Fall Meeting
Hudson Mohawk Chapter of the AVS
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
1
Oct. 6, 2014
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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
1
Department of Physics, Applied Physics, and Astronomy
2
Department 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
2
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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
1
Department of Physics, Applied Physics, and Astronomy
2
Department 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.
3
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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
2
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.; BorcaTasciuc, 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.
4
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
OPTICAL METROLOGY FOR DSA PATTERNING USING MMSE BASED SCATTEROMETRY
D. Dixita, A. C. Diebolda
a
SUNY 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 (PSb-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 linewidth, 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.
14nm
14nm
28nm
28nm
6nm
23 nm
32nm
7nm
84nm
7nm
13nm
13nm
Fig. 1 Final profile of the
scatterometry model for 3xLo unetched sample.
84nm
Fig. 2 Final profile of the
scatterometry model for 3xLo
etched sample.
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.
5
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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.
6
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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 offaxis 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)
c)
b)
Figure 1: LEED images for growth of graphene by backfilling the UHV chamber with 5 mTorr of C 2H4
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).
7
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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 elph 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
1
Lacy, Nanoscale Research Letters, 2011, 6:636.
Hanaoka, Y. et al, Materials Transactions, vol. 43, No. 7 (2002) pp. 1621-1623.
3
Timalsina, Y. P. et al, Applied Physics Letters, 103, 191602 (2013).
2
8
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
POSTER PRESENTATIONS
TAILORING ELECTRICAL CONTACT RESISTIVITY AT METAL-THERMOELECTRIC INTERFACES USING A
MOLECULAR NANOLAYER
Thomas Cardinal1, Devender 1, Theo Borca-Tasciuc2, Ganpati Ramanath 1*
1
Department 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
1
SUNY 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
1
SUNY 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
1
General 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.
9
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
POSTER PRESENTATION ABSTRACTS
TAILORING ELECTRICAL CONTACT RESISTIVITY AT METAL-THERMOELECTRIC INTERFACES
USING A MOLECULAR NANOLAYER
Thomas Cardinal1, Devender1, Theo Borca-Tasciuc2, Ganpati Ramanath1*
1
Department 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.
10
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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, Ge1xSnx(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.
(a)
Sn Ge
CaF2 cap
Initial stage
(b)
Ge atom
Later stage
Sn atom
Ge1-xSnx
[111]
CaF2
nanorods
CaF2 cap
CaF2
nanorods
glass
glass
11
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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
2
unfavorably coupled electrical and thermal properties to realize high ZT nanomaterials.
12
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
ADVANCED METROLOGY METHODS FOR CHARACTERIZATION OF GRAPHENE
AND SPIN DEVICE MATERIALS
Avery Green1, Tuan Vo2, George Orji3, Alain Diebold1
1
SUNY 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.
13
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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 Xray 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 MNLfunctionalized 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.
14
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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
1
SUNY 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 twodomain 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).
15
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
In-situ Ar Plasma Cleaning of Samples Prior to Surface Analysis
Vincent S. Smentkowski,A Hong Piao,A and C.A. MooreB
A
B
General Electric Global Research Center, Niskayuna, NY 12309,
XEI 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.
1
I. Yamada, J. Matsuo, N. Toyoda and A. Kirkpatrick, Mater. Sci. Eng., R 34, 231 (2001).
S. Ninomiya, K. Ichiki, H. Yamada, Y. Nakata, T. Seki, T. Aoki and J. Matsuo, Rapid Commun. Mass
Spectrom., 23, 3264 (2009).
3
V. S. Smentkowski, G. Zorn, A. Misner, G. Parthasarathy, A. Couture, E. Tallarek, and B. Hagenhoff, J.
Vac. Sci. Technol A., 31, 30601 (2013).
4
M. 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).
5
I. Yamada, J. Matsuo, Z. Insepov, D. Takeuchi, M. Akizuki, and N. Toyoda, J. Vac. Sci. Technol A 14(3) 780
(1996).
6
I. Yamada, J. Matsuo, and N. Toyoda, Nuclear Instruments and Methods in Physics Research B, 206, 820
(2003).
7
V.S. Smentkowski, C.A. Moore, J. Vac. Sci. Technol. A. 31 (2013) 06F105.
2
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Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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
17
Fall Meeting
Hudson Mohawk Chapter of the AVS
Oct. 6, 2014
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.
Selected G-S curves of Au-FeP-Au junctions, bias=-0.1V
Selected G-S curves of Au-FeP-Au junctions, bias=-0.1V
-4
2.0x10
-4
2.0x10
steps
-4
-4
1.0x10
steps
-5
5.0x10
Conductance (G0)
Conductance (G0)
-4
1.5x10
1.5x10
-4
1.0x10
-5
5.0x10
0.0
0.0
0.5nm
Tip displacement (nm)
0.5nm
Tip displacement (nm)
Figure 2 Typical G-S curves of FeP
molecular junctions that have a step
-4
at ~1.5×10 G0.
Figure 1 Typical G-S curves of FeP
molecular junctions that have a step
-4
-5
at ~1.0×10 G0. Steps at ~5×10 G0
-5
and ~2.5×10 G0 are also shown.
18