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Since 2020, synchrotron radiation facilities in several Asia-Pacific countries have been collaborating in a major project called "SYNAPSE"(Synchrotrons for Neuroscience: an Asia-Pacific Scientific Enterprise). They use x-ray imaging to attack in a coordinated fashion one of the major issues in modern science: the structure of animal and human brains, including neurons and connections. The objective is to develop Google-like maps also including detailed structural and functional information for selected regions of interest. The sheer mass of data needed for the objective poses huge problems for the acquisition, processing, storage and use of images. In order to complete the task within a reasonable time, the key element of the SYNAPSE strategy is the parallel and coordinated work of several facilities on the same specimens. This article reviews different aspects of the enterprise, including the foundations of synchrotron radiation, coherence and of its role in advanced imaging, electron accelerators, x-ray optics and detectors. This will provide the foundation for an extensive presentation of the different components of SYNAPSE, with an overview of results already obtained within the consortium.

Mapping the large neural networks of animal and human brains is a fundamental but so far elusive task, because of the massive amount of data and the consequent prohibitively long image taking and processing times. We developed an effective strategy called “AXON” (Accelerated X-ray Observation of Neurons) to solve this problem. AXON can achieve comprehensive whole-brain mapping within a reasonable time by combining fast image taking and processing, plus two other critical performances: three-dimensional (3D) imaging with high and isotropic spatial resolution, and multi-scale resolution. We successfully tested this strategy with coordinated experiments at four synchrotron facilities in Japan, Taiwan, Singapore and Korea on two animal models, Drosophila and mouse. Its performances notably allowed full 3D mapping of the Drosophila brain in a few days. With reasonable improvements, AXON can deliver full mapping of large animal and human brains on a realistic time scale of a few years.

X-ray irradiation has been extensively used in recent years as a fabrication step for nanoparticles and nanoparticle systems. A variant of this technique, continuous-flow X-ray irradiation, has recently been developed, and offers three important advantages: precise control of the irradiation dose, elimination of convection effects in the precursor solution, and suitability for large-scale production. Here, the use of this method to fabricate Au nano-meshes of interest as transparent and flexible electrodes for optoelectronics is reported. The study includes extensive characterization of the synthesis parameters and of the product properties, with rather encouraging results.

Gold sputtered on quartz can exhibit particle- or film-like morphologies. For Au coverage less than equivalent thickness of 3 nm, well-dispersed Au nanoparticles (Au NPs) forms. Depending on size, the colour of these samples, which are associated with surface plasmon resonance (SPR) excitation, can appear pink and/or blue. Exposing these samples to an ambient environment oxidizes these NPs and the degree of oxidation is more significant with smaller NPs. Smaller NPs have larger surface-to-volume ratio and a greater number of under-coordinated surface Au atoms, thus making these samples more susceptible to oxidation. The oxidation process is accompanied by a redistribution of the valence-band electrons where the 5d and 6s electrons become less delocalized for metallic bonding and the appearance of a valence band maxima at ~ 2 eV results. As the oxidation proceeds, the initial SPR peaks were also blue-shifted. As the amount of sputtered Au increases, a labyrinth-like network of coalesced Au-particles forms before the film-like morphology eventually emerges. In comparisons to Au-NPs, these samples appear more bulk-like and thus do not exhibit SPR nor show any significant degree of oxidation in the ambient air environment.

We present a facile and direct method for selectively depositing amorphous aluminium oxide micro-flake or nanoparticles on graphene oxide (GO) by irradiating the GO film with a focused laser beam through a solution containing aluminium cations. Micro-landscapes comprising aluminium oxide (alumina) based compounds directed by the laser beam are constructed. The morphology and density of the deposited alumina are engineered through the variation of concentration of the solution used, the power and scanning speed of the laser. This method facilitates the rapid process of merging Al, O, C into the same matrix and thus resulted in the formation of carbon incorporated amorphous aluminium oxide that exhibits distinctive blue fluorescence upon UV excitation. This process is akin to the act of blue micro-highlighting on the surface of GO film. The GO film proves to be an ideal platform for the mask-free and non-contact micro-patterning process. The fluorescence micropattern is stable and continues to be fluorescence active even after a period of 397 days.

Pristine trivanadate (LiV3O8) and doped lithium trivanadate (LiV3–xMxO8, M = Zn/Co/Fe/Sn/Ti/Zr/Nb/Mo, x = 0.01/0.05/0.1 M) compounds were prepared by a simple reflux method in the presence of the polymer, Pluronic P123, as the chelating agent. For comparison, pristine LiV3O8 alone was also prepared in the absence of the chelating agent. The Rietveld-refined X-ray diffraction patterns shows all compounds to exist in the layered monoclinic LiV3O8 phase belonging to the space group of P21/m. Scanning electron microscopy analysis shows the particles to exhibit layers of submicron-sized particles. The electrochemical performances of the coin cells were compared at a current density of 30 mA/g in the voltage window of 2–4 V. The cells made with compounds LiV2.99Zr0.01O8 and LiV2.95Sn0.05O8 show a high discharge capacity of 245 ± 5 mA h/g, with an excellent stability of 98% at the end of the 50th cycle. The second cycle discharge capacity of 398 mA h/g was obtained for the compound LiV2.99Fe0.01O8, and its capacity retention was found to be 58% after 50 cycles. The electrochemical performances of the cells were correlated with the electrical properties and the changes in the structural parameters of the compounds.

We present a graphene oxide (GO) film as a superior substrate for the controlled anchoring and micropatterning of a blinking silver nanocluster–nanoparticle hybrid. Localised laser reduction of the GO film in the presence of AgNO3 solution results in the controlled deposition of Ag nanoparticles (NPs) onto the reduced GO (rGO) film. Upon irradiation by blue light, some of these NPs turn into nanoblinkers (AgO/Agn hybrid) exhibiting dynamic tricolored fluorescence intermittency. Via the scanning laser beam, a wide variety of micropatterns with a high density of nanoblinkers are achieved on the GO/rGO film. Most remarkably, the nanoblinkers formed on GO/rGO remain vibrant even after a period of 1 year, unlike other substrates (CNT, SiO2/Si wafer) studied. Furthermore, both the micro-patterns and tricoloured blinking behaviour are preserved upon their transfer from the GO film onto other surfaces such as glass and a PDMS film. The hybrid material can also be used to detect Rhodamine B dye where the fluorescing colour of the Ag nanoblinkers changes upon interaction with the dye. The shade of fluorescence and the blinking rate of the nanoblinkers are highly dependent on the duration of interaction between the nanoblinkers and the Rhodamine B molecules.

The kinetics of plasma oxidation of GeSn at low temperature is investigated. The oxidation process is described by a power-law model where the oxidation rate decreases rapidly from the initial oxidation rate with increasing time. The oxidation rate of GeSn is higher than that of pure Ge, which can be explained by the higher chemical reaction rate at the GeSn-oxide/GeSn interface. In addition, the Sn atoms at the interface region exchange positions with the underlying Ge atoms during oxidation, leading to a SnO2-rich oxide near the interface. The bandgap of GeSn oxide is extracted to be 5.1 ± 0.2 eV by XPS, and the valence band offset at the GeSn-oxide/GeSn heterojunction is found to be 3.7 ± 0.2 eV. Controlled annealing experiments demonstrate that the GeSn oxide is stable with respect to annealing temperatures up to 400 °C. However, after annealing at 450 °C, the GeO2 is converted to GeO, and desorbs from the GeSn-oxide/GeSn, leaving behind Sn oxide.

Room temperature growth of HfO2 thin film on clean 2H-MoS2 via plasma-sputtering of Hf-metal target in an argon/oxygen environment was studied in-situ using x-ray photoelectron spectroscopy (XPS). The deposited film was observed to grow akin to a layer-by-layer growth mode. At the onset of growth, a mixture of sulfate- and sulfite-like species (SOx2− where x = 3, 4), and molybdenum trioxide (MoO3), are formed at the HfO2/MoS2 interface. An initial decrease in binding energies for both Mo 3d and S 2p core-levels of the MoS2 substrate by 0.4 eV was also observed. Their binding energies, however, did not change further with increasing HfO2 thickness. There was no observable change in the Hf4f core-level binding energy throughout the deposition process. With increasing HfO2 deposition, MoO3 becomes buried at the interface while SOx2− was observed to be present in the film. The shift of 0.4 eV for both Mo 3d and S 2p core-levels of the MoS2 substrate can be attributed to a charge transfer from the substrate to the MoO3/SOx2−-like interface layer. Consequently, the Type I heterojunction valence band offset (conduction band offset) becomes 1.7 eV (2.9 eV) instead of 1.3 eV (3.3 eV) expected from considering the bulk HfO2 and MoS2 valence band offset (conduction band offset). The formation of these states and its influence on band offsets will need to be considered in their device applications.

In this work, real-time morphological evolution occurring on the GeSn(111) surface during in-situ annealing in a N 2 environment is examined using a phase contrast optical microscope equipped with a heating stage. Apart from isolated immobile Sn-rich dot-like islands, mobile teardrop-shaped islands are also found at the moving boundary separating the smooth and roughen regions on the surface. As the boundary grows, Sn-poor wire-like feature emerges. The rate of growth occurs with an activation energy of ~1.4eV and appears to be akin to liquid phase epitaxy where the Sn-rich droplets leads the formation of wire-like features and the movement is due to the directional flow of Ge atoms through the droplet. DFT calculations suggest that the morphological instability is thermodynamically driven, where the relaxation of the inherent strain occurs with Sn atoms preferentially segregating from the bulk-lattice and agglomerating at the surface. The formation of these heterogeneous surfaces would restrict the thermal budget for GeSn alloys to be monolithically integrated into Silicon or Germanium devices.

When graphene supported on SiO 2 is fluorinated, XPS reveals an increase in concentration of chemically-adsorbed fluorine (higher F/C ratio with C-CF, C-CF 2 , C-F and C-F 2 but no C-F 3 ) on the graphene surface with time. Raman I D /I G ratio, i.e. a measure of non-sp2to Sp2 bonding states, increases with time before showing a decrease suggesting a surface morphology change owing to C-F bonding followed by disordering of the π-electron system. AFM surface morphology scans reveal that defects (holes), which increases in size with time, are observed to form preferentially at the boundary of the graphene flakes. Synchronized Kelvin-Probe Force-Microscopy (KPFM) mapping of the graphene region surrounding these holes shows a higher work-function, ϕ, giving rise to a donut-shape contact potential difference (CPD) which increases from 4.9 ± 0.1 eV to 5.4 ± 0.1 eV with fluorination. Together with XPS and Raman results, the increase in ϕ can be attributed to the presence of a higher concentration of fluorine in the graphene region (C-F/C-F 2 bonds) surrounding these holes. The formation of the hole-defects on graphene and its subsequent increase in size with fluorination is thus a result of aggregation of adsorbed fluorine and removal of carbon likely in the form of CF 4 or C 2 F 4 .

Chemisorbed molecular nanocorrals on semiconductor surfaces are of both fundamental and technical importance. 1-Propanethiol molecules adsorbed on Si(111)-(7×7) were investigated using high-resolution energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and periodic density functional theory (DFT) calculations. HREELS spectra show that the 1-propanethiol molecules undergo S–H bond dissociative adsorption on Si(111)-(7×7). STM images reveal the temperature-dependent site selectivity for the binding of C3H7S- fragments. At room temperature, C3H7S- prefers to bind to faulted subunits compared to unfaulted subunits. At 110 K, C3H7S- binding on center adatoms over corner adatoms is dominant, resulting in an ordered array of molecular nanocorrals. DFT calculations were performed on a periodic slab including the entire 7×7 reconstruction rather than on a cluster model. The theoretical studies suggest that the temperature-dependent site selectivity originates from the thermal-plus-electron-indu...

We report a novel optical property in WS2 monolayer. The monolayer naturally exhibits beautiful in-plane periodical and lateral homojunctions by way of alternate dark and bright band in the fluorescence images of these monolayers. The interface between different fluorescence species within the sample is distinct and sharp. This gives rise to intriguing concentric triangular fluorescence patterns in the monolayer. The novel optical property of this special WS2 monolayer is facilitated by chemical heterogeneity. The photoluminescence of the bright band is dominated by emissions from trion and biexciton while the emission from defect-bound exciton dominates the photoluminescence at the dark band. The discovery of such concentric fluorescence patterns represents a potentially new form of optoelectronic or photonic functionality.

Evidence for the influence of Si(001)-(2 × 1) surface reconstruction on the elongation direction of CoSi 2 flat islands is discussed in this paper. Step height analysis of these flat islands shows that flat island heights, H A , follow discrete values of N A such that H A = mN A + c , where N A = 1, 2, 3, …, m is equivalent to the number of monoatomic step height (1.4 A) of the Si(001) surface, and c is the initial island height when N A = 0. The N A values were found to be correlated to the flat island elongation direction with respect to the (2 × 1) dimer rows. For a given terrace, the preferred elongation direction of these flat islands is parallel to the Si dimer rows. As a result, orthogonally elongated islands are clearly resolved on adjacent terraces, which are separated by monoatomic steps. The endotaxial growth of these flat islands is thus also influenced by the anisotropic adatom diffusion due to (2 × 1) surface reconstruction.

Enhanced photoresponse is obtained from phosphorene-phosphorene-suboxide. A scanning focused laser beam is employed as a straightforward approach to convert part of a phosphorene film into phosphorene suboxide, creating a functional junction in situ on an optoelectronic device based on phosphorene. As a result, the photoelectrical properties of the optoelectronic device are significantly improved.

The recent increasing research interest in two-dimensional (2D) layered materials has led to an explosion of in the discovery of novel physical and chemical phenomena in these materials. Among the 2D family, group-VI transition metal dichalcogenides (TMDs), such as represented by MoS2 and WSe2, are remarkable semiconductors with sizable energy band gaps, which make the TMDs promising building blocks for new generation optoelectronics. On the other hand, the specificity and tunability of the band gaps can generate particularly strong light-matter interactions between TMD crystals and specific photons, which can trigger complex and interesting phenomena such as photo-scattering, photo-excitation, photo-destruction, photo-physical modification, photochemical reaction and photo-oxidation. Herein, we provide an overview of the phenomena explained by various interactions between lasers and the 2D TMDs. Characterizations of the optical fundamentals of the TMDs via laser spectroscopies are reviewed. Subsequently, photoelectric conversion devices enabled by laser excitation and the functionality extension and performance improvement of the TMDs materials via laser modification are comprehensively summarized. Finally, we conclude the review by discussing the prospects for further development in this research area.

The successful design and synthesis of earth-abundant and efficient catalysts for the oxygen evolution reaction (OER) will be a major step forward towards the use of electrochemical water splitting as an environmentally-friendly process for producing H2 fuel. Due to their poor activity, copper-based materials have not been considered apt for catalysing OER. In this work, we demonstrate that unique copper(II) oxide nanostructures obtained via hydrothermal synthesis and subsequent hydrogen peroxide treatment exhibit unusually high and sustainable OER activity. In 0.1 M KOH electrolyte, the CuO nanostructures catalyse OER with current densities of 2.6–3.4 mA cm−2 at 1.75 V (vs. RHE). The calculated turnover frequency (per Cu site) of ~2 × 10−3 s−1 for O2 production is markedly higher than that of high-surface area electrodeposited Cu metal nanoparticles by 40–68 times. The OER activity of the CuO nanostructures is also stable, approaching about half of 20% IrOx/Vulcan XC-72 after an hour-long OER. In situ Raman spectroscopy at OER-relevant potentials recorded compelling evidence that CuIII active species may be responsible for the unusual OER activity of the CuO nanostructures, as indicated by its signature vibration at 603 cm−1. This hitherto unobserved peak is assigned, with the aid of the model compound NaCuIIIO2, to the Cu–O stretching vibration of CuIII oxide. This feature was not found on electrodeposited Cu metal, which exhibited correspondingly weaker OER activity. The enhanced catalysis of O2 evolution by the CuO nanostructures is thus attributed to not just their higher surface area, but also the higher population of CuIII active sites on their surface.

Metal/semiconductor-oxide interface is a major focus in condensed matter physics due to its rich fundamental properties and potential novel electronic applications. Our understanding of the impact of native oxide on metal/semiconductor-oxide interface (e.g. Ge) remains nonetheless elusive. Herein, we address this by purposefully exposing a clean Ge(0 0 1) surface to ambient environment (up to 600 days). The extend of Ge oxidation and binding energy (BE) shifts in the core-levels of Ge X-ray photoelectron peaks (Ge3d and Ge2p3/2) are found to correlate directly with the GeOx/Ge (x ≤ 2) atomic composition. A universal scaling in the band offsets at the GeOx/Ge heterojunction with increasing Ge-oxide content is established independent of oxidation time. A maximum upward band bending of ~0.6 eV is observed in the electronic band structure, which can be attributed to the presence of Ge valence states (Ge1+, Ge2+, Ge3+, Ge4+) at the GeOx/Ge junction formed during oxidation. Our results exemplify the importance of native oxide on semiconductor in determining the fundamental properties of semiconductor-oxide interfaces.

Electroless plating of metals is an important industry process. However, the reducing agents and chemicals needed for electroless plating comprise of non-biodegradable and bio-hazardous species which adds to the environmental-deterioration cost along with the price of the chemicals. We recently discovered that the electrochemical properties of Graphene can serve as an excellent reducing agent for electroless plating processes. We demonstrate the use of Graphene for Copper electroless plating in this work, and the resulting Copper layer possess better electrical and thermal properties than the Copper itself due to the presence of the Graphene. The theoretical basis of such technology as have been published elsewhere show that such technology can be applied to metals such as Nickel, Titanium, Aluminum, Gold, Silver, and Cobalt.

We report a functional hybrid made of silver nanoparticles (AgNPs) embedded in an amorphous aluminium oxide (alumina) film. This laser-initiated process allows formation of AgNPs and amorphous alumina in localized regions defined by the scanning laser beam. Due to metal enhanced fluorescence, this hybrid exhibits strong blue fluorescence emission under ultraviolet excitation. Upon irradiating with electrons at dosages of 1 to 20 mC cm−2, AgNPs become more metallic while the Al film is further oxidised. As a result, the fluorescing property is intensified. Using a hybrid irradiated with 10 mC cm−2, the electronic conductivity of the sample is improved by 11.5 times compared to that of the as-synthesized hybrid film. Excitation by UV light on the sample results in an increase in the detected current of nearly 29 times. Given that the electron beam patterned message is selectively visible only under UV or blue light irradiation, this hybrid film is thus a possible platform for steganographic transmission.

The shape transition of the CoSi2 islands from nanowire to nanodot and vice versa can be controlled by using different growth temperatures. High growth temperatures favor the formation of ridge nanowires and flat square-nanodots. At lower growth temperatures, the nanowires become more dot-like while flat nanodots are more wire-like. The islands' length, width and height follow the Arrhenius relation with activation energies ranging from 0.4 – 1.6 eV. The shape-transition of these nanowires and nanodots are kinetically limited by thermally-activated processes.

The effect of surface passivation on tin distribution in Ge1-xSnx(001)/Ge(001) are studied using first principles calculations. The segregation of Sn atoms towards the surface were suppressed when the clean surface is fully passivated with hydrogen adatoms while changing the passivating species to halogen adatoms resulted in enhancing Sn segregation towards the surface. This effect strengthens when moving down the Group-VII elements from fluorine to iodine. For both hydrogenated and halogenated surfaces, aggregation of sn atoms is not favored.

Using the small polaron model, we show clearly that oxygen vacancy defects are detrimental to the electrochromic responses of molybdenum oxide (MoO3). The observed phenomenon is explained by studying the oxidation states of the molybdenum (Mo) metal, which is central to the site specific small polaron model. First, we used the small polaron pair to explain the red-shift between the absorption peak induced by the vacancy defects and the inserted lithium (Li). Next, we show that any Mo5+ defects results in either a poor cathodic optical pair, or forms a site that is inactive for Li insertion. The main reason for the latter is due to the inability to generate Mo4+ in the reported optimal potential range. Finally, if the oxide starts with any intrinsic Mo4+ defect, we provided evidence to show that Mo6+–Mo4+ remains the only possible site for Li insertion, thereby greatly reducing available active sites. This optical modulation from Li insertion into this aforementioned pair is also low when compared with the...

Few-layer MoS2 film has been successfully assembled over an array of CNTs. Using different focused laser beams with different wavelengths, site selective patterning of either the MoS2 film or the supporting CNT array is achieved. This paves the way for applications and investigations into the fundamental properties of the hybrid MoS2/CNT material with a controlled architecture. Through Raman mapping, straining and electron doping of the MoS2 film as a result of interaction with the supporting CNT array are detected. The role of the MoS2 film was further emphasized with a lower work function being detected from Ultra-violet Photoelectron Spectrsocopy (UPS) measurements of the hybrid material, compared to the CNT array. The effect of the changes in the work function was illustrated through the optoelectronic behavior of the hybrid material. At 0 V, 3.49 nA of current is measured upon illuminating the sample with a broad laser beam emitting laser light with a wavelength of 532 nm. With a strong response to external irradiation of different wavelengths, and changes to the power of the excitation source, the hybrid material has shown potential for applications in optoelectronic devices.

Adsorption of butadiene monoxide on Si(111)-(7×7) has been scrutinized by high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The experimental results indicate that surface reaction occurs through a [2+2]-like cycloaddition, which is further supported by the DFT studies.

We show that by using different x-ray irradiation times of BSA-coated Au nanoparticles (NPs) we can change their ultraviolet-stimulated photoluminescence and shift the spectral weight over the visible spectral range. This is due to the interplay of two emission bands, one due to BSA and the other related to gold. The emission properties did not change with time over a period of several months. (C) 2014 Published by Elsevier B.V.

Annealing of strained Ge1−xSnx epitaxial layers grown on Ge(0 0 1) substrate results in two distinctive regimes marked by changes in composition and morphology. Annealing at low temperatures (200–300 °C or Regime-I) leads to surface enrichment of Sn due to Sn segregation, as indicated by X-ray photoelectron spectroscopy (XPS) results, while the bulk Sn composition (from X-ray diffraction (XRD)) and the surface morphology (from atomic force microscopy (AFM)) do not show discernible changes as compared to the as-grown sample. Annealing at temperatures ranging from 300 °C to 500 °C (Regime-II) leads to a decrease in the surface Sn composition. While the Ge1−xSnx layer remains fully strained, a reduction in the bulk Sn composition is observed when the annealing temperature reaches 500 °C. At this stage, surface roughening also occurs with formation of 3D islands. The island size increases as the annealing temperature is raised to 600 °C. The decrease in the Sn composition at the surface and in the bulk in Regime-II is attributed to additional thermally activated kinetic processes associated with Sn desorption and formation of Sn-rich 3D islands on the surface.

We developed a new digital etch process that allows precise etching of Germanium or Germanium-tin (Ge1−x Sn x ) materials. The digital etch approach consists of Ge1−x Sn x oxide formation by plasma oxidation and oxide removal in diluted hydrochloric acid at room temperature. The first step is a self-limiting process, as the thickness of oxide layer grows logarithmically with the oxidation time and saturates fast. Consistent etch rates in each cycle were found on the Ge1−x Sn x samples, with the surfaces remaining smooth after etch. The digital etch process parameters were tuned to achieve various etch rates. By reducing the radio frequency power to 70 W, etch rate of sub-1.2 nm was obtained on a Ge0.875Sn0.125 sample. The digital etch process was employed to fabricate the Ge1−x Sn x fin structures. Extremely scaled Ge0.95Sn0.05 fins with 5 nm fin width were realized. The side walls of the Ge0.95Sn0.05 fins are smooth, and no crystal damage can be observed. This technique provides an option to realize aggressively scaled nanostructure devices based on Ge1−x Sn x materials with high-precision control.

The reaction mechanism and regioselectivity of methyl oxirane (C3H6O) adsorbed on Si(111)-(7 × 7) have been studied using high-resolution electron energy loss spectroscopy (HREELS), in situ scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The experimental results demonstrate that methyl oxirane chemically binds to Si(111)-(7 × 7) through both dative-bonded addition and ring-opening reaction via cleavage of C–C or one C–O bond within the epoxy group. The STM images also reveal that the adsorption is site-selective with a preference for center adatoms on the faulted half of the (7 × 7) unit cell. The DFT calculations further show that breaking the C(CH3)–O bond is most kinetically favorable with a relatively small barrier of ∼3 kcal/mol. The dative-bonded states are observable on the surface only after three adjacent adatom–rest atom pairs within one-half unit cell are fully reacted with the methyl oxirane molecules during the ring-opening reaction.

Germanium-tin (GeSn) has high hole mobility and is a promising channel material for scaling the supply voltage towards 0.5 V for high performance p-channel field-effect transistors (pFETs) in the sub-10 nm technology nodes. In this paper, we discuss the research and development of using GeSn as the channel material of pFETs for enhancing the hole mobility and drive current. This includes GeSn planar pFETs, GeSn nanowire (NW) pFETs, as well as GeSn tunneling FETs (TFETs). Low-temperature Si2H6 passivation was developed to realize high-quality gate stack on GeSn. GeSn Planar pFETs with Various Sn Compositions and Surface Orientations GeSn (100)-oriented pFETs were demonstrated to have higher hole mobility than Ge pFETs [1]-[2]. With increasing Sn concentration in GeSn, the light hole effective mass at the G point is reduced [3], leading to higher hole mobilities. An important enabling process module for realization of high performance GeSn pFETs is the low-temperature Si2H6 passivation to achieve high-quality gate stack on GeSn [4]-[7], as shown in Fig. 1 (a) and (b). Further mobility enhancement can be achieved by a two-step Si2H6 passivation technique [8]. In addition, various channel surface orientations for the GeSn pFETs have been investigated [9], with the (111) orientation giving a higher hole mobility for a given Sn content in the channel. Fig. 1 (c) compares the effective hole mobilities of Si2H6-passivated GeSn pFETs with various Sn compositions and surface orientations at an inversion carrier density Ninv of 1 × 1013 cm-2. Uniaxially Compressive Strained GeSn Nanowire pFETs Besides planar GeSn pFETs, uniaxially compressive strained GeSn NW pFETs were realized using a CMOS compatible top-down approach [10] (Fig. 2). The uniaxial compressive strain leads to a significant reduction of the hole effective mass and an increase in the separation between light hole and heavy hole bands of GeSn compared to unstrained and biaxially compressive strained GeSn, which could enhance hole mobility. GeSn Tunneling FETs With increasing Sn content, the band gap of GeSn is reduced and GeSn becomes a direct band gap material. GeSn is therefore promising for the design of the tunneling junction in tunneling field-effect transistor (TFET) [11]-[12]. By incorporating Sn into Ge to shift the Г valley down and reduce the bandgap, GeSn TFETs with enhanced drive current and reduced subthreshold swing (SS) were demonstrated (Fig. 3). References [1] G. Han et al., IEDM Tech. Dig., 2011, pp. 402. [2] S. Gupta et al., IEDM Tech. Dig., 2011, pp. 398. [3] K. L. Low et al., J. Appl. Phys., vol. 112, 103715, 2012. [4] X. Gong et al., Symp. on VLSI Technology, 2012, pp. 99. [5] X. Gong et al., IEEE Trans. Elect. Dev., vol. 60, pp. 1640, 2013. [6] P. Guo et al., J. Appl. Phys., vol. 114, 044510, 2013. [7] X. Gong et al., IEEE Trans. Dev. Mat. Reliability, vol. 13, pp. 524, 2013. [8] P. Guo et al., submitted for publication. [9] X. Gong et al., IEEE Electron Device Lett., vol. 34, pp. 339, 2013. [10] X. Gong et al., Symp. on VLSI Technology, 2013, pp. T34. [11] Y. Yang et al., IEDM Tech. Dig., pp. 370. [12] Y. Yang et al., J. Appl. Phys., vol. 113, 194507, 2013.