TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: Each of the multiple nano-ribbons: includes at least one semiconductor material; and is separated from at least another nano-ribbon of the multiple nano-ribbons by at least one separation region associated with the second distance. The semiconductor material is: doped; and silicon. The separation region is filled with at least one fill material. Each of the multiple nano-ribbons or parts includes at least one semiconductor material different from the fill material. All of the multiple nano-ribbons are substantially parallel to each other. Each of the multiple nano-ribbons or parts corresponds to the first end at a first surface and is substantially perpendicular to the first surface. The cross-sectional area is substantially uniform along a height direction for each of the multiple nano-ribbons or parts. The multiple nano-ribbons or parts are parts of a thermoelectric device. The first distance is at least 500 mu m. The multiple nano-ribbons or parts include: multiple roughened sidewall surfaces respectively; and multiple nanoholes through corresponding nano-ribbons in corresponding sidewalls respectively. At least one of the multiple first voids is: completely surrounded by at least one solid material of the porous semiconductor substrate; and open to an area outside the porous semiconductor substrate. The porous semiconductor substrate further includes at least one second void, where each of the second voids is not connected with any void, each of the second voids corresponds to a second cross-sectional area associated with a second distance across of 5-500 nm and each of the second voids is separated from at least another void by the second distance. The multiple voids include multiple nanoholes. Preferred Method: The method further comprises: filling the separation regions between at least two of the multiple nano-ribbons with fill materials; roughening sidewalls of the multiple nano-ribbons respectively; and forming multiple nanoholes in corresponding sidewalls through the multiple nano-ribbons respectively. The method of making porous structure further comprises: filling the multiple first voids with fill materials; roughening sidewalls of at least some of the multiple first voids, where the process for etching the nonporous semiconductor substrate through the second portions of the surfaces is performed to form the porous semiconductor substrate further including the second voids; filling the second voids with fill materials; and roughening sidewalls of at least some of the second voids. The process for etching the semiconductor substrate or nonporous semiconductor substrate through the second portions of the first surface includes a wet etching process through the second portions of the first surface. The wet etching process includes an electroless or electrolytic chemical etching process.