Final Nano Whiskers

NANO

WHISKERS

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 (22C to 25C) ; whiskers grow faster

Moisture: high humidity (85% RH)

Whiskers vs. Dendrites

Whiskers

Hair like shape

Grow perpendicular to the surface (90o)

Doesnt 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

Satmexs 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 Kunichi 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 2C 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: C60Organic: Toluene

Polar: WaterStored 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 Nanowhiskers

Physical structure Needle- whiskers

Chemical structure cellulose

Interactions Hydrogen bond

Tensile modulus ~130 GPa

Tensile strength 10 GPa

Electrical resistivity 1010 - 1016 ohms cm

Thermal conductivity Insulator

Density 1.2 g/cm3

Coef. Thermal expan 8 -16X 10-6

Preparation of Cellulose Nanowhiskers

Cellulose Nanowhiskersregenerated 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 Bioceramicsto human bone

Gas sensor

SnO2 Nanowhiskers showed a high sensitivity of 2350 ppm ethanol gas at 300C, which is much higher than that of regular SnO2 films.

FE-SEM image of SnO2Nanowhiskers 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.

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