2007 AATCC = Materials Design Competiton 1st Place Winner

From: Subject: 2007 AATCC Materials Design Competiton 1st Place Winner Date: Fri, 14 Oct 2011 12:30:40 -0400 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_001B_01CC8A6D.155174F0" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6109 This is a multi-part message in MIME format. ------=_NextPart_000_001B_01CC8A6D.155174F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: mhtml:http://www.aatcc.org/members/students/CZ_ Nanowire_Arrays_for_Radiation_Sensor_Poster.mht!CZ_Nanowire_Arrays_for_Radiation_Sensor_Poster_files/slide0001.htm 2007 AATCC = Materials Design Competiton 1st Place Winner Room Temperature Radiological Nanowire Sensors for Low and=20 Medium Energy Radiation Detection Brett = Pearson,=20 Daniel Peterson, and Michael Saterlie

Significant Features=20 of the UNR Radiation Nano-sensor

vSynthesis=20 of CZT nanowires in single-step electrodeposition technique=20 vRoom temperature = detection=20 vMiniaturized = Size=20 vAble to detect = low and=20 medium energy radiation vVery fast = response time=20 vVery low noise = level=20 (resistance: 1012=20 Ωcm)=20 vFeasible to = synthesis very=20 large area detectors at low cost vVery high energy = resolution and increased reliability vAbility to scale = up=20 process for large production University of=20 Nevada, Reno

= Since=20 the September 11, 2001 attacks on the U.S., there has been nationwide = alarm and=20 an overwhelming rise in the demand for increased safety measures. This desire for increased = protection has=20 led to the intense investigation into various types of detectors, which = can=20 identify and possibly prevent an attack from occurring. The investigation has provided = a large=20 and expanding demand for radiological sensors.

=20 Previous radiological detectors contain single crystal sensors = which are=20 very expensive and slow to make. = In=20 addition, a large volume of the sensor material is needed to obtain more = surface=20 area and therefore increase detection efficiency. The University of Nevada, Reno = has=20 developed a new sensor design that remains extremely competitive in = sensor=20 technology. We have = improved sensor=20 design by incorporation of nanotechnology and producing nanowires of the = sensor=20 material in a titania substrate.=20 Introduction Technology

=20 Cadmium zinc telluride (CZT) is a room temperature = operating compound=20 semiconductor widely used in infrared, X-ray, and gamma ray radiation = detection=20 applications. CZT is = highly=20 advantageous over many other compound semiconductors due to its large = band gap,=20 and high resistivity, which allows for a reduction in the background = noise level=20 during detection. CZT is = among the=20 highest resistive compound semiconductors, being on the order of = 1012 W cm, where high resistivity is ideal for passive = detectors.

= The=20 nanowires in our technology provide the necessary surface area for = detection and=20 a one dimensional path for the excited electrons to travel toward the=20 detector. This greatly = increases=20 detection efficiency and overall production can be managed in much less = time=20 than conventional bulk detector methods. =20 Figure 1 shows a schematic of how the sensor works. =20 The flowchart to the right shows the relatively simple production = process. The six steps = shown can=20 produce fifteen sensors per glovebox daily. The first two steps are = extremely=20 similar in the fact that they use an electric annodization-type process, = differing only in chemicals and CZT growth under pulsing voltage. Figure 3 shows both process=20 setups. Anodize titania foil to form = nanopores Grow CZT nanowires through pulsed=20 electrodeposition = process Sputter surface=20 with gold Connect wires to=20 gold surfaces Annealed at 350=B0C in a CVD furnace for 1 hour (flowing argon atmosphere) = Clean with=20 methanol DC 20 V at 25 =B0C for 45 min 0.5 M phosphoric acid and 0.14 M sodium fluoride at a pH of 2.0 25 x 10-3 M NaClO4 was used as the supporting electrolyte Propylene carbonate solution with 5x10-3M = CdCl2=20 +=20 10x10-3M = ZnCl2+ = 0.5x10-3M = TeCl4=20 Voltage varied between =960.4 V and =961.2 V pulsed for 1 second each for 30 min. Production=20 Process

Figure 1:=20 Radiation energy gets absorbed by the nanowires (shown in red) an excites an = electron. =20 The loose electron travels up the nanowire toward = the gold surfrace where it is = conducted out the wire toward the = detector. =20 The signal is first amplified before reaching the = detector. =

V=20 DC power=20

Figure 2:=20 (a) titania foil annodization at constant 20V compared to (b) CZT = nanowire=20 growthat pulsed -0.4V to -1.2V. Both samples placed in = solution between the cathode and=20 annode.

(a) (b)

Figure 3:=20 (a) and (b) show nanoporous titania created with diameter ~70-100nm and = length=20 ~400-500nm. (c) shows annealed CZT nanowires = ~70-100nm=20 diameter grown in porous titania. =

(a) (b) (c)

Figure 4: X-Ray Diffraction of the sensors (a) before = and (b)=20 after annealing. It can = be=20 observed that the CZT phase of the nanowires = becomes=20 more developed in the annealing process resulting in increased quality of = desired CZT=20 detection properties.

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