Nano Whiskers

NANO NANO WHISKERSWHISKERS

General Definition• WHISKERS- One of the long stiff tactile

bristles or hairs that grow near the mouth and elsewhere on the head of most mammals

METALLURGY• Metal whiskering is a crystalline metallurgical

phenomenon involving the spontaneous growth of tiny, filiform hairs from a metallic surface.

Types of metal whiskers

• Zinc Whiskers • Silver Whiskers• Gold Whiskers • Cadmium Whiskers• Aluminum Whiskers • Lead (Pb) Whiskers • Indium Whiskers• Tin whiskers

Pictures of Metal whiskers

Properties of whiskers

• Shapes: Whiskers may be straight, kinked, hooked or forked

• Growth Rate: Growth rates from 0.03 to 9 mm/yr

• Whisker Diameter: 10 um and rarely less than 100 nm

• Temperature: room temperatures (22°C to 25°C) ; whiskers grow faster

• Moisture: high humidity (85% RH)

Whiskers vs. Dendrites

Whiskers• Hair like shape• Grow perpendicular to

the surface (90o)• Doesn’t require

dissolution of metal/ presence of electromagnetic field

Dendrites• Fern shaped• Grow across the surface• Growth requires

dissolution of metals in electromagnetic field

Mechanism of Growth

• A Single accepted explanation of the mechanism has not been established.

• Theories suggest that metal whiskers may grow in response to a mechanism of stress relief (especially "compressive" stress) .

Video Demonstration of Tin whiskers Growth

Commonly Accepted Factors

• Residual stresses within the metal plating • Intermetallic Formation • Externally Applied Compressive Stresses • Bending or Stretching • Scratches or nicks • Coefficient of Thermal Expansion Mismatches

Recent Attention to Metal Whiskers?

• To reduce the use of potentially hazardous materials such as lead (Pb), so the alternatives to the widely used tin-lead alloys used for plating.

• Restriction of certain Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE)

Failures by Whiskers

• Galaxy IV satellite in 1998- Tin whiskers• F-15 Radar- Tin whiskers• Heart Pacemaker Recall- Tin whiskers• computer server rooms – Zinc whiskers• Paper mills- Silver whiskers• Satmex’s Solidaridad HS 601 - Zinc whisker

Nano Whiskers

• The single crystalline metallic hair-like structure in the nanometer scale

• Also called as nanowires or nanorods.

Fullerene, C60 Nano WhiskersHistory

• C60 Nanowhiskers were discovered in 2001 in Japan by Kun’ichi Miyazawa during the preparation of a lead zirconate titanate sol gel.

• Thin fibrous structures that grow in the solution were named C60 Nanowhiskers.

• The C60 Nanowhiskers are prepared by the liquid-liquid interfacial precipitation method.

Preparation of C 60 Nanowhiskers:• Add 5ml of organic solvent to 20ml glass vial• Measure out enough C60 to form saturated solution in organic solvent (using C60

solubility table)• Sonicate solution of solvent and C60 until thoroughly dissolved• Layer with 5ml of polar solvent• Place in 2°C refrigerator for several days until whisker formation is observed, black

dusty material on the bottom of the vial• Pipette small sample of solution and whiskers onto glass slide and allow solvent to

dry

Properties of C60 Nano whiskers

• The Nanowhiskers were found to be C60 fullerene molecules arranged into a hollow tube by face-centered cubic packing.

• Nanowhiskers measure from a couple hundred nanometers to one micrometer in diameter and several millimeters in length

• Various experiments have been carried out testing different solvent solutions and the effects of environment on Nanowhiskers growth.

Solvent Solutions Tested

Organic layer Polar layer

Toluene Iso propyl alcohol

Carbon disulfide Iso propyl alcohol

Cholro benzene Iso propyl alcohol

Pyridine Iso propyl alcohol

Toluene Acetone

Toluene Water

Carbon: C60

Organic: ToluenePolar: Water

Stored in: SolutionMagnification: 60x

Transmission Electron Microscope 8000x

Silicon Nanowhiskers

• Molecular Beam Epitaxy• Silicon wafers were used as substrates• Desorption of the oxide layer by a thermal

annealing at 850 °C.• Afterward, a thin Au film was deposited at a

substrate temperature of 525 °C with thicknesses between 1.5 nm and 2 nm.

• The size of the thereby generated droplets could be chosen between 70 and 200 nm.

SEM cross section images of Silicon whiskers grown on a Silicon substrate for a) 60 min b) 120 min growth time at TS 525 °C.

TEM cross section image of a Silicon whisker with a length of about 300nm and a diameter of 95 nm on a Silicon substrate.

Crossed Nanowhiskers

• Bi-2212 superconducting single crystal Nano whiskers have been fabricated by annealing a melt quenched glass Bi3Sr2Ca2Cu3Ox precursor.

• A couple of Nano Whiskers obtained were placed crosswise on a YSZ single crystal substrate and then heat treated at 830o C for 25 minute to form Nano-scale junction

• Glass-ceramic method were used for preparation of the whiskers

• Bi2O3; SrCO3; CaCO3 and CuO were mixed to give a composition of Bi3Sr2Ca3Cu3O10+x.

• The mixture was melted in an alumina crucible at 11000C for 2 h.

• The melt was then rapidly quenched between two cold copper plates

• After the heat treatment cycle, whiskers were grown on the surface of the glass sheets

• Then a couple of whiskers were placed crosswise on a Yittria stabilized Zirconia, (YSZ:(ZrO2)1-m(Y2O3)m)) substrate and heat treated at 8300C for 25 min. to form Nano-scale junction.

Cellulose Nanowhiskers

Properties Cellulose NanowhiskersPhysical structure Needle- whiskersChemical structure celluloseInteractions Hydrogen bondTensile modulus ~130 GPaTensile strength 10 GPaElectrical resistivity 1010 - 1016 ohms cmThermal conductivity InsulatorDensity 1.2 g/cm3

Coef. Thermal expan 8 -16X 10-6

Preparation of Cellulose Nanowhiskers

• Cellulose Nanowhiskers regenerated from aqueous sodium hydroxide − urea solvent system on the basis of their temperature-dependent solubility.

• AFM topography image of cellulose Nanowhiskers after drying on a mica surface

Nanowhiskers in use

Water Repellant• In Nature, many small

tubes or whiskers keep water and solid at minimal contact for super hydrophobia (extreme water repellency)

water droplet

Stain Resistance• Billions of Nanowhiskers(10 nm long) create a thin cushion of air above

the cotton fabric, smoothing out wrinkles and allowing liquids to bead up and roll off without a trace.

• Water droplets form spherical globules • Rough nanoscale surface picks up dirt• Water and dirt roll off• Biomimicry

Bioceramics • The calcium phosphate

Nanowhiskers produced by microwave assisted method can be used as Bioceramics to human bone

Gas sensor• SnO2 Nanowhiskers showed

a high sensitivity of 23–50 ppm ethanol gas at 300◦C, which is much higher than that of regular SnO2 films.

• FE-SEM image of SnO2 Nanowhiskers synthesized by thermal evaporation

Electronics

• Nio2 Nanowhiskers having long life-cycle, High specific capacitance, high power, high stability, and low cost of the electrode materials are favorable factors for commercial applications

• Anisotropic Etching of SiC Whiskers were used as building blocks in the fabrication of sensors, cellular probes, electronic, optoelectronic, electromechanical, and other devices.

Be the Best and Betray the Worst.