The question asks about the first experimental evidence that electrons exhibit wave-like characteristics. This phenomenon is a cornerstone of quantum mechanics, demonstrating the wave-particle duality of matter.

Electron Wave-like Characteristics: Davisson and Germer Experiment

While the concept of wave-particle duality for matter was first proposed theoretically, its experimental verification was crucial. The groundbreaking experiment that confirmed the wave nature of electrons was conducted by Davisson and Germer.

De Broglie Hypothesis: Paving the Way

Before any experimental proof, Louis de Broglie, in 1924, put forward the revolutionary hypothesis that all matter, including electrons, possesses wave-like properties. He proposed that the wavelength (known as the de Broglie wavelength) associated with a particle is inversely proportional to its momentum. The de Broglie wavelength \(\lambda\) for a particle with momentum \(p\) (or mass \(m\) and velocity \(v\)) is given by the formula:

$$ \lambda = \frac{h}{p} = \frac{h}{mv} $$

where \(h\) is Planck's constant.

De Broglie's hypothesis suggested that if electrons have wave properties, they should be able to exhibit diffraction and interference phenomena, similar to light waves.

Davisson and Germer Experiment: Confirming Electron Waves

The experimental confirmation of de Broglie's hypothesis for electrons came in 1927 from Clinton Davisson and Lester Germer at Bell Labs in the USA. Their experiment provided the first direct evidence for the wave nature of electrons.

Experimental Setup and Observation

• Davisson and Germer directed a beam of electrons onto a nickel crystal target.
• They observed that the electrons were scattered from the crystal, and the intensity of the scattered electrons varied with the angle of scattering.
• Crucially, they found that at certain angles, there were peaks in the intensity of the scattered electrons, forming a diffraction pattern. This pattern was very similar to the diffraction patterns produced when X-rays (known waves) are diffracted by crystals.

The diffraction pattern observed by Davisson and Germer was a clear indication that electrons were behaving as waves. The maxima in the scattered electron intensity could be explained by constructive interference of electron waves scattered from the regular atomic planes within the nickel crystal lattice, analogous to Bragg's law for X-ray diffraction.

Interpretation and Significance

By applying Bragg's law to the observed diffraction pattern and relating it to the crystal's atomic spacing, Davisson and Germer were able to calculate the wavelength of the electron waves. This experimentally determined wavelength matched very closely with the de Broglie wavelength calculated for the electrons used in their experiment. This strong agreement provided compelling and irrefutable experimental evidence that electrons indeed exhibit wave-like characteristics.

Their experiment was a landmark achievement, providing the first direct experimental proof of de Broglie's hypothesis and firmly establishing the wave-particle duality for matter, just as it had been established for light.

Pioneers in Physics: Why Other Options Don't Fit

• Huygens: Christiaan Huygens was a prominent physicist from the 17th century known for his wave theory of light. While he made significant contributions to understanding wave phenomena, his work predates the discovery of electrons and quantum mechanics, and thus, he did not provide experimental evidence for the wave-like characteristics of electrons.
• De Broglie: Louis de Broglie proposed the hypothesis of matter waves (including electrons) theoretically. He did not conduct an experiment to prove this himself. His contribution was the theoretical prediction.
• Dirac: Paul A.M. Dirac was a pivotal figure in quantum mechanics, known for developing the relativistic wave equation for the electron (the Dirac equation) and predicting the existence of antimatter. His work is theoretical and advanced quantum mechanics, but he did not perform the specific experiment that first showed the wave-like characteristics of electrons.

Therefore, the experimental evidence for the wave-like characteristics of the electron was first provided by Davisson and Germer.