , Cao Yu , Liang Xuelei 
Published: December 2024

Semiconducting carbon nanotubes (s-CNTs) are promising channel materials for both high-performance ultra-scaled field-effect transistors (FETs) and thin film transistors (TFTs) due to their excellent electronic properties. Many research groups have demonstrated the application of s-CNTs in either logical computing circuits or large area electronics. However, before the CNT-based electronics technology takes real impact, many challenges should be overcome, such as achieving high purity of s-CNTs, reliable methods for their deposition and alignment, development of scalable and cost-effective production techniques, and corresponding quality characterization metrology. In this presentation, we will report our progress on the s-CNT materials and their application for FETs and TFTs.
Conjugated polymer wrapping method was used to extract s-CNTs from the raw CNT materials. We have developed a closed-loop recycling strategy, in which raw materials (CNTs and polymers) and solvents were all recycled and reused for multiple separation cycles, thus high-purity (99.9999%) and high structural quality s-CNTs were mass produced. The cost was reduced to ~ 1% in comparison with commercially available products, and total yield was increased to 36% in comparison with 2%–5% of usual separation methods.
Highly unform and density-controllable thin films of random-oriented CNTs (R-CNTs) were fabricated by a dip-coating method on 4-inch/8-inch Si wafers and 2.5th generation (G2.5) backplane glasses (370 mm × 470 mm). Ultra-clean wafer-scale aligned s-CNTs (A-CNTs) were fabricated by a modified dimension-limited self-alignment (m-DLSA) method. To quantify the overall quality of both R-CNT and A-CNT films, we proposed a four-parameter metrology which includes the local tube density (DL), global density uniformity (Cv), local degree of order (OL), and the relative tube proportion in a certain orientation (Pθ) at a location. The four-parameter metrology is not only powerful for overall quality evaluation of CNT films, but also able to predict the performance fluctuation of fabricated devices.
TFTs fabricated using the R-CNTs show mobility of 45-55 cm2/Vs with a high-performance uniformity (Cv ≈ 11%–13%) on a 4-inch wafer. A micro-LED display with 32×32 pixels were driven successfully by 2T1C AMTFT back plane based on R-CNT TFTs. Top-gated FETs based on A-CNTs exhibit excellent electronic performance with an on-state current (Ion) of 2.2 mA/μm, peak transconductance (gm) of 1.1 mS/μm, low contact resistance (Rc) of 191 Ω•μm and negligible hysteresis, among the best reported performance of CNT FETs. We believe our progress in the s-CNT materials will greatly push the CNT-based electronics technology into practical applications.
(Invited) Active Matrix Organic/Perovskite Light Emitting Diodes Based on MoS2 Thin Film Transistors
Authors: Kim Soo Young 
Published: December 2024

Electronic applications are continuously developing and taking new forms, including foldable, rollable and wearable displays. These wearable displays are applicable in human healthcare monitoring and robotics, and their operation relies on organic light emitting diodes (OLEDs). The development of semiconducting materials with high mechanical flexibility has remained a challenge and has restricted application to unusual format electronics. This talk presents a wearable full color OLED display using a two-dimensional (2D) material-based backplane transistor.[1,2] The 18x18 thin-film transistor array was fabricated on a thin MoS2 film that was transferred to Al2O3 (30 nm)/polyethylene terephthalate (6 m). Red, green, and blue OLED pixels were deposited on the device surface. This 2D material offered excellent mechanical and electrical properties and proved to be capable of driving circuits for the control of OLED pixels. Furthermore, the uniform deposition of perovskite light-emitting diodes (PeLEDs) and their integration with backplane thin-film transistors (TFTs) remain challenging for large-area display applications. Herein, an active-matrix PeLED display fabricated via the heterogeneous integration of cesium lead bromide (CsPbBr3) LEDs and MoS2-based TFTs is presented.[3] The single-source evaporation method enables the deposition of highly uniform perovskite thin films over large areas. PeLEDs are integrated with MoS2 TFTs to fabricate an active-matrix PeLED display with an 8×8 array, which exhibits excellent brightness control capability and high switching speeds. This study demonstrates the potential of PeLEDs as candidates for next generation displays and presents a novel approach for fabricating optoelectronic devices via the heterogeneous integration of 2D materials and perovskites, thereby paving the way toward the fabrication of practical future optoelectronic systems.
References
[1] “Flexible active-matrix organic light-emitting diode display enabled by MoS2 thin-film transistor”, Science Advances, vol. 4, eaas8721 (2018)
[2] “Full-color active-matrix organic light-emitting diode display on human skin based on a large-area MoS2 backplane”, Science Advances, vol. 6, eabb5898 (2020)
[3] “Perovskite light-emitting diode display based on MoS2 backplane TFT”, Advanced Materials, , vol. 36, p.2309531 (2024)
Interfacial Engineering to Decouple Electrical and Thermal Conductivities in an Energy Efficient Low Thermal Budget Additive Manufacturing Technique for Flexible Thermoelectric Generators
Authors: Huang Jiyuan , Ambade Rohan B. , Lombardo Jacob , Brooks Ben , Poosapati Aswani , Banerjee Priyanshu , Saeidi-Javash Mortaza , Zhang Yanliang , Madan Deepa 
Published: December 2024

The global focus on renewable and consistently available energy sources has given rise to research into alternative sources of energy harvesting, such as thermoelectric generators (TEG). TEG devices provide the solid-state conversion of waste heat into electrical power by utilizing the Seebeck effect. Thermoelectric (TE) performances can be measured by a dimensionless figure of merit (ZT). To increase the ZT value of a TE material, it is necessary to increase both the electric conductivity (EC) and Seebeck coefficient (SC) while minimizing the total thermal conductivity (TC) of the material. These values are highly interdependent and difficult to independently control.
The scalability of traditional thermoelectric generators (TEGs) has been held back by the inclusion of a high-temperature, long-duration curing process to produce high-performance thermoelectric (TE) films. Additive manufacturing has been investigated as a more time, energy, and cost-efficient method compared to traditional manufacturing techniques. Importantly, additive manufacturing allows for design freedoms including the addition of flexibility in the fabrication of TEGs. With a growing interest in the widespread adoption of TEGs to capture low waste heat energy from non-planar surfaces like the human body, the need for flexible, high performance, and energy-efficient TE manufacturing techniques is increasing.
This work investigates the synergistic effect of a small amount of chitosan binder (0.05wt%), a micron and nanosized particle size distribution, the application of mechanical pressure (20 MPa), thickness variation (170µm vs 300µm) – on the performance of p-Bi0.5Sb1.5Te3 (p-BST) and n-Bi2Te2.7Se0.3 (n-BTS) TE composite films manufactured using a low thermal budget manufacturing technique. The combination of these four factors controls the micro and nanostructure of the films to decouple their electrical and thermal conductivity effectively. This resulted in figures of merit (ZTs) of 0.89 and 0.5 for p-BST and n-BTS, respectively - comparable to other additive manufacturing methods despite eliminating the high-temperature, long-duration curing process. The process was also used to fabricate a 6-couple f-TEG device which could generate 357.6 µW with a power density of 5.0 mW/cm 2 at a ∆T of 40 K. The device demonstrated air stability and flexibility for 1000 cycles of bending. Finally, the device was integrated with a voltage step-up converter to power a LED and charge and discharge capacitor at a ∆T of 17 K, demonstrating its applicability as a self- sufficient power source.
(Invited) Structure and Function Tuning of Nanostructured Titania for Photochemical and Electrochemical Applications
Authors: Nishida Hisataka , Han Do Hyung , Park Hyunsu , Kondo Yoshifumi , Cho Sunghun , Seo Yeongjun , Goto Tomoyo , Sekino Tohru 
Published: December 2024

Titania nanotubes (TNTs) [1], that essentially has ultraviolet light responsibility, have been modified by various chemical protocols such as peroxo functional groups modification and transition metal doping via facile solution chemical routes. When peroxo functional groups (-O-O-) were introduced to the lattice of TNT by hydrogen peroxide solution treatment of pristine TNTs or by bottom-up chemical synthesis from peroxo titanium complex precursor [2,3], yellowish powders were obtained. Optical band gap energy of titania nanostructures was decreased to 2.6 eV that was lower than that of pure TNTs of typically around 3.4 eV. This large red-shift of optical absorption edge might be due to the addition of electron states owing to excess oxygen to titanium oxide lattice and followed variation of energy level of conduction band for the peroxo-modified TNTs (hereafter as PTNTs).
Further materials tuning could also be possible by cation doping such as copper ions to the pristine TNT as well as PTNT by Cu2+ ion adsorption and followd UV-light irradiation to control oxidation state of copper ions. These Cu-modified nanotubes exhibited additional optical absorption band among visible light regions, provably due to the formation of d-d transition level in TNT and/or PTNT crystals. Such modifications of nanostructure titania allowed to show the photocatalytic performance enhanced under the visible light irradiating.
Photo-irradiation induced active species during light irradiation of photocatalytic performance investigations were identified by using various radical trap agencies. It was found that the photo-exited electron played a major role for visible-light driven photocatalytic degradation of organic molecules via the formation of superoxide anion radicals. Addition of cupper species made enhancement of hydrogen formation under the visible light irradiation and followed water splitting.
Such photo-induced functions might be expected to contribute not only to environmental cleaning but also to application as photochemical hydrogen generation. Detailed synthesis processes, formation mechanisms, chemical and photochemical properties will be discussed.
References:
[1] T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, K. Niihara, Langmuir, 14, 3160-63 (1998).
[2] H. Park, T. Goto, D. H. Han, S. Cho, H. Nishida, T. Sekino, ACS Applied Nano Materials, 3, 7795–7803(2020).
[3] H. Park, D. H. Han, T. Goto, S. Cho, Y. Morimoto, T. Sekino, Nanoscale Advances, 4, 3573-3584 (2022).
(Invited) A Brief Overview and Outlook on the Progress of III-Nitride Semiconductor Materials
Authors: Freitas Jaime A. 
Published: December 2024

In the last three decades, III-Nitride (GaN, AlN, InN, and its alloys) semiconductors have revolutionized both the optoelectronic and electronic device industries. Despite a previous lack of native substrates, a number of devices exceeding the performance of those fabricated from well-developed semiconductors were realized. More recently, bulk GaN (ammonothermal) and AlN (physical vapor transport) substrates were developed and commercialized. Both substrates are characterized by low dislocation density, a single crystal nature, and high flatness; but they lack full control of the electrical properties. Films deposited by vapor transport techniques (HVPE and CVD) and molecular beam epitaxy allowed the growth of device layers with high crystalline quality and improved electrical properties. These films have intrinsic free carrier concentrations that are several orders of magnitude lower than that of the substrates. This demonstrates the usefulness of this new type of substrate to fabricate highly efficient optoelectronic and electronic devices. Despite that, low acceptor solubility limit and the high activation of energy of the p-type dopants leads to low free hole concertation at room temperature.
Many relevant figures of merit related to electronic device performance scale superlinearly with the band gap; hence, ultra-wide band gap (UWBG) materials (Eg > 3.4 eV) have the potential for far superior performance than conventional WBG materials such as GaN and SiC [1]. UWBG materials will be critical enablers of future electronic components and systems, and a fundamental understanding of their synthesis and properties is critical to exploiting their advantages. In particular, cubic boron nitride, among the semiconductor materials in the UWBG group (c-BN, AlN, Ga2O3, and diamond), with a band gap of ~6 eV and thermal conductivity of 13 W/mK (second only to diamond, 20 W/mK) offers the best combination of breakdown voltage and specific on-resistance [2,3]. Another advantage of c-BN over other UWBG semiconductors is that it can be doped with donors and acceptors, enabling the fabrication of bipolar devices.
The development of WBG and UWBG substrates will be reviewed and a brief overview of the intrinsic properties of selected semiconductors will be presented.
[1] J.Y. Tsao et al., Adv. Electron. Mater. 4, 1600501 (2018)
[2] N. Miyata et al., Phys. Rev. B 40, 12028 (1989)
[3] L. Vel et al., Mat. Sci. Engineer. B 10, 149 (1991)
This work supported by the Office of Naval Research