350 keV Ar Ion Irradiation Induced Modifications of Cu-C70 Nanocomposite Thin Film
Malaviya National Institute of Technology, India
Metal based fullerene nanocomposite is an interesting area for the researchers due to their enhanced optical, electrical and mechanical properties in comparison to pure fullerene thin film. Fullerene, in the form of thin film, is itself a multi-application system and its application can be further enhanced by adding small amount of metal as nanoparticulates in it. The present study deals with the enhanced absorption of fullerene C70 on incorporating Cu nanoparticles into it due to plasmonic resonance. Cu-C70 nanocomposite thin films are synthesized by thermal co-deposition technique on glass and silicon substrates. These films are irradiated with 350 keV Ar ion beam at different fluences ranging from 1×1013 to 3×1016 ions/cm2 using ECR ion source based accelerator facility at Inter University Accelerator Centre New Delhi. The optical and structural studies on pristine and irradiated films have been performed using UV-visible absorption spectroscopy and Raman spectroscopy, respectively. Optical studies reveal that there is no signature of surface plasmon resonance band (SPR) in pristine Cu (10%)-C70 thin film which may be due to low concentration of Cu in fullerene C70 matrix. With increasing fluence of 350 keV Ar beam, signature of SPR band is clearly visible at ~ 627 nm for a dose of 1×1015 ions/cm2. With further increase in dose, SPR band is shifted to lower wavelength. At fluence 3×1016 ions/cm2, a blue shift of ~ 24 nm is obtained and a comparatively sharp SPR band is observed at ~ 603 nm. Raman spectroscopy on pristine and irradiated sample of Cu-C70 nanocomposites confirms the transformation of fullerene in amorphous carbon (a-C) at fluence 3×1014 ions/cm2. The blue shift of Cu nanoparticles in fullerene C70 matrix is explained in terms of Maxwell-Garnett Effective medium theory.
Cu-C70 Nanocomposite Thin Film: Synthesis, Characterization and Irradiation
Malaviya National Institute of Technology, India
Fullerene molecule has been very interesting material for researchers due to its potential applications that covers a wide range of areas including organic solar cells. Due to its excellent electron accepting nature, C60 and C70 has been widely used in polymer-fullerene bulk heterojunction organic solar cell in different configurations. In organic solar cells, among four most fundamental issues, the absorption of light comes on the priority. Higher the absorption of light in the active layer of the solar cell more is the probability of formation of excitons and will ultimately affect the efficiency of the cell. Another way to improve the efficiency of the solar cell is to incorporate metal nanoparticles in the active layer which will act as a strong source of energy due to its interesting localized surface plasmon resonance (SPR). In the present study, Cu nanoparticles are synthesized in fullerene C70 matrix in the form of thin film using thermal co-evaporation technique. Thin film is synthesized on different substrates such as glass, quartz, silicon, copper coated TEM grid for different types of characterizations. UV-visible absorption spectrum of pristine Cu-C70 nanocomposite thin film shows that the signature of SPR is absent in pristine film which may be attributed to the low concentration of Cu nanoparticles in C70 matrix. The deposited nanocomposite thin films are irradiated with 120 MeV Ag ion beam at the fluences of 1×1012, 3×1012, 6×1012, 1×1013 and 3×1013 ions/cm2 using Pelletron accelerator at IUAC, New Delhi. At fluence 3×1013 ions/cm2, the SPR band of Cu nanoparticles starts arising at ~ 672 nm. The position and width of the SPR peak is explained with the help of MAG theory and thermal spike model.
Effect of Implantation Temperature on the Blistering/Exfoliation in Hydrogen Implanted Ge for Potential Layer Transfer Applications
1Department of Physics, Indian Institute of Technology Delhi, India; 2Nanoscale Research Facility (NRF), Indian Institute of Technology, New Delhi, India
We investigate the effect of implantation temperature on the surface blistering/exfoliation of hydrogen (H) implanted Ge. Samples were implanted with H+ ions of energy 100 keV and fluence 1 × 1017 cm–2. The implantation was carried out at liquid nitrogen (LN2) temperature and room temperature (RT). H-implanted samples were subjected to annealing at different temperatures for studying the blistering kinetics. Various characterization techniques such as optical microscopy, atomic force microscopy (AFM), stylus profilometry and secondary ion mass spectroscopy have been used for studying the samples. Surface blistering has not been observed in the as-implanted state. Post-implantation annealing between 300 and 450 °C for 30 min showed the formation of surface blisters and craters. The lateral size and height of the blisters varied from 4 to 25 µm and 20 to 300 nm, respectively. For the annealing at 500 °C for 30 min, large surface area exfoliation was observed in both cases. However, large surface area exfoliation was found to be more in the sample implanted at RT. In both cases, the depth of the exfoliated region, which corresponds to the thickness of the transferred layer, was measured about 695 nm using AFM sectional analysis. The root mean square (RMS) surface roughness for the exfoliated region varied with the implantation temperature. Measurements showed that for the scan area of 10 × 10 µm2, the RMS value of the exfoliated region was about 22 and 30 nm, respectively, for the implantation at LN2 temperature and RT. This study is useful in understanding the surface blistering/exfoliation process in H-implanted Ge for layer transfer applications.
Electrical Studies of a Highly Modulated Zinc Oxide Using a Hybrid Atomic Layer Deposition Process
Nano Research Group, Electronics and Computer Science, University of Southampton, United Kingdom
Atomic layer deposition (ALD) has been established as an excellent method for achieving high-quality, uniform and conformal layer. Zinc Oxide (ZnO) is one of the most popular oxides that can be produced by ALD with a range of precursors available. Both thermal-ALD and plasma-enhanced ALD processes are available for ZnO deposition in which water vapour and oxygen plasma are used as oxidants, respectively. Commonly, properties of undoped-ZnO film are modulated in thermal-ALD process by varying the growth temperature. These films tend to have high carrier concentration. Tuning of electrical properties through other parameters in ALD is rarely reported with the exception in Thomas et al work, a highly tunable ZnO with resistivity spanning across six orders magnitude is obtained using a plasma-enhanced thermal ALD (PET-ALD) ZnO process. Another recent study have also reported the capability of tuning ZnO using a single plasma-enhanced ALD (PE-ALD) process which allows the modulation of its resistivity and carrier concentration up to 3 orders by varying the oxygen plasma time.
In this work, a hybrid ALD process for the modulation of material properties in undoped ZnO is proposed. By combining the thermal ALD and PE-ALD techniques, it allows a wide and yet refined tuning of the ZnO film resistivity and carrier density by adjusting either the plasma condition or the thermal process cycles. The doping mechanism of this process and its effect on the Fermi level of the deposition ZnO thin films are also studied using Hall measurement, X-ray photoelectron spectroscopy and Kelvin probe force microscopy.
 Tynell, T. & Karppinen, Semicond. Sci. Technol. 29, 43001(2014).
 Godlewski, M. et al., Microelectron. Eng. 85, 2434–2438(2008).
 Thomas, M. A. & Cui, J. B., ACS Appl. Mater. Interfaces 4, 3122–8(2012).
 Huang, R. et al., Microelectron. Eng. 161, 7–12(2016).
Electron Beam Lithography using AZ5214E Photoresist for Plasmonic Applications
Nanyang Technological University, Singapore
Plasmonic nanostructures and nanogaps have gained much attention for their ability for strong light confinement at metal-dielectric interfaces that results in a wide range of applications. However, metal nanostructures and nanogaps are typically fabricated in two different platforms due to the challenges associated with their geometry. The former is realized by metal lift-off pattern transfer from electron beam patterns, while the latter is by ion milling of thin metal films. The fabrication of plasmonic structures based on nanogaps by electron beam lithography (EBL) has proved challenging due to the large patterning area and the need for optimizing the sidewall angle necessary for successful lift-off pattern transfer, thus resulting in high exposure dose and long writing time. We propose an electron beam lithography process based on a widely-used UV photoresist AZ5214E which serves as a flexible platform for realizing metal nanostructures and nanogaps. By combining ultraviolet and e-beam radiation, we show that this EBL process can work in positive-tone, negative-tone, and image-reversal tone. We present the submicron patterning capability of this process in the image-reversal mode based on an exposure dose much lower than the typical dose for negative e-beam resist. We show the achievable resolution of 300 nm, which is much higher than the 2-μm resolution of the same resist based on UV exposure. Finally, we demonstrate high aspect ratio patterns with 60 nm feature width and 300 nm thickness, and the fabrication of gold nanoslots with 60 nm gap width and 120 nm gold thickness when combined with gold electroplating.
GeSn Alloy Fabricated by Magnetron Sputtering
Nanyang Technological University, Singapore
GexSn1-x is one of the most promising materials in optoelectronics for its direct band-gap nature. Ge has a pseudo-direct band-gap material for its direct gap being slightly larger than its indirect gap. By alloying with Sn atoms, it can be tuned into direct band-gap material. The characteristic wavelength can cover from close-infrared to mid-infrared which is hardly achieved by mainstream direct band-gap materials. In this paper, we report GeSn alloy fabricated by a multi-target magnetron sputtering system. It is found that the electrical and optical properties of the alloy are sensitive to the preparation conditions as well as the composition. By optimizing the growth conditions, high quality GeSn alloy are obtained.
InAsSb grown by MOCVD
Nanyang Technological University, Singapore
We report high quality InAsSb films grown on Ge substrates with a GaAs intermediate layer via metal-organic chemical vapor deposition. The properties of the grown InAsSb films are systematically analysed. It is found that the grown InAsSb films by this method have high quality with very smooth, mirror-like morphology, and high optical quality. In particular, strong PL peak at around 3550 nm can be observed even at room temperature, which demonstrates the capabilities of the grown InAsSb films for room temperature MIR optoelectronic application. This work provides a simple and feasible strategy for the growth of high quality InAsSb films on Ge substrate.
InSb Nanowires Hetero-epitaxially Grown on GaAs, Si Substrate by MOCVD
Nanyang Technological University, Singapore
It is significant for InSb being integrated successfully into other material systems like GaAs, However, the quite large lattice mismatch of InSb to GaAs (14.6%) poses a big challenge for high crystalline quality hetero-epitaxy of InSb on GaAs. A way of addressing the misfit issue is to synthesize InSb in one-dimensional nanowire (NW) instead of thin films. In this work, InSb NWs have been synthesized hetero-epitaxially on GaAs, Si substrate. The effects of growth conditions on the InSb NWs on GaAs, Si substrates have been studied carefully. A dependency of InSb NWs on GaAs could be observed on both growth temperature and V/III ratio. For the growth of InSb NWs on Si substrate, the window in term of temperature is quite narrow. The InSb nanowires obtained on Si substrate has an interesting structure of diameter-modulated (DM), which has never been observed in previous reports. The disturbance of the vapor concentration (In, Sb) during the growth was attributed to the formation of the diameter-modulated (DM) InSb nanowires.
Ion Irradiation Induced SPR of Au Nanoparticles in Carbon
1Department of Physics, Malaviya National Institute of Technology, India; 2Department of Physics, National Institute of Technology (NIT), Rourkela, India
Nanocomposite thin films are of interest because they combine not only the properties of two materials but also provide the possibility of generation of new novel properties. Since one material is having atleast one dimension in nano meter regime, it gives the advantages of nanomaterials also. The optical and structural properties of these nanocomposite thin films can be tailored using energetic ion irradiation technique. With the help of swift heavy ion irradiation, nanosized ion tracks can be created into the target material and within these tracks, materials is modified due to the generation of very high temperature. In the present work, nanoparticles of gold in carbon matrix are synthesized by co-sputtering of gold and graphite in high vacuum chamber using neutral Ar atom beam. Films are deposited on glass substrate, Si and TEM grids. These films are irradiated with 120 MeV Au ions at different fluences 1×1012, 5×1012, 1×1013 and 3×1013 ions/cm2 using Pelletron accelerator. The Au nanoparticles are found to be too small (1.5 ± 0.01 nm) to excite the plasmon resonance in the pristine film. With ion irradiation, a clear but broad SPR peak is seen at ~ 526 nm for the film irradiated at a fluence of 1×1013 ions/cm2, which is slightly red shifted to ~ 529 nm at a fluence of 3×1013 ions/cm2 with a broader width. The red shift is ascribed to the growth of the particles due to enhanced diffusion and ostwald ripening. The average particle size at 3×1013 ions/cm2 fluence is found to be 2.1 ± 0.03 nm.
 R. Singhal, D.C. Agarwal, Y.K. Mishra, F. Singh, J.C. Pivin, R. Chandra, D. K. Avasthi, J. Phys. D: Appl. Phys. 42, 155103 (2009).
 U. Kreibig, M. Vollmer, Optical properties of metal clusters. Springer Series in Materials Science, Springer, Berlin, vol. 25 (1995).
KdotPsoft: Modelling and Simulation of Semiconductors and Device Physics
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore
Semiconductor quantum wells (QWs) are heterostructures in which a thin well layer of a lower bandgap material is sandwiched between two barrier layers of higher bandgap material. The well layer which is typically around 5 – 20 nm thick induces quantum confinement effect only in one dimension, whereas the movement in the other dimensions is unrestricted. This profoundly affects the density-of-states (DOS) of QWs and determines its electronic structure. Currently, they form an area of great scientific research interest, due to wide variety of potential applications in electronic and photonic devices. In this work, we introduce a new platform, KdotPsoft, to simulate such semiconductor QWs. The core machinery of our simulator is based on the 10 band k·p perturbation theory model. It takes into consideration the strain induced in the QW, which can modify the electronic states and degeneracy. Having accounted for these effects, it can calculate the energy eigenvalues for any QW combination composed of III-V, II-VI or group IV materials or alloys thereof. It is even capable of simulating the effect of dilute nitride and bismide doping in conventional III-V materials, which has been of increasing research interest recently. KdotPsoft also gives the flexibility of simplifying the 10-band model to 8-band, 6-band and 4-band models by adjusting the nitrogen level, Kane matrix element, and spin-orbit splitting energy respectively. It can be used to comprehensively study the band lineups, energy dispersion relation, DOS, polarization-dependent transition matrix element strengths, optical gain/absorption spectra, spontaneous emission rate, radiative current density, electric field effects on the QW, etc. KdotPsoft is an ideal platform to model and study semiconductors and device physics applications, such as multiple quantum wells (MQW), quantum cascaded lasers (QCL), vertical-cavity surface-emitting laser (VCSEL), etc. As a demonstration, we will show the results for some III-V and II-VI QWs.
Silicon Dioxide Capping Effects on Polypeptide Assisted Gold Nanocrystal Memory
1National University of Kaohsiung, Taiwan; 2National Cheng Kung University, Taiwan
A nanocrystal memory embedded with gold nanoparticles (Au NPs) has been successfully fabricated by a spin-coating-derived chemical solution process. We use bio-compatible Poly-L-Lysine (PLL) and Poly-L-Glutamic (PLGA) as medium to synthesize Au NPs. These two polypeptides provide dual function: (1) to provide a function group to synthesize Au NPs, and (2) to offer a site for fixing the NPs firmly. HfO2 oxide and Al electrode were then deposited in sequence on Au NPs embedded samples to construct the nanocrystal memory structure. However, keeping NPs nano-size and high density during device process is significant for high-performance application; therefore stability of Au NPs is an important issue.
To improve the stability of NPs, the Au NPs embedded samples was covered by SiO2 capping layer by dipping into the SiO2 precursor solution. In this study, two kinds of SiO2 precursors: (1) (3-Aminopropyl)trimethoxysilane (APTMS), and (2) Tetraethyl orthosilicate (TEOS) were used for forming capping layer. Both organic precursors could react with polypeptides to produce SiO2. However, their different reaction mechanism led to distinct structures, thereby affecting the electrical properties. As compared to the TEOS-mediated SiO2, the APTMS-mediated SiO2 was fabricated directly on the surface of GNPs, exhibiting more ability to suppress aggregation and growth of NPs. The Scanning Electron Microscope (SEM) analysis demonstrated that GNPs with high density and good uniformity was formed under the well-controlled process. Capacitance-voltage(C-V) measurements indicated memory performance has been significantly improved by the incorporation of capping layer.
Theoretical Model of GexSn1-x/Ge Quantum Well with Build-in Compressive Strain
Nanyang Technological University, Singapore
We developed a theoretical model based on 8-band k.p method to calculate the temperature-dependent band structure of GexSn1-x/Ge quantum well. The E-k dispersion relation is calculated using two different sets of Luttinger-Kohn’s Hamiltonian effective mass parameters. The spontaneous emission rate spectra including and excluding the contribution of indirect L subbands are compared. Instead of the expected direct band-gap energy transition, we observe indirect band-gap energy transitions which are verified by having abnormal temperature-dependent spontaneous emission rate even for large Sn fraction up to 24%. This phenomenon can be explained by the effect of quantum restriction and build-in compressive strain through our model which are the main obstacles for realizing direct band-gap GeSn/Ge quantum well.
Lattice Displacement and Electrical Property of Li-ion Implanted GaN Single Crystal
1Hosei University, Japan; 2Osaka Kyoiku University, Japan
Li shows donor or acceptor-like behavior in most compound semiconductors. In Li-ion implanted GaN, Li mainly occupies interstitial sites in the center of the c-axis hexagons below 700 K . In the present study, Ga and N lattice displacements in Li-ion implanted GaN were evaluated by Rutherford backscattering using proton beam. Li-ion implantation into GaN single crystal wafer was performed with energies of 50 keV ( ion fluence ; 2 x 1014 cm-2) , 80 keV (3 x 1014 cm-2) and 120 keV (5 x 1014 cm-2) at room temperature. The aligned spectra were obtained from scattering along the <0001> channeling directions. The number of displaced Ga and N atoms estimated from χmin (the ratio between aligned and random) were 8.8 × 1020 cm-3 and 4.3 × 1021 cm-3, respectively. The displacement concentration of N atoms is larger than that of Ga atoms. This suggests that N interstitial (Ni) relating to the displacement of N atoms is introduced in Li-ion implanted GaN. This result is similar to that of the neutron irradiated GaN . The sheet resistance was 2.6 x 102 W/sq. for un-implanted samples and 1.3 x 103 W/sq. for Li-ion implanted ones. Since Ni atoms form the deep acceptor level at 960 meV below the bottom of the conduction band , the origin of the high resistivity after the Li-ion implantation would be mainly attributed to the carrier compensation effect due to the deep level of Ni. The resistance decreased to 1.1 x 102 W/sq. by annealing at 973 K for 20 min in N2 flow, suggesting the recovery of the implantation induced defects.
 M. Daimer, et al. J. Appl. Phys. 84, 3085 (1998).
 T. Nakamura, K. Kamioka, K. Kuriyama, K. Kushida, Solid State Commun. 205, 1(2015).
Influence of pH Value on the Functional Amine Molecular Assisted Synthesis of Gold Nanoparticles
National University of Kaohsiung, Taiwan
Nanometer scaled particles can be obtained by the Turkevich method or Brust method through reducing or aggregating precursors, but having problems about complex process and organic residue. In this work, we used 3-aminopropy-trimethoxysilane (APTMS) to reduce Au nanoparticles (Au NPs) on substrate. The APTMS was spin coated on the substrates by the self-assembly monolayer (SAM) process. Then the substrates were immersed into an aqueous of chloroauric acid for several hours. After the substrates have been annealed, Au NPs with high coverage density were fabricated on substrates.
Au NPs can be produced on an APTMS-assembled substrate by the reaction of the amine group of the APTMS molecules and the gold complex ions of the chloroauric acid under a well-controlled solution process. The reaction highly depended on the pH values of solution, having different influences on the characteristics of the amine group and the gold complex ions. As compared to high and low pH environment, the APTMS substrate at pH value near neutral adsorbed a larger amount of gold ions with partly precipitated Au NPs. The gold ions completely transformed to Au NPs after annealing, leading to a good uniformity and high dispersion density of Au NPs on substrate. The formation mechanism of Au NPs was discussed in terms of solution pH value in this present study.