Fall Meeting Hudson Mohawk Chapter of the AVS Oct. 6, … · Fall Meeting Hudson Mohawk Chapter of...

Fall Meeting Hudson Mohawk Chapter of the AVS Oct. 6, 2014

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Rensselaer Polytechnic Institute Russell Sage Dining Hall

Troy, NY 12180

AGENDA

2:00 PM Reception and Refreshments 2:20 PM Welcome, David Jung, Aramco Services Company

National AVS Update, Vin Smentkowski, GE Chapter Election

2:45 PM Oral Presentations 4:45 PM Poster Presentations and Dinner 6:45 PM Best Poster and Oral Presentation Awards

and Brief Chapter Update 7:00 PM Adjourn 7:00 PM Brief meeting of Chapter Board Members


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ORAL PRESENTATIONS 1. ELECTRON TRANSPORT AND INELASTIC ELECTRON TUNNELING SPECTROSCOPY OF PORPHYRIN IN

A MOLECULAR JUNCTION Teresa A. Esposito1, Alexandra Krawicz2, Peter H. Dinolfo2, Kim Lewis1 1Department of Physics, Applied Physics, and Astronomy 2Department of Chemistry and Chemical Biology Rensselaer Polytechnic Institute, Troy NY 12180

2. EFFECTS OF CHLORINE AND SULFUR DOPING ON THE THERMOELECTRIC POWER FACTOR IN

NANOSTRUCTURED BISMUTH TELLURIDE Devender†, Rutvik J. Mehta†, Vincent Smentkowski+, Theodorian Borca-Tasciuc#, Ganpati Ramanath† †Department of Materials Science and Engineering, and #Department of Mechanical Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180. +General Electric Global Research Center, Niskayuna, NY 12309.

3. OPTICAL METROLOGY FOR DSA PATTERNING USING MMSE BASED SCATTEROMETRY

D. Dixit and A. C. Diebold SUNY College of Nanoscale Science and Engineering, Albany, NY 12203

4. LOW PRESSURE CHEMICAL VAPOR DEPOSITION SYNTHESIS OF CHALCOGENIDE NANOSTRUCTURES

Robin Jacobs-Gedrim, Fan Yang, Mariyappan Shanmugam, Nikhil Jain, Eui Sang Song and Bin Yu SUNY College of Nanoscale Science and Engineering, Albany, NY 12203

5. INFLUENCE OF SUBSTRATE ORIENTATION ON THE GROWTH OF GRAPHENE ON Cu SINGLE CRYSTAL

SURFACES Tyler R. Mowll, Zachary R. Robinson, Parul Tyagi, Eng Wen Ong, Carl A. Ventrice, Jr. SUNY College of Nanoscale Science and Engineering, Albany, NY 12203

6. TEMPERATURE DEPENDENT ELECTRON TRANSPORT IN EPITAXIAL COPPER THIN FILMS

Y. Timalsina, A. Horning, K. M. Lewis, and T.-M. Lu Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th

Street, Troy, NY 12180


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ORAL PRESENTATION ABSTRACTS

ELECTRON TRANSPORT AND INELASTIC ELECTRON TUNNELING SPECTROSCOPY OF PORPHYRIN IN A MOLECULAR JUNCTION

Teresa A. Esposito1, Alexandra Krawicz2, Peter H. Dinolfo2, Kim Lewis1

1Department of Physics, Applied Physics, and Astronomy 2Department of Chemistry and Chemical Biology Rensselaer Polytechnic Institute, Troy NY 12180

Organometallic molecules, such as porphyrin, are being investigated as circuit elements for organic electronics. Porphyrins are highly conjugated aromatic molecules that have shown electronic properties that exhibit high and low conductance states. These conductance states may be related to conformational changes in the molecule. To investigate these conductance states we plan to perform inelastic electron tunneling (IET) spectroscopy of porphyrin molecules in an electromigrated nanogap. IET spectroscopy is an important technique in determining the vibrational modes of a molecule adsorbed to a metal oxide and is found by identifying peaks in the second derivative of the junction characteristics (d2I/dV2). We form nanogaps via electromigration of a 30 × 100 nm gold wire, producing gaps of ~2-3 nm, which is approximately the length of a porphyrin molecule. Each end of the porphyrin molecule is functionalized with a thiol group (-SH) which will covalently bond to the gold, forming a molecular junction. We simultaneously measure I-V, dI/dV, d2I/dV2 of the junction at 4.2 K and 300 K. Figure 1 shows 5,15-di-4(S-acetylphenyl)-10,20-diphenyl porphyrin in an electromigrated nanogap. This molecule can be functionalized further by adding a metal ion in the center.

Figure 1. A schematic of a broken nanowire shown with 5,15-di-4(S-acetylphenyl)-10,20-diphenyl

porphyrin in the nanogap. The nanowire is 30 × 100 nm and the gap is approximately 2-3 nm in width.


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EFFECTS OF CHLORINE AND SULFUR DOPING ON THE THERMOELECTRIC POWER FACTOR IN NANOSTRUCTURED BISMUTH TELLURIDE

Devender†, Rutvik J. Mehta†, Vincent Smentkowski+, Theodorian Borca-Tasciuc#, Ganpati Ramanath†

†Department of Materials Science and Engineering, and #Department of Mechanical Aerospace and

Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180. +General Electric Global Research Center, Niskayuna, NY 12309.

Introducing sub-atomic percent dopants such as sulfur into pnictogen chalcogenides is attractive to obtain a high thermoelectric power factor.1,2 Here, we show that parts per million chlorine can confound the effect of sulfur doping on the power factor even though both dopants are electron donors. Hall measurements reveal that pellets with 400 to 1000 ppm Cl doping exhibit 10-fold higher electron concentrations than n=1-5×1018 cm-3 obtained with a similar sulfur level without chlorine, indicating that chlorine is a stronger donor. Eliminating chlorine leads to the surprising trend of increase in both the

2.5×104 -1m-1 -230 µVK-1 at 750 ppm sulfur doping. X-ray absorption spectroscopy reveals that sulfur substitutes Bi at 6c sites and Cl occupies the 3a interstitial sites, providing different mechanisms of altering the electronic band structure, and hence, properties. To further our understanding of effect of Sulfur on electronic band structure, we carried out electrical transport and thermoelectric properties measurements on single nanoflake of pnictogen chalcogenides. Our analysis reveals that unlike conventional dopants, Sulfur affects the density of states near the Fermi energy in pnictogen chalcogenides. Our results thus show that the controlled use of more than one dopant of the same type

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figure-of-merit thermoelectric materials. References 1. Mehta, R. J.; Zhang, Y. L.; Zhu, H.; Parker, D. S.; Belley, M.; Singh, D. J.; Ramprasad, R.; Borca-

Tasciuc, T.; Ramanath, G. Nano Letters 2012, 12, 4523-4529. 2. Mehta, R. J.; Zhang, Y. L.; Karthik, C.; Singh, B.; Siegel, R. W.; Borca-Tasciuc, T.; Ramanath, G. Nature

Materials 2012, 11, 233-240.


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OPTICAL METROLOGY FOR DSA PATTERNING USING MMSE BASED SCATTEROMETRY

D. Dixita, A. C. Diebolda

aSUNY College of Nanoscale science and Engineering

Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. In the coming years, DSA integration could be a standard complementary step with other lithographic techniques for nano patterning but one of the most critical challenges for translating it into high volume manufacturing is to achieve low defect density and high stability. The defect inspection capability is fundamental to defect reduction in DSA process, as it provides process engineers with information on the numbers and types of defects and consequently optimize materials and process parameters. Optical scatterometry is a fast, accurate, non-destructive and diffraction based optical metrology technique used to extract important feature dimensions like line-width, line-shape, and sidewall-angle (SWA) of the complex periodic grating structure. Mueller matrix spectroscopic ellipsometry (MMSE) based scatterometry is used to optically characterize Polystyrene-b-Polymethylmethacrylate (PS-b-PMMA) patterns (un-etched-Fig. 1) and PS line space patterns (etched-Fig. 2) fabricated with DSA patterning. A regression-based (inverse-problem) scatterometry approach is used to calculate the line-width, line-shape, sidewall-angle, and thickness of these DSA structures. In addition, anisotropy and depolarization calculations are used to determine the sensitivity of MMSE to DSA pattern defectivity. As pattern order decreases, the mean squared error (MSE) value increases, depolarization value increases, and anisotropy value decreases. These specific trends are used in the current work as a method to judge the degree of alignment of the DSA line-space patterns across the wafer. Acknowledgements: We acknowledge funding from SRC. We are thankful to Erik Hosler, Richard Farrell, Vimal Kamineni, and Moshe Preil of GLOBALFOUNDRIES for providing us the samples and mentoring this project. We also gratefully acknowledge Joe Race and Brennan Peterson from Nanometrics Inc. for the help in scatterometry modeling and analysis.

84nm

28nm 14nm

13nm 7nm

32nm

84nm

28nm 14nm

13nm

7nm

23 nm 6nm

Fig. 1 Final profile of the scatterometry model for 3xLo un-etched sample.

Fig. 2 Final profile of the scatterometry model for 3xLo etched sample.


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Low Pressure Chemical Vapor Deposition Synthesis of Chalcogenide Nanostructures

Robin Jacobs-Gedrim, Fan Yang, Mariyappan Shanmugam, Nikhil Jain, Eui Sang Song and Bin Yu

College of Nanoscale Science & Engineering, SUNY Albany, Albany, NY. The synthesis of low-dimensional III-VI and V-VI chalcogenide nanostructures are demonstrated using a low pressure chemical vapor deposition (LPCVD) approach. Control of the nanomaterial dimensions to ultra-small size scales, beyond what has previously been reported, can be achieved in both the formation of nanowires through the vapor-liquid-solid (VLS) mechanism and the formation of nanoplates through the vapor-solid (VS) mechanism. The LPCVD process conditions, source materials, and specific catalysts / substrates, which promote the growth of the nanostructures are detailed. The chemical and nanoscale properties of these unique nanostructures are investigated with SEM, AFM, HRTEM/STEM, XPS, and Electronic Transport measurements. The LPCVD synthesized nanostructures are shown to have application in energy harvesting / storage and computer logic / memory applications.


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INFLUENCE OF SUBSTRATE ORIENTATION ON THE GROWTH OF GRAPHENE ON Cu SINGLE CRYSTAL SURFACES

Tyler R. Mowll, Zachary R. Robinson, Parul Tyagi, Eng Wen Ong, Carl A. Ventrice, Jr.

SUNY College of Nanoscale Science and Engineering

Albany, New York 12203

A systematic study of graphene growth on on-axis Cu(100) and Cu(111) single crystals oriented within 0.1° from the surface normal and a vicinal Cu(111) crystal oriented 5° off-axis has been performed. Initial attempts to grow graphene by heating each crystal to 900°C in UHV, followed by backfilling the chamber with C2H4 at pressures up to 5x10-3 torr did not result in graphene formation on either the on-axis Cu(100) or on-axis Cu(111) surfaces. For the vicinal Cu(111) surface, epitaxial graphene was formed under the same growth conditions. By backfilling the chamber with C2H4 before heating to the growth temperature, epitaxial graphene was formed on both the on-axis Cu(100) and off-axis Cu(111) surfaces, but not the on-axis Cu(111) surface. By using an argon overpressure, epitaxial overlayers could be achieved on all three Cu substrates. These results indicate that the most catalytically active sites for the dissociation of ethylene are the step edges, followed by the Cu(100) terraces sites and the Cu(111) terrace sites. The need for an argon overpressure to form graphene the on-axis Cu(111) surface indicates that the Cu sublimation rate is higher than the graphene growth rate for this surface. This research was supported by NSF (DMR-1006411)

a)

b)

Figure 1: LEED images for growth of graphene by backfilling the UHV chamber with 5 mTorr of C2H4 and 45 mTorr of Ar then heating to 900 °C. Growth was done on a) an on-axis Cu(100) substrate where a two-domain epitaxy is observed (red and blue circles), b) an on-axis Cu(111) substrate with a predominantly single-domain epitaxy (red circle), and c) an off-axis Cu(111) substrate with a predominantly single-domain epitaxy (red circle) with some second domain growth (white circle).

c)


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TEMPERATURE DEPENDENT ELECTRON TRANSPORT IN EPITAXIAL COPPER THIN FILMS

Y. Timalsina, A. Horning, K. M. Lewis, and T.-M. Lu

Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY

Electrical resistivity in metals arises mainly from electron scattering by lattice vibrations called phonons. Electrons are also scattered from the surface and grain boundaries of the material but these scattering processes do not contribute substantially to resistivity in bulk metals. In thin metal films, however, the effects of surface and grain boundary scattering become significant when the thickness of the film is reduced below the mean free path of the conduction electrons.1 For example, a dramatic increase in resistivity is observed in copper (Cu) films less than 50 nm thick (comparable to the mean free path of electrons in Cu).2 Therefore, it is necessary to examine the contributions of distinct scattering sources and their collective effect on the resistivity of thin Cu films to develop a thorough understanding of basic electron transport in thin films. Temperature dependent resistivity measurement down to cryogenic temperature, e.g., 5 K, is seen as a reliable approach for studying the influence of various scattering mechanisms in ultrathin metal films. We, herein, report temperature dependent electrical resistivity of epitaxial copper thin films between 5 and 500 nm thick measured over a wide range of temperatures (5 – 300 K) using the Van der Pauw contact method. We demonstrate that the resistivity is well described by incorporating an enhanced el-ph coupling in the Bloch-Gruneisen formula, which is an approximate solution of the Bloch-Boltzmann equation. We observe that there is an increase in el-ph coupling as the film thickness decreases and that the values of the el-ph coupling constant are in good agreement with previously reported experimental values.3

1Lacy, Nanoscale Research Letters, 2011, 6:636. 2Hanaoka, Y. et al, Materials Transactions, vol. 43, No. 7 (2002) pp. 1621-1623. 3Timalsina, Y. P. et al, Applied Physics Letters, 103, 191602 (2013).


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POSTER PRESENTATIONS

TAILORING ELECTRICAL CONTACT RESISTIVITY AT METAL-THERMOELECTRIC INTERFACES USING A MOLECULAR NANOLAYER Thomas Cardinal1, Devender1, Theo Borca-Tasciuc2, Ganpati Ramanath1* 1Department of Materials Science and Engineering and 2Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY. METAL ENHANCED Ge1-xSnx ALLOY FILM GROWTH ON GLASS SUBSTRATES USING BIAXIAL CaF2 BUFFER LAYER* J. K. Dash, L. Chen, T.-M. Lu, G.-C. Wang, L.H. Zhang+ and K. Kisslinger+ Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, and +Brookhaven National Lab Center for Functional Nanomaterials, Upton, NY. MODELING THE THERMOELECTRIC FIGURE OF MERIT OF NANOBULK Bi2Te3 AS A FUNCTION OF DOPING, POROSITY, AND GRAIN STRUCTURE

Andrew Gaul, Devender, Rutvik Mehta, Ganpati Ramanath, Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute, Troy, NY. ADVANCED METROLOGY METHODS FOR CHARACTERIZATION OF GRAPHENE AND SPIN DEVICE MATERIALS Avery Green1, Tuan Vo2, George Orji3, Alain Diebold1 1SUNY College of Nanoscale Science and Engineering, 257 Fuller Rd, Albany, NY and 2IBM, 257 Fuller Road, Albany, NY, and 3National Institute of Standards and Technology, Gaithersburg, MD. Workfunction tuning at the Au-HfO2 interface using organophosphonate nanolayers Matthew Kwan and Ganpati Ramanath Rensselaer Polytechnic Institute, Materials Science and Engineering Department, Troy, NY. INFLUENCE OF CHEMISORBED OXYGEN ON THE GROWTH OF GRAPHENE ON Cu(100) AND Cu(111) BY CHEMICAL VAPOR DEPOSITION Eng Wen Ong1, Zachary R. Robinson1,2, Tyler R. Mowll1, Parul Tyagi1, Seamus Murray3, Heike Geisler3, and Carl A. Ventrice, Jr.1 1SUNY College of Nanoscale Science and Engineering, Albany, NY 12203, 2U.S. Naval Research Laboratory, Washington, DC, and 3Department of Chemistry, SUNY College at Oneonta, Oneonta, NY. In-situ Ar Plasma Cleaning of Samples Prior to Surface Analysis Vincent S. Smentkowski,1 Hong Piao,1 and C.A. Moore2 1General Electric Global Research Center, Niskayuna, NY, and 2XEI Scientific, Inc., Redwood City, CA. CVD GROWTH OF MONOLAYER MoS2 Eui Sang Song, Mariyappan Shanmugam, Nikhil Jain, Fan Yang, Robin Jacobs-Gedrim and Bin Yu College of Nanoscale Science and Engineering, State University of New York, Albany, NY. CHARACTERIZATION OF IRON PORPHYRIN (FeP) MOLECULAR CONDUCTANCE BY STM MOLECULAR BREAK JUNCTION METHOD Qi Zhou and Kim M. Lewis, Rensselaer Polytechnic Institute, Troy, NY.


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POSTER PRESENTATION ABSTRACTS

TAILORING ELECTRICAL CONTACT RESISTIVITY AT METAL-THERMOELECTRIC INTERFACES USING A MOLECULAR NANOLAYER

Thomas Cardinal1, Devender1, Theo Borca-Tasciuc2, Ganpati Ramanath1*

1Department of Materials Science and Engineering and 2Department of Mechanical, Aerospace

and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY.

Tailoring the electrical contact properties of metal-thermoelectric materials interfaces is crucial for realizing high efficiency energy devices involving solid-state refrigeration and waste heat recovery. Here, we show that introducing an octanedithiol nanolayer at Cu/Bi2Te3 interfaces decreases electrical contact resistivity from ρc = 260 ± 42 μΩcm2 to ρc = 36 ± 19 μΩcm2. In contrast, introducing the nanolayer at Ni/Bi2Te3 interfaces increased the contact resistivity from ρc = 42 ± 2 μΩcm2 to ρc = 82 ± 21 μΩcm2. Additionally, Rutherford Backscatter spectroscopy shows that the nanolayer not only inhibits interdiffusion at Cu/Bi2Te3 interfaces but also suppresses interfacial Cu2Te phase formation. X-ray photoelectron spectroscopy showing that octanedithiol binds more readily with Cu than Ni suggests that nanolayer-induced interface bond strengthening is a major contributor to the observed property enhancements. These findings would be important for designing metal-contacts for device applications.


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METAL ENHANCED Ge1-xSnx ALLOY FILM GROWTH ON GLASS SUBSTRATES

USING BIAXIAL CaF2 BUFFER LAYER*

J. K. Dash, L. Chen, T.-M. Lu, G.-C. Wang, L.H. Zhang+ and K. Kisslinger+

Department of Physics, Applied Physics and Astronomy Rensselaer Polytechnic Institute, Troy, NY 12180, USA

+Brookhaven National Lab, Center for Functional Nanomaterials, Upton, NY

Ge1-xSnx alloy films are an attractive candidate for silicon based optoelectronic devices. In this work, Ge1-

xSnx(111) alloyed films were grown on glass substrates by sequential physical vapor deposition of a biaxial CaF2 buffer layer and a Sn heteroepitaxial layer at room temperature, followed by a Ge layer grown at low temperatures (200 - 350 oC). The predeposited Sn on the CaF2 layer enhances the Ge diffusion and crystallization. The Sn substitutes into the Ge lattice to form a biaxial Ge1-xSnx alloyed film. See schematics below for the evolution of growth. The epitaxy relationships were obtained from x-ray pole figures from the samples with Ge1-xSnx < ̅ >// CaF2< ̅ > and Ge1-xSnx < ̅ >// CaF2< ̅ >. The crystallization and biaxial texture formation start at about 200 oC with the best biaxial Ge1-xSnx film grown at about 300 oC, which is 100 oC lower than the growth temperature of biaxial pure Ge film without Sn on the CaF2/glass substrate. The microstructure, texture and Sn concentration of the Ge1-xSnx films were characterized by x-ray diffraction, x-ray pole figure analysis, and transmission electron microscopy. The spatial chemical composition of Sn in Ge1-xSnx was measured by energy dispersive x-ray spectroscopy and was found to be nearly uniform throughout the thickness of the alloyed film. Raman spectra show shifts of Ge-Ge, Ge-Sn, and Sn-Sn vibration modes due to the percentage change of substitutional Sn in Ge as a function of growth temperature. This growth method is an alternative cost effective way to grow biaxial semiconductor films on amorphous substrates [CrystEngComm., in press]. *Work supported by NSF DMR-1104786, NY State Foundation of Science, Technology and Innovation (NYSTAR) through Focus Center-New York. TEM study was carried out in whole at the Center for Functional Nanomaterials, Brookhaven National Laboratory, operated by the U.S. Department of Energy, Office of Basic Sciences, under contract no. DE-AC02-98CH10886.

[111]

(a)Initial stage

glass

CaF2

nanorods

CaF2 cap

GeSn

(b)Later stage

glass

CaF2

nanorods

CaF2 cap

Ge1-xSnx

Sn atomGe atom


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MODELING THE THERMOELECTRIC FIGURE OF MERIT OF NANOBULK Bi2Te3 AS A FUNCTION OF DOPING, POROSITY, AND GRAIN STRUCTURE

Andrew Gaul, Devender, Rutvik Mehta, Ganpati Ramanath, Theodorian Borca-Tasciuc

Rensselaer Polytechnic Institute

Designing thermoelectric materials with a high figure of merit ZT is a challenge because it requires

-stimulated wet-chemical synthesis techniques have allowed the production of a new class of sulfur doped, nanostructured bulk n-type Bi2Te3. We used Boltzmann transport equation to understand and optimize both the thermal and electronic transport properties of nanobulk materials to obtain insights into strategies for maximizing ZT. By modeling scattering due to nanostructuring and doping we are able to explain the transport properties in single crystal Bi2Te3 as well as nanobulk Bi2Te3. Our results show that density > 95%, ~60 nm grain size, and 600 ppm sulfur impurities can yield a 50% higher ZT of ~0.6 than the single-crystal. We will also present preliminary results on the effect of sulfur on the charge carrier concentration and its consequent effect

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unfavorably coupled electrical and thermal properties to realize high ZT nanomaterials.


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ADVANCED METROLOGY METHODS FOR CHARACTERIZATION OF GRAPHENE AND SPIN DEVICE MATERIALS

Avery Green1, Tuan Vo2, George Orji3, Alain Diebold1

1SUNY College of Nanoscale Science and Engineering, Albany, NY, 2IBM, 257 Fuller Road, Albany, NY, and 3National Institute of Standards and Technology, Gaithersburg, MD

The realization of usable two-dimensional and complex magnetic materials has emphasized the need for advanced methods of characterization at the macroscopic and microscopic scales. Transmission electron microscopy (TEM), variable angle spectroscopic ellipsometry (VASE), x-ray reflectometry (XRR), and atomic force microscopy (AFM) are useful techniques that can measure crystalline purity, lattice parameters, thickness, optical properties, electron density, and various energetic events. All of these techniques are able to measure the thickness of a feature, and can therefore be used complementarily to verify the data taken and analyzed for each particular technique. Though they are all useful, none is ideal for all situations. AFM is strictly used to extract surface height. VASE accurately measures insulators and semiconductors. XRR can measure metallic samples that VASE cannot. TEM can take good data for almost any material that can be shaved into a small, thin sample.

In implementing these techniques, we improve our ability to highlight advantageous characteristics that can be used in fabrication, and are able to accurately and non-invasively measure fabricated features. With TEM, VASE, AFM, and XRR, models can be made to measure material characteristics and thicknesses with angstrom-level accuracy.


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Workfunction tuning at the Au-HfO2 interface using organophosphonate nanolayers

Matthew Kwan, Ganpati Ramanath

Rensselaer Polytechnic Institute, Materials Science and Engineering Department, Troy, NY 12180. We show that the effective work function of Au on HfO2 can be tuned from 0 to 0.5 eV using molecular nanolayers (MNL) of mercaptan-terminated organophosphates with different lengths. Variable angle X-ray photoelectron spectroscopy (XPS) indicates that all the MNLs form monolayers tethered to the HfO2 and Au surfaces by the phosphonic acid and the mercaptan group respectively. Ultraviolet photoelectric spectroscopy (UPS) is used to measure the change in vacuum level of Au/MNL/HfO2 stacks to determine the metal work function shift at the interface. Measuring the vacuum level after the deposition of each layer allows us to determine the work function shift contributions from each interface, namely, the MNL-Au and MNL-HfO2. These results, interpreted together with work function shifts of MNL-functionalized surfaces of the metal and the dielectric, provide a comprehensive picture of how factors such as bonding, molecular orientation and MNL morphology contribute to the shifts.


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INFLUENCE OF CHEMISORBED OXYGEN ON THE GROWTH OF GRAPHENE ON Cu(100) AND Cu(111) BY CHEMICAL VAPOR DEPOSITION

Eng Wen Ong1, Zachary R. Robinson1,2, Tyler R. Mowll1, Parul Tyagi1, Seamus Murray3, Heike Geisler3, and Carl A. Ventrice, Jr.1

1SUNY College of Nanoscale Science and Engineering, Albany, NY, 2U.S. Naval Research Laboratory,

Washington, DC, and 3Department of Chemistry, SUNY College at Oneonta, Oneonta, NY

The influence of chemisorbed oxygen on the growth of graphene by catalytic decomposition of ethylene in a UHV chamber on both the Cu(100) and Cu(111) surfaces has been studied. The crystal structure of the graphene films was characterized with in-situ LEED, and the growth morphology was monitored by ex-situ SEM. For the clean Cu(100) substrate, heating from room temperature to the growth temperature while dosing with ethylene resulted in the formation of epitaxial graphene films. The

crystal quality was found to depend strongly on the growth temperature. At 900 C, well-ordered two-domain graphene films were formed. For the Cu(111) surface, heating from room temperature to the growth temperature while dosing with ethylene did not result in the formation of graphene. This is attributed to the lower catalytic activity of the (111) surface and the relatively high vapor pressure of the Cu surface. The use of an Ar overpressure to suppress Cu sublimation during the growth resulted in the formation of predominately single-domain epitaxial graphene films. Predosing either the Cu(100) or Cu(111) surface with a chemisorbed layer of oxygen before graphene growth was found to adversely affect the crystal quality of the graphene overlayers by inducing a much higher degree of rotational disorder of the graphene grains with respect to the substrate. The SEM analysis revealed that the nucleation rate of the graphene islands dropped by an order of magnitude after predosing either the Cu(100) or Cu(111) surface with a chemisorbed oxygen layer before growth. On the other hand, the average area of each graphene island was observed to increase by at least an order of magnitude. Therefore, the presence of oxygen during graphene growth affects both the relative orientation and average size of grains within the films grown on both substrates.

This research was supported in part by the NSF (DMR-1006411).


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In-situ Ar Plasma Cleaning of Samples Prior to Surface Analysis

Vincent S. Smentkowski,A Hong Piao,A and C.A. MooreB

AGeneral Electric Global Research Center, Niskayuna, NY 12309, BXEI Scientific, Inc., 1755 E. Bayshore Rd., Suite 17, Redwood City, CA 94063

The surface of as received samples is often contaminated with adsorbed layers of hydrocarbons. These surface contaminants can attenuate or mask underlying species of interest, inhibiting or compromising accurate analysis. In-situ ion beam sputtering is often used to remove the outer layer of a sample surface and thus remove contaminants, however this erosion process is inherently destructive and can alter the surface of interest. Moreover there are also many materials that can not be cleaned using monoatomic ion beam sputtering as the material(s) may decompose and deposit a layer of fragments onto the outer surface of the material to be analyzed. Recently gas cluster ion beams (GCIB) have been developed1,2, which allows for depth profile analysis of organic layers with minimal degradation3 (and references therein). GCIBs have also been used for low damage surface cleaning4,5,6. A non line-of-sight protocol which is able to clean large (mm or greater) areas is desired. We recently demonstrated that ambient air plasma processing can be used to clean the outer surface of samples7, however ambient air plasma treatment can result in oxidation of the material. In this presentation we report our first attempts at in-situ plasma cleaning of samples using Ar prior to XPS and ToF-SIMS analysis. We compare Ar plasma cleaning with air plasma cleaning, and report key findings. 1I. Yamada, J. Matsuo, N. Toyoda and A. Kirkpatrick, Mater. Sci. Eng., R 34, 231 (2001). 2S. Ninomiya, K. Ichiki, H. Yamada, Y. Nakata, T. Seki, T. Aoki and J. Matsuo, Rapid Commun. Mass Spectrom., 23, 3264 (2009). 3V. S. Smentkowski, G. Zorn, A. Misner, G. Parthasarathy, A. Couture, E. Tallarek, and B. Hagenhoff, J. Vac. Sci. Technol A., 31, 30601 (2013). 4M. Akizuki, M. Harada, Y. Miyai, A. Doi, T. Yamaguchi, J. Matsuo, G.H. Takoka, C.E. Ascheron, and I. Yamada, Surface Review and Letters, 03 (1), 891(1996). 5I. Yamada, J. Matsuo, Z. Insepov, D. Takeuchi, M. Akizuki, and N. Toyoda, J. Vac. Sci. Technol A 14(3) 780 (1996). 6I. Yamada, J. Matsuo, and N. Toyoda, Nuclear Instruments and Methods in Physics Research B, 206, 820 (2003). 7V.S. Smentkowski, C.A. Moore, J. Vac. Sci. Technol. A. 31 (2013) 06F105.


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CVD GROWTH OF MONOLAYER MoS2

Eui Sang Song, Mariyappan Shanmugam, Nikhil Jain, Fan Yang, Robin Jacobs-Gedrim and Bin Yu

College of Nanoscale Science and Engineering State University of New York, Albany, NY 12203, USA

The growth of monolayer MoS2 through chemical vapor deposition using selected precursor reagents of MoO3 and sulfur is studied. Four distinct growth phases which arise depending on the ratio of reagents present are identified: monolayer MoS2, hexagonal MoS2 nanosheets, rectangular MoOxSy nanosheets, and triangular MoOxSy islands. The analysis of these different growth elements using material characterization tools (Auger electron spectroscopy, Raman spectroscopy, etc.) will be presented.

Fig 1: A) monolayer MoS2, B) rectangular MoOxSy nanosheets,

C) Triangular MoOxSy islands and D) hexagonal MoS2 nanosheets


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CHARACTERIZATION OF IRON PORPHYRIN (FeP) MOLECULAR CONDUCTANCE BY STM MOLECULAR BREAK JUNCTION METHOD

Qi Zhou and Kim M. Lewis

Department of Physics, Applied Physics, & Astronomy Rensselaer Polytechnic Institute, Troy, New York 12180

In this work, conductance of FeP molecules between gold electrodes is studied by the molecular break junction method using scanning tunneling microscopy (STM). The electrochemically etched gold STM tip is brought into contact with FeP molecules that were deposited on a flat gold substrate (RMS ~0.6 nm over 1μm2). The tip is then retracted from the substrate until the last molecular junction breaks. During the retraction, conductance versus tip displacement (G-S) curves are obtained. The curves show steps at conductance values near 2.5×10-5G0, 5×10-5G0, 1.0×10-4G0 (see Figure 1) and 1.5×10-4G0 (see Figure 2), which indicate molecular conductance. A histogram of conductance is constructed to determine the most probable conductance range for a single molecule. We expect to observe conductance switching behavior for single FeP molecular junctions, according to our previous studies. G-S measurements from dimer formed FeP will be studied to determine its effects on molecular conductance. Our investigation will provide insight into molecular conductance switching in FeP molecular junctions.

0.0

5.0x10-5

1.0x10-4

1.5x10-4

2.0x10-4

steps

Selected G-S curves of Au-FeP-Au junctions, bias=-0.1V

Co

nd

ucta

nce (

G0)

Tip displacement (nm)0.5nm

0.0

5.0x10-5

1.0x10-4

1.5x10-4

2.0x10-4

Co

nd

ucta

nce (

G0)

Tip displacement (nm)0.5nm

Selected G-S curves of Au-FeP-Au junctions, bias=-0.1V

steps

Figure 1 Typical G-S curves of FeP

molecular junctions that have a step

at ~1.0×10-4

G0. Steps at ~5×10-5

G0

and ~2.5×10-5

G0 are also shown.

Figure 2 Typical G-S curves of FeP

molecular junctions that have a step

at ~1.5×10-4

G0.

Fall Meeting Hudson Mohawk Chapter of the AVS Oct. 6, … · Fall Meeting Hudson Mohawk Chapter of...

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