resultados de investigaciones subgraduada realizada en los cursos

Universidad de Puerto Rico en Humacao Departamento de Física y Electrónica

Año Académico 2011-2012

Número 7

RESULTADOS DE INVESTIGACIONES SUBGRADUADA

REALIZADA EN LOS CURSOS FISI 4161-65

Tabla de Contenido

Composite Nanofibers of Electroactive Polymers Prepared Via Electrospinning.

William Serrano Advisor: Nicholas Pinto

4

Devices and Sensors Based on PVDF-TrFE/SWNT’s Composites. Manuel Bonilla

Advisors: Idalia Ramos and Nicholas Pinto

5

Electrical Characterization of CVD Graphene. Yarelys Dávila Advisor: Nicholas Pinto 6

Electrical Characterization of Field Effect Transistors Made From C-nanotubes Covered with

Poly(3-hexylthiophene). Luis O. Pomales Advisor: Nicholas Pinto

7

Observation Report for the Year 2009, Humacao University Observatory. D. Centeno,

L. Rivera-Rivera, E. Franco, V. Maldonado, M. De Jesús, R.A. Rodríguez, A. J. Sosa,

M. Rosario, M. Díaz Advisors: R. J. Muller and J. C. Cersosimo

7

Study of Formation of Polymeric Fibers Containing Magnetic Nanoparticles.

Jean Carlo Serrano Advisor: Rogerio Furlan

8

Study of Formation of Polyvinylidene Fluoride Nanofibers Using Acetone as Solvent.

William Serrano García Advisor: Rogerio Furlan

9

Writing Polymeric Patterns Using an Atomic Force Microscope. Godohaldo J. Pérez Medina

Advisors: Rogerio Furlan and Luis G. Rosa

10

Study of Ionized Hydrogen in the Carina Region. Milennys Velázquez Flores, Clarissa

Vázquez Colón, Grace Fontanes, Milzaida Sanabria Advisor: J. C. Cersosimo

11

Nanoscale Fabrication of the Ferroelectric Polymer Poly(vinylidene Fluoride with Trifluoroeth-

ylene) P(VDF-TrFE) 75:25 Thin Films by Atomic Force Microscope Nanolithography.

Omar Vega, David Delgado, Freddy Wong, Rosette González Advisor: Luis G. Rosa

12


REALIZADA EN LOS CURSOS FISI 4161-65 Page 2 Número 7

Número 7 Page 3 RESULTADOS DE INVESTIGACIONES SUBGRADUADA


Weak Screening of a Large Dipolar Molecule adsorbed on Graphene. Lingmei Kong, G.J. Pérez

Medina, J.A. Colón Santana, F. Wong, M. Bonilla Advisors: Luis G. Rosa, D.A. Colón Amill,

L. Routaboul, P. Braunstein, B. Doudin, Chang-Mook Lee, Jaewu Choi, Jie Xiao and P.A.

Dowben

13

The Effect of Thermal Annealing on the Efficiency of Semitransparent Organic Solar Cells.

Gabriel Calderón, Héctor Carrasco Rodríguez, Jorge Marcano Bermúdez

Advisor: Josee Vedrine-Pauléus

14

Radiation Hazard on Long-Haul Airplane Flights. V. De La Rosa

Advisor: Ernesto P. Esteban

15

On the Carcinogenic Effects of Galactic Cosmic Rays at Low Earth Orbit and Deep Space.

P. Agosto Advisor: Ernesto Esteban

16

Polyaniline-Carbon Nanotubes Composite Actuator. Sabrina Rosa, Carlos Camargo

Advisors: Idalia Ramos and Eva Campo

17

Aluminum Nitride Nanofibers Fabricated Using Electrospinning and Nitridation.

Xenia Barbosa Advisors: Idalia Ramos, Eva Campo and Jorge Santiago

18

Synthesis of Electrospun Indium Gallium Nitride Nanofibers. Joshua L Robles García

Advisor: Idalia Ramos

18

Renovable Energy From Waves Using Magnetic Induction. Carlos Calderón, Kenneth Benítez

Advisor: Juan A. González Sánchez

19

Approaching an Organic Semi-metal: Electron Pockets at the Fermi Level for a Pbenzoqui-

nonemonoimine Zwitterion. Zhengzheng Zhang, José Alvira, Omar Vega, Gerson Díaz,

Julian Velev Advisors: Luis G. Rosa, Lucie Routaboul, Pierre Braunstein, Bernard Doudin,

Yaroslav B. Losovyj and Peter A. Dowben

20

La Edad del Cráter de Giordano Bruno. Luis O. Pomales Advisors: Abraham Ruiz y

William A. Bruckman

21-23

Número 7

Composite Nanofibers of Electroactive Polymers Prepared

Via Electrospinning

Page 4 RESULTADOS DE INVESTIGACIONES SUBGRADUADA


William Serrano

Advisor: Nicholas J. Pinto

Nanofibers of poly(vinylidene fluoride-trifluoroethylene)- PVF2-TrFE, a ferroelectric copolymer, blended

separately with each of the following conducting polymers, PEDOT-PSSA, PANi and P3HT were prepared

in air at room temperature using the electrospinning technique. The presence of the conducting polymer

assisted in the fabrication of PVF2-TrFE fibers at surprisingly low polymer concentrations in solution. UV/

VIS spectroscopy showed that the conducting polymer was uniformly incorporated into the PVF2-TrFE

solution with no polymer segregation. In the electrospinning process it is known that the net charge density

in the electrospinning jet and reduced surface tension lead to uniform fibers without beads. Scanning electron

microscope images indeed show a reduction in the beading effect and an increase in fiber formation when a

conducting polymer is incorporated into the composite. The fiber diameters increased with increasing PVF2

-TrFE concentrations. These electroactive polymers have the potential of combining charge storage with

conducting properties. Simple devices like diodes and field effect transistors have been fabricated from the

composite nanofibers and tested successfully. This work presents a quick, cheap and reliable way of

preparing functional polymer composite nanofibers under ambient laboratory conditions and in device

fabrication.

Figure 1: SEM images of electrospun fibers of (a) 13wt% PVF2-TrFE; (b) 13wt% PVF2-TrFE/P3HT; (c) 15wt%

PVF2-TrFE; (d) 15wt% PVF2-TrFE/P3HT. All images have the same magnification and the scale bar in each

represents 10 mm.

Devices and Sensors Based on PVDF-TrFE/SWNT’s Composites

Manuel Bonilla

Advisors: Idalia Ramos and Nicholas Pinto



Page 5 Número 7

Sensor devices were prepared using PVDF-TrFE/SWNT’s composite and compared with a pure SWNT’s

sensor. Current as function of time measurement at room temperature shows an improved sensitivity a

faster response time in the presence of acetone for the composite resistor device that was fabricated putting

the composite solution between two gold electrodes in n doped Si substrate. The pure SWNT’s resistor

produced a faster response time that the composite in the presence of NO2. Schottky diodes were prepared

with the PVDF-TrFE/SWNT’s composite and the n doped Si. Successful rectification was obtained and

changes in the turn on voltage and in the Ion/Ioff ratio were observed as the diode was in the environments

of different gases. The composite improve the sensitivity of the devices that can be prepared fast and can

be used to prepare a device with both diode and resistor functionalities. These sensor and the diodes can be

reused after gas removal.

R/R

N2

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

T(s)

0 500 1000 1500 2000 2500 3000

R/R

N2

0.2

0.3

0.4

0.5

0.6

0.7

0.8

(a)

(b)

Fig. 1.Normalized resistance of individual sensors switching the gas ambience between (a) N2 and acetone (b) N2 and N02. PVDF-TrFE/ SWNT’s is in black and SWNT’s. in red. The arrows indi-cate the moment when the specified gas was introduced

Figure 1 shows the normalized resistance of the pure

SWNT and the composite PVDF-TrFE/SWNT sensors

in the presence of acetone and NO2 gases. The

response to acetone is rapid and true saturation can be

observed, while for NO2 the sensor does not appear to

saturate in the 300s time interval of the measurements.

Nevertheless, in the four cycles presented in Figure 1,

there is reproducibility. The response times of these

sensors is presented in Table 1 and shows that compo-

site sensors are much faster than pure SWNT sensor for

acetone. This could be due the presence of the polymer

that speeds gas entry into the fiber. From Figure 1 we

see that acetone increases the resistance due to polymer

swelling while NO2 decreases it and could be related to

the doping effect that NO2 has on organic materials eg.

graphene[2].

FE/SWNT were fabricated and tested in acetone and

NO2. The composite sensors had a faster response time

in acetone compared to NO2. A Schottky diode was

also prepared using these same materials and the

device retained its rectifying behavior in the presence

of the sensing gas and there is recovery upon gas

removal.

This work was funded by NSF under grants PREM

0934195 and RUI 0965023. References [1]C. Staii, A.T. Johnson, Jr., M. Chen, A. Gelperin Nano Lett. Vol. 5, No. 9, pp.

1774-1778 August 2005.

[2] F. Schedin , A. K. Geim , S. V. Morozov, E. W. Hill , P. Blake, M. I. Katsnel-son & K. S. Novoselov Vol.6, pp. 652 – 655 July2007

Table 1 Composite and pure SWNT’s sensors response time and recovery time

Sample PVDF-TrFE/SWNT’s SWNT’s

Sensing gas Acetone NO2 Ace-tone

NO

2 Response time(s) 5 200 15 180

Recovery time (s) 100 235 120 200

Page 6 Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA


Electrical Characterization of CVD Graphene

Yarelys Dávila

Advisor: N.J. Pinto

Graphene is a one atom thick carbon sheet that can be obtained via exfoliation of graphite or via chemical

vapor deposition (CVD). By using a very simple shadow masking technique, gold contact pads were evapo-

rated over the graphene thereby eliminating chemical etching that is required when using photolithography

and often leads to sample contamination. CVD graphene was electrically characterized in a FET configura-

tion under different experimental conditions that include UV exposure, gas sensing and temperature. Our

measurements yielded a carrier mobility of up to 3000 cm2/V-s for some devices. Exposure to UV dopes

graphene in a controlled manner. The doping level could be maintained indefinitely in vacuum or could be

completely reversed by slight heating in air without loss of device performance. The FET’s were also tested

at different temperatures with little change in the transconductance response. Exposure to ammonia gas

n-doped graphene while exposure to NO2 p-doped it. The figure below shows UV doping of CVD graphene.

(a) The conductivity (G) versus gate voltage (Vg) curves for different doping time, measured at room tem-

perature and a pressure of 10-2 Torr. Dotted lines are fitted line to obtain the carrier mobilities shown in the

inset table.

Electrical Characterization of Field Effect Transistors made from

C-nanotubes Covered with Poly(3-hexylthiophene)

Luis O. Pomales

Advisor: N.J. Pinto

Organic transistors were fabricated using a thin film of regio-regular poly(3-hexylthiophene-2,5-diyl) spun

from a 0.5 wt% solution in CHCl3 on doped Si/SiO2 substrates with and without CNT’s. The performance of

devices with percolating networks of CVD grown single-wall carbon nanotubes (SWNT’s) between the

source (S) and drain (D) electrodes and without SWNT’s are compared. Nanotubes are used as a way to

shorten the effective mean distance between the S/D terminals while retaining the wide spacing macroscopic

shadow mask technique for S/D fabrication. We found that devices made with SWNT’s do not exhibit S/D

current saturation but have a charge mobility of 1.2x10-2 cm2/V-s and an on/off ratio of 9, while the device

without SWNT’s show clear saturation with a charge mobility of 8.6x10-4 cm2/V-s and an on/off ratio of 870.

The devices made with nanotubes possess a larger off state current although they show a ~14X increase in

the mobility which can thus be increased without using sophisticated lift-off techniques to shorten the S/D

distance.

Número 7 Page 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA


Observation Report for the Year 2009,

Humacao University Observatory

D. Centeno, L. Rivera-Rivera, E. Franco, V. Maldonado,

M. De Jesús, R.A. Rodríguez, A.J. Sosa, M. Rosario, M. Díaz

Advisors: R. J. Muller and J.C. Cersosimo

We report measurements of position angle and separation of 120 binary stars observed during the year

2009. We obtained the data using the 31 inch NURO Telescope at the Anderson Mesa location of Lowell

Observatory near Flagstaff, Arizona, in May and September. We gathered the data using the 2K x 2K CCD

camera - NASACAM - at the prime focus of the telescope. The data was analyzed at the Humacao

University Observatory.

Número 7

Jean Carlo Serrano

Advisor: Rogerio Furlan

Micro- and nanofibers find applications in several areas, including electronics, chemistry, energy, biomedicine,

and textile, among others. Functional fibers or fibers with multi-compositions can be obtained by electrospin-

ning of polymeric solutions blended with additional compounds as, for example, nanoparticles, carbon

nanotubes, ceramics, etc. The incorporation of magnetic nanoparticles in fibers has been considered a topic of

interest, particularly in the case of iron (II, III) oxide (magnetite, Fe3O4). This is a material with magnetic,

catalytic, conductive, and biological properties. Also, the presence of these nanoparticles can be used to orient

the fibers during electrospinning, applying appropriately a magnetic field. In this work solutions were pre-

pared using 0.25 g of poly (ethylene oxide) (PEO, a bio-compatible polymer, Sigma Aldrich, molecular

weight: 2,000,000), 10 ml of chloroform (J. T. Baker, 1% ethanol) and different amounts (1.6% wt., 3.2% wt.,

6.2% wt., 12%wt., and 21% wt.) of iron oxide (II, III) nanopowder / nanoparticles (Fe3O4, 98+%, 20-30 nm,

US Research Nanomaterials, Inc.). In order to guarantee that the nanoparticles were completely dispersed, the

solutions were sonicated before deposition for 45 minutes. The electrospinning setup used electrodes made of

aluminum with dimensions of 5.0 cm x 2.5 cm x 1.2 cm. The electrode separation was 14 cm. Polymer was

injected inside the electric field by positioning the tip of a tuberculin syringe 2 cm above and 0.5 cm far from

the middle of the upper extremity of the positive electrode. A voltage between 20 kV and 25 kV was applied

to the positive electrode and the negative electrode was grounded. This modification of the conventional elec-

trospinning setup allows obtaining oriented fibers. The obtained fibers presented a good degree of orientation

and dimensions of micrometers. They presented regions with agglomerates of nanoparticles and their diameter

increased as the concentration of nanoparticles in the solution increased. Energy Dispersive Spectroscopy

(EDS) confirmed the agglomeration. Further studies will consider polymeric solutions with different concen-

trations and other types of polymers that can allow obtaining particles homogenously distributed in nanofibers.



Study of Formation of Polymeric Fibers Containing Magnetic Nanoparticles

Optical microscope image of a fiber collected on top of a silicon

substrate (12% wt. of Fe3O4; applied voltage of 25 KV

Page 9

Study of Formation of Polyvinylidene Fluoride Nanofibers Using

Acetone as Solvent

William Serrano García

Advisor: Rogerio Furlan


REALIZADA EN LOS CURSOS FISI 4161-65 Número 7

This work addressed the formation of Poly (vinylidene difluoride) (PVDF, a Piezoelectric polymer) fibers to

be used as structural material for chemical sensors applications. The idea is to incorporate, further, other

materials, as Vulcan (carbon black) to obtain conductive nanofibers and copper phthalocyanine to improve

adsorption and electrochemical response. Solutions were prepared by weight per cent of PVDF and Ace-

tone. We used concentrations of 5, 10, 15 and 20wt%. Fibers were formed using electrospinning with the

following conditions: electrodes separation of 22-25 cm and applied voltage of 10 kV. For low concentra-

tions of PVDF (5wt %), only drops with a little formation of fibers were deposited on the collector

(aluminum foil). Increasing the concentration to 10 wt%, nanofibers and large beads are observed. For a

concentration of 15 wt%, homogeneous fibers with typical diameters approximately of 1µm - 4µm can be

obtained. Increasing further the concentration to 20 wt%, large agglomerates of polymer are observed with

the nanofibers. Thus, this preliminary study allowed us to establish process conditions for the continuation

of this work. For this purpose, a concentration of 15 wt% will be adopted.

5 wt%

10 wt%

15 wt%

20 wt%

Page 10

In this work we investigate the use of a novel ink containing polyacrylonitrile (PAN) and N, N dimethylfor-

mamide (as solvent) to define patterns using Atomic Force Microscopy (AFM). PAN is a largely used

polymer that has been explored as a precursor to obtain carbon nanofibers. Also block copolymers

containing PAN have been pyrolyzed to obtain well-organized nanostructured carbon materials. An AFM

(Digital Instruments, model Dimension 3100) was used to define polymeric squares on oxidized silicon

substrates covered with gold (~100 nm deposited by evaporation). The contact tips are prepared, for

writing, in the following manner: they are immersed in a solution containing 25 mg of PAN (average

molecular weight 150,000) and 5 ml of N, N dimethylformamide (DMF) for ten seconds and the excess

solution is allowed to run off. The tip is then rinsed in pure DMF for another ten seconds and allowed to

dry. Finally the tip is submerged once more in the PAN solution and allowed to dry. Once the tip is

mounted and focused, polymeric structures are defined and identified on the surface. The AFM is set up to

operate in contact mode using scan angle of 90°. Structures could be seen using friction images (scale

of .2V). The surface is scanned three times, twice to write the polymeric structure and once to read it. The

typical parameters used to write were: scan size 1µm, frequency 2Hz, deflection setpoint 4V. Larger

frequencies, and smaller scan sizes or deflection setpoints were sometimes used. The typical parameters

used to read were: scan size 5µm, frequency 4Hz, deflection set point 1V. These parameters were used to

successfully define and observe 1µm2 squares on a gold substrate. Once an image had been taken by the

AFM, it was flattened to enhance contrast. These conditions were based on results obtained using a 0.5

mM supersaturated MHA (mercaptohexadecanoicacid) solution with ethanol. Using this very known ink,

images of squares with 1 µm2 could be observed using friction mode (scale of 0.2 V). This work was

presented in NCUR 2012 and a paper was submitted for publication in the proceedings of this conference.

Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA


Writing Polymeric Patterns Using an Atomic Force Microscope

Godohaldo J. Pérez Medina

Advisors: Rogerio Furlan and Luis G. Rosa

Polymeric structure defined by writing two times a square area of 1µm2, using a frequency of 2Hz, and a

deflection set point of 4V. After reading (scan size 5µm, frequency 4Hz, deflection set point 1V) the

lateral dimensions of the polymeric structure defined were 0.96 µm by 1.01 µm.

Page 11

Study of Ionized Hydrogen in the Carina Region

Milennys Velázquez Flores, Clarissa Vázquez Colón, Grace Fontanes, Milzaida Sanabria

Advisor: J. C. Cersosimo, PhD.



A typical characteristic of the Carina Nebula is its complex kinematical structure, which is observed in opti-

cal and radio lines. Due to the existence of many young and massive stars, there are considerable amounts of

ionized gas. By using observations of the atomic transition H166α radio recombination line (RRL) the

behavior of the kinematics of the ionized gas in the region was studied. In this work a grid of about 600 pro-

files, obtained with the Parkes Radiotelescope, has been analyzed. Each profile was processed in order to fit

a base line and after that a Gaussian fit was made for each position. The radial velocity resolution of the

profiles is about 4 km s-1 .

Finally, the region was mapped for different radial velocity at interval of 10 km s-1. A set of maps shows the

kinematics of the gas which suggests a shell like structure of ionized gas. It is apparent that the structure is

spatially correlated with the young open clusters Trumple 14. As a result it is suggesting that the ionized gas

is being blown out by the stellar wind of the young stars of the cluster.

Figure 1: Presentation at the Junior Technical Meeting.

From left to right: Milennys, Milzaida, Grace & Clarissa.



Nanoscale Fabrication of the Ferroelectric Polymer Poly(vinylidene

Fluoride with Trifluoroethylene) P(VDF-TrFE) 75:25 Thin Films by Atomic

Force Microscope Nanolithography

Omar Vega, David Delgado, Freddy Wong, Rosette González

Advisor: Luis G. Rosa

Thin films of an organic ferroelectric system, poly(vinylidene fluoride with trifluoroethylene) P(VDF-

TrFE) 75:25 layers, have been deposited on highly ordered pyrolytic graphite (HOPG) and silicon

dioxide (SiO2) by the horizontal Schaefer method of Langmuir-Blodgett (LB) techniques. It is possible

to “shave” or mechanically displace small regions of the polymer film by using atomic force micro-

scope nanolithography techniques such as nanoshaving, leaving swaths of the surface cut to a depth of

4 nm and 12 nm exposing the substrate. The results of fabricating stripes by nanoshaving two holes

close to each other show a limit to the material “stripe” widths of an average of 153.29 nm and 177.67

nm that can be produced. Due to the lack of adhesion between the substrates and the polymer P(VDF-

TrFE) film, smaller “stripes” of P(VDF-TrFE) cannot be produced, and it can be shown by the

sequencing of nanoshaved regions that “stripes” of thin films can be removed.

Page 13 Número 7



Weak Screening of a Large Dipolar Molecule Adsorbed on Graphene

Lingmei Kong, G.J. Pérez Medina, J.A. Colón Santana, F. Wong, M. Bonilla,

Advisors: Luis G. Rosa, D.A. Colón Amill, L. Routaboul, P. Braunstein, B. Doudin, Chang-Mook Lee,

Jaewu Choi, Jie Xiao and P.A. Dowben

We compare the electronic structure of a quinonoid zwitterionic type molecule adsorbed on both gold and

graphene on copper substrates. This (6Z)-4-(butylamino)-6- butyliminio)- 3-oxocyclohexa-1,4-dien-1-

olate, C6H2(NHR)2(O)2 where R = n- C4H9, film is made of small molecules with a large intrinsic di-

pole of 10 Debyes. We find that the photoemission and inverse photoemission final states are well

screened for these dipolar molecules on gold. This is not observed when they are adsorbed on graphene

on copper. This weaker screening results in a larger highest occupied molecular orbital to lowest

unoccupied molecular orbital gap for the molecules on graphene.

The Effect of Thermal Annealing on the Efficiency of Semitransparent

Organic Solar Cells

Gabriel Calderón Ortiz, Héctor Carrasco Rodríguez, Jorge Marcano Bermúdez

Advisor: Josee Vedrine-Pauléus



Most modern devices we use require some type of energy. The most common way to obtain this energy

comes from petroleum. This in turn creates an environmental problem because of emissions released into

the atmosphere. One of the ways to reduce the consumption and dependence on petroleum is to develop

and improve current alternative energy technologies.

Solar cells provide an alternative and environmentally friendly source of energy from the sun. In this work,

we fabricate organic solar cells and characterize their conduction under a simulated solar light source.

In our study, we analyzed the effect of annealing polymeric blends on cell efficiency while maintaining the

samples under ambient atmosphere. The organic cells have an active region composed of electron-donor

poly(3-hexylthiophene) (P3HT) and electron acceptor penyl-C61-butyric acid methyl ester (PCBM) mate-

rials to form a pn heterojunction. These organic polymers, with the addition of poly (3,4-

ethylenedioxythiophene) poly(styrenesulfonate (PEDOT:PSS) are used in thin films on an indium tin oxide

(ITO) coated glass substrate because it is a transparent conductor.

The fabrication process for making the solar cells is mostly carried out inside a vacuum chamber filled

with nitrogen gas to limit the effect of degradation on polymers from oxygen, heat, and humidity. We

attempted to find an optimal annealing temperature for P3HT:PCBM whereby the solar cell can generate

current with greater efficiency. The samples were annealed at these temperatures-80˚C, 100˚C, 120˚C and

140˚C. We investigated the effect of annealing on the solar cell efficiency by measuring their current-

voltage characteristics under the given conditions.

Our preliminary results show a correlation between solar cell efficiency and annealing temperature of the

P3HT:PCBM- as the temperature increases, solar cell efficiency decreases. We will continue further

experiments to determine efficiency at temperatures lower than 100 ˚C and at higher temperatures to

confirm this correlation.

Figure 1. Annealing temperature vs. Efficiency. Cell

efficiency was measured/calculated using the Keithley

IV Characterization software program. This graph shows

the data for the 100˚C-annealed cell when exposed to

simulated solar light.

Page 15 Número 7



V. De La Rosa


Radiation Hazards on Long-Haul Airplane Flights

The possible carcinogenic effects of galactic cosmic rays (GCR) on long-haul airplane flights are

investigated. To mimic a carcinogenesis process, we have modified the mathematical Jones model of

radiation-induced myelopoiesis by adding new compartments corresponding to mutated and cancerous

cells populations. This new biomathematical model can be written in terms of a set of non-linear

differential equations.

At different Earth's altitudes and latitudes, we assume n mutations and a given cosmic ray dose rate, to

estimate the evolution of cell survival curves and cancerous cell populations. Two applications are

considered.

First, we found that regardless of latitude there is no cosmic rays carcinogenic effects on the airplane's

crew, when flying during 20 years (100 hours/month) at altitudes less than 60000 ft. However, if the

altitude increases and the flight is nearer Earth´s poles, a carcinogenesis process could be initiated.

Second, we considered an actual flight from New York to Athens, and found that the evolving cancer

cell population can be quantified at any given time t by a linear quadratic and quartic relationship.

Pilots flying in this route 40 years (100 hours/month) could be at cancer risk at the end of their careers.



On the Carcinogenic Effects of Galactic Cosmic Rays at

Low Earth Orbit and Deep Space

P. Agosto


By necessity and curiosity humans destiny is to colonize and to habitat other planets. In doing so, one of

the challenging problems is to understand, to estimate, and to mitigate the carcinogenic effects of galactic

cosmic rays (GCR) on humans.

We have developed a simple but not trivial biomathematical model to estimate the possible carcinogenic

effects of the interaction between CGR and astronauts’ tissue. This deterministic model was built on top

of the experimental and theoretical work done by Jones et al [1], and it does not neglect microgravity

effects.

Two radiation environments were studied. At the International Space Station (ISS), it is estimated that

only after eleven consecutive mission’s astronauts cancer risks will increase. However, for the interplane-

tary travel from Earth to Mars, a cancer initiation process could begin as soon astronauts arrive to Mars.

ISS exposed to GCR In Fig. 1, survival curves look similar except for the first expedition. The GCR irra-

diation effects on tissue are more harmful beginning the second flight. Notice also, that sub-lethal repair is

very efficient. ISS astronauts fully replenish normal cells in about two months. The cancer cell popula-

tion is given in Fig. 2. The cancer threshold (0.00025) is reached at about 175 months. This implies that

increasing cancer risks for astronauts at the ISS is negligible.

10 20 30 40 50 60 70months

0.9700.9750.9800.9850.9900.9951.000

S

Survival .Curve

50 100 150 200Months

0.0001

0.0002

0.0003

0.0004

Nc

Cancerous Cell Population.for.Fcc 50 Fnn


REALIZADA EN LOS CURSOS FISI 4161-65 Page 17

Polyaniline-Carbon Nanotubes Composite Actuator

Sabrina Rosa and Carlos Camargo

Advisors: Idalia Ramos, University of Puerto Rico at Humacao; Barcelona, Spain; Eva Campo,

University of Pennsylvania; Jaume Esteve, Centre Nacional de Microelec-tronica, Barcelona, Spain

The understanding of photoactuation in Carbon Nanotubes (CNT)-polymer composites can contribute to

the development of micro-and-nano-optical-mechanical systems for applications that include intracellu-

lar motors, artificial muscles, and tactile displays for blind people. The integration of CNTs into

polymers combines the good processability of polymers with the functional properties of CNTs. CNTs-

polymer composite fibers were fabricated using the electrospinning technique. Electrospinning process

orients the CNTs along the precursor stream and can contribute to enhance photo actuation properties.

The addition of polyaniline, an electroactive conductive polymer is expected to enhance the actuation

strain of the composite. Aim of this research is to study photoactuation in MWCNT-Polyanilile electro-

spun fibers. Fibers were characterized using Scanning Electron Microscopy, Atomic Force Microscopy,

and X-Ray Diffraction. Results demonstrate evidence of photo-actuation after irradiating the fibers with

visiblelight. Tests are being conducted to understand the mechanisms of the composites response to light

stimulation.

Research Sponsored by Partnership for Research and Education in Materials (NSF-DMR 0934195).

Page 18 Número 7 RESULTADOS DE INVESTIGACIONES SUBGRADUADA


Aluminum Nitride Nanofibers Fabricated Using

Electrospinning and Nitridation

Xenia Barbosa

Advisors: Idalia Ramos, University of Puerto Rico at Humacao,

Eva Campo and Jorge Santiago, University of Pennsylvania

Aluminum Nitride (AlN) and other nitride semiconductors are important materials in the fields of optoelec-

tronics and electronics. AlN nanofibers were synthesized using electrospinning and subsequent heating

under N2 and NH3 atmospheres. The precursor solution for electrospining contains aluminium nitrate and

cellulose acetate. The electrospun nanofibers were heated in N2 to eliminate the polymer and produce

Al2O3, and then nitridized at a temperature of 1200ºC under NH3 flow. Scanning Electron Microscopy

(SEM) observations demonstrate the production of fibers with diameters ranging from a few nanometers to

several micrometers. X-Ray Diffraction and UV-VIs analyses show the production of AlN nanofibers with

hexagonal wurzite structure and a band gap of approximately approximately 6 eV. Current-Voltage

measurements on a single AlN fiber with gold electrodes suggest the formation of a Schottky contact.

The fabrication method and results from the fibers characterization will be presented.

This work was funded by NSF-DMR-0934195

Synthesis of Electrospun Indium Gallium Nitride Nanofibers

Joshua L. Robles-García

Advisor: Idalia Ramos

InGaN is a novel material for the development of optoelectronic devices because its band gap can be chan-

ged from 3.4 eV to 0.7 eV by varying the indium concentration. InGaN nanofibers have been produced

using the electrospinning technique and a precursor solution composed of indium nitrate (III), gallium

nitrate (III), and cellulose acetate dissolved in dimethylacetamide and acetone. After electrospinning the

fibers are sintered in nitrogen at 400°C to decompose the polymer and the nitrates. Then, they are nitridi-

zed at 650°C under an ammonia gas flow to complete the production InxGa1-xN, were x is the InN molar

fraction and varies as 0.25, 0.5 and 1. GaN (x=0) nanofibers produced in previous work and sintered at

900°C are used for comparison. Scanning Electron Microscopy (SEM) show the production of long and

continuous fibers with diameters of hundreds of nanometers and up to a few micrometers. X-ray

Diffraction (XRD) analysis of the fibers shows the production of fibers with wurtzite InN and GaN peaks.

Ultraviolet-visible (UV-Vis) spectra were obtained to analyze the changes in band gap with In concentra-

tion. The band gap of the electrospun InxGa1-xN fibers varies from 3.4 nm for x=0 (GaN) to 2.2 nm for x=1

(InN).



Page 19 Número 7

Renovable Energy From Waves Using Magnetic Induction

Carlos Calderón and Kenneth Benítez

Advisor: Juan A. González Sánchez

The purpose of this project is to apply the principle of magnetic induction, constructing an acrylic box in

order to convert mechanic energy into electromotive force (EMF) from the ocean wave shock. First we

started testing with different springs to determine an efficient way to increase the impact of the oscillation

caused by the waves.

Figure 1. AutoCAD Design of the Renovable Energy Device

Voltage vs. time results were

plotted using HPVEE data

acquisition software and

strength tests were performed

to find the best spring constant

using Hooke's law. We chose

6500 Gauss axial cylindrical

neodymium magnets.

After that we started to design the box using

AutoCAD, taking into account the center of

mass calculations. To complete the design and

construction 3 inches in diameter coils with

1000 turns were placed. Finally, we tested our

machine on the beach and the pool of UPR-H

campus.

Figure 2 Voltage vs. Time on the first wave of impact


REALIZADA EN LOS CURSOS FISI 4161-65 Page 20 Número 7

Approaching an Organic Semi-metal: Electron Pockets at the Fermi Level

for a pbenzoquinonemonoimine Zwitterion

Zhengzheng Zhang, José Alvira, Omar Vega, Gerson Díaz, Julian Velev

Advisors: Luis G. Rosa, Lucie Routaboul, Pierre Braunstein, Bernard Doudin, Yaroslav B. Losovyj and

Peter A. Dowben

There is compelling evidence of electron pockets, at the Fermi Level, in the band structure for an organic

zwitterion molecule of the p-benzoquinonemonoimine type. The electronic structure of the zwitterion

molecular film has a definite, although small, density of states evident at the Fermi level as well as a

nonzero inner potential and thus is very different from a true insulator. In spite of a small Brillouin zone,

significant band width is observed in the intermolecular band dispersion. The results demonstrate that

Bloch’s theorem applies to the wave vector dependence of the electronic band structure formed from the

molecular orbitals of adjacent molecules in a molecular thin film of a p-benzoquinonemonoimine type

zwitterion.

El cráter Giordano Bruno (GB) de 22km de diámetro esta ubicado en las coordenadas (Lat: 35.96, Lon:

102.86) correspondiente a la cara opuesta de la Luna. De aparente reciente formación, Hartung (1976)

sugirió que el mismo se formó en la edad media y fue responsable de la explosión del 18 de junio de 1178

reportado por el monje e historiador ingles Gervasio de Canterbury. Morota et al. (2009), usaron imágenes

de la sonda japonesa SELENE (Kaguya), y el modelo de Nukum et al. (1983), para estimar la edad del

cráter en unos 4 millones de años. Joven geológicamente pero no es histórico.

Nosotros aplicamos el mismo método de conteo de cráteres pequeños en el suelo nuevo alrededor del cráter

pero usando el modelo de Bruckman et al. 2007, el cual contempla una tasa mayor de impactos en el

número acumulativo, N(>D) = A τ D -3.3 /3.3, debido a el coeficiente A, el cual es significativamente

mayor. Dicho coeficiente esta basado observaciones de Poveda et al, (1999) y mediciones del número acu-

mulativo de bólidos en la atmosfera terrestre (Silber et al. 2009). Para una superficie no saturada, N(>D)

= Φ τ, donde Φ es el flujo acumulativo de impactos y τ es el tiempo que ha estado expuesta recibiendo

impactos.

En la figura a continuación se muestra una imagen del Lunar Reconnaissance Orbiter donde se amplía parte

del suelo recién formado con cráteres nuevos alrededor del GB. El área total de contaje para cráteres de

>200m fue de 960km2. Para los cráteres >100m, el área total fue de 240km2. Para cráteres >50m y

>25m, el área fue 60km2 y 15km2, respectivamente. La región de conteo se dividió en 21 parcelas de

45.7km2 en la cual se contaban todos los cráteres mayores a 200m. Luego se hace un acercamiento en la re-

gión central, con la siguiente resolución que representa un área 11.4km2 para contar los cráteres de 100m.

Así sucesivamente para los de 50m y 25m con un área de conteo de 2.85km2 y 0.71km2,, respectivamente.

Este proceso se repitió en las 21 parcelas lo que asegura que los 4 tipos de cráteres contados se distribuyen

uniformemente en toda la región.

La Edad del Cráter de Giordano Bruno

Page 21

Luis O. Pomales

Advisors: Abraham Ruiz y William A. Bruckman





La edad estimada para el cráter de GB fue de 92,000 ± 46,000 años. Esa sería un valor máximo para la edad

debido a la posibilidad de contaminación por cráteres secundarios. En este caso la contaminación es poco

probable por ser un impacto geológicamente joven. La incertidumbre en la edad proviene principalmente de la

calibración del modelo con los datos de Grive y Shomaiker (1994). A continuación se muestra la relación de

Número Acumulativo vs. Diámetro para cráteres mayores de 25m, 50m, 100m y 200m. La pendiente de 3.48

nos confirma que es una superficie no saturada cuyo número de cráteres N (>D) esta determinada por Φ τ .

Definitivamente el cráter de GB no es el responsable del evento reportado en 1178.

Es extremadamente joven pero no histórico.

Sin embargo, hemos identificado otro cráter de poco más de 4km de diámetro, llamado provisionalmente,

cráter Rafael Muller (RM), en la posición Lat -32.99, Lon -4.47 a 390km al Noreste del cráter de Tycho. La

figura a continuación presenta una imagen del cráter y parte de su región alrededor ampliada a la misma

escala que en el GB. Al comparar ambas regiones es fácil ver que en el RM hay menos cráteres y son más

pequeños que en el GB, por consiguiente es más joven.

El conteo de cráteres en esa región nos permite establecer, según el modelo (Bruckman et al. 2009) su edad

en unos 640 años ± 320 anos. Considerando las incertidumbres, podemos señalar que este cráter es un buen

candidato para ser el responsable de la alega explosión en la Luna reportada hace 834 años.



Además de la coincidencia cronológica, el RM resuelve un problema que no ha sido explicado satisfactoria-

mente por los que proponen que el cráter de GB es responsable del evento de 1178. Un cráter tan grande

como ese removió cerca de 900km3 material de las cuales 10 millones de toneladas alcanzaron la Tierra

(Gault and Schultz, 1991) causando una lluvia de estrellas sin precedente por varias semanas (Withers,

2001). Hasta el momento no se ha encontrado registros históricos ni evidencias geológicas que den cuenta

de tan fenomenal lluvia de estrellas en esa época. Por otro lado un impacto de 22km de diámetro en la Luna

o la Tierra es poco probable. Según los modelos mas usados son uno cada dos millones de anos. Según el

modelo de Bruckman et al. (2012) la tasa de impactos para cráteres de 22 km es de 3 por cada millón de

años.

Por otro lado, el cráter RM excavó casi 300 veces menos que el GB, por lo que el material transferido a la

Tierra y la consecuente lluvia de estrellas, se reduce en ese mismo orden. El cráter RM tuvo una potencia

de más de 300MT y excavó cerca de 3km3 de material. El polvo levantado, sin duda fue suficiente para

reflectar la luz del Sol hacia la cara oscura de la Luna, iluminando parte del disco, consistente con lo

reportado por Gervasio de Canterbury.

Referencias:

Bruckman, W. A., Ruiz, A., and Ramos, E. RevMex (Series de Conferencias) Vol. 35, p.19. (2009)

Bruckman, W. and A., Ruiz, A., (2012) en preparación.

Grive and Showmaker, E., 1994: The record of Past Impacts on Earth, T. Gehrels, Editor: University of Ari-

zona Press.

GAULT D. E. AND SCHULTZ P. H. (199 1) Ejecta from lunar impacts:

Where is it on Earth? Meteoritics 26, 336-337.

Hartung, J. B. (1976) Was the Formation of a 20-km-Diameter Impact Crater on the Moon Observed on

June 18, 1178? Meteoritics, v. 11(3), p. 187-194

Morota, T., Haruyama, J., Miyamoto, H., Honda, C., Ohtake, M., Yokota, Y., Matsunaga, T., Hirata, N.,

Demura, H., Takeda, H., Ogawa, Y., and Kimura, J. (2009) Meteoritics and Planetary Science, v. 44(80),

p. 1115-1120.

Poveda, A., Herrera, M. A., et al. 1999, Planet. Space Sci., 47, 679

Withers, P., Meteoritics and Planetary Science, v. 36(4), p. 525-529 (2001)

Nota de los editores

La inclusión de la investigación y la labor creativa son fundamentales para el

desarrollo integral de los estudios subgraduados. Los miembros del Departa-

mento de Física y Electrónica reconocen la importancia de estos elementos

como parte fundamental de la labor académica. La aplicación del conoci-

miento en la búsqueda de nuevas verdades y la interpretación del mundo que

nos rodea, permite el desarrollo del pensamiento crítico; es una herramienta

académica innovadora para motivar y satisfacer la curiosidad intelectual del

los/las estudiantes. Además contribuye al desarrollo social y cultural

agilizando la inserción en el ciclo económico de Puerto Rico y del mundo.

La inmersión de estudiantes en investigación subgraduada se hace desde los

inicios del programa de Bachillerato de Física Aplicada a la Electrónica, en

1987, mediante el ofrecimiento del curso Investigación Subgraduada (FISI

4161). La usual contratación de Profesores con peritaje en investigación

capturó el interés de los estudiantes de Bachillerato para involucrarse en tan

digna tarea. El esmero y dedicación de los profesores ayudó a ellos mismos

a trasformar las técnicas de enseñanza debido al desafío que implica investi-

gar y formar a estudiantes en la disciplina.

La consecuencia de estos esfuerzos condujo a aumentar el ofrecimiento

debido al interés de los estudiantes en hacer investigación. En consecuencia

se atendió la demanda de los estudiantes, incluyendo los curso de Investiga-

ción Subgraduada (FISI 4162 FISI 4163 y FISI 4164). Los cuatro cursos

mencionados se ofrecen regularmente desde agosto de 1993. El compromi-

so permitió a la academia refinar las estrategias de enseñanza-aprendizaje,

que en esencia son el modelo tomado por el constructivismo, el método de

prueba y error.

Después de veinticuatro años de esfuerzo, el Departamento cuenta con una

decena de profesores que escriben propuestas, consiguen fondos externos y

hacen presentaciones en reuniones internacionales de ciencia, y publican

periódicamente en revistas de circulación internacional. En el Departamento

hay tres laboratorios dedicados a la investigación y un laboratorio de instruc-

ción equipado con instrumentos de primera línea en el que se ofrecen dos

cursos de concentración. También otras facilidades de investigación son los

recursos del Observatorio Astronómico de Humacao, en el cual la prepara-

ción obtenida por los estudiantes les facilita tener opción de seguir estudios .

Vale destacar el compromiso de la Institución (UPRH) que hace posible la

investigación subgraduada, es por ello que me complace reconocer a las

diferentes administraciones que están y han colaborando en este esfuerzo.

El reconocimiento es también extendido a los profesores por la labor de

adiestramiento a los estudiantes. La revista de investigación subgraduada fue

concebida para que sea un instrumento administrativo que permita la visibili-

dad de esta actividad, pero además es un documento dirigido a los estudian-

tes, profesores y la comunidad científica de Puerto Rico, con el propósito de

divulgar las actividades académicas que han sido pioneras en el Sistemas

UPR junto con otros Recintos. Este instrumento estará además disponible en

la Internet para permitir el acceso a todas las comunidades.

Proyectos Auspiciadores:

1. Puerto Rico Space Grant Consortium (NASA)

2. Puerto Rico Alliance for Minority Participation (LSAMP)

3. NSF

- Penn-UPR Partnership for Research and Education in Materials (DMR-0353730)

- Research in Undergraduate Institutions ( RUI)

5. RISE Program at UPRH

6. PRIDCO

Universidad de Puerto Rico en Humacao

Departamento de Física y Electrónica

Call Box 860

Humacao PR 00792

www.uprh.edu/fisica

Tel. 787-850-9344-9381 Fax: 787-850-9308

Documents

resultados de investigaciones subgraduada realizada en los cursos