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Ferroelectric semiconductor junctions based on graphene/In2Se3/graphene van der Waals heterostructures @article{57c01f0ace344ec7900bea7cd90d8404, title = "Ferroelectric semiconductor junctions based on graphene/In2Se3/graphene van der Waals heterostructures", abstract = "The miniaturization of ferroelectric devices offers prospects for non-volatile memories, low-power electrical switches and emerging technologies beyond existing Si-based integrated circuits. An emerging class of ferroelectrics is based on van der Waals (vdW) two-dimensional materials with potential for nano-ferroelectrics. Here, we report on ferroelectric semiconductor junctions (FSJs) in which the ferroelectric vdW semiconductor α-In2Se3 is embedded between two single-layer graphene electrodes. In these two-terminal devices, the ferroelectric polarization of the nanometre-thick In2Se3 layer modulates the transmission of electrons across the graphene/In2Se3 interface, leading to memristive effects that are controlled by applied voltages and/or by light. The underlying mechanisms of conduction are examined over a range of temperatures and under light excitation revealing thermionic injection, tunnelling and trap-assisted transport. These findings are relevant to future developments of FSJs whose geometry is well suited to miniaturization and low-power electronics, offering opportunities to expand functionalities of ferroelectrics by design of the vdW heterostructure.", author = "Shihong Xie and Anubhab Dey and Wenjing Yan and Zakhar Kudrynskyi and Nilanthy Balakrishnan and Oleg Makarovskiy and Zakhar Kovalyuk and Eli Castanon and Oleg Kolosov and Kaiyou Wang and Amalia Patane", year = "2021", month = aug, day = "20", doi = "10.1088/2053-1583/ac1ada/meta", language = "English", volume = "8", journal = "2D Materials", issn = "2053-1583", publisher = "IOP Publishing Ltd.", number = "4", } . 2D Materials.

Interfacial ferroelectricity in marginally twisted 2D semiconductors @article{15e8293cbbe7411f8d4265f48e7b4ebb, title = "Interfacial ferroelectricity in marginally twisted 2D semiconductors", abstract = "Twisted heterostructures of two-dimensional crystals offer almost unlimited scope for the design of novel metamaterials. Here we demonstrate a room-temperature ferroelectric semiconductor that is assembled using mono- or few- layer MoS2. These van der Waals heterostructures feature broken inversion symmetry, which, together with the asymmetry of atomic arrangement at the interface of two 2D crystals, enables ferroelectric domains with alternating out-of-plane polarisation arranged into a twist-controlled network. The latter can be moved by applying out-of-plane electrical fields, as visualized in situ using channelling contrast electron microscopy. The interfacial charge transfer for the observed ferroelectric domains is quantified using Kelvin probe force microscopy and agrees well with theoretical calculations. The movement of domain walls and their bending rigidity also agrees well with our modelling results. Furthermore, we demonstrate proof-of-principle field-effect transistors, where the channel resistance exhibits a pronounced hysteresis governed by pinning of ferroelectric domain walls. Our results show a potential venue towards room temperature electronic and optoelectronic semiconductor devices with built-in ferroelectric memory functions.", author = "Astrid Weston and Eli Castanon and Vladimir Enaldiev and Fabio Ferreira and Shubhadeep Bhatacharjee and Shuigang Xu and Hector Corte-Leon and Zefei Wu and Nickolas Clark and Alex Summerfield and Teruo Hashimoto and Yunze Gao and Wendong Wang and Matthew Hamer and Harriet Read and Laura Fumagalli and Andrey Kretinin and Sarah Haigh and Olga Kazakova and Andre Geim and Vladimir Falko and Roman Gorbachev", year = "2021", month = aug, day = "14", doi = "arXiv:2108.06489", language = "English", journal = "arXiv", issn = "2331-8422", }. arXiv.

Shihong Xie and Anubhab Dey and Wenjing Yan and Zakhar Kudrynskyi and Nilanthy Balakrishnan and Oleg Makarovsky and Zakhar D. Kovalyuk and Eli Castanon and Oleg V. Kolosov and Kaiyou Wang and Amalia Patane(2021). Ferroelectric semiconductor junctions based on graphene/In2Se3/graphene van der Waals heterostructures . 2D Materials. {IOP} Publishing

Opportunities in Electrically Tunable 2D Materials Beyond Graphene: Recent Progress and Future Outlook @article{8a51bddf3a8d4a529d79d70f695f005c, title = "Opportunities in Electrically Tunable 2D Materials Beyond Graphene: Recent Progress and Future Outlook", abstract = "The interest in two-dimensional and layered materials continues to expand, driven by the compelling properties of individual atomic layers that can be stacked and/or twisted into synthetic heterostructures. The plethora of electronic properties as well as the emergence of many different quasiparticles, including plasmons, polaritons, trions and excitons with large, tunable binding energies that all can be controlled and modulated through electrical means has given rise to many device applications. In addition, these materials exhibit both room-temperature spin and valley polarization, magnetism, superconductivity, piezoelectricity that are intricately dependent on the composition, crystal structure, stacking, twist angle, layer number and phases of these materials. Initial results on graphene exfoliated from single bulk crystals motivated the development of wide-area, high purity synthesis and heterojunctions with atomically clean interfaces. Now by opening this design space to new synthetic two-dimensional materials {"}beyond graphene{"}, it is possible to explore uncharted opportunities in designing novel heterostructures for electrical tunable devices. To fully reveal the emerging functionalities and opportunities of these atomically thin materials in practical applications, this review highlights several representative and noteworthy research directions in the use of electrical means to tune these aforementioned physical and structural properties, with an emphasis on discussing major applications of beyond graphene 2D materials in tunable devices in the past few years and an outlook of what is to come in the next decade.", author = "Eli Castanon and Tom Vincent and Jiayun Liang and Simrjit Singh and Xiaotian Zhang and Amber McCreary and Deep Jariwala and Olga Kazakova and {Al Balushi}, Zakaria", year = "2021", month = mar, day = "26", doi = "arXiv:2103.14194", language = "English", journal = "arXiv", issn = "2331-8422", }. arXiv.

Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy @article{d7b1ac49c3c84654842abdc44eef8665, title = "Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy", abstract = "The ability of a material to conduct heat influences many physical phenomena, ranging from thermal management in nanoscale devices to thermoelectrics. Van der Waals 2D materials offer a versatile platform to tailor heat transfer due to their high surface-to-volume ratio and mechanical flexibility. Here, the nanoscale thermal properties of 2D indium selenide (InSe) are studied by scanning thermal microscopy. The high electrical conductivity, broad-band optical absorption, and mechanical flexibility of 2D InSe are accompanied by an anomalous low thermal conductivity (κ). This can be smaller than that of low-κ dielectrics, such as silicon oxide, and it decreases with reducing the lateral size and/or thickness of InSe. The thermal response is probed in free-standing InSe layers as well as layers supported by a substrate, revealing the role of interfacial thermal resistance, phonon scattering, and strain. These thermal properties are critical for future emerging technologies, such as field-effect transistors that require efficient heat dissipation or thermoelectric energy conversion with low-κ, high electron mobility 2D materials, such as InSe.", keywords = "InSe, SThM, scanning thermal microscopy, nanotermal, nanoscale heat transport, anistotropy, heat transport, 2D materials, vdW materials, TMD", author = "David Buckley and Zakhar Kudrynskyi and Nilanthy Balakrishnan and Tom Vincent and Debarati Mazumder and Eli Castanon and Zakhar Kovalyuk and Oleg Kolosov and Olga Kazakova and A. Tzalenchuk and Amalia Patane", note = "This is the peer reviewed version of the following article:Buckley, D., Kudrynskyi, Z. R., Balakrishnan, N., Vincent, T., Mazumder, D., Castanon, E., Kovalyuk, Z. D., Kolosov, O., Kazakova, O., Tzalenchuk, A., Patan{\`e}, A., Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy. Adv. Funct. Mater. 2021, 2008967. https://doi.org/10.1002/adfm.202008967 which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/adfm.202008967 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving. ", year = "2021", month = mar, day = "10", doi = "10.1002/adfm.202008967", language = "English", volume = "31", journal = "Advanced Functional Materials", issn = "1616-301X", publisher = "John Wiley & Sons, Ltd", number = "11", } . Advanced Functional Materials.

Buckley, David, Kudrynskyi, Zakhar R., Balakrishnan, Nilanthy, Vincent, Tom, Mazumder, Debarati, Castanon, Eli, Kovalyuk, Zakhar D., Kolosov, Oleg, Kazakova, Olga, Tzalenchuk, Alexander, et al. (2021). Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy .

Calibrated kelvin-probe force microscopy of 2d materials using pt-coated probes @article{d50873ace46241f39eb5fe7fe6db10a7, title = "Calibrated kelvin-probe force microscopy of 2d materials using pt-coated probes", abstract = "Nanoscale characterization techniques are fundamental to continue increasing the performance and miniaturization of consumer electronics. Among all the available techniques, Kelvin-probe force microscopy (KPFM) provides nanoscale maps of the local work function, a paramount property related to many chemical and physical surface phenomena. For this reason, this technique has being extremely employed in the semiconductor industry, and now is becoming more and more important in the growing field of 2D materials, providing information about the electronic properties, the number of layers, and even the morphology of the samples. However, although all the collective efforts from the community, proper calibration of the technique to obtain reliable and consistent work-function values is still challenging. Here we show a calibration method that improves on current procedures by reducing the uncertainty. In particular, it allows grading probes more easily, thus being a tool to calibrate and to judge calibration in itself. The calibration method is applied to optimize Pt-coated probes, which are then used to characterize the work function of a 2D material, i.e. graphite flakes. The results demonstrate that the metallic probes are stable over time and exposure to high humidity levels, and that the calibration allows comparing measurements taken with several different probes on different samples, thus completely fulfilling the requirement of a good calibration method. ", keywords = "Kelvin-probe, Nanocharacterization, Spm, Work function", author = "E.G. Castanon and A.F. Scarioni and H.W. Schumacher and S. Spencer and R. Perry and J.A. Vicary and C.A. Clifford and H. Corte-Le{\'o}n", year = "2020", month = sep, day = "30", doi = "10.1088/2399-6528/abb984", language = "English", volume = "4", journal = "Journal of Physics Communications", issn = "2399-6528", publisher = "IOP Science", number = "9", } . Journal of Physics Communications.

Contactless probing of graphene charge density variation in a controlled humidity environment @article{0654f57e771a468c9f6a3851ea6f4036, title = "Contactless probing of graphene charge density variation in a controlled humidity environment", abstract = "The electronic properties of graphene are highly sensitive to atoms and molecules adsorbed on its surface and to changes in its environment, such as temperature and humidity. In this paper, we examine the effect of humidity on the local carrier concentration of different types of graphene prepared by mechanical exfoliation, chemical vapour deposition and epitaxial growth on SiC, using in-situ Raman spectroscopy. We present a systematic and comparative study of the changes in Raman response using a vector analysis method to produce spatial maps of doping variation as a function of humidity. We also quantify the humidity induced carrier concentration change for different types of graphene. This study illustrates the effects of humidity on the electronic properties of graphene and provides a simple, contactless and quantitative method to directly evaluate water-induced doping effects in graphene, that are crucial for tailored device performance.", keywords = "Carrier concentration, Chemical vapor deposition, Electronic properties, Humidity control, Silicon carbide, Chemical vapour deposition, Comparative studies, Controlled humidities, Electronic properties of graphene, In-situ Raman spectroscopy, Mechanical exfoliation, Quantitative method, Temperature and humidities, Graphene", author = "K. Brown and T. Vincent and E.G. Castanon and F.S. Rus and C. Melios and O. Kazakova and C.E. Giusca", year = "2020", month = aug, day = "15", doi = "10.1016/j.carbon.2020.03.037", language = "English", volume = "163", pages = "408--416", journal = "Carbon", issn = "0008-6223", publisher = "Elsevier", } . Carbon.

Buckley, David J, Black, Nicola C G, Castanon, Eli G, Melios, Christos, Hardman, Melanie, Kazakova, Olga (2020). Frontiers of graphene and 2D material-based gas sensors for environmental monitoring .

(2021). Opportunities in Electrically Tunable 2D Materials Beyond Graphene: Recent Progress and Future Outlook.

Characterisation of local thermal properties in nanoscale structures by scanning thermal microscopy @conference{f12d0dacdde542ebb5286c1339d70039, title = "Characterisation of local thermal properties in nanoscale structures by scanning thermal microscopy", abstract = "Local characterisation of material thermal properties has become increasingly relevant, but also increasingly challenging, as the size of thermally-active components has been reduced from the micro- to the nano-scale [1]such as in devices based on semiconductor quantum dots and quantum wells, polymer nanocomposites, multilayer coatings, nanoelectronic and optoelectronic devices. In this scenario, thermal management arises as one of the main issues to be treated as the proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport and imposes a limit on theoperation speed and the reliability of the new devices [2]. It therefore becomes critical to fully characterise the local nanoscale heat transport properties of different materials currently used in various industrial applications such assemiconductors, insulators, polymers etc, operating under different conditions and with varying doping levels [3]. Specifically, silicon is of interest due to its ubiquity in most sensors, electronic components or photovoltaic cells.In the present study, we compare doped and intrinsic semiconductor to polymeric sample that have been characterised both topographically and thermally by means of scanning thermal microscopy (SThM). Thermal characterisation of the samples was performed with a modified AFM system (NT-MDT Solver) in ambientconditions using a commercial probe with Pd microfabricated resistive heater and custom electronics allowing the measurement of local heat transport between the apex of the probe and the sample [4]. We demonstrate this approach on the set of the reference materials samples of sufficiently large size to be independently measured using standard thermal conductivity methods [5]. In order to improve the quality of the SThM measurements, sample temperature was stabilised via a combination of a Peltier heater mounted underneath the sample and thermistors monitoring the temperature of the sample in a closed loop setup, with the temperatures of the probe base and surrounding air continuously monitored. The setup allowed us to simultaneously acquire topographical and thermal measurements in the contact mode. During the measurements, approach-retraction curves (as shown in Figure 1), were taken at 16 different points of thesample{\textquoteright}s surface. The SThM electronics produced a voltage output (“thermal signal”) due to the change of the probe resistance proportional to the change in the probe temperature. Probe response is best represented as where is the thermal signal of the probe when it is not in contact with the sample, and is thermal signal when it establishes contact with the surface. This ratio is shown to be directly related to the thermal conductivity of the samples [4].Our results for the 4 different materials – intrinsic, p++ and n++ doped Si, as well as the polymer are shown in Fig.2. In the measurement conditions of ambient pressure and temperature, single crystalline Si [100] is showingthe highest value of the thermal conductivity, with the doped Si species showing lower thermal conductivity with smaller values DV/V, due to phonon-electron scattering that are dominating on the nanoscale [6].Our measurements show that the SThM can reliably discriminate between group IV semiconductors presenting different doping concentrations based on the thermal conductivity, with a lateral resolution of about 20-50 nm.Further steps will focus on obtaining quantitative data from the DV/V measurements, using for this purpose, specially prepared reference samples of controlled geometry that can be characterised independently via large scale techniques such as flash thermoreflectance [5].", keywords = "scanning thermal microscopy, SThM, nanoscale heat transport, oxides, semiconductors", author = "Eli Castanon and Charalambos Evangeli and Jean Spiece and Robinson, {Benjamin James} and Severine Gomes and Olga Kazakova and Kolosov, {Oleg Victor}", year = "2017", month = jul, day = "3", language = "English", note = "MMC2017 : Microscience and Microscopy Congress 2017, mmc2017 ; Conference date: 03-07-2017 Through 06-07-2017", url = "https://mmc-series.org.uk/conference", } . MMC2017, Manchester, United Kingdom, 3/07/17.